Discuss the sequelae associated with the repair of specific cardiac lesions.
Secundum ASD is associated with a 30% incidence of mitral valve prolapse. Patients need to be followed for the development of mitral regurgitation, which occurs in 5–10% of patients, or ventricular dysrhythmias. Early and late atrial dysrhythmias may occur, particularly if the patient was over the age of 20 years at the time of repair or if the dysrhythmias were present before surgery. Patients who develop paroxysmal or chronic atrial fibrillation will require anticoagulation to prevent systemic embolization. The risk of late development of atrial flutter or fibrillation 25–30 years following repair is 4% if the repair was done before age 10 years and 58% if it was carried out after age 40 years. The presence of a large left-to-right shunt prior to surgery is an additional risk factor for development of late atrial dysrhythmias. The most commonly observed dysrhythmias after repair of sinus venosus defects are sinus node dysfunction and sick sinus syndrome, which occur in at least 10% of patients.
The incidence of residual VSD following surgery is less than 5%. Patients with sub-arterial VSD may have aortic insufficiency, which is an indication to close even a small defect. In 3% of cases, the regurgitation is progressive. Many patients (30–50%) will exhibit a right bundle branch block on electrocardiogram (ECG). In older repairs, where a right ventriculotomy was commonly performed, serious ventricular dysrhythmias are seen in at least 34% of patients, with a 1–2% incidence of sudden death. Complete heart block is one of the risk factors of VSD closure, but with better surgical techniques the incidence is less than 2%. It is a late sequela in patients who exhibit bifas-cicular block following surgery (right bundle branch block and left anterior hemiblock). The majority of patients whose defects are closed before the age of 2 years have normal cardiovascular function; however, they have a higher risk for dysrhythmias than the normal population. Patients operated on later in life may have persistence of depressed myocardial reserve and progressive pulmonary hypertension.
Fifty percent of patients with CoA have other associated cardiac lesions. Bicuspid aortic valve is seen in 85% of patients and 3–10% have berry aneurysms of the circle of Willis. Thirty-five percent of patients with Turner syn-drome have CoA.
The technique of repair has changed over the years. Resection of the coarcted aorta and end-to-end anastomosis is the preferred surgical technique at this time. Older repairs included patch aortoplasty, subclavian flap aorto-plasty, and interposition graft. Patch aortoplasty, which has a high incidence of aortic aneurysm formation that may rapidly expand and lead to aortic rupture and death, has been abandoned. Subclavian patch repair is still used occa-sionally. Blood pressure measurements in the left arm may be unreliable following this procedure. Bridging grafts are occasionally used in older patients with repeated coarcta-tions. Repair in infancy is associated with a 15–20% inci-dence of recoarctation. Most of these patients can be managed effectively with balloon angioplasty. Balloon angioplasty of a primary coarctation in the newborn is not effective. A long-term sequela of balloon angioplasty is the development of an aortic aneurysm at the angioplasty site (2–14%).
Patients with repaired coarctation are at risk for devel-opment of late hypertension in the absence of recoarcta-tion. Age at time of surgical repair is the strongest predictor for this complication. Repair after age 5 years has a 75% incidence of systolic hypertension at 25-year follow-up. Long-term survivors have an accelerated risk of coronary artery disease, myocardial infarction, and premature death. In addition, because of the high incidence of bicuspid aor-tic valve, 7–10% of patients develop aortic valvular disease requiring aortic valve replacement. In the perioperative period, patients who are normotensive at rest may develop significant hypertension with minimal stimulation. This may be due to underlying hypertensive disease or to unrec-ognized recoarctation.
AV septal defects are the most common cardiac defect associated with Down syndrome. The complete form results in severe congestive heart failure and pulmonary hypertension. The defect is usually repaired in infancy because of symptoms and to prevent development of obstructive pulmonary vascular disease. Primum atrial septal defects present similar to secundum ASD, unless associated with significant mitral regurgitation. Although the cleft mitral valve is competent in the majority of patients, 10–15% of patients have mitral valve regurgitation at the time of the initial surgery. Because of the abnormal-ity of the mitral valve, long-term mitral insufficiency remains a serious problem after repair of primum defects and complete canals. More than 60% of patients followed long term after repair of partial AV septal defects have evi-dence of mitral regurgitation, which may eventually require mitral valve replacement. After repair of complete AV septal defects in infancy, the incidence of mitral regurgitation requiring re-intervention is quoted at about 7%. First-degree heart block is seen in 50% of patients after repair. Patients are at risk for development of malignant tachydys-rhythmias as they age.
Older repairs of TOF have resulted in right ventricular dysfunction due to pulmonary insufficiency and a high incidence of dysrhythmias from extensive right ventriculo-tomies. Incomplete relief or right ventricular outflow obstruction, demonstrated by a RV:LV systolic pressure ratio of greater than 0.5, is an independent predictor of late mortality after repair. Repair at an older age is also associ-ated with higher long-term mortality, as is the presence of a large outflow patch. The majority of patients are symptom-free following repair. There is, however, in the survivors of the earlier repairs a 6% incidence of sudden death and at least a 10% incidence of inducible ventricular tachycardia requiring AICD implantation. Nearly a third of patients at late follow-up have atrial tachycardias, which can also cause sudden death. Most patients have a right bundle branch block on the ECG. The presence of ventricular ectopy must be thoroughly evaluated preoperatively. Patients need to be evaluated for residual lesions, VSD, or right ventricular hypertension prior to a procedure. Sympathetic stress in the setting of right ventricular hyper-tension and an old ventriculotomy scar increases the propensity for ventricular dysrhythmias. Patients with sig-nificant pulmonary insufficiency may tolerate rapid fluid shifts poorly. Vascular access may be difficult in patients with multiple previous cardiovascular procedures. Patients with residual shunts are at risk for paradoxical emboli.
TGA represents 5–7% of all congenital cardiac defects and is the most common cause of cyanotic congenital heart disease in the newborn. In this lesion, the aorta arises from the right ventricle and the pulmonary artery from the left, creating two parallel circulations. Unless some mixing between the circulations occurs, either through a patent ductus arteriosus, ASD, or VSD, survival past the neonatal period is not possible. Prior to surgical interventions 90% of patients with this lesion died within the first year of life. Surgical repair is aimed at either improving mixing, redi-recting flow of systemic venous and pulmonary venous return to the pulmonary artery or aorta, or at anatomically correcting the problem. The initial physiologic repair for this condition was “switching” the blood return at the atrial level with the help of an intra-atrial baffle, the Mustard and Senning operations. This resulted in the right ventricle becoming the systemic ventricle and the creation of exten-sive suture lines in the atria. There is now more than 30-year follow-up for these patients. Twenty-year survival is 80% but late morbidity is common. Less than 20% of patients are in sinus rhythm and more than 10% of patients have developed right ventricular failure requiring either trans-plantation or conversion to an arterial switch. The intra-atrial baffle leads to systemic venous obstruction in 10–20% of patients, which may not be clinically apparent except for mild facial swelling. Monitoring of the central venous pres-sure may be quite misleading under these circumstances and may cause superior vena cava syndrome. Obstruction of the right pulmonary veins due to baffle shrinkage occurred in 5–10% of patients. Also the Senning procedure frequently required reoperation because of unilateral pul-monary venous hypertension. The most serious long-term complication, however, is the severe dysrhythmias which follow both operations. Sinus node dysfunction or atrial flutter can result in sudden death (25%). Late right ven-tricular dysfunction leads to ventricular tachycardia. Patients may be on multiple antiarrhythmic drugs and may require pacemaker implantation to prevent complications from this therapy. Patients with sick sinus syndrome require a pacemaker. Patients with tachydysrhythmias are presently treated with radiofrequency ablation, if possible, but may require an implantable anti-tachycardia device. After the Mustard procedure, 50% of patients required a pacemaker by age 30 years. Patients following the atrial switch procedure may have limited cardiac reserve. There may also be difficult central access problems and the course of central lines on the chest radiograph will appear quite abnormal, since the catheter will traverse from the superior vena cava along the baffle into the mitral valve, left ventri-cle, and then the pulmonary artery.
Because of the disappointing long-term results of the atrial switch procedures, anatomic correction at the arterial level has been the preferred approach since the mid-1980s. It involves transsection of both great vessels with reloca-tion of the aorta above the pulmonary valve and the left ventricle, and the pulmonary artery above the aortic valve and the right ventricle. The coronary arteries are discon-nected and relocated to the neo-aorta. Long-term follow-up is available for only 15 years, but already there is a significant reduction in dysrhythmias, better systemic ventricular function, and better exercise tolerance. In the initial series, supravalvular pulmonary stenosis occurred in more than 10% of patients requiring dilatation or reoper-ation. With modifications in the surgical technique this complication has become rare. Aortic insufficiency is now seen in long-term survivors, who may eventually require valve replacement. In addition, 1–3% of patients have asymptomatic occlusion of one coronary artery on follow-up coronary angiography. Patients following the arterial switch should be evaluated for supravalvular stenosis and may be at risk for development of myocardial ischemia due to coronary stenosis. They are otherwise similar to a person with a structurally normal heart.
A multitude of complex congenital cardiac lesions have only one functional ventricle to support the systemic circulation or can only be repaired by converting them to single-ventricle physiology. Some of the more common lesions that are “repaired” in this way include tricuspid atre-sia, double inlet left or right ventricle, hypoplastic left heart syndrome, and pulmonary atresia with intact septum with hypoplastic right ventricle. In infancy, these patients undergo a procedure to balance pulmonary blood flow between the systemic circulation and the pulmonary circulation. This involves either the creation of an aortopulmonary shunt for pulmonary perfusion or banding of the pulmonary artery to restrict excessive flow. In hypoplastic left heart syndrome, the aorta is reconstructed in the same procedure (Norwood I). At about 6 months of age, in order to relieve the volume load on the single ventricle, the venous return from the upper extremity is diverted directly into the lung by anastomosis of the superior vena cava to the pulmonary artery (Bi-Glenn). The prior shunt or band is taken down at that time. All patients remain cyanotic following these procedures. The oxygen saturation in these patients is in the eighties when the cardiac output is normal because blood that equally perfuses the systemic and pulmonary circulation mixes in the single ventricle. The final stage consists of separating the two circu-lations (Fontan) by diverting inferior vena cava (IVC) blood to the pulmonary artery. There have been several modifica-tions of this procedure over the years. At present, the IVC is channeled either through an intra-atrial lateral baffle or via an extracardiac conduit to the pulmonary artery.
Since pulmonary blood flow and hence cardiac output depend on a pressure gradient between the central venous pressure and the mean pulmonary or intrathoracic pres-sure, PVR has to be low and myocardial function relatively normal to avoid excessively high central venous pressure. Patients have limited potential to increase cardiac output because of limited flow across the venous channels. At pres-ent, a fenestration is created between the IVC channel and the right atrium (creating a right-to-left shunt) to allow decompression of high venous pressure, which would maintain cardiac output at the expense of full oxygenation.
Survival after these procedures is 60–73% at 15 years.
Patients are at risk for several long-term problems. The persistently elevated central venous pressure leads to a pro-tein-losing enteropathy in 5–13% of patients over 10 years, and to persistent pleural effusions. Atrial suture lines and atrial distention lead to a high incidence of atrial tachydys-rhythmias. Atrial flutter occurs in 40–50% of patients 15 years following the procedure. In patients whose single ventricle is a right ventricle, ventricular function deterio-rates progressively. Only half of Fontan patients have nor-mal cardiac function 10 years after the repair. Patients also tend to develop spontaneous thrombosis and need to be on chronic low-dose anticoagulation. Afterload-reducing agents are prescribed to protect myocardial function and maintain low left atrial pressures. Maintenance of sinus rhythm is equally important to maintain cardiac output. All patients have reduced exercise tolerance.
Key considerations for anesthetic management are:
· Thorough preoperative cardiac evaluation including echocardiography is required to assess function of the atrioventricular valve and ventricle.
· Maintenance of adequate preload, sinus rhythm, and avoidance of cardiodepressant drugs is essential.
· Spontaneous ventilation should be maintained if at all pos-sible to minimize any increase in intrathoracic pressure.
· If controlled ventilation is necessary, positive intratho-racic pressure should be kept to a minimum.
· Central venous pressure lines should be used only when absolutely indicated because of the risk of thrombosis and obstruction to venous return.
· Regional anesthesia should be carefully titrated to allow for adjustment for acute preload and afterload reductions.
· Patients require endocarditis prophylaxis.
· Meticulous attention is necessary to prevent introducing air bubbles, since these patients are at risk for paradoxical emboli in the presence of a fenestration or baffle leak.