Assessment of early post-infarction ischemia: correlation between ambulatory electrocardiographic monitoring and
N C Chandra1, P Ouyang, R T Abell
1Division of Cardiology, Francis Scott Key Medical Center, Baltimore, Maryland 21224.
Insights
Ambulatory electrocardiographic monitoring (AECG) shows significant correlation with treadmill test (ETT) results for detecting ischemia after myocardial infarction (MI). However, AECG has low sensitivity, limiting its use in identifying early post-MI ischemia in certain patients.
Area of Science:
- Cardiology
- Diagnostic Imaging
- Clinical Electrophysiology
Background:
- Treadmill testing (ETT) is standard for identifying high-risk patients post-myocardial infarction (MI) based on demand-related ischemia.
- Ambulatory electrocardiographic monitoring (AECG) can predict outcomes in some patient groups, but its relation to post-MI ETT findings is unclear.
Purpose of the Study:
- To investigate the relationship between ST changes detected by AECG and ischemia identified by post-MI treadmill testing.
Main Methods:
- 52 post-MI patients underwent 24-hour AECG and Naughton treadmill testing.
- Patients with specific baseline ECG abnormalities or on digoxin were excluded.
- All tests were performed blindly and patients maintained consistent medication regimens.
Main Results:
- ETT was positive in 36% of patients; AECG detected ischemia in 27%.
- A significant correlation (p < 0.02) was found between AECG and ETT results.
- AECG demonstrated high specificity (85%) but low sensitivity (47%) for predicting a positive ETT.
Conclusions:
- AECG monitoring shows significant correlation with post-MI treadmill test results, particularly with high specificity.
- The low sensitivity of AECG suggests limited utility for identifying early post-MI ischemia in patients with baseline ST abnormalities or limited exercise capacity.
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.
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