Noninvasive Technique for Detection of Electrical Activity During the P-R Segment

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Abstract
Many recent clinical studies of the His-Purkinje system have utilized intracardiac catheter recordings. This study describes a technique for recording activity of the ventricular specialized conduction system from the body surface. Unlike the standard electrocardiographic signals, approximately one mV at the body surface, the electrical activity of the His-Purkinje system is in the microvolt range at the body surface. In 15 anesthetized dogs, His bundle electrograms, standard ECG recordings, and a highly amplified, filtered bipolar lead across the chest were recorded. The application of signal averaging to the surface leads allows for extraction of the periodic signal (His-Purkinje activity) from random electrical noise. The heart was paced from the right atrium to insure periodicity of the heart rate and to obtain a valid average. By pacing at progressively higher rates, there was a progressive increase in the P-R segment, so that a series of potentials (defined here as the C complex) could be observed occurring prior to ventricular activity. The morphology and temporal relationships of His bundle (H) activity and the G complex to ventricular activity remained constant at all paced rates. H-V times averaged 29 ± 2 msec; correspondingly, the onset of G to V was 29 ± 2 msec. Procainamide was used to alter His-Purkinje conduction times. Comparison of the preventricular activity with the His bundle electrogram showed almost identical time intervals in the control and after drug administration, H-V = 37 ± 3 msec. Thus by using the signal averaging technique, signals that are associated with the His-Purkinje system can be detected on the body surface and validated in various experimental situations.