What are the primary types of bicuspid aortic valves?

Classification of Bicuspid Aortic Valve Types

Bicuspid aortic valves are classified into three primary morphological types based on cusp fusion patterns: fused BAV (90-95% of cases), 2-sinus BAV (5-7%), and partial-fusion BAV, with the most common subtype being right-left coronary cusp fusion (70-80% of all BAV). 1

Primary Morphological Classification

Fused BAV (90-95% of all BAV cases)

This represents the vast majority of bicuspid valves and includes three distinct fusion patterns 1:

• Right-left coronary cusp fusion (Type 1): Accounts for 70-80% of all BAV cases, resulting in a larger anterior cusp and smaller posterior cusp, with both coronary arteries typically arising from the anterior cusp 1

• Right-noncoronary cusp fusion (Type 2): Represents 20-30% of BAV cases, producing a larger right cusp than left cusp, with one coronary artery arising from each cusp 1

• Left-noncoronary cusp fusion (Type 3): The rarest fusion pattern at 3-6% of cases 1

2-Sinus BAV (5-7% of all BAV cases)

This less common variant includes two phenotypes 1:

• Laterolateral orientation: True bicuspid valve with symmetric cusps positioned laterally 1

• Anteroposterior orientation: Cusps positioned in anterior-posterior configuration 1

Partial-Fusion BAV

Characterized by short fusion of one commissure, representing a minority of cases 1

Clinical Significance of Morphological Types

The specific fusion pattern has important prognostic implications for both valve dysfunction and aortopathy development:

Valve Dysfunction Patterns:

• Right-left fusion (Type 1) is more commonly associated with moderate-to-severe aortic regurgitation (32.3% vs 6.8%) 2
• Right-noncoronary fusion (Type 2) predominantly presents with moderate-to-severe aortic stenosis (66.2% vs 46.2%) 2
• Patients with right-noncoronary fusion are more likely to have aortic regurgitation requiring intervention 1

Aortopathy Patterns:

• Right-left fusion shows larger aortic sinus dimensions and more severe aortic wall degeneration, with patients requiring surgery at younger ages (mean 51.3 years vs 58.7 years) 3, 4
• Right-noncoronary fusion is associated with larger ascending aorta and arch dimensions, with more frequent ascending aortic dilatation extending to the transverse arch 1, 4, 2
• Type 1 fusion demonstrates higher prevalence of normal aortic shape (60% vs 32%) 4

Associated Aortopathy Phenotypes

Each valve morphology can be associated with three distinct aortopathy patterns 1:

• Ascending phenotype (70-75%): Dilatation predominantly at the tubular (supra-coronary) tract 1

• Root phenotype (15-20%): Dilatation predominantly at the sinuses of Valsalva, more commonly associated with right-left fusion 1

• Extended phenotype (5-10%): Equal dilatation of sinusal and tubular segments or ascending dilatation extending into the proximal arch 1

Diagnostic Approach

The diagnosis is most reliable when two cusps are visualized in systole with only two commissures framing an elliptical systolic orifice on short-axis transthoracic echocardiography. 1, 5

Key Diagnostic Features:

• Short-axis systolic view is the primary diagnostic view showing two cusps instead of three 5
• Only two commissures are visible with an elliptical (not stellate) systolic orifice 1, 5
• Diastolic images may be misleading when a raphe (fusion line) mimics a third commissure 1, 5
• Long-axis views may show asymmetric closure line or systolic doming but are less specific 1

Important Diagnostic Pitfalls:

• Extensive calcification in adults often obscures the number of cusps, making differentiation from tricuspid valves difficult 1, 5
• Transesophageal echocardiography may be necessary when transthoracic image quality is suboptimal 1, 5
• CMR demonstrates higher accuracy for valve morphology assessment compared to TTE (96% vs 73%) when compared to pathology specimens 1

Clinical Management Implications

When BAV is first diagnosed, initial transthoracic echocardiography to assess aortic diameters at multiple levels is mandatory, followed by CCT or CMR of the entire thoracic aorta. 1

The specific morphological type should guide surveillance intensity and surgical timing, as right-noncoronary fusion carries higher risk for extensive aortopathy requiring earlier intervention 1, 2.