Conotruncal Rotation #8 — Anatomically Corrected Malposition of the Great Arteries (ACMGA, TGA Type)

Conotruncal Rotation (TGA-Type) — Anatomically Corrected Malposition of the Great Arteries (ACMGA)

Anatomically corrected malposition (ACMGA/ACM) is a rare conotruncal anomaly in which the great arteries arise from their morphologically appropriate ventricles (VA concordance), yet show an abnormal spatial relationship—often appearing “TGA-like” (parallel/side-by-side great vessels) despite non–TGA physiology. In classic segmental terms, the prototypic form is [S,D,L]: situs solitus, D-loop ventricles, and L-malposition of the great arteries. [1,2]

Key concept: “Malposition” refers to position/relationship of the great arteries; “transposition” is reserved for VA discordance (great arteries arising from morphologically inappropriate ventricles). [2]

1) Conotruncal-rotation logic in this module (the “TGA-type shift” rule)

Within your conotruncal-rotation framework, ACMGA is interpreted as the product of coupled lateral shifts of the two great arteries that create a TGA-type spatial relationship without losing VA concordance:

1. Posterior great artery (PA in this module) → rightward shift (+++)
2. Anterior great artery (Ao in this module) → leftward shift (++)

This paired shift produces the parallel great-artery geometry that can mimic TGA on imaging, even though the aorta still connects to the LV and the PA to the RV. [1,2]

2) Defining anatomic hallmarks (what “ACMGA” looks like)

ACMGA is not a single lesion, but a recognizable anatomic pattern defined by three coupled features:

1. Ventriculoarterial concordance (the “corrected” part)
• Ao from LV, PA from RV (physiology depends on associated defects). [1,2]
2. Abnormal great-artery relationship (the “malposition” part)
• Great arteries frequently appear parallel, with the aorta commonly anterior and leftward in the classic [S,D,L] form. [1,2]
3. Conal anatomy (the key substrate for VSD alignment and outflow geometry)
• Bilateral conus or subaortic conus are commonly described, and conal variation explains much of the heterogeneity in LVOT/RVOT morphology and surgical planning. [1,3]

Clinical corollary: Heart position variants such as mesocardia/dextrocardia are reported relatively often in ACMGA presentations and may add to diagnostic confusion. [4,9]

3) Septal–outflow geometry in your slide (IF becomes “septal-aligned”)

A high-yield feature in your diagram is the behavior of the infundibular fold (IF):

• IF attaches to the IVS at the VSD margin
• and becomes functionally parallel to the IVS

In this conotruncal-rotation interpretation, the IF behaves less like an “offset wedge” separating two discrete outflow tracts and more like a septal-aligned outflow partition, which strongly determines where the VSD opens and which semilunar valve it preferentially aligns with.

4) The VSD signature in this module: subaortic, beneath the anterior aorta

In the ACMGA pattern depicted here, the VSD has a characteristic directionality:

• VSD type: subaortic
• Alignment: beneath the anterior Ao, with the most anterior extension tracking toward the aortic outflow

This is consistent with the broader ACMGA literature in which VSD and outflow obstruction (particularly subaortic/LVOT obstruction) are important associated lesions and often drive presentation and management. [4,7]

5) Differentiation from TGA (and why ACMGA is often misread)

ACMGA vs TGA is a relationship trap:

• In TGA, the defining feature is VA discordance, producing obligatory “switched” physiology unless surgically corrected.
• In ACMGA, the great arteries may look “TGA-like,” but VA concordance is preserved, and physiology depends on associated anomalies (e.g., VSD, LVOT obstruction, RVOT obstruction). [1,2,4]

Common pitfall: In fetal and early postnatal imaging, ACMGA can be misdiagnosed as TGA because the great vessels may appear parallel and “non-spiraling”; systematic segmental analysis is therefore essential. [4,10]

6) Surgical meaning (what this framework helps anticipate)

Because ACMGA is primarily a spatial + conal anatomy problem, surgical strategy is typically determined by associated lesions and geometry, not by the label alone:

1. VSD management
• When the VSD is subaortic and well-aligned, repair may be conceptually straightforward (closure/baffle decisions guided by alignment and outlet geometry), but exposure and margins can be dictated by the conal/IF configuration. [6,8]
2. Outflow obstruction
• Subaortic (LVOT) obstruction can be a major driver of symptoms and operative indication in some phenotypes (including tunnel-type obstruction). [4,7]
3. Coronary anatomy and great-artery rotation
• Coronary patterns in ACM have been linked to the degree of aortopulmonary rotation, which can carry practical implications for incisions and patch strategies in outflow reconstruction. [5]
4. Expected outcomes (heterogeneous; anatomy matters)
• Reported surgical results are generally favorable in situs solitus with AV concordance (e.g., [S,D,L]), while outcomes are significantly worse when AV discordance and/or hypoplastic right-heart structures are present—highlighting that “ACMGA” is a pattern that can coexist with multiple AV relationships and complexity tiers. [8]

References (PubMed-verified)

[1] Van Praagh R, Durnin RE, Jockin H, Wagner HR, Korns M, Garabedian H, Ando M, Calder AL. Anatomically corrected malposition of the great arteries (S, D, L). Circulation. 1975;51(1):20-31.

[2] Anderson RH, Becker AE, Losekoot TG, Gerlis LM. Anatomically corrected malposition of great arteries. Br Heart J. 1975;37(10):993-1013.

[3] Oku H, Shirotani H, Yokoyama T, et al. Anatomically corrected malposition of the great arteries—case reports and a review. Jpn Circ J. 1982;46(6):583-594.

[4] Sridhar A, Subramanyan R, Verma S, Abraham S. Anatomically corrected malposition of great arteries. Ann Pediatr Cardiol. 2010;3(2):187-189.

[5] Huang SC, Chiu IS, Lee ML, Wu CS, Chiu HH, Chang CI, Wu MH, Wang JK. Coronary artery anatomy in anatomically corrected malposition of the great arteries and their surgical implications. Eur J Cardiothorac Surg. 2011;39(5):705-710.

[6] Kirklin JW, Pacifico AD, Bargeron LM Jr, Soto B. Cardiac repair in anatomically corrected malposition of the great arteries. Circulation. 1973;48(1):153-159.

[7] Colli AM, de Leval M, Somerville J. Anatomically corrected malposition of the great arteries: diagnostic difficulties and surgical repair of associated lesions. Am J Cardiol. 1985;55(11):1367-1372.

[8] Rittenhouse EA, Tenckhoff L, Kawabori I, Mansfield PB, Hall DG, Brown JW, King H. Surgical repair of anatomically corrected malposition of the great arteries. Ann Thorac Surg. 1986;42(2):220-228.

[9] Clarke CJ, Jayakumar KA, Hoyer AW. Anatomically corrected malposition of the great arteries. Pediatr Cardiol. 2010;31(4):562-563.

[10] Bravo-Valenzuela NJ, Carrilho MC, Peixoto AB, Bezerra MS, Araujo Júnior E. Anatomically corrected malposition of the great arteries: a challenging fetal diagnosis. J Matern Fetal Neonatal Med. 2019;32(18):3097-3101.