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PARACHUTE MITRAL VALVE
     

This condition consist of the following anomalies:

1) a "parachute " deformity of the mitral valve,

2) supravalvular ring of the left atrium,

3) subaortic stenosis, and

4) aortic coarctation (figures 23a).


Figure 44g-1

The " parachute mitral valve" has the usual two mitral valvular leaflets and commissures, but the chordae, instead of diverging to insert into two papillary muscle, converge into one major papillary muscle (figure 44g-1 and figure 44g-2).


Figure 44g-2

The analogy to a parachute is suggested by the shape of the deformed valve. The mitral leaflets resemble the canopy of a parachute, the chordae, its shrouds or strings, and the papillary muscle, the harness. The chordae are often short and thick; this, coupled with theirconvergent papillary insertion,allows little mobility of the leaflets. The effect creates a stenotic mitral valve since the leaflets are held in close apposition. The only effective communication between the left atrium and the left ventricle is through the interchordal spaces. In aggregate these spaces did not allow free egress of blood from the left atrium.

The following (click here for video) and picture shows an example of a parachute mitral valve.

SUPRAVALVULAR RING OF THE LEFT ATRIUM

This entity is a circumferential ridge of connective tissue that arises at the base of the atrial surface of the mitral leaflets and protrudes into the inlet of the mitral valve. In the fully developed deformity it acts as a stenosing, perforated diaphragm. In some cases it protrudes only slightly and causes no obstruction to the egress of blood from the left atrium.


Background:

Supravalvar mitral ring is a rare congenital heart defect, of surgical importance, characterized by an abnormal ridge of connective tissue on the atrial side of the mitral valve. Often circumferential in shape, the supravalvar ring may encroach on the orifice of the mitral valve and may adhere to the mitral valve leaflets and restrict their movements. While a supravalvar mitral ring may allow normal hemodynamic flow from the left atrium to the left ventricle (LV), it often causes significant obstruction to mitral valve inflow.

While it can occur as an isolated defect, in nearly 90% of patients supravalvar mitral ring is found in combination with other congenital heart defects. Awareness of anatomic variations in patients with supravalvar mitral ring and preoperative recognition of the lesion are important.

Pathophysiology:

Supravalvar mitral ring is a circumferential ridge or membrane arising from the left atrial wall overlying the mitral valve and frequently attached to the mitral valve annulus. Variable in thickness and extent, it ranges from a thin membrane to a thick discrete fibrous ridge. The membranous variety may be difficult to detect, since the membrane often adheres to the anterior mitral valve leaflet while remaining just proximal to the posterior mitral leaflet. Adhesion to the valve may impair opening movement of the leaflets, and this may be the main mechanism of mitral valve inflow obstruction in some patients.

In others, the ring may be large enough to protrude into the mitral valve inflow and cause obstruction. The supramitral ring also may be incomplete and eccentric, allowing unobstructed flow through the mitral valve.

Supravalvar mitral ring rarely occurs as an isolated defect, and other congenital heart defects coexist in most (90%) patients. The mitral valve itself often is abnormal and stenotic at the valvar or subvalvar level with fusion of leaflets, small valve orifice, and abnormal papillary muscles being common abnormalities.

Shone syndrome describes a combination of 4 congenital heart defects: supravalvar mitral ring, parachute mitral valve, subvalvar aortic stenosis, and aortic coarctation.

Other common associated lesions in patients with supravalvar mitral ring are ventricular septal defect (VSD), patent ductus arteriosus (PDA), atrioventricular canal defect, and tetralogy of Fallot.

Less commonly associated defects include atrial septal defect, left superior vena cava, and Wolff-Parkinson-White syndrome. Lesions such as transposition of the great arteries and double outlet right ventricle uncommonly are complicated by the presence of a supravalvar mitral ring.

Obstruction to mitral inflow results from a reduction in mitral valve orifice area. When significant, a diastolic pressure difference occurs between the left atrium and LV. Left atrial and pulmonary venous pressures increase, leading to exudation of fluid into the pulmonary interstitium, which causes increased lung stiffness. Breathlessness and tachypnea are secondary to the interstitial edema and diminished pulmonary compliance. In severe cases, frank pulmonary edema can occur.

An associated atrial septal defect may decompress the left atrium, thereby reducing or masking severity of the mitral valve obstruction.

Associated lesions, such as VSD or PDA, which increase LV output, will exacerbate the manifestations of mitral inflow obstruction. Conversely, supravalvar mitral ring may be difficult to detect in the presence of conditions with diminished pulmonary blood flow, such as tetralogy of Fallot.

Persistently elevated pulmonary venous hypertension leads to pulmonary arterial hypertension, a rise in pulmonary vascular resistance, and eventually, failure of the right ventricle. Tricuspid regurgitation is a common accompaniment of right heart failure from pulmonary hypertension.

Frequency:

Internationally: No data are available on incidence of supravalvar mitral ring. In most patients, the supravalvar mitral ring is detected during investigation for other congenital heart disease (CHD).

Race: No specific race predilection exists.

Sex: No specific sex predilection exists.

Age: No specific age predilection exists.

History: Supravalvar mitral ring can be diagnosed in one of the following ways:

Supravalvar mitral ring most commonly is diagnosed as an associated finding in other CHD.

Supravalvar mitral ring occasionally may be found as the cause of congenital mitral stenosis (MS) in symptomatic children with dyspnea or pulmonary hypertension. The severity of symptoms depends upon the level of left atrial and pulmonary venous hypertension.

Most patients become symptomatic by age 2 years.

Rarely, this condition may be detected as an incidental finding in asymptomatic patients undergoing echocardiography for some unrelated reason.

Symptoms of supravalvar mitral ring with MS include one or more of the following:

1. Dyspnea, nocturnal cough, and tachypnea from pulmonary venous congestion and increased lung stiffness

2. Frequent respiratory infections and wheezing from pulmonary congestion, increased fluid exudation, and airway narrowing

3. Poor feeding, failure to thrive, fatigue, and sweating from heart failure and reduced cardiac output

4. Occasionally acute pulmonary edema or generalized edema

5. Hemoptysis and syncope in older patients

Physical: Physical signs in supravalvar mitral ring usually relate either to the associated CHD or to pulmonary arterial hypertension. Children with significant mitral obstruction frequently are quite sick, with tachypnea and respiratory distress. Diminished cardiac output and poor perfusion lead to a low volume pulse and peripheral cyanosis. Systemic venous pressure may be elevated with the development of congestive heart failure (CHF). A prominent parasternal heave indicates right ventricular hypertrophy from pulmonary hypertension.

The pulmonary component of the second heart sound is accentuated, Yet, unlike acquired mitral valvar stenosis, an opening snap of the mitral valve is not heard in supravalvar mitral ring. An apical middiastolic murmur of MS may be audible at the apex, especially in the left lateral decubitus, and it may exhibit presystolic accentuation. The murmur is very prominent when supravalvar mitral ring is associated with VSD or PDA, causing a large mitral inflow.

Patients with chronic mitral obstruction develop signs of tricuspid regurgitation and CHF, such as hepatomegaly, engorged neck veins, large expansile CV waves in the jugular venous pulse, and a systolic murmur that accentuates in inspiration at the lower left sternal border.


DIFFERENTIALS

 

Cor Triatriatum
Mitral Valve, Double Orifice


Other Problems to be Considered:

Pulmonary hypertension, congenital heart disease


Lab Studies:

No specific laboratory blood tests are required for diagnosis.

Imaging Studies:

1. Imaging studies are essential to define the anatomy of the ring and mitral valve, to assess the severity of obstruction, and to identify any associated defect before undertaking surgical treatment.

2. Chest x-ray

a. Left atrial enlargement, the most common abnormality on chest x-ray in patients with mitral obstruction, is diagnosed by the findings of straightening of the left cardiac border (mitralization), widening of the tracheal carina, and elevation of the left bronchus. In older children, the enlarged left atrium may be seen as a double density near the right cardiac border.

b. The left atrium tends to enlarge in a posterior direction. A barium-swallow study of the esophagus in lateral projection shows a rounded indentation of the anterior wall.

c. Prominent upper lobe pulmonary veins, increased interstitial markings, and Kerley lines indicate pulmonary venous hypertension. In severe cases, alveolar edema produces a hazy appearance in the hilar regions of both lung fields.

d. The pulmonary trunk and its branches become dilated with the rise in pulmonary arterial pressure. Cardiac contour reflects right ventricular hypertrophy.

3. Echocardiography

a. Two-dimensional echocardiogram with Doppler is the most important tool for the diagnosis and detailed assessment of patients with supravalvar mitral ring. It identifies the lesion and quantifies severity of the obstruction.

b. Perform a systematic and diligent scan of the mitral valve and left atrium, using multiple transthoracic views and paying particular attention to evaluate all components of the mitral valve apparatus. Use parasternal, apical, and subcostal views to visualize the mitral inflow region.

c. Using this technique allows the physician to view the supravalvar mitral ring and define its exact position, size, and extent, and to assess the relation of the ring to the mitral valve leaflets.

d. Occasionally, a thin membrane may so closely adhere to the valve leaflets that it is difficult to demonstrate by 2-dimensional echo. With an adherent membrane, the movements of mitral valve leaflets may be impaired, characterized by diminished excursions and a flattened E-F slope on motion mode (M-mode) echo of the mitral valve.

e. Inspect mitral valve chordae and papillary muscles for any associated abnormality. Exclude other associated defects, particularly subaortic stenosis, VSD, and coarctation of the aorta.

f. The pulmonary artery, right ventricle, and right atrium enlarge with the development of pulmonary arterial hypertension.

g. Use M-mode echocardiography of the pulmonary valve, which often shows such signs of pulmonary hypertension as an abbreviated A wave, midsystolic closure, and systolic flutter of pulmonary leaflets.

4. Doppler echocardiography

a. Doppler interrogation and color-flow mapping reveal the pattern of flow through the mitral valve, diagnose the presence and severity of obstruction, and demonstrate additional areas of abnormal flow in valvar or subvalvar mitral regions. The characteristic finding is turbulent flow with increased velocity across the supravalvar mitral ring into the mitral valve.

b. Quantify the severity of mitral obstruction by measuring the mean velocity of diastolic flow through the mitral valve. The mean diastolic velocity as well as the pressure half-time (time taken for the peak diastolic velocity to fall to half its initial value) correlate well with the severity of obstruction.

c. Measure the peak velocity of the tricuspid regurgitant jet in the right atrium for an estimate of systolic right ventricular pressure.

Other Tests:

5. Transesophageal echocardiography

a. Transesophageal echocardiography generally is not necessary to assess supravalvar mitral ring with obstruction in children, as adequate information can be obtained from transthoracic windows.

b. In older patients, heavily built individuals, and in patients with emphysematous chests, transesophageal study can provide additional, clear views to inspect all components of the supravalvar mitral ring and mitral valve.

c. Thrombi in the left atrium may be detected.

d. Intraoperative transesophageal echo is useful for patients of all ages to assess adequacy of repair in the operating room.

5. Electrocardiogram

a. The electrocardiogram in isolated supravalvar mitral ring demonstrates left atrial enlargement, right ventricular hypertrophy, and right atrial enlargement in proportion to the degree of obstruction.

b. Presence of additional defects will influence the electrocardiogram accordingly.

Procedures:

1. Cardiac catheterization

a. Cardiac catheterization is not necessary if echo provides all anatomic and hemodynamic data in patients with supravalvar mitral ring; however, it can provide additional information on the severity of mitral obstruction, especially in the presence of other associated CHD.

b. Proximal left atrial pressure and pulmonary venous pressure both are elevated. A pressure difference can be demonstrated in diastole between the left atrium and LV. Since entry into the left atrium may be difficult and require transseptal puncture, pressure recorded in the pulmonary artery wedge position usually is a reliable indicator of left atrial pressure.

c. Pulmonary artery pressure is elevated in chronic mitral obstruction. Associated shunts and other obstructive lesions also are identified and quantified at cardiac catheterization.

2. Cardiac angiography

a. With the availability of high-quality 2-dimensional and Doppler echocardiography, cardiac angiography has a limited role in the assessment of patients with supravalvar mitral ring. Echocardiography is superior to angiography in defining the anatomic and functional abnormality.

b. Left atrial angiogram in the caudally angulated right anterior oblique view and 4-chamber view may demonstrate the supravalvar mitral ring. A closely adherent ring may, however, be difficult to visualize and differentiate from valvar mitral stenosis, since the left atrium and appendage are enlarged and clearance of contrast from the left atrium into the LV is delayed.

c. An LV angiogram provides additional anatomic information about the mitral valve, ventricular septum, left ventricular outflow tract, and aortic arch.

TREATMENT

Medical Care: Evaluate patients with supravalvar mitral ring on an outpatient basis. Admit patients to the hospital for cardiac catheterization, treatment of severe heart failure or pulmonary edema, and for surgical treatment.

1 Goals of medical treatment

a. To relieve symptoms caused by pulmonary venous congestion and CHF

b. To stabilize the patientís condition before undertaking detailed assessment and surgical repair

c. To serve as an adjunct to surgical repair in the postoperative period

D. Control of heart failure by medical therapy may be the preferred option in small infants. Controlling CHF may permit deferral of surgery temporarily.

Surgical Care:

1. Goals of surgical therapy

a. Perform surgical repair in all symptomatic patients with supravalvar mitral stenosis to relieve the obstruction.

b. Perform an early operation for supravalvar mitral ring in the presence of severe heart failure, pulmonary edema, or pulmonary arterial hypertension.

c. Adjust the type of operation depending on the anatomy of the supravalvar ring and mitral valve apparatus and any associated congenital heart defect. Make every effort to define the anatomy in detail before undertaking surgery. In many patients, the supravalvar ring can be excised completely while any associated mitral valve abnormality is repaired simultaneously. If the supravalvar ring is densely adherent to the mitral valve leaflet or the mitral valve apparatus is grossly abnormal, replacement of the mitral valve may be necessary.

d. Selected cases of supravalvar ring with mitral stenosis may be amenable to balloon dilatation, but results are less successful than with operation.

2. Presence of a normal underlying mitral valve is associated with a better surgical outcome than with abnormal valve tissue.

a. In patients who require resection at an early age the prognosis is poor. Mortality is high, with risk of recurrent supravalvar mitral stenosis in survivors, probably because of continuing turbulence across the small LV inflow tract.

Consultations: Consult a cardiologist and cardiothoracic surgeon.

Diet:

1. No special diet is required in asymptomatic patients with supravalvar mitral ring.

2. Advise patients to avoid excess intake of salt or to reduce salt intake in the presence of heart failure. Use salt restriction cautiously in infants.

3. Restrict fluid intake to approximately 60-80 mL/kg/d in infants with CHF.

Activity: Advise patients with pulmonary venous congestion or CHF to avoid strenuous exertion. Asymptomatic children without pulmonary hypertension may participate in normal activities.


MEDICATION

 

 

Caption: Picture 1. Mitral stenosis, supravalvular ring. Seen here is a 2-dimensional echocardiogram in parasternal long-axis view showing a supravalvar mitral ring (small arrows) close to and adherent to the mitral valve leaflet (large arrow). The ring and the restricted opening of the mitral valve cause mitral obstruction. A large ventricular septal defect also is present. LA = left atrium, LV = left ventricle, AO = aorta, RV = right ventricle

 

 

 

 

Caption: Picture 2. Mitral stenosis, supravalvular ring. Seen here is a 2-dimensional echocardiogram with color flow imaging in the parasternal long-axis view showing turbulent flow (arrow) in diastole from left atrium (LA) to left ventricle (LV), caused by an obstructive supravalvar mitral ring. RV = right ventricle.

 

 

 

Caption: Picture 3. Mitral stenosis, supravalvular ring. This 2-dimensional echocardiogram in the apical view shows the supravalvar mitral ring (small arrows) adherent to the mitral valve leaflet (large arrow). LA = left atrium, LV = left ventricle, RA = right atrium, RV = right ventricle.

 

 

 

 

Caption: Picture 4. Mitral stenosis, supravalvular ring. This image is a 2-dimensional echocardiogram with color flow imaging in apical view showing turbulent flow (arrow) in diastole from left atrium (LA) to left ventricle (LV), caused by an obstructive supravalvar mitral ring. RA = right atrium, RV = right ventricle

 

 

 

 

Caption: Picture 5. Mitral stenosis, supravalvular ring. Simultaneous recording of pressures in the pulmonary artery wedge position (PAW) and the left ventricle (LV) shows a large gradient in diastole across the mitral valve. The PAW pressure is markedly elevated.

 

 

 

Picture 6. Mitral stenosis, supravalvular ring. Shown here is an M-mode echocardiogram of the mitral valve in a patient with supravalvar mitral ring causing obstruction. The mitral valve leaflets show diminished excursion and a markedly reduced E-F slope in diastole. RV = right ventricle, LV = left ventricle, MV = mitral valve.

SUBAORTIC STENOSIS

Two types of subaortic stenosis occur---the muscular and the membranous. The muscular type is characterized by localized protusion of hypertrophied ventricular septal tissue into the left ventricular outflow tract. The membraneous type is characterized by circumferential endocardial thickening in the left ventricular outflow tract. In some cases the two types co-exist.

COARCTATION of the AORTA

Coarctation of the aorta (figure 23a) may coexist as well.

Shoke,J.D.,and others,The Developmental Complex of "Parachute Mitral Valve",Supravalvular Ring of Left Atrium,Subaortic Stenosis,And Coarctation of Aorta,American Journal Cardiology,1963;11:714-725.

Brickner,M.E. and others,Congenital Heart Disease inAdults, N.Engl.J.Med., Vol.342.N.4, Jan.27,2000