title: Anti-arrhythmic effects of hypercalcemia in hyperkalemic, Langendorff-perfused mouse hearts.
abstract: The present study examined the ventricular arrhythmic and electrophysiological properties during hyperkalemia (6.3 mM [K+] vs. 4 mM in normokalemia) and anti-arrhythmic effects of hypercalcemia (2.2 mM [Ca2+]) in Langendorff-perfused mouse hearts. Monophasic action potential recordings were obtained from the left ventricle during right ventricular pacing. Hyperkalemia increased the proportion of hearts showing provoked ventricular tachycardia (VT) from 0 to 6 of 7 hearts during programmed electrical stimulation (Fisher's exact test, P<0.05). It shortened the epicardial action potential durations (APDx) at 90, 70, 50 and 30% repolarization and ventricular effective refractory periods (VERPs) (analysis of variance, P<0.05) without altering activation latencies. Endocardial APDxand VERPs were unaltered. Consequently, ∆APDx(endocardial APDx-epicardial APDx) was increased, VERP/latency ratio was decreased and critical intervals for reexcitation (APD90-VERP) were unchanged. Hypercalcemia treatment exerted anti-arrhythmic effects during hyperkalemia, reducing the proportion of hearts showing VT to 1 of 7 hearts. It increased epicardial VERPs without further altering the remaining parameters, returning VERP/latency ratio to normokalemic values and also decreased the critical intervals. In conclusion, hyperkalemia exerted pro-arrhythmic effects by shortening APDs and VERPs. Hypercalcemia exerted anti-arrhythmic effects by reversing VERP changes, which scaled the VERP/latency ratio and critical intervals.
authors: School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, SAR, P.R. China.
authors: Gary
authors: G
authors: Tse
authors: Department of Cardiology, Tongji University Affiliated Tongji Hospital, Shanghai 200065, P.R. China.
authors: Bing
authors: B
authors: Sun
authors: School of Medicine, Imperial College London, London SW7 2AZ, UK.
authors: Sheung Ting
authors: ST
authors: Wong
authors: Department of Physiology, McGill University, Montreal, Quebec H3G 1Y6, Canada.
authors: Vivian
authors: V
authors: Tse
authors: School of Medicine, Imperial College London, London SW7 2AZ, UK.
authors: Jie Ming
authors: JM
authors: Yeo
keywords: action potential duration; hypercalcemia; hyperkalemia; ventricular arrhythmia