Commissural Fusion Definition
Commissural fusion is a pathological condition where the edges of two cardiac valve cusps or leaflets are joined together at their commissures (the points where adjacent leaflets meet). 1
Key Characteristics
Commissural fusion represents an abnormal adhesion between valve leaflets that restricts normal valve opening and separation during cardiac motion. 1 This structural abnormality prevents the cusps or leaflets from separating fully during valve opening, leading to functional stenosis and impaired hemodynamics. 1
Classification by Severity
The ACC/AHA/ASE guidelines classify commissural fusion into distinct categories based on the degree of leaflet separation 1:
- Absent: Normal cusp separation with valve motion (no fusion present) 1
- Partial: Cusps or leaflets do not separate fully during valve motion 1
- Complete: Two or more cardiac valve cusps or leaflets do not separate at all with valve motion 1
- Unknown: Presence of commissural fusion cannot be determined 1
Anatomic Locations
Mitral Valve
Commissural fusion in the mitral valve occurs at two specific locations 1:
- Anterolateral commissure: Located anteriorly in the ventricle under the aortic valve's left coronary cusp 1
- Posteromedial commissure: Located posteriorly in the ventricle under the aortic valve's noncoronary cusp 1
Aortic Valve
Commissural fusion in the aortic valve can occur at three locations 1:
- Left-noncoronary commissure: Fusion between the left coronary cusp and noncoronary cusp 1
- Right-left coronary commissure: Fusion between the right coronary cusp and left coronary cusp 1
- Right-noncoronary commissure: Fusion between the right coronary cusp and noncoronary cusp 1
Pathophysiology and Clinical Significance
Commissural fusion is the dominant mechanism causing clinically important mitral stenosis of rheumatic origin, along with leaflet thickening and subvalvular apparatus alterations. 2 The fusion of commissures prevents normal valve opening, resulting in stenosis with reduced effective orifice area and increased transvalvular gradients. 3, 4
The presence and severity of commissural fusion directly determines the success of interventional procedures such as percutaneous balloon valvotomy. 1 Marked fusion and severe calcification of commissures are associated with increased complication rates and higher incidence of recurrent symptoms following intervention. 1 The procedure's success depends fundamentally on the ability to split fused commissures. 1
Etiologies
Rheumatic heart disease is the most common cause of commissural fusion, accounting for approximately 77% of cases requiring surgical intervention. 2 Other causes include 5, 6:
- Rheumatic fever sequelae: The classic cause with commissural fusion developing during the latent period following acute rheumatic fever 2
- Bioprosthetic valve failure: Commissural fusion can occur as a unique pathologic feature in failing bioprosthetic valves, particularly in patients with prior rheumatic disease 5
- Continuous-flow LVAD support: Non-inflammatory commissural fusion develops in >50% of patients supported by continuous-flow left ventricular assist devices, especially when the aortic valve remains continuously closed 6
Clinical Implications
Commissural fusion leads to progressive valve stenosis with predictable hemodynamic consequences including increased regurgitant fractions, reduced effective orifice areas, and augmented transmitral mean gradients. 3 The natural history following rheumatic fever shows a mean interval of 16.3 years before symptom onset, with progressive deterioration from mild to severe disability over approximately 9 years. 2