Subvalvular aortic stenosis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Aortic insufficiency is more common in this form of aortic stenosis and occurs in 50 to 75% of patients.

Epidemiology and Demographics

Aortic subvalvular stenosis is the second most common form of congenital left ventricular outflow tract obtruction and occurs in 8-30% of all forms of left ventricular outflow tract obstruction. The level of obstruction is located just beneath the aortic valve. HOCM (a.k.a. idiopathic hypertrophic subaortic stenosis or IHSS) is not present at birth and is not considered a congenital lesion.

Pathophysiology

There are several varieties of congenital aortic subvalvular stenosis (or subaortic stenosis):

1. Membranous: A fixed localized membrane 0.5 to 2 cm below the level of the aortic valve and attached to the septum and the base of the anterior mitral leaflet.
2. Fibromuscular:
   • More commonly there is a fibromuscular membrane or tunnel with a significant muscular component which can sometimes be hard to distinguish from IHSS. This is a more severe form and is often associated with a small aortic root.
   • Associated aortic insufficiency (AI) is often present due to the high speed jet of blood through the aortic cusps resulting in fibrosis and retraction.
3. Congenital anomalies of the mitral valve:
   • Attachment to ventricular septum of accessory chordae from anterior mitral leaflet
   • Redundant AV valve tissue causing subaortic obstruction.
4. Aneurysm of the membranous ventricular septum

Natural History

The symptoms are similar to that of valvular aortic stenosis but begin earlier in infancy or early adulthood.

Diagnosis

Symptoms

The symptoms are similar to that of valvular aortic stenosis but begin earlier in infancy or early adulthood.

Echocardiography

• High doppler gradient and normal AV.

• It may require a repeat TTE or TEE

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Treatment

The membrane can be resected as shown in the videos below:

ACC / AHA Guidelines- Recommendations for Surgical Intervention (DO NOT EDIT)

“

Class I 1. Surgical intervention is recommended for patients with SubAS and a peak instantaneous gradient of 50 mm Hg or a mean gradient of 30 mm Hg on echocardiography- Doppler. (Level of Evidence: C) 2. Surgical intervention is recommended for SubAS with less than a 50 mm Hg peak or less than a 30 mm Hg mean gradient and progressive AR and an LV dimension at end-systolic diameter of 50 mm or LV ejection fraction less than 55%. (Level of Evidence: C) Class III 1. Surgical intervention is not recommended to prevent AR for patients with SubAS if the patient has trivial LVOT obstruction or trivial to mild AR. (Level of Evidence: C) Class IIb 1. Surgical resection may be considered in patients with a mean gradient of 30 mm Hg, but careful follow-up is required to detect progression of stenosis or AR. (Level of Evidence: C) 2. Surgical resection may be considered for patients with less than a 50 mm Hg peak gradient or less than a 30 mm Hg mean gradient in the following situations: a. When LV hypertrophy is present. (Level of Evidence: C) b. When pregnancy is being planned. (Level of Evidence: C) c. When the patient plans to engage in strenuous/ competitive sports. (Level of Evidence: C)

”

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ACC / AHA Guidelines- Recommendations for Key Issues to Evaluate and Follow-Up(DO NOT EDIT)

Class I

1. Lifelong cardiology follow-up, including evaluation by and/or consultation with a cardiologist with expertise in ACHD, is recommended for all patients with SubAS, repaired or not. (Level of Evidence: C)

2. The unoperated asymptomatic adult with stable LVOT obstruction due to SubAS and a mean gradient less than 30 mm Hg without LV hypertrophy or significant AR should be monitored at yearly intervals for increasing obstruction, the development or progression of AR, and the evaluation of systolic and diastolic LV function. (Level of Evidence: B)

Class IIa

1. Stress testing to determine exercise capability, symptoms, ECG changes or arrhythmias, or increase in LVOT gradient is reasonable in the presence of otherwise equivocal indications for intervention. (Level of Evidence: C)