ACCURACY OF THE UNIPOLAR ELECTROGRAM FOR IDENTIFICATION OF THE SITE OF ORIGIN OF VENTRICULAR ACTIVATION

Introduction: The purpose of this study was to determine the accuracy of the unipolar electrogram for identifying the earliest site of ventr icular activation, The earliest site of ventricular activation may be identified with the unipolar electrogram by the absence of an R wave, However, the accuracy of this technique is unknown, Methods and Result s: A single ventricular premature complex was induced mechanically at the tip of an electrode catheter to simulate a ventricular premature d epolarization site of origin, Unipolar electrograms were recorded from the right ventricular septum at the tip electrode and at 2, 5, 8, and 11 mm from the electrode tip in 20 patients, No R waves were detected at the ventricular premature depolarization site of origin, R waves w ere detected in 4 of 20 patients (20%) at 2 mm from the tip electrode and 7 of 20 patients (35%) at 5, 8, and 11 mm from the tip electrode, An R wave was not observed at distances. 11 mm from the site of tachyc ardia origin in 13 of 20 patients (65%), Conclusions: While an R wave in the unipolar electrogram can be seen as close as 2 mm from the site of impulse origin, the absence of an R wave as an indicator of the si te of impulse origin in the right ventricle is highly inaccurate, Ther efore, the absence of an R wave in the unipolar electrogram is unlikel y to be an adequate guide for identification of an effective target si te for ablation of right ventricular tachycardia.