Rastelli Classification of Complete AVSD #1: Rastelli Type A

Date
September 21, 2026
URL
https://x.com/WithAScalpel/status/2101993090089210314?s=20
Categories
AVSD

Rastelli Classification of Complete AVSD #1: Rastelli Type A

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1. Morphologic Concept

Complete atrioventricular septal defect (AVSD) is defined fundamentally by a common atrioventricular junction, rather than simply by the coexistence of an ostium primum atrial septal defect, an inlet ventricular septal defect, and an abnormal atrioventricular valve. The common junction is guarded by a common atrioventricular valve with superior and inferior bridging leaflets extending across the ventricular septum. Variations in the relationship of the superior bridging leaflet (SBL) to the ventricular septum form the basis of the classic Rastelli classification.[1,2]

In Rastelli Type A, the SBL is effectively divided at the level of the ventricular septum because its central portion is attached to, or supported from, the crest of the ventricular septum. This contrasts with Type B, in which the bridging leaflet has anomalous chordal attachment within the right ventricle, and Type C, in which the SBL bridges freely across the septum without direct septal attachment.[3]

The supplied teaching illustration emphasizes the defining Type A relationship: division of the SBL over the septal crest, the resulting right-sided anterosuperior component, the elongated left ventricular outflow geometry, and the posteroinferiorly displaced atrioventricular conduction system.

Although Type A is commonly described as the most frequent Rastelli morphology, reported proportions vary substantially according to patient selection, era, associated abnormalities, and the morphologic definitions used. Therefore, percentages such as approximately 60% should be regarded as descriptive estimates rather than fixed epidemiologic constants.[3,4]

2. Superior Bridging Leaflet Anatomy

The most important feature of Type A is not simply that the SBL crosses the ventricular septum, but how it is restrained at the septal crest.

The SBL extends from the left ventricular side toward the right ventricle. In Type A, its central portion has attachment to the superior aspect of the ventricular septum, often through leaflet tissue and short chordal structures. This attachment produces an apparent division between the left-sided bridging component and the right-sided anterosuperior leaflet component. The extent and exact configuration of this attachment are variable; therefore, Rastelli Type A should not be interpreted as a single invariant anatomy.[3,4]

This distinction is surgically important. The valve should be analyzed as a common valve spanning a common junction rather than as separate malformed mitral and tricuspid valves. In particular, the zone of apposition between the left-sided portions of the superior and inferior bridging leaflets represents part of the common-valve architecture and should not simply be equated with a congenital “mitral cleft.”[1,2]

The relationship between the bridging leaflets, ventricular septum, and papillary muscles determines:

  • the effective size and shape of the ventricular component of the defect;
  • the geometry of the reconstructed left atrioventricular valve;
  • the feasibility of leaflet-to-septal approximation;
  • the potential for residual atrioventricular valve regurgitation; and
  • the width of the left ventricular outflow tract (LVOT).[2,4]

3. Ventricular Septal Relationship and the “Scooped-Out” LV

A characteristic feature of AVSD is deficiency of the normal atrioventricular septal structures with inlet–outlet disproportion of the left ventricle. The ventricular inlet is relatively shortened, while the distance from the atrioventricular junction toward the aortic valve is elongated. Because the aortic root is no longer normally wedged between the atrioventricular valves, the LVOT assumes a long, narrow configuration.[1,2,5]

In Type A, direct attachment of the SBL to the ventricular septal crest can accentuate the apparent deep indentation or “scooping” of the left ventricular inlet septum. This is more than a visual morphologic feature. It determines where the bridging leaflet meets the septum, how deeply the ventricular component extends beneath the valve, and how much leaflet tissue must ultimately participate in septal reconstruction.

The vertical depth of the ventricular component should therefore be assessed independently of the Rastelli label. Two patients classified as Type A can have substantially different VSD depths, leaflet mobility, chordal anatomy, and valve competence.

4. Relationship to the Left Ventricular Outflow Tract

The LVOT in AVSD is intrinsically different from the normal LVOT. Loss of normal aortic wedging produces an elongated outflow tract, historically described angiographically as a “gooseneck” deformity. Morphometric studies confirm that this geometry reflects both shortening of the ventricular inlet and lengthening of the outlet.[5,6]

Rastelli Type A anatomy may provide an additional substrate for obstruction because the SBL or its tensor apparatus is directly related to the ventricular septum. Direct leaflet attachment, anterior displacement of the left-sided papillary muscle, abnormal chordal structures, and a narrow elongated outflow tract may act alone or together to reduce the effective LVOT area.[6-8]

This does not mean that every Type A AVSD has clinically important LVOT obstruction. Rather, Type A anatomy contains several features that can increase susceptibility to obstruction in selected patients. LVOTO may be evident before repair or may become progressive after repair as the child grows and ventricular geometry changes.

Preoperative echocardiography should therefore assess not merely the Doppler gradient but the anatomical substrate:

1. SBL–septal relationship. Determine whether leaflet tissue or chordae extend into the outflow pathway.

2. Papillary muscle position. An anteriorly displaced anterolateral papillary muscle can pull the bridging leaflet toward the septum and narrow the outflow tract.

3. LVOT dimensions and length. A long narrow tunnel may be important even without a significant resting gradient.

4. Discrete secondary lesions. Fibromuscular tissue or a subaortic membrane may coexist with the intrinsic AVSD geometry.

5. Surgical geometry. Reconstruction should avoid placing the bridging leaflet or patch material excessively toward the LVOT.[6-8]

5. Echocardiographic Identification

Modern echocardiography generally provides sufficient detail to identify the relevant morphology before surgery. The Rastelli subtype itself is less important than accurately defining the individual components that influence repair.[9]

Subcostal and apical imaging should establish the presence of the common atrioventricular junction and demonstrate the relationship of the bridging leaflets to the ventricular septum. In Type A, the central SBL appears tethered to the septal crest rather than freely bridging across the ventricular component.

The examination should additionally define:

  • balance of the common atrioventricular junction between the ventricles;
  • size and depth of the ventricular component;
  • morphology and mobility of the superior and inferior bridging leaflets;
  • papillary muscle position;
  • chordal attachments crossing the ventricular septum or LVOT;
  • severity and mechanism of left and right atrioventricular valve regurgitation;
  • LVOT dimensions and Doppler velocity;
  • ventricular function; and
  • associated lesions.

Three-dimensional echocardiography may facilitate en-face assessment of common-valve geometry, particularly when the relationship between bridging leaflets, commissures, and the septal crest is complex.

6. Conduction System Anatomy

The conduction axis in AVSD differs fundamentally from normal anatomy. Because of the deficiency of the atrioventricular septal structures, the atrioventricular node is displaced posteriorly and inferiorly from the normal apex of the triangle of Koch.[2,10]

The usual landmarks of the normal triangle of Koch are therefore unreliable if interpreted conventionally. Morphologic studies have shown that the relationship of the inferior bridging leaflet to the ventricular septum provides an important surgical landmark for estimating where the conduction axis penetrates.[10] Modern phase-contrast computed tomographic analysis has reinforced the abnormal position and course of the conduction tissues in AVSD.[11]

The practical implication is particularly important during closure of the ventricular component. Deep sutures placed near the posteroinferior margin of the defect can injure the penetrating conduction axis. The VSD patch or leaflet-septal suture line should therefore be constructed with deliberate awareness of the displaced conduction pathway rather than by applying landmarks used for an isolated perimembranous VSD.

7. Surgical Implications of Type A Anatomy

Rastelli classification was developed during an era when understanding the common anterior/bridging leaflet was essential for planning intracardiac reconstruction. It remains useful descriptively, but Rastelli Type A does not mandate a specific repair technique.

Contemporary complete AVSD repair may employ a two-patch technique, traditional single-patch repair, or modified single-patch repair. Comparative series suggest that satisfactory outcomes can be obtained with more than one approach; selection should depend on the actual ventricular component, leaflet morphology, valve tissue available for reconstruction, and surgeon experience.[12]

Two-patch repair

With a two-patch strategy, the ventricular component is closed separately beneath the common valve. The bridging leaflets are then related to the superior margin of the VSD patch, followed by reconstruction of the atrial component.

For Type A anatomy, particular attention is required where the SBL is already associated with the septal crest. The surgeon must determine which attachments should be preserved and whether any chordal structures restrict leaflet mobility or compromise the LVOT.

Modified single-patch repair

In a modified single-patch repair, the bridging leaflets are brought toward the ventricular septal crest, effectively obliterating the ventricular component without a separate VSD patch. Type A morphology may appear anatomically favorable for this concept because the SBL already has a close relationship with the septum. However, VSD depth rather than Rastelli subtype alone is more relevant when deciding whether such approximation can be achieved without distortion.

Excessive downward traction risks deforming the left atrioventricular valve, reducing leaflet coaptation, or narrowing the LVOT. Conversely, inadequate approximation may leave a residual ventricular shunt.

Valve reconstruction

After septal reconstruction, the left-sided valve must be evaluated dynamically. The objective is adequate coaptation without excessive restriction. Closure of the left-sided zone of apposition is frequently performed when required to achieve competence, but the extent should be individualized. Overaggressive closure can create stenosis, particularly when the left component of the common junction or mural leaflet is small.

When native bridging leaflet tissue is deficient or geometrically unfavorable, selected centers have described leaflet augmentation, but this represents a specialized reconstructive strategy rather than a routine requirement of Type A anatomy.[13]

8. Down Syndrome and Rastelli Morphology

Complete AVSD has a strong association with trisomy 21, but Rastelli subtype should not be used as a genetic marker. Morphologic studies have reported differences in the distribution of leaflet configurations between patients with and without Down syndrome, but these observations are cohort-dependent and do not support a universal percentage for Type A among patients with trisomy 21.[14]

The more clinically useful approach is to define the anatomy directly rather than infer it from syndromic status. In any patient, surgical planning should be based on ventricular balance, bridging-leaflet morphology, valve regurgitation, VSD depth, chordal relationships, LVOT geometry, and associated cardiac lesions.

Key Surgical Principles

  • Type A is defined by the SBL–septal relationship. The superior bridging leaflet is attached or tethered to the ventricular septal crest rather than freely bridging the defect.
  • The Rastelli label is descriptive, not a surgical algorithm. Actual leaflet, chordal, VSD, and ventricular geometry should determine the repair.
  • Assess the LVOT anatomically, not only by gradient. Direct leaflet attachment, papillary muscle displacement, and intrinsic inlet–outlet disproportion can create latent obstruction.
  • Preserve useful leaflet and chordal attachments. Division should be undertaken only when necessary for valve reconstruction or relief of obstruction.
  • Avoid distortion during ventricular closure. Excessive leaflet-to-septal traction can produce left AV valve regurgitation, stenosis, or LVOT narrowing.
  • Respect the displaced conduction axis. The AV node and penetrating bundle lie posteroinferiorly compared with their normal positions.
  • Completion assessment must include more than residual shunting. Left and right AV valve competence, ventricular inflow gradients, LVOT patency, ventricular function, and residual VSD should all be evaluated before leaving the operating room.

References

  1. Anderson RH, Baker EJ, Ho SY, Rigby ML, Ebels T. The morphology and diagnosis of atrioventricular septal defects. Cardiol Young. 1991. doi:10.1017/S1047951100010362.
  2. Adachi I, Uemura H, McCarthy KP, Ho SY. Surgical anatomy of atrioventricular septal defect. Asian Cardiovasc Thorac Ann. 2008;16. doi:10.1177/021849230801600616. PMID: 18984764.
  3. Gallo P, Wilkinson JL, Macartney FJ, Gerlis LM, Anderson RH. Morphology and classification of complete atrioventricular defects. Br Heart J. 1979;42:633-639. doi:10.1136/hrt.42.6.633. PMID: 534580.
  4. Akiba T, Becker AE, Neirotti RA, Tatsuno K. Valve morphology in complete atrioventricular septal defect: variability relevant to operation. Ann Thorac Surg. 1993. doi:10.1016/0003-4975(93)91163-H. PMID: 8347012.
  5. Suzuki K, Ho SY, Anderson RH, et al. Morphometric analysis of atrioventricular septal defect with common valve orifice. J Am Coll Cardiol. 1998. doi:10.1016/S0735-1097(97)00456-7. PMID: 9426043.
  6. Ebels T, Ho SY, Anderson RH, Meijboom EJ, Eijgelaar A. The surgical anatomy of the left ventricular outflow tract in atrioventricular septal defect. Ann Thorac Surg. 1986. doi:10.1016/S0003-4975(10)63023-8. PMID: 3707240.
  7. Chang CI, Becker AE. Surgical anatomy of left ventricular outflow tract obstruction in complete atrioventricular septal defect: a concept for operative repair. J Thorac Cardiovasc Surg. 1987. doi:10.1016/S0022-5223(19)36162-8. PMID: 3682859.
  8. Gallo P, Formigari R, Hokeyem NJ, et al. Left ventricular outflow tract obstruction in atrioventricular septal defects: a pathologic and morphometric evaluation. Clin Cardiol. 1991. doi:10.1002/clc.4960140611. PMID: 1810690.
  9. Nayak S, Kanakriyeh M, Varadarajan P. Echocardiographic assessment of atrioventricular canal defects. Echocardiography. 2020. doi:10.1111/echo.14961. PMID: 33368544.
  10. Seo JW, Zuberbuhler JR, Ho SY, Anderson RH. Surgical significance of morphological variations in the atrial septum in atrioventricular septal defect for determination of the site of penetration of the atrioventricular conduction axis. J Card Surg. 1992. doi:10.1111/j.1540-8191.1992.tb01022.x. PMID: 1482825.
  11. Yoshitake S, Kaneko Y, Morita K, et al. Reassessment of the location of the conduction system in atrioventricular septal defect using phase-contrast computed tomography. Semin Thorac Cardiovasc Surg. 2020. doi:10.1053/j.semtcvs.2020.03.011. PMID: 32450213.
  12. Backer CL, Stewart RD, Bailliard F, Kelle AM, Webb CL, Mavroudis C. Complete atrioventricular canal: comparison of modified single-patch technique with two-patch technique. Ann Thorac Surg. 2007. doi:10.1016/j.athoracsur.2007.04.129. PMID: 18036931.
  13. Baird CW, Kreutzer C, Sanders SP, Borisuk MJ, del Nido PJ. Augmentation of bridging leaflets in repair of atrioventricular canal defects. Ann Thorac Surg. 2017. doi:10.1016/j.athoracsur.2017.02.036. PMID: 28633249.
  14. Marino B. Atrioventricular septal defect—anatomic characteristics in patients with and without Down's syndrome. Cardiol Young. 1992. doi:10.1017/S1047951100007861.