Age-related electrophysiological and histological changes in rabbit hearts: age-related changes in electrophysiology

Because of the known higher incidence of cardiac arrhythmia in aged patients we tried to define the underlying arrhythmogenic substrate by quantifying those electrophysiological alterations in aged rabbit hearts, which are commonly believed to be arrhythmogenic, relating them to histological findings in the same hearts. This is the first investigation that analyses the effect of ageing on the epicardial excitation spreading. Isolated hearts from young (ten weeks) and old (1.5-2 years) white New Zealand rabbits were perfused according to the Langendorff-technique, submitted to epicardial potential mapping for 60 min and investigated histologically. Electrophysiological data in aged hearts showed a) a higher variability of the activation pattern, b) an increased dispersion of the epicardial potential duration; c) a prolongation of the AV-conduction time and of the duration of the epicardial activation signal, which was fractionated in aged hearts. Histological findings showed extensive incorporation of fat cells and connective tissue in ventricular and AV-node tissues, which may explain the prolonged conduction time, and a marked hypertrophy of the ventricular myocytes. The observed high dispersion, the broadened and fractionated epicardial activation signal and the enhanced variability of the activation patterns may be due to the observed long strands of collageneous tissue separating ventricular muscle fibres in aged hearts. These changes help to explain the enhanced susceptibility to arrhythmogenic stimuli with age.