Bicuspid Aortic Valve

Bicuspid aortic valve (BAV), also known as bicommissural aortic valve, is a congenital heart disease in which two of the leaflets of the aortic valve fuse during foetal development, resulting in a two-leaflet (bicuspid) valve instead of the normal three-leaflet (tricuspid) valve. This condition affects approximately 1.3% of adults and is the most common cause of heart disease present at birth. Normally, the mitral valve is the only bicuspid valve, located between the heart's left atrium and left ventricle. The primary function of heart valves is to ensure the unidirectional flow of blood within the heart.

Signs and Symptoms

Many individuals with BAV may remain asymptomatic, while others may experience symptoms such as fatigue and reduced stamina for cardio-intensive activities. This is often due to poor heart performance caused by stress on the aortic wall.

Complications

Calcification

Over time, BAV may become calcified, leading to aortic stenosis, which manifests as heart murmurs. Aortic regurgitation can also occur if the leaflets do not close correctly. Severe cases may require surgical intervention. The heart is put under additional stress to pump blood through a stenotic valve or to handle regurgitated blood through a leaking valve. Progressive aortic dilation due to bicuspid aortopathy can ultimately lead to aortic valve rupture.

Aortic Lesions

Patients with BAV are prone to ascending aortic aneurysmal lesions due to deviations in the extracellular matrix of the aorta, particularly reduced Fibrillin-1. Abnormal degradation of the valve matrix is believed to be caused by an imbalance between MMP2 (Matrix Metalloproteinases 2) and TIMP1 (tissue inhibitors of metalloproteinase). This increases the risk of aortic dissection and aneurysm. Regular monitoring with CT scans or MRI is essential to evaluate the size of the proximal aorta.

Aortic Narrowing

BAV can cause aortic stenosis, preventing the valve from opening fully and reducing blood flow from the heart to the body. It may also lead to aortic regurgitation, where blood leaks back into the left ventricle. Coarctation of the aorta, a congenital narrowing near the ductus arteriosus, is also associated with BAV.

Pathophysiology

Fusion of aortic valve leaflets occurs most commonly between the right coronary and left coronary leaflets (≈80%), followed by the right coronary and noncoronary leaflets (≈17%), and least commonly between the noncoronary and left coronary leaflets (≈2%). Each fusion pattern is associated with specific areas of aortic dilation.

Hemodynamics

Hemodynamic patterns in the aorta play a very important role in predicting complications. BAV outflow is helical and occurs at high velocities throughout the ascending aorta, causing eccentric blood flow and increasing wall shear stress (WSS). This displacement correlates with dilation in specific aortic regions depending on the leaflet fusion pattern.

Aortic Disease

Different BAV leaflet fusion patterns lead to dilation in various aortic regions. RL fusion is linked to mid-ascending aorta dilation, while RN fusion affects the root, distal ascending aorta, and transverse arch. 4D MRI measurements of blood flow are advantageous for determining the timing and location of surgical repairs.

Diagnosis

BAV diagnosis can be assisted with echocardiography or MRI. 4D MRI is particularly useful for visualising blood flow patterns in three dimensions, helping in the accurate identification of abnormalities.

Classification

Bicuspid aortic valves can have three configurations:

1. Two symmetric leaflets
2. Tricuspid architecture with fusion of two leaflets
3. Tricuspid architecture with fusion of three leaflets

Treatment

Treatment for complications stemming from BAV typically involves surgical intervention, such as aortic valve replacement or balloon valvuloplasty.

Prognosis

Over one-third of individuals with BAV experience significant complications, including aortic valve narrowing, backward blood flow, dilation of the ascending aorta, and heart valve infection. Regular surveillance with transthoracic echocardiograms is advised for those with aortic regurgitation and dilation of the ascending aorta.

Epidemiology

BAV is the most common cardiac valvular anomaly, occurring in 1–2% of the population, with a higher prevalence in males. It is a heritable condition, often associated with mutations in the NOTCH1 gene and observed in Turner syndrome.

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Self-assessment MCQs (single best answer)

What is the prevalence of Bicuspid Aortic Valve (BAV) in adults?

Which of the following is NOT a potential complication of BAV?

Which gene mutation is commonly associated with BAV?

What imaging technique is particularly useful for visualising blood flow patterns in BAV?

Which BAV fusion pattern is most common?

Which of the following is a symptom that may be experienced by individuals with BAV?

What percentage of individuals with BAV experience significant complications?

What is the primary function of heart valves?

What type of surgical intervention might be required for severe cases of BAV complications?

Which patient population is more prone to having BAV?