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

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 +/- 7.5 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 chi 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.