Left ventricular activation time in left ventricular hypertrophy and in left bundle-branch block.

Simultaneous tracings of right and left ventricular leads were taken in 6 dogs with experimentally produced left bundle-branch block, and in 30 clinical cases of left ventricular hypertrophy. In the experimental study it was found that the initial phase of the QRS complex in the right epicardial lead did not change its configuration or its duration after the production of left bundle-branch block. This observation offers a new concept of the septal and left ventricular activation in left bundle-branch block. It was coneluded that a considerable portion of the cases of left bundle-branch block.