Aim: 

Significant alterations of cardiac electrophysiological properties occur during the normal aging process. However, a detailed knowledge of the changes in cardiac electrophysiology in the elderly is lacking. Thus, the aim of the present study is to determine specific age-related changes in ventricular myocardial structure and activation patterns.

Methods: 

Multiple epicardial electrograms were recorded in vivo in control and aged rats, during normal sinus rhythm and ventricular pacing. Electrical data were related to morphometric and immunohistochemical parameters of the underlying ventricular myocardium.

Results: 

In aged hearts QRS duration was significantly delayed while conduction velocity did not change significantly, as compared to control hearts. Moreover, ventricular activation patterns displayed variable numbers of epicardial breakthrough points. Morphological analysis in aged rats revealed that heart weight and myocyte transverse diameter increased significantly, scattered microfoci of interstitial fibrosis were mostly present in the ventricular subendocardium and gap junction connexin expression decreased significantly, as compared to controls.

Conclusions: 

Our results show that increased total ventricular activation time is not due to delayed myocardial conduction irrespective of structural remodeling. They rather suggest that abnormal activation patterns are induced by the occurrence of impaired impulse propagation through the conduction system leading to uncoordinated and delayed myocardial excitation.