Cardiomyocyte aging and hypertrophy: atrial and ventricular changes in normal and myopathic Syrian hamsters.

Cardiac eccentric hypertrophy is associated with complex architectural and metabolic alterations. Atrial and ventricular myocyte diameters in cardiomyopathic (Bio 14.6) and age-matched control (F1b) Syrian hamsters were compared and histopathology was examined by electron microscopy. The mean diameter of ventricular myocyte diameters increased with age in both F1b and Bio 14.6 hamsters. Significantly greater hypertrophy was noted in the Bio 14.6 left ventricle myocytes than the F1b. Histo- and cytopathologic findings included amitotic myocardial divisions and focal myocyte necrosis in Bio hearts. Sarcomere length appeared to be similar across age and strain; however, wider sarcomeres were found in conjunction with wider diameters of myopathic left ventricle myocytes. Moreover, F1b hamsters' atrial myocytes maintained a static diameter, while those of the Bio 14.6 showed hypertrophy even preceding ventricular changes. These findings indicated that the cardiomyopathic heart is characterized by a continued fiber hypertrophy despite cardiac decompensation. Other histopathological findings included amitotic myocardial divisions, focal necrosis and sarcoplasmic widening of Z-lines. In addition, vascular smooth muscles of Bio 14.6 demonstrated vacuolization.