Basic Science and Experimental Studies Increased Myosin Heavy Chain-b With Atrial Expression of Ventricular Light Chain-2 in Canine Cardiomyopathy

Background: Dilated cardiomyopathy is a naturally occurring disease in humans and dogs. Human studies have shown increased levels of myosin heavy chain (MHC)-b in failing ventricles and the left atria (LA) and of ventricular light chain (VLC)-2 in the right atria in dilated cardiomyopathy. Methods and Results: This study evaluates the levels of MHC-b in all heart chambers in prolonged canine right ventricular pacing. In addition, we determined whether levels of VLC2 were altered in these hearts. Failing hearts demonstrated significantly increased levels of MHC-b in the right atria, right atrial appendage, LA, left atrial appendage (LAA), and right ventricle compared with controls. Significant levels of VLC2 were detected in the right atria of paced hearts. Differences in MHC-b expression were observed between the LA and the LAA of paced and control dogs. MHC-b expression was significantly greater in the LA of paced and control dogs compared with their respective LAA. Conclusions: The cardiac myosin isoform shifts in this study were similar to those observed in end-stage human heart failure and more severe than those reported in less prolonged pacing models, supporting the use of this model for further study of end-stage human heart failure. The observation of consistent differences between sampling sites, especially LA versus LAA, indicates the need for rigorous sampling consistency in future studies. (J Cardiac Fail 2007;13:680e686)