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is strong consensus that patients with third- or second-degree AVB (Mobitz type II) must receive permanent cardiac pacing therapy if symptomatic or with risk factors. In asymptomatic patients without risk factors, opinion on the benefit of cardiac pacing diverges, and permanent pacing may be considered.567,569

8.4.3 Post-operative atrioventricular block Post-operative high-degree AVB is estimated to occur in 13% of patients undergoing surgery for CHD.518,569,570 In children, transient early post-operative AVB usually resolves within 710 days.571 In adults with CHD, there are no data to support a different waiting period before deciding for permanent pacing post-operatively than after other cardiac surgery. After recovery from complete AVB, bifascicular block occasionally persists, which is associated with an increased risk of late recurrent AVB and sudden death.572 The prognosis is poor for patients with untreated post-operative complete AVB.573

8.4.3.1 Indications for pacemaker implantation There is a strong recommendation for permanent pacing in patients with persistent second- or third-degree AVB. In patients with persistent bifascicular block associated with transient AVB or permanent prolonged PR interval, consensus for pacemaker implantation is modest. Post-operative HV interval determination may help to estimate the risk in patients with prolonged PR or bifascicular block.573 In patients with bifascicular block and long PR after surgery for CHD, the risk of extensive damage to the conduction system is high,572 therefore pacemaker implantation may be indicated even without HV measurement. Implantation of epicardial leads should be considered during surgery in patients with complex CHD and a high lifetime risk of pacemaker implantation, in order to reduce the rate of reoperation. 8.4.4 Cardiac resynchronization Standard indications for CRT may be considered in CHD, taking into account that the anatomy, morphology of the systemic ventricle, and cause of dyssynchrony, as well as QRS morphology, may be atypical.574 Multidisciplinary teams in experienced centres should be involved in the decision-making process.

8.5 Pacing in hypertrophic

cardiomyopathy 8.5.1 Bradyarrhythmia AVB in hypertrophic cardiomyopathy (HCM) should generally be treated according to the recommendations in this guideline (see section 5.2). Certain genetically inherited subtypes of HCM are more prone to develop AVB, as is the case with transthyretin amyloidosis, AndersonFabry and Danon diseases, PRKAG2 syndrome, and mitochondrial cytopathies.575,576 An ICD/CRT-D rather than a pacemaker should be considered in patients with symptomatic bradycardia who have LVEF <_35% or otherwise fulfil the criteria for primary prevention of SCD by current guidelines.576 (For extended literature on conduction disorders in HCM see the Supplementary data, section 8.5.)

8.5.2 Pacing for the management of left ventricular outflow tract obstruction In patients with symptoms caused by LV outflow tract obstruction, treatment options include drugs, surgery, septal alcohol ablation, and AV sequential pacing with a short AV delay. Three small, randomized, placebo-controlled studies and several long-term observational studies reported reductions in LV outflow tract gradients, and variable improvement in symptoms and quality of life with AV sequential pacing.577582 Myectomy achieved superior haemodynamic results compared with DDD pacing,583 but is a more invasive and higher risk intervention. In one trial, a subgroup analysis suggested that older patients (>65 years) are more likely to benefit from DDD AV sequential pacing.579 A recent meta-analysis—comprising 34 studies and 1135 patients—found that pacing reduced the LV outflow gradient by 35%, with a non-significant trend towards reduction in NYHA class.584 Shared decision-making should be employed when considering the treatment of choice for patients with obstructive HCM.

Recommendations for cardiac pacing in patients with congenital heart disease

Recommendations Classa Levelb

In patients with congenital complete or highdegree AVB, pacing is recommended if one of the following risk factors is present: a. Symptoms b. Pauses >3 the cycle length of the ventricu-

lar escape rhythm c. Broad QRS escape rhythm d. Prolonged QT interval e. Complex ventricular ectopy f. Mean daytime heart rate <50 b.p.m. I C In patients with congenital complete or highdegree AVB, permanent pacing may be considered even if no risk factors are present.566 IIb C

Continued In patients with persistent post-operative bifas-

cicular block associated with transient complete AVB, permanent pacing may be considered.572 IIb C In patients with complex CHD and asymptomatic bradycardia (awake resting heart rate <40 b.p.m. or pauses >3 s), permanent pacing may be considered on an individual basis. IIb C

AVB = atrioventricular block; BBB = bundle branch block; b.p.m. = beats per minute; CHD = congenital heart disease; ECG = electrocardiogram. aClass of recommendation. bLevel of evidence. ESC 2021

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