Essentials of Cardiology

14 Essentials of Cardiology





Congenital Heart Disease



Incidence


Congenital heart disease (CHD) represents the most common form of congenital pathology, with an estimated incidence of 0.3% to 1.2% of live births.1 CHD is a major cause of morbidity and mortality during the neonatal period. However, with advances in medical and surgical management, including significant contributions related to anesthesia care, survival to adulthood is the expectation for most infants and children with CHD.24


A bicuspid aortic valve (Video 14-1)image is the most common cardiac defect, occurring in up to 1% of the population.5,6 Ventricular septal defects (VSD) (Video 14-2)image represent the next most common congenital pathology,5,711 followed by secundum atrial septal defects (ASD) (Video 14-3)image.5,12 Among cyanotic lesions, tetralogy of Fallot (TOF) predominates, affecting almost 6% of children with CHD (Fig. 14-1).13 In the first week of life, d-transposition of the great arteries (Fig. 14-2) is the most frequently encountered cause of cardiac cyanosis; TOF is sometimes not detected until later in life because cyanosis is absent or only mild desaturation is present.





Segmental Approach to Diagnosis


Several classification schemes have been proposed to characterize and categorize various congenital cardiac defects.1420 The segmental approach to the diagnosis of CHD assumes a sequential, systematic analysis of the three major cardiac segments (i.e., atria, ventricles, and great arteries) to describe the anatomic abnormalities. The principle of this scheme is that specific cardiac chambers and vascular structures have characteristic morphologic properties that determine their identities, rather than their positions within the body.21 An organized, systematic identification of all cardiac structures or segments and their relationships (i.e., connections or alignments between segments) is carried out to define a child’s anatomy.22


The initial approach is to determine the cardiac position within the thorax and the arrangement or situs of the thoracic and abdominal organs. The cardiac position can be described in terms of its location within the thoracic cavity (Fig. 14-3) and the direction of the cardiac apex. Although the cardiac position within the thorax may be considered independent of the cardiac base-apex axis, for simplicity the following terms are used: levocardia if the heart is in the left hemithorax (as is normally the case); dextrocardia if the heart is located in the right hemithorax; and mesocardia if the heart is displaced rightward but not completely in the right thoracic cavity. An abnormal location of the heart within the thorax (i.e., cardiac malposition) may result from displacement by adjacent structures or underlying noncardiac malformations (e.g., diaphragmatic hernia, lung hypoplasia, scoliosis).



The visceral situs, or sidedness, of the abdominal organs (i.e., liver and stomach) and atrial situs are considered independently (Fig. 14-4). Visceral situs is classified as solitus (i.e., normal arrangement of viscera, with the liver on the right, stomach on the left, and a single spleen on the left), inversus (i.e., inversion of viscera, with the liver on the left and stomach on the right), or ambiguous (i.e., indeterminate visceral position). Abnormal arrangements or sidedness of the abdominal viscera, heart, and lungs suggests a high likelihood of complex cardiovascular disease. The atrial situs, atrioventricular (AV) connections, ventricular looping (i.e., position of the ventricles as a result of the direction of bending of the straight heart tube in early development), ventriculoarterial connections, and the relationship between the great vessels are then delineated.



Associated malformations are described, including number and size of septal defects and valvar or great vessel abnormalities. Whereas many types of congenital defects fall neatly into this classification scheme, others (e.g., heterotaxy syndromes, conditions associated with malposition of the heart and abdominal organs) are often more difficult to precisely define.



Physiologic Classification of Defects


The wide spectrum of cardiovascular malformations in the pediatric age group presents a challenge to the clinician who does not specialize in the care of these children. Even for those with a focus or interest in cardiovascular disease, the range of structural defects and the varied associated hemodynamic perturbations can be overwhelming.


A physiologic classification system can facilitate understanding of the basic hemodynamic abnormalities common to a group of congenital or acquired lesions and assist in patient management (Table 14-1).23,24 Several classification schemes have been proposed, including some that categorize structural defects as simple or complex lesions, consider the presence or absence of cyanosis, or consider whether pulmonary blood flow is increased or decreased.2527 The following approach groups pediatric heart disease into six broad categories according to the underlying physiology or common features of the pathologies.


TABLE 14-1 Physiologic Classification of Congenital Heart Disease (Representative Lesions)








Single-Ventricle Lesions


This category is the most heterogeneous group, consisting of defects associated with AV valve atresia (i.e., tricuspid atresia), heterotaxy syndromes, and many others.28 In some cases, both atria empty into a dominant ventricular chamber (i.e., double-inlet left ventricle), and although a second rudimentary ventricle may be present, the physiology is that of a single-ventricle or univentricular heart. Other cardiac malformations with two distinct ventricles (i.e., unbalanced AV septal defect) may also be considered in the functional single-ventricle category because of associated defects that may preclude a biventricular repair. A common feature of these lesions is complete mixing of the systemic and pulmonary venous blood at the atrial or ventricular level. Another common finding is aortic or pulmonary outflow tract obstruction.


Affected children are a challenge to the practitioner and require careful delineation of their anatomy. An important goal in single-ventricle management involves optimization of the balance between the pulmonary and systemic circulations early in life. This is a critical issue because low pulmonary vascular resistance and limitation of the ventricular volume load represent a prerequisite for later palliative strategies and favorable outcomes in these children. These considerations are also relevant during anesthesia management for noncardiac surgery (see Chapter 21).26,29,30




Acquired Heart Disease



Cardiomyopathies


The term cardiomyopathy usually refers to diseases of the myocardium associated with cardiac dysfunction.31,32 They have been classified as primary and secondary forms. The most common types in children are hypertrophic, dilated or congestive, and restrictive cardiomyopathies. Other forms include left ventricular noncompaction3335 and arrhythmogenic right ventricular dysplasia.36 Secondary forms of cardiomyopathies are those associated with neuromuscular disorders such as Duchenne muscular dystrophy, glycogen storage diseases (i.e., Pompe disease), hemochromatosis or iron overload, and mitochondrial disorders. Chemotherapeutic agents such as anthracyclines may result in dilated cardiomyopathy.37 It is important to understand the hemodynamic processes behind the myocardial disease and implications for acute and chronic management.


Hypertrophic cardiomyopathy (HCM) is characterized by ventricular hypertrophy without an identifiable hemodynamic cause that results in increased thickness of the myocardium. This accounts for almost 40% of cardiomyopathies in children.3841 The condition represents a heterogenous group of disorders, and most of the identified genetic defects exhibit autosomal dominant inheritance patterns.42,43 This is the most common cause of sudden cardiac death (SCD) in athletes.44,45 Most children with HCM do not have systemic outflow tract obstruction (i.e., nonobstructive cardiomyopathy). It is unclear whether the few with hypertrophic obstructive cardiomyopathy, previously known as idiopathic hypertrophic subaortic stenosis, are at increased risk for SCD compared with children without obstruction.44


Most children with HCM present for evaluation of a heart murmur, syncope, palpitations, or chest pain. Occasionally, an abnormal electrocardiogram (ECG) leads to referral. An accurate family history is essential. An apical impulse is often prominent. Auscultation may reveal a systolic ejection outflow murmur that becomes louder with maneuvers that decrease preload or afterload (e.g., standing, Valsalva maneuver) or increased contractility. The murmur decreases in intensity with squatting and isometric hand grip. A mitral regurgitant murmur may also be present. The ECG meets criteria for left ventricular hypertrophy in most children (Fig. 14-5). In some, the electrocardiographic findings may be striking (Fig. 14-6). A hypertrophied, nondilated left ventricle is a diagnostic feature determined by echocardiography (Video 14-4, A and B)image.45 In many children, the hypertrophy may be asymmetric (Video 14-5, A and B)image. Echocardiography is the primary imaging modality for long-term assessment of wall thickness, ventricular dimensions, presence and severity of obstruction, systolic and diastolic function, valve competence, and response to therapy. Other diagnostic approaches such as cardiac catheterization and magnetic resonance imaging (MRI) may add helpful information in some cases.




The care of children with HCM includes maintenance of adequate preload, particularly in those with dynamic obstruction. Diuretics are not indicated and often worsen the hemodynamic state by reducing left ventricular volume and increasing the outflow tract obstruction. Drugs that augment myocardial contractility (e.g., inotropic agents, calcium infusions) are not well tolerated. Patients usually undergo continuous electrocardiographic monitoring (i.e., Holter recording) and exercise testing for risk stratification.46 β-Blockers and calcium channel blockers are the primary agents for outpatient drug therapy.47 Therapies range widely and include longitudinal observation with medical management of heart failure and arrhythmias, implantation of cardioverter-defibrillators, surgical myotomy or myectomy, transcatheter alcohol septal ablation, and cardiac transplantation.


Dilated cardiomyopathy (DCM), also known as congestive cardiomyopathy, is characterized by thinning of the left ventricular myocardium, dilation of the ventricular cavity, and impaired systolic function.4850 The broad number of etiologies range from genetic or familial forms to those caused by infections,51 metabolic derangements, toxic exposures, and degenerative disorders.52,53 Chronic tachyarrhythmias can also lead to DCM that may or may not improve after the rhythm disturbance is controlled.5456


Most children with DCM present with signs and symptoms of congestive heart failure (e.g., tachypnea, tachycardia, gallop rhythm, diminished pulses, hepatomegaly). The chest radiograph typically demonstrates cardiomegaly, pulmonary vascular congestion, and in some cases, atelectasis (Fig. 14-7). The ECG may identify the likely cause of the cardiac dysfunction in those with cardiomyopathy due to rhythm disorders or anomalous origin of the left coronary artery from the pulmonary root (ALCAPA). The echocardiogram can confirm the diagnosis by demonstrating a dilated left ventricle with decreased systolic function (Video 14-6, A and B)image.57 Therapy in the acute setting is supportive and aimed at stabilization. Management may include afterload reduction, inotropic support, and mechanical ventilation. Unlike children with HCM, those with DCM have a volume-loaded, poorly contractile ventricle. Gentle diuresis is beneficial. The infusion of large fluid boluses may be poorly tolerated and result in hemodynamic decompensation and cardiovascular collapse. The outcomes of children with dilated cardiomyopathy vary. For most, recovery of left ventricular systolic function occurs, but others eventually require cardiac transplantation.58 In a subset of children with severe disease, mechanical circulatory support may be necessary as a bridge to recovery or cardiac transplantation (Fig. 14-8) (see Chapter 19).5961




Restrictive cardiomyopathy (RCM) is the least common of the major types of cardiomyopathies (5%) and portends a poor prognosis when it manifests during childhood.6267 The disorder is characterized by diastolic dysfunction related to a marked increase in myocardial stiffness resulting in impaired ventricular filling. Most cases are thought to be idiopathic. Presenting symptoms are nonspecific and primarily respiratory. Occasionally, the diagnosis is made after a syncopal or sudden near-death event. The physical examination may demonstrate hepatomegaly, peripheral edema, and ascites.


The echocardiographic hallmark of RCM is that of severe atrial dilation and normal- to small-sized ventricles (Video 14-7)image. The marked diastolic dysfunction leads to increased end-diastolic pressures, left atrial hypertension, and secondary pulmonary hypertension. Children with RCM are prone to thromboembolic complications, and anticoagulation therapy is frequently recommended. This is an important consideration during perioperative care because adjustments in the anticoagulation regimen may be necessary. Atrial and ventricular tachyarrhythmias may also occur. Optimal medical treatment is controversial because no specific agents or strategies have been shown to significantly alter outcomes.67 Similar to children with HCM, diuretics often cause a decrease in the needed preload with detrimental effects on hemodynamics. Inotropic agents are not indicated because systolic function is preserved and the arrhythmogenic properties of inotropic drugs can induce a terminal event. In many centers, cardiac transplantation has been effectively used.68,69



Myocarditis


Myocarditis is defined as inflammation of the myocardium, often associated with necrosis and myocyte degeneration. In the United States, it is most often caused by a viral infection. Over the past 20 years, the spectrum of viral pathogens causing myocarditis has changed, such that adenovirus, enteroviruses (e.g., coxsackievirus B), and parvovirus have become the most frequent causes of fulminant disease.7072


The overall incidence of myocarditis is unknown because it is frequently underdiagnosed and unrecognized as a nonspecific viral syndrome. A large, 10-year, population-based study on cardiomyopathy found an annual incidence of 1.24 cases per 100,000 children younger than 10 years of age; only a fraction of cases represented those with myocarditis.73 The diagnosis is made using clinical history, physical examination, and imaging modalities. Myocarditis is highly suspected when a child presents with new-onset congestive heart failure or ventricular arrhythmias without evidence of structural heart disease. The ECG typically demonstrates low-voltage QRS complexes with tachycardia, which sometimes is ventricular in origin. Chest radiography often shows cardiomegaly with pulmonary vascular congestion (Fig. 14-9). Echocardiography displays ventricular dilation with decreased systolic function, similar to DCM, and it is useful in the exclusion of alternative diagnoses, such as pericardial effusion or anomalous origin of a coronary artery. Myocarditis is a clinical diagnosis because definitive confirmation requires the analysis of tissue obtained through myocardial biopsy in the catheterization laboratory or the operating room (rarely performed).74



Many children with myocarditis have subclinical or mild clinical disease, whereas others progress to overt heart failure or arrhythmias, or both. Among children with heart failure, approximately one third will regain full ventricular function, one third will recover but continue to demonstrate impaired systolic function, and one third will require cardiac transplantation.75,76 A subset of children, not all of whom initially manifest severe symptoms in the acute period, will progress to have DCM.


Although no specific therapies have been identified to directly treat the myocardial injury, a variety of strategies have been employed.7780 The current paradigm includes diuresis and afterload reduction to improve myocardial performance without placing a large burden on an already failing heart.81 Rhythm disturbances are treated appropriately. Therapy with immune modulation or suppression with intravenous immunoglobulin is the standard of care at many centers.8183 Mechanical circulatory support may be required in fulminant disease.8489



Rheumatic Fever and Rheumatic Heart Disease


Acute rheumatic fever and rheumatic heart disease are leading causes of acquired cardiac disease in developing countries and still occur, albeit infrequently, in developed countries.90 In the United States, the availability of antibiotic therapy for streptococcal pharyngitis has markedly reduced the incidence of this disease, but sporadic cases still occur.91 In children, the peak incidence occurs between 5 and 14 years of age.


Rheumatic fever results from infection by particular strains of group A β-hemolytic Streptococcus or Streptococcus pyogenes leading to a multisystemic inflammatory disorder. The incubation period for most strains of group A β-hemolytic Streptococcus is typically 3 to 5 days, although some children present with a more remote history of pharyngitis.


The clinical diagnosis of rheumatic fever is based on the modified Jones criteria.92 Major criteria include carditis, polyarthritis, chorea, subcutaneous nodules, and erythema marginatum. Without a history of rheumatic fever or echocardiographic evidence of typical valvular involvement, the diagnosis in children requires evidence of a prior streptococcal infection along with two major criteria or one major and two minor criteria. Fever and arthritis are common symptoms. The polyarthritis has a migratory pattern, typically affecting large joints. Cardiac involvement or carditis occurs in almost 50% of children with their first attack of rheumatic fever. Rheumatic heart disease represents a sequela of the acute process, and it most frequently affects the mitral and aortic valves.


Primary prevention of rheumatic fever and rheumatic heart disease begins with prompt recognition and appropriate treatment of the initial streptococcal infection.93,94 Secondary prevention, with ongoing therapy in individuals with a known history of rheumatic fever, has been extremely effective in preventing recurrent attacks. Although there is debate regarding the optimal regimen, intramuscular injections of benzathine penicillin every 3 to 4 weeks appear to be most efficacious.95


In a subset of children with severe cardiac involvement, elective or emergent surgery may be required.96 Valvular disease, rather than global myocarditis, is often the cause of congestive symptoms; medical management therefore has limited efficacy. Valve repair is preferred to replacement.



Infective Endocarditis



Causes and Treatment


Children with structural or acquired heart disease are at risk for infective endocarditis.97,98 The risk to a great extent is based on the nature of the cardiac condition. The infection results from deposition of bacteria or other pathogens on tissues in areas of abnormal or turbulent blood flow. The diagnosis of endocarditis is made clinically by applying the modified Duke criteria (Table 14-2).99,100 Major criteria include demonstration of microorganisms and evidence of pathologic lesions. The presentation of the disease may be acute or subacute. New or changing heart murmurs may indicate the development of regurgitation or obstruction on an affected valve. Among the physical findings may be signs of systemic embolization (i.e., minor criteria). Splinter hemorrhages (i.e., linear streaks under the nail beds), Janeway lesions (i.e., painless macules on the hands or feet), Osler nodes (i.e., small, painful nodules on the fingers), and Roth spots (i.e., retinal hemorrhages with clear centers) may also be present. Inflammatory markers, such as erythrocyte sedimentation rate and C-reactive protein, are typically increased, albeit nonspecific. Microscopic hematuria, as a manifestation of renal involvement, is frequently seen.


TABLE 14-2 Modified Duke Criteria for Infective Endocarditis



*Duke Clinical Criteria for Infective Endocarditis requires two major criteria or one major and three minor criteria or five minor criteria to establish the diagnosis.


For definition, see en.wikipedia.org/wiki/HACEK_endocarditis


Modified from Li JS, Sexton DJ, Mick N, et al. Proposed modifications to the Duke criteria for the diagnosis of infective endocarditis. Clin Infect Dis 2000;30:633-8.


Acute bacterial endocarditis is most commonly caused by Staphylococcus aureus.101,102 The clinical presentation includes high fevers, chills, myalgias, fatigue, and lethargy. Some children present in a critically ill state or in shock. Both left- and right-sided endocarditis can occur in children with CHD.103 Children with indwelling venous catheters have an expanded spectrum of pathogens known to cause acute endocarditis, including coagulase-negative staphylococcal species or other nonbacterial organisms.


Subacute bacterial endocarditis (SBE) often has a more indolent course and presentation. Children present with low-grade fevers, malaise, anemia, and fatigue. Most frequently, one of the Viridians streptococcus group and Enterococcus species is the underlying pathogen.


Initial evaluation for bacterial endocarditis includes serial blood cultures drawn from separate sites before initiation of antimicrobial therapy. The temporal frequency of cultures depends on the clinical scenario and stability of the child. In up to 20% of children with evidence of endocarditis, a pathogen cannot be isolated (i.e., negative culture), requiring empirical treatment throughout. Transthoracic echocardiography is routinely performed to evaluate evidence of vegetations or other abnormalities.104 Although visualization of a vegetation establishes the diagnosis, a negative study does not exclude the diagnosis. Depending on how strongly the diagnosis is suspected, further imaging, including transesophageal echocardiography, may be necessary (Video 14-8, A and B)image.105 These imaging modalities are also valuable during follow-up.


Parenteral antibiotics are initiated after blood cultures are collected. Broad-spectrum agents are used initially, and after a pathogen has been identified, the antibiotic regimen is narrowed.97 Daily blood cultures are obtained until three consecutive cultures remain sterile. A prolonged course of therapy (e.g., 4 to 6 weeks) is required in all children. This can be facilitated by placement of a peripherally inserted central catheter (PICC) line. Home therapy for endocarditis may be feasible in some patients, but it depends on many factors, including clinical status, initial response to antibiotics, sensitivity of organism to antimicrobial therapy, and ability of infrastructure to support outpatient treatment of a serious infection (e.g., parental or family member’s ability, home health care provider).


In addition to medical therapy, some children require surgical intervention. Failure of medical therapy (i.e., inability to clear the bacteremia), abscess formation, refractory heart failure, and serious embolic phenomenon are indications for surgical intervention. Typically, the procedures involve resection of a vegetation, tissue débridement, or repair of consequent cardiac abnormalities. These children should subsequently receive antibiotic prophylaxis for endocarditis before at-risk procedures for the rest of their lives.


A high level of suspicion for endocarditis must be maintained when evaluating a child with known heart disease and with persistent bacteremia (or fungemia) or a fever of unknown origin. The same holds true for any child with foreign material in the heart or vascular tissue, such as indwelling central venous catheters, pacemakers or defibrillators, and closure devices.106



Endocarditis Prophylaxis


The risk for developing endocarditis from transient bacteremia is extremely low in children with normal intracardiac anatomy, however, certain cardiac conditions are predisposed to acquiring endocarditis. The American Heart Association guidelines do not recommend antibiotic prophylaxis based exclusively on an increased lifetime risk of endocarditis, but they propose that it should be restricted to those at greatest risk for an adverse outcome resulting from endocarditis. Children in this category include those with prosthetic cardiac valves, a history of endocarditis, certain congenital heart defects, after specific interventions, and cardiac transplant recipients with valvular disease (Table 14-3).107


TABLE 14-3 Cardiac Conditions Associated with the Greatest Risk of Adverse Outcomes from Endocarditis



*Except for the conditions listed, antibiotic prophylaxis is no longer recommended for other forms of CHD.


Prophylaxis is recommended because endothelialization of prosthetic material occurs within 6 months after the procedure.


Modified with permission from Wilson W, Taubert KA, Gewitz M, et al., editors. Prevention of infective endocarditis: guidelines from the American Heart Association. A guideline from the American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee, Council on Cardiovascular Disease in the Young, and the Council on Clinical Cardiology, Council on Cardiovascular Surgery and Anesthesia, and the Quality of Care and Outcomes Research Interdisciplinary Working Group. Circulation 2007;116:1736-54.


Transient bacteremia may occur during dental procedures that involve the gingival tissues or the periapical region of teeth or perforation of the oral mucosa. Although several respiratory tract procedures are associated with transient bacteremia, no definitive data demonstrate a cause-and-effect relationship between these procedures and endocarditis. Caution may be warranted for children at high risk undergoing invasive procedures of the respiratory tract that involve incision or biopsy of the mucosa. In contrast to previous guidelines, routine prophylactic administration of antibiotics solely to prevent endocarditis is not recommended for those undergoing genitourinary or gastrointestinal tract procedures. However, for specific clinical scenarios, antibiotic prophylaxis may be considered in these children. Routine endoscopy or transesophageal echocardiography does not merit routine antibiotic administration.108 Prophylaxis is not considered necessary for cardiac catheterization; and although many practitioners routinely administer antibiotics during transcatheter placement of devices, there is insufficient evidence to support this practice.109


The guidelines recommend the administration of antibiotic prophylaxis 30 to 60 minutes before the procedure to achieve adequate tissue levels of antibiotics before bacteremia occurs (Table 14-4).107 The standard prophylactic regimen for children is for oral amoxicillin. For the child who is allergic to penicillin or ampicillin, oral alternatives include cephalexin, clindamycin, azithromycin, or clarithromycin. In children who are unable to ingest oral medications, alternative antibiotics include ampicillin, cefazolin, and ceftriaxone by an intravenous or intramuscular route. If the child is allergic to penicillin or ampicillin and unable to swallow oral medications, cefazolin, ceftriaxone, or clindamycin may be used.



Although many health care providers have adopted the updated recommendations, some have been hesitant to alter their practice regarding endocarditis prophylaxis, particularly when caring for patients with CHD undergoing gastrointestinal or genitourinary procedures.110 Only the American Dental Association has adopted the new guidelines for endocarditis prophylaxis; other associations such as the gastrointestinal and genitourinary groups remain uncommitted to the new guideline.



Kawasaki Disease


Kawasaki disease (i.e., mucocutaneous lymph node syndrome) represents a fairly common and potentially fatal form of systemic vasculitis of unknown origin.111115 It is seen predominantly in infants and young children. The disease can affect the coronary arteries resulting in dilation and aneurysm formation.116,117


The diagnosis relies on clinical features. To meet criteria, a child must have persistent fevers and at least four of the following findings118,119:



Nonspecific findings may include irritability, hydrops of the gallbladder, sterile pyuria, arthritis, and aseptic meningitis. Acute-phase reactants and thrombocytosis are usually present.


Intravenous gamma globulin (IVIG) and high-dose aspirin are recommended during the acute phase of the disease. The incidence of coronary artery aneurysms is significantly reduced if IVIG is administered within the first 10 days of the illness.119 The presence of coronary artery aneurysms is considered diagnostic for Kawasaki disease (Fig. 14-10). In children with coronary artery aneurysms, low-dose aspirin therapy is administered, in some cases in combination with anticoagulants or antiplatelet drugs.120 Myocardial ischemia and infarction, although uncommon, are important potential complications.117,121 Anesthetic care in these children requires careful consideration regarding myocardial oxygen demand and supply; on rare occasions, coronary revascularization may be necessary.




Cardiac Tumors


Because cardiac tumors are rare in children, the natural history and optimal treatment strategies are often determined from limited case series.122124 Atrial myxomas represent more than 90% of cardiac tumors in adults, but in children, they tend to be rhabdomyomas or fibromas.125 Less common types include hemangiomas, myxomas (Video 14-9)image, Purkinje cell tumors, and teratomas. In adults, most tumors are found in the left atrium, but cardiac tumors in children occur in all four cardiac chambers. Malignant primary tumors are rare, and data on their outcomes are limited. Other nonprimary cardiac tumors, such as neuroblastoma, can invade vascular structures and extend into the heart.


Rhabdomyomas are the most common primary cardiac tumors in children. They often involve the ventricular septum and left ventricle and are multiple in most cases.126 Although they are considered benign, children may present with cardiomegaly, congestive heart failure, arrhythmias, or sudden death. The significance of a rhabdomyoma is determined largely by its size and any obstruction it may cause. Many tumors regress over time or completely resolve; surgery is not indicated unless symptoms are present.127,128 Many children with cardiac rhabdomyomas have associated tuberous sclerosis.129,130


Cardiac fibromas are the second most common type of pediatric primary cardiac tumors.131 They are typically single and involve the ventricular free wall. In a subset of fibromas, the tumor can invade the conduction system.132 Surgery or cardiac transplantation may be required.133,134 The tumors can be very large, and complete surgical resection may result in severely depressed cardiac function. Partial resections have been found to result in an arrest in growth with good outcomes while sparing cardiac function.128


The primary concerns in the perioperative care of children with cardiac tumors are the impact of the mass on hemodynamics and the associated abnormalities of cardiac rhythm.135



Heart Failure in Children



Definition and Pathophysiology


Heart failure has become a major field of interest and investigation in pediatric cardiology and the subject of various publications,136 scientific meetings, and several textbooks.137,138 Pediatric heart failure results from markedly different causes from those reported in adults.139 The cellular basis of heart failure, compensatory mechanisms, and therapeutic advances represent areas of interest in children.136138,140,141 The following discussion highlights key concepts as they relate to anesthetic practice.


Heart failure is considered to be a pump failure and a circulatory failure involving neurohumoral aspects of the circulation.142 Several conditions may ultimately compromise the ability to generate an adequate cardiac output to meet the systemic circulatory demands. This disease state does not necessarily imply impairment of ventricular systolic function, but diastolic heart failure is an increasingly recognized clinical entity.



Etiology and Clinical Features


Causes of heart failure vary with age. In the perinatal period, cardiac dysfunction may be related to birth asphyxia or sepsis or may represent an early presentation of CHD. The neonate with heart failure frequently presents with clinical signs of a low cardiac output state. Causes include left-sided outflow obstruction (e.g., aortic stenosis, aortic coarctation, hypoplastic left heart syndrome), severe valve regurgitation (e.g., Ebstein anomaly), or absent pulmonary valve syndrome.


During the first year of life, most cases of heart failure are caused by structural heart disease. Other causes include cardiomyopathies due to inborn errors of metabolism or acute events such as myocarditis. In infants with heart failure, tachypnea, dyspnea, tachycardia, feeding difficulties, and failure to thrive are prominent symptoms.143 Physical examination reveals grunting respirations, rales, intercostal retractions, a gallop rhythm, and hepatosplenomegaly. Frequently, a mitral regurgitant murmur is present.


Beyond the first year of life, heart failure is a consequence of previous surgical interventions, unpalliated or unrepaired cardiovascular disease, cardiomyopathies, myocarditis, or anthracycline therapy for a malignancy. Occasionally, a child may present with severe ventricular systolic impairment related to ongoing myocardial ischemia as a result of a coronary artery anomaly or rarely due to acquired pathologies such as Kawasaki disease. Older children with heart failure exhibit exercise intolerance, fatigue, and growth failure, whereas adolescents have symptoms similar to those of adults.



Treatment Strategies


Therapy is tailored to the cause of the cardiac dysfunction and may include supportive care, mechanical ventilation, inotropic support, afterload reduction, prostaglandin E1 therapy to maintain pulmonary or systemic blood flow, maneuvers to balance the systemic and pulmonary circulations, catheter-based interventions, or surgery.144148 Maintaining organ perfusion is the main goal of therapy for acute heart failure. Pharmacologic agents include inotropes (used on a very-short-term basis, if necessary) and inodilators. Although the administration of digoxin was the mainstay of chronic therapy in the past, this is no longer the case. Favored agents for use in children include diuretics, angiotensin-converting enzyme inhibitors, and β-blockade.149,150 Newer agents that have received increasing attention in the management of pediatric heart failure include nesiritide (a recombinant form of human B-type natriuretic peptide)151153 and carvedilol (a third-generation β-blocker).154156



Anesthetic Considerations


Anesthesia for children with heart failure can be quite challenging. The severity of the condition and degree of baseline decompensation can influence the likelihood of an untoward event and the potential for hemodynamic instability and a bad outcome. Several publications have addressed the risks associated with anesthesia in this setting.157159 It is important to first reexamine the risk–benefit ratio in these patients before going forward with the planned procedure. In most surgical settings, tracheal intubation and mechanical ventilation are indicated. The need for invasive monitoring should be based on the clinical situation, anticipated nature of the procedure, and impact on hemodynamic state.



Syndromes, Associations, and Systemic Disorders: Cardiovascular Disease and Anesthetic Implications


Many disorders, including those resulting from chromosomal abnormalities, single-gene defects, gene deletion syndromes, known associations (i.e., nonrandom occurrence of defects), and teratogenic exposure, may manifest as cardiovascular disease. The coexistence of frequently associated multiple organ system comorbidities with cardiovascular disease presents several challenges to the anesthesia care provider.



Chromosomal Syndromes



Trisomy 21


Trisomy 21 (i.e., Down syndrome) is the most frequent chromosomal anomaly, occurring with a frequency of 1 case per 800 live births. The incidence increases sharply with advanced maternal age. The syndrome results from trisomy 21 in most children, but it may occur from a balanced or unbalanced chromosome translocation or mosaicism. The phenotypes are indistinguishable. Affected children are typically smaller than normal for age. Craniofacial features include microbrachycephaly, short neck, oblique palpebral fissures, epicanthal folds, Brushfield spots, small and low-set ears, macroglossia, and microdontia with fused teeth. Mandibular hypoplasia and a broad flat nose are typical. A narrow nasopharynx with hypertrophic lymphatic tissue (e.g., tonsils, adenoids) in combination with generalized hypotonia frequently leads to sleep apnea. Other conditions include mental retardation, cervical spine disorders with vertebral and ligamentous instability (i.e., subluxation risk), thyroid disease, leukemia, obesity, subglottic stenosis,160 and gastrointestinal problems.


Airway issues include the potential for upper airway obstruction due to a large tongue, postextubation stridor,161 and cervical spine injury.162164 Vascular access can be challenging. Subjectively, children have small and abnormal radial vessel sizes,164a vascular hyperreactivity, and fragile tissue consistency, and they may suffer from more complications after arterial cannulation.


Cardiovascular defects occur in 40% to 50% of children with Down syndrome, and it has been recommended that they all should undergo screening for CHD in early infancy.165 The most common lesions include AV septal defects (Video 14-10)image, VDSs, TOF, and PDA. Bradycardia under anesthesia occurs commonly, although the mechanism is poorly understood.166,167 Pulmonary hypertension may result from the cardiac pathology or from chronic hypoxemia due to upper airway obstruction (i.e., obstructive sleep apnea) and should be considered in their management.168 Reduced nitric oxide bioavailability has been reported in patients with Down syndrome, leading to endothelial cell dysfunction169 and possibly explaining the observed increased pulmonary vascular reactivity.



Trisomy 18


Trisomy 18 (i.e., Edwards syndrome) is recognized as the second most common chromosomal trisomy (incidence of 1 case per 3500 live births). Most children exhibit microcephaly, delayed psychomotor development, and mental retardation.170 Characteristic craniofacial features include micrognathia or retrognathia, microstomia, malformed ears, and microphthalmia.171 These abnormalities can affect airway management.172,173 Skeletal anomalies include clenched fingers and severe growth retardation. Neurologic problems include developmental delay, hypotonia, and central nervous system malformations. The high mortality rate for children with trisomy 18 is related to cardiac and renal problems, feeding difficulties, sepsis, and apnea caused by neurologic abnormalities.


Cardiovascular disease is present in most children with trisomy 18 and consists primarily of VSDs and polyvalvular disease.174,175 Implications for anesthesia care include the high incidence of congestive heart failure and aspiration pneumonia.173 These children may require interventions to address associated gastrointestinal or genitourinary anomalies.




Turner Syndrome


Turner syndrome is a genetic disorder characterized by partial or complete X chromosome monosomy.178 The estimated incidence is 1 case per 5000 liveborn female infants. A high degree of spontaneous abortion is seen among affected fetuses. Features of this syndrome include webbed neck, low-set ears, multiple pigmented nevi and micrognathia, lymphedema, short stature, and ovarian failure.179 Systemic manifestations include cardiac defects (notably aortic coarctation and bicuspid aortic valve), hypertension, hypercholesterolemia, renal anomalies (up to 33%), liver disease, and inflammatory bowel disease. Obesity is common in older children, as is a high incidence of endocrine abnormalities such as hypothyroidism and diabetes.178,180



Gene Deletion Syndromes



Williams Syndrome


Williams syndrome is a congenital disorder with an incidence of 1/20,000 live births. In most cases, the long arm of chromosome 7 is deleted, altering the elastin gene.181,182 The absence of this gene is detected by fluorescence in situ hybridization (FISH). Features of Williams syndrome include characteristic elfin facies, outgoing personality, endocrine abnormalities (including hypercalcemia and hypothyroidism), mental retardation, growth deficiency, and altered neurodevelopment. Cardiovascular abnormalities can include valvar and supravalvular aortic stenosis (Fig. 14-11) and aortic coarctation.183,184 This arteriopathy can also involve the origin of the coronary arteries or other vessels. Diffuse narrowing of the abdominal aorta may be associated with renal artery stenosis.



Several reports have described unanticipated events during anesthesia for these children.185187 Two conditions can increase anesthetic morbidity and the potential for mortality: coronary artery stenosis leading to myocardial ischemia and severe biventricular outflow tract obstruction. A thorough cardiac evaluation of all children is advisable because the spectrum of disease and the potential devastating implications in affected individuals varies.188 Children occasionally may require further evaluation before undergoing anesthetic care. Even asymptomatic children and those without evidence of clinical cardiovascular disease may be at risk for morbidity and death in the perioperative period.187 Extreme vigilance and particular attention to signs of myocardial ischemia is warranted, as is a plan of action in the event of acute decompensation. This syndrome is one of the leading causes of cardiac arrest in the Pediatric Perioperative Cardiac Arrest (POCA) registry.189


Children with Williams syndrome may exhibit some degree of muscular weakness, and the cautious use and application of muscle relaxants has been recommended.188 Associated neurodevelopmental delay, attention-deficit disorder, and autistic behavior often requires adequate premedication. Subclinical hypothyroidism has a high prevalence among these children.190 Renal manifestations include renovascular hypertension, reduced function, and hypercalcemia-induced nephrocalcinosis.



Chromosome 22q11.2 Deletion Syndrome: DiGeorge and Velocardiofacial Syndrome


The 22q11.2 deletion syndrome, with an estimated incidence of approximately 1 case per 3000 live births, encompasses DiGeorge, conotruncal face, and velocardiofacial syndromes. The syndrome is also known as CATCH 22, a mnemonic for cardiac defects, abnormal facies, thymic hypoplasia, cleft palate, and hypocalcemia, all of which are commonly present.191 Cardiac malformations, speech delay, and immunodeficiency are the most common features of the chromosome 22q deletion syndromes. Because no single feature is overwhelmingly associated with the deletion, the diagnosis should be considered for any child with a conotruncal anomaly, neonatal hypocalcemia, or any of the less common features when seen in association with dysmorphic facial features.


Cardiac malformations are often described as conotruncal anomalies; however, outflow tract problems are also frequently seen.192 The remainder of the cardiac defects encompasses an enormous spectrum of pathologies. Only a few children have a normal cardiovascular system. As a consequence of thymic hypoplasia, children typically have diminished T-cell numbers and function. Their immunodeficiency requires the use of irradiated blood products and strict aseptic precautions during vascular access. Neurodevelopmental features include primarily speech delay and attention-deficit disorders. Psychiatric disorders are well described in these individuals.193



Single-Gene Defects



Noonan Syndrome


Noonan syndrome, an autosomal dominant syndrome, occurs with a frequency of 1 case per 1000 to 2500 live births. Dysmorphic features include neck webbing, low-set ears, chest deformities, hypertelorism, and short stature.194 The diagnosis of Noonan syndrome depends primarily on clinical features.195 In neonates, the facial features may be less apparent; however, generalized edema and excess nuchal folds may be present as in Turner syndrome. The facial features are more difficult to detect in later adolescence and adulthood.


The disorder is associated with a high incidence of CHD (about 50%), and pulmonary valve dysplasia or stenosis is the most common feature.196 HCM may develop during the first few years of life (10% to 20%).197 Clinical problems may also include developmental delay and bleeding diathesis.198



Marfan Syndrome


Marfan syndrome is a multisystem disorder with variable expression resulting from a mutation in the fibrillin gene, a connective tissue protein, located on chromosome 15.199 Clinical manifestations typically involve the cardiovascular, skeletal, and ocular systems.200,201 Cardiovascular pathology includes mitral valve prolapse and regurgitation, ascending aortic dilation (Fig. 14-12), and main pulmonary artery dilatation. The risk of aortic dissection rises considerably with increasing aortic size but may occur at any point in the course of the disease.202 Cardiac arrhythmias may be related to valvular heart disease, cardiomyopathy, or congestive heart failure.



β-Blocker therapy and aggressive blood pressure control has been the standard of care in children with aortic root dilation203 and should be continued perioperatively. Aortic root replacement in Marfan syndrome has been associated with a greater risk of repeat dissection and recurrent aneurysm compared with other children who have undergone similar interventions.204 It is wise to maintain hemodynamics near baseline values in the perioperative period. After aortic root surgery some individuals may require chronic anticoagulation therapy. Preoperative hospitalization may be necessary to adjust the anticoagulation regimen in anticipation of surgery in these children. In emergency cases, administration of coagulation factors and other blood products may be required. In addition to vascular pathology, children with Marfan syndrome have a predisposition for ventricular dilation and abnormal systolic function.205,206


Several factors can result in pulmonary disease in these children.207 Chest wall deformities and progressive scoliosis can contribute to restrictive lung disease. The fibrillin defect may affect lung development and homeostasis, impairing pulmonary function. Development of a pneumothorax is relatively common.



Associations




CHARGE Association


CHARGE association is characterized by congenital anomalies that include coloboma, heart defects, choanal atresia, retardation of growth and development, genitourinary problems, and ear abnormalities. The association is estimated to occur at a rate of 1 case per 10,000 to 12,000 live births. The cause is unknown although many theories have been suggested.211,212


Specific genetic abnormalities have also been identified in some individuals.213,214 Cardiac defects occur in as many as 50% to 70% of children and commonly include conotruncal and aortic arch anomalies.215 Delayed growth and development usually results from cardiac disease, nutritional problems, and/or growth hormone deficiency. Most children have some degree of cognitive impairment. Anesthetic implications, in addition to those related to the cardiac defects, focus on the airway216; a retrospective review of 50 cases reported upper airway abnormalities in 56% of children apart from choanal atresia and cleft lip and palate.217



Other Disorders


Tuberous sclerosis is a rare genetic disease with an autosomal dominant inheritance pattern and an incidence of approximately 1 case per 25,000 to 30,000 births.218 In a relatively large number of children, it can be attributed to spontaneous mutations. This systemic disease primarily manifests as cutaneous and neurologic symptoms, but cardiac and renal lesions are frequent findings.


The presence of upper airway nodular tumors, fibromas, or papillomas in affected children may interfere with airway management. Developmental delay, autism, attention-deficit disorder, and aggressive behavior are common. Brain tumors and renal tumors (60% to 80%) may produce significant comorbidities. Cardiac pathology includes cardiac rhabdomyoma in 60% of children and coexisting CHD in 33% of cases.219221 Cardiac abnormalities with obstruction to flow, heart failure, arrhythmias, conduction defects, or preexcitation may affect the selection of anesthetic agents. Preoperative evaluation in most cases should include an ECG to assess arrhythmia, conduction defects, or preexcitation.219 Blood pressure and renal function should also be assessed. Anticonvulsants should be optimized and continued until the morning of surgery. Baseline medical treatment should be resumed as soon as possible because seizures are the most common postoperative complication.222 A child with mental retardation may require premedication with oral midazolam or ketamine, or both, to facilitate parental separation.



Selected Vascular Anomalies and Their Implications for Anesthesia



Aberrant Subclavian Arteries


An aberrant or anomalous subclavian artery usually arises from the descending aorta as a separate vessel distal to the usual last subclavian artery in a posterior location. In a left aortic arch, this arrangement is as follows. The first branch is the right carotid artery, followed by the left carotid artery and the left subclavian artery. The aberrant right subclavian artery, rather than arising proximally from the innominate artery as the first arch branch, originates distal to the last (left) subclavian artery as the fourth branch and courses behind the esophagus toward the right arm. This variant is one of the most common aortic arch anomalies. It occurs in 0.4% to 2% of the general population and may or may not be associated with CHD.223 This anomaly has a high incidence among children with Down syndrome and is associated with VSDs, TOF, and other lesions. In a right aortic arch, the anomalous left subclavian artery originates distal to the origin of the right subclavian artery (Fig. 14-13). This anomaly may be seen in the context of conotruncal malformations. The diagnosis of an aberrant subclavian artery is made by most currently available imaging modalities.



This anomaly has several implications:



May 25, 2016 | Posted by in ANESTHESIA | Comments Off on Essentials of Cardiology
Premium Wordpress Themes by UFO Themes