PATHOPHYSIOLOGY AND NATURAL HISTORY Retrograde concealed conduction in the atrioventricular node: dilferential manifestations related to level of intranodal penetration

Although concealed conduction in the atrioventricular node (AVN) has been the focus of numerous experimental and clinical studies, little is known about the differential effects on AVN functional behavior of prior concealed retrograde impulse penetration alone vs prior anterograde or dual AVN activation. This study was undertaken specifically to investigate this aspect of human AVN physiology in patients without intact ventriculoatrial conduction to provide a model with which to analyze concealed retrograde AVN conduction. In 13 such patients AVN behavior during a subsequent anterograde input was characterized for each of three different manners of prior AVN activation: anterograde alone (method I), simultaneous anterograde and retrograde excitation (method II), or equivalently timed retrograde concealed AVN penetration alone (method 1II). In all patients evidence for retrograde AVN concealment was documented by longer anterograde conduction in the AVN during method III than that observed when the retrograde impulse was omitted (method IV). Furthermore, in these patients lacking intact ventriculoatrial conduction, anterograde conduction in the AVN was facilitated and refractoriness was decreased during dual excitation vs anterograde activation alone (method II vs method I). However, when each of methods I and II were compared with concealed retrograde AVN penetration alone (method III), two patterns of AVN responses were observed: In 1 1 of 13 patients (group A) conduction in the AVN was "worse" and refractoriness was greater both in methods I and II compared with method II1; in the remaining two patients (group B) the opposite relationships were observed. The results suggest that among patients with no ventriculoatrial AVN conduction there exist at least two subpopulations whose AVN functional characteristics differ markedly when the effects of anterograde and dual excitation are compared with equivalently timed concealed retrograde activation alone. These findings may be related to differences in level of retrograde AVN concealment in groups A and B, which can be unmasked by the outlined pacing techniques. Circulation 70, No. 3, 392-401, 1984. CONCEALED CONDUCTION in the atrioventricular node (AVN) is an electrophysiologic phenomenon that has continued to stimulate considerable experimental and clinical investigation ever since its classic demonstration 60 years ago.'-" Among the various manifestations of intranodal concealment of impulses, the effects of retrograde concealment in the AVN on subsequent anterograde conduction have been of special interest to both electrocardiographers and physiologists. From the data available it is apparent that the consequences of retrograde concealed conduction on subsequent anterograde impulse propagation may vary From the Natalie and Norman Soref and Family Electrophysiology Laboratory, University of Wisconsin, Milwaukee Clinical Campus, Mount Sinai Medical Center, Milwaukee. Address for correspondence: Michael H. Lehmann. M.D., Mount sinai Medical Center, 950 North 12th St.. Milwaukee, WI 53233. Received Feb. 22, 1984; revision accepted April 19. 1984. depending on whether (1) the AVN is penetrated by an isolated retrograde impulse or (2) the invading retrograde impulse is associated with concomitant anterograde intranodal penetration, resulting in dual AVN excitation. Both particular settings of concealed retrograde conduction have been extensively investigated.2 4-11I 13 To our knowledge, however, there exists no study in animals or human beings that systematically compares within the same subject the AVN effects of concealed retrograde conduction caused by a solitary blocked impulse with the effects of dual excitation. This investigation was undertaken specifically to address this issue as well as to explore in detail the actual magnitude of alteration in anterograde AVN conduction and refractoriness engendered by a retrogradely blocked impulse. Our electrophysiologic analysis was accomCIRCULATION 392 by gest on A ril 5, 2017 http://ciajournals.org/ D ow nladed from PATHOPHYSIOLOGY AND NATURAL HISTORY-ARRHYTHMIA plished with pacing protocols that permitted direct comparison of the effects of identically timed solitary vs simultaneous anterograde and (concealed) retrograde impulses on subsequent anterograde AVN conduction. We report new findings in this interesting area of human cardiac physiology and attempt to provide a unifying explanation for the observed phenomena.