Echocardiographic assessment of mitral valve motion, cardiac structures, and ventricular function in dogs with atrial fibrillation.

Eleven dogs with atrial fibrillation were examined echocardiographically. During atrial fibrillation, there was no evidence of atrial contraction in the left ventricle or aorta, or on the mitral valve leaflets. Measurement of cardiac structures in echocardiograms showed decreased sizes for the aorta (P less than 0.01), interventricular septum (P less than 0.01), and posterior left ventricular wall (P less than 0.02). Evidence of decreased contractility of the left ventricle was noticed with the decreased amplitude of motion of the posterior left ventricular wall (P less than 0.001) and decreased fractional shortening (P less than 0.01). Not every QRS resulted in systolic or diastolic motion in the mitral and aortic valve leaflets, thus helping to account for the pulse deficits normally seen during atrial fibrillation.