The physiological determinants and risk correlations of elevated heart rate.

A number of studies have shown that fast heart rate is associated with high blood pressure and metabolic disturbances, and that it is a strong precursor of hypertension, atherosclerosis, and cardiovascular events. Subjects with tachycardia often also exhibit increased plasma insulin, overweight, and higher hematocrit. These relationships have been observed also in the elderly and among hypertensive individuals and have held true after controlling for smoking, alcohol intake, and physical activity habits. In three different populations studied with a mixture analysis we demonstrated that the heart rate-blood pressure association was mostly explained by a subpopulation of subjects with high heart rates who had higher levels of blood pressure, total cholesterol, triglycerides, postload glucose, and plasma insulin. The clustering of these risk factors may explain why cardiovascular morbidity is higher in individuals with fast heart rates. Sympathetic overactivity seems to be responsible for both the increase in heart rate and blood pressure, and for the metabolic abnormalities. In addition to being a marker of sympathetic overactivity, tachycardia seems to have a direct action in the induction of risk. Studies in cholesterol-fed monkeys have shown that the reduction of heart rate could retard the development of coronary atherosclerosis. Furthermore, fast heart rate increases the pulsatile nature of the arterial blood flow and increases arterial wall stress. Antihypertensive drugs that lower the heart rate seem to have a good potential for prolonging life expectancy in humans.