Clinical evaluation of His-bundle electrogram recorded from the body surface.

A noninvasive method of recording His-bundle activity was developed in our laboratory. This technique is based on the principle of high-gain amplification of the external signals, use of appropriate filters to eliminate random noise, and averaging of the amplified signals over 200-500 cardiac cycles to improve the signal-to-noise ratio. Using this technique we were able to demonstrate external His-bundle activity and to measure the extent His-bundle-ventricular (H-V) interval in 29 of 51 (60%) patients referred to our unit for evaluation of conduction abnormalities or history of collapse. The external technique was validated by the intracardiac electrode method. External H-V interval was reproducible when tested i eight normal subjects and four patients of variation was 4.5% for external H-V interval of 30-90 ms duration). Failure to obtain distinct external His-bundle deflection was largely due to contamination with atrial or ventricular noise. Analysis of all the records showed that the demonstration of external His-bundle activity was directly proportional to the length of the PR segment. The external H-V interval could be measured in all patients with PR segments longer than 100 ms but in less than half in whom the PR segment was shorter than 55 ms. We conclude that the noninvasive technique of recording His-bundle activity is simple and reproducible and can be used at the bedside. It possesses a distinct advantage over the intracardiac technique in that it can be employed in sequential studies. However, in its present state of development, its use is mainly confined to the analysis of conduction disturbances.