Some form of congenital heart disease is present in 75/1,000 live births. 1 The majority of these patients live into adulthood, with approximately one half million adults living with congenital heart disease in the United States. Sudden cardiac death is now the leading cause of mortality in this patient population.2,3 Advances in surgery for congenital heart disease have saved or prolonged the lives of thousands. As with any successful operation or procedure, there are trade-offs for success. Many years removed from their initial surgery, these patients are now at risk for morbidity and mortality from bradyarrhythmias and tachyarrhythmias. Arrhythmias are common in this population and occur for a number of reasons. Some forms of congenital heart disease predispose to arrhythmia at baseline. After repair, the substrate created by scars, grafts, patches and suture lines further predispose to arrhythmia. These substrate abnormalities lead to slowed conduction and macroreentrant arrhythmias. 4 Repaired congenital heart disease patients are further at risk for the development of arrhythmias due to abnormal hemodynamic changes within the affected cardiac chambers. 5 Once these patients develop arrhythmias, they can develop electrical remodeling as well. 6,7 Developing an electrophysiology program for the treatment of arrhythmia in adult congenital heart disease requires a complete understanding of the anatomy and physiology underlying congenital heart disease. It also requires a detailed understanding of the individual patient’s surgical corrective and palliative procedures, which may vary significantly. Expertise in all areas of interventional electrophysiology is essential to successfully treat the congenital heart disease patient population. The frequency of underlying conduction system disease in this population, as well as the increased frequency of ventricular dysfunction that develops from the time of initial operation, make the options for pharmacologic antiarrhythmic therapy limited. Treatment of arrhythmia with ablation and implanted devices is often required. The 2008 ACC/AHA guidelines for the treatment of adults with congenital heart disease give a class I recommendation for ablation and device implantation procedures to be undertaken at centers that “have significant experience with the complex anatomy and distinctive arrhythmia substrates encountered in congenital heart defects.” 8 The UCLA Congenital Heart Disease Center is responsible for the care of thousands of adult patients with congenital heart disease. These numbers only continue to grow. Review of the electrophysiologic complexity of treating the full spectrum of adult congenital heart disease patients is beyond the scope of this article. In order to demonstrate some important issues related to ablation and device therapy, we will focus on three groups that are often very difficult to manage that commonly present to centers such as ours. Specifically, we will discuss atrial arrhythmias in patients after the Mustard and Fontan operations, as well as the management of ventricular arrhythmias in patients with a history of repaired tetralogy of Fallot. At last review, the Adult Congenital Heart Disease Center at UCLA is responsible for the care of approximately 250 patients with tetralogy of Fallot, 225 patients with transposition of the great arteries and 100 patients with univentricular hearts that have received a Fontan operation. Many of these patients are also cared for at the UCLA Cardiac Arrhythmia Center. Ablation Nowhere in clinical cardiac electrophysiology is the team concept more important than during ablation of complex arrhythmias in adult congenital heart disease patients. These procedures are long and complex. Commonly used catheters and techniques often require modification to allow for testing and delivery of therapy in severely dilated chambers with conduits and grafts that may have become stenotic or calcified in the years after surgery. Catheter contact to form a necessary line of block can often be a significant challenge, leading to an increased likelihood of recurrence. Given the complex anatomy and physiology, multiple circuits are often present. Scars, patches and grafts predispose to reentrant arrhythmias in these patients. As with any reentrant rhythm involving scar, small areas of viable myocardial tissue within areas of dense scar often provide the milieu for the reentrant rhythm. Entrainment mapping and electroanatomical mapping can help localize the reentrant circuit and the optimal site for ablation. The addition of three-dimensional mapping techniques is an essential complementary tool in mapping complex reentrant circuits, as generally accepted fluoroscopic landmarks are often inaccurate in this setting. In the optimal situation, three-dimensional mapping systems can be integrated with magnetic resonance imaging or computed tomographic scans to allow for the most complete understanding of the patient’s individual anatomy. Advances in ablation technology have further increased the success rates in this patient population. Irrigated tip catheters, which have been shown to deliver more extensive lesions, may also provide some benefit in treating tachyarrhythmias in the congenital heart disease population, as recently shown by Triedman and colleagues. 9 The healed ventriculotomy scar of a patient with repaired tetralogy of Fallot is an excellent example of scars and patches predisposing to reentrant arrhythmias. The substrate for monomorphic ventricular tachycardia in this population is most often slow conduction at the site of the ventriculotomy scar or ventricular septal defect patch as previously discussed. Slow conduction in these regions typically causes a right ventricular outflow tract ventricular tachycardia with a left bundle branch morphology. Macroreentrant atrial arrhythmias are a common abnormality in patients with transposition of the great arteries status-post Mustard or Senning operations. The Mustard procedure entails insertion of a pericardial or Dacron baffle to redirect systemic flow across the mitral valve into the left ventricle and pulmonary artery, while redirecting pulmonary venous return across the tricuspid valve and into the right ventricle and aorta. 10 Complete transposition of the great arteries is now primarily treated with an arterial switch operation, which will likely decrease the arrhythmia burden. However, at the current time, the majority of adults who have undergone repair and are presenting with arrhythmias are status-post Mustard or Senning operations. Patients with repaired transposition are prone to significant bradyarrhythmia, and therefore often do not tolerate antiarrhythmic medical therapy. 11 This makes the need for interventional management of their tachyarrhythmias even more important. Macroreentrant atrial tachycardia or flutter after a Mustard operation frequently relies on a critical zone of slow conduction between the atrial baffle and coronary sinus and between the atriotomy incision and the tricuspid annulus. 12 Advances in intracardiac mapping have allowed for improved identification of critical areas of conduction within the reentrant circuit. The Fontan operation was designed primarily for the treatment of patients with tricuspid atresia, pulmonary stenosis and single ventricle. Numerous modifications of this procedure have been developed over the years. Common to all modifications of the Fontan operation, venous blood is redirected to bypass some or all of the right heart. Supraventricular arrhythmias are common in this population, with rates of atrial tachyarrhythmias as high as 50% after 10 years. 13 Atrial arrhythmias result in significant morbidity, with a detrimental effect on cardiac output and increased risk of thrombosis. 14 In this population, atrial arrhythmias can often lead to the same hemodynamic instability in patients with congenital heart disease that might be more frequently associated with ventricular tachycardia. Supraventricular arrhythmias in this population can be complex, and multiple circuits are often present. Cardiac Device Implantation While indications for pacemaker implantation have remained relatively unchanged over recent years, indications for implantable cardioverter-defibrillators (ICDs) have increased. 15 This increase in indications for implantation, and the prolonged life expectancy of patients with repaired congenital heart disease, has led to an increasing number of patients in this population being implanted with ICDs. Venography is often warranted prior to implantation. Obstructed or stenotic conduits and baffles can inhibit lead placement. This is especially true in patients with previously implanted transvenous leads. Bar-Cohen and colleagues reported a 25% likelihood of partial or complete venous obstruction at 6.5 years follow-up. 16 Lead positioning is complicated by the underlying anatomy. Leads often cannot be placed in classic positions such as the right atrial appendage, which may no longer be present, or the ventricular apex, which may be limited by areas of fibrosis that adversely affect threshold and sensing values. 17 One must also be aware of the increased risk of thromboemboli if a patient has residual shunting or develops baffle leaks. The need for device implantation in patients with repaired tetralogy of Fallot is common. The majority of these patients start with a right bundle branch block. 18 Patients with post-operative bifascicular block often have associated His-purkinje system disease and are at high risk for development of complete heart block. 19 Repaired tetralogy patients have an increased incidence of atrial arrhythmias. 20,21 However, the increased risk of monomorphic ventricular tachycardia and the associated risk of sudden cardiac death are the most concerning electrophysiologic consequences of tetralogy of Fallot and its subsequent repair. 22-24 Risk of sudden cardiac death in this population at baseline is 0.15% per year,3 but the risk increases with a late repair, baseline QRS duration >180 milliseconds, 25 elevated right ventricular systolic pressures, frequent ventricular ectopy, inducible sustained ventricular tachycardia on electrophysiologic study and left ventricular systolic dysfunction. 26 Khairy and colleagues recently published their cohort of tetralogy of Fallot patients, and demonstrated that patients in this population have a high frequency of appropriate shock after ICD implantation regardless of whether the device was implanted for primary or secondary prevention. 27 Sinus node dysfunction can occur with any patient after surgical manipulation of the high right atrium. Sinus node dysfunction is very common after Fontan, Mustard and Senning operations. Fontan patients do not have, or do not have direct, transvenous access to the ventricle; therefore, ventricular leads must be placed epicardially, or in some situations, can be placed through the coronary sinus as demonstrated by Estner and colleagues. 28 Endocardial pacemaker or implantable cardioverter-defibrillator implantation in a patient with complete transposition of the great arteries can often be accomplished by placing leads into the sub-pulmonic left ventricle with access via the atrial baffle. Implantation can be complicated by baffle stenosis or leak. Lead/Device Extractions Patients with a history of repaired congenital heart disease that are implanted with a pacemaker or ICD are significantly younger than the average patient implanted without such cardiac history. The relative young age of these patients means they will require multiple generator replacements, each of which carries a risk of infection and subsequent need for extraction. Complex anatomy leads to an increased risk of lead failure. 29 Once extraction becomes necessary, the complex anatomy associated with repaired congenital heart disease may increase the risk of extraction. Though reports are limited, numerous case reports have demonstrated successful endovascular explantation of devices in this population. 30-32 Telescoping sheaths have been used. Our experience has been that the use of laser sheaths may further decrease the risk and increase the success rate. Cooper and colleagues reported the first case series of laser sheath extraction of devices in children and young adults with congenital heart disease in 2003, 31 with Khairy and colleagues publishing their data in 2007. 32 Laser extraction is now feasible and safe in these patients when performed in centers with experience in complex congenital heart disease patients. Summary Conduction abnormalities and arrhythmias after surgical repair of congenital heart disease are caused by a combination of underlying electrophysiologic substrate and the postoperative substrate that depends on the type of procedure performed, the timing of the procedure and the postoperative hemodynamics. 33 The international experience with ablation and device implantation in this complex patient population is growing. However, the highest procedural volume remains in tertiary care centers that have a close relationship with congenital heart disease specialists. At UCLA, as part of our Specialized Program for Arrhythmias in Congenital Heart Disease, we are fortunate enough to have such a relationship. In collaboration with our colleagues in the UCLA Congenital Heart Disease Center, we are making strides to improve the techniques and success rates in this ever-growing population.