Congenital Mitral Stenosis

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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.

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.

The etiology of congenital MS remains unknown. However, prevalence of MS in offspring of family members (especially the mother) with left ventricular outflow tract obstruction is increased.

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

No racial or sex predilection is known in congenital MS.

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.

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.

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.

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.

Counsel the patient and families regarding the appearance and worsening of symptoms.

Prior to any invasive or surgical application, advise the patient regarding subacute bacterial endocarditis prophylaxis.

Monitor prothrombin time (PT) and international normalized ratio (INR) if the patient is on anticoagulation medication.

Advise pregnant mothers to avoid taking warfarin, avoid strenuous activity and excessive salt intake, and have their blood pressure frequently monitored.

For patient education resources, see the Heart Health Center, as well as Mitral Valve Prolapse.

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M Silvana Horenstein, MD Assistant Professor, Department of Pediatrics, University of Texas Medical School at Houston; Medical Doctor Consultant, Legacy Department, Best Doctors, Inc

M Silvana Horenstein, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American Medical Association

Disclosure: Nothing to disclose.

Henry Walters, III, MD Associate Professor of Surgery, Wayne State University School of Medicine; Chief, Department of Surgery, Division of Cardiovascular Surgery, Children’s Hospital of Michigan

Henry Walters, III, MD is a member of the following medical societies: Alpha Omega Alpha, American Association for Thoracic Surgery, American Medical Association, International Society for Heart and Lung Transplantation, Phi Beta Kappa, Society of Thoracic Surgeons

Disclosure: Nothing to disclose.

Michael D Pettersen, MD Consulting Staff, Rocky Mountain Pediatric Cardiology, Pediatrix Medical Group

Michael D Pettersen, MD is a member of the following medical societies: American Society of Echocardiography

Disclosure: Received income in an amount equal to or greater than $250 from: Fuji Medical Imaging.

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Julian M Stewart, MD, PhD Associate Chairman of Pediatrics, Director, Center for Hypotension, Westchester Medical Center; Professor of Pediatrics and Physiology, New York Medical College

Julian M Stewart, MD, PhD is a member of the following medical societies: American Academy of Pediatrics, American Autonomic Society, American Physiological Society

Disclosure: Received research grant from: Lundbeck Pharmaceuticals<br/>Received grant/research funds from Lundbeck Pharmaceuticals for none.

Stuart Berger, MD Executive Director of The Heart Center, Interim Division Chief of Pediatric Cardiology, Lurie Childrens Hospital; Professor, Department of Pediatrics, Northwestern University, The Feinberg School of Medicine

Stuart Berger, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American College of Chest Physicians, American Heart Association, Society for Cardiovascular Angiography and Interventions

Disclosure: Nothing to disclose.

Ira H Gessner, MD Professor Emeritus, Pediatric Cardiology, University of Florida College of Medicine

Ira H Gessner, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American Heart Association, American Pediatric Society, Society for Pediatric Research

Disclosure: Nothing to disclose.

Congenital Mitral Stenosis

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