Abstract
In general, patients with congenital heart disease (CHD) are prone to two forms of ventricular tachyarrhythmias: (1) macroreentrant monomorphic ventricular tachycardia (VT) related to scar or prosthetic materials used during surgical repair, such as that observed in patients with repaired tetralogy of Fallot, ventricular septal defects repaired through a ventriculotomy incision, and Ebstein anomaly; and (2) polymorphic VT and ventricular fibrillation with the risk of sudden cardiac death which occur in the setting of a generalized ventricular myopathic process related to chronic pressure and volume overloads, that ultimately result in advanced degrees of hypertrophy, fibrosis, and ventricular dilation. The latter type can be observed in patients with transposition of the great arteries after Mustard or Senning operations, congenital aortic outflow obstruction, tetralogy of Fallot, unrepaired ventricular septal defect with Eisenmenger syndrome, and univentricular hearts with Fontan circulation. Although the incidence of sudden death in the general CHD population is relatively low (<0.1% per year), it accounts for 20%–25% of all late deaths in adults with CHD.
The experience with catheter ablation of VT in CHD is limited. Most information concerning patients with monomorphic VT and CHD pertains to tetralogy of Fallot, as compared with other forms of CHD. Several reports have described single-center experiences spanning several eras of technological advances. The limited acute and long-term success rates are related to the complexity of the underlying congenital defect and surgical repair and the complexity of the reentry circuits.
Keywords
congenital heart disease, ventricular tachycardia, tetralogy of Fallot, Mustard, Senning, transposition of the great arteries
Outline
Pathophysiology, 968
Epidemiology and Natural History, 968
Initial Evaluation, 969
Risk Stratification, 969
Principles of Management, 970
Implantable Cardioverter-Defibrillator, 970
Antiarrhythmic Drug Therapy, 970
Surgical Repair and Ablation, 971
Catheter Ablation, 971
Electrocardiographic Features, 971
Mapping, 972
Vascular and Cardiac Access, 972
Identification of Barriers and Potential Lines of Block, 972
Identification of the Critical Isthmus, 972
Ablation, 973
Pathophysiology
In general, patients with congenital heart disease (CHD) are prone to two forms of ventricular tachyarrhythmias: (1) macroreentrant monomorphic ventricular tachycardia (VT) related to scar or prosthetic materials used during surgical repair, such as that observed in patients with repaired tetralogy of Fallot, ventricular septal defects repaired through a ventriculotomy incision, and Ebstein anomaly; and (2) polymorphic VT and ventricular fibrillation (VF) (with the risk of sudden cardiac death [SCD]) which occur in the setting of a generalized ventricular myopathic process related to chronic pressure and volume overloads that ultimately result in advanced degrees of hypertrophy, fibrosis, and ventricular dilation. The latter type can be observed in patients with transposition of the great arteries after Mustard or Senning operations, congenital aortic outflow obstruction, tetralogy of Fallot, unrepaired ventricular septal defect (VSD) with Eisenmenger syndrome, and univentricular hearts with Fontan circulation.
Most information concerning patients with monomorphic VT and CHD pertains to tetralogy of Fallot, as compared with other forms of CHD. Tetralogy of Fallot is the most common cyanotic congenital cardiac malformation. The core lesion is an underdeveloped subpulmonary infundibulum, which is superiorly and anteriorly displaced, resulting in the well-known tetrad of pulmonic stenosis, ventricular septal defect, aortic override, and right ventricular (RV) hypertrophy. Correction of the anomaly involves patch closure of the ventricular septal defect and relief of right ventricular outflow tract (RVOT) obstruction, which typically requires resection of a large amount of RV muscle. When the procedure was first performed, it was not done through the tricuspid valve but required a ventriculotomy. The pulmonic valve annulus is usually small, and repair with a transannular patch leads to chronic pulmonic insufficiency, which can be severe if associated with downstream obstruction caused by pulmonary arterial stenosis, and can eventually precipitate RV dilatation and dysfunction.
Macroreentry is the most common mechanism for sustained ventricular arrhythmias in adults with repaired tetralogy of Fallot. The sites of the diastolic activation and delayed conduction along the reentrant circuit have been shown to have significant abnormalities such as interstitial or replacement fibrosis, adiposis, and degeneration of the myocardium. The scattered surviving myocyte islets embedded in the extensive adiposis or fibrosis can form an electrical maze around the ventriculotomy incision and patch repairs, resembling the histological findings in the border zone of infarcted myocardium. Furthermore, RV remodeling induced by pressure overload (caused by inadequate relief of obstruction) and volume overload (secondary to severe pulmonic regurgitation) promotes hypertrophy and fibrosis, which can potentially result in slow conduction, providing the link between impaired hemodynamics and VT.
Using intraoperative mapping, monomorphic VT after surgical correction of tetralogy of Fallot has been classified into two types: (1) VT originating from the RVOT, which is considered to be related to prior right ventriculotomy or reconstruction of the RVOT ( Fig. 30.1 ); and (2) VT originating from the RV inflow tract septum, which is thought to be related to closure of the ventricular septal defect. Reentry circuit isthmuses are located within anatomically defined pathways bordered by unexcitable tissue.
Epidemiology and Natural History
CHD is the most common form of birth defect, with an estimated 0.5% to 1% of live newborns afflicted by moderate or severe types. Currently, more than 1 million adults are living with CHD in the United States, and this group now outnumbers children with CHD, reflecting the marked improvements in the early diagnosis and surgical and medical management of CHD. Ventricular arrhythmias late after repair of CHD are an increasingly common finding, predominantly in patients with tetralogy of Fallot, and contribute to mortality and morbidity in this population.
The incidence of SCD in the general CHD population is relatively low (less than 0.1% per year), but it accounts for 20% to 25% of all late deaths in adults with CHD. The risk of SCD is higher in patients with complicated hemodynamic lesions, including tetralogy of Fallot (0.2% to 0.3% per year), D-transposition of the great arteries with Mustard or Senning baffles, congenitally corrected transposition of the great arteries, left-sided obstructive lesions, Eisenmenger syndrome, and Ebstein anomaly.
Although ventricular ectopy and nonsustained VT are relatively common, sustained monomorphic VT is rare in the general adult CHD population, with an annual incidence of 0.1% to 0.2%. Notably, the incidence of arrhythmias increases as the patient ages. In patients with tetralogy of Fallot, serious ventricular arrhythmias are rare during the first 10 to 15 years following corrective surgery. This quiescent period is followed by a steady increase in the incidence of ventricular arrhythmias, primarily monomorphic VT, which are prevalent in 15% of adult patients late after surgery. By 35 years of follow-up, the incidence of VT is 11.9%, with an 8.3% risk of SCD. Since the mid-1990s, surgical repair of the tetralogy of Fallot has usually been performed using a combined approach through the RA and the pulmonary artery. In these cases, there is no incision in the RV free wall around which reentry can occur, although reentry around the ventricular septal defect patch can still take place. In addition, a limited RV incision may still be needed when patch augmentation for the RVOT or pulmonary annulus is necessary.
Tetralogy of Fallot is the most common substrate for sustained VT and is typically cited as the archetypal lesion when VT in the adult CHD patient population is discussed. Nonetheless, serious ventricular arrhythmias can also develop in other types of congenital heart malformations, even in the absence of direct surgical scarring to ventricular muscle, including congenital aortic stenosis, transposition of the great arteries when the RV supports the systemic circulation, severe Ebstein anomaly, certain forms of single ventricle, and ventricular septal defect with pulmonary arterial hypertension. The appearance of ventricular arrhythmias in these cases commonly coincides with deterioration in overall hemodynamic status.
Initial Evaluation
Patients with CHD presenting with symptoms suggestive of ventricular arrhythmias, such as palpitations, dizziness, and syncope, require careful evaluation to help document cardiac rhythm during clinical symptoms. This is typically achieved by ambulatory cardiac monitoring or implantation of a loop recorder. Electrophysiological (EP) testing can also be considered when the index of suspicion is high.
Importantly, new-onset or worsening ventricular arrhythmias can herald deterioration of the hemodynamic status, which requires a thorough evaluation of ventricular function and residual lesions. In addition, detailed evaluation of cardiac function and anatomy and knowledge of the congenital anomaly and previous surgical procedures are very important. This evaluation can require transthoracic or transesophageal echocardiography, right or left heart catheterization, angiography of the desired cardiac chamber, and cardiac magnetic resonance imaging.
Risk Stratification
Noninvasive Risk Stratification
Some subgroups of patients with CHD are recognized as being at risk for life-threatening ventricular arrhythmias and SCD, including those with large scars from a prior ventriculotomy (e.g., tetralogy of Fallot repair) and those who develop advanced degrees of ventricular dysfunction from longstanding hemodynamic burdens (e.g., congenital aortic stenosis, single ventricle).
Although controversy still exits, several noninvasive risk factors for VT and SCD have been identified in the CHD patient population. Tetralogy of Fallot is the one condition for which such data are fairly extensive. QRS duration exceeding 180 milliseconds, left ventricular (LV) systolic dysfunction (ejection fraction less than 50 %), and LV diastolic dysfunction (LV end-diastolic pressure ≥12 mm Hg) have consistently predicted adverse outcome. In addition, symptomatic nonsustained VT and atrial arrhythmias are associated with increased SCD risk. Asymptomatic nonsustained VT has been associated with inducible sustained VT by programmed ventricular stimulation and with clinical ventricular tachyarrhythmias in implantable cardioverter-defibrillator (ICD) recipients, but its value for SCD risk prediction is limited. Several other clinical characteristics, such as RV pressure overload and RV systolic dysfunction, have been proposed as risk factors for SCD but with inconsistent validation in the literature. A risk score to predict appropriate ICD shocks in tetralogy patients with ICDs for primary prevention indications was derived from six clinical variables (surgical, hemodynamic, electrocardiographic, and EP factors) identified by multivariate analyses ( Table 30.1 ). Patients with fewer than 3 points (low risk) experienced no appropriate shocks. In patients with 3 to 5 points (intermediate risk) and more than 5 points (high risk), the annual rates of appropriate shocks were 3.8% and 17.5%, respectively. Although these risk-stratification schemes can provide reasonable sensitivity, they have suboptimal specificity for patients at high risk because of the small population size and the relatively low incidence of SCD in CHD patients (approximately 2% per decade of follow-up in patients with repaired tetralogy of Fallot repair).
| Variable | Exponential Values of Beta Coefficients | Points Attributed |
|---|---|---|
| Prior palliative shunt | 3.2 | 2 |
| Inducible sustained ventricular tachycardia | 2.6 | 2 |
| QRS duration ≥180 msec | 1.4 | 1 |
| Ventriculotomy incision | 3.4 | 2 |
| Nonsustained ventricular tachycardia | 3.7 | 2 |
| Left ventricular end-diastolic pressure ≥12 mm Hg | 4.9 | 3 |
| Total points | 0–12 | |
For congenital malformations other than tetralogy of Fallot, SCD risk predictors have not been clearly defined. Severely impaired systolic function of the systemic ventricle (ejection fraction ≤35%) has been associated with ventricular arrhythmias and SCD; however, QRS duration has been inconsistently noted to predict SCD. Recurrent unexplained syncope in the presence of ventricular dysfunction may also identify a high-risk group. Factors such as nonsustained VT, prior palliative shunt, ventriculotomies, and atrial tachyarrhythmias have been proposed, but uncertainty remains as to their true prognostic significance. Notably, among ICD recipients, adults with non–tetralogy of Fallot congenital lesions are significantly less likely to receive appropriate ICD therapy than those with tetralogy of Fallot (11.5% vs. 27.3%).
Electrophysiological Testing
In patients with repaired tetralogy of Fallot, inducible monomorphic or polymorphic sustained VT by programmed ventricular stimulation is independently associated with a nearly fivefold higher rate of clinical VT or SCD on follow-up. Sustained VT is inducible in approximately 35% of this patient population, which is similar to that reported in patients with prior myocardial infarction (MI) and LV ejection fractions less than 40% and spontaneous nonsustained VT. Independent risk factors for inducible sustained VT include: (1) age older than 18 years at the time of testing, (2) history of palpitations, (3) prior palliative surgery, (4) frequent or complex ventricular ectopy or nonsustained VT, and (5) cardiothoracic ratio of greater than 0.6 on chest radiograph. The diagnostic value of EP testing (sensitivity, 77%; specificity, 80%; diagnostic accuracy, 79%) and prognostic significance (relative ratio, 4.7 for subsequent clinical VT or SCD) compares favorably with programmed ventricular stimulation in post-MI patients. However, the yield of EP testing remains too imperfect and too impractical to be recommended as a general screening tool and the timing and frequency of testing remain to be elucidated. Nonetheless, EP testing may be considered in selected patients with concerning symptoms (e.g., palpitations, dizziness, or unexplained syncope) or Holter findings, when VT is suspected but not yet proven. In addition, the subpopulation of patients deemed at intermediate risk of SCD based on a combination of other parameters may benefit most from risk stratification with an EP study.
For congenital malformations other than tetralogy of Fallot, the value of programmed ventricular stimulation in risk stratification remains uncertain. Inducibility of sustained VT at EP study does not appear to predict clinical VT or SCD in patients with transposition of the great arteries and Mustard or Senning baffles.
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