Heart rate as a cardiovascular risk factor

Mounting evidence shows that elevated heart rate measured in resting conditions is associated with an increased risk of developing hypertension and atherosclerosis and that it is a potent predictor of cardiovascular morbidity and mortality. Several important epidemiological studies have shown that these relationships are present not only within general populations but also among hypertensive individuals, with important implications for the treatment of hypertension. The reason for the heart rate-mortality association is not well understood. Because of its co-aggregation with blood pressure, obesity, metabolic disturbances and lipid abnormalities, heart rate has been overlooked as a risk factor. However, in most studies the risk related to fast heart rate remained highly significant after controlling for other major risk factors for atherosclerosis, suggesting that heart rate plays a direct role in the induction of the risk. The strong association between tachycardia and sudden death found in the Chicago People Gas Company study, the Framingham heart study and the Cardiovascular Study in the Elderly points to the effects of sympathetic overactivity and decreased vagal tone in favouring the occurrence of life-threatening arrhythmias. Moreover, experimental studies in animals suggest that the haemodynamic disturbances related to high heart rate have a direct impact on the arterial wall, thus promoting the development of atherosclerotic plaques. Preliminary results from animal models and pooled data from intervention studies in post-myocardial infarction patients suggest that drug-induced reduction of heart rate may be beneficial in several clinical conditions.