Supravalvular Aortic Stenosis (SVAS) is a rare form of congenital heart disease affecting the aorta, the large blood vessel carrying oxygenated blood from the heart to the rest of the body. It is characterized by a narrowing of the aorta immediately above the aortic valve, obstructing normal blood flow. This restriction forces the heart to pump harder, leading to significant strain on the cardiac muscle over time. Severity ranges widely, from mild cases with minimal symptoms to life-threatening obstructions requiring intervention in infancy.
Anatomy of Supravalvular Aortic Stenosis
The term “supravalvular” indicates the location of the defect: the narrowing occurs in the ascending aorta just beyond the leaflets of the aortic valve. This obstruction increases the afterload—the pressure the left ventricle must generate to push blood past the restriction. Over time, this struggle causes the muscular wall of the left ventricle to thicken, a process known as left ventricular hypertrophy.
The narrowing manifests in distinct morphological types:
- The discrete or “hourglass” type, which is the most common, presents as a ring-like constriction at the sinotubular junction.
- The diffuse type involves a longer, generalized narrowing (hypoplasia) along the entire ascending aorta.
- The membranous form is a thin, diaphragm-like structure with a small central opening stretching across the aortic lumen.
Genetic Basis and Associated Syndromes
The structural defect in SVAS is rooted in the body’s connective tissue due to problems with the protein elastin. The condition is often described as an elastin arteriopathy because it stems from a deficiency in this protein, which provides elasticity and strength to arterial walls. The gene responsible for producing elastin, known as \(ELN\), is located on chromosome 7q11.23.
The genetic mechanism usually involves a deletion or mutation in one copy of the \(ELN\) gene, resulting in haploinsufficiency—an insufficient amount of functional elastin protein. This deficiency leads to a disorganized and thickened arterial wall. While SVAS can occur in isolation (nonsyndromic SVAS) due to point mutations in \(ELN\), it is far more frequently associated with Williams Syndrome (WS).
Williams Syndrome is a complex genetic disorder resulting from a larger microdeletion on the same chromosomal region, 7q11.23, encompassing the \(ELN\) gene along with other genes. The deletion of \(ELN\) is responsible for the associated cardiovascular anomalies, including SVAS and narrowing in other arteries. The inheritance pattern for SVAS is typically autosomal dominant, meaning only one copy of the altered gene is needed to cause the disorder.
Recognizing Symptoms and Diagnostic Methods
The clinical presentation of SVAS varies. In infants and young children, symptoms can include difficulties with feeding, failure to gain weight, and heart failure in severe cases. For many patients, the first sign is the detection of a characteristic heart murmur during a routine physical examination.
As stenosis progresses, symptoms related to reduced blood flow and increased heart strain may appear:
- Shortness of breath.
- Chest pain, especially with physical activity.
- Episodes of syncope or dizziness.
- A differential in blood pressure or pulse between the right and left arms (Coanda effect).
Diagnosis primarily relies on imaging, with echocardiography serving as the foundational screening and monitoring tool. This non-invasive ultrasound technique allows physicians to visualize the narrowed segment and measure the pressure gradient across the obstruction. To fully map the extent of the vascular disease, especially when the narrowing is diffuse or involves other arteries, supplemental imaging such as Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) is often used.
Treatment Strategies and Long-Term Monitoring
Patients with mild, asymptomatic stenosis are managed with regular monitoring and may not require immediate intervention. Medical management involves using medications, such as diuretics, to control blood pressure or manage symptoms of heart failure.
For patients with a significant pressure gradient or those who develop symptoms like chest pain or syncope, surgical repair is the definitive treatment. The goal is to widen the narrowed segment of the aorta to restore normal blood flow through a procedure known as aortoplasty. Aortoplasty involves opening the narrowed area and using a patch of synthetic material or tissue to enlarge the aortic diameter.
Specific surgical techniques are designed to relieve the obstruction while preserving the function of the aortic valve. For diffuse narrowing, the patch may need to be extended further into the ascending aorta to fully relieve the gradient. Despite successful initial surgery, SVAS requires lifelong cardiac follow-up due to the systemic nature of the underlying elastin defect.
Long-term monitoring is necessary because there is a considerable lifetime risk of needing repeat procedures, with reintervention rates estimated to be around 31% over 30 years after the initial repair. Clinicians must regularly screen for the recurrence of narrowing (restenosis) at the surgical site. There is also a risk of aneurysm formation in the remaining aortic wall and the potential for narrowing in the coronary arteries, which can lead to complications such as myocardial infarction.