Ventricular arrhythmias in the elderly

Mosaic Deficiency in Mitochondrial Oxidative Metabolism Promotes Cardiac Arrhythmia during Aging

Aging is a progressive decline of body function, during which many tissues accumulate few cells with high levels of deleted mitochondrial DNA (mtDNA), leading to a defect of mitochondrial functions. Whether this mosaic mitochondrial deficiency contributes to organ dysfunction is unknown. To investigate this, we generated mice with an accelerated accumulation of mtDNA deletions in the myocardium, by expressing a dominant-negative mutant mitochondrial helicase. These animals accumulated few randomly distributed cardiomyocytes with compromised mitochondrial function, which led to spontaneous ventricular premature contractions and AV blocks at 18 months. These symptoms were not caused by a general mitochondrial dysfunction in the entire myocardium, and were not observed in mice at 12 months with significantly lower numbers of dysfunctional cells. Therefore, our results suggest that the disposition to arrhythmia typically found in the aged human heart might be due to the random accumulation of mtDNA deletions and the subsequent mosaic respiratory chain deficiency.

Cardiac electrophysiological alterations in heart/muscle-specific manganese-superoxide dismutase-deficient mice: prevention by a dietary antioxidant polyphenol

Cardiac electrophysiological alterations induced by chronic exposure to reactive oxygen species and protective effects of dietary antioxidant have not been thoroughly examined. We recorded surface electrocardiograms (ECG) and evaluated cellular electrophysiological abnormalities in enzymatically-dissociated left ventricular (LV) myocytes in heart/muscle-specific manganese-superoxide dismutase-deficient (H/M-Sod2^−/−) mice, which exhibit dilated cardiomyopathy due to increased oxidative stress. We also investigated the influences of intake of apple polyphenols (AP) containing mainly procyanidins with potent antioxidant activity. The QRS and QT intervals of ECG recorded in H/M-Sod2^−/− mice were prolonged. The effective refractory period in the LV myocardium of H/M-Sod2^−/− mice was prolonged, and susceptibility to ventricular tachycardia or fibrillation induced by rapid ventricular pacing was increased. Action potential duration in H/M-Sod2^−/− LV myocytes was prolonged, and automaticity was enhanced. The density of the inwardly rectifier K⁺ current (I_K1) was decreased in the LV cells of H/M-Sod2^−/− mice. The AP intake partially improved these electrophysiological alterations and extended the lifespan in H/M-Sod2^−/− mice. Thus, chronic exposure of the heart to oxidative stress produces a variety of electrophysiological abnormalities, increased susceptibility to ventricular arrhythmias, and action potential changes associated with the reduced density of I_K1. Dietary intake of antioxidant nutrients may prevent oxidative stress-induced electrophysiological disturbances.

The prevalence of various arrhythmias in normotensive and hypertensive elderly patients

The prevalence of the most frequent arrhythmias was studied in a geriatric day hospital. Patients older than 65 years have been considered, of them 118 were normotensive and 56 hypertensive subjects. Comparison of the two groups revealed no statistically significant difference either in the frequency of occurrence or in the type of arrhythmias. Dividing the hypertensive patients in the Lown's classes, only those of class 3 or over displayed a considerably higher frequency of arrhythmias than the normotensive subjects. The results demonstrate the age-dependent increase of the prevalence of arrhythmias in general, and the increased occurrence of complex ventricular types in the hypertensive subjects.