Myocardial morphological characteristics and proarrhythmic substrate in the rat model of heart failure due to chronic volume overload.

Chronic volume overload leads to cardiac hypertrophy and later to heart failure (HF), which are both associated with increased risk of cardiac arrhythmias. The goal of this study was to describe changes in myocardial morphology and to characterize arrhythmogenic substrate in rat model of developing HF due to volume overload. An arteriovenous fistula (AVF) was created in male Wistar rats between the inferior vena cava and abdominal aorta using needle technique. Myocardial morphology, tissue fibrosis, and connexin43 distribution, localization and phosphorylation were examined using confocal microscopy and Western blotting in the stage of compensated hypertrophy (11 weeks), and decompensated HF (21 weeks). Heart to body weight (BW) ratio was 89% and 133% higher in AVF rats at 11 and 21 weeks, respectively. At 21 weeks but not 11 weeks, AVF rats had pulmonary congestion (increased lung to BW ratio) indicating presence of decompensated HF. The myocytes in left ventricular midmyocardium were significantly thicker (+8% and +45%) and longer (+88% and +97%). Despite extensive hypertrophy, there was no excessive fibrosis in the AVF ventricles. Distribution and localization of connexin43 were similar between groups, but its phosphorylation was significantly lower in AVF hearts at 21st week, but not 11th week, suggesting that HF, rather than hypertrophy contributes to the connexin43 hypophosphorylation. In conclusion, volume overload leads to extensive eccentric hypertrophy, but not to myocardial fibrosis. Increased vulnerability to arrhythmia in this HF model is possibly related to gap junction remodeling with hypophosphorylation of connexin43.