Effects of upright posture on anterograde and retrograde atrioventricular conduction in patients with coronary artery disease, mitral valve prolapse or no structural heart disease

To assess the effects of posture on anterograde and retrograde atrioventricular conduction, electrophysiologic testing was performed in 25 patients in both the supine and 45 ° upright positions on a tilt table. Retrograde conduction was present during ventricular pacing in 17 patients in the supine position; all 17 continued to manifest retrograde conduction in the upright position. In all patients with absent retrograde conduction while supine, retrograde conduction could not be demonstrated while upright. Upright posture significantly (p < 0.05) shortened the sinus cycle length (from 808 ± 34 to 678 ± 26 ms, mean ± standard error of the mean), AH interval during sinus rhythm (78 ± 6 to 69 ± 6 ms), and AH interval during atrial pacing at cycle length 500 ms (123 ± 13 to 91 ± 9 ms). Total atrioventricular conduction time during atrial pacing shortened significantly (from 169 ± 1.3 to 136 ± 10 ms), as did ventriculoatrial conduction time during ventricular pacing (from 192 ± 9 to 178 ± 7 ms). Upright posture also significantly shortened both anterograde block cycle length (390 ± 20 to 328 ±17 ms) and retrograde block cycle length (466 ±27 to 354 ± 18 ms). However, the effect of upright posture on retrograde block cycle length was significantly greater than on anterograde block cycle length: a 21% decrease retrograde vs a 14% decrease anterograde (p < 0.05). These effects may produce clinically important changes in characteristics of arrhythmias that depend on the properties of anterograde and retrograde conduction. Electrophysiologic testing in both the supine and upright positions may better define retrograde conduction properties than supine testing alone.