Signs and implications of ischemia in unstable coronary artery disease
Sammanfattning: Signs and implications of ischemia in ECG at rest and at a predischarge exercise test (ET), were assessed in 911 patients with suspected or definite unstable coronary artery disease (CAD) - i.e. unstable angina or non-Q-wave myocardial infarction (MI). Included in the study were men below 70 years of age admitted to the coronary care units of 8 hospitals,without signs of myocardial dysfunction or other serious disease. Randomization to acetylsalicylic acid (ASA) 75 mg daily or placebo was performed in 796 patients, as a part of the RISC study. A symptom limited predischarge ET was performed by 855 patient,, In initial ECG:s at rest, ST-changes were a more unfavourable sign regarding cardiac eventsthan isolated T-inversion, while those with no ST-segment or T-wave changes had the best prognosis. However, among patients on ASA treatment, ST -depression in ECG at rest was of some, although limited prognostic value.Concerning the ET evaluation, multiple logistic regression analysis showed that exercise induced ST -depression and exercise tolerance were independent predictors of MI or death, while ST -depression, exercise tolerance and provoked chest pain were independent predictors of future severe angina. When both ST-depression and work capacity was considered, a 'high risk' response at ET implied a !-year rate for cardiac death of 3.6% and for Ml+death of 15.4%. The corresponding figures for a 'low risk' response were 0% and 3.9%. The differences between patients with 'high risk' and 'low risk' responses at the ET were highly significant also regarding future severe angina. The prognostic value of the ET remained high in subgroups based on cardiac enzyme levels, age, findings in ECG at rest, and medication at time for the ET.The risk of cardiac death or MI was comparably increased in all patients with ST-depression at exercise, regardless of the presence or absence of chest pain. Thus, evaluation of prognosis should be based on the presence of myocardial ischemia, whether symptomatic or not. ASA 75 mg daily reduced the risk of MI or death at least as well in patients with 'silent ischemia' as in those with 'symptomatic ischemia' at the ET, and should be a mainstay of the treatment of symptom-free individuals.Among patients on ASA treatment, the finding of ST-depression alone at exercise was an insufficient indicator of the irreversible end points, due to the reduced absolute risk of MI or death. When both ST -depression and exercise tolerance were used in the evaluation, it was possible to identify a definite low-risk subset (40% of the ASA group) with a !-year rate ofMI or death of 2.9%, where further invasive investigation does not seem warranted. In ASA treated patients, the 'high risk' response at the ET implied a risk of MI or death of 13.4% during the following year. In this relatively large subset additional prognostic tests would be useful. Until such methods arc readily available and evaluated, early coronary angiography and possible revascularization should be considered in patients with severe ischemia.
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