Alterations in left atrial transport and mitral valve blood flow resulting from aortic regurgitation

The instantaneous pattern of mitral valve blood flow and the atrioventricular pressure gradient were studied in calves before and after induction of acute aortic regurgitation. The timing of atrial contraction, the heart rate, and the left ventricular end-diastolic pressure were varied independently. It was found that in the presence of aortic regurgitation: (1) With heart rates of 110 to 120 per minute and P-R intervals greater than 0.18 second, or with heart rates of 65 to 75 per minute and P-R intervals greater than 0.12 second, there was a reversal of the diastolic pressure gradient across the mitral valve; (2) with diastolic reversal of the atrioventricular pressure gradient, mitral regurgitation occurred; (3) the occurrence of mitral regurgitation was independent of left ventricular end-diastolic pressure, and the volume of regurgitant flow ranged from 5 to 19 per cent of the forward mitral valve flow; (4) due to aortic regurgitation, the reversed diastolic mitral flow did not decrease ventricular volume. The volume of diastolic mitral regurgitation that occurs with aortic regurgitation and an anatomically normal mitral valve is small, and apparently causes no alteration in ventricular volume. Care must be exercised, however, in the interpretation of left ventricular cineangiocardiograms in patients with aortic regurgitation, since diastolic mitral regurgitation might be mistaken for evidence of organic mitral valve disease.