INTRODUCTION AND PURPOSES: The purpose of this study was to check the beneficial effect of isosorbide-5-mononitrate (IS-5-MN) in patients with myocardial postinfarction silent ischemia, and to evaluate the possible appearance of tolerance after prolonged treatment.
Methods: We have studied 20 patients, all males, with a history of infarction (11 with inferoposterior infarction and 9 with anterior infarction) and having a positive effort test by electrocardiographic criteria (ischemic S-T depression > 1 mm). The study was designed in two parts, first crossover with placebo, double-blind and then open during 100 days; until day 20, 40 mg/12 hours of IS-5-MN were administered and from then on 40 mg/8 hours of the drug. Effort tests were carried on days, 1, 20, 34 and 100, first basal ones and then at 3 and 6 hours after the administration of the medication.
Results: The time of S-T segment depression was prolonged in relation to the tests carried out with placebo and to its basal values (Placebo-basal: 235 +/- 97, Placebo-3 hours: 196 +/- 92, Placebo-6 hours: 201 +/- 80, day 1-basal: 197 +/- 84, day 1-3 hours: 420-96, day 1-6 hours: 381 +/- 93, day 20-basal: 221 +/- 81, day 20-3 hours: 384 +/- 121, day 20-6 hours: 389 +/- 112, day 34-basal: 272 +/- 91, day 34-3 hours: 437 +/- 102, day 34-6 hours: 362 +/- 100, day 100-basal: 269 +/- 102, day 100-3 hours: 389 +/- 112, day 100-6 hours 369 +/- 111). The duration of the effort was prolonged in relation to the placebo values (Placebo-basal: 480 +/- 100, Placebo-3 hours: 445 +/- 73, Placebo-6 hours: 430 +/- 79, day 1-basal: 450 +/- 95, day 1-3 hours: 510 +/- 79, day 1-6 hours: 532 +/- 86, day 20-basal: 524 +/- 93, day 20-3 hours: 535 +/- 77, day 20-6 hours: 519 +/- 77, day 34-basal: 517 +/- 85, day 34-3 hours: 567 +/- 87, day 34-6 hours: 558 +/- 94, day 100-basal: 520 +/- 89, day 100-3 hours: 593 +/- 91, day 100-6 hours: 590 +/- 92). This effect lasted throughout the 100 days of the study.
Conclusions: Therefore, in patients with silent ischemia after myocardial infarction, the administration of 40 mg/12 hours as well as of 40 mg/8 hours of IS-5-MN shows an obvious anti-ischemic effect; with long-term treatment, the effect persists without evidence of tolerance phenomenon.