Abstract
Studies on intraventricular conduction in the presence of bundle branch blocks by using direct leads have been carried out by the investigators such as Sodi-Pallares, Prinzmetal and Scher. In spite of the bulk of data, they are far from completeness in explaining the detailed mechanism of the modification in conduction which occurs in these conditions.It is essential to obtain the over-all picture of the mechanism of conduction in bundle branch blocks for the refinement of theoretical explanations of the ECG patterns of clinical bundle branch blocks.Such a knowledge should offer an important clue to the function and its peculiarity of the specialized conducting muscle fibers. Thus, conductions in the ventricular free walls as well as the interventricular septum in experimentally produced B. B. B. in the canine heart were investigated in this study.Three types of electrodes for direct leads were employed, i. e., one for multiple lead recordings, one for contiguous bipolar leads, and one for unipolar leads, all of which were specially designed for the purposes of this study.The electrodes which were provided with arrowheads were pierced through the cardiac muscle while protected with an injection needle; this technique and the design of the electrodes permitted to fix the electrodes at one site without risk of shift during the experiment.The locations of the electrodes were checked after each experimental animal was dead.To produce B. B. B. experimentally, a sickleshaped scalpel was introduced into the cardiac cavity through the ventricular free wall to incise the portion of the septal muscle close inferiorly to the bifurcation of His' bundle.R.B.B.B. was obtained by cutting at a relatively small area in the anterior portion of the right septal surface, while L.B.B.B. was produced by cutting from the extreme front to the back at a level of 1 cm below the aortic valve; this difference may be due to the difference in the anatomical structures of the two B.B.An eight-channel direct-writing electrocardiograph and a two-beam cathode ray oscilloscope were used for recording.The paper in the electrocardiograph was run with a speed of 150 cm/sec.; the photographic paper of a continuous recording unit to record the waves on the oscilloscope was run with a speed of 20 cm/sec. Such high speeds were mandatory to register minute differences in time accurately.The peak of the main deflection of the contiguous bipolar lead was accepted as the indicator of the arrival time of activation; in unipolar lead ECGs, the onset of the steepest portion of their downward deflection was used. The time was measured from the earliest QRS onest of the multiple simultaneous recordings. These two indicators coincided each other very well as Durrer's observations.Results Incontrast to the conduction in the non-blocked side which remains the same as before, the conduction in the blocked side exhibits drastic changes.A) R.B.B.B.1. Epicardial surface of the right ventricular free wall In R.B.B.B., the excitation started at the portion of the posterior wall adjoining the septum, then the portion of the anterior wall adjoining the septum, spread from posterior to anterior, from below upward, and ended at the basal portion of the antero-lateral wall, while in the normal, the conduction started at the central lower area of the anterior surface, and ended at the basal portion of the portero-lateral or lateral wall.
