The morphology of unipolar potentials predicts the depth of activation foci

Background The depth of an arrhythmic focus is a major determinant of ablation procedural outcome. This study examined the relationship between the morphology of unipolar potentials and the depth and horizontal distance to activation foci. Methods Unipolar left ventricular epicardial mapping was performed in 7 open‐chest dogs, using silicon sheets with 12 unipolar electrodes 1 mm apart, during bipolar pacing from an octopolar plunge electrode with 1‐mm interelectrode spacing. The morphology of the unipolar electrograms was classified as QS, rS, qrS, qRS, rsr'S, or rsR'S. Results A QS complex was recorded immediately above a subepicardial or mid‐myocardial pacing site. An rS complex was recorded away from a subepicardial pacing site. A positive wave originating from a down sloping deflection (R‐in‐QR) such as r wave in qrS, R wave in qRS, r ′ wave in rsr'S or R′ wave in rsR'S complexes was observed when the recording was above a deep myocardial pacing site or away from a mid‐myocardial pacing site. The amplitude of negative wave immediately before R‐in‐QR (Q‐in‐QR) was inversely correlated with the horizontal ( R =−0.40; P <0.0001) and linear ( R =−0.22; P =0.0006) distance to the pacing site, and the amplitude of R‐in‐QR was positively correlated with the horizontal ( R =0.25; P =0.0001) and linear ( R =0.29; P <0.0001) distance to the pacing site. The amplitude of the initial r wave was not correlated with the depth or horizontal and linear distance to the pacing site. Conclusion The morphology of unipolar electrograms predicted the horizontal distance and the depth of nearby foci of activation.