Heart rate more than fitness marker
medwireNews: Long-term follow up of men in the Copenhagen Male Study has separated out the effects of resting heart rate and physical fitness on mortality risk.
The study, which appears in Heart, shows that a higher resting heart rate is associated with an increased risk for mortality, even after accounting for objectively measured physical fitness at baseline.
"This suggests that a high resting heart rate is not a mere marker of poor physical fitness but is an independent risk factor," say lead researcher Magnus Thorsten Jensen (Copenhagen University Hospital Gentofte, Denmark) and co-workers.
The 2798 men in the study were aged about 63 years at baseline, and 1082 died over the following 16 years. Resting heart rate, ascertained in 1985-86, was negatively associated with physical fitness, which was assessed using the Åstrand bicycle ergometer test in 1970-71.
This association has led to suggestions that the link between heart rate and mortality is mediated purely through physical fitness. However, in this study, heart rate remained predictive of mortality after accounting for fitness (maximal oxygen uptake) and other confounders including age. Specifically, compared with people with a resting heart rate of 50 beats per minute (bpm) or lower, those with a heart rate of 51-60 bpm had a significant 1.40-fold increase in mortality risk, and the risk continued to rise with higher resting heart rate, up to a 3.06-fold increase for those with a heart rate above 90 bpm.
When the researchers assessed heart rate as a continuous variable, they found that each 10 bpm increase was associated with a 16% rise in mortality risk, again independent of confounders including age and physical fitness.
Of note, there was a borderline significant (p=0.07) interaction with smoking status, such that the effects of higher heart rate on mortality risk were more pronounced in smokers. Each 10 bpm rise in heart rate was associated with a 20% increase in mortality risk in smokers and a 14% increase in nonsmokers.
Although the interaction did not quite attain significance, the researchers note that it supports findings from another cohort study. "Considering that the number of smokers globally is about 1 billion, this is yet another argument for preventive measures against tobacco consumption and might have therapeutic implications in terms of heart rate monitoring and perhaps modification in smokers," they conclude.
medwireNews (www.medwirenews.com) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2013
By Eleanor McDermid, Senior medwireNews Reporter