Retrograde Pre-excitation

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Abstract
The purpose of this report was to compare antegrade (atrioventricular [A-V]) and retrograde (ventriculoatrial [V-A]) conduction times in 124 consecutive patients who exhibited bidirectional conduction during diagnostic studies where His bundle recordings were obtained. None of these patients had any evidence of antegrade pre-excitation. The mean age was 64 ± 13 (range 32-89 years). The QRS complex was abnormal (≧ 0.11 sec) in 46 patients. The control mean P-R, A-H, and H-V times were 170 ± 37, 80 ± 21, 49 ± 8 msec, respectively. The A-V and V-A times were measured from local bipolar right ventricular (RV) and right atrial (RA) electrograms obtained via pacing catheters placed in the high RA and RV apex. Both RA and RV were paced at identical cycle lengths and the rate was progressively increased until block developed or to a cycle length of 400-330 msec. The V-A time was longer than A-V in 45 (group A), equal in 11 (group B), and shorter in 68 patients. Of the latter 68 patients (group C) in 49 V-A time was 172 ± 36 as compared to 197 ± 38 msec for A-V time, and while the interval lengthened at higher pacing rates, it remained shorter than A-V time throughout (197 ± 40 versus 261 ± 51 msec). In the remaining 19 patients (group D) the V-A was not only shorter than A-V (176 ± 27 versus 207 ± 49 msec) but remained unchanged up to the highest paced rates, whereas A-V time progressively lengthened 269 ± 81 msec). In group D a constant V-A time in all probability is indicative of retrograde impulse transmission through tissue other than the A-V node, i.e., bypass pathways functioning only in a retrograde direction. Progressively increasing A-V and V-A times in groups A to C suggest bidirectional conduction through a single common pathway. Our data demonstrate that: 1) V-A is less often longer (35%) and more often shorter (56%) than A-V; 2) In some patients retrograde pre-excitation and V-A may occur through bypass pathways, functional in the retrograde direction only. These findings may be of clinical significance.