SECTION V - LEFT VENTRICULAR OUTFLOW TRACT OBSTRUCTION & BICUSPID AORTIC VALVE

Part l - Background Information

Definition: This section concerns left ventricular outflow tract obstruction (LVOTO) in the setting of concordant atrioventricular and ventriculoarterial connections. (Neither hypertrophic cardiomyopathy nor interrupted aortic arch will be considered here.)

LVOTO can occur at several levels:

• Supravalvar LVOTO may occur rarely in isolation as an hourglass deformity. It is more often diffuse however, involving the major arteries to varying degrees and begins at the superior margin of the sinuses of Valsalva.
• Valvar LVOTO in the adult patient with CHD is usually due to bicuspid aortic valve (rheumatic and trileaflet calcific aortic stenosis are excluded here). It usually occurs in isolation but is associated with other abnormalities, the most common being coarctation of the aorta (which should be sought), PDA, or ascending aortopathy.
• Subvalvar LVOTO is usually either a discrete fibromuscular ridge which partially or completely encircles the left ventricular outflow tract or is a long fibromuscular narrowing beneath the base of the aortic valve. Occasionally, there is a tunnel-like narrowing of the whole left ventricular outflow tract with a small aortic root. Rarely, abnormal insertion of the mitral valve or accessory mitral leaflet may cause significant obstruction.

The concurrence of both left ventricular inflow tract obstruction (including supravalvar mitral ring, parachute mitral valve) and left ventricular outflow tract obstruction (including subvalvar LVOTO, bicuspid aortic valve and aortic coarctation) is known as Shone syndrome.

 
Part II - Prevalence and Genetics

Supravalvar LVOTO is usually part of Williams syndrome, which is a contiguous gene syndrome associated with neurodevelopmental and multisystem manifestations caused by a deletion at chromosome 7q11.23, but may be familial with normal facies, or associated with rubella syndrome.

Bicuspid aortic valve is the most common congenital cardiac anomaly occurring in 1-2% of the population with a male predominance (4:1).

Subvalvar LVOTO has also a male predominance (2:1). A genetic predisposition has been suggested as there are reports of a familial incidence.

 
Part III - History and Management of Unoperated Patients

Supravalvar LVOTO is usually progressive and aortic regurgitation is common. With Williams syndrome, there are often associated peripheral pulmonary artery or systemic arterial (including coronary ostial) stenoses, which may worsen, resolve or remain unchanged. Systemic hypertension is common.

Valvar LVOTO commonly progresses as the patient grows but the rate is variable. Some patients with bicuspid aortic valve will not experience any problems, although there is the lifelong risk of endocarditis. Others will develop aortic stenosis (especially after calcification of the valve in the sixth decade), aortic regurgitation, aortic dissection or aneurysmal aortic root dilation (irrespective of altered hemodynamics or age) (51,52). If there is associated coarctation, this should usually be dealt with first (unless there is critical LVOTO; if both are severe, they may be dealt with at one operation via an anterior approach with an ascending to descending aortic graft and concomitant aortic valve replacement).

Subvalvar LVOTO often progresses, but the rate is variable, and low gradients may remain for many years. It is often associated with aortic regurgitation (up to 60% of cases) through an otherwise normal valve which has been damaged by the subvalvar jet of blood. It may also progress, but seldom becomes more than moderate. There may be associated small VSDs. These patients are particularly prone to endocarditis. Tunnel-like subvalvar LVOTO is progressive and requires surgery for relief of obstruction although this may be technically difficult because the aortic root is small. Subvalvar LVOTO may occur with a variety of associated lesions.

 
Part IV - Diagnostic Work Up

An adequate initial workup:

• Documents the level(s) of obstruction.
• Quantitates the severity and anatomy of the obstruction(s).
• Identifies associated abnormalities including aortic regurgitation, proximal aortic dilation, aortic coarctation and the associated anomalies of Williams and Shone syndromes.

The diagnostic workup should include at a minimum:

• A thorough clinical assessment.
• ECG.
• Chest x-ray.
• Transthoracic echo-Doppler examination by an appropriately trained individual to determine the level(s) of obstruction, septal thickness, size of both the aortic root and ascending aorta.

The diagnostic workup may require:

• TEE to define the anatomy precisely if unclear from TTE.
• Exercise testing.
• A heart catheterization ± provocative testing to assess the hemodynamics and severity of obstruction.
• Coronary angiography and aortography if surgery is being planned.
• MRI to assess associated lesions such as pulmonary artery stenoses or aortic coarctation and to measure left ventricular mass and function.
• Abdominal aortography to identify significant renal or other arterial stenoses.

 
Part V - Indications for Intervention

Supravalvar LVOTO may require intervention for a cath gradient or mean echo gradient of > 50 mmHg if the obstruction is discrete. Criteria for intervention for diffuse obstruction are not well defined but are probably similar since the end effect on the coronary arteries and the myocardium are the same.
Grade: C	Level: V	Ref: 53

Valvar LVOTO requires intervention for symptoms (dyspnea, angina, presyncope or syncope) or, arguably, "critical" aortic stenosis (valve area < 0.6cm2). Intervention may be indicated occasionally for other reasons (e.g. a person with a lesser degree of obstruction who wishes to play vigorous sports or wishes to become pregnant). Bicuspid aortic valves may also require intervention for moderate or severe regurgitation associated with exertional symptoms, or left ventricular end systolic dimensions > 55mm or LVEF < 55%.; aortic root replacement is required for ascending aortic dissection and should be considered prophylactically for proximal aortic dilation (> 55 mm).
Grade: C	Level: IV	Refs: 53-61

Subvalvar LVOTO should be considered for intervention when a resting cath gradient or mean echo gradient is > 50 mmHg, symptoms develop, or if combined with progressive aortic regurgitation which is more than mild. If there is an associated VSD, the gradient may be underestimated and important subvalvar LVOTO may become manifest only after VSD closure.
Grade: C	Level: IV	Refs: 62-67

Re-operation is indicated after valvotomy or after surgery for: Recurrent LVOTO (same criteria as above). Severe aortic regurgitation. Combined restenosis with moderate or greater regurgitation especially if symptoms or progressive LV dilation is present.
Grade: C	Level: IV	Refs: 55-58,60,68,69

 
Part VI - Interventional Options

Patients who require operation for supravalvar LVOTO should be operated on by congenital heart surgeons with experience with the technique.
Grade: C	Level: V	Refs: 18,19

Supravalvar LVOTO requires patch aortoplasty or, rarely, replacement of the proximal ascending aorta.

Valvar LVOTO may be treated with balloon valvuloplasty (if the valve is non-calcified); open aortic valvotomy; or valve replacement using a mechanical valve, biological valve or pulmonary autograft (Ross procedure which consists of replacing the aortic valve with the patient's pulmonary valve and implanting a homograft in the pulmonary position). Aortic valve disease, isolated or in combination with supravalvar or subvalvar stenosis, has been increasingly treated by pulmonary autografts, especially in young adults. The choice depends on the availability and skills of the team available and the preference of the patient.

Pulmonary autograft (Ross procedure) and balloon valvuloplasty for valvar LVOTO should be performed in centres and by people with substantial experience in these procedures.

Grade: Consensus

Discrete subvalvar LVOTO requires surgical resection almost invariably associated with myomectomy or myotomy. In older patients, the aortic valve may also need to be replaced or repaired because of significant aortic regurgitation.

Tunnel-like subvalvar LVOTO may require augmentation of the LVOTO using the Konno procedure (aortoventriculoplasty with aortic valve replacement) or other modifications for enlargement of the outflow tract. In the past, a left ventricular apex-to-aorta valved conduit was implanted if it was impossible to relieve the LVOTO adequately by any other means, but the long-term durability was unacceptable and the procedure has been abandoned. Some of these patients are still alive.

Subvalvar LVOTO associated with repair of AVSD often recurs if the fibromuscular tissue alone is excised. Patch enlargement of the infundibular septum and patch enlargement of the superior bridging leaflet of the left AV (mitral) valve or left AV (mitral) valve replacement may be required.

Patients who require operation for subvalvar LVOTO should be operated on by congenital heart surgeons with experience with the technique.
Grade: C	Level: V	Refs: 18,19

 
Part VII - Interventional Outcomes

Supravalvar LVOTO should have a low operative mortality.. Recurrence of obstruction is uncommon. The long-term durability of the patches or conduits used to relieve the obstruction may be a problem and surveillance should include assessment for aneurysm and endocarditis.

Valvar LVOTO treated by valvotomy or valvuloplasty is associated with progressive recurrent stenosis and calcification, and/or progressive regurgitation, and may eventually require valve replacement.

Patients with subaortic stenosis who require valve replacement will have a course similar to those who have valve replacement for acquired valvar LVOTO.

Patients with pulmonary autografts have excellent hemodynamic characteristics, require no anticoagulation, and have much reduced risk of thromboembolism. However the pulmonary autograft may deteriorate with time, as may the pulmonary homograft leading to stenosis and/or regurgitation. These patients need long-term follow up
Grade: C	Level: V	Refs: 70,71

Recurrence of fibromuscular subvalvar LVOTO is not uncommon (up to 20% over a decade, particularly if the aortic root is small).

Tunnel-like subvalvar LVOTO with extensive repair with or without aortic valve replacement has a high recurrence risk (72) although newer techniques may improve this.

Clinically important aortic regurgitation following subvalvar LVOTO repair is not uncommon (up to 25% of patients).

 
Part VIII - Pregnancy

LVOTO lesions associated with increased maternal and fetal risk during pregnancy include severe LVOTO with or without symptoms, aortic regurgitation with functional class III to IV, LVOTO with severe LV dysfunction, and mechanical prosthetic valves requiring anticoagulation. The latter underscores the importance, when feasible, of valve reconstruction or consideration of a bioprosthesis or pulmonary autograft procedure rather than replacement with a mechanical prosthesis in women having preconception cardiac surgery (73).

Patients with mild to moderate LVOTO and normal LV function can usually be managed conservatively through the entire pregnancy. Patients with more severe obstruction (cath gradient or mean echo gradient > 50 mmHg prior to pregnancy) or symptoms should be advised to delay conception until relief of LVOTO is performed. Balloon dilation of a severely stenotic bicuspid valve during pregnancy can reduce the hazards of gestation, labor and delivery (74,75).

Aortic regurgitation with LVOTO can usually be managed medically with a combination of diuretics and/or vasodilators. Surgery during pregnancy should be contemplated only for the control of refractory functional class III or IV symptoms.

The presence of bicuspid aortic valve and ascending aortic medial abnormality may predispose to spontaneous aortic dissection in the third trimester.

 
Part IX - Follow up

All patients should have regular cardiology follow up. Patients with Williams or Shone syndrome and those with complex LVOTO with or without repair should be followed by an ACHD cardiologist. Particular attention should be paid to: Progressive/recurrent stenosis at any level. Aortic regurgitation. Ventricular function and/or dilation. Aortic root dilation. Right ventricle-pulmonary artery conduit and pulmonary autograft degeneration, leading to neoaortic valve regurgitation and coronary abnormalities following a Ross procedure. Endocarditis prophylaxis is recommended for prosthetic valves and for any residual lesions.

Grade: Consensus