Effects of upright posture on atrioventricular nodal reentry and dual atrioventricular nodal pathways

Abstract

The electrophysiologic effects of upright posture (45 ° upright tilt) were studied in 17 patients with dual atrioventricular (AV) nodal pathways, AV nodal reentry or both. Discontinuous AV nodal conduction curves were observed in 16 patients while supine, but in only 11 patients while upright. Fast pathway refractoriness was shortened: the anterograde fast pathway effective refractory period decreased from 360 ± 22 to 275 ± 14 ms (mean ± standard error of the mean), the anterograde fast pathway block cycle length shortened from 448 ± 28 to 348 ± 20 ms and the retrograde fast pathway block cycle length shortened from 425 ± 29 to 338 ± 24 ms (all p < 0.01). The anterograde slow pathway Mock cycle length shortened from 378 ± 29 to 316 ± 17 ms (p < 0.05). AV nodal reentrant tachycardia was induced in 5 patients while supine (2 sustained, 3 nonsustained) and in 6 patients while upright (4 sustained, 2 nonsustained). Tachycardia cycle length shortened during upright posture, from 413 ± 30 to 345 ± 22 ms (p < 0.01), primarily due to shortened anterograde slow pathway conduction time, from 322 ± 23 to 268 ± 20 ms (p < 0.05). Upright posture thus enhances conduction in patients with dual AV nodal pathways, facilitating AV nodal reentry. Electrophysiologic testing in the upright position may yield additional clinically important information in patients with dual AV nodal pathways.