Role of heart rate in pathophysiology of chronic stable angina.

11 patients with chronic, stable, effort angina, off medication apart from glyceryl trinitrate, were monitored continuously by electrocardiogram (ECG) during normal, unrestricted daily activity. Computerised ECG analysis demonstrated during 33 twenty-four hour periods of monitoring, 278 episodes of transient ischaemic ST segment depression of which 52 were associated with angina. In the 15 minutes preceding the onset of ischaemia, heart rate did not increase in 164 episodes, increased slightly (greater than or equal to 5 beats/min) in 61, and increased moderately or markedly (greater than or equal to 10 beats/min) in 53. Findings were similar when episodes with or without angina or episodes of different severity were analysed separately. In all patients, periods of sinus tachycardia exceeding the control rate by more than 30 beats/min and lasting more than 10 minutes, often occurred in the absence of angina and/or ST segment depression. Also, in 65% of the ischaemic episodes, heart rate at the beginning of the ST change was either below or less than 10 beats/min above the modal value of the twenty-four hour heart rate. This suggests that increased myocardial demand is not necessarily the only or the most common cause of acute ischaemia in patients with chronic effort angina during unrestricted daily activity. Factors which only transiently interfere with myocardial oxygen supply are probably important in this syndrome.