What are all the causes of systolic anterior motion (SAM) of the mitral valve?

Etiologies of systolic anterior motion of the mitral valve

Systolic anterior motion (SAM) of the mitral valve results from Venturi/drag forces acting on a mitral valve apparatus that is anatomically predisposed, in the setting of flow and loading conditions that permit anterior displacement into the left ventricular outflow tract (LVOT). [1,2]

The main causes can be grouped into (1) structural mitral valve/subvalvular apparatus abnormalities, (2) dynamic LVOT–predisposing cardiac physiology, and (3) iatrogenic or procedure-related alterations that create a susceptible mitral configuration. [1,2,3]

Predisposing mitral valve and subvalvular apparatus abnormalities

Hypertrophic obstructive cardiomyopathy (HOCM) with anatomic mitral–subvalvular features that promote SAM and LVOT obstruction. [1,2]
Elongated anterior mitral leaflet and excess functional anterior leaflet tissue, including elongated chordae that allow the anterior leaflet to protrude into the LV cavity during systole. [2,3,4]
Abnormal papillary muscle position or displacement that reduces effective chordal support and increases anterior leaflet displacement into the LVOT. [2,5]
Mispositioning or abnormal morphology of mitral valve components including elongation of leaflets/chordae and papillary muscle hypertrophy or aberrant insertion. [2]
Mitral valve prolapse with anatomically elongated or redundant tissue capable of moving anteriorly into the LVOT. [1,4]
Accessory mitral valve tissue that increases complexity of the mitral apparatus and can predispose to abnormal systolic motion. [2]

Dynamic LV physiology that permits SAM

Hyperdynamic LV function that increases the LVOT flow velocity and drag forces acting on the anterior mitral leaflet. [1,3]
Small LV cavity that increases intraventricular flow acceleration and promotes SAM. [1,2]
Reduced preload that makes SAM more permissive by reducing LV cavity size and loading. [1]
Increased inotropic state that enhances contractility and contributes to SAM permissiveness. [1]
Decreased afterload that facilitates LVOT flow conditions that promote SAM. [1]
Situations where physiological changes create an anatomically susceptible geometry plus permissive loading (reduced preload, increased inotropy, decreased afterload). [1]

Hypertrophic cardiomyopathy–associated SAM

HOCM with mitral SAM as a common contributor to LVOT obstruction, driven by the interaction between LVOT anatomy, mitral apparatus geometry, and high-velocity systolic flow. [1,3]

SAM after mitral valve repair

Post–mitral valve repair SAM due to residual or altered anterior leaflet length beyond the desired coaptation zone after repair, which can allow leaflet segments to float into the LVOT and generate SAM. [4]
SAM after mitral valve surgery in the presence of a permissive postoperative LVOT flow environment with altered leaflet tethering or coaptation geometry. [3,6]

SAM after aortic valve replacement in patients with predisposing LVOT geometry, where increased blood velocity through the LVOT and a small hypertrophied LV cavity contribute to SAM. [1]
SAM after transcatheter or surgical aortic valve interventions in the context of dynamic LVOT obstruction physiology that can coexist with severe mitral regurgitation driven by SAM. [7]

Summary list of clinical “causes” by mechanism

Underlying HOCM (most common disease-associated context) with mitral apparatus susceptibility. [1,2]
Mitral valve apparatus anatomy predisposing to anterior leaflet displacement (elongated anterior leaflet, elongated chordae, abnormal papillary muscle position). [2,3,4]
Permissive hemodynamics that create high-velocity LVOT flow and small LV cavity (reduced preload, increased inotropy, decreased afterload). [1,3]
Iatrogenic mitral configuration after repair that leaves residual anterior leaflet segment length and abnormal coaptation geometry enabling SAM. [4,6]
Iatrogenic or procedural LVOT flow states after aortic valve replacement/TAVR that create high LVOT velocity and dynamic obstruction physiology permitting SAM. [1,7]

Common clinical clarifications impacting “cause” designation

SAM can occur even without classic LV hypertrophy when mitral leaflet/subvalvular geometry and LVOT flow conditions permit anterior leaflet motion. [8]
SAM is not a static diagnosis of mitral valve disease alone. The same patient may show SAM only under permissive loading or contractility states. [1,8]
The mechanism of SAM is multifactorial and depends on geometric and flow interactions between the mitral apparatus and LVOT dynamics. [1,2,3]