We prospectively followed 257 patients with bifascicular and trifascicular conduction-system disease and intact atrioventricular conduction who had undergone His-bundle studies. Forty-seven per cent had associated coronary-artery disease, and 23 per cent primary conduction-system disease. His-ventricular interval was moderately prolonged in 43 per cent and markedly prolonged in 12 per cent. During an average follow-up period of 25 months 50 patients died. However, death was sudden in only 27, and 17 of the sudden deaths were not due to bradyarrhythmias. Actuarial analysis showed an overall mortality rate (mean ± S.E.) of 19±2.6 per cent at two years, mortality from sudden death being 10±2.6 per cent. Permanent heart block occurred in 12. No clinical symptoms (including syncope), electrocardiographic findings, electrophysiologic data or their combination identified patients at high risk of sudden death. Sudden death due to bradyarrhythmia is uncommon in patients with bundle-branch block and intact atrioventricular conduction. Therefore, routine prophylactic use of permanent pacemakers in all such patients is inappropriate. Pacemaker implantation should be reserved for those with documented symptomatic bradyarrhythmias. (N Engl J Med 299:209–215, 1978) PATIENTS with chronic bifascicular and trifascicular conduction-system disease in whom symptomatic bradyarrhythmias develop require permanent pacemakers. However, the management of “asymptomatic” patients with these conduction abnormalities is unclear because it is not known who or how many will acquire high-degree atrioventricular block with its associated symptoms and high mortality. There has been a concern for these patients for two reasons: the anatomic arrangement of the conduction system suggests that they are vulnerable to the development of complete heart block,1 2 3 4 5 and isolated observations and retrospective studies suggest that they might indeed be.6 7 8 9 10 11 12 13 14 15 16 Retrospective studies evaluating these patients have been of limited.
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