Left ventricular dysfunction increases left atrial pressures and causes
atrial remodeling. In human subjects, increased left atrial size is a powerful
predictor of mortality and adverse events in a broad range of cardiac pathologic
conditions. Moreover, structural remodeling of the atrium plays an important
role in the pathogenesis of atrial tachyarrhythmias. Despite the potential value
of the atrium in assessment of functional endpoints in myocardial disease,
atrial pathologic alterations in mouse models of left ventricular disease have
not been systematically investigated. Our study describes the geometric,
morphologic and structural changes in experimental mouse models of cardiac
pressure overload (induced through transverse aortic constriction), myocardial
infarction and diabetes. Morphometric and histological analysis showed that
pressure overload was associated with left atrial dilation, increased left
atrial mass, loss of myofibrillar content in a subset of atrial cardiomyocytes,
atrial cardiomyocyte hypertrophy, and atrial fibrosis. In mice undergoing
non-reperfused myocardial infarction protocols, marked left ventricular systolic
dysfunction was associated with left atrial enlargement, atrial cardiomyocyte
hypertrophy and atrial fibrosis. Both infarcted animals and pressure overloaded
mice exhibited attenuation and perturbed localization of atrial connexin-43
immunoreactivity, suggesting gap junctional remodeling. In the absence of
injury, obese diabetic db/db mice had diastolic dysfunction, associated with
atrial dilation, atrial cardiomyocyte hypertrophy and mild atrial fibrosis.
Considering the challenges in assessment of clinically relevant functional
endpoints in mouse models of heart disease, study of atrial geometry and
morphology may serve as an important new tool for evaluation of ventricular
function.