Abstract
It is not unusual for the cardiac anaesthetist to encounter adults with palliated, corrected or newly diagnosed congenital heart disease (CHD). It is essential, therefore, that the anaesthetist has an appreciation of the types of CHD, surgical procedures and perioperative management.
It is not unusual for the cardiac anaesthetist to encounter adults with palliated, corrected or newly diagnosed congenital heart disease (CHD). It is essential, therefore, that the anaesthetist has an appreciation of the types of CHD, surgical procedures and perioperative management.
Arterial Shunts
Variants to arterial shunts include the modified Blalock–Taussig (B–T) shunt (Figure 21.1), the systemic-to-pulmonary shunt and the central shunt.
Figure 21.1 The modified B–T shunt
Physiology
Arterial shunts are used to augment pulmonary blood flow (PBF) in a variety of conditions with inadequate PBF. Some conditions have biventricular anatomy (e.g. Fallot’s, pulmonary atresia/VSD, transposition of the great arteries (TGA)/VSD/PS). Others have functionally single ventricle anatomy (e.g. tricuspid atresia/TGA/PS, pulmonary atresia/intact ventricular septum). Behaviour following the shunt is influenced by the underlying anatomy; patients with biventricular anatomy are usually more stable and tolerate the volume load of the shunt better.
Many neonates are duct-dependent preoperatively and receiving a prostaglandin E2 (PGE2) infusion (Chapter 20). The duct is usually tied at the time of shunt placement. Blood flow through the shunt will be influenced by the shunt radius and length:
Typical shunt sizes are 3.5–4.0 mm in diameter, although these may need to be modified in light of the PA size and the PVR.
Surgery
The most widely used procedure is the modified B–T shunt, which can be performed via either by thoracotomy or midline sternotomy. This involves placement of a small-calibre Gore-Tex® tube graft between the innominate artery and the PA (the original description anastomosed the subclavian artery directly to the PA). This is generally performed on the right side without CPB unless the child is very unstable or a more complex repair is required. The term ‘central shunt’ involves a similar procedure but implies a shunt between the aorta and the PAs, usually with a short Gore-Tex® graft. It is usually performed via sternotomy and delivers a higher blood flow.
Postoperative Management
It is important to establish the underlying anatomy:
Single or biventricular anatomy?
Any other source of pulmonary blood supply other than the shunt (is the ductus arteriosus still open)?
A shunt procedure requiring CPB implies unstable haemodynamics and the need for careful monitoring. Shunts with underlying biventricular anatomy tend to be more stable but all neonates with arterial shunts can be unstable with a low diastolic pressure and the risk of sudden coronary ‘steal’, leading to unheralded cardiac arrest. There is a need to balance the pulmonary:systemic blood flow (QP:QS) in a functionally single ventricle. If the shunt is the only source of PBF, aim for an SaO2 of ~75–80% and QP:QS = 1:1 (see Figure 21.13). Too small a shunt or an obstructed shunt results in hypoxaemia; a trial of inhaled NO may be helpful in differentiating a structural shunt problem from an elevated PVR. Only the latter is reactive and responds to inhaled NO. Too high a shunt flow leads to a low diastolic pressure, pulmonary congestion and a ventricular volume overload. Attempts to reduce the PBF by increasing the PVR are seldom effective. Lowering the SVR with vasodilators is more effective at balancing the QP:QS ratio. Surgical revision of the shunt may be necessary.
Start heparin infusion on return to the ICU when the patient is stabilized and not bleeding (10 IU kg–1 h–1).
Atrial Septal Defects
Incidence and Associations
ASDs account for 8% of all CHD. Most occur in isolation, but recognized associations include Holt-Oram, Turners and maternal rubella syndromes, as well as Down syndrome in the specific case of primum ASDs.
Anatomy
Defects occur at different sites (Figure 21.2):
Secundum ASDs are the most common – the majority can be closed with a device in the catheter laboratory. Features making device closure unlikely are: a very large defect, the lack of an inferior or lateral rim of tissue and relatively large defects in smaller children. All other types of defect require surgical closure.
Primum ASDs are part of the spectrum of atrioventricular (A-V) septal defects (AVSDs, see below) and are more correctly called ‘partial AVSDs’. They are always associated with a cleft in the left A-V (‘mitral’) valve, which is repaired as part of the procedure.
Sinus venosus ASDs are associated with anomalous drainage of the upper right pulmonary veins into the root of the SVC (Figure 21.3). These can be baffled back to the LA with a patch repair
Coronary sinus ASDs are very rare, and are associated with unroofing of the coronary sinus, thus, closing the defect leaves the CS draining into the LA creating a small, haemodynamically insignificant right-to-left shunt.
Figure 21.2 View inside the RA
Physiology
Left-to-right shunts cause a volume load on pulmonary circulation. Most children are symptomless but plethoric lungs may predispose to chest infections and failure to thrive. Very large shunts may result in effort intolerance. PHT is not associated with isolated ASDs in children.
Surgery
Small detects can be repaired by simple suture closure. Larger defects require patch repair with either autologous pericardium or prosthetic patch material. Intraoperative echocardiography should focus on pulmonary venous drainage in a sinus venosus ASD and on the left A-V valve function in partial AVSD repair.
Postoperative Care
Surgery is generally of low risk and children can be weaned from ventilation and extubated shortly after surgery. Sinus venosus ASD repair involves the root of the SVC and there is a risk of causing SVC obstruction. If the face looks plethoric or the SVC pressure is high, arrange echocardiographic or contrast evaluation. Nodal rhythms may occur with high atrial incisions (e.g. sinus venosus ASD).
Some units ‘fast-track’ ASD repairs to a monitored ‘step-down’ facility on the day of surgery.
Atrioventricular Septal Defects
AVSDs are also called A-V canal defects or endocardial cushion defects. They may be complete or partial.
Incidence and Associations
AVSDs account for 4% of all CHD. Both complete and partial AVSD are strongly associated with Down syndrome.
Anatomy
There is a defect in the centre of the heart with a single valve (the common A-V valve), straddling both ventricles, and a hole above and below it. In partial AVSD, the VSD component has closed, leaving only an ASD (see Figure 21.4).
Physiology
A complete AVSD behaves like a large VSD (i.e. a left-to-right shunt, leading to a high PBF and heart failure in neonates). In addition, the common A-V valve can be regurgitant, adding to the heart failure. All require surgical closure before 6 months of age. Later repair is associated with significant risk of irreversible PHT.
In partial AVSDs (also called primum ASDs), the ventricular component has closed, there is less of a left-to-right shunt and a lower likelihood of heart failure. Repair is generally undertaken before 5 years of age.
Surgery
Operative mortality for repair of complete AVSD is ~ 4%, whereas that for partial AVSD repair is ~ 1%. Usually, the VSD is closed with one patch, the ASD with another, sandwiching the valve between them (Figure 21.5) – alternatively the procedure can be performed with a single patch, fixing the valve to the crest of the ventricular septum, particularly if the VSD is relatively shallow. Surgery recreates two separate A-V valves. However, anatomically the valve between the LA and LV is not a true ‘mitral’ valve and is referred to as the ‘left A-V valve’. The cleft in the left A-V valve is closed as part of the repair to create a competent valve. The repair of cAVSD in babies without Down syndrome is typically more complicated (poor A-V valve function) compared to babies with Down syndrome. Intraoperative echocardiography should focus on looking for any residual VSD, assessing left and right A-V valve function and ensuring that the LVOT is unobstructed.
Figure 21.5 Surgery for an AVSD
Postoperative Management
An LA line is useful and a PA line is inserted where concern exists about PHT. Echocardiography is repeated to exclude a residual VSD, and to assess ventricular and A-V valve function. The cardiac rhythm should be confirmed as there is a risk of heart block. Babies are usually in marked heart failure preoperatively with pulmonary congestion and may take time to wean from the ventilator. The risks and management of PHT are described below. Partial AVSD repairs are generally uncomplicated. All have had left A-V valve repair and should have an echocardiogram to document the AV-valve function.
Bidirectional Cavopulmonary Shunt
The bidirectional cavopulmonary shunt (BCPS) is also called a cavopulmonary (CP) shunt, a modified Glenn shunt and Hemi-Fontan shunt. It represents one of the staged palliative procedures for children with a functionally single ventricle circulation (see Staged Palliation of the Functionally Univentricular Heart). It accounts for 3–4% of all CHD (e.g. tricuspid atresia, double-inlet LV, hypoplastic left heart syndrome (HLHS)), unbalanced AVSD, PA/interventricular septum (IVS)). It is usually the second stage after an initial Norwood operation, B–T shunt or PA band but it may be the first operation if the QP:QS ratio is balanced and no surgery is required in the neonatal period.
A BCPS is carried out at around 4–6 months of age. The SVC is anastomosed to the PA, and the IVC remains connected to the RA (Figure 21.6). If the patient has previously had an arterial shunt, this is usually taken down. In other patient groups, a decision is taken as to whether to ligate the main PA or to leave some antegrade PBF. The original Glenn operation involved direct anastomosis of SVC to the surgically isolated right PA.
Figure 21.6 The BCPS
Physiology
These procedures involve connecting the systemic veins directly into the pulmonary circulation, thus bypassing the right side of the heart completely. They rely on venous pressure to drive the PBF and are only possible if the PVR is low. A failing ventricle or a high PVR may preclude these procedures. If a CP (‘venous’) shunt was created in the early neonatal period, the high PVR would result in an excessively high SVC pressure and a low PBF – hence an arterial shunt is initially needed, which provides a higher driving pressure and guarantees an adequate PBF.
Postoperative Management
Arterial saturation is typically 80–85%. An SVC line and IVC (or common atrial) line is typically required. The SVC pressure equates to the PAP (typically 14–18 mmHg). The difference between the PAP and atrial/IVC pressure gives the TPG. A TPG of 8–10 mmHg generally implies a low PVR and a favourable outcome. If the TPG is greater than 15 mmHg a mechanical holdup (e.g. anastomotic narrowing, anastomotic thrombosis or PA narrowing) must be excluded before considering inhaled NO to reduce the PVR. The SVC and PA pressures may be elevated (>20 mmHg) with a normal TPG as a consequence of a high atrial pressure, secondary to ventricular dysfunction. Management is aimed at lowering the atrial pressure (vasodilators, inotropes), which will lead to a lowering of the SVC and PA pressures. Haemodynamics are generally good since the volume loading of the ventricle is substantially reduced by this procedure. Hypertension is common and may require treatment.
Ideally, infants are weaned from positive-pressure ventilation as soon as possible to reduce intrathoracic pressure and improve the PBF. Any SVC line should be removed as soon as possible to reduce the risk of thrombosis. A high SVC pressure may result in pleural effusions (sometimes chylothorax), venous congestion of the head and neck, and headaches.
Certain congenital heart lesions are associated with an interruption of the IVC and azygous vein continuation such that IVC blood enters the SVC. A BCPS in this setting (called a Kawashima operation) results in all venous blood other than hepatic venous return contributing to the PBF – the SaO2 is higher at around 85–90%.
Coarctation of the Aorta
Incidence and Associations
Coarctation of the aorta (CoA) accounts for 6% of all CHD. It is associated with Turner syndrome, bicuspid AV (up to 40% of cases) and VSDs.
Anatomy
CoA is narrowing of the aorta in the region of the ductal insertion, i.e. distal to the left subclavian artery. It can occasionally occur proximal to the left subclavian artery.
Aortic interruption is an extreme form of coarctation where there is complete separation of the aortic components, the distal component being supplied by the ductus. Interruption is (almost) always associated with some sort of intracardiac shunt, usually a VSD or aorto-pulmonary window. It is commonly associated with 22q11 deletion. Interruption is a much more complex lesion, requiring repair on CPB and carrying much higher risk.
Physiology
The presentation depends on the severity of narrowing:
Severe CoA typically presents in the neonatal period as the duct closes – the aorta is virtually occluded, causing circulatory collapse, acute LV failure and loss of lower limb pulses
Moderate CoA presents more subtly with a degree of LV failure in childhood (rare)
Less severe CoA presents with chance finding of a murmur, an abnormal CXR or upper-limb hypertension/radio-femoral delay
Management of the Neonate
Administration of prostaglandin E2 (PGE2) by infusion reopens the duct and re-establishes flow to the lower body. Ductal tissue is often involved in CoA, and the severity of CoA may also be reduced with PGE2. Neonates with severe CoA usually have considerable heart failure. They may require full resuscitation with ventilation/inotropic support. The condition can usually be stabilized with these measures. Rarely, the duct will not reopen and emergency surgery is required.
Surgery
Surgery is carried out via a left thoracotomy, and is associated with ~1% perioperative mortality. It is repaired either with resection and end-to-end anastomosis or with subclavian flap angioplasty (Figure 21.7). Both have excellent results although the former is regarded by most as being the ‘gold standard’. Sacrificing the subclavian artery in the neonate does not cause limb ischaemia and at worse may result in reduced limb growth. Repair of the associated hypoplastic aortic arch may require CPB via sternotomy. An arterial line should be placed in the right brachial/radial artery to ensure monitoring can be continued with a clamp on the aortic arch. Ideally, two arterial lines, one in the right arm and one femoral, can be placed.
Figure 21.7 Surgery of CoA
Older children/adolescents are now mostly treated by interventional catheterization with covered stenting rather than a surgical approach.
Complications: The risk of recurrence is 2-4%; the majority can be successfully dilated with balloon angioplasty. Injury to recurrent laryngeal nerve or thoracic duct is rare. There is also a risk of paraplegia (due to spinal ischaemia <0.5% – virtually unknown in neonates). Protective measures include core cooling to 35 °C and keeping the clamp time to less than 30 minutes. Full or partial CPB can be used, allowing for more profound cooling.
Postoperative Management
The femoral pulses should be monitored. Echocardiography is used to assess LV function and confirm adequate arch repair. Patients may have hypertension, requiring treatment (β-blocker). Limb function should be documented once the effects of muscle relaxants have worn off.
Fallot’s Tetralogy
Fallot’s tetralogy is also called tetralogy of Fallot, ToF and Fallot.
Incidence and Associations
Fallot’s tetralogy accounts for 6% of all CHD. It is associated with many syndromic conditions, affecting 20% of patients with Di George syndrome/22q11 deletion, CHARGE (coloboma, heart defects, choanal atresia, retardation of growth or development, genital or urinary abnormalities, and ear abnormalities and deafness) association, VACTERL (vertebral anomalies, anal atresia, cardiovascular abnormalities, tracheo-oesophageal fistula, oesophageal atresia, renal, limb defects) and Down syndrome.
Anatomy
The key anatomical features are a perimembranous VSD with aortic override and multilevel RV outflow obstruction (Figure 21.8). The degree of right outflow tract obstruction is variable and tends to worsen with time as the RVH progresses. Important variants are tetralogy of Fallot with multiple VSDs and the presence of an anomalous left coronary artery (2–5%) – in the latter, repair usually requires a conduit to jump over the coronary artery as it crosses the outflow tract.
Figure 21.8 Anatomy of tetralogy of Fallot
Absent PV syndrome is a rare type of Fallot with similar intracardiac anatomy but no true PV. The PAs beyond the valve have marked post-stenotic dilatation and may cause compression of the airways and bronchomalacia. Treatment is similar but involves plication of the aneurysmal central PAs and respiratory assessment.
Physiology
Management depends on the degree of cyanosis at presentation and associated lesions. Cyanotic neonates are usually palliated with a systemic-to-pulmonary shunt procedure (usually a B–T shunt), or with an RVOT stent placed in the cardiac catheter laboratory. Although some centres favour complete neonatal repair, the majority favour delaying surgery in stable infants until they are 3-9 months of age.
Cyanotic ‘spelling’ typically develops in the first 6 months of life and is treated with β-blockers, which relieve infundibular muscle spasm and reduce the degree of cyanosis. Patients can ‘spell’ severely on induction of anaesthesia and if this fails to respond to oxygen therapy and volume infusion then a systemic vasoconstrictor (epinephrine/norepinephrine/phenylephrine) may be required to increase the systemic afterload and so improve the PBF.
Surgery
Surgery results in 2–3% early mortality. Muscle bundles in the RVOT are resected and the VSD is closed, usually via the RA. The PV and main PA usually need to be opened out and patched to enlarge the outflow tract sufficiently, requiring a ‘transannular’ incision and patch. This relieves obstruction but leaves significant PR (Figure 21.9).
