What is the murmur typically heard with Systolic Anterior Motion (SAM)?

Murmur Typically Heard with Systolic Anterior Motion (SAM)

The murmur typically heard with Systolic Anterior Motion (SAM) is a midsystolic, crescendo-decrescendo murmur that results from left ventricular outflow tract obstruction (LVOTO). 1, 2

Characteristics of SAM-Associated Murmur

• SAM causes dynamic left ventricular outflow tract obstruction as the mitral valve leaflet(s) move toward the interventricular septum during systole 1, 2
• The resulting murmur is typically midsystolic (systolic ejection) with a crescendo-decrescendo configuration 1
• The murmur is usually grade 2-3/6 or higher in intensity, depending on the severity of obstruction 1
• It is best heard at the left sternal border and apex 1
• The murmur may be accompanied by mitral regurgitation due to incomplete leaflet coaptation caused by the anterior motion of the mitral valve 1, 2

Pathophysiology of SAM

• SAM most commonly occurs in hypertrophic cardiomyopathy (HCM) but can also occur in structurally normal hearts or after mitral valve repair 1, 2, 3
• The mechanism involves either a drag effect or possibly a Venturi phenomenon that pulls the mitral valve leaflet(s) toward the septum 1
• SAM results in both subaortic obstruction and concomitant mitral regurgitation, which is typically directed posteriorly into the left atrium 1
• When the mitral regurgitation jet is directed centrally or anteriorly, or if multiple jets are present, additional intrinsic mitral valve abnormalities should be suspected 1

Dynamic Auscultation Findings

• The murmur of SAM typically increases with maneuvers that decrease left ventricular volume or increase contractility 4
• Standing from a squatting position will increase the murmur intensity 4
• Valsalva maneuver will increase the murmur intensity, unlike most other systolic murmurs which decrease 4
• The murmur decreases with squatting, handgrip, or other maneuvers that increase afterload or ventricular volume 1, 4

Clinical Significance and Management

• SAM with significant LVOTO (gradient ≥30 mmHg) is pathophysiologically important and associated with disease progression 1
• In critical care settings, SAM can occur in patients with hyperdynamic left ventricles, especially those on vasopressors 2
• Management typically includes volume loading, beta-blockers, and reducing inotropic agents if present 2, 5
• In cases following mitral valve repair, most patients with SAM can be successfully treated medically 3
• Severe or persistent SAM may require surgical intervention, especially if associated with structural valve damage 6, 5

Differential Diagnosis

• The midsystolic murmur of SAM must be differentiated from other causes of midsystolic murmurs, such as aortic stenosis, innocent flow murmurs, and functional mitral regurgitation 1
• Echocardiography is essential for confirming the diagnosis of SAM and assessing the degree of LVOTO and associated mitral regurgitation 1, 2
• The dynamic nature of the murmur with positional changes and Valsalva maneuver helps distinguish it from fixed obstructions like valvular aortic stenosis 4