The pulse; from adagio to prestissimo; the prognostic importance of heart rate increase and its associations with cardiovascular risk factors

As in nature and music, dynamics are essential for life. However, chronotropic incompetence is an underappreciated condition, and is often overlooked in clinical practice. The reasons for this are numerous, including multiple definitions, confounding effects of aging and medications, and the need for formal exercise testing for definitive diagnosis. The popular definition of maximum pulse rate is the ability to reach 80% of age predicted maximal pulse rate: 220 – age, However, the dynamic phrase ‘heart rate reserve’ might be a more precise measure in that resting heart rate is also taken into account. Baseline heart rate is by itself a significant prognostic indicator. Resting heart rate above 90 beats/min has been shown to be associated with mortality from coronary heart disease. However, also, a resting heart rate that is currently considered as ‘normal’ in the general population has specifically been associated with the incidence of certain major cardiovascular diseases and death, with the risk starting at lower resting heart rate levels in men compared with women. Although most studies support the notion that augmented heart rate is an independent risk factor for cardiovascular mortality and morbidity, the link between sudden cardiac death and elevated heart rate is perhaps the most compelling. This is further underlined by The Norwegian Timolol Multicentre Study Group, which documented the effect of the beta-blocker Timolol on mortality and reinfarction after acute myocardial infarction, confirming the prognostic importance of pharmacological reduction of heart rate at rest in this population. The association between coronary artery disease (CAD) and sudden death in men has been shown to remain significant even after adjustment of multiple risk factors in a cohort in the Framingham study. Several mechanisms might thus be operable for the positive effects of beta-blockers, including reduction of ischaemia in patients with CAD and modulation of betareceptor density in heart failure. However, the consistently favourable effects of beta-blockade in patients with ischaemic heart disease emphasize the significance of sympathetic blockade with associated augmentation in vagal activity. The reduced heart rate has also been shown to be associated both with severity of coronary atherosclerosis in young patients after myocardial infarction and with rate of progression of atherosclerotic disease per se. Also in the general population changes in long-term individual resting heart rate may provide additional prognostic information. In the Tromsø Study surveys, among five long-term resting heart rate trajectories defined, increasing and elevated trajectories were associated with an increased risk of myocardial infarction and total death in men. The importance of increased baseline heart rate and its potential relationship to adverse cardiovascular events is further underlined in another cohort of the Framingham Heart Study, in which increased heart rates were associated with a prothrombotic state with significant age-adjusted increases in fibrinogen, viscosity, factor VII antigen and impaired fibrinolytic potential.