Mitral Stenosis

Presentation and Causes of Mitral Stenosis

Mitral stenosis (MS), also known as mitral valve stenosis, is a condition in which the opening between the left atrium and left ventricle of the heart, also known as the mitral valve orifice, is narrowed.¹ This condition is a type of valvular heart disease.¹ The narrowing of the mitral valve orifice can be caused by a number of issues, including infective endocarditis, mitral calcifications, congenital heart defects, and rheumatic heart disease.¹

Rheumatic heart disease mitral stenosis is the most common type of mitral stenosis. Symptomatic MS typically presents 20 to 40 years after the initial episode of rheumatic fever due to recurrent acute carditis that occurs in these patients.^1,2 In rheumatic heart disease, damage to the heart likely occurs because of a cross-reactive immune response that targets heart tissues while also targeting the streptococcal antigen that can be present during these infections.²

When the mitral valve heals after these recurrent episodes of inflammation associated with rheumatic heart disease, it also thickens. This leads to mitral stenosis and other associated changes within the heart over time.³ In developed countries such as the United States, the estimated incidence of rheumatic disease is 1 in 100,000.¹

Narrowing of the mitral valve orifice caused by MS creates an increase of pressure in the left atrium and the pulmonary vasculature.¹ This increase in pressure can then lead to sequelae such as pulmonary hypertension, increased size of the left atrium, atrial fibrillation, and heart failure.¹

Diagnostic Workup

The diagnostic workup of mitral stenosis includes noninvasive approaches (for example, auscultation, electrocardiogram [ECG], chest imaging, echocardiogram and exercise echocardiogram) and invasive approaches (for example, cardiac catheterization).¹

Because enlargement of the left atrium may be present in patients with MS, ECG findings may be consistent with left atrial enlargement.⁴ An increased P-wave area of greater than 24 ms x mv measured from ECG lead II typically indicates that atrial enlargement associated with mitral stenosis is present.⁴ The most common chest radiograph findings associated with mitral valvular disease include increased central density, enlargement in transverse diameter, widening of the carina, straightening of the left border, and others.⁵

However, the primary mode of evaluation for MS is echocardiography, because it allows for a detailed assessment of cardiac anatomy and hemodynamics in patients with mitral stenosis.³ Mitral stenosis grading is based on echocardiographic criteria and includes the Wilkins score, which assesses leaflet mobility, thickness, calcification, and subvalvular thickening, and the Padial score, which specifically grades mitral valve leaflet thickening.¹ The Wilkins score is reported as Grades 1 to 4 with Grade 1 having the best outcomes.¹

Echocardiography findings that are consistent with rheumatic disease include the presence of a commissural fusion, “fish mouth” appearance of the mitral valve orifice, leaflet thickening, and shortening and fusion of the chordae tendineae.² Occasionally, cardiac CT scanning or cardiac MRI may also be performed if echocardiography imaging quality is poor or to assess for associated coronary artery disease.³

Exercise echocardiography may be a helpful part of the diagnostic workup because it can unmask clinically or hemodynamically severe mitral stenosis in patients who report that they are asymptomatic at rest but have findings consistent with severe MS based on echocardiographic evaluation.²

Finally, diagnostic cardiac catheterization allows for direct measurement of pressures within the heart, which may be helpful in guiding selection of appropriate interventions.³ Diagnostic cardiac catheterization may also be performed if an assessment of associated coronary artery disease is needed.³

Differential Diagnosis of Mitral Stenosis

The differential diagnosis for mitral stenosis includes obstructive lesions such as left atrial myxoma and endocarditis.^1,2 Additionally, if the diagnosis is mitral stenosis, etiologies of MS should be differentiated.² These etiologies include rheumatic heart disease, mitral annular calcification, radiation valvulitis, prior surgery involving the mitral valve, congenital disease, and systemic inflammatory disorders.²

Relevant Measures & Metrics

Normally, the mitral valve area is 4 to 6 cm², and increased left atrial pressure typically develops when that area is less than 2cm². In fact, so long as the mitral valve orifice area is larger than 1.5 cm², patients are typically asymptomatic.³

Accordingly, measures for classifying the severity of mitral stenosis have been adapted from the ACC/AHA 2020 Valve Guidelines and include measurement of the mitral valve area ≤1.5 cm², diastolic pressure half-time ≥150 ms, and elevated pulmonary artery systolic pressure (PASP) >50mm Hg, in severe cases of MS.¹

Mitral Stenosis Complications & Risks

As mentioned above, mitral stenosis due to rheumatic heart disease is typically asymptomatic for decades after the initial episode of rheumatic fever.¹ Indeed, mitral stenosis itself is a complication of rheumatic fever and rheumatic heart disease, so appropriate medical management of Group A streptococcus pharyngitis with antibiotics is an important mode of prevention of the complication of MS.³

When symptoms of mitral stenosis do develop, the disease can progress quickly to complications such as pulmonary hypertension.¹ Another complication of mitral stenosis is atrial fibrillation.² Death can occur within three years in patients experiencing pulmonary hypertension.¹ Other most common causes of death related to MS are heart failure, abnormal valve anatomy and resultant turbulent blood flow across it, and thromboembolic complications.³

Management strategies for mitral stenosis include medical therapies (for example, diuretics and beta blockers for symptomatic relief) and interventions.² The procedure of choice for the management of MS is the percutaneous mitral balloon valvuloplasty, and eligibility is based on the echocardiography-determined Wilkins score discussed above.²

There are several contraindications to this procedure, including mitral valve area greater than 1.5cm², thrombus in the left side of the heart, mitral regurgitation that is more than mild, severe bi-commissural calcification, absence of commissural fusion, severe concomitant valve disease, or concomitant coronary artery disease requiring surgery.³ Surgical approaches are also available and include commissurotomy, mitral valve replacement, and mitral valve repair.²

References

1 .Shah S, Sharma S. Mitral stenosis. In: StatPearls. NCBI Bookshelf version. StatPearls Publishing: 2022. Accessed August 30, 2022.

2. Harb S, Griffin B. Mitral valve disease: a comprehensive review. Curr Cardiol Rep. 2017;19(73): 73.

3. Wunderlich N, Dalvi B, Ho S, Küx H, Siegel R. Rheumatic mitral valve stenosis: Diagnosis and treatment options. Curr Cardiol Rep. 2019;21(3):14. doi: 10.1007/s11886-019-1099-7

4. Zeng C, Wei T, Zhao R, Wang C, Chen L, Wang L. Electrocardiographic diagnosis of left atrial enlargement in patients with mitral stenosis: the value of the P-wave area. Acta Cardiol. 2003;58(2):139-41. doi: 10.2143/AC.58.2.2005266

5. Sultana H, Rahman M, Begum M, et al. Chest radiography in the evaluation of mitral valvular disease and its correlation with echocardiography. Mymensingh Med J. 2021;30(2):292-300.

Author Bio

Anna Courant is a nurse practitioner and writer.