ventricular contraction,47 and biventricular resynchronization may produce a significant increase in cardiac output.45 This method, therefore, may be an effective strategy for patients with biventricular dysfunction occurs who do not respond adequately to replacement of the pulmonary valve Although most attention has been directed toward assessment of problems in the right heart, there are other important late anatomic problems For example, aortic dilation and valvar incompetence is recognized increasingly with duration of followup,48 and the risk of endocarditis is significant Nonetheless the issues of pulmonary incompetence and the resulting secondary functional and conduction disturbances dominate the clinical picture in most patients Postoperative Conduction Disturbances and Arrhythmias Complete right bundle branch block is frequently produced following surgical correction of tetralogy and is primarily benign The duration of the QRS complex in this setting appears to be loosely related to the size of the right ventricle and, in turn, related to the risk of late ventricular arrhythmia As such its documentation and intermittent assessment is important in the late follow-up of these patients Although heart block can be a cause of death at or soon after surgery and may cause some late sudden deaths, it is unlikely to account for the majority of deaths Multiple ventricular premature beats may be a harbinger of more serious ventricular arrhythmias Ventricular arrhythmias, rather than conduction defects, are more likely to be the basis for sudden death.49 In this light, the use of ambulatory monitoring has greatly increased the detection of arrhythmias after surgical correction of congenitally malformed hearts, bringing with it many dilemmas in management.50 Disturbances of rhythm—such as frequent unifocal ventricular extrasystoles, more complex couplets, multifocal extrasystoles, and even asymptomatic nonsustained ventricular tachycardia—were reported in two-fifths or more of patients undergoing 24-hour monitoring on medium-term follow-up.51 Attempts were made in these and other series to correlate arrhythmias with residual hemodynamic disorders, such as poorly relieved subpulmonary obstruction, but the results were conflicting What has emerged is that frequency of arrhythmias correlates well with age at operation.50 One possible explanation for this finding is the presence with older age of increasing amounts of fibrosis in the right but not the left ventricle.52,53 Not only age but more extensive surgery54 and the extent of the ventriculotomy55 are associated with an increase in ventricular arrhythmias Whether asymptomatic arrhythmias predict the risk of sudden death is a different matter Sudden death occurs in about 6% of patients over the long term,33 or 4.5 per 100 patientsyears,56 but can it be predicted? As discussed previously, poor right ventricular systolic or diastolic function, residual subpulmonary obstruction, and a residual ventricular septal defect have all been associated with a poor prognosis, possibly owing to arrhythmias The presence in asymptomatic patients of complex ventricular arrhythmias on 24-hour tape recordings, nonetheless, did not identify a group at risk.57 In an early study, prolongation of the QRS complex of 180 ms or more was shown to predict a 95% probability of near-miss sudden death from sustained ventricular arrhymias.38 Conversely, no patient with sustained ventricular tachycardia dying suddenly had a duration less than 180 ms Prolongation of the QRS complex was associated with right ventricular dilation and often with pulmonary regurgitation, although this was not quantified in the study When restrictive right ventricular physiology was identified on late follow-up, duration of the QRS complex was always less than 180 ms In these patients, the right ventricle has a limited end-diastolic volume, since antegrade diastolic pulmonary flow owing to atrial systole limits the amount of pulmonary regurgitation The myocardial structure that prevents right ventricular dilation even in the presence of pulmonary regurgitation is not currently known, but it appears to be protective in the long term against sudden death and sustained ventricular arrhythmias What emerges from these studies is that a mechanoelectrical interaction in the right ventricle, namely ventricular dilation and stretch, may underlie ventricular electrical instability Such mechanisms have already been established for the left ventricle.58,59 Of particular interest is that a decrease in right ventricular volume, caused by a Valsalva maneuver, can terminate ventricular tachycardia in some patients.60 Electrophysiologic studies have indicated a reentry mechanism for sustained ventricular arrhythmias in this setting, which requires areas of slow conduction.61 Further support to the notion that inhomogeneity in depolarization and repolarization may form the substrate for malignant ventricular arrhythmias late after repair of TOF comes from the finding that, in patients with a duration of the QRS complex greater than 180 ms, there are increased dispersions of the QT, QRS, and JT intervals in those with but not those without episodes of ventricular tachycardia.62 Fragmented electrograms indicative of localized areas of slowed conduction, however, have also been recorded from the inflow region,63 the outflow tract,64 and throughout the right ventricle in the absence of sustained ventricular tachycardia.65 It could be, therefore, that the mechanisms for nonsustained and sustained ventricular arrhythmias are different This is an important consideration when we consider management of arrhythmias or disorders of conduction during follow-up It must also not be forgotten that atrial arrhythmias, albeit less dramatic in their effects, are equally as prevalent as ventricular arrhythmia in these patients and are a significant cause of late morbidity Treatment of Arrhythmias and Conduction Disturbances at Followup As discussed, attention to the hemodynamic factors that may enhance the risk of arrhythmia is clearly important and modification of residual lesions such as pulmonary valve replacement for chronic PI may be preventative, although data for this are still somewhat lacking Nonetheless patients are at continued risk of rhythm disturbance, and all require careful surveillance The aims of treatment are relief of symptoms and prevention of sudden death Nonsustained ventricular tachycardia is present in two-fifths or more of asymptomatic patients on followup, but the incidence of late sudden death is low and cannot be predicted from analysis of 24-hour tape recordings For this reason routine treatment of asymptomatic patients with nonsustained tachycardia is not currently indicated,50 but those with symptomatic ventricular arrhythmia require intervention Although some patients will be amenable to transcatheter ablation, many will require insertion of an implantable defibrillator if there is symptomatic ventricular arrhythmia or unexplained syncope The situation is much less clear in those with inducible ventricular arrhythmia; exact criteria for its primary prevention are not well established.66 In many, there will be associated severe pulmonary incompetence Therefore surgical repair or replacement of the pulmonary valve—often with coincident antiarrhythmic surgery and sometimes with insertion of an implantable defibrillator—will usually be performed Atrial arrhythmias usually respond to medical therapies in the first instance, but increasingly catheter-based ablation of pathways is performed and is more successful in the early to middle term Many will also fulfil criteria for surgery to the pulmonary valve, and an additional maze procedure may be indicated