Characteristics of ventriculoatrial conduction in patients with enhanced atrioventricular nodal conduction.

To study the characteristics of the ventriculoatrial conduction system in patients capable of rapid antegrade atrioventricular conduction, electrophysiologic studies were performed in 23 subjects capable of 1:1 atrioventricular conduction at atrial cycle lengths less than or equal to 300 ms (Group I), and in 23 subjects with normal 1:1 atrioventricular conduction (Group II). During ventricular pacing, ventriculoatrial block at all cycle lengths was seen in 5/23 (22%) in Group I and in 7/23 (30%) in Group II patients (p = NS). In the remainder, the minimum ventricular pacing cycle length maintaining 1:1 ventriculoatrial conduction was 359 +/- 85 ms in Group I, compared to 444 +/- 118 ms in Group II (p less than .02). Both flat and exponential VA conduction interval curves, drawn as a function of pacing cycle length, were observed in both groups. Discontinuous ventriculoatrial conduction curves were seen in 5/18 (28%) Group I and 1/16 (6%) Group II patients (p = NS). In conclusion, retrograde ventriculoatrial conduction, when present in patients capable of rapid 1:1 atrioventricular conduction, is maintained at shorter cycle lengths than in patients with normal atrioventricular conduction. Quantitative, rather than qualitative, differences distinguish the two groups.