What are the classification types of a bicuspid aortic valve?

Classification of Bicuspid Aortic Valve

There are 3 main types of bicuspid aortic valve (BAV): the fused type (90-95% of cases), the 2-sinus type, and the partial-fusion type, with the fused type subdivided into three specific phenotypes based on which cusps are conjoined. 1, 2

Type 1: Fused BAV (90-95% of all BAV cases)

The fused type is characterized by 2 of the 3 cusps appearing fused or joined within 3 distinguishable aortic sinuses, creating 2 functional cusps of usually different sizes and shapes. 1

Three Phenotypes of Fused BAV:

1. Right-Left Cusp Fusion (70-80% of BAV cases)

• Most common phenotype across all BAV variations 1
• Commissures positioned at 10 and 4 o'clock on short-axis imaging 1
• Associated with aortic stenosis progression, though can also present with aortic root dilatation and regurgitation (termed "root phenotype") 1
• Strongly associated with aortic coarctation in children 1
• More common in males 1

2. Right-Non-Coronary Cusp Fusion (20-30% of BAV cases)

• Second most common phenotype 1
• Commissures positioned at 1 and 7 o'clock on short-axis imaging 1
• Associated with larger arch dimensions and ascending aorta dilatation 3
• Higher prevalence of myxomatous mitral valve disease compared to right-left fusion 3

3. Left-Non-Coronary Cusp Fusion (3-6% of BAV cases)

• Least common phenotype 1
• Commissures positioned at 2 and 8 o'clock on short-axis imaging 1

Critical Features to Document in Fused BAV:

Raphe Presence:

• A congenital fibrous ridge between fused cusps occurs in approximately 70% of fused BAV cases 1
• Raphe presence is associated with progression to aortic stenosis and increased likelihood of future valve surgery 1
• May not be initially visible on echocardiography but can become apparent years later 1

Valve Symmetry (Based on Non-Fused Cusp Commissural Angle):

• Symmetrical: 160-180° angle 1, 4
• Asymmetrical: 140-159° angle 1, 4
• Very asymmetrical: 120-139° angle 1, 4
• Greater asymmetry correlates with increased fusion length, decreased non-functional commissure height, and higher rates of severe aortic regurgitation 4

Type 2: Two-Sinus BAV

This type has only 2 aortic sinuses rather than the typical 3 sinuses seen in fused BAV. 2

Two Phenotypes:

• Latero-lateral phenotype 2
• Antero-posterior phenotype 2

Type 3: Partial-Fusion (Forme Fruste) BAV

This represents an incomplete fusion pattern and is the rarest type. 2

Clinical Implications by Phenotype

Imaging Characteristics:

• All fused BAV types demonstrate oval ("American football shape") systolic opening on short-axis views, contrasting with the triangular opening of tricuspid valves 1
• The non-fused cusp typically shows eccentric dominance with compensatory enlargement compared to the fused cusps 1

Surgical Considerations:

• Acquired fusion from calcification or rheumatic disease can mimic congenital BAV 1
• Intraoperative differentiation: congenital fusion shows lower pseudocommissure attachment, obtuse angle between fused cusps, and absent cleavage plane on ventricular aspect 1

Common Pitfall: Do not confuse acquired tricuspid valve fusion from calcification with congenital BAV—surgical inspection or pathological examination may be required for definitive diagnosis when imaging is equivocal. 1