Circulation, Vol 83, 1940-1950, Copyright © 1991 by American Heart Association
PS Rahko
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.
ARTICLES
Doppler and echocardiographic characteristics of patients having an Austin Flint murmur
Department of Medicine, University of Wisconsin Medical School, Madison.
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