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Rastelli classification complete AV canal defect types A B C chordal attachment
Here is a detailed explanation of the figure:
Rastelli Classification of Complete AV Canal Defects (Fig. 35)
What is a Complete AV Canal (CAVC) Defect?
A Complete Atrioventricular Canal defect (also called Complete Atrioventricular Septal Defect, CAVSD) is a congenital heart anomaly characterized by:
- A primum atrial septal defect (hole in the lower atrial septum)
- A common AV valve (instead of separate mitral and tricuspid valves)
- A variable ventricular septal defect (inlet VSD)
The Rastelli classification (1966) subdivides complete CAVC into Types A, B, and C based on the anatomy of the superior (anterior) bridging leaflet of the common AV valve - specifically how its chordae tendineae attach to the ventricular septum.
Anatomical Labels in the Diagram
The diagram shows a superior (bird's eye) view of the common AV valve orifice:
| Abbreviation | Meaning |
|---|---|
| RSL | Right Superior Leaflet (right component of anterior bridging leaflet) |
| RLL | Right Lateral Leaflet |
| RIL | Right Inferior Leaflet (right component of posterior bridging leaflet) |
| LSL | Left Superior Leaflet (left component of anterior bridging leaflet) |
| LLL | Left Lateral Leaflet |
| LIL | Left Inferior Leaflet (left component of posterior bridging leaflet) |
| SL | Superior Leaflet (single, undivided - seen only in Type C) |
The central shaded band represents the ventricular septum (crest/rim of the interventricular septum).
Type A (Most Common - ~75% of cases)
Key feature: The anterior bridging leaflet is divided into a distinct Left Superior Leaflet (LSL) and Right Superior Leaflet (RSL). Both components attach via chordae tendineae directly to the crest of the ventricular septum.
- Chordal insertions go straight down to the top of the septum
- This creates a fairly defined separation between the left and right ventricular portions of the valve
- The bridging is minimal - the leaflet barely crosses the septum
- Surgical significance: Relatively straightforward repair; the leaflets can be divided at the cleft and sutured to a patch closing the VSD
Type B (Rarest - <5% of cases)
Key feature: The anterior bridging leaflet is still nominally divided, but the chordae from the left-sided component (LSL) cross over the septum and attach to an anomalous papillary muscle on the right ventricular side of the septum.
- The left superior leaflet "bridges" or overrides the septum more than in Type A
- Chordal attachments are to an aberrant/anomalous right ventricular papillary muscle, not the septal crest
- This crossing of the septum by the chordae makes surgical repair more complex
- Surgical significance: Rare and technically demanding; the anomalous papillary muscle must be accounted for during patch repair
Type C (Associated with Tetralogy of Fallot)
Key feature: The anterior bridging leaflet is completely undivided - forming a single large leaflet labeled SL (Superior Leaflet) that freely floats over both ventricles.
- There is no cleft between left and right superior leaflet components - they are fused into one
- It is "free-floating" with NO chordal attachments to the ventricular septum
- Chordae attach laterally to papillary muscles in the left (LLL side) and right (RLL side) ventricles
- The space beneath this leaflet is wide open, allowing unrestricted communication between both ventricles (large inlet VSD)
- Commonly associated with Tetralogy of Fallot, Double-outlet right ventricle, and other conotruncal anomalies
- Surgical significance: Most complex repair; a two-patch technique is often required
Summary Comparison Table
| Feature | Type A | Type B | Type C |
|---|---|---|---|
| Superior leaflet | Divided (LSL + RSL) | Divided (LSL + RSL) | Undivided (single SL) |
| Chordal attachment | To septal crest | To anomalous RV papillary muscle | Free-floating (no septal attachment) |
| Bridging extent | Minimal | Moderate (crosses septum) | Maximal (free-floating) |
| Frequency | ~75% | <5% (rarest) | ~20% |
| Associated anomalies | Down syndrome (Trisomy 21) | Variable | Tetralogy of Fallot |
| Surgical complexity | Least complex | Most complex (rare anatomy) | Complex (two-patch often needed) |
Clinical Relevance
- The Rastelli classification guides surgical planning - the surgeon needs to know where the chordae are before deciding how to divide the common valve and patch the septal defects
- Type A is the most amenable to the classic single- or two-patch repair
- Type C often requires careful attention to avoid distorting the "free-floating" leaflet during the repair
- The most common association overall is with Down syndrome (Trisomy 21), occurring in ~60-70% of complete CAVC cases
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