Increased mortality and shortened life span of heart rate at 80-99 beats/min: Assessing the benefits of physical activity from a prospective cohort of 515,303 individuals

[[abstract]]Introduction: Resting heart rate (HR), an independent risk factor for all-cause and cardiovascular disease (CVD), has not been universally recognized as an important CVD risk factor in healthy subjects. Heart rate at 80-99 beats/min has been implicated with increased CVD risk but no guideline exists as to how this risk can be modified. Objectives: The objectives of the study are two-folds: First is to quantify the mortality risks among those with heart rate in the range of 80-99 beats/min, including a subgroup free of CVD risks. Second is to assess the beneficial effect of exercise in moderate intensity among those with 80-99 beats/min, and to see to what extent physical activity could attenuate or reverse the increased risks of heart rate. Methods: The cohort, 515,303 healthy subjects, free of heart disease, came from a private health screening program between 1994 and 2008. Heart rate was determined by ECG reading. Individuals were classified by exercise volume (MET-Hour/Week) into inactive and active, which includes low active and fully active. A “CVD risk-free” sub-cohort was created, by excluding those with major CVD risks. Deaths, 16,849, were identified from national death file as of 2011. Results: For those with heart rate 80-99 beats/min, constituting one quarter of the cohort, had mortality risks increased by approximately 40% for all-cause and CVD mortality, in the total cohort and in the CVD risk-free sub-cohort. For every beat increase above 70 beats/min, life span was shortened by 4 months, or a loss of 3.3 years/10 beats. The 4-8 years loss from 80-99 beats/min was mitigated or eliminated, if being active, by gaining 5 years. Conclusion: Those with 80-99 beats/min had 40% increased mortality and shortened life span by 4-8 years. Each beat above 70 beats/min shortened life-span by 4 months, but regular physical activity substantially reduced or eliminated such risks. One quarter of the general population could benefit and extend life span by minimal amount of exercise in reducing this overlooked risk