Activation of subendocardial Purkinje fibers and muscle fibers of the left septal surface before and after left bundle branch block

Abstract

Through utilization of a technique developed in this laboratory it has been possible to study the sequence of activation of the Purkinje fibers and muscle fibers beneath the endocardium of the left interventricular septal surface at the same 21 specific points before and after left bundle branch block (LBBB). It has been demonstrated that activation of the Purkinje system (P) at a specific point on the septum precedes that of the adjacent muscle fibers both before and after LBBB. It is concluded, therefore, that activation of the muscle fibers of the left septal surface is a direct result of excitation spreading to these fibers from the subendocardial Purkinje network both before and after LBBB. After LBBB the time required for complete activation of the left septal surface is considerably less than the control value; this finding is consistent with the concept that, after LBBB, activity spreads within the homolateral subendocardial Purkinje system, which has been activated simultaneously at multiple points, and then spreads to the adjacent muscle fibers of the left septal surface. Representative recordings from all points on the specialized conducting system (SCS) have been presented, including bipolar electrograms from the bundle of His (BH), right bundle branch (RBB), right Purkinje-papillary junction (RPPJ), free-running Purkinje fibers which extend from the base of the right anterior papillary muscle to the endocardium of the wall of the right ventricle (FRP), left bundle branch (LBB), anterior false tendon of the left ventricle (AFT), left anterior Purkinje-papillary junction (LAPPJ), and peripheral Purkinje fibers of the left septal surface at multiple sites (P). In order to facilitate the orderly presentation of data, a system of nomenclature based on the abbreviation for each of the anatomic points from which electrical potentials are recorded has been suggested for use in studying the specialized conducting system (SCS) of the heart.