The signal-averaged electrocardiogram in predicting coronary artery disease

Lack of impact of myocardial ischemia on the signal-averaged ECG assessment by time-domain analysis

BACKGROUND

Late potentials represent an arrhythmogenic substrate in chronically infarcted myocardium. It is hypothesized that acute transient ischemia enhances anisotropic electrical ventricular activation and facilitates reentry mechanisms. Study aim was the prospective assessment of the impact of dipyridamole-induced myocardial ischemia on the signal-averaged ECG.

METHODS

Dipyridamole stress thallium-201 SPECT imaging was utilized to avoid noise contamination of the signal-averaged ECG from exercise and to document evidence and localization of myocardial ischemia or persistent perfusion defects in 68 patients with suspected coronary artery disease. Before and during dipyridamole-induced vasodilatation serial signal-averaged ECG was performed to evaluate the influence of transient ischemia on the occurrence of late potentials.

RESULTS

There was a significant difference between heart rate at rest and heart rate under dipyridamole influence in patients with inducible ischemia (70 +/- 13 vs. 87 +/- 13; P < 0.0001) in contrast to patients without dipyridamole-induced ischemia (74 +/- 20 vs. 80 +/- 16; n.s.). The number of averaged beats and achieved noise level was comparable between both groups. Thirty-three of 68 patients (49%) revealed dipyridamole-induced ischemia; however, no changes of the SAECG parameters, such as QRS, RMS, LAS at 25-250 and 40-250 Hz bandpass filtering in the leads X, Y, Z and vector magnitude, respectively, were observed as a result of ischemia.

CONCLUSION

These results suggest that transient myocardial ischemia does not affect the signal-averaged ECG. Clinically, the signal-averaged ECG analysis seems not to be helpful in identifying patients with silent ischemia.

Relation between the initial portion of the signal-averaged QRS complex and cardiac function and infarct size in patients with myocardial infarction

We analyzed signal-averaged electrocardiograms (ECG) obtained in 50 patients with recent myocardial infarction (RMI: 25 anterior and 25 inferior) and 20 normal subjects to determine the relationship between the initial portion of the signal-averaged QRS complex and cardiac function and infarct size. We examined (1) the root mean square voltage (RMS10-40, microV), (2) the integration (A10-40, microV.msec) at 10-msec intervals over the first 40 msec of the signal-averaged QRS complex, and (3) the intervals (T) of the magnitude of the signal-averaged ECG achieved at 10-microV intervals over the first 40 microV (T10-40, msec). The mean RMS10-40 (p < 0.01) and A10-40 (A10, p < 0.05; A20-40, p < 0.01) were significantly lower and the T10-40 (p < 0.01) was significantly longer in RMI patients than in normal subjects. The RMS10-40 (p < 0.01) and A10-40 (p < 0.05) were significantly lower and the T10-40 (T10.20, p < 0.01; T30.40, p < 0.05) was significantly longer in patients with anterior RMI patients than in patients with inferior RMI. The A30 was correlated with the ejection fraction and total creatine kinase (CK) release in all patients (r = 0.73, and -0.78, respectively, p < 0.001). These results suggest that the A30 may be an important predictor of ventricular dysfunction and infarct size in patients with RMI.

Ambulatory (Holter) electrocardiography signal-averaging: a current perspective

Signal-averaging is an emerging new application of the ambulatory ECG. Whereas real-time signal-averaging of the high-resolution ECG has led to the measurement of abnormal QRS complex parameters and to the detection of ventricular late potentials in patients with a history of ventricular tachycardia or fibrillation at increased risk of an arrhythmic event, similar measurements can also be derived from ambulatory ECG tape recordings. This review describes the technical differences between real-time and ambulatory high-resolution ECG signal-averaging, and the early clinical studies that correlated measured QRS complex parameters and defined the agreement of late potential detection with the two technologies. Although there appears to be a promising cost-effective benefit from ambulatory ECG signal-averaging, limitations imposed by the technical differences must be recognized, and additional investigation is needed to define the appropriate clinical use and criteria for best diagnostic and prognostic value.