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Kusumoto et al 2018 Bradycardia Clinical Practice Guidelines

August 20, 2019 Circulation. 2019;140:e382–e482. DOI: 10.1161/CIR.0000000000000628 e428

CLINICAL STATEMENTS AND GUIDELINES indicated. However, unlike SND, infranodal atrioventricular block regardless of the presence or absence of symptoms warrants a pacemaker because the patient could suffer from sudden onset complete atrioventricular block resulting in syncope and subsequent harm (Figure 7).

Recommendation-Specific Supportive Text

1.	 Older observational studies have documented the natural history of untreated patients with seconddegree Mobitz type II and third-degree atrioventricular block, and they demonstrated that these patients have recurrent symptoms including syncope and heart failure.S6.4.4-1,S6.4.4-4 There are also observational studies that have demonstrated a mortality benefit with pacing therapy. One study from the 1970s showed that despite having other cardiac comorbidities such as prior MI and heart failure, there was an improvement in survival compared with similar patients who did not receive a pacemaker.S6.4.4-6 A 5-year survival benefit was also shown in a study from the 1980s evaluating patients with second-degree Mobitz type II and 2:1 atrioventricular block. Importantly, in patients with high-grade atrioventricular block, although those with symptoms had a worse prognosis than those without symptoms, the prognosis was poor overall for both groups if left untreated.S6.4.4-3,S6.4.4-5 2.	 Patients with certain neuromuscular disorders such as one of the muscular dystrophies or Kearns-Sayre syndrome often develop cardiac involvement; those with certain myotonic dystrophies such as myotonic dystrophy type 1, Emery-Dreifuss, and limb-girdle type 1B have a high incidence of conduction abnormalities.S6.4.4-10 Up to 20% of patients with myotonic dystrophy type 1 have evidence of atrioventricular block on their ECG or intermittent second-degree or third-degree atrioventricular block on 24-hour ambulatory electrocardiographic monitoring.S6.4.4-

9,S6.4.4-12 More than 50% of patients with a normal ECG may have evidence of infra-Hisian block at EPS demonstrating the clinical use of the EPS in these patients. One study found that 46.7% of patients with an HV interval ≥70 ms developed high-grade atrioventricular block.S6.4.4-14 Although there are no randomized trials assessing whether pacing reduces sudden cardiac death or all-cause mortality, a large retrospective study showed a 75% lower risk of sudden death in those with a pacemaker.S6.4.4-15 Some of the patients will have concomitant ventricular arrhythmias or systolic dysfunction requiring implantable cardioverter defibrillator (ICD) therapy in addition to pacing support.S6.4.4-8,S6.4.4-11 Serial ECGs in these patients can be performed in follow-up to assess for development of conduction abnormalities.S6.4.4-13

3.	 Diagnosing atrioventricular block in the setting of AF can be less straightforward than evaluating patients in sinus rhythm. Atrioventricular block should be suspected if a slow regular ventricular response is observed, and a wide QRS might indicate the presence of infranodal block. Retrospective studies using ambulatory electrocardiographic monitoring have had conflicting results; in 1 study, pauses >3 seconds even when they occurred in the setting of AF, were mostly asymptomatic, while in the other 2 studies, most pauses >3 seconds were symptomatic. All 3 of these studies had a mix of patients with AF and sinus rhythm and subgroup analyses were not done.S6.4.4-2,S6.4.4-16,S6.4.4-17 If the pauses are causing symptoms or if the pauses are attributable to infranodal block, the recommendation is similar to patients who are in normal sinus rhythm. In the asymptomatic patient, there is no specific pause duration that warrants permanent pacing. 4.	 Beta blockers have been recommended as guideline-directed medical therapy for heart failure and after MI.S6.4.4-18,S6.4.4-19 Atrioventricular block was usually an exclusion criterion for large trials that demonstrated the benefit of beta blockers in these patient populations.S6.4.4-20–S6.4.4-22 Atrioventricular block can develop secondary to drugs such as amiodarone or sotalol that may be important for the management of AF. The benefit of any medication that exacerbates atrioventricular block must be balanced with potentially deleterious effects of right ventricular pacing.S6.4.4-23,S6.4.4-24 5.	 Cardiac sarcoidosis is an infiltrative cardiomyopathy that is known to predispose patients to both bradycardia and tachyarrhythmias. Systemic corticosteroids have been shown in small case studies to resolve atrioventricular block in some patients although the response rate has been reported to be in the 30% to 60% range.S6.4.4-25,S6.4.4-27,S6.4.4-29 In 1 study of 30 patients with cardiac sarcoid, 5 had atrioventricular block and 2 of the 3 patients who received corticosteroids within 30 days of the initial diagnosis had complete resolution of atrioventricular block, while both of the 2 patients who received corticosteroids >30 days of the initial diagnosis had persistent atrioventricular block.S6.4.4-38 However, even if atrioventricular block resolves, the recurrence rate of atrioventricular block and future risk of ventricular arrhythmias remains unclear.S6.4.4-39 In patients with type I AL cardiac amyloidosis, there appears to be a high incidence of bradycardia and atrioventricular block. One small study showed that all 25 patients

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