DIASTOLIC MITRAL REGURGITATION WITH ATRIOVENTRICULAR-CONDUCTION ABNORMALITIES - RELATION OF MITRAL FLOW VELOCITY TO TRANSMITRAL PRESSURE-GRADIENTS IN CONSCIOUS DOGS

Diastolic mitral regurgitation is a common finding that can be detected with use of Doppler echocardiographic techniques in patients with atrioventricular (AV) conduction abnormalities. With use of simultaneous hemodynamic and Doppler techniques, mitral flow velocity, mitral valve motion and transmitral pressure gradient were studied during 50 cardiac cycles each of spontaneous or atrial paced first- and second-degree AV block in five lightly sedated dogs. Diastolic mitral regurgitation was detected during atrial relaxation on all beats in which ventricular contraction was delayed > 190 ms. In all dogs the diastolic regurgitation was associated with a reverse transmitral pressure gradient (3.7 +/- 1.1 mm Hg in first-degree AV block and 3.2 +/- 1.5 mm Hg in second-degree AV block) that occurred primarily as the result of a decrease in atrial pressure with atrial relaxation. These reverse pressure gradients were as large as the maximal forward transmitral gradients in early diastole (2.9 +/- 0.9 mm Hg in first-degree AV block and 3.1 +/- 0.7 mm Hg in second-degree AV block) and larger than the maximal forward pressure gradients at atrial contraction (1.7 +/- 0.5 and 1.4 +/- 0.6 mm Hg, respectively, p < 0.05). The maximal reverse pressure gradient during atrial relaxation was also as large as the reverse pressure gradient in mid-diastole (2.7 +/- 0.9 and 2.8 +/- 1.0 mm Hg, respectively), associated with deceleration of early diastolic mitral flow. Peak diastolic mitral regurgitation velocity coincided with the maximal reverse transmitral gradient and was usually larger than anterograde mitral flow velocity. In second-degree AV block the velocity and duration of diastolic regurgitation were variable, with smaller reverse transmitral gradients and peak flow velocities on beats with a shorter QP interval. The mitral valve opened widely with a forward transmitral pressure gradient, and demonstrated rapid and near closure with a reverse transmitral pressure gradient. The smallest valve opening coincided with the maximal reverse pressure gradient and the peak velocity of diastolic regurgitation. Complete valve closure occurred only with ventricular systole. These results demonstrate that a reverse transmitral pressure gradient is present during diastolic mitral regurgitation in AV block, is related to the peak velocity and duration of regurgitation and is equal to or larger than the diastolic forward transmitral gradient. The results also suggest a role for a reverse diastolic transmitral gradient in causing near closure of the mitral valve leaflets and preventing significant regurgitant volume during diastole. However, complete closure of the mitral valve appears to occur only during ventricular systole.