From the Guidelines
An Austin Flint murmur is caused by severe, chronic aortic regurgitation (AR) leading to a low-pitched, rumbling diastolic murmur at the left ventricular (LV) apex. This condition occurs when the backward flow of blood from the aorta, due to a leaky aortic valve, interferes with the normal functioning of the mitral valve, resulting in turbulent blood flow and the characteristic murmur. According to the 2008 focused update incorporated into the ACC/AHA 2006 guidelines for the management of patients with valvular heart disease 1, an Austin Flint murmur may be either mid-diastolic or presystolic and is often present in patients with severe, chronic AR. The murmur is typically heard best at the cardiac apex and can mimic mitral stenosis, although no actual mitral valve narrowing exists. Key characteristics of the Austin Flint murmur include:
- Low-pitched, rumbling sound
- Mid-to-late diastolic timing
- Best heard at the cardiac apex
- Associated with severe, chronic aortic regurgitation
- Can mimic mitral stenosis without actual mitral valve narrowing. The severity of the Austin Flint murmur typically correlates with the degree of aortic regurgitation, as noted in the guidelines 1.
From the Research
Causes of Austin Flint Murmur
The Austin Flint murmur is a mid-diastolic murmur that occurs in patients with severe aortic regurgitation. The causes of this murmur can be attributed to the following factors:
- Mechanical interaction between the aortic regurgitant jet and the anterior mitral leaflet opening, as depicted by two-dimensional color Doppler echocardiography 2
- Geometric and hemodynamic consequences of the regurgitant jet, which can be understood using three-dimensional transesophageal echocardiography 2
- High-frequency diastolic oscillation of the anterior mitral leaflet, which is a common echocardiographic feature in aortic regurgitation, although its presence does not correlate with the Austin-Flint murmur 3
- Reflux of blood from the aorta into the left ventricle during diastole, which is characteristic of aortic regurgitation 4
Echocardiographic Features
Echocardiography is a key diagnostic tool for determining the severity of aortic regurgitation and the presence of an Austin Flint murmur. The following echocardiographic features are associated with severe aortic regurgitation and may be related to the Austin Flint murmur:
- Early mitral valve closure
- Diastolic flutter
- Absence of the a-wave 5
- Premature mitral valve closure, i.e., a negative QC time 5
Theories and Mechanisms
Several theories have been proposed to explain the mechanism of the Austin Flint murmur, including the interaction between the aortic regurgitant jet and the mitral valve leaflets 2, 6. However, the exact mechanism is not fully understood and may involve complex geometric and hemodynamic factors.