Correlation of pathologic Q waves on the standard electrocardiogram and the epicardial electrogram of the human heart.

To evaluate the relationship between abnormal Q waves on the standard ECG and localized ventricular excitation, unipolar epicardial electrograms were recorded over the left ventricle during aortocoronary bypass surgery in 36 patients. Of 20 without standard ECG Q waves, six had abnormal epicardial Q waves, three anterioly and three inferiorly. Of 16 patients with standard ECG Q waves, four had both precordial and anterior epicardial Q waves while seven had Q waves in leads III and aVF and inferior epicardial Q waves. Three of the 14 had Q waves in both precordial and inferior leads of the ECG but epicardial Q waves only from the antero-apical region in two and only from the inferior wall in one. Two patients with Q waves in both III and aVF had no epicardial Q waves. Thus, the standard electocardiogram underestimates epicardial Q waves. If Q waves are present in the standard ECG, they correlate with the presence, although not invariably the location of Q waves on the epicardial electrogram.