Conotruncal Rotation (NGA Pattern) in [S,D,N] DORV

Anatomic Logic, Infundibular “Building Blocks,” and Surgical Implications

This module frames double-outlet right ventricle (DORV) as a disorder of outflow (conal) development and conotruncal rotation, best understood by tracking (1) which great artery is posterior vs anterior (NGA reference) and (2) how the infundibular septum partitions the outlet into distinct infundibula. Experimentally and morphologically, DORV behaves as an essentially infundibular malformation, arising when normal incorporation of the posteromedial conus is disturbed. [1]

1. Segmental setting: what [S,D,N] implies

1. S (situs solitus)

Normal atrial arrangement.

2. D-loop

The morphologic RV lies to the right, LV to the left.

3. N (normally related great arteries; NGA reference)

The aorta is the posterior great artery (typically posterior/rightward), and the pulmonary artery is the anterior great artery (typically anterior/leftward).

Interpretive question (NGA framework):

Which vessel is posterior vs anterior—and how did each “shift” relative to the ventricles/outlet septum to produce the observed VA connection?

2. Infundibular interrelationships: the “hidden” determinant behind Ao position and VSD type

A key refinement from morphologic series is that the relationship of the great arteries to each other is not sufficient to define surgical anatomy; instead, one must determine the infundibular interrelationship (i.e., how the outlet septum is inserted and how it creates anterior/posterior or side-by-side infundibula). [2]

Two dominant infundibular configurations (pathology series)

• Type A: Anterior + posterior infundibula (≈ 70%)

In this pattern, the aorta most often connects to the posterior infundibulum (reported ~91% within this subgroup), and when it does, the VSD is commonly subaortic (reported ~81%). [2]

• Type B: Side-by-side infundibula (≈ 26%)

In this pattern, the pulmonary trunk connects to the medial infundibulum, and the VSD is commonly subpulmonary (reported ~92%). [2]

Clinical translation:

Infundibular architecture predicts (a) where the aorta “lands” and (b) which VSD type becomes the dominant LV outflow window—subaortic vs subpulmonary—thereby steering the repair pathway. [2]

3. The key rotation/shift signature in [S,D,N] DORV (NGA-type DORV with subaortic VSD)

Your slide’s pattern can be described as a Type A (anterior/posterior infundibula) phenotype with a posterior aorta that has shifted toward the RV outlet territory:

1. Great-artery shift
• Posterior Ao shifts rightward (+) → increased RV commitment of the posterior great artery.
• Anterior PA shifts mildly leftward → maintains the anterior/leftward identity of the PA (NGA reference).
2. Infundibular fold (IF) behavior
• Slight counterclockwise rotation of the IF with orthogonal crossing of the IVS.
• Morphologically, this emphasizes that the outlet partition plane is crossing (rather than “running along”) the IVS—an arrangement that tends to “present” a subaortic window beneath the posterior great artery.
3. VSD location
• Subaortic VSD (beneath the posterior Ao): the LV reaches its physiologic target (the posterior great artery in NGA) through the closest septal communication, which is therefore positioned subaortic.

4. Why this geometry produces a subaortic VSD (mechanistic summary)

In the NGA reference, the posterior great artery (Ao) is the natural systemic outlet. In [S,D,N] DORV, a rightward shift of the posterior Ao increases its RV commitment, but the LV still requires an egress pathway; the VSD becomes the functional LV outflow portal, and in this configuration it aligns subaortic, consistent with the dominant Type A infundibular arrangement reported in morphologic series. [2]

5. Surgical meaning: “routing logic” and the anatomy that must be checked

Large surgical-anatomic series emphasize that the aorta is most commonly right-posterior but may vary widely, and that subaortic VSDs are frequent—features that directly shape whether a two-ventricle repair with intraventricular tunneling is feasible and how complex it will be. [3]

Practical checklist (especially for subaortic VSD / NGA-type DORV)

1. Is LV-to-Ao routing direct and unobstructed?
• A subaortic VSD often supports an intraventricular tunnel (baffle) to the aorta, but tunnel geometry must avoid creating new LVOT obstruction. [3]
2. What are the “tunnel limiters”?

Key anatomic constraints that govern tunnel construction include:

1. Prominent conal (outlet) septum
2. Tricuspid valve attachments to the conal septum
3. Distance between the pulmonary and tricuspid valves (space available for a safe, non-obstructive tunnel) [4]
3. Is RV-to-PA outflow adequate (or obstructed)?
• Subpulmonary or RVOT obstruction frequently coexists and may require muscle resection and/or RVOT augmentation at the time of repair. [4]

Imaging implication

Because infundibular interrelationships can be missed if one focuses only on great-artery position, preoperative imaging should explicitly aim to define:

• Outlet septum / infundibular septum orientation
• VSD commitment and distance to each arterial valve
• AV valve chordal attachments that may constrain the tunnel

This “infundibular-first” definition can be obtained with careful echocardiography and, when needed, angiography (and in modern practice, CT/MRI for 3D clarification). [2]

References

[1] Arteaga M, de la Cruz MV, Sanchez C, Diaz GF. Double outlet right ventricle: experimental morphogenesis in the chick embryo heart. Pediatr Cardiol. 1982;3(3):219-227.

[2] de la Cruz MV, Cayré R, Arista-Salado Martinez O, Sadowinski S, Serrano A. The infundibular interrelationships and the ventriculoarterial connection in double outlet right ventricle. Clinical and surgical implications. Int J Cardiol. 1992;35(2):153-164.

[3] Wilcox BR, Ho SY, Macartney FJ, Becker AE, Gelis LM, Anderson RH. Surgical anatomy of double-outlet right ventricle with situs solitus and atrioventricular concordance. J Thorac Cardiovasc Surg. 1981;82(3):405-417.

[4] Takeuchi K, del Nido PJ. Surgical management of double-outlet right ventricle with subaortic ventricular septal defect. Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu. 2000;3:34-42.