Effort angina is the result of acute
myocardial ischemia on exercise due to an imbalance between myocardial
oxygen demand and supply. During exercise,
ischemia is provoked by an increase in myocardial
oxygen needs (
tachycardia, increased blood pressure, etc.) which cannot be met by increased coronary blood flow. The commonest cause of insufficient flow is
coronary atherosclerosis. Coronary
spasm does, however, play a role, whether it occurs during exercise on normal or atheromatous coronary vessels. Classical anti-anginal
therapy is directed towards a reduction in the intense
adrenergic activity associated with exercise, and to the limitation of myocardial oxygen consumption.
Calcium inhibitors which cause peripheral vasodilation, decrease ventricular wall tension and coronary resistance, are usually reserved for unstable or resistant angina. We studied 10 patients with stable effort angina for over 2 years with significant (greater than 70 per cent) atheromatous lesions on coronary angiography unsuitable for surgical treatment. The patients underwent a randomised double blind trial to compare the effects of
propranolol,
diltiazem and placebo. Exercise ECG was performed after a treatment period of one week, 3 hours after
drug administration. The results showed a significant improvement of work capacity with
propranolol and
diltiazem as compared to placebo.
Propranolol (160 mg/day) was more effective than
diltiazem (180 mg/day) in 6 patients. In 4 cases, the improvement with
diltiazem and
propranolol was the same. The association of the two drugs in one open study in 5 patients was even more effective in 3 patients. The small number of patients studied makes it impossible to draw any firm conclusions. Although
calcium inhibitors are the treatment of choice in coronary
spasm and betablockers in effort angina,
diltiazem exerts an anti-anginal effect by reduction of myocardial oxygen consumption without depression of myocardial contractility, as other workers have shown.