The electrogenesis of terminal QRS notches in normal subjects.

This study was undertaken to explore the mechanisms responsible for the low amplitude, low frequency notches commonly recorded at the end of the QRS complex. Such waves were registered in tracings from twenty-three of fifty normal volunteers evaluated. In fourteen cases, notches were localized to the lateral precordial leads (V3-6), in six they were limited to right precordial leads (V1-2) and in three, notches were found in both right and lateral lead records. Isopotential maps were constructed from potentials registered from one-hundred-fifty torso electrodes. Results demonstrated that: 1) notches in lateral precordial leads (V3-V6) were due to either movement of or changes in potential of early ventricular repolarization effects; and 2) notches in right precordial leads (V1-V2) were caused by migration of terminal ventricular activation currents. These findings document the necessity for study of factors that determine the spatial as well as the temporal and magnitude parameters of electrocardiographic waveforms.