What are the causes of mild Systolic Anterior Motion (SAM) of the Mitral Valve (MV) and can it be incidental?

From the Guidelines

Mild Systolic Anterior Motion (SAM) of the mitral valve can be caused by several conditions, including hypertrophic cardiomyopathy (HCM), and can sometimes be an incidental finding on echocardiography in patients without symptoms or significant cardiac disease. The causes of mild SAM are varied and can include mitral valve repair surgery, severe left ventricular hypertrophy from hypertension, dehydration, use of inotropic medications, and anatomical variations of the mitral valve apparatus 1. According to the 2020 AHA/ACC guideline for the diagnosis and treatment of patients with hypertrophic cardiomyopathy, LVOT obstruction, which is often associated with SAM, is present in approximately 75% of patients with HCM 1.

Key Points to Consider

• Mild SAM can be an incidental finding on echocardiography, but it should be evaluated by a cardiologist to determine its clinical significance 1.
• The severity of SAM can be classified as mild, moderate, or severe, with mild being defined as mild abnormal anterior motion of the mitral valve cusp/leaflet toward the septum during left ventricular contraction 1.
• Patients with mild incidental SAM typically do not require specific treatment but may benefit from follow-up echocardiograms to monitor for progression 1.
• If SAM is related to dehydration or medication effects, addressing these factors can resolve the finding, and for those with underlying structural heart disease, treatment would be directed at the primary condition 1.

Clinical Implications

The management of SAM, particularly in the context of HCM, involves identifying the site and characteristics of obstruction, which can be valvular, dynamic LVOTO, fixed subvalvular, or midcavitary due to hypertrophied/anomalous papillary muscles and/or hyperdynamic LV function with systolic cavity obliteration 1. The 2024 AHA/ACC/AMSSM/HRS/PACES/SCMR guideline for the management of hypertrophic cardiomyopathy recommends that obstruction is considered present if peak LVOT gradient is $30 mm Hg, and resting or provoked gradients $50 mm Hg are generally considered capable of causing symptoms 1. Therefore, it is crucial to evaluate and manage SAM in the context of the underlying cardiac condition to prevent progression and improve outcomes.

From the Research

Causes of Mild Systolic Anterior Motion (SAM) of the Mitral Valve (MV)

• Systolic anterior motion (SAM) of the mitral valve can be caused by various factors, including hypertrophic cardiomyopathy (HCM) 2, 3, mitral valve repair 4, and other conditions such as postural hypotension following left intrapericardial pneumonectomy 5.
• The mechanisms of SAM are complex and depend on the functional status of the ventricle, with the mitral leaflets partially obstructing the outflow tract of the left ventricle 6.
• SAM can occur in the normal population, but is typically observed in patients with HCM or following MV repair 3.

Incidental SAM

• Mild SAM can be incidental, as seen in a case report of a 29-year-old male with asymmetrically hypertrophied left ventricle and systolic motion of anterior mitral valve, which was incidentally discovered during elective non-cardiac surgery 2.
• In this case, the patient was asymptomatic, and the SAM was deemed non-significant, with a mean gradient of 10 mm Hg across the left ventricular outflow tract (LVOT) 2.
• The management of incidental SAM is typically conservative, with emphasis on close surveillance for signs and symptoms attributable to development of significant LVOT obstruction in patients with HCM 2.

Diagnosis and Assessment

• Echocardiography, including 2D and 3D imaging, has a central diagnostic role in assessing SAM, allowing for the identification of the anatomical location of the mitral valve apparatus involved in SAM and the assessment of consequent LVOT obstruction 2, 3.
• Transesophageal echocardiography (TEE) can also be used to diagnose SAM, particularly in cases where the condition is suspected but not clearly visible on transthoracic echocardiography (TTE) 2, 5.
• Computational fluid dynamics (CFD) and cardiac magnetic resonance imaging (MRI) can also be used to assess SAM and provide a better quantitative evaluation of the pathological condition 6.