Left atrial and ventricular remodeling in chronic mitral regurgitation.

OBJECTIVE: This study describes the structural and mechanical changes in the left atrium and left ventricle in a canine model of chronic mitral regurgitation in an attempt to identify markers linked to the onset of atrial tachyarrhythmias or left ventricle dysfunction.

METHODS: Animals underwent baseline and terminal echocardiography and cardiac magnetic resonance imaging. Under echocardiographic guidance, chordae tendinae were avulsed until there was severe mitral regurgitation, defined by regurgitant jet area to left atrium area more than 70%. At terminal surgery, rapid atrial pacing was performed to test inducibility of atrial tachyarrhythmias.

RESULTS: Twelve canines underwent mitral valve chordae avulsion and were kept alive for an average of 8.8 ± 1.3 months. Left atrium volume increased more than 111% (P < .01), left ventricle end-systolic volumes increased more than 57% (P < .01), and left ventricle end-diastolic volumes increased more than 48% (P < .01). Increased left ventricle mass was negatively correlated to ejection fraction (P = .01). During rapid atrial pacing, 6 canines developed inducible atrial arrhythmias. There were no differences in left atrium volume, function, or left ventricle strain between canines with atrial tachyarrhythmias and those without. Independently, 6 developed left ventricle dysfunction with an average decrease in ejection fraction of 16% ± 4%. Canines with reduced ejection fraction experienced markedly increased left atrial volume at minimal filling (P = .02) and impaired left ventricle global radial strain (P = .05).

CONCLUSIONS: Our experimental canine model replicated electrophysiological and hemodynamic consequences of clinical mitral regurgitation. Although left atrium function and left ventricle strain did not associate with atrial tachyarrhythmia inducibility, left atrial volume at minimal filling, left ventricle mass, and left ventricle global radial strain emerged as potential indicators of left ventricle dysfunction. These markers may have clinical value in guiding timely surgical intervention.