Determination of the Left Bundle Branch Refractoriness by Distal His Bundle Pacing in Patients with Left Bundle Branch Block

Electrophysiological studies were carried out in two patients with an idiopathic leff bundle branch block. Consisfenl distal His bundle pacing resulted in the normalization of the QRS complex in both pa lien ts. Extrastimulation during basic distal His pacing at several cycle lengths was carried out successfully. Using this technique, the refractory periods of the left bundle branches were measured and found to be within the normal range. In addition, they decreased with the shortening of the basic cycle length. These results demonstrated the possibility of determining the refractoriness of the left bundle branch by His bundle pacing in patients with left bundle branch block. Hypotheses are postulated about the presumed location of the lesion responsible for the left bundle branch block.