Background: The purpose of this study was to investigate the genesis of the Austin Flint murmur using Doppler and echocardiographic imaging.
Methods and results: A total of 51 patients having significant aortic insufficiency and an anatomically normal mitral valve were evaluated. They were divided into two groups; 30 patients had an audible Austin Flint murmur (AFM+) and 21 did not (AFM-). All patients had a complete M-mode, two-dimensional, and Doppler echocardiographic examination to characterize left ventricular size and function, motion of the mitral valve, transmitral flow velocities, direction of the aortic insufficiency jet, and severity of aortic insufficiency. There was no significant difference in severity of aortic insufficiency between groups. There was, however, a significant difference in direction of the insufficiency jet. In the AFM+ group compared with the AFM- group, for the parasternal long-axis view 24 (80%) versus eight (38%) had their insufficiency jet directed at the mitral valve, for the apical five-chamber view the values were 25 (83%) versus five (24%), and for the apical long-axis view the values were 27 (90%) versus five (24%); for all comparisons p less than 0.01. There was also a greater frequency of localized anterior mitral leaflet distortion by two-dimensional echocardiography (AFM+:23 [77%] versus AFM-:five [24%]; p less than 0.001) and a greater frequency of Doppler striations overlying the aortic insufficiency jet (AFM+:25 [83%] versus AFM-:seven [33%]; p less than 0.001). Regarding transmitral flow velocities, there was no significant difference in filling patterns or absolute velocities during early or late diastole between groups. There was no gradient by Doppler analysis or by hemodynamics (n = 26) across the mitral valve in either group. There also was no difference in the frequency of preclosure of the mitral valve (AFM+:two versus AFM-:three). Systolic function was similar in both groups, but the left ventricular end-diastolic dimension was significantly greater in the AFM+ group (6.8 +/- 0.8 cm) than in the AFM- group (6.2 +/- 0.7 cm, p = 0.008).
Conclusions: The results of this study suggest that the primary factor responsible for the Austin Flint murmur is the presence of an aortic insufficiency jet directed at the anterior mitral leaflet. This, combined with the biphasic pattern of transmitral flow, distorts the shape of the anterior mitral leaflet as it opens and closes during diastole, making it shudder. The leaflet's shuddering sets up vibrations and shock waves that distort the aortic insufficiency jet, causing the observed Doppler striations and probably the sound of the murmur. There is no evidence from this study to support prior theories that have proposed functional mitral stenosis or diastolic mitral regurgitation as the source of the murmur.