Left Atrial and Ventricular Remodeling in Chronic Mitral Regurgitation.

Objective: This study described the structural and mechanical changes in the left atrium (LA) and left ventricle (LV) in a canine model of chronic mitral regurgitation (MR), in an attempt to identify markers linked to the onset of atrial tachyarrhythmias (ATA) or LV dysfunction.

Methods: Animals underwent baseline and terminal echocardiography and cardiac magnetic resonance imaging. Under echocardiographic guidance, chordae tendinae were avulsed until there was severe MR, defined by regurgitant jet area to LA area (RJA/LAA) of >70%. At terminal surgery, rapid atrial pacing was performed to test inducibility of ATA.

Result: Twelve canines underwent mitral valve chordae avulsion and were survived for an average of 8.8 ± 1.3 months. LA volume increased over 111% (p < 0.01), LV end systolic volumes increased over 57% (p < 0.01), and LV end diastolic volumes increased over 48% (p < 0.01). Increased LV mass was negatively correlated to ejection fraction (EF) (p = 0.01). During rapid atrial pacing, six canines developed inducible atrial arrhythmias. There were no differences in LA volume, function or LV strain between canines with ATAs and those without. Independently, six developed LV dysfunction with an average decrease of EF of 16 ± 4%. Canines with reduced EF experienced markedly increased LAV_min (p = 0.02) and impaired LV global radial strain (GRS) (p = 0.05).

Conclusion: Our experimental canine model replicated electrophysiological and hemodynamic consequences of clinical MR. Although LA function and LV strain did not associate with ATA inducibility, LAV_min , LV mass, and LV GRS emerged as potential indicators of LV dysfunction. These markers may have clinical value in guiding timely surgical intervention.