Noninvasive recording of the His bundle electrogram: value of supplementary verapamil.

We obtained noninvasive recordings of the His bundle electrogram using the Marquette high resolution MAC unit in 65 patients and 5 normal subjects. Overlap of atrial activity prevented identification of a His potential in 25 subjects, in 23 of whom the PR interval was equal to or less than 160 ms. After intravenous verapamil (10 mg) the AH interval was lengthened, with an increase in the PR interval of 10-60 (mean 20) ms. A characteristic His bundle electrogram was recorded in 48 of the 70; in 8 there was persistent atrial activity and in 4 electrical interference could have obscured a His potential. In 10 patients the absence of a His complex despite a clear "window" of at least 70 ms between the end of atrial activity and the onset of ventricular depolarization suggested that its vector was outside the plane of the electrode arrangement, or that there was a prolonged H-V interval; the latter has been confirmed in 2 patients. Intracardiac His bundle recordings in 25 subjects who had characteristic surface electrical activity of the His bundle disclosed good correlation between invasive and noninvasive measurements of the H-V interval. This noninvasive technique using portable equipment, which permits serial evaluation of the His bundle electrogram, may facilitate prospective studies in patients with conduction disease.