SYSTOLIC ANTERIOR MOTION (SAM) OF THE MITRAL VALVE

SYSTOLIC ANTERIOR MOTION OF THE MITRAL VALVE

 

 

DEFINITION – SAM is defined as displacement of distal portion of anterior mitral leaflet towards the LVOT during systole.

 

Termini et al described it first as a complication of MV repair

Incidence is 1-16%

It leads to – LVOT Obstruction, Residual MR, Decreased cardiac output.

 

 

MECHANISM OF SAM –

 

 2 mechanisms – Venturi effect and Drag effect

 

Both describe the AML being drawn into LVOT by pulling(venturi) or pushing (drag)

As LV contracts and ejects blood into aorta it creates drag or push on redundant AML drawing its tip in outflow tract creating turbulence to flow that further creates a venturi or pull effect on AML resulting in MR.

Once the mitral valve touches the septum à a narrowed orifice occurs. Pressure difference across the orifice becomes the new hydrodynamic force across the mitral leaflet. This pressure difference pushes the leaflet further into the septum, narrowing the orifice further

 

Three features are necessary for SAM, mitral-septal contact and obstruction:

 

• anterior position of mitral coaptation
• an angle of flow onto the mitral valve, such that flow gets behind the mitral valve (angle of attack)
• chordal slack

 

 

It develops in myxomatous MR when the coaptation point to the septal distance is reduced.

And  is caused by long PML pushing the coaptation point towards the septum

Anterior and inward displacement of papillary muscles bring coaptation point closer to LVOT.

The coaptation length of mitral leaflets is also important.

 

 

CHORDAL SAM –

 

• Systolic anterior motion of the mitral chordae
• Chordal SAM is  transient, benign, and should be differentiated from leaflet systolic anterior motion after mitral annuloplasty  
• Chordal anomalies like elongation and buckling and redundant chordae cause chordal SAM
• Also,surgical interventions on the chordae such as transection,translocation,reimplantation can lead to SAM.
• Leaflets do not “touch” the interventricular septum nor cause a subaortic gradient in chordal SAM

 

 

“FUNCTIONAL” SAM –

 

has also been described in association with pheochromocytoma, induction of general anaesthesia, catecholamine infusion and hypovolaemia in critical patients,hypertensive heart disease, diabetes mellitus, acute myocardial infarction, after mitral valve repair and even in asymptomatic patients during pharmacologic stress with dobutamine.

 

 

GRADING OF SAM -

 

Grade 1 – AML buckling towards LVOT 10 mm away from septum

Grade 2 - AML buckling towards LVOT within 10 mm  from septum

Grade 3 - AML buckling and touching septum but less than 30% of systole

Grade 4 - AML buckling and touching septum but more than 30% of systole

 

 

SEVERITY OF SAM –

 

Mild – No LVOTO, Negligible MR – medical management

Moderate – Pmax – 20 -50 mmHg,Moderate MR – Surgical management

Severe – Pmax >50 mmHg, Severe MR -  Surgical management

 

 

HEMODYNAMIC CONSEQUENCES OF SAM -

 

• Prolongation of systolic ejection
• Reduction in stroke volume
• Disrupts MV functioning ® Mitral Regurgitation
• Diastolic dysfunction
• Microvascular dysfunction
• Intolerant to tachyarrythmias

 

 

PREDICTORS OF SAM -

 

Physiologic conditions –

 

Hyperadrenergic state

Decrease preload

Decreased afterload

 

Mitral Valvular factors –

 

Large AML with redundant tissue

Anterior displacement of leaflet coaptation point

AL/PL length ratio < or = 1.3

PL length > 15 mm

Coaptation point – septum distance < or = 25 mm

Anterior displacement of the papillary muscle

Inappropriately sized mitral annuloplasty ring

Chordal anomaly

 

Ventricular factors –

 

Basal ventricular septum > 15mm

Aorto-mitral angle (<120 degrees)

Hyperdynamic LV

Bulging septum

Small LVID in systole

 

Clinical Conditions –

 

Hypertrophic CMP

Post mitral valve repair surgery

Post aortic valve replacement surgery

Dobutamine pharmacologic stress test

Hypertensive heart disease

Acute myocardial infarction

Pheochromocytoma

Diabetes mellitus

 

 

FACTORS ACCENTUATING SAM –

 

Hypovolemia

Excessive afterload reduction – vasodilators , anesthetic agents

Hyperdynamic ventricular function – increased sympathetic tone, inotropes

 

 

TREATMENT OF SAM –

 

Volume loading

β-blockade

Vasoconstriction

Disopyramide

Surgery –

• Sliding posterior leaflet valvuloplasty to move the coaptation point to a more posterior location, thus keeping the anterior leaflet redundancy from obstructing the LVOT
• Reduce the height of PML.This moves the coaptation point away from interventricular septum
• Edge-to-edge repair of sewing A2 to P2, creating a double-orifice mitral valve.
• Assymetric Alfieri stitch 
• Posterior leaflet ventricularization 
• Modified sliding leaflet technique 
• Posterior leaflet folding plasty 
• Loop technique - Artificial chordae used 
• Chordal translocation - PML secondary chordae are transected and moved to the AML 
• Removal of excess AML tissue
• AML retention plasty 
• Annular enlargement 
• Annular plication 
• Ultimately, valve replacement.

 

 

SAM in HOCM –

 

Thickened interventricular septum and abnormal chordal attachment to AML in presence of hypertrophied and hypercontractile ventricle results in SAM. Here, drag phenomenon is important role than venture.

In HOCM, SAM begins before initiation of ventricular ejectionperhaps reducing the importance of venture effect.

HOCM has septal hypertrophy, D shaped LV altering MV anatomy,papillary muscles displaced anteriorly and inward all lead to SAM

 

 

CONDITIONS in which SAM may occur are  -

 

• hypertrophic cardiomyopathy
• membranous subaortic stenosis
• dextraposition of the great vessels with subpulmonic obstruction
• pulmonary hypertension
• concentric left ventricular hypertrophy
• hyperkinetic states(including aortic insufficiency and hypovolemia)
• mitral valve prolapse

 

 

References –

 

Julius M. Gardin Systolic Anterior Motion in the Absence of Asymmetric Septal Hypertrophy A Buckling Phenomenon of the Chordae Tendineae Circulation 63, No. 1, 1981.

 

Edmund Kenneth Kerut Mitral Systolic Anterior Motion (SAM) with Dynamic Left Ventricular Out?ow Obstruction Following Aortic Valve Replacement.Echocardiography, Volume 24, July 2007

 

Cohen DJ Systolic anterior motion of the chordal apparatus after mitral ring insertion. Am Heart J 1992 Sep;124(3):666-70.

 

Devin W. Kehl Medical Management (β Blocker ± Disopyramide) of Left Ventricular Outflow Gradient Secondary to Systolic Anterior Motion of the Mitral Valve After Repair.The American Journal of Cardiology Volume 118,Issue 7,1 October 2016, Pages 1053–1056

 

Mukul Chandra Kapoor Systolic anterior motion of the mitral valve in hypovolemia and hyper-adrenergic states. Indian J Anaesth 2014 Jan-Feb; 58(1): 7–8.

 

Robin Varghese et al Management of systolic anterior motion after mitral valve repair: An algorithm.The Journal of Thoracic and Cardiovascular Surgery Volume 143,Issue 4,Supplement, April 2012, Pages S2–S7

 

Michael Ibrahim Modern management of systolic anterior motion of the mitral valve Eur J Cardiothorac Surg (2012) 41 (6): 1260-1270.

 

Leonid Sternik Systolic Anterior Motion of the Mitral Valve after Mitral Valve Repair A Method of Prevention. Tex Heart Inst J.2005; 32(1): 47–49.

 

Problem-Based Tranesophageal Echocardiography – Deepak K. Tempe

 

Comprehensive Textbook of Perioperative Transesophageal Echocardiography – Robert M.Savage

 

Mark V Sherrid Obstructive hypertrophic cardiomyopathy: echocardiography, pathophysiology, and the continuing evolution of surgery for obstruction.The Annals of Thoracic Surgery Volume 75,Issue 2,February 2003, Pages 620-632.

- by Dr Amarja