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 pa tients we tried to define the underlying arrhythmogenic substrate by q uantifying those electrophysiological alterations in aged rabbit heart s, which are commonly believed to be arrhythmogenic, relating them to histological findings in the same hearts. This is the first investigat ion that analyses the effect of ageing on the epicardial excitation sp reading. 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 i nvestigated histologically. Electrophysiological data in aged hearts s howed a) a higher variability of the activation pattern, b) an increas ed dispersion of the epicardial potential duration; c) a prolongation of the AV-conduction time and of the duration of the epicardial activa tion signal, which was fractionated in aged hearts. Histological findi ngs showed extensive incorporation of fat cells and connective tissue in ventricular and AV-node tissues, which may explain the prolonged co nduction time, and a marked hypertrophy of the ventricular myocytes. T he observed high dispersion, the broadened and fractionated epicardial activation signal and the enhanced variability of the activation patt erns may be due to the observed long strands of collageneous tissue se parating ventricular muscle fibres in aged hearts. These changes help to explain the enhanced susceptibility to arrhythmogenic stimuli with age. (C) 1997 Elsevier Science Ireland Ltd.