Assessment of early post-infarction ischemia: Correlation between ambulatory electrocardiographic monitoring and exercise treadmill testing

Abstract

purpose: Demand-related myocardial ischemia detected by treadmill testing is commonly used to identify high-risk patients after myocardial infarction (MI). Although ischemia detected by ambulatory electrocardiographic monitoring (AECG) has also been shown to predict poor outcome in some patient groups, the relationship between AECG-detected ischemic ST changes and post-MI treadmill ischemia is unknown. patients and methods: We screened 94 patients after MI with 24-hour AECG monitoring and a Naughton treadmill test. Forty-two patients were excluded because of left bundle branch block, left ventricular hypertrophy, abnormal baseline ST segments, or digoxin therapy. In the remaining 52 patients, AECG was performed 5.1 ± 2.2 days after MI (mean ± SD) and the treadmill test 8.4 ± 2.2 days after MI. Each patient was taking the same drugs for both studies, had no interim revascularization procedures, and all studies were interpreted blindly. results: The treadmill test (ETT) was positive for ST changes and/or thallium reperfusion defects in 19 of 52 patients (36%). The AECG was positive for ischemia (ST depression greater than 1 mm, for more than 1 minute) in 14 of 52 patients (27%) (Group I), with 9.9 ± 8.2 ischemic episodes per patient lasting 13.5 ± 7.4 minutes per episode. The AECG was negative for ischemia in the remaining 38 patients (73%) (Group II). The ETT and AECG correlation was as follows: 9 patients with AECG-detected ischemic ST changes had positive ETT results; 10 patients without AECG-detected ischemic ST changes had positive ETT results; 5 patients with AECG-detected ischemic ST changes had negative ETT results; and 28 patients without AECG-detected ischemic ST changes had negative ETT results (p <0.02 by χ 2). The predictive accuracy of a positive AECG identifying a positive ETT was 65% (specificity 85%, sensitivity 47%), and the predictive accuracy of a negative AECG identifying a negative ETT was 74%. Group I patients were older than Group II patients (63.6 ± 8.2 years versus 53.2 ± 10.6 years p <0.02), more commonly had painless ETT ischemia (43% versus 18% p = 0.08), and tended to have positive ETT results at a lower level of exercise (366 ± 210 seconds versus 588 ± 212 seconds, p = 0.04). conclusion: Ischemic ST changes as detected by AECG monitoring correlate significantly with post-MI treadmill test results with a high specificity, albeit a low sensitivity. In patients without baseline ST-segment abnormalities and limited exercise capability, AECG monitoring may be of limited use in identifying early post-MI ischemia.