Electrophysiologic Studies on Various Conducting Accessory Pathways in Ventricular Pre-excitations Using Recording Technique of His Bundle Electrograrns.

The electrophysiological properties of the specialized conduction system in 2 sub-jects of control group (non-ventricular pre-excitation group) and 4 cases of ventricular pre-excitation group were studied using the recording technique of His bundle electrograms and artificial rapid atrial pacing. This article stressed that the clinical use of the direct writing recorders in recording His bundle electrograms can provide considerable informations. Technical considerations were made on the feasibility of using a standard direct writer recorder for recording the distinguishable His bundle potentials. Atrial pacing was initiated at a rate slightly above the patient's control rate. Pacing rates were gradually increased up to approximately 500 beats/min in a systematic way. The response to atrial pacing in normal conduction system showed that the gradual increase in pacing rate produced the progressive increase in conduction time between the atrium and His bundle (P-H or A--H) and the development of Wenckebach periods at rates ranging at least 150 beats/min or higher. Five patients who showed normal electrocardiographic findings were confirmed to develop functional conduction disturbances of the atrioventricular conduction system with atrial pacing at rates lower than 140 beats/min. It is concluded that atrial pacing ranging up to 150 beats/min proved not to be satisfactory in the detection of latent functional abnormalities in the atrioventricular conduction system. In ventricular pre-excitation group three types of mechanisms on ventricular preexcitation were demonstrated in this study. 1) One type of mechanisms of the ventricular pre-excitation classified as classical W-P-W syndrome is a direct atrioventricular connection which bypassed the normal A-V conduction system. Increasing atrial pacing rates in this type resulted in various degrees of anomalous W-P-W QRS complexes and varying degrees of conduction disturbances in normal conduction system. These anomalous W-P-W QRS complexes are proved to be due to various degrees of fusion beat through both the normal conduction system and this accessory bypass. It was also shown that the conduction time through this accessory bypass was not influenced by atrial pacing using the rates up to approximately 500 beats/min. 2) A second type of the mechanisms which was suggested in this study consists of the supra-Hisian and infra-Hisian pathways. This type also showed classical W-P-W syndrome electrocardiographically. Atrial pacing during the periods of the normal atrioventricular conduction resulted in intermittent occurrence of various degrees of W-P-W fusion complexes and varying degrees of conduction disturbances in the conduction system. The conduction time through this type of pathways is not lengthened by atrial pacing. H-V interval was not changed by atrial pacing but the shortness of H-V interval in this type may be consistent with infra-Hisian pathway because H-V interval which was demonstrated in normal sinus rhythm was within normal value. 3) A third type of mechanisms which explains short P-R interval and normal QRS complexes (Lown-Ganong-Levine syndrome) may be the presence of partial bypass of the A-V node or the accelerated conduction in the atrioventricular conduction system. Increase in atrial pacing rates produced an attenuated degree of prolongation of the A-H interval whithout a change in conduction time distal to the proximal His bundle.