[Silent myocardial ischemia in patients after myocardial infarction]

Twenty-six men and women, aged 36-65 years, were studied 8-12 weeks after the first myocardial infarction with regard to silent ischemic ST-segment depression and heart rate by using 24-hour ambulatory electrocardiography and bicycle exercise testing. In 22 patients ambulatory ST-segment recordings revealed 81 episodes of ST-segment depression, including 34 (41.9%) painful and 47 (58.1%) painless episodes. Mean maximal ST-segment depression during symptomatic and asymptomatic episodes was 3.6 +/- 1.0 mm and 2.4 +/- 1.1 mm, respectively (p less than 0.02). Painless episodes most frequently occurred between 06.00 a.m. and 12.00 a.m. Ambulatory monitoring revealed a twofold increase in painful episodes at heart rate below 100 beats/min, whereas at heart rate above 125/min painless episodes were more frequent. Exercise testing showed a sevenfold increased incidence of ST-segment depression also at heart rate above 125 beats/min. In conclusion, silent myocardial ischemia is a frequent event in patients shortly after the first myocardial infarction, and painless episodes occur particularly frequently at high heart rates. Episodes of silent ischemia are found more frequently during ambulatory ECG monitoring than exercise testing. Studies on silent myocardial ischemia may be particularly relevant in the detection of the risk of myocardial infarction.