What is Systolic Anterior Motion (SAM)?

Systolic Anterior Motion (SAM) of the Mitral Valve

Systolic Anterior Motion (SAM) is defined as the abnormal anterior movement of the mitral valve leaflet toward the interventricular septum during systole, which can cause left ventricular outflow tract obstruction (LVOTO) and mitral regurgitation. 1

Pathophysiology and Mechanisms

• SAM occurs when the mitral valve leaflets are displaced anteriorly during systole, making contact with the interventricular septum and causing obstruction to blood flow 1
• Two principal mechanisms contribute to SAM:
  1. Septal hypertrophy with narrowing of the left ventricular outflow tract, creating abnormal blood flow vectors that dynamically displace the mitral valve leaflets anteriorly 1
  2. Anatomic alterations in the mitral valve and apparatus, including longer leaflets and anterior displacement of the papillary muscles, making the valve more susceptible to abnormal flow vectors 1
• SAM is likely attributable to a drag effect or possibly a Venturi phenomenon during high-velocity ejection 1

Clinical Significance

• SAM is most commonly associated with hypertrophic cardiomyopathy (HCM), where it occurs in approximately 75% of patients 1
• SAM can also occur in structurally normal hearts under certain conditions such as hypovolemia, excessive catecholamine states, or following mitral valve repair 2, 3, 4
• SAM results in:
  • Left ventricular outflow tract obstruction (LVOTO) 1
  • Mitral regurgitation (usually mild-to-moderate) due to incomplete leaflet coaptation 1
  • High intracavitary pressures 1
  • Impaired stroke volume 1
  • Increased risk of heart failure and poorer survival 1

Diagnosis

• Echocardiography is the primary diagnostic tool for identifying SAM 1
• On echocardiography, SAM is graded as:
  • None: Normal mitral valve cusp/leaflet motion
  • Mild: Mild abnormal anterior motion of the mitral valve cusp/leaflet toward the septum during left ventricular contraction
  • Moderate: Moderate abnormal anterior motion of the mitral valve cusp/leaflet toward the septum
  • Severe: Severe abnormal anterior motion of the mitral valve cusp/leaflet toward the septum 1
• A peak LVOT gradient ≥30 mm Hg is considered indicative of obstruction 1
• Provocative maneuvers may be necessary to elicit SAM in patients with low or absent resting gradients, including:
  • Standing
  • Valsalva maneuver
  • Exercise
  • Amyl nitrite inhalation 1

Clinical Manifestations

• SAM can produce a loud apical systolic ejection murmur 1
• Physical examination may reveal:
  • Harsh crescendo-decrescendo systolic murmur best heard over the lower left sternal border 1
  • Posteriorly directed mitral regurgitation murmur 1
  • Prominent point of maximal impulse that may be bifid or trifid 1
  • Carotid double pulsation (pulsus bisferiens) 1
  • Fourth heart sound (S4) due to a noncompliant left ventricle 1, 5

Management

• Treatment depends on the underlying cause and severity of symptoms 6, 4
• For SAM associated with HCM:
  • Medical therapy includes beta-blockers and calcium channel blockers to reduce contractility 6
  • Septal reduction therapy (surgical myectomy or alcohol septal ablation) may be considered for patients with drug-refractory symptoms and LVOT gradients ≥50 mm Hg 1
• For SAM in other settings (e.g., post-mitral valve repair, hypovolemia):
  • Volume loading to increase preload 2, 3, 4
  • Beta-blockers to reduce contractility 2, 4
  • Avoiding vasodilators and inotropes that can worsen obstruction 2, 3
  • Surgical correction may be required in refractory cases 6, 4

Prognosis

• SAM is associated with an increased risk of heart failure and mortality, particularly in patients with HCM 1
• In patients with HCM, outflow obstruction is a strong, independent predictor of disease progression to HCM-related death (relative risk vs. nonobstructed patients: 2.0) 1
• The risk of death due specifically to heart failure and stroke is even higher (relative risk vs. nonobstructed patients: 4.4) 1
• Most cases of SAM following mitral valve repair can be successfully managed with medical therapy 4