average heart rate below 50 beats/min, abrupt pauses in the ventricular rate that are two to three times the basic sinus cycle length, or cases associated with symptoms due to chronotropic incompetence Sinus bradycardia with complex congenital heart disease and a resting heart below 40 beats/min or ventricular pauses exceeding 3 seconds Congenital heart disease and impaired hemodynamics as a result of sinus bradycardia or loss AV synchrony Unexplained syncope in a patient with prior congenital heart surgery complicated by transient compete AV block with residual fascicular bock after a careful evaluation to exclude other causes of syncope Class IIB (weight of evidence/opinion is less well established): Transient third-degree AV block that reverts back to sinus rhythm with residual bifascicular block Congenital third-degree AV block in children or adolescents with an acceptable rate, narrow QRS complex, and normal ventricular function Asymptomatic sinus bradycardia after biventricular repair of congenital heart disease with a resting heart rate less than 40 V or pauses in the ventricular rate exceeding 3 seconds Class III (there is evidence or general agreement that pacing is not useful/effective and in some cases may be harmful): Transient third-degree AV block with return of normal AV conduction in an otherwise asymptomatic patient Asymptomatic bifascicular block with or without first-degree AV block in the absence of prior transient third-degree AV block after surgery for congenital heart disease in the absence of prior transient complete AV block Asymptomatic type I second-degree AV block Asymptomatic sinus bradycardia with the longest relative risk interval less than 3 seconds and minimum heart rate more than 40 beats/min Pacing for Bradycardia-Tachycardia Syndrome Sinus bradycardia alternating with AF/flutter, IART, or sinus node reentry tachycardia is a common problem following surgery for congenital heart disease Most of these postoperative tachycardias are reentrant and thus uniquely susceptible to overdrive pacing.183 Typical anatomic substrates that are prone to tachy-brady arrhythmias include those of patients following atrial switch procedure, Fontan, and extensive atrial surgery.184 Recent recommendations support permanent pacing (class IIA) for ACHD and sinus or junctional bradycardia for the purpose of preventing recurrent IART.44 Recent recommendations by the Pediatric and Congenital Electrophysiology Society further recommend use of a device with atrial antitachycardia capability.44 Antiarrhythmic drug therapy—along with other strategies that include catheter ablation or surgical revision with creation of lines of block to prevent intraatrial reentry tachycardia circuits—should also be considered within the armamentarium of managing complex adult congenital heart disease.44 Pacing for Syncope and Breath-Holding Spells The use of DDD pacing for adult patients with recurrent neurally mediated syncope and prolonged pauses may be reasonable, especially in those with minimal or no prodrome.40 For such patients, pacing may increase the time from the onset of symptoms or to the loss of consciousness However, the use of pacemakers in children and adolescents is controversial, since there is a considerable placebo effect The use of pacing in this situation is extremely rare and case reports have acknowledged the use of pacing in those with extreme pauses For the rare child with pallid breath-holding spells, cardiac pacing may be considered.38,40 Patients undergoing pacemaker implantation in this subcohort tend to eventually outgrow the proclivity for permanent pacing; often some level of reassurance can be provided to the parents Pacing for Long-QT Syndrome A subset of patients with LQTS fail to respond to β-blockers or LCSD; as a result they have ongoing symptoms and/or periods of TdP Antibradycardia pacing with a moderately high baseline heart rate (80 to 90 beats/min) has been used as an adjunct to β-blockers in LQTS.185 The rationale is that an increased heart rate shortens the QT together while also minimizing pause-related QT prolongation Although the sole use of antibradycardia pacing has diminished somewhat with the advent of the ICDs, there remains a role for pacing Some high-risk neonates with a very long QT interval may have functional 2 : 1 block and thus may benefit from pacing This group of patients is at high risk, but a multimodal treatment regimen of pacing, β-blockers, and LCSD may be helpful Recent data suggest that these high-risk patients may have a better than expected outcome if such a strategy is deployed.133 Isolated secondary AV block may be seen in utero and should raise suspicion for a LQTS.128 Proven pause-dependent initiation of ventricular arrhythmias with or without LQTS is a class I indication Pacing may also be of some benefit in patients with LQT3 with significant sinus bradycardia The increasing use of ICDs in high-risk LQTS patients is of proven benefit and is likely to be safer than pacing alone, despite the potential problem of T-wave oversensing and defibrillator shocks causing adrenergic surges and electrical storm The quality of life in children (8 to 18 years of age) with cardiac implantable electronic devices as perceived by the children and their parents is similar to that of children with severe congenital heart disease As always, the decision to implant a device, pacemaker or defibrillator, should be individualized and both the acute and long-term issues with the device must be carefully and thoroughly discussed with the patient and his or her family Pacing for Hypertrophic Cardiomyopathy Dual-chamber pacing can theoretically diminish the LV outflow obstruction in hypertrophic cardiomyopathy by changing the activation sequence of the ventricular myocardium In patients with hypertrophic cardiomyopathy, typically the AV node conduction is intact and a short-programmed AV interval is required to alter the activation sequence The response to pacing is variable, and although this technology seems reasonable to alter the physiology, the results have largely not demonstrated a benefit ... support permanent pacing (class IIA) for ACHD and sinus or junctional bradycardia for the purpose of preventing recurrent IART.44 Recent recommendations by the Pediatric and Congenital Electrophysiology Society further recommend use of a device with atrial antitachycardia capability.44