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:
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 –
“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 -
PREDICTORS OF SAM -
Physiologic conditions –
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
Ventricular factors –
Basal ventricular septum > 15mm
Aorto-mitral angle (<120 degrees)
Small LVID in systole
Clinical Conditions –
Post mitral valve repair surgery
Post aortic valve replacement surgery
Dobutamine pharmacologic stress test
Hypertensive heart disease
Acute myocardial infarction
FACTORS ACCENTUATING SAM –
Excessive afterload reduction – vasodilators , anesthetic agents
Hyperdynamic ventricular function – increased sympathetic tone, inotropes
TREATMENT OF SAM –
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 -
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.