Ventricular pro-arrhythmic phenotype, arrhythmic substrate, ageing and mitochondrial dysfunction in peroxisome proliferator activated receptor-γ coactivator-1β deficient (Pgc-1β(−/−)) murine hearts

INTRODUCTION: Ageing and age-related bioenergetic conditions including obesity, diabetes mellitus and heart failure constitute clinical ventricular arrhythmic risk factors. MATERIALS AND METHODS: Pro-arrhythmic properties in electrocardiographic and intracellular recordings were compared in young and aged, peroxisome proliferator-activated receptor-γ coactivator-1β knockout (Pgc-1β(−/−)) and wild type (WT), Langendorff-perfused murine hearts, during regular and programmed stimulation (PES), comparing results by two-way ANOVA. RESULTS AND DISCUSSION: Young and aged Pgc-1β(−/−) showed higher frequencies and durations of arrhythmic episodes through wider PES coupling-interval ranges than WT. Both young and old, regularly-paced, Pgc-1β(-/-) hearts showed slowed maximum action potential (AP) upstrokes, (dV/dt)(max) (∼157 vs. 120–130 V s(-1)), prolonged AP latencies (by ∼20%) and shortened refractory periods (∼58 vs. 51 ms) but similar AP durations (∼50 ms at 90% recovery) compared to WT. However, Pgc-1β(-/-) genotype and age each influenced extrasystolic AP latencies during PES. Young and aged WT ventricles displayed distinct, but Pgc-1β(−/−) ventricles displayed similar dependences of AP latency upon (dV/dt)(max) resembling aged WT. They also independently increased myocardial fibrosis. AP wavelengths combining activation and recovery terms paralleled contrasting arrhythmic incidences in Pgc-1β(-/-) and WT hearts. Mitochondrial dysfunction thus causes pro-arrhythmic Pgc-1β(−/−) phenotypes by altering AP conduction through reducing (dV/dt)(max) and causing age-dependent fibrotic change.