FIG 73.11 (A) ECG demonstrating preoperative sinus rhythm in a 7-yearold female with congenitally corrected transposition of the great arteries and hypoplastic left ventricle who underwent an extracardiac conduit Fontan with tricuspid valvuloplasty (B) Postoperative ECG of the same patient demonstrating high-grade AV block with junctional escape beats Note intermittently conducted P waves (red arrows) Bradyarrhythmia is more common after the atriopulmonary Fontan than the lateral tunnel or external cardiac conduit (Fig 73.12) Heart rate variability, a subtle marker of sinus node dysfunction, is reduced in lateral tunnel and external conduit Fontan in equal measure when compared with healthy controls.108 There is some suggestion that the external conduit may be associated with more sinus node dysfunction than the lateral tunnel,9,109 but this is not a consistent finding.106 Sinus node dysfunction may relate more to the nature of the prior superior vena cava pulmonary anastomosis (as well as native sinus node function) because that surgery is close to the sinus node and sinus node artery.109 Atrial pacing, which usually must be epicardial and may require extensive thoracic surgery to be achieved, is generally reserved for those with symptomatic chronotropic incompetence Depending on the anatomy, it may be feasible to place transvenous atrial leads; however, it is not unusual to have to place leads in nonstandard positions because areas of viable myocardial tissue can be limited (Fig 73.13) FIG 73.12 Sinus bradycardia and junctional rhythm in an asymptomatic 33-year-old male with an atriopulmonary Fontan FIG 73.13 Chest radiography of a 53-year-old female with tricuspid atresia who underwent a modified Fontan with right atrium (RA) to right ventricle (RV) valved conduit and required transvenous atrial pacing Note the low position of the atrial lead It is not unusual to have to place leads in uncommon positions in the Fontan population since areas of viable myocardial tissue can be limited A Melody valve has been placed in the RA to RV conduit Ventricular pacing should be avoided or minimized as far as possible because of the risk of causing ventricular dyssynchrony and pacemaker-induced cardiomyopathy, cardiac failure, and atrioventricular valve regurgitation.109 Fontan patients with ventricular pacing have a fivefold risk of transplant or death compared with matched nonpaced controls.110 The value of cardiac resynchronization therapy is being explored; results are generally disappointing, but there may be a place in specific cases such as postpacing cardiomyopathy or when there is a systemic left ventricle and left bundle branch block (Fig 73.14)