Mitral Stenosis
The murmur characterized by low-frequency (half frequency), an opening snap after S2, and occurring during early diastole is mitral stenosis.
Characteristic Acoustic Features
The classic auscultatory findings of mitral stenosis include:
Opening snap: A high-pitched sound occurring shortly after S2 (typically 40-110 msec after A2), produced when the stenotic mitral valve suddenly opens and the stiffened leaflets reach their maximal excursion into the left ventricle 1
Low-pitched middiastolic murmur: A rumbling, low-frequency murmur that occurs during early ventricular filling, reflecting the relative disproportion between the narrowed valve orifice and diastolic blood flow volume 1
Presystolic accentuation: In patients with sinus rhythm, the murmur may intensify just before S1 due to increased flow across the stenotic valve during atrial contraction 1
Anatomic Location and Radiation
Best heard at the cardiac apex (left ventricular apex) using the bell of the stethoscope with the patient in the left lateral decubitus position 2. The murmur typically does not radiate widely due to its low-frequency characteristics.
Pathophysiologic Mechanism
The middiastolic murmur results from turbulent blood flow across the narrowed mitral valve orifice during ventricular filling 1. The opening snap occurs when the stenotic valve leaflets, which are thickened and fused at the commissures, suddenly halt their opening motion as they reach maximal excursion 1.
Dynamic Auscultation Characteristics
Respiration: As a left-sided murmur, it becomes louder during expiration when venous return to the left heart increases 1, 2
Exercise: The murmur intensifies with both isotonic and isometric (handgrip) exercise due to increased flow across the stenotic valve 1
Positional changes: The murmur becomes louder with squatting or passive leg raising due to increased venous return 1
Important Clinical Pitfall
Do not confuse with the Austin-Flint murmur of severe chronic aortic regurgitation, which also produces a low-pitched, rumbling diastolic murmur at the apex. The critical distinguishing feature is that an opening snap is absent in isolated aortic regurgitation 1. The Austin-Flint murmur results from the regurgitant jet causing functional mitral stenosis by preventing full opening of the anterior mitral leaflet.
Clinical Significance
Mitral stenosis remains an important cause of morbidity and mortality, with rheumatic heart disease being the most common etiology worldwide, though degenerative calcific changes are increasingly recognized in developed countries 3. The presence of an opening snap with a middiastolic murmur warrants echocardiographic evaluation to confirm the diagnosis and assess severity 2.