Effect of physiological mechanical perturbations on intact human myocardial repolarization

Objective: The objective of this study was to investigate the relationship between acute decreases in right ventricular volume during Valsalva strain (with resultant changes in autonomic neural tone) and measures of local end ocardial repolarization. time independent of heart rate and autonomic neura l tone. Methods: Patients implanted with a Stimulus to T wave (Stim-T) sens ing pacemaker specially adapted to output a validated measure of beat to be at local repolarization (n=9) performed Valsalva manoeuvers (40 mmHg for 15 s) while paced at a cycle length of 500 ms. Stim-T intervals were measured before and after autonomic blockade (Block: 0.03 mg/kg i.v. atropine+/-0.1 5 mg/kg propranolol). Right ventricular end diastolic volume was estimated by simultaneous 2D-echocardiography, Results: Without autonomic blockade, c ompared to baseline, repolarization significantly prolonged during Valsalva strain (1.1+/-0.7%) and shortened during release (-1.4+/-1.0%). After bloc k, strain related repolarization prolongation was also observed (1.0+/-0.6% ), with significantly less release related repolarization shortening (-0.8/-0.8%) compared to pre-block (P<0.05). Right ventricular end diastolic vol ume decreased during strain by 11+/-10 and 9+/-16% from baseline, pre- and post-block respectively (P<0.05). Conclusion: In a chronically instrumented human model, an acute physiologic volume reduction modestly prolongs right ventricular repolarization independent of changes in rate or autonomic ton e. (C) 2000 Elsevier Science B.V. All rights reserved.