A utoregulation is an important physiological mechanism whereby blood flow to an organ is kept relatively constant as perfusing pressure changes. For all organs except the heart, autoregulation can be examined by changing aortic pressure and measuring the resulting organ flow. In the left ventricle, however, changing aortic pressure alters myocardial oxygen consumption, which itself alters myoc...

The last two decades have witnessed the recognition of a significant relationship between the autonomic nervous system and cardiovascular mortality, including sudden cardiac death. Experimental evidence for an association between a propensity for lethal arrhythmias and signs of either increased sympathetic or reduced vagal activity has encouraged the development of quantitative markers of auton...

A key challenge in reducing the burden of cardiovascular disease is matching patients to treatments that are most appropriate for them. Different cardiac assessment tools have been developed to address this goal. Recent research has focused on heart rate motifs, i.e., short-term heart rate sequences that are overor under-represented in long-term electrocardiogram (ECG) recordings of patients ex...

In 1981 a study on heart rate variability (HRV) and on the neural control of the heart was published in Science. Since then, the number of papers concerning this topic has increased exponentially. Some aspects of the relationship between HRV and the neural control of the cardiovascular system are now clear, for example: a decreased SDNN (a measure of variance) during a period of 24 hours is a w...

THE RHYTHM OF THE HEART has not only fascinated cardiologists but also inspired poets and musicians. Indeed, the periodic beat of the heart was used to define the speed of music. In music notation, the traditional Italian term “moderato” originally referred to one beat of the measure per walking pace (76–80 paces/min) or heartbeat ( 72 beats/min). The use of the heartbeat to define the speed of...

II, V1 and V,, was determined during atrial pacing at 90 beats/min and 130 beats/min before and after i.v. administration of propranolol, 0.1 mg/kg, and atropine, 0.02 mg/kg. Significant reductions (p < 0.01) of QT were induced by the paced increases in heart rate before drugs (10%), after propranolol (10%) and after the combination of atropine and propranolol (9%). Propranolol caused no signif...