The control of heart rate: the physiology of the sinoatrial node and the role of the I f current

A heart will beat approximately 25 ×10 8 times during the course of a human being's life. The observation that most mammals share the same number of heart beats per lifetime, be it a mouse (600 bpmfor 2 years) or a giant tortoise (6 bpmfor 200 years), has led people to suggest that if we slowed our heart rate we might live longer! While there may not be a causal relationship in fit healthy animals, there is an impressive literature accumulating suggesting that there is a clear and strong association between a lower heart rate and improved prognosis in a variety of diseases. It is, of course, in cardiovascular disease where the slowing of heart rate with specific bradycardic agents may offer the most advantage. The question as to whether I f inhibition can specifically improve morbidity and life expectancy in cardiovascular disease is one we only recently have had the tools to answer, and the introduction of ivabradine into the armamentarium offers a unique opportunity to address this question. We will know a lot more when the BEAUTIFUL trial (MorBidity-mortality EvAlUaTion of the If inhibitor ivabradine in patients with coronary disease and left ventricULar dysfunction) concludes in December 2007.