Dominic Abrams (Division of Cardiac Electrophysiology, Boston Children’s Hospital, Boston, USA) writes on the importance of arrhythmia management in congenital heart disease patients and identifies the reasons why it remains a major challenge for interventional eletrophysiology.
A major success of the last three decades has been the significant increase in survival of children undergoing congenital cardiac surgery leading to an ever expanding population of young adults with congenital heart disease, such that by the year 2010 adults accounted for two-thirds of the entire congenital heart disease population (Marelli AJ et al, Circulation 2014;130:749-56).
Chamber dilatation resulting from long-term haemodynamic stress coupled with repeated surgical intervention creates an ideal environment for both atrial and ventricular reentrant arrhythmias, and often the first re-emergence of cardiac disease in otherwise well-palliated patients who have been stable for many years is arrhythmia. As arrhythmias in this population are associated with double the risk of cerebrovascular events and heart failure, and a 50% increase in mortality (Bouchardy Jet al, Circulation 2009;120:1679-86)prompt recognition and management are imperative.
Whilst the electroanatomic substrate in congenital heart disease is ideal for reentrant circuits, it is important to recognise that simple arrhythmia mechanisms such as atrioventricular reentry tachycardia mediated by accessory pathways (particularly associated with specific lesions such as Ebstein’s anomaly and congenitally corrected transposition of the great arteries) and atrioventricular nodal reentry tachycardia also occur. These mechanisms should therefore always be suspected in the adult with congenital heart disease patient with a significant arrhythmia history who has never required cardioversion. Similarly, the ECG in these patients may be misleading; ‘pseudonormalisation’ of the ECG may be seen in Ebstein’s anomaly patient where anterograde conduction via a right-sided accessory pathway eliminates the right ventricular conduction disease typically seen in the condition, whereas a ‘pseudopreexcitation’ pattern not created by a pathway may be seen in other lesions such as hypoplastic left heart syndrome.
Prior to an interventional electrophysiology study, it is essential to understand the venous anatomy, location of the cardiac conduction system and where possible to identify sites of surgical access from prior operative reports that may act as central obstacles to conduction within reentrant circuits. For the purposes of arrhythmia mechanism, adults with congenital heart disease patients can be divided into two basic groups; those who have undergone biventricular repair (eg. atrial septal defect, tetralogy of Fallot, TGA) and those who have single ventricular physiology or a Fontan-type circulation.
In patients with a biventricular circulation typical atrial flutter remains the most common mechanism, accounting for 60-70% of mapped circuits in reported series. However, due to structural and electrocardiographic abnormalities often in association with rapid atrioventricular nodal conduction, the ECG appearance and arrhythmia cycle length frequently deviate from those classically associated with typical flutter. Entrainment mapping at the cavotricuspid isthmus at the start of the procedure rapidly determines if the arrhythmia is isthmus-dependent, and can dictate the course of the remainder of the study. Right atrial circuits may also use the atriotomy as a central obstacle, or may be dependent on narrow, slowly-conducting gaps within the crista terminalis.
In the single ventricular circulation arrhythmia, mechanisms are often more varied. In the initial atriopulmonary Fontan used for many years but now obsolete, the right atrium acted as the sub pulmonary chamber leading to severe atrial dilatation and often extensive areas of scarred and low-voltage myocardium. Arrhythmias circuits of significant anatomical length were frequently dependent on varying degrees of fixed and functional conduction block at the position of the crista, and despite often successful ablation the emergence of new circuits and ongoing arrhythmia remained a major problem. Surgical evolution of the procedure, in part to eliminate large sections of the right atrium from the systemic venous-pulmonary circulation, led to the development of the total cavopulmonary circulation. This allows inferior vena caval flow to be channeled to the pulmonary arteries either via an intracardiac conduit created along the posterolateral wall of the right atrium, or an extracardiac conduit. In the intracardiac variant typical atrial flutter remains a prevalent mechanism, where the wave front propagates around an anterior atrioventricular valve with the conduit replacing the role of the crista as a posterior line of conduction block. Initially described in animal models, this has now been borne out in clinical experience. Both focal and reentrant arrhythmias may also occur within the intracardiac conduit. Whether the extracardiac total cavopulmonary circulation, which eliminates both atria from the cavopulmonary circulation is associated with a lesser burden over time remains uncertain.
Given the accelerated atrial remodeling and associated ventricular dysfunction that are so prevalent in adults with congenital heart disease, it is no surprise that atrial fibrillation is an increasing problem as the population ages, although no studies regarding specific mechanisms have yet been conducted. It is possible the etiology may vary, originating in the pulmonary veins associated with systemic ventricular failure in lesions such as congenitally corrected transposition of the great arteries, but may have differing origins in those with predominately right heart disease such as tetralogy of Fallot. Without question, the management of atrial fibrillation in adults with congenital heart disease is going to be a major challenge for interventional electrophysiology and adult congenital heart specialists in the next decade.
Dominic Abrams is with the Division of Cardiac Electrophysiology, Boston Children’s Hospital, Boston, USA