We conducted a prospective study in which 554 patients with chronic bifascicular and trifascicular conduction abnormalities were followed for an average of 42.4±8.5 months. Heart block occurred in 19 patients, and 17 were successfully treated. The actuarial five-year mortality from an event that could conceivably have been a bradyarrhythmia was 6 per cent (35 per cent from all causes). Of the 160 deaths, 67 (42 per cent) were sudden; most of these were not ascribable to bradyarrhythmia but to tachyarrhythmia and myocardial infarction. Mortality was higher in patients with coronary-artery disease (P<0.01) and congestive heart failure (P<0.05). Patients in whom syncope developed before or after entry into the study had a 17 per cent incidence of heart block (2 per cent in those without syncope)(P<0.05); however, no single variable was predictive of which patients were at high risk of death from a bradyarrhythmia. The predictors of death were increasing age, congestive heart failure, and coronary-artery disease; the predictors of sudden death were coronary-artery disease and increasing age. The risks of heart block and of death from a bradyarrhythmia are low; in most patients, heart block can be recognized and successfully treated with a pacemaker. (N Engl J Med. 1982; 307:137–43.) A PROSPECTIVE evaluation of the natural history of chronic bifascicular and trifascicular conduction abnormalities was initiated in December 1973 to determine the frequency of heart block, death, sudden death, and death due to bradyarrhythmias and to establish the value of clinical, electrocardiographic, and electrophysiologic indexes as prognostic indicators of these major clinical events. Our preliminary results have been presented previously.1 Methods The methodology of the study has been described in detail1 and has not been changed since the beginning of the project. In brief, all electrocardiograms obtained at the University of Oregon Medical School from December 1973 to December 1979.
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