Relation between ST-depression and chest pain in patients with coronary heart disease receiving no treatment and after beta-blockade and combined alpha-beta-blockade.

The bicycle exercise tolerance was studied in ten patients with angina pectoris after one week's treatment with an alpha-beta-blocker (labetalol 300 mg b.d.), alpha-beta-blocker (propranolol 80 mg b.d.) and placebo. The ST-segment of the ECG was continuously evaluated by on-line computerized averaging of complexes which greatly reduces noise and eliminate artefacts caused by varying baseline. Blood pressure was lowest with labetalol and heart rate lowest with labetalol and of heart rate during exercise was equally well depressed by both drugs. They also attenuated ST-depression at a given load but enhanced ST-depression for a given heart rate. At heart rate 100/min ST-depression was significantly greater with propranolol than with labetalol. It is concluded that provided ST-depression during treatment with B-blockers is correlated to myocardial ischemia in the same way as without such treatments used, other factors, e.g. an increase in cardiac size, will contribute more to the ischemia. labetalol may cause less increase in cardiac size than propranolol.