The effects of atropine on atrio-ventricular conduction in patients with Wolff-Parkinson-White syndrome. Studies with His bundle electrogram.

The effects of atropine on normal and anomalous A-V pathways were investigated using HBE in 40 cases consisting of 25 subjects without pre-excitation (group I) and 15 cases with WPW syndrome (group II). In group I, A-H interval shortened with a mean decrease of 30% following the administration of atropine (p less than 0.001), while P-A and H-V intervals as well as QRS duration remained unchanged. In group II the electrocardiogram showed WPW syndrome pattern (pattern W) in 12, normalization (pattern N) in 1 and both patterns (pattern WN) in 2 cases during the control study. In 10 cases pattern W persisted after atropine. Atropine changed pattern W to WN in 2 cases, WN to W in 1, WN to N in 1 and N to WN in one case. P-d interval remained constant. Atropine had no effect on the conduction time within atrium. His-Purkinje system and anomalous A-V pathway, but accelerated the transmission through A-V node. Atropine decreased the QRS duration of pattern W in 11 of 13 cases showing pattern W or WN both before and after atropine. Since the QRS duration showing pattern W correlated with P-H interval and (see article) and had the negative correlation with H-d interval (p less than 0.001), fusion mechanism was considered as the genesis of electrocardiographic pattern in most cases with WPW syndrome. Atropine influence was negative on QRS complex of pattern W i2 cases showing the co-existence of Kent bundle and James fibers or exclusive Kent bundle conduction. In the latter case the selection of antiarrhythmic agents should be made with caution. A-V dissociation with junctional rhythm developed in 9 cases (4 in group II) within 2 and a half minutes after atropine. The duration was as short as 15 seconds or less in 6 cases. The continuous tracing is necessary not to miss the AV dissociation. The disappearance of delta wave after atropine was observed during the change to pattern WN and the occurrence of A-V junctional rhythm or beat in 5 of 12 cases showing pattern W prior to the drug administration, and right bundle branch block was disclosed in 2 cases. The normalization of QRS complex also made it possible to measure His-Purkinje conduction time. In this point atropine is superior to the other antiarrhythmic agents which prolong H-V interval. Paroxysmal supraventricular tachycardia induced after atropine revealed shorter A-H with fixed H-V and V-A intervals, compared with the tachycardia before atropine in one case. The administration of atropine serves as an aid to evaluate the participation of anomalous A-V pathway in the tachycardia circuit.