Curtis S. Bergquist and Matthew A. Romano
This chapter is a revision and update of that included in previous editions of the TSRA Review written by Michael O. Kayatta (2nd edition) and Tom C. Nguyen (1st edition).
Pathophysiology
The vast majority of cases of mitral stenosis (MS) develop as a complication of rheumatic fever. Rheumatic heart disease develops as the mitral valve undergoes chronic inflammation and fibrosis as a complication of an autoimmune reaction that develops due to cross-reactivity to a Streptococcal antigen. This phase typically progresses over decades in the developed world, but can be faster in the developing world due to recurrent Group A Strep infections. Other causes of non-rheumatic MS include senile mitral calcification, congenital heart defects, and tumors. Mitral annular calcification, unlike rheumatic MS, is thought to be a degenerative process which increases with age in response to annular injury. In this situation, calcium builds in the mid hinge point of the posterior annulus and extends anteriorly towards the trigones and vertically into the left ventricle. Patients with severe mitral annular calcification (MAC) can also have calcification that extends onto the leaflets, but it does not lead to commissural fusion like in rheumatic MS. A parachute mitral valve (where the chords attach to a dominant papillary muscle) is a congenital defect seen in Shone complex and can cause significant MS. Atrial myxomas can cause physiologic MS if they become large and occlude the mitral orifice.
Diagnosis
Patients with MS can present with decreased exercise capacity, embolic events, atrial fibrillation, or be asymptomatic. Auscultation may reveal an opening snap after S2 followed by an apical diastolic murmur. Left atrial (LA) enlargement is the most common finding on CXR in patients with severe MS. A normal EKG is common in early MS, but in advanced MS, the P waves become wide, notched, and M-shaped. Detailed cardiac imaging is necessary for complete evaluation and procedural planning and should include transthoracic echocardiography (TTE), transesophageal echocardiography (TEE) and multi-detector computed tomography (MDCT). TTE is the modality most commonly used for diagnosis, and also provides important information about global heart function, other valvar abnormalities, pulmonary hypertension, or RV dilatation. TEE with 3D is used to provide detailed anatomic assessment of annular calcification, annular dimensions, leaflet anatomy and left ventricular outflow tract (LVOT) anatomy. MDCT, which consists of EKG gated CT angiography across multiple phases provides detailed anatomic reconstruction including degrees of MAC, annular dimensions, thickness, height, and extension of calcification into the LA and LV, and the aortomitral angle and LVOT anatomy. Additionally, MDCT enables placement of a virtual prosthesis and prediction of neo-LVOT area.
Staging of rheumatic MS
- A (at risk): Doming of valve during diastole but with no alterations in flow
- B (progressive): Commissural fusion, rheumatic valve changes; mitral valve area (MVA) >1.5 cm2 with mild-moderate LA enlargement
- C (asymptomatic severe): MVA <1.5 cm2, diastolic pressure half time >150 ms, severe LA enlargement, elevated pulmonary artery systolic pressure (>30 mmHg)
- D (symptomatic severe): Same as stage C but with decreased exercise tolerance and/or dyspnea
Treatment
In general, MS is not treated until it becomes symptomatic. Patients are routinely followed with transthoracic echocardiography at intervals corresponding to severity of stenosis and symptoms. The first-line therapy for symptomatic patients with severe MS (Stage D) is percutaneous mitral balloon commissurotomy (PMBC) as long as the valve morphology is favorable. The Wilkins score is commonly used to assess favorability; its components are leaflet mobility, valve thickness, subvalvar thickening, and valvar calcification. Stage C patients may be considered for PMBC if they develop atrial fibrillation. A stress echocardiography may be used to help identify those who are truly asymptomatic and help distinguish between Stage C and Stage D. Patients may develop recurrent MS after PMBC. They may be candidates for redo PMBC if echocardiography reveals re-fusions of the commissures.
Mitral valve surgery is recommended in Stage D patients when valve morphology is not favorable for PMBC or if there is a significant amount of mitral regurgitation (MR). It may also be considered if the patient is undergoing cardiac surgery for another cause, especially if valve morphology isn’t ideal for PMBC.
The 2020 ACC/AHA guidelines for treatmentare summarized below.
PMBC (all contingent on PMBC performed at Comprehensive Valve Center)
Class I:
- NYHA II-IV, Stage D, favorable morphology with less than moderate (2+) MR, no LA clot
Class IIa:
- NYHA I (asymptomatic), Stage C, favorable morphology with less than moderate (2+) MR, no LA clot, PAS >50 mmHg
Class IIb:
- NYHA I (asymptomatic), Stage C, favorable morphology with less than moderate (2+) MR, no LA clot, new onset afib
- NYHA II-IV with rheumatic MS and MVA >1.5 cm2, PA wedge >25 mmHg or mean mitral gradient >15 mmHg during exercise, can be performed at Comprehensive Valve Center
- NYHA III-IV, Stage D, suboptimal valve anatomy, not candidates / at high risk for surgery
Surgery
Class I:
- NYHA III-IV, Stage D, with 1) unfavorable valve morphology for PMBC (not candidate), 2) failed previous PMBC, 3) require other cardiac procedures, or 4) do not have access to PMBC
Patients with MS developing from severe MAC are not candidates for PMBC as the etiology is not commissural fusion. They may be considered for mitral valve surgery, though the advanced degree of MAC can make valve replacement difficult to impossible. Atrial to ventricular conduits can be considered in extreme cases. Congenital MS is typically treated surgically, and cardiac tumors causing MS are resected surgically as well.
Transcatheter mitral valve replacement for mitral stenosis is under clinical investigation. Currently there are 2 FDA approved trials that are enrolling patients with strict inclusion criteria. The devices under investigation are delivered transapically. However, total transfemoral devices are being developed and nearing feasibility trial status. Off-label use of aortic transcatheter valves in MAC have been reported (“valve-in-MAC”); however, the results from registry data have been quite poor.
Suggested Readings
- Otto CM, Nishimura RA, Bonow RO, et al. 2020 ACC/AHA Guideline for the Management of Patients with Valvular Heart Disease: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2021;143(5):e72-e227.
- Chapter 42 of Cohn’s Cardiac Surgery in the Adult, 5th edition.
- Abramowitz Y, Jilaihawi H, Chakravarty T, Mack MJ, Makkar RR. Mitral Annulus Calcification. J Am Coll Cardiol. 2015;66(17):1934-41.
