Can you provide data on the morphology of atrioventricular valves in atrioventricular canal defects?

Morphology of Atrioventricular Valves in AVCD

The key morphologic features of atrioventricular valves in AVCD include a common atrioventricular junction with bridging leaflets (superior and inferior), a trifoliate left atrioventricular valve, and variable papillary muscle arrangements—all of which are best classified using the Rastelli system (A, B, C) based on superior bridging leaflet attachments 1, 2.

Core Anatomic Features

The defining characteristic is the common atrioventricular junction rather than separate right and left junctions 3. This fundamentally distinguishes AVCD from other cardiac defects and drives all associated morphologic abnormalities.

Valve Leaflet Morphology

The atrioventricular valve structure includes:

• Bridging leaflets (superior and inferior) that cross the ventricular septum 2, 3
• A trifoliate left atrioventricular valve that does NOT resemble a cleft mitral valve 3
• When bridging leaflets are fused to each other, dual orifices exist rather than a common orifice 3
• The left mural leaflet, whose size correlates with late regurgitation risk 4

Rastelli Classification System

The guideline emphasizes the Rastelli classification as the standard descriptor 1:

• Type A: Superior bridging leaflet divides and attaches to both ventricles
• Type B: Superior bridging leaflet has anomalous right ventricular papillary muscle attachments
• Type C: Superior bridging leaflet is undivided and attached entirely to the right ventricle

This classification guides surgical approach and predicts outcomes 1.

Papillary Muscle Anatomy

Papillary muscle spacing is a critical prognostic morphologic feature 4. Recent data shows:

• Widely spaced papillary muscles increase odds of late left atrioventricular valve regurgitation by 3.6-fold (P = 0.026) 4
• Closely spaced or asymmetric papillary muscles have better outcomes: only 17% develop moderate/severe late regurgitation versus 40% with widely spaced muscles 4

Predictive Morphologic Markers

Valve Angle Measurement

The angle of the atrioventricular valve components relative to the crux of the heart predicts postoperative regurgitation 5:

• Angles ≤59° predict severe regurgitation with 79% specificity 5
• Mean angle in patients with moderate/severe regurgitation: 57° ± 13° versus 83° ± 9° in those with no/mild regurgitation (P = 0.002) 5

Left-Sided Structure Hypoplasia

Relative hypoplasia of left-sided structures indicates more severe disease requiring earlier intervention 6:

• Ascending aorta z-score: -1.2 in early intervention group versus -0.3 in elective repair group (P < 0.0001) 6
• Aortic isthmus z-score: -2.1 versus -1.4 (P = 0.005) 6
• Pulmonary-to-aortic valve diameter ratio: 1.47 versus 1.38 (P = 0.008) 6

Associated Morphologic Features

Beyond the valve itself, AVCD anatomy includes 1, 3:

• Unwedging of the subaortic outflow tract due to the common junction 3
• Disproportion between inlet and outlet dimensions of the left ventricle 3
• Primum atrial septal defect and inlet ventricular septal defect 1, 2

Clinical Caveat

One-third of patients with significant late regurgitation had no significant early postoperative regurgitation 4, indicating that initial valve morphology and repair quality—not just immediate surgical results—determine long-term outcomes. This underscores why preoperative morphologic assessment of papillary muscles, mural leaflet size, and valve angles is essential for risk stratification.