What is the character of the a2 cusp in a bicuspid aortic valve?

Characteristics of A2 in Bicuspid Aortic Valve

In a bicuspid aortic valve, the A2 cusp is typically larger and asymmetric compared to the other cusp, often resulting from fusion of the right and left coronary cusps (80% of cases) or right and non-coronary cusps (20% of cases). 1

Anatomical Features of Bicuspid Aortic Valve

Cusp Fusion Patterns

• Most common pattern (80%): Fusion of right and left coronary cusps
  • Results in larger anterior (A2) and smaller posterior cusp
  • Both coronary arteries arise from the anterior cusp
• Less common pattern (20%): Fusion of right and non-coronary cusps
  • Results in larger right cusp than left cusp
  • One coronary artery arises from each cusp
• Rare patterns: Fusion of left and non-coronary cusps or "true" bicuspid valve with two equally sized cusps 1

Diagnostic Features of A2

• Best visualized in systole showing only two commissures framing an elliptical systolic orifice
• Diastolic images may misleadingly appear as three cusps when a raphe (fusion line) is present
• Long-axis views often show:
  • Asymmetric closure line
  • Systolic doming
  • Diastolic prolapse of one or both cusps 1

Echocardiographic Identification

The diagnosis of bicuspid aortic valve is most reliable when:

• Two cusps are seen in systole
• Only two commissures are visible
• An elliptical systolic orifice is present 1

In adults, superimposed calcific changes often obscure the number of cusps, making determination between bicuspid and tricuspid valve difficult. In these cases, indirect hints such as geometry and dilatation of the aortic root and ascending aorta may suggest the presence of a bicuspid valve. 1

Calcification Patterns

• Calcification in bicuspid valves is often more asymmetric compared to tricuspid valves
• In younger patients (children, adolescents, young adults), bicuspid valves may be stenotic without extensive calcification
• In most adults, stenosis of bicuspid valves typically results from superimposed calcific changes 1

Clinical Implications

Aortopathy Association

• Bicuspid aortic valve is strongly associated with aortic dilatation (bicuspid valvulo-aortopathy)
• Type I fusion pattern (right-left coronary cusp fusion) is more commonly associated with aortic dilatation than Type II (right-noncoronary cusp fusion), particularly at the level of:
  • Sinuses of Valsalva
  • Ascending aorta 2

Monitoring Requirements

• When a bicuspid aortic valve is first diagnosed, complete imaging of the thoracic aorta is necessary
• Annual monitoring of the aortic root/ascending aorta with transthoracic echocardiography is recommended
• Additional imaging with CMR/CCT every 3-5 years is recommended 1

Surgical Considerations

Prophylactic aortic surgery should be considered when:

• Aortic diameter reaches ≥45 mm, or lower with additional risk factors
• Concomitant aortic valve surgery is being performed and aortic diameter is ≥45 mm 1, 3

The unique morphology of the A2 cusp in bicuspid aortic valves has important implications for valve repair techniques, including tricuspidization with cusp extension, which can provide reliable palliation of symptomatic bicuspid aortic valve disease. 4

Common Pitfalls in Identification

• Mistaking a raphe for a commissure in diastole
• Overlooking bicuspid morphology in heavily calcified valves
• Failing to assess in systole when the bicuspid nature is most apparent
• Not considering associated aortopathy when bicuspid valve is identified 1