Unexplained sinus bradycardia: clinical significance and long-term prognosis in apparently healthy persons older than 40 years.

The significance of sinus bradycardia (SB) in clinically healthy, non-endurance-trained, middle-aged and older persons is unknown. From 1,172 normal volunteers, aged 40 to 96 years, enrolled in the Baltimore Longitudinal Study of Aging, 47 subjects, aged 58 +/- 13 years, with SB (less than 50 beats/min) were identified by rest electrocardiography and were compared with a group of control subjects matched for age and sex. The prevalence of unexplained SB was approximately 4% and was nearly identical in men and women. At the latest follow-up examination, after a mean follow-up of 5.4 years, the SB group had a higher prevalence of associated conduction abnormalities (first-degree atrioventricular [AV] block, left-axis deviation, and complete or incomplete right bundle branch block) than the control group (43% vs 19%, p less than 0.05). On maximal treadmill exercise testing, performed in 44 patients within 1 visit of their most recent examination showing SB, maximal heart rate (157 +/- 18 beats/min) did not differ significantly from that of control subjects (163 +/- 19 beats/min); exercise duration, however, was greater in the former group, 11.0 +/- 2.8 vs 9.7 +/- 3.1 minutes (p less than 0.05). No patients with SB had syncope, high-degree AV block or other manifestation of sick sinus syndrome during follow-up. Angina pectoris, myocardial infarction, congestive heart failure or cardiac death occurred in 8% of patients with SB and 11% of control subjects over the observation period (difference not significant).(ABSTRACT TRUNCATED AT 250 WORDS)