Comparison of epicardial and body surface ECG potentials in man

Simultaneously measured epicardial electrograms and body surface electrocardiograms in human subjects were compared. Unipolar electrograms were recorded from up to three epicardial sites in each of 21 patients one week after aortocoronary bypass surgery. Simultaneously, electrocardiograms were recorded from 37 body surface electrodes. The epicardial electrograms from ventricular sites correlated well during the QRS complex with body surface electrocardiograms at geometrically similar positions. In particular, most posterior epicardial sites correlated best with posterior body surface regions, contrary to model predictions. P waves recorded from the right atrial surface showed a sharp negative deflection not evident in body surface P waves. A large intersubject variation was evident when the magnitude of epicardial potentials was compared with the body surface potentials. The findings are relevant to the interpretation of surface maps, the estimation of epicardial potentials from surface maps, and the positioning of body surface electrodes.