Validation of a real-time electrocardiographic monitor for detection of myocardial ischemia secondary to coronary artery disease

Abstract

A new real-time electrocardiographic (ECG) monitor (QMED Monitor One^TM) was evaluated to assess its accuracy in detecting ischemic ST-segment changes in 43 patients (34 men, 9 women, mean age 56 ± 11 years) during exercise stress testing. The output of QMED was compared with ST-segment measurements from a Marquette CASE-II computer (ECGM) using a bipolar lead CM₅, defining a positive ECG as at least 1 mm of planar or downsloping ST depression. Results were concordant in 33 patients, 15 with both positive and 18 both negative responses, yielding an accuracy (expressed as sensitivity, specificity, positive and negative predictive accuracy) of 83%, 72%, 68% and 86%, respectively. Seven false-positive QMED episodes occurred: 4 due to excess baseline wander or noise in the control ECG, which may have been prevented by reapplication of electrodes, and all 7 episodes were correctly discounted by inspection of the sample ischemic ECG output, yielding an accuracy of 81%, 100%, 100% and 85%. Mean duration and maximal magnitude of ST depression in patients with a positive ECG response was 7.9 ± 7 minutes and 1.7 ± 0.6 mm for QMED and 8.9 ± 7 minutes and 2.2 ± 0.7 mm for ECGM. The 3 false-negative QMED events were relatively brief and mild ischemic episodes and slight differences in electrode placement between the 2 systems may account for this discrepancy in 2 of the patients. Real-time ST monitoring with QMED is sufficiently reliable for clinical use. Optimal specificity depends on the ability to inspect sample ECG traces to verify a stable baseline and confirm episodes of ischemic ST-segment shift.