Data from a long-term prospective study of healthy, middle-aged Norwegian men suggests that a low heart rate during moderate-intensity exercise is linked with future risk of AF.
"We found that the men who did not exceed 100 bpm at the end of six minutes of workload had a significantly increased AF risk," write Dr Irene Grundvold (Oslo University Hospital, Norway) and colleagues in the paper published July 21, 2013 inCirculation: Arrhythmia and Electrophysiology. In an analysis by tertile, those with heart rates <110 bpm after six minutes of moderate-intensity exercise had a significantly increased risk of AF compared with those with a heart rate >125 bpm.
There is evidence that individuals who participate in longstanding endurance training might have an increased risk of AF as they get older, according to the researchers. One other study of Norwegian master cross-country skiers found that a low resting heart rate was a long-term predictor of AF.
With this background, Grundvold et al wanted to determine if a low heart rate during moderate-intensity exercise predicted incident AF in healthy middle-aged Norwegian men. Slightly more than 2000 men participated in the prospective cardiovascular health survey between 1972 and 1975. All men were healthy and had no evidence of cardiovascular disease.
During a median of 30 years of follow-up, 13% of the men developed AF at a mean age of 71 years. In a multivariate analysis, age, resting systolic blood pressure, relative heart volume, left ventricular hypertrophy, and a low heart rate when engaged in moderate-intensity cycling on a stationary bike (100 W) were all predictors of AF. For those with a heart rate >100 bpm during exercise, the risk of AF decreased by 15% (hazard ratio 0.85; p=0.04) compared with those with lower heart rates.
"The present main results--an increased AF risk associated with low heart rate at moderate exercise in healthy men--might suggest involvement of an inappropriate heart rate response to exercise with prolonged parasympathetic activation," suggest Grundvold and colleagues. "Vagally mediated paroxysmal AF may be particularly important in athletic men without apparent heart disease."
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