Proceedings of the Physiological Society, 30‐31 March 1990, University College London Meeting: Communications

Abstract

Contraction-excitation feedback is implied when changes in ventricular loading conditions influence the time course of repolarization (Lab, 1982) (and hence refractoriness). We were interested in seeing if action potential duration changes with changing load in man. We used a 15s valsalva manoeuvre to manipulate pressure/volume and recorded monophasic action potentials from the left ventricular endocardium as a measure of the time course of repolarization. Twenty-three patients were studied undergoing routine cardiac catheterization procedures (using a femoral approach). Local ethical committee approval was obtained. Patients were divided into three groups: (1) those with no angiographic evidence of abnormal wall motion or history of myocardial infarction (n = 7); (2) those with a history of myocardial infarction but with normal wall motion (n = 5); and (3) those with angiographic evidence of abnormal wall motion with or without previous infarction (n = 10).During the initial stress phase as venous return was restricted peak systolic pressure in group 1 fell from 138+31 mmHg (mean+S.D.) to a plateau level of 97+37 mmHg (P< 0-02) (Anova); during the recovery phase it increased from 66 + 26 to 109 + 32 mmHg (P < 0-0001). In group 1 during the stress phase monophasic action potential duration shortened from 311+47 ms to 295 + 47 ms (P < 0-001) and lengthened during the recovery phase (285 + 44 ms to 304 + 44 ms; P < 0-0001). In group 3 some patients showed monophasic action potential duration changes in the opposite direction, the resulting mean values showing no significant difference for either phase. The patients in group 2 showed an in-between pattern.This study provides evidence that changes in ventricular loading conditions may influence the timing of repolarization in man. We feel alterations in the sympathetic response are unlikely to account for these findings. These effects on repolarization were often opposite in direction in the presence of abnormal wall motion. This could generate local electrical gradients which may well be relevant to the association of arrhythmias with left ventricular dysfunction.Supported by the British Heart Foundation. REFERENCE LAB, M. J. (1982). Circ. Re8. 50,[758][759][760][761][762][763][764][765][766] 9P