Objectives: The aim of the study was to determine the mechanism of the Austin Flint murmur.
Background: More than 100 years after the initial description of the Austin Flint murmur, the etiology of the murmur remains unclear.
Methods: M-mode and two-dimensional echocardiography, conventional and color flow Doppler study, and cine nuclear magnetic resonance (cine NMR) imaging were performed in 24 patients with clinically moderate or severe aortic regurgitation. Mitral valve area was determined by planimetry and pressure half-time measurement. Overlap of the aortic regurgitation and mitral inflow jets was graded 0 (no overlap) to 4 (marked overlap) by Doppler study and cine NMR imaging. The volume of signal loss resulting from turbulent blood flow secondary to the aortic regurgitation jet was determined on cine NMR images, and the extent of contact with the left ventricular endocardium was graded 0 (no contact) to 4 (extensive contact).
Results: The presence of an Austin Flint murmur did not correlate with mitral valve area (2.7 +/- 0.8 cm2 with the murmur vs. 2.5 +/- 0.7 cm2 without), overlap of the aortic regurgitation and mitral flow jets (3 +/- 1 vs. 2.3 +/- 1.2), diastolic mitral regurgitation (50% vs. 71%) or fluttering of the anterior mitral valve leaflet (70% vs. 50%). The presence of an Austin Flint murmur correlated best with the volume of signal loss associated with the aortic regurgitation jet on cine NMR imaging (65 +/- 16 ml with the murmur. vs. 38 +/- 11 ml without, p less than 0.001) and the extent of contact of this signal loss with the left ventricular endocardium (2.9 +/- 0.5 vs. 1.5 +/- 0.4, p less than 0.0001).
Conclusions: The Austin Flint murmur is caused by the aortic regurgitation jet abutting the left ventricular endocardium, resulting in the generation of a low-pitched diastolic rumbling.