Congenital Mitral Stenosis

Updated: Apr 29, 2014
  • Author: M Silvana Horenstein, MD; Chief Editor: Stuart Berger, MD  more...
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Overview

Background

The mitral valve is the inlet valve to the left ventricle (LV). The normal mitral valve is a complex apparatus composed of an annulus and 2 leaflets that are attached by chordae tendineae to 2 papillary muscles. The papillary muscles arise from the walls of the LV and secure the chordae and mitral leaflets, preventing prolapse of the valve during ventricular systole.

Proper function of the mitral valve requires an intact mitral valve apparatus and satisfactory LV function. Mitral stenosis (MS) results from any pathologic process that narrows the effective mitral valve orifice at the supravalvular, valvular, or subvalvular levels. MS can be congenital or acquired.

Congenital MS, a rare entity, takes several forms. These include hypoplasia of the mitral valve annulus, mitral valve commissural fusion, double orifice mitral valve, shortened or thickened chordae tendinae, and parachute mitral valve, in which all chordae attach to a single papillary muscle. The most common associated malformations are coarctation of the aorta, aortic valve stenosis, and subvalvular aortic stenosis. The association of multiple levels of left-sided inflow and outflow tract obstruction is termed the Shone complex.

Severe hypoplasia, or atresia, of the mitral valve results in a hypoplastic LV cavity size that is not capable of sustaining the systemic cardiac output. This situation is considered part of the spectrum of the hypoplastic left heart syndrome and is not considered further in this article. This article deals with MS that, although occasionally severe, allows enough blood flow into the LV to sustain the systemic cardiac output.

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Pathophysiology

MS obstructs blood flow into the LV, elevating left atrial pressure in proportion to severity of the stenosis. This, in turn, restricts pulmonary venous return to the left atrium, elevating pulmonary vascular and, consequently, right heart pressures. Elevated hydrostatic pressure in the pulmonary capillaries forces fluid into the alveoli and interstitial space, producing pulmonary congestion. Congested bronchial veins may encroach on small bronchioles, with subsequent increase in airway resistance.

As a compensatory mechanism, pulmonary vasoconstriction occurs. The right ventricle (RV) pressure increases, resulting in RV hypertrophy. Elevated pulmonary pressure can progress to fixed pulmonary arterial hypertension from medial hypertrophy and intimal thickening of the pulmonary arterioles. The RV eventually fails, and pulmonary blood flow decreases, decreasing systemic blood flow. If the reduction in cardiac output is critical, end organ failure with renal and/or hepatic insufficiency, shock, and metabolic acidosis can occur. RV failure results in systemic venous congestion with development of hepatomegaly, ascites, and pedal edema.

Hemodynamic changes in severe congenital MS are illustrated in the image below.

Hemodynamic changes in severe congenital mitral va Hemodynamic changes in severe congenital mitral valve stenosis (MS). MS causes an obstruction (in diastole) to blood flow from the left atrium (LA) to the left ventricle (LV). Increased LA pressures are transmitted retrograde to pulmonary veins and pulmonary capillaries, resulting in capillary leak with subsequent development of pulmonary edema. To overcome pulmonary edema, the arterioles constrict, increasing pulmonary pressures. With time, capillaries develop intimal thickening, causing fixed (permanent) pulmonary hypertension. The right ventricle (RV) hypertrophies to generate enough pressure to overcome the increased afterload. Eventually, the RV fails, which manifests as hepatomegaly and/or ascites, edema of the extremities, and cardiomegaly on radiography.
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Prognosis

Untreated newborns with severe MS have a grim prognosis. Surgical intervention is ideally avoided for as long as possible. Mechanical mitral valve replacement in a small infant or child is a high-risk procedure and carries a guarded prognosis.

Operative results and long-term outcome are widely variable and highly depends on the abnormalities that are present.

Mitral valve replacement entails a less than 5% mortality risk in young, healthy patients without other significant cardiac abnormalities.

Morbidity/mortality

In the fetus, mitral valve obstruction does not interfere with normal growth and development, even if the mitral valve is atretic. This is because the amount of pulmonary venous return to the left atrium is small and the fetal bronchocollateral circulation is adequate to relieve the obstructive effects. In this case, the RV supplies all of the systemic blood flow via the ductus arteriosus, and the patient presents with hypoplastic left heart syndrome.

Less severe forms of MS permit normal fetal circulatory pathways to continue with normal development of the LV and ascending aorta. After birth, if congenital MS is left untreated, morbidity and mortality are high, with mean survival estimated at 3 years. Associated cardiac lesions such as coarctation of the aorta and aortic valve stenosis such as in the Shone complex increase morbidity and mortality.

Complications

If MS is left untreated, the following complications may arise:

  • Pulmonary edema
  • Right heart failure with progression to congestive heart failure
  • Renal insufficiency (due to congestive heart failure)
  • Progression to pulmonary hypertension
  • Atrial arrhythmias: Atrial arrhythmias such as fibrillation or flutter occur more frequently in patients with chronic left atrial enlargement. Initiation and perpetuation of these arrhythmias has been attributed to a vertical line of conduction delay that runs between the pulmonary veins.
  • Thrombus formation in the dilated left atrium (due to stasis of blood)
  • Embolization of left atrial thrombus, stroke
  • Dysphagia from compression of esophagus by the enlarged left atrium

Complications of medical treatment include the following:

  • Diuretics may provoke dehydration (decreased preload) with subsequent compromise in cardiac output that may precipitate prerenal renal failure.
  • Warfarin may cause bleeding, such as intracranial hemorrhage and GI bleeding.

Complications of surgery include the following:

  • Mitral commissurotomy may cause significant postoperative mitral regurgitation, which may necessitate subsequent mitral valve replacement.
  • The risks of mitral valve replacement include those associated with anticoagulation, valve thrombosis, valve dehiscence, infective endocarditis, valve malfunction, and embolic events.

Complications of percutaneous balloon valvuloplasty include the following:

  • Safety depends on the mitral valve morphology and on the operator's experience. Very few forms of congenital MS are amenable to balloon valvotomy. Percutaneous balloon valvotomy should not be performed in patients with pre-existing moderate-to-severe mitral valve regurgitation.
  • The most frequent complication after percutaneous balloon valvuloplasty is mitral regurgitation.

Race

No racial predilection is known.

Sex

No sex predilection is known in congenital MS.

Age

Congenital MS is usually detected in infancy if MS and/or associated heart lesions are severe enough to produce physical findings or to provoke overt symptoms.

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Epidemiology

Frequency

United States

Congenital MS is rare, occurring in 0.5% of patients with congenital heart disease (CHD).

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