American physician Austin Flint first described his namesake murmur in 1862. In his own poetic words: "The murmur is oftener rough than soft. The roughness is often peculiar. It is a blubbering sound, resembling that produced by throwing the lips or the tongue into vibration with the breath of respiration."
The murmur is best described in modern terms as a low-pitched mid to late diastolic rumble heard best at the apex of the heart and is associated with severe aortic regurgitation.
An echocardiogram-based study found the Austin Flint murmur was not associated with rapid mitral inflow, as others had previously suggested. The authors concluded that the murmur resulted from the regurgitant aortic jet alone. Another study of echocardiogram findings found that the sound auscultated resulted from the abutment of the aortic regurgitant jet against the left ventricular epicardium. A prior study had suggested that the Austin Flint murmur arose from a regurgitant aortic jet directed at the anterior mitral leaflet resulting in shuddering of the leaflet. The authors hypothesized that this shuddering resulted in vibrations and shock waves that ultimately distorted the regurgitant aortic jet and caused the familiar sound heard in the Austin Flint murmur. Ultimately, there is no consensus about the cause of the sound auscultated as the Austin Flint murmur.
One would expect the prevalence of the Austin Flint murmur to correlate with that of severe aortic regurgitation. In the Framingham study, the incidence of moderate to severe aortic regurgitation was less than 1% in age groups under 70 years old. In the 70 to 83-year-old age group, the incidence was 2.2% for men and 2.3% for women. However, not all patients with severe aortic regurgitation will have an Austin Flint murmur; therefore, the true prevalence of the murmur is currently unknown.
In developing countries, the most common cause of aortic regurgitation remains rheumatic heart disease. In developed countries, aortic regurgitation occurs most often in young patients with a bicuspid aortic valve and in advanced age when the burden of calcific aortic disease is at its highest.
The Austin Flint murmur is a rumbling diastolic murmur best heard at the apex of the heart that is associated with severe aortic regurgitation and is usually heard best in the fifth intercostal space at the midclavicular line. Younger patients are more likely to have a history of a bicuspid aortic valve or rheumatic heart disease, while older patients are more likely to suffer from calcific valvular disease. A blood pressure reading on the patient will show an increased pulse pressure (systolic blood pressure, diastolic blood pressure) due to the backflow of blood through the aortic valve during diastole. You may be able to palpate a "water hammer" pulse, which is also known as "Corrigan's pulse." This finding characterized demonstrates arterial swelling followed by a brisk diastolic fall.
Patients may endorse a history of syncope or lightheadedness associated with an inability to maintain forward flow through the aortic valve and the significant difference between systolic and diastolic pressure. Decreasing exercise tolerance and the inability to perform activities of daily living are screening criteria for all patients.
The most appropriate test to order in a patient with an Austin Flint murmur is a transthoracic Doppler echocardiogram. A cardiac MRI indicates if the echocardiogram images are suboptimal due to body habitus. In severe asymptomatic aortic regurgitation, the AHA/ACC recommends yearly monitoring with a transthoracic echocardiogram. This monitoring interval should be shortened in patients that remain asymptomatic despite LV dilation.
Treatment and management of a patient with an Austin Flint murmur are the same as other patients with severe aortic regurgitation regardless of whether there is auscultation of an Austin Flint murmur. Medical management consists of treating hypertension with afterload reducing agents such as dihydropyridine calcium channel blockers or angiotensin-converting enzyme inhibitors/angiotensin receptor blockers.. Definitive management is with aortic valve replacement. Metallic prosthetic valves are a preferred choice in younger patients who can tolerate anticoagulation due to increased longevity compared to bioprosthetic valves.. Elderly patients and patients with contraindications to anticoagulation should undergo implantation of bioprosthetic valves, which do not require the same lifelong anticoagulation therapy as a metallic valve. Patients who are poor surgical candidates, as determined by calculating the Society of Thoracic Surgeons' cardiac risk score (STS score), can be evaluated for the implantation of a transcatheter aortic valve replacement.
The Austin Flint murmur can be differentiated from organic mitral stenosis by the presence of an opening snap in mitral stenosis. Further differentiation is achievable with amyl nitrate inhalation, which will decrease the intensity of the Austin Flint murmur due to a decrease in afterload. The murmur of mitral stenosis will increase in both duration and intensity with amyl nitrate inhalation.
The prognosis of patients with severe aortic regurgitation associated with the Austin Flint murmur depends on a variety of factors. Within ten years of diagnosis of severe aortic regurgitation, 75% of patients will either pass away or require valve replacement. Predictors of survival include: age, functional class, comorbidities, atrial fibrillation, and left ventricular end-systolic diameter corrected for body surface area. Those with severe left ventricular dysfunction have a survival rate of 62% compared to 96% in patients with preserved left ventricular function.
The first consultation for a patient with an Austin Flint murmur should be with a cardiologist. The cardiologist can medically manage the patient while they coordinate care with prompt referral to a cardiothoracic surgeon for evaluation of surgical aortic valve replacement. If the patient is not a candidate for a surgical aortic valve replacement due to an elevated STS score, an interventional cardiologist trained in structural heart disease should provide a consult to evaluate the patient for a transcatheter aortic valve replacement.
The auscultation of an Austin Flint murmur in a patient correlates with that patient having severe aortic regurgitation. Coordinated care between the cardiologist, cardiothoracic surgeon, and an interventional cardiologist is integral in managing these complex patients. In patients that are candidates, surgical aortic valve replacement is the gold standard. [Level 1] In patients with prohibitively high STS scores, the surgeon should discuss the option for a transcatheter aortic valve approach with the patient. [Level 1]
The recovery time from an aortic valve replacement is 4 to 8 weeks. The most important factors in recovery are nutrition and exercise. Nutritional guidance should be provided before discharge, and follow up with a nutritionist after discharge may be beneficial in high-risk patients. When anticoagulation is appropriate, a board-certified cardiology specialty pharmacist should also provide input. Patients that are elderly or with significant comorbidities benefit from cardiac rehabilitation, which has shown to increase aerobic capacity and quality of life. [Level 1]
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