Effects of upright posture on atrioventricular accessory pathway conduction

Abstract

The etectrophysiologic effects of 45 ° head-up tilt were studied in 19 patients with atrioventricular accessory pathways. Upright posture enhanced both anterograde and retrograde accessory pathway conduction when compared to the supine position: the anterograde block cycle length decreased from 374 ± 52 ms (mean ± standard error) (supine) to 303 ± 33 ms (tilt) (p < 0.05); anterograde effective refractory period decreased from 286 ± 17 to 249 ± 10 ms (p < 0.05); retrograde block cycle length shortened from 331 ± 36 to 291 ± 35 ms (p < 0.05); retrograde effective refractory period decreased from 312 ± 26 ms to 274 ± 15 ms (p < 0.05). During induced atrial fibrillation the mean RR interval and the shortest RR interval between preexcited beats decreased approximately 10% with head-up tilt. During orthodromic reciprocating tachycardia, tachycardia cycle length shortened 15%. Tachycardia rate during electrophysiologic study in the head-up position more closely approximated the rate of clnical tachycardia than did the rate in the supine position. Head-up tilt significantly enhances anterograde and retrograde accessory pathway conduction, increases the rate of arrhythmias using an accessory pathway and may be clinically useful in the assessment of patients with an accessory pathway.