The great successes of congenital heart surgery have created a new class of cardiology patient: the adult with congenital heart disease (CHD). It is estimated that there are nearly three million patients older than 18 years of age with CHD in Europe and North America, and for the first time ever there are more adults living with congenital heart defects than children with CHD. Cardiac arrhythmias of all varieties ( Table 17.1 ) are prevalent in the adult group, often complex and difficult to manage, and significantly complicate the long-term care of these patients.
| Lesion | IART | AFIB | WPW | VT/SCD | SAN DYSFXN | SPONT AV-BLK | SURGAV-BLK | Twin AV Nodes |
|---|---|---|---|---|---|---|---|---|
| ASD (late repair) | + | + | — | — | + | — | — | — |
| ASD (Holt-Oram syndrome) | + | — | — | — | — | ++ | — | — |
| VSD (transatrial repair) | + | — | — | — | — | — | + | — |
| VSD (repair through ventriculotomy) | — | — | — | + | — | — | + | — |
| Common AV canal defect | + | — | — | — | — | + | ++ | — |
| Tetralogy of Fallot | ++ | — | — | ++ | — | — | + | — |
| Congenital aortic stenosis | — | + | — | ++ | — | — | + | — |
| Coarctation aorta (residual gradient or late repair) | — | — | — | ++ | — | — | — | — |
| Congenital mitral valve disease | + | ++ | — | — | — | — | + | — |
| Ebstein’s Anomaly | ++ | + | +++ | + | — | — | — | — |
| D-TGA (Mustard or Senning) | +++ | — | — | ++ | +++ | — | — | — |
| L-TGA | + | + | ++ | + | — | +++ | ++ | — |
| Single ventricle (atrio-pulmonary Fontan) | +++ | + | — | + | +++ | — | — | — |
| Single ventricle (new-style Fontan) | + | — | — | + | + | — | — | — |
| Single ventricle (palliated) | + | ++ | — | + | — | — | — | — |
| Heterotaxy (right atrial isomerism) | + | — | — | — | — | — | — | ++ |
| Heterotaxy (left atrial isomerism) | + | — | — | — | +++ | ++ | — | — |
Cellular cardiac electrophysiology in CHD patients is thought to be generally similar to that of the normal population, but anatomic malformations, the effects of a variety of hemodynamic and environmental stressors, and surgical scarring produce a complex arrhythmogenic substrate. The result is a high and increasing frequency of acquired arrhythmias that are rarely seen in normal young adult hearts, including atrial and ventricular reentrant tachycardias, heart block, and sinus node dysfunction. In addition, any arrhythmias prevalent in the normal population may also occur in CHD.
The presence of CHD significantly alters arrhythmia risk, its potential severity, and the safety and feasibility of various therapies. Clinical manifestations of arrhythmia in adult congenital heart disease (ACHD) range from clinically occult arrhythmia to sudden death, which is the mode of death in 20% to 25% of ACHD patients. Incessant arrhythmias may cause progressive hemodynamic deterioration and are associated with thrombosis and embolic events. Symptoms, frequent need for hospitalization, and adverse effects of antiarrhythmic drugs constitute a significant burden on quality of life. Risk assessment for identification of patients appropriately treated with implantable cardiac defibrillators (ICDs) is difficult because ACHD populations are small, anatomically diverse, and have relatively low rates of sudden death. Recently, research on the natural history and management of arrhythmia in ACHD has been carefully collated and examined, and evidence-based recommendations for care have become available. In this context, this review addresses the identification, evaluation, and management of the more common forms of arrhythmia seen in ACHD.
Bradycardia
sinus node dysfunction
Gradual loss of sinus rhythm occurs over time after the Mustard and Senning operations and after all varieties of Fontan procedures, along with attenuated chronotropic response. Patients with heterotaxy syndromes, particularly left atrial isomerism, may also have congenital abnormalities of the sinus node. Loss of sinus rhythm appears to increase risk of mortality, may be hemodynamically adverse, and is associated with the occurrence of paroxysmal atrial tachycardias.
Direct surgical injury to the sinus node artery and the node itself has been observed and may be the cause of long-term sinus node dysfunction in some patients. However, loss of sinus rhythm is observed to occur in populations of ACHD patients over decades, which implies the action of other ongoing processes most likely related to scarring and chronic hemodynamic abnormality. Abnormalities of atrial electrophysiology identified in postoperative CHD patients include prolonged sinus node recovery times, intraatrial conduction times, and atrial refractoriness.
Atrioventricular Block
Interventricular conduction abnormalities and particularly right bundle-branch block are common after CHD surgery, but complete and permanent postoperative heart block is rare in recent decades, occurring in 1% to 3% of cases. It is most often seen in small patients undergoing repair of ventricular septal defects (VSDs) of any sort and after left ventricular outflow tract and mitral valve surgeries and is caused by direct surgical injury to the specialized conduction system or by indirect damage due to inflammatory response. In the era before cardiac pacing systems appropriate for ACHD patients were widely available, postoperative heart block had an extremely high mortality rate, even when an escape rhythm was present.
Complete heart block also occurs spontaneously in patients with certain structural heart defects, especially endocardial cushion defects and congenitally corrected transposition, plausibly related to the aberrant anatomy of the specialized conduction system that renders them vulnerable. Heart block may progress at any stage of life in these patients, irrespective of surgery.
Pacemaker Issues
Pacing is clearly indicated for high-grade heart block in ACHD, most commonly encountered in the postoperative patient. Clinical experience demonstrates the value of atrioventricular (AV) synchrony and favors implantation of dual-chamber pacemakers if size and access permit, but the value of “physiologic” as compared with simpler pacing modalities is not well established in ACHD. Other indications such as sinus node dysfunction with or without concomitant atrial tachycardia are more controversial, and recommendations have largely been based on clinical judgment. In patients with sinus node dysfunction and junctional escape rhythms, severe resting bradycardia, chronotropic incompetence, and/or prolonged pauses, pacing may alleviate symptoms of fatigue, dizziness, or syncope. In asymptomatic patients, decisions to pace for hemodynamic indications are unclear and must be coordinated with careful plans for clinical re-evaluation on follow-up.
Options for cardiac pacing in ACHD patients may be limited because of congenital and acquired abnormalities of systemic venous and cardiovascular anatomy. The presence of an intracardiac shunt increases the risk of stroke, limiting some patients to epicardial lead placement. Placement of atrial leads by epicardial or transvenous route may be technically challenging and must avoid inadvertent stimulation of the phrenic nerve. Excellent sensing of atrial electrical activity by pacing systems is crucial to avoid asynchronous atrial pacing, which may provoke atrial tachycardia. The effect of these technical constraints is that pacing systems must not infrequently be adapted on an individual basis to patient-specific lead placement and maintenance issues ( Fig. 17.1 ).
Recently, the utility of cardiac resynchronization effected by multisite pacing has been investigated in ACHD. Acute hemodynamic studies and small clinical series suggest the possibility that both left and right ventricular resynchronization may have some clinical value, but also highlight the fact that it is exceedingly difficult to construct validated and reproducible measures of ventricular function in this heterogeneous and anatomically complex population. At present, the only class I indication for resynchronization in patients with CHD are those with a systemic left ventricle (LV) and complete left bundle branch block with a QRS greater than 150 ms in duration.
Atrial Tachycardias
Macroreentrant atrial tachycardias, often denoted as intraatrial reentrant tachycardias (IARTs), are prevalent in many adults with congenital heart defects, including both atypical reentry circuits and more typical forms of atrial flutter noted to occur in the normal heart. These tachycardias tend to have a relatively stable cycle length and P-wave morphology, suggesting that they are organized by a fixed substrate. They are most common among patients who have undergone surgical procedures involving extensive atrial dissection and repair. The importance of surgical injury to the atrium is supported by observations in animal models patterned after Mustard and Fontan surgeries, which reliably cause tachycardias similar to those seen clinically. Atrial tachyarrhythmias are associated with hemodynamic issues and thromboembolism. Although stroke after cardioversion in ACHD patients seems rare, intravascular and intracardiac thromboses are associated with atrial tachycardias, with a prevalence of intracardiac thrombi in 42% of patients undergoing echocardiography before cardioversion has been reported.
Increased risk for mortality is also observed, with predictors of mortality including several factors that cooccur with atrial tachycardias, including single ventricle physiology and unfavorable hemodynamics. Late follow-up of patients with a prior surgical history of Fontan, Mustard, or Senning procedures suggests mortality including sudden cardiac death at a rate of 1% to 2% per year. Risk factors identified for IART include older age at operation and length of follow-up. About one-half of patients with classic right atrial–right ventricular or atriopulmonary Fontan procedures develop IART within 10 years of surgery. Those who undergo the lateral tunnel variant of the procedure with cavopulmonary connection or the extracardiac Fontan operation may be at lower risk. Patients who have had a Mustard and Senning procedure for transposition of great arteries are at risk of developing sinus node dysfunction and IART, often concurrently. IART is more prevalent than ventricular tachycardia (VT) in patients with repaired tetralogy of Fallot and more likely to be associated with symptoms.
Drug Therapy
Although some small studies have suggested otherwise, clinical experience generally suggests that antiarrhythmic drug therapy is unlikely to suppress recurrences of IART. Experimental models of atrial reentry have given us a good understanding of the potential salutary effects of New York Heart Association class IC and class III drugs, and symptomatic arrhythmias can sometimes be suppressed in individual patients using these agents. However, proarrhythmia and adverse effects on ventricular and nodal function may limit their value. Antiarrhythmic drugs with pure class III activity have not been widely used in IART and may prove useful. In general, antiarrhythmic therapy used in this setting should consider issues of sinus node dysfunction, impaired AV nodal conduction, and ventricular dysfunction, and be monitored closely.
The frequent occurrence of thrombosis in adult patients with CHD and atrial tachycardia suggests that warfarin or other potent anticoagulant therapy is indicated in most of these patients. Recently, there has been interest in the use of novel oral anticoagulant agents for this purpose. Recommendations for both acute and long-term anticoagulation generally followed those used for adults with propensity to thromboembolism due to arrhythmia. AV nodal blocking drugs may also be used, but are often difficult to titrate because of the relatively slow cycle length and fixed conduction ratios often seen in IART.
Pacemaker Therapy
Atrial antibradycardia pacing alone sometimes results in symptomatic improvement and decreased tachycardia frequency. In patients with sinus node dysfunction, this may also be the result of improved hemodynamics with appropriately timed atrial activation. Automatic antitachycardia pacing has also been of value for some patients. The overall efficacy of the atrial pacing is variable, and there are significant technical difficulties associated with lead placement in these patients. Few endocardial or epicardial sites are generally available and able to generate sensed electrograms of sufficient quality to ensure reliable atrial sensing. Endovascular placement of atrial leads may also increase risk of thrombosis.
Catheter Ablation
A proposed curative approach to IART has been to create or extend lines of conduction block, using catheter-based and/or surgical techniques. This anatomic approach to therapy involves the design of a lesion or lesions based on an understanding of the relation of macroreentrant circuits to the underlying cardiac anatomy. It can be understood in the same way as catheter and surgical ablation procedures for VT and the maze procedure for atrial fibrillation.
Acute procedural success rates reported for radiofrequency catheter ablation for IART range from 72% to 77%, depending to some extent on the complexity of the underlying defects. Longer-term outcomes suggest that arrhythmia symptoms and quality of life are improved in most patients after IART ablation, but recurrence is frequent, occurring in one-third to one-half of patients. Catheter ablation procedures usually target individual macroreentrant circuits, seeking a vulnerable site for application of a radiofrequency lesion. Review of IART ablation experience has shown that, in patients with a right AV valve, the isthmus between that valve and the inferior vena cava commonly supports IART, similar to common atrial flutter. When this isthmus is present, as is the case in patients with Mustard and Senning procedures, tetralogy of Fallot, and other biventricular repairs, techniques developed for atrial flutter may be used to perform and assess the effectiveness of the ablation. Even in these familiar anatomies, however, the observation of multiple IART circuits is common and other anatomic or surgical features relevant to ablation may be difficult to locate fluoroscopically, and the use of three-dimensional electroanatomical mapping system stick guide ablative therapy is recommended. It may also be difficult to generate the large and confluent lesions sometimes needed to interrupt these circuits, and for similar reasons, advanced ablative technology such as catheter irrigation is associated with improved acute success rates. Further advances in our understanding of the arrhythmia substrate and the technology available to visualize and modify it will be necessary to improve this important clinical outcome ( Fig. 17.2 ).
