His Bundle Electrograms in Patients with Short P-R Intervals, Narrow QRS Complexes, and Paroxysmal Tachycardias

Abstract

His bundle electrograms were recorded in three patients with short P-R intervals, narrow QRS complexes, and a history of paroxysmal tachycardias. During sinus rhythm or atrial stimulation with long cycle lengths, the shortening of the P-R interval was due to a decrease in the low right atrium-His (LRA-H) interval (representing A-H conduction time). The latter was also short during retrograde (V-A) conduction. These findings support the existence of an A-V nodal bypass operation in both directions. In one patient, the LRA-H interval did not lengthen when the atrial rate was increased. Intermittent atrial pacing was performed in the two other patients. The LRA-H interval was short at long coupling intervals, but it started to increase (progressively) at a given Stimulus 1 -Stimulus 2 interval. Apparently, the refractory period of the accessory bundle was encountered so that the impulse was propagated, with various degrees of delay, through the A-V node. A James bundle need not be present in all patients with similar electrocardiograms. Abnormalities of unknown origin could cause this phenomenon. Reciprocating tachycardias were induced by stimulation of the atria in one patient. The triggering beat consistently had a long A-V conduction time. Although in this case retrograde (V-A) propagation most probably occurred through the accessory communication, the possibility of a functional intranodal dissociation of a single anatomical pathway could not be excluded.

Intermittent AV conduction disturbances in patients with AV nodal bypass tracts. Possible mechanisms of unusual variant of tachycardia-bradycardia syndrome.

“…Whereas the PR interval and HV interval were normal (150 and 55 ms, respectively), the AH interval was short (40 ms). The latter suggested the presence of an electrophysiological AV nodal bypass tract (Castellanos et al, 1971;Coumel et al, 1972;Caracta et al, 1973). The His bundle origin of the corresponding deflection was validated by His bundle pacing (Fig.…”

“…1, 3, and 5 the interval elapsing between the inscription of the atrial deflection (recorded from the vicinity of the AV node) and the H deflection did not represent 'normal' AV nodal conduction time (Castellanos et al, 1971). Rather it reflected differences in arrival of excitation at these sites .…”

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“…In the presence of partial or complete A-V nodal bypass tracts (Brechenmacher et al .. 1974) or enhanced A-V nodal conduction, the normal A-V nodal delay is considerably attenuated (Aranda et al, 1976;Castellanos et al, 1971;Hope et a/., 1977) with a correspondingly short A-V nodal FRP (Bissett et al .. 1975;Camm et al, 1978;Seipel et al, 1976). This naturally occurring model may allow the delivery of sufficiently closely coupled H 1 -H2 impulses to result in infra nodal delay or block (Aranda et al, 1976;Camm et al .. 1978).…”

Re-entry via Mahaim fibres as a possible basis for tachycardia.

“…Circus movement can revolve within the atrioventricular node itself (Goldreyer and Bigger, 1971;Denes et al, 1973), or may use a combination of normal and accessory pathways of conduction. Though the latter are most often direct communications between the atria and ventricles (Kent) (Durrer et al, 1967;Castillo and Castellanos, 1970;Grolleau et al, 1970;Wellens et al, 1971;Touboul et al, 1972), atrio-His bundle accessory pathways (James) have also been invoked in the generation of re-entrant rhythms (Castellanos et al, 1971;Mandel et al, 1971;Coumel et al, 1972b). In addition, the initiation of reciprocal excitation within an anatomical circuit composed of normal atrioventricular and accessory Mahaim pathways remains a possibility (Durrer et al, 1970).…”