Diurnal variation in ischemic threshold and nitrate efficacy in patients with stable angina pectoris

Diurnal variation in exercise-induced ischemic threshold expressed by the rate-pressure product at 1 mm ST segment depression and time to moderate angina were evaluated in 141 patients with stable angina pectoris in a randomized double-blind study. The diurnal variation in the efficacy of 10 and 20 mg of isosorbide-5-mononitrate was also evaluated. Two ischemic peaks were found at 10 a.m. and 10 p.m. in the placebo group by both ischemic threshold and time to anginal pain. Nitrate efficacy was greater in the morning in all treatment groups and this effect was eliminated in the β-blocker group. Activation of the sympathetic nervous system in the morning is suggested as a possible explanation.