Background: Low resting heart rate (HR) has been associated with atrial fibrillation (AF) in athletes. We aimed to study whether low HR at rest or during exercise testing was a predictor of AF in initially healthy middle-aged men.
Methods and results: A total of 2014 healthy Norwegian men participated in a prospective cardiovascular survey, including a standardized bicycle exercise test in 1972 to 1975. During ≤35 years of follow-up (53,000 person-years of observation), 270 men developed incident AF, documented by scrutiny of health charts in all Norwegian hospitals. Risk estimation was analyzed with Cox proportional hazard models. Low exercise HR after 6 minutes exercise on the moderate workload of 100 W (HR100W) was a predictor of incident AF. Men with HR100W <100 beats per minute (n=260) were characterized by high physical fitness, low resting and low maximum HR, and they had 1.60-fold AF risk (95% confidence interval, 1.11-2.26) compared with men with HR100W ≥100 beats per minute when adjusted for age, systolic blood pressure, and physical fitness. Additional adjustment for relative heart volume slightly reduced the association. The subgroup of men (n=860) with hypertensive blood pressure measurements at baseline had the highest risk difference between low and high HR100W with hazard ratio 2.08 (1.19-3.45).
Conclusions: Our data indicate that low exercise HR on a moderate workload is a long-term predictor of incident AF in healthy middle-aged men. Elevated baseline blood pressure substantially amplifies this risk. The present results suggest a relationship between increased vagal tone, high stroke volumes and incident AF, and particularly so in physically fit men.
Keywords: atrial fibrillation; epidemiology; exercise test; heart rate; men.