Ablation of Ventricular Tachycardia With Congenital Heart Disease

Introduction

Ventricular tachycardia (VT) is a well-known late consequence after surgical repair of a variety of congenital heart defects. For the purpose of this chapter it seems appropriate to make a distinction between two different forms of VT in this population. One type of VT is based upon morphologic/anatomic variants of the heart defect itself or to ventricular incisions and patches that allow initiation and perpetuation of a stable ventricular macroreentrant circuit resulting in a stable monomorphic VT. Because of the underlying electrophysiologic mechanism, these tachycardias are amenable to endocardial mapping and catheter ablation, which will be discussed in detail within this chapter. The best example of this clinical entity is unoperated/native and postoperative tetralogy of Fallot and its variants. The second type of VT mainly occurs in severely diseased ventricular myocardium with significant fibrosis and myocardial disarray resulting in less organized, rapid polymorphic VT and ventricular fibrillation with the risk of sudden cardiac death. Because of the underlying electrophysiologic mechanism, these tachycardias cannot be treated sufficiently by catheter ablation. Accordingly, implantable cardioverter-defibrillator (ICD) implantation is the recommended therapy in these patients. Common varieties of congenital heart defects associated with these types of ventricular tachyarrhythmias are obstructive left ventricular outflow tract lesions, d-transposition of the great arteries after atrial switch procedure with failing systemic right ventricle, tetralogy of Fallot with significantly impaired right ventricular function, and univentricular hearts with a Fontan circulation. In selected patients, however, both types of VT may be present. Accordingly, patients with significantly impaired hemodynamics after ICD implantation for fast VT may benefit from endocardial mapping and catheter ablation with the aim to decrease number of ICD shocks as monomorphic VT may trigger polymorphic rapid VT and ventricular fibrillation. In selected patients, ablation of premature ventricular beats that trigger ventricular fibrillation may result in a significant reduction of ICD shocks.

Ventricular tachyarrhythmias are a clinical problem that is encountered in daily routine practice of all physicians involved in the care of adult patients with congenital heart defects. In a multicenter trial involving 793 patients with repaired tetralogy of Fallot, sustained monomorphic VT occurred in 4.5% of the patients during a mean postoperative follow-up of 21 years. Sudden cardiac death was noted in another 2% of the patients. In a second multicenter trial covering 556 adult patients with tetralogy of Fallot ventricular arrhythmias were prevalent in 14.6%.

Because nowadays almost 90% of all newborns born with congenital heart defects survive with adequate quality of life into adulthood, the number of patients presenting with congenital heart defects and VT will increase over time.

Anatomy

Most experience on pathophysiology and management of patients with VT and congenital heart disease has been gathered on tetralogy of Fallot. Even in patients with a favorable result after surgical repair, VT is often associated with significant symptoms like syncope and sudden cardiac death. In general, annual incidence of sudden cardiac death after repair of tetralogy of Fallot has been estimated to be 0.15% with increasing risk in adulthood. Several risk factors including anatomic, surgical, hemodynamic, and electrophysiologic parameters have been identified, but the positive predictive value is quite low. For all congenital heart defects, the combination of anatomic abnormalities, surgical scars, and patches/conduits as well as chronic pressure/volume overload leading to myocardial fibrosis and scarring may finally result in formation of a substrate for the development of VT.

Tetralogy of Fallot includes a spectrum of delicate morphologic features that may serve as a substrate for a macroreentrant tachycardia even in the unoperated/native state. The muscular outlet/conal septum is deviated anteriorly and superiorly relative to the remaining interventricular septum giving rise to a large ventricular septal defect with overriding of the aorta, which is partly committed to the hypertrophied right ventricle. Hypertrophied septoparietal trabeculations result in subpulmonary obstruction. The conal septum may extend toward the ventricular–infundibular fold, a thin sheet of muscle interposed between the inlet and outlet portions of the right ventricle. Accordingly, a substrate for a macroreentrant circuit incorporating the conal septum is present even in the unoperated state ( Fig. 35.1 ).

Surgical repair of tetralogy of Fallot should result in complete closure of the ventricular septal defect and preservation of right ventricular form and function with an unobstructed right ventricular outflow tract incorporating a competent pulmonary valve. Surgical repair has made consistent progress over the last 50 years. In the beginning, surgical techniques were restricted to palliative procedures by augmenting pulmonary blood flow through creation of systemic-to-pulmonary artery shunts. Significant for the development of ventricular arrhythmia substrates, early repair techniques included closure of the ventricular septal defect and relief of right ventricular outflow tract obstruction by extensive resection of right ventricular outflow tract muscle via a large right ventriculotomy. In addition, repair after shunting was performed in childhood after long-persisting cyanosis and systemic right ventricular systolic pressure.

Today, corrective surgery is performed early in infancy (within the first 6 months of life) via a transatrial/transpulmonary approach thereby avoiding right ventriculotomy and its associated scarring and risk for the development of VTs. Closure of the ventricular defect with an artificial patch while paying special attention to the specialized conduction system and resection of hypertrophied right ventricular muscle is typically performed via the tricuspid valve. Pulmonary valvotomy and resection of subpulmonary muscle bundles is accomplished through an incision in the main pulmonary artery. Nowadays, when relieving right ventricular outflow tract obstruction, attention is focused on preservation of the pulmonary valve even at the expense of some residual stenosis to reduce the risk of late pulmonary insufficiency and right ventricular outflow tract aneurysm formation. Depending on the individual anatomy, surgeons try to avoid right ventricular outflow tract patch enlargement as well as transannular patch augmentation because of the association with late VTs ( Fig. 35.2 ).