Classification

The myriad of classification and nomenclature schemes for CHD make consensus difficult regarding the best methods to organize these lesions. The following classification scheme for the anesthesiologist to categorize CHD, as well as some acquired forms of pediatric heart disease, is useful:

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  Left-to-right shunt lesions: two ventricles

  
  
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  Right-to-left shunt lesions: two ventricles

  
  
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  Complete-mixing two-ventricle lesions

  
  
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  Complete-mixing single-ventricle lesions

  
  
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  Obstructive lesions without shunting

  
  
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  Regurgitant lesions without shunting

  
  
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  Cardiomyopathies

Another useful approach to CHD involves the stage of repair: unrepaired, palliated, completely repaired with residual defects, or completely repaired with no residual defects. Table 3-1 summarizes the major lesions in these categories. The anatomy, pathophysiology, and approach to anesthesia are detailed in the sections addressing the individual lesions.

Pathophysiology

When approaching the patient with congenital heart disease, after classification into the scheme previously noted, the anesthesiologist should determine the pathophysiologic consequences of the patient’s lesion, then construct a set of hemodynamic goals for the anesthetic care of that patient. After these goals are decided, the anesthesiologist can plan anesthetic and vasoactive drug administration, ventilation strategies, and strategies for preload and afterload management to achieve these goals ( Fig. 3-1 ).

General approach to pathophysiology in patients with congenital heart disease (CHD).

A, Hemodynamic consequences and goals for intracardiac and extracardiac shunting lesions. Hypoxic gas mixtures are used infrequently, and risk/benefit should be assessed carefully. LV, Left ventricular; PVR, pulmonary vascular resistance; SVR, systemic vascular resistance; Fi o ₂ , fraction of inspired oxygen. B, Obstructive lesions. RV, Right ventricular; L → R, left-to-right; R → L, right-to-left. C, Regurgitant lesions. CVP, central venous pressure; RAP, right atrial pressure; LAP, left atrial pressure; PCWP, pulmonary capillary wedge pressure. D, Mixing lesions. Qp/Qs, pulmonary/systemic blood flow ratio; paco ₂ , arterial carbon dioxide partial pressure.

(Data from Andropoulos DB: Hemodynamic management. In Andropoulos DB, et al, editors: Anesthesia for congenital heart disease, ed 2, Oxford, UK, 2010, Wiley-Blackwell.)

When considering patients with two ventricles without obstructive or shunting lesions, the four major determinants of cardiac output are preload, afterload, heart rate, and contractility. The patient with CHD has additional dimensions for consideration. Because of the frequent presence of mixing lesions resulting in arterial desaturation, additional parameters are addressed to optimize cardiac output and oxygen (O ₂ ) delivery, including hemoglobin (Hb) concentration. Many cyanotic patients depend on increased Hb levels for O ₂ -carrying capacity (14-17 g/dL). A “normal” Hb level for an infant or young child of 11 g/dL is often too low for these patients. Also, the mixed venous oxygen saturation (Sv o ₂ ) is important because, of necessity, Sv o ₂ is lower in patients with arterial desaturation with the same O ₂ extraction. Therefore, raising Sv o ₂ is a way to increase arterial oxygen saturation (Sa o ₂ , Sp o ₂ ) in the patient with right-to-left (R-L) shunting or mixing lesions. Besides increasing Hb, decreasing O ₂ consumption by using deeper anesthetic levels, lowering temperature, or lowering myocardial O ₂ consumption are also important to increase Sv o ₂ ( Fig. 3-2 ).

Determinants of cardiac output and oxygen delivery in congenital heart disease.

(Data from Andropoulos DB: Hemodynamic management. In Andropoulos DB, et al, editors: Anesthesia for congenital heart disease, ed 2, Oxford, UK, 2010, Wiley-Blackwell.)

Avoiding any introduction or entrainment of air bubbles into the venous circulation is an important consideration in all patients with CHD, particularly those with obligatory R-L shunting or complete intracardiac mixing. In these patients, even a small amount of air may rapidly pass into the arterial circulation and lodge in a coronary artery, causing myocardial ischemia and possibly ventricular fibrillation, or into the cerebral circulation, causing cerebral ischemia. However, even in patients with predominantly left-to-right (L-R) shunting, Valsalva maneuvers and other conditions can cause paradoxical air embolus. Techniques for infusion of intravenous (IV) fluids and injection of drugs must meticulously avoid this problem.

Hemodynamic Management

Patients with congenital heart disease undergoing an anesthetic procedure may require inotropic, lusitropic (improving diastolic ventricular function), and vasodilator or vasoconstrictor support to achieve the optimal hemodynamic state. Tables 3-2 and 3-3 list currently available agents and their dosages. With many choices but few data, the anesthesiologist often is unable to choose one drug over another from similar classes. Therefore it is often preferable to become familiar with a limited number of agents to use for hemodynamic management.

Two of the most common drugs in modern practice for inotropic support are milrinone and epinephrine. Milrinone is a phosphodiesterase-III inhibitor that prolongs the actions of cyclic adenosine monophosphate (cAMP), and has inotropic, lusitropic, and mild pulmonary and systemic vasodilator properties. Therefore, milrinone is particularly useful in patients with normal or high systemic vascular resistance (SVR) and failing ventricles with a degree of pulmonary hypertension. Single-ventricle patients in need of such hemodynamic support are particularly responsive to milrinone. A loading dose of 50 to 75 μg/kg, given over 30 minutes, rapidly achieves therapeutic plasma levels; this can be problematic because of milrinone’s vasodilating properties. For this reason, the infusion is often initiated without a loading dose. Infusion rates of 0.375 to 0.75 μg/kg/min are effective. Risk of tachycardia or atrial and ventricular arrhythmias is minimal for milrinone.

For patients in need of significant inotropic support, epinephrine, at low dose of 0.02 to 0.04 μg/kg/min, moderate dose of 0.05-0.09 μg/kg/min, or high dose of 0.1-0.2 μg/kg/min is effective. Patients requiring high-dose epinephrine for longer than several hours are candidates for mechanical support of the circulation. For hypotension, vasopressin at 0.02 to 0.04 units/kg/hr is effective in increasing SVR; again, patients requiring vasopressin for more than several hours should be evaluated for other means of circulatory support.

Ventilatory Management

Management of ventilation in patients with congenital heart disease often has exaggerated effects on cardiac function, pulmonary vascular resistance (PVR), and cardiopulmonary interaction not seen in patients with normal hearts. Appropriate ventilatory management during anesthesia can help achieve hemodynamic goals, or if used inappropriately, can be harmful to the patient with CHD. Therefore, planning ventilation strategy is as important as the anesthetic or vasoactive agents when attempting to achieve a set of hemodynamic goals.

For example, the neonate’s pulmonary vasculature is exquisitely sensitive to fraction of inspired oxygen concentration (Fio ₂ ), arterial carbon dioxide partial pressure (Pa co ₂ ), and pH; maintenance of these parameters is the cornerstone of achieving the goals for PVR. Many neonates will need a higher PVR to shunt blood away from the lungs, toward the systemic circulation through a patent ductus arteriosus (PDA) before surgical repair, to lower pulmonary/systemic blood flow ratio (Qp/Qs). Low Fi o ₂ , often 0.21, along with lowering minute ventilation to elevate Pa co ₂ , is often used to achieve this goal. Conversely, in the infant with elevated PVR causing R-L shunting or poor cardiac output, high Fi o ₂ and hyperventilation to produce mild to moderate hypocarbia is effective at lowering PVR.

Positive-pressure ventilation (PPV) often has detrimental effects on single-ventricle patients who have undergone the Fontan operation. The absence of a right ventricular pumping chamber means that flow through the Fontan circuit depends significantly on negative intrathoracic pressure from spontaneous respiration creating a pressure gradient from the extrathoracic veins; positive pressure decreases this gradient and reduces flow. In contrast, PPV may actually improve ventricular function in patients with a failing left or systemic ventricle. The intrathoracic positive pressure is transmitted to the pericardial space, which reduces the transmural wall tension across the ventricle, compared to spontaneous ventilation with negative intrathoracic pressure. This decreased wall tension reduces the work of the ventricle, resulting in more efficient contraction. These examples illustrate the importance of careful planning of ventilatory strategy in patients with CHD.

Volatile Anesthetics

Although halothane is no longer available in the United States because of its profound myocardial depressant effects, it is useful to review studies in CHD patients comparing new agents to halothane. A study using transthoracic echocardiography comparing halothane, isoflurane, and sevoflurane in 54 children with two-ventricle CHD reported that halothane at 1 and 1.5 minimum alveolar concentration (MAC) caused significant myocardial depression, resulting in a decline in mean arterial pressure (MAP decline of 22% and 35%), ejection fraction (EF decline of 15% and 20%), and cardiac output (CO decline of 17% and 21%), respectively, in patients age 1 month to 13 years undergoing cardiac surgery ( Fig. 3-3 ). Sevoflurane maintained both CO and heart rate (HR) and had less profound hypotensive effects (MAP decrease 13% and 20% at 1 and 1.5 MAC) and negative inotropic effects (EF preserved at 1 MAC, 11% decrease at 1.5 MAC) compared with halothane. Isoflurane, in concentrations as high as 1.5 MAC, preserved CO and EF, had less suppression of MAP (22% and 25%) than halothane, increased HR (17% and 20%), and decreased SVR (20% and 22%).

Hemodynamic changes assessed by echocardiography.

In 54 patients with CHD with two ventricles: A, ejection fraction; B, cardiac output. H, Halothane; S, sevoflurane; I, isoflurane; F/M, fentanyl/midazolam; MAC, minimal alveolar concentration. See text for details.

(Data from Rivenes SM, et al: Anesthesiology 94:223-229, 2001.)

The effects of volatile anesthetics on pulmonary (Qp) and systemic (Qs) blood flow in 30 biventricular patients and in L-R shunts has also been assessed. Halothane, isoflurane, and sevoflurane did not change Qp/Qs as measured by echocardiography. Russell et al. compared halothane with sevoflurane in the prebypass period in 180 children with a variety of cardiac diagnoses, including 14 with single-ventricle physiology and 40 with tetralogy of Fallot. The incidence of significant hypotension, bradycardia, and arrhythmia requiring drug treatment with atropine, phenylephrine, epinephrine, or ephedrine was higher with halothane (two events per patient vs. one). Serum lactate also increased slightly with halothane.

Patients with a single functional ventricle constitute an increasing proportion of patients undergoing anesthesia for both cardiac and noncardiac surgery, and studies of hemodynamic effects of anesthetic agents are limited. Ikemba et al. studied 30 infants with a single functional ventricle immediately before their bidirectional cavopulmonary connection, randomized to receive sevoflurane at 1 and 1.5 MAC, or fentanyl/midazolam at equivalent doses. Myocardial performance index (MPI), a transthoracic echocardiographic measurement of ventricular function that can be applied to single-ventricle patients, was unchanged with any of these regimens compared with baseline, indicating that either sevoflurane or fentanyl/midazolam can be used in this population to maintain hemodynamic stability.

In normal children, desflurane usually produces tachycardia and hypertension during the induction phase, followed by a slight reduction in HR and systolic blood pressure (BP) during steady state at 1 MAC anesthetic level. There are no reports of its hemodynamic profile in patients with congenital heart disease.

In summary, isoflurane and sevoflurane have had some study in the CHD population, and both maintain normal cardiac output at anesthetic concentrations in patients with normal, or only slightly compromised, ventricular function. There have been no published studies of these agents in patients specifically with significantly depressed myocardial function; these volatile anesthetics should be used with caution in these patients.

Opioids and Benzodiazepines

Midazolam is often used with fentanyl anesthesia to provide sedation and amnesia, as a substitute for low-dose volatile anesthetics, particularly in hemodynamically unstable patients and young infants, in whom the myocardial depressant effects of volatile agents are more pronounced. Fentanyl and midazolam combinations have been studied in two different clinical dose regimens to simulate 1 and 1.5 MAC of volatile agents: fentanyl , 8- to 18-μg bolus followed by 1.7 to 4.3 μg/kg/hr infusion, then repeat bolus at 50% of original doses followed by 50% increase in infusion, depending on age; and midazolam, 0.29-mg/kg bolus followed by 139 μg/kg/hr infusion, then repeat bolus at 50% of original dose, followed by 50% increase in infusion, for all ages; for induction and the prebypass period in congenital heart surgery in biventricular patients (see Fig. 3-3 ). Vecuronium was used for muscle relaxation to isolate the effects of the other two agents on hemodynamics. Measurements of cardiac output and contractility were made by echocardiography. Fentanyl/midazolam caused a significant decrease (22%) in CO despite preservation of contractility, predominantly from a decrease in HR.

Propofol

Williams et al. measured the hemodynamic effects of propofol (50-200 μg/kg/min) in 31 patients age 3 months to 12 years undergoing cardiac catheterization. Propofol significantly decreased MAP and SVR; however systemic CO, HR, and mean pulmonary artery pressure (PAP), as well as PVR, did not change. In patients with cardiac shunts, the net result was a significant increase in the R-L shunt, a decrease in the L-R shunt, and decreased Qp/Qs, resulting in a significant decrease in Pa o ₂ and Sa o ₂ , as well as reversal of the shunt from L-R to R-L in two patients. Another study of cardiac catheterization showed that patients could experience a 20% decrease in HR or MAP. These effects of propofol, causing venodilation and vasodilation, decreased HR, and possibly decreased contractility with significant induction doses, mandate caution with this agent in patients who are preload and afterload dependent. Such patients include those with dilated cardiomyopathy and coronary artery lesions requiring higher coronary perfusion pressures.

Ketamine

Despite the potential adverse effects of dysphoria, hallucinations, excessive salivation, tachycardia, and hypertension, ketamine has been a mainstay in the induction of general anesthesia in patients with congenital heart disease. Administered intravenously (IV) or intramuscularly (IM), ketamine will reliably maintain HR, BP, and systemic CO at an induction dose of 1 to 2 mg/kg IV or 5 to 10 mg/kg IM, with a maintenance dose of 1 to 5 mg/kg/hr in patients with a variety of congenital diseases, including tetralogy of Fallot.

Several studies addressed exacerbation of pulmonary hypertension (PH). Morray et al. demonstrated that in cardiac catheterization patients, 2 mg/kg of ketamine caused a minimal (< 10%) increase in mean PAP, and pulmonary/systemic vascular resistance ratio (Rp/Rs), with no change in direction of shunting or Qp/Qs. Hickey et al. studied postoperative cardiac surgery patients with normal Pa co ₂ and found that ketamine at 2 mg/kg had no effect on PAP or calculated PVR, in patients with normal or with elevated baseline PVR. Ketamine, 2-mg/kg load followed by 10 μg/kg/min infusion, did not change PVR in 15 children with severe PH, when breathing spontaneously with a baseline of 0.5 MAC sevoflurane. Recent reports indicate that ketamine is effective and safe for patients with CHD and with PH receiving noncardiac anesthetics, as long as the airway is managed properly to avoid significant hypercarbia or hypoxemia.

Etomidate

Etomidate is an imidazole derivative and sedative-hypnotic induction agent thought to be devoid of cardiovascular effects, thus achieving widespread use in patients with limited cardiovascular reserve. Few reports address the hemodynamic effects of etomidate in children with congenital heart disease. In 20 patients with a variety of congenital defects studied in the cardiac catheterization laboratory (CCL), etomidate (0.3-mg/kg bolus followed by 26 μg/kg/min infusion) had similar effects as ketamine (4 mg/kg followed by 83 μg/kg/min infusion): a slight increase in HR but no change in MAP during induction or the 60-minute infusion. Sarkhar et al. studied etomidate (0.3-mg/kg bolus) in 12 children undergoing cardiac catheterization for device closure of atrial septal defect (ASD) or radiofrequency ablation of atrial arrhythmias. There were no significant changes in any hemodynamic parameter (HR, MAP, filling pressures, SVR or PVR, Qp/Qs, Sv o ₂ ). A case report of stable hemodynamics with etomidate induction in a pediatric patient with end-stage cardiomyopathy receiving a second anesthetic 4 weeks after cardiovascular collapse with ketamine induction demonstrates the utility of this drug in this population. Etomidate has been used for induction of anesthesia in adults with congenital cardiac conditions such as ruptured aneurysm of the sinus of Valsalva, as well as for cesarean section in a patient with uncorrected coronary artery–to–pulmonary artery fistula, with no cardiovascular effects in these patients.

Thus, etomidate seems best utilized in patients with the most limited cardiac reserve. It appears particularly useful in teenagers or adults with poorly compensated, palliated CHD presenting for cardiac transplantation or revision of previous surgeries. Temporary adrenal suppression will occur with even one induction dose of etomidate.

Dexmedetomidine

Dexmedetomidine has been studied as an adjunct agent in general anesthesia for pediatric cardiac surgery. Dexmedetomidine, 0.5-μg/kg load followed by 0.5 μg/kg/hr infusion, with an isoflurane-fentanyl-midazolam anesthetic, significantly reduced HR, MAP, and cortisol, blood glucose, and serum catecholamine response in children age 1 to 6 years undergoing cardiac surgery with bypass, compared with the baseline anesthetic. Chrysostomu et al. studied 38 pediatric patients (average age 8 years) after biventricular repair with cardiopulmonary bypass; 33 were extubated. Dexmedetomidine infusion rate varied from 0.1 to 0.75 μg/kg/hr (mean 0.3), and desired sedation was achieved in 93% and analgesia in 83% of patients. There was no respiratory depression, but hypotension was observed in 15% of patients.

Pharmacokinetics and Intracardiac Shunts

The presence of a right-to-left intracardiac shunt decreases the rate of rise of the concentration of inhaled anesthetic in the arterial blood, as a portion of the systemic cardiac output bypasses the lungs and then dilutes the anesthetic concentration in the systemic arterial blood. The anesthetic concentration in the blood thus never equals the exhaled concentration. Inhaled induction is noticeably slower in cyanotic CHD patients. Huntington et al. studied six children with R-L shunts from a fenestrated Fontan operation whose average Qp/Qs was 0.58. These patients achieved an arterial anesthetic concentration (Fa) of only 55% of inspired halothane concentration (Fi) after 15 minutes during wash-in of 0.8% halothane. After closure of R-L shunt (occlusion of Fontan fenestration in CCL), the Fa of halothane equaled the Fi. This difference between Fa and Fi is greater during induction or washout and greater with less soluble drugs (sevoflurane, desflurane, nitrous oxide) than with more soluble drugs (halothane).

In the face of significant R-L intracardiac shunting, IV agents given by bolus may pass directly into the left side of the heart with less dilution by systemic venous blood and passage through the pulmonary vascular system. This may result in transiently high arterial, brain, and cardiac concentrations of drugs such as lidocaine. IV induction agents and muscle relaxants may also achieve sufficient arterial and brain concentrations more rapidly with R-L intracardiac shunts.

Left-to-right intracardiac shunts have minimal effect on the speed of induction with inhaled anesthetic agents. The recirculation of blood through the lungs results in increased uptake of anesthetic and in a higher blood anesthetic concentration in the pulmonary capillaries, reducing anesthetic uptake. The two effects cancel each other. Only in severe congestive heart failure from L-R shunt, with significant interstitial and alveolar edema, would L-R intracardiac shunting be expected to slow inhalation induction, from the combined effects of diffusion limitation and ventilation/perfusion mismatch, resulting in alveolar dead space ventilation with no uptake of any new anesthetic agent.

History and Physical Examination

Preoperative assessment should include a detailed description of the patient’s cardiac anatomy, cardiac surgery history, and catheter-based interventions. Residual defects after surgery are important because many patients and parents assume these are completely repaired after complex surgery. All diagnostic echocardiographic and catheterization studies should be reviewed with careful attention to ventricular function, atrioventricular valve competency, and PVR measurement ( Figs. 3-4 and 3-5 ). Cardiac MRI and CT angiographic images and data should also be reviewed, particularly in delineating extracardiac anatomy such as the aorta and its branches ( Figs. 3-6 and 3-7 ). A history of thrombosis or occlusion of veins or arteries will help guide invasive catheter placement, and knowledge of previous interventions helps determine appropriate locations (e.g., avoidance of left radial arterial line in patients who had aortic coarctation repaired with left subclavian flap technique). The patient or caregiver should be questioned about the patient’s functional status, limitations on activity, and other cardiac symptomatology.

Preoperative echocardiographic findings in CHD.

A, Perimembranous ventricular septal defect (VSD). Color flow Doppler image depicts left-to-right shunting through defect in membranous septum (arrow). B, Complete atrioventricular canal, transesophageal view. Four-chamber view demonstrates ostium primum atrial septal defect (ASD; arrow ) and inlet VSD (arrow with asterisk). C, Cor triatriatum. Obstructive membrane in left atrium (LA) (arrowheads) divides cavity into proximal and distal portions. RA, right atrium. D, Dextrotransposition of the great arteries (d-TGA). Pulmonary artery (PA) arises from left ventricle (LV), and aorta (AO) arises from right ventricle (RV). Associated perimembranous VSD is seen (arrow).

(Modified from Russell IA, Miller-Hance WC: Transesophageal echocardiography in congenital heart disease. In Andropoulos DB, et al, editors: Anesthesia for congenital heart disease, ed 2, Oxford, UK, 2010, Wiley-Blackwell.)

Hypoplastic left heart syndrome (HLHS).

Catheterization diagram of infant with HLHS after stage I palliation and bidirectional cavopulmonary anastomosis (Glenn anastomosis). This one-page document summarizes history, anatomy, and physiology and contains a wealth of information necessary to plan anesthetic care. Numbers in circles are oxygen saturations, numbers without circles are pressures; arrows indicate catheter course; a, a-wave pressure; v, v-wave pressure; m, mean pressure; ABG, arterial blood gas; BSA, body surface area; LSVC, presence of left superior vena cava; Qp, pulmonary blood flow; Qs, systemic blood flow; PAR, pulmonary artery resistance; U, Wood units; Rp:Rs, pulmonary-to-systemic vascular resistance ratio; VO ₂ , oxygen consumption.

Magnetic resonance angiograms of coarctation.

A, Severe coarctation (arrows) of the aorta in 15-year-old male patient, just distal to left subclavian artery. B, Large collateral arterial vessels are seen in posterosuperior aspect of thorax, and a large internal mammary artery is present (arrowheads).

(From Mossad EB, Joglar JJ: Preoperative evaluation and preparation. In Andropoulos DB, et al, editors: Anesthesia for congenital heart disease, ed 2, Oxford, UK, 2010, Wiley-Blackwell.)

Severe aortic coarctation.

This 19-year-old male patient was diagnosed with aortic coarctation using narrow-collimation contrast-enhanced multislice computed tomography (CT). Axial CT image shows severe aortic coarctation. The main pulmonary artery is seen branching into the right and left pulmonary arteries. The ascending aorta is imaged in cross-section alongside the pulmonary artery. In comparison, the black arrow indicates the severely narrowed proximal descending thoracic aorta. Enlarged internal mammary arteries (double white arrows) and numerous enlarged collateral vessels (arrowheads) are also present.

(From Mossad EB, Joglar JJ: Preoperative evaluation and preparation. In Andropoulos DB, et al, editors: Anesthesia for congenital heart disease, ed 2, Oxford, UK, 2010, Wiley-Blackwell.)

Chronic medication use should also be reviewed. Many patients with CHD are taking medications for afterload reduction (angiotensin-converting enzyme [ACE] inhibitors), diuresis (furosemide, other diuretics), pulmonary hypertension (endothelin receptor antagonists, prostacyclins, phosphodiesterase inhibitors), arrhythmias (β-blockers, amiodarone), and systemic anticoagulation (aspirin, low-molecular-weight heparin, warfarin). The anesthetic implications of all medications should be considered. In general, all cardiac medications should be continued up to and including the day of surgery, with the exception of anticoagulants. Aspirin use is common in infants with systemic-to-pulmonary artery and other shunts and is often safe to continue for peripheral surgery. Other agents (e.g., heparin, warfarin) must be addressed with the surgeon and cardiologist, depending on the indication and the procedure.

On physical examination, signs of poor cardiac output and long-standing cyanosis may include peripheral vasoconstriction and clubbing, respectively. Pulse oximetry readings on room air or baseline O ₂ delivery should be noted. In addition, the volar aspect of the wrists should be examined for scars indicating previous arterial cutdown that may complicate arterial line placement. A careful airway examination is necessary because of the association of CHD with a number of craniofacial syndromes that may complicate airway management. Pulmonary examination to assess degree of respiratory distress is important. The major examination findings are discussed later for each lesion.

Depending on the severity of cardiovascular disease, comorbidities, and the proposed procedure, extensive preoperative testing may be warranted. Common laboratory tests include hemoglobin and hematocrit, platelet count, coagulation studies, and electrolytes. Exercise stress testing, electrocardiogram (ECG), and Holter study may also be indicated. Table 3-6 summarizes important preanesthetic considerations in the CHD population.

Premedication and Monitoring

Premedication plays a significant role in allaying anxiety in patients with congenital heart disease. Many patients, both pediatric and adult, have undergone multiple procedures, and providing a comfortable separation from family members and transfer to the OR can enhance the perioperative experience. Anxiolysis can also reduce myocardial O ₂ consumption and sympathetic stimulation. However, excessive sedation can also be detrimental in the CHD patient. Hypoxemia and hypercarbia from hypoventilation can decrease pulmonary blood flow in patients with systemic-to-pulmonary arterial shunts or passive pulmonary blood flow (Fontan) and can cause cardiovascular collapse in patients with PH.

Common premedications in CHD children include oral or IV midazolam, ketamine, and pentobarbital. Common anxiolytics in adults include oral diazepam and IV diazepam, midazolam, and ketamine. Patients with CHD receiving premedication should be monitored closely for signs of respiratory depression and poor CO, with pulse oximetry and ECG monitoring.

The use of invasive monitoring depends on the patient’s physiology, the procedure, and the need for close BP control and frequent arterial blood gases (ABGs). Sites for arterial catheter placement depend on previous surgery. For example, patients with classic or modified Blalock-Taussig shunts will often have spuriously low BP when monitored on the ipsilateral upper extremity. In addition, patients with left subclavian flap repair of aortic coarctation will have unreliable BP measurements on the left upper extremity. Arterial cutdown for previous surgeries can also complicate percutaneous arterial catheter placement.

Central venous pressure (CVP) monitoring can also be helpful, but it is important to understand the patient’s venous anatomy before placement. Depending on the stage of palliation, the superior vena cava (SVC) may be connected to the pulmonary artery, and pressure measurement in the SVC reflects PAP, not true CVP. Measurement of CVP in the patient with a superior cavopulmonary connection requires a catheter in the inferior vena cava (IVC). After the Fontan operation, both the SVC and the IVC are connected to the pulmonary arteries, and pressure measured in these locations is not equivalent to atrial pressure. In addition, CVP catheter placement in the internal jugular vein of an infant with a planned single-ventricle palliation is discouraged because a stenosis or thrombosis of the SVC can preclude further palliation.

Cerebral oximetry monitoring using near-infrared spectroscopy (NIRS) is often considered routine during cardiac surgery, but it can also be used during noncardiac surgery to trend O ₂ delivery and CO. Somatic oximetry with the same device, using a probe placed on the flank at the tenth thoracic–first lumbar vertebral (T10-L1) level, is an important monitor of systemic O ₂ delivery in single-ventricle infants and may be considered for major noncardiac surgery in these patients.

Transesophageal echocardiography (TEE) can be used to monitor function and filling intraoperatively and assist the anesthesiologist in adjusting pharmacologic therapy and fluid administration during major surgery in patients with complex CHD.

Airway and Ventilation Management

Depending on the type of procedure planned and patient selection, a natural airway, laryngeal mask airway (LMA), or endotracheal tube (ETT) can all be used safely. Knowledge of the patient’s cardiac lesion and function and the goals for ventilation and oxygenation are critical. Pulmonary hypertension is exacerbated by hypoxemia and hypercarbia, so airway and ventilation management should be planned accordingly. Left-to-right shunt lesions such as ventricular septal defects, truncus arteriosus, and systemic-to-pulmonary arterial shunts can become unstable with the administration of high concentrations of inspired O ₂ and with hypocarbia.

Anesthetic Techniques

When delivered with care, any anesthetic drug can be used in the patient with congenital heart disease. Myocardial depressants should be avoided in patients with poor ventricular function and who would poorly tolerate a BP decrease. Regional anesthetic techniques are also used in many patients with CHD, but careful assessment, including knowledge of anticoagulant therapy, is important for planning these techniques. Plans for emergence and tracheal extubation should also be considered. Tracheal extubation with deep levels of anesthesia can avoid the increased PVR that can accompany light planes of anesthesia and straining against an ETT. However, use of tracheal extubation must be weighed against the potential for airway obstruction, which can be disastrous in patients with PH.

Postoperative Care Plan and Disposition

Before anesthetizing a CHD patient for a procedure, the clinician should have a postoperative care plan. Depending on the lesion, preoperative status, and procedure, it is often necessary to reserve a bed in an intensive care unit (ICU) or a patient floor. Patients with delicate physiology (e.g., systemic shunt-dependent pulmonary flow, poor ventricular function) are usually admitted to the ICU or cardiology ward after administration of most anesthetics. At a minimum, these patients need a period of observation (4-6 hours) to ensure that they are hemodynamically stable in their baseline cardiac rhythm, maintaining stable S o ₂ without airway or pulmonary problems, and can take oral fluids before discharge home.

Although procedures can be performed in CHD patients at freestanding outpatient surgical facilities, careful preoperative evaluation must occur. If there is any potential for instability or need for hospital admission, the lack of proximity to skilled help, drugs, and equipment precludes safe anesthesia care in these facilities, and the procedure should be performed in a hospital setting with adequate backup provisions.

Infective Endocarditis Prophylaxis

Infective endocarditis (IE) is a serious cause of morbidity and mortality, and patients with congenital heart disease have an increased incidence of IE, 1.1 per 1000 patient-years, compared with the general population, 1.7 to 6.2 per 100,000 patient-years.

The American Heart Association (AHA) published new guidelines for IE prevention in 2007. The committee found that very few cases of IE could be prevented by the administration of antimicrobial endocarditis prophylaxis. As a result, the indications were narrowed considerably over previous versions of the guidelines. Patients must first have a cardiac indication; these are now limited to the presence of a prosthetic valve, previous endocarditis, and some forms of CHD. The CHD indications include unrepaired cyanotic CHD, complete repair with a prosthetic patch or material but only in the first 6 months after the procedure, and those with residual defects near the site of a patch. Transplant patients with valvulopathy are also included. In addition, a procedural indication must exist for IE prophylaxis. These include dental work with disruption of gums or mucosa; airway procedures such as tonsillectomy; and gastrointestinal (GI), genitourinary (GU), or skin, soft tissue, and orthopedic procedures involving infected tissue. Simple GI, GU, or other procedures without infection are no longer indications for prophylaxis. Box 3-2 and Table 3-7 summarize the major recommendations involving dental procedures and antibiotic regimens.

The American College of Obstetrics and Gynecology (ACOG) and AHA do not recommend IE prophylaxis for uncomplicated vaginal or cesarean deliveries, regardless of the type of maternal cardiac disease. The maternal cardiac conditions associated with the highest risk of adverse outcome from IE are appropriate for antibiotic administration only if the patient has an established infection that could cause bacteremia.

Patients at Greatest Anesthetic Risk

Patients with congenital heart disease are known to be at much higher risk for perioperative cardiac arrest and death than those without cardiac disease. A Mayo Clinic study of 92,881 pediatric anesthetic procedures from 1988 to 2005 revealed that 88% of the 80 arrests involved patients with CHD. The rate of cardiac arrest was several hundred–fold higher for patients with CHD. Recent data also show which CHD patients are at the highest risk for cardiac arrest and death during or shortly after anesthesia ( Box 3-3 ).

The Pediatric Perioperative Cardiac Arrest Registry evaluated 393 pediatric patients (127 with heart disease) who had anesthetic-related cardiac arrest from 1994 to 2005. About 59% of these patients were unrepaired, and 26% were palliated, so only 15% had undergone reparative surgery. Single-ventricle diagnosis was most common (19%), with hypoplastic left heart syndrome (HLHS) in the most patients. Mortality was only 25% after cardiac arrest in this group. Left-to-right shunt lesions were the next most common diagnosis, with 18%, but mortality was low (17%) after arrest. Left-sided obstructive lesions were seen in 16%, but with high mortality (45%). Aortic stenosis had the single highest mortality rate after cardiac arrest under anesthesia (62%). Data on anesthetic-related 24-hour and 30-day mortality for 101,885 pediatric anesthetic patients from 2003 to 2008 at Royal Children’s Hospital in Melbourne, Australia, revealed 10 anesthetic-related deaths, five in patients with PH with or without CHD; eight had complex CHD, PH, or both.

Left-to-Right Shunt Lesions

Left-to-right shunt lesions are among the most common CHD lesions that the anesthesiologist will encounter. The level of shunting can occur at any location between intracardiac chambers (i.e., ventricular septal defect [VSD] or atrial septal defect [ASD]), or extracardiac structures (i.e. patent ductus arteriosus [PDA]). The pathophysiologic consequences of L-R shunt depend on several factors: the size of the defect, pressure gradient between chambers or arteries, the pulmonary/systemic vascular resistance (PVR/SVR) ratio, the relative compliance of right and left ventricles, and blood viscosity ( Fig 3-8 ).

Pathophysiology of left-to-right shunting lesions.

Flow diagram depicts factors that affect left-to-right shunting at atrial, ventricular, and great artery level and pathophysiology produced by these shunts. A large shunt will result in left ventricular (LV) failure, right ventricular (RV) failure, and pulmonary edema. Increased pulmonary blood flow and pulmonary artery pressures lead to pulmonary hypertension and eventually Eisenmenger’s syndrome. These final common outcomes are highlighted in bold. PVR, Pulmonary vascular resistance; SVR, systemic vascular resistance; LA, left atrial; BP, blood pressure; RVEDV, right ventricular end-diastolic volume; RVEDP, right ventricular end-diastolic pressure; LVEDP, left ventricular end-diastolic pressure; LVEDV, left ventricular end-diastolic volume; R → L, right to left.

(Data from Walker SG: Anesthesia for left-to-right shunt lesions. In Andropoulos DB, et al, editors: Anesthesia for congenital heart disease, ed 2, Oxford, UK, 2010, Wiley-Blackwell.)

In general, atrial-level shunting produces the least degree of change, resulting in increased right ventricular (RV) filling and mild increases in RV end-diastolic volume and pressure. Symptoms are minimal, and these shunts may be tolerated for decades. Ventricular-level shunting is often more problematic, and if the defect is large and unrestrictive, RV pressure is close to left ventricular (LV) pressure, also elevating pulmonary artery (PA) pressure and flow significantly. Qp/Qs greater than 3:1 will produce significant increases in left atrial (LA) and LV blood flow, LV end-diastolic pressure (LVEDP) and volume (LVEDV), and can lead to pulmonary venous congestion, pulmonary edema, and respiratory distress. Smaller, restrictive ventricular defects, where RV pressure is significantly lower than LV pressure, produce lesser elevations in Qp/Qs, and pulmonary congestion is less severe.

Shunts at the great artery level, if large, are the most problematic. In young infants, these lesions can produce a “steal” of blood flow away from the aorta to the PA, lowering diastolic BP and causing coronary ischemia, heralded by global LV dysfunction and dilation, poor CO, and ST-segment changes on ECG. Any L-R shunt that is large enough, particularly at the ventricular or great artery levels, produces pulmonary hypertension, which, if left untreated over years, may become irreversible. This syndrome results from increased shear stress and circumferential stretch on the pulmonary arterioles causing endothelial dysfunction and vascular remodeling. Smooth muscle cells proliferate, extracellular matrix increases, and intravascular thrombosis occurs in the smaller arterioles. This increases PVR, and eventually the shunt inverts, resulting in cyanosis (Eisenmenger’s syndrome). Although encountered less frequently in contemporary practice, patients with Eisenmenger’s syndrome are always at high risk under anesthesia and require careful assessment and planning (see later discussion).

Ventilatory management during general anesthesia will affect pathophysiology, especially with large L-R shunts in small infants, whose pulmonary vasculature will respond vigorously to changes in Fi o ₂ and Pa co ₂ . Hyperoxygenation and hyperventilation usually lower PVR greatly and increase the L-R shunt, which may cause lower diastolic pressure, coronary steal, and large increases in both RV and LV volumes, leading to acute myocardial dysfunction. Generally, lower Fi o ₂ and normocarbia are the goal during anesthesia in these infants, to limit increases in pulmonary blood flow. Positive end-expiratory pressure (PEEP) also limits increases in Qp/Qs. Any anesthetic regimen can be used in these patients; most agents are pulmonary vasodilators, and none, even ketamine, is a pulmonary vasoconstrictor ( Box 3-4 ; see also Pulmonary Hypertension).

Patent Ductus Arteriosus

The patent ductus arteriosus (PDA) is the connection between the pulmonary artery and lesser curve of the arch of the aorta, which during fetal life carries blood from the PA to the aorta, bypassing the lungs so that only 5% to 10% of the fetal cardiac output passes through the lungs ( Fig. 3-9 ). Normally, patency is maintained by low fetal oxygen tension (P o ₂ ), low levels of circulating prostanoids produced by the placenta, and lack of prostanoid metabolism by the lungs. At birth, with onset of respiration and expansion of the lungs, oxygenation, and decreased levels of prostanoids, the PDA constricts, and normally is functionally closed by 48 to 72 hours of life, and anatomically closed by 2 weeks, producing the ligamentum arteriosum. However, some PDAs never close, and it is one of the most common, simple CHD lesions.

Patent ductus arteriosus with resultant left-to-right shunting.

Some of the blood from the aorta crosses ductus arteriosus and flows into pulmonary artery (arrows).

(Modified from Brickner ME, Hillis LD, Lange RA: N Engl J Med 342:256-263, 2000.)

Isolated PDA incidence is 1:2000 to 1:5000 live births and accounts for 3% to 7% of congenital heart disease. PDA is more common in premature infants but may be encountered at any age, including adults. It is also a component of many more complex cardiac diseases, and early neonatal survival depends on the PDA for many lesions, including stenosis or atresia of the pulmonary or aortic valves (e.g., pulmonary atresia, HLHS). Maintaining ductal patency with prostaglandin E ₁ (PGE ₁ ) for such lesions is mandatory until surgical or catheter palliation or correction can be performed.

Flow through the PDA is normally left to right (i.e., aorta to PA). The amount of flow depends on the diameter, length, and tortuosity of the PDA and the relative pressure and resistances in the aorta and PA. Anatomic variations range from a tiny PDA with almost no flow to large, aneurysmal, calcified PDA in adults, with very high pressures from years of exposure to aortic pressure and flows. The pathophysiologic consequences of a PDA range from minimal through significant increases in Qp/Qs (> 2:1), causing increases in RV volume and pressure and possible increases in LA and LV flow to the point that LVEDV and LVEDP are elevated, which can increase pulmonary venous pressure and cause transudation of fluid through pulmonary capillaries into the interstitial and alveolar spaces. This is particularly common in premature infants, who may be ventilator dependent solely as a result of the PDA. In addition, patients with very large PDA may have a large steal of flow from the aorta to the PA, lowering diastolic BP and potentially causing coronary ischemia. Over time, patients with a large, long-standing PDA may develop irreversible elevations in PA pressure, leading to reversal of the shunt and Eisenmenger’s syndrome. Many patients with small PDA are asymptomatic, with increasing symptomatology according to the PDA size and Qp/Qs. Recurrent respiratory infections, difficulty feeding, diaphoresis, and impaired growth are seen in infants with large PDA. Occasionally, congestive heart failure (CHF) is seen.

Physical examination in isolated PDA usually reveals an acyanotic child, with Sp o ₂ of 95% to 100% on room air. Peripheral pulses are easily palpable because of the increased pulse pressure resulting from lowered diastolic BP. Precordial examination yields a vigorous cardiac impulse, with the LV apex often displaced to the left. A compensatory tachycardia at rest is often present. With a small shunt, there may only be a soft grade I-II/VI systolic murmur over the left infraclavicular area. With increasing shunt, the murmur will become louder and longer, and with very large PDA there is a continuous, machinery-like murmur, loudest just after the second heart sound (S ₂ ), which is often accentuated. Examination of the lungs may reveal tachypnea, retractions, and fine rales if there is significant pulmonary congestion.

Diagnostic testing in patients with PDA includes an ECG, which often reveals evidence of LA and LV enlargement and in more severe cases, RV enlargement as well. Rhythm is normally sinus, although adults may develop atrial fibrillation from long-standing atrial enlargement. Chest radiograph findings range from near-normal to cardiomegaly with increased pulmonary vascular markings in larger PDA. Transthoracic echocardiogram is the most useful diagnostic modality and is often sufficient to make an accurate diagnosis as to size, tortuosity, direction of shunting, and enlargement of cardiac chambers and any associated defects. Both two-dimensional and color Doppler images, as well as pulsed and continuous-wave Doppler studies, are obtained for a complete picture of anatomy and physiology. The PDA is often larger than the aorta and the branch PAs in premature infants. In PDA with complex or questionable anatomy, additional studies (e.g., CT angiography, MRI) are performed. These studies are particularly useful if a coarctation of the aorta is suspected, often present in the juxtaductal position. Cardiac catheterization is performed only in particularly difficult cases or when PDA is associated with device closure in the CCL.

Closure of the PDA is performed by one of three methods: thoracotomy with ligation or ligation/division, video-assisted thoracoscopy (VATS) with ligation, or endovascular closure with coils, plugs, or other devices in the CCL. Robotic-assisted VATS has also been reported. Choice of closure method depends on the size of the patient, anatomy of the PDA, and institutional practice, including surgeon and cardiologist preference. In general, premature and other small infants will have left thoracotomy with extrapleural dissection and closure of the PDA; larger infants can undergo thoracotomy or VATS repair. Surgical closure is used for large or tortuous PDAs or when coarctation of the aorta may be present. In the modern era, most small to moderate PDAs in larger infants and children are occluded in the CCL. Adult patients with large, aneurysmal PDAs may require cardiopulmonary bypass (CPB) or even deep hypothermic circulatory arrest (DHCA) through a thoractomy or sternotomy.

Anesthetic considerations in PDA patients include thorough preoperative evaluation with complete examination and assessment of all diagnostic studies, to assess the degree of L-R shunting and pathophysiologic severity. Packed red blood cells must be available in the OR or CCL, in case of tearing or rupture of the PDA, which although rare, can cause catastrophic bleeding. Standard monitors are applied before induction, and inhalational induction with sevoflurane or IV induction with various agents can be accomplished. An arterial line, preferably in the right radial artery, is indicated for small infants undergoing surgery, as well as other patients with significant pathophysiology. In the CCL the cardiologist will acquire femoral arterial access for monitoring and approach to the PDA. A central venous catheter is needed only for large PDAs accompanied by significant pathophysiology. For thoracotomy or VATS in small infants, single-lung ventilation (SLV) is usually unnecessary; the technical difficulty and time required often are significant. Insufflation of CO ₂ with lung retraction for VATS, or simple retraction and packing for thoracotomy in small infants, is usually sufficient for surgical exposure. Alternately, the endotracheal tube may be advanced into the right main bronchus in a small infant; the problem with this approach is that the right upper-lobe bronchus is often close to the carina and is occluded by the ETT. In larger patients, SLV can be provided by bronchial blockers, or in larger patients (> 30 kg), a small, left-sided double-lumen ETT, and will assist with surgical exposure, particularly in VATS.

Any combination of inhaled or IV agents may be used for maintenance of anesthesia, keeping in mind the severity of pathophysiology. Severely ill neonates with large PDA will be intolerant of the myocardial depressant and hypotensive effects of significant concentrations of halogenated anesthetics. Nitrous oxide (N ₂ O) should be avoided because of its potential to expand closed air spaces. In small infants with large L-R shunts, high Fi o ₂ accompanied by hyperventilation to lower Pa co ₂ will often excessively lower PVR, resulting in large increases in Qp/Qs, more diastolic steal of systemic blood flow, and large increases in both LV and RV volumes, all of which may lead to acute myocardial failure. Inotropic support with dopamine or epinephrine may be needed in some patients, particularly the premature infant. Precise ventilation, with a microprocessor-controlled anesthesia ventilator capable of delivering small tidal volumes, or hand ventilation, may be required.

Premature infants often undergo thoracotomy at the bedside in the neonatal ICU, to avoid the stresses of transport to a distant OR. A complete anesthesia setup, with all necessary equipment and drugs, is brought to the bedside. Normally the infant’s NICU ventilator is used, and anesthesia is provided with fentanyl (30-50 μg/kg) and small doses of midazolam, along with neuromuscular blockade with vecuronium, pancuronium, or other nondepolarizing agent. This approach provides sufficient anesthesia to prevent hemodynamic response to surgery, while allowing hemodynamic stability in these fragile patients. During PDA ligation, particularly in premature infants, the anesthesiologist must have a method to monitor lower-extremity perfusion, such as pulse oximeter probe on the toe or foot. The PDA is often larger than the descending thoracic aorta, and the aorta has been mistakenly ligated in some cases; disappearance of pulse oximeter signal on the lower extremity must immediately be noted, and the surgeon must ensure that the correct structure has been occluded. Ligation of the left PA is also possible in small infants. Method of occlusion can be with vascular clips; however, many surgeons believe the most secure method is ligation at both ends of the PDA with heavy silk sutures or oversewing, followed by ligation to ensure permanent occlusion. A thoracostomy tube is typically placed, although some surgeons do not place these tubes in premature infants. A postoperative chest radiograph is obtained in all patients.

In small infants with significant pathophysiology, the trachea is left intubated to allow recovery from both the cardiac and the pulmonary effects of a large PDA. In almost all other patients, the trachea can be extubated at the end of the procedure. Postoperative analgesia can include thoracic nerve blocks or wound infiltration by the surgeon, or possibly thoracic epidural analgesia (not usually used because recovery is typically rapid). Opioids and nonsteroidal anti-inflammatory drugs (NSAIDs) are used for postoperative pain. Postoperative stay for uncomplicated PDA ligation is short, usually 24 to 48 hours; CCL closure is usually followed by discharge home the same day.

According to the latest AHA infective endocarditis guidelines, acyanotic patients with unrepaired or repaired PDA do not require prophylaxis.

Aortopulmonary Window

Aortopulmonary (AP) window is an abnormal connection between the intrapericardial components of the aorta and pulmonary artery. AP window is a rare lesion, only 0.1% to 0.6% of congenital heart defects. About half of patients also have associated cardiac defects (e.g., PDA, VSD). The AP window can range from small, circular communication to total absence of the septum between the aorta and PA. Some AP window defects have a tubular communication. The pathophysiology of an AP window is similar to that of a large PDA and depends on size of the communication and relative SVR and PVR. AP window is usually diagnosed in early infancy, with the presence of a systolic or continuous murmur similar to that of a PDA, with pulmonary overcirculation, tachypnea, poor feeding and growth, and signs of CHF. Diastolic coronary steal may impair ventricular function. Diagnosis is by echocardiography. Repair is most often done in early infancy, almost always with CPB; the AP window is repaired by patching if large, or by direct suture ligation if small. Older children with suitable defects may have an AP window occluded in the CCL with various closure devices. Anesthetic management is the same as for the patient with a large PDA, with the same approach to pathophysiologic derangements. Approach to the infant undergoing repair with CPB is the same as for any complex case.

Atrial Septal Defect

Atrial septal defects (ASD) represent 5% to 10% of congenital heart defects and are classified as secundum (80% of defects), primum, sinus venosus, or coronary sinus ASDs ( Fig. 3-10 ). The secundum ASD is in the middle of the atrial septum, in the fossa ovalis, and results from lack of proper formation of the secundum septum. A primum ASD is low in the atrial septum, just above the tricuspid valve, a result of abnormal formation of the septum primum. It is often associated with a cleft mitral valve or with partial or complete atrioventricular (A-V) canal defects. Sinus venosus ASDs are usually found just below the SVC orifice but may also be found just above the IVC orifice. This lesion is often associated with partial anomalous pulmonary venous return (PAPVR; see later). A coronary sinus ASD, or “unroofed coronary sinus,” results from lack of a partition between the coronary sinus and left atrium, allowing LA blood to drain into the right atrium. This defect is usually associated with a persistent left SVC. Finally, a probe-patent foramen ovale (PFO) is present in up to one third of normal individuals, resulting from failure of fusion of the overlapping primum and secundum septae. As long as LA pressure is higher than right atrial (RA) pressure, ASD is asymptomatic; however, paradoxical embolus and stroke or transient ischemic attack may occur if RA exceeds LA pressure, as during a Valsalva maneuver.

Atrial septal defects.

A, Atrial septal anatomy. Schematic diagram shows the location of atrial septal defects, numbered in decreasing order of frequency: 1, secundum; 2, primum; 3, sinus venosus; 4, coronary sinus type. IVC, Inferior vena cava; PT, pulmonary trunk; RV, right ventricle; SVC, superior vena cava. B, Secundum atrial septal defect (ASD), right atrial view. SVC, Superior vena cava; RAA, right atrial appendage; CS, coronary sinus; TV, tricuspid valve; RV, right ventricle.

(Modified from Porter CJ, Feldt RH, Edwards WD, et al: Atrial septal defects. In Emmanouilides GC, Riemenschneider TA, Allen HD, Gutgesell HP, editors: Moss and Adams heart disease in infants, children, and adolescents: including the fetus and young adult, Baltimore, 1995, Williams & Wilkins.)

Flow through the ASD is left to right, and symptomatology depends on the size of the shunt. Because of the low pressure in the atria and small interatrial pressure gradients, the magnitude of the shunt is usually 2:1 or less. Ventricular compliance also affects degree of shunting; the relatively stiff right ventricle in the first few months of life prevents significant shunt. Symptoms are often minimal, and may go undetected for many years, even decades. Exercise intolerance is one of the usual symptoms; more severe symptoms (e.g., CHF, atrial flutter/fibrillation) are late signs and usually in patients over age 40. Pulmonary hypertension during childhood is rare but occurs in about 20% of patients age 20 to 40 and half of patients over 40. Rarely, fixed pulmonary pressures result in Eisenmenger’s syndrome. LV and RV sizes and function remain normal, but right atrium and right ventricle are enlarged with the added volume load. Systemic CO and Sa o ₂ are normal ( Box 3-5 ).

Physical examination reveals an acyanotic child, usually in no distress. Patients with ASD often have no symptoms until later in life. Cardiac examination is usually abnormal, with a fixed, split S ₂ the most consistent finding. This results from increased RV volume, delaying full ejection and keeping the pulmonary valve open later, and eliminating the respiratory variation. The murmurs are soft, I-II/VI, systolic, and at the left upper sternal border. A soft mid-diastolic murmur may be present with large shunts. In many ASD patients the physical examination findings are subtle, resulting in delayed diagnosis. ECG normally reveals sinus rhythm; biatrial enlargement, right-axis deviation, and first-degree A-V block may be seen in some patients. As noted, atrial fibrillation or flutter is a late sign usually seen only in unrepaired adults. Chest radiograph reveals cardiomegaly, increased PA size, and increased pulmonary vascular markings in patients with moderate to large L-R shunts.

Diagnostic modalities for ASD include transthoracic echocardiography, the most useful test, which typically is sufficient to make the diagnosis and plan treatment. Two-dimensional (2D) echocardiography defines the size, position, and morphology of the defect, ventricular size and function, and any associated intracardiac lesions (e.g., PAPVR). Color flow Doppler defines the direction of blood flow and its velocity, to assess the relative LA and RA pressures. Agitated saline contrast injection during a Valsalva maneuver can diagnose an R-L shunt through a PFO by the early appearance of microbubbles in the left atrium. Cardiac MRI and CT are not used for ASD diagnosis, except in cases of complex or uncertain anatomy, with associated defects not well defined by echocardiography. Cardiac catheterization is only used in conjunction with planned device closure of the ASD.

Most patients with an unrepaired ASD will tolerate anesthesia well without hemodynamic compromise. The usual techniques and drug doses used for patients without heart disease can be employed. Air bubbles must be avoided in any IV fluids; paradoxical embolization can occur during Valsalva-type maneuvers. Patients with CHF, atrial arrhythmias, or PH must be carefully evaluated and the anesthetic planned accordingly. Infective endocarditis prophylaxis for ASD patients is only indicated after patch repair in the first 6 months.

Secundum ASDs with adequate rims of tissue in all dimensions or PFOs are normally closed in the CCL, with various devices deployed by large sheaths introduced via the femoral vein. For children, general anesthesia is normally employed, and the device is positioned with the aid of fluoroscopy and TEE necessitating a general anesthetic. In older patients, it is possible to use sedation without endotracheal intubation, if an intracardiac echo catheter technique is used. These procedures usually are not accompanied by major hemodynamic instability or blood loss. Larger defects, or other types of ASDs (sinus venosus, primum, coronary sinus) are closed surgically with CPB; minimally invasive techniques with tiny sternotomy incisions can be used. Most patients have short CPB and aortic cross-clamp times, and repair is with autologous pericardial patch or direct suture closure. The majority of these patients can be extubated in the OR and do not experience much bleeding or hemodynamic instability.

Ventricular Septal Defect

Ventricular septal defect (VSD) is the most common form of congenital heart disease; up to 20% of patients have this lesion as an isolated defect. In addition, as many as 40% to 50% of all patients have a VSD as some component of their CHD. VSD anatomy is highly variable, but four main types are encountered, as follows:

• 1.
  

  Perimembranous VSD is the most common form (75%-80% of VSDs) is found in the middle of the ventricular septum, underneath the septal leaflet of the tricuspid valve.

  
  
• 2.
  

  Subarterial or outlet VSD (5%-15%) is high in the outlet septum, underneath the aortic and pulmonary valves.

  
  
• 3.
  

  Muscular VSD (2%-7%) can be found anywhere in the muscular septum.

  
  
• 4.
  

  Inlet-type VSD (5%) is located in the inlet septum underneath the tricuspid valve.

Many other variations and combinations of VSD range from tiny muscular VSDs that close spontaneously to very large and multiple defects ( Fig. 3-11 ).

Anatomic position of ventricular septal defects.

A, Subarterial or outlet defect; B, papillary muscle of the conus; C, perimembranous defect; D, marginal muscular defects; E, central muscular defects; F, inlet defect; G, apical muscular defects.

(Redrawn from Graham TP Jr, Gutgesell HP: Ventricular septal defects. In Emmanouilides GC, et al, editors: Moss and Adams heart disease in infants, children, and adolescents: including the fetus and young adult, Baltimore, 1995, Williams & Wilkins.)

Left-to-right shunt through the VSD depends on the size of the defect, the relative pressures in the right and left ventricles, and the relative ventricular compliances, as well as the PVR and SVR. If the VSD is small and restrictive, there is significant resistance to flow, the pressure drop across the VSD is large, and Qp/Qs is less than 2:1. As the VSD size increases, resistance is less and flow greater, until the defect is termed unrestrictive; LV and RV pressures are similar, Qp/Qs increases significantly to 3:1 or greater, and relative PVR/SVR ratio becomes the important determinant of flow. In clinical practice, Qp/Qs ranges from essentially 1:1 with a tiny VSD to extreme elevations of 5:1 or greater in infants with very large VSD and low PVR. Certainly, elevated PVR may develop with months or years of high pressure and flows into the pulmonary arteries. If left untreated, the increased PVR can become fixed and suprasystemic, and flow direction can reverse to produce an R-L shunt, cyanosis, and Eisenmenger’s syndrome. Although unusual before several years of life, Eisenmenger’s syndrome can occur as early as 1 to 2 years in patients with large VSDs ( Box 3-6 ).

Physical examination findings range from asymptomatic patients to those with severe CHF. Infants with large VSD are normally acyanotic with Sp o ₂ of 95% to 100%. Tachypnea is common, reflecting the pulmonary congestion, and a compensatory tachycardia to maintain systemic CO in the face of a large L-R shunt is often present. Feeding is often tiring for these infants, and growth is often poor, both from inadequate caloric intake and from a very high metabolic rate accompanying increased myocardial work. CHF is heralded by retractions, fine rales, hepatomegaly, jugular venous distention, and diaphoresis. Cardiac examination reveals an active precordium, displacement of the ventricular apex to the left, and a murmur, which is usually a grade II-III/VI pansystolic murmur between the second and third left intercostal spaces. Smaller, restrictive defects produce more turbulent flow and may be accompanied by a grade IV/VI murmur. Large VSD in young infants whose PVR has not yet experienced its physiologic fall may have minimal or no murmur, explaining why some of these patients are diagnosed late. Qp/Qs greater than 3:1 will also produce a mid-diastolic flow murmur at the cardiac apex. Heart sounds are normal unless PVR is significantly elevated. ECG findings are not specific for VSD, are usually sinus rhythm, and may exhibit right-axis deviation with significant shunts. Chest radiography normally reveals cardiomegaly and increased pulmonary vascular markings, in proportion to the size of the L-R shunt. Echocardiography is the mainstay of diagnosis, with 2D echocardiography revealing the size, position, and shape of the defect, ventricular size and function, and associated intracardiac defects (see Fig. 3-4 , A ). MRI, CT, and cardiac catheterization are required only for complicated VSD with associated defects or for hemodynamic catheterization if PVR is a concern.

Patients with an unrepaired small VSD are relatively asymptomatic and will tolerate any of the common anesthetic techniques and drugs. Again, no bubbles must be introduced into the venous circulation by drug injection or IV fluids; paradoxical R-L shunt can easily occur with elevated PVR or Valsalva-type maneuvers. Infants under age 1 year with a large VSD often have very labile PVR, and rapid increases can occur with hypercarbia, acidosis, or hypoxemia; these patients may experience periods where PVR is higher than SVR, leading to R-L shunt and further hypoxemia, which can be life threatening. Conversely, excessive decreases in PVR, which often accompany high Fi o ₂ and hyperventilation, can greatly increase Qp/Qs, with adverse hemodynamic consequences, including acute RV and LV dilation and dysfunction, low diastolic BP resulting in coronary ischemia, and in some patients, cardiac arrest. Indeed, in 127 infants and children with CHD experiencing cardiac arrest under anesthesia, 18% had an L-R shunt lesion, with VSD the most common. Thus, even relatively simple lesions have the potential for extreme pathophysiologic derangements. When anesthetizing an infant with an unrestrictive VSD, it is prudent to decrease the Fi o ₂ to low levels (0.21-0.3) and to avoid hyperventilation, in order to prevent excessive increases in Qp/Qs.

VSD closure can sometimes be carried out in the CCL, with devices similar to those used for ASD closure, if the VSD is suitably accessible. However, this procedure may have significant hemodynamic instability and blood loss. Complications, including complete A-V block, can be seen in up to 11% of patients, with mortality in 3%. The vast majority of VSDs are closed surgically in the first 2 years of life, with CPB, and patching of the VSD with polyester fiber (Dacron) or the patient’s own pericardium using a transatrial approach. Contemporary surgical series from excellent centers report mortality of 0.5%, with no complete A-V block and no VSD recurrences or reoperations. Many patients older than 6 to 12 months are candidates for early tracheal extubation and rapid ICU discharge. Infectious endocarditis prophylaxis is not indicated for unrepaired isolated VSD or repaired VSD after 6 months with no residual defects.

Atrioventricular Canal

Atrioventricular canal (AVC) results from failure of the endocardial cushion to form early in fetal development. This defect is present in 3% to 5% of patients with CHD and is particularly prevalent in trisomy 21 patients, 20% to 33% of whom have AVC.

The three major variants of AVC are partial, transitional or intermediate, and complete AVC. The unifying feature of all types is the presence of a common A-V junction, with either a single A-V valve, or if separated, both tricuspid and mitral valves at the same level in the heart, rather than complete septation, with tricuspid annulus inferior and mitral annulus superior. Partial AVC consists of an ostium primum ASD and a cleft in the anterior leaflet of the mitral valve. There is no VSD component in this lesion. Transitional AVC consists of the ostium primum ASD, common A-V valve, and a small inlet VSD component that may be covered by A-V valve tissue. There is some degree of A-V valve regurgitation in this lesion.

Complete AVC is characterized by the primum ASD, common A-V valve, and a large inlet VSD. Complete A-V canal is further subdivided according to the arrangement of the anterior bridging leaflet of the common A-V valve and the position of its chordal attachments. In Rastelli type A the bridging leaflet is mostly contained on the LV side, and the chordae are attached to the crest of the ventricular septum ( Fig. 3-12 ). In Rastelli type B the bridging leaflet is more on the RV side, and the papillary muscle of the leaflet is attached to the right side of the ventricular septum. Type B is rare. Rastelli type C is the most common, and the superior bridging leaflet is unattached to the ventricular septum. Other variants of complete AVC include RV or LV dominant, with discrepant ventricular size; tetralogy of Fallot with complete AVC; and complete AVC with LV outflow tract obstruction.

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