Anatomically corrected malposition of the great arteries.
A rare case of anatomically corrected malposition of the great arteries with bilaterally absent conus and ventricular septal defect is presented. Embryogenic mechanism responsible for the malformation, diagnostic problems of imaging and the increased risk posed for intraventricular surgical repair of associated defect are discussed here.
Keywords: Malposition, Corrected malposition of great arteries, Conotruncal rotation, Anatomically corrected malpositions, Cardiogenesis of malpositions.
Anatomically corrected transposition of the great arteries, later to be termed anatomically corrected malposition (ACM) of the great arteries,1 is a rare malformation. In this condition, the transposition of the great arteries is not present and the great arteries are normally connected to their appropriate ventricles. The abnormality lies in the inter-arterial relationship which is of parallel vessels. In case of the D-loop ventricles, the great vessels are in L- malposition, and in L-loop ventricles, the great arteries are in D-malposition.1-4 We report here a case of ACM with bilaterally absent conus, which is an even more rare association.4,5
An eight-month-old boy, one of a pair of twins, born of full-term, normal delivery, weighing below the 3rd percentile, was referred to a paediatric cardiologist due to the presence of a murmur, recurrent chest infection and failure to gain weight. The other twin had no cardiac problems. On examination, the heart and respiratory rates were normal.
Clinical examination showed normal first heart sound. The second heart sound was loud with close splitting, suggesting pulmonary arterial hypertension. There was a grade 2/6 pansystolic murmur at the left lower sternal border. The chest x-ray showed upright apex, moderate cardiac enlargement, computed tomography (CT) ratio of 0.6 and increased pulmonary vascularity (Figure-1.A). Pulmonary arterial prominence was not present at the usual position, and the right border below the superior vena cava position showed a prominent, rounded bulge which, in retrospect, was interpreted as the enlarged main pulmonary artery. Preoperative echocardiographic imaging showed situs solitus, and D-loop ventricles with the pulmonary artery to the right of aorta, i.e. L-malposed (Figure-1.B-1.D). The great vessels were normally connected and transposition was not present. There was no conal muscle under the aorta or the pulmonary artery. Mitral-aortic valve and pulmonary-tricuspid valve continuity was imaged.
The pulmonary and aortic annuli were contiguous and both vessels' valve annuli were at the same level. There was a large, doubly-committed ventricular septal defect. The main pulmonary artery was somewhat anterior and to the right, and the aorta was to the left in parallel pattern. Cardiac catheterisation was undertaken to clarify the diagnosis. Angiography confirmed situs solitus and D-loop ventricles, that is, the right-sided right ventricle and the concordant atrioventricular connections, the great vessels, were in L- malposition, but the ventriculoarterial connections were concordant, i.e. normally connected (Figure-2.A-B); the subarterial conus was bilaterally absent. Angiogram showed that the left and right coronary arteries arose normally from the aorta, and the anterior descending artery came from the left coronary artery (Figure-2). Haemodynamics showed pulmonary arterial hypertension and a large left-to-right shunt.
The child underwent closure of the ventricular septal defect through the tricuspid valve; no abnormal coronary artery crossing the right ventricular outflow tract was found. Intraoperatively, the diagnosis of ACM and bilaterally absent conus was confirmed.
ACM is a rare malformation and bilaterally absent conus is an even more rare association. The L-malposition of the great arteries occurs on D-loop ventricles, and the D- malposition of the great arteries occurs on L-loop ventricles. No transposition was present because the great arteries were normally connected to their respective ventricles.
Two basic types of ventriculoarterial and intra-vessel relations have been described in ACM:1 D-loop ventricles and L-malposition of the great arteries, as in our case; and second, L-loop ventricles and D-malposition of the great arteries. These types can occur in situs solitus, situs inversus or asplenia syndrome,1,3 levocardia or dextrocardia. A myriad of associated defects including juxtaposed atrial appendages, tricuspid atresia in ventricular septal defects, arch hypoplasia, and coarctation of aorta, various conal abnormalities such as hypoplastic conus, bilaterally present or absent under the pulmonary artery and/or the aorta, have been reported.1-5 The association of bilaterally absent conus, as in our case, is rare.4
The inter-arterial and ventriculoarterial relationship develops after a complex set of events.6-8 In normal hearts, the great vessels are such that the pulmonary artery is superior, left and anterior due to the persistence and continued growth of subpulmonary conus, and the aorta is posterior, inferior and right to the pulmonary artery1 due to the absorption of the subaortic conus. Thus, the right ventricular outflow tract crosses the aorta anteriorly connected to the pulmonary artery, and the absorption of the subaortic conus connects the aorta to the left ventricle and mitral-aortic continuity.
After the septation of the conotruncus, the aorta lies to the right of the pulmonary artery in parallel, above the right ventricle. The most important mechanism which normally brings the aorta posterior and above the left ventricle is an 80-110 degree counter-clockwise rotation of the conotruncus looking from the ventricles downstream.7
The subaortic conus is absorbed and the subpulmonary conus growth brings the pulmonary artery superiorly to the left of aorta so that the right ventricular outflow tract crosses the aorta anteriorly.
Our invoking of over-rotation of the conotruncus as a cause of ACM is based on observations on human embryos as well as experimental animals.
The normal 110 degree conotruncal rotation (Figure-3.A- B) would produce normally positioned great arteries, while a 90 degree rotation produces anterior pulmonary artery and posterior aorta. Less than 90 degree counter- clockwise rotation of the conotruncus would lead to a gradual left and anterior positioning of the pulmonary artery, and a right and posterior shift of the aorta. Approximately 180 degrees of over-rotation would produce reversal of the starting position of the great arteries, that is, aorta to the left and pulmonary artery to the right, side by side and parallel with each other above their related ventricles, as seen in anatomically corrected malpositions. Rotational abnormalities of the conotruncus such as arrest of the rotation in experimental animals, produces a double outlet right ventricle. The transposition of the great arteries is caused by arrested conotruncus rotation.
Conal muscular abnormalities such as shortened conus have been associated with arrested conotruncal rotation in animal experimentation. The evidence of conotruncal rotation and rotational abnormalities is well-established in recent studies.11,12
Over-rotation of the conotruncus in L-loop ventricles leads to D-malposition, and over-rotation in D-loop ventricles leads to L-malposition types of ACM (Figure- 4.A-B and Figure-5.A-B).
The arrested conotruncal rotation in D-loop ventricles is well-established in experimental animal studies, and it has been shown to result in complete transposition. Therefore by extending the same logic, L-loop ventricles arrested conotruncal rotation would create corrected transposition (Figure-6.A-B).9-11 ACMs must be differentiated from corrected transposition of great arteries because it can pose difficulties for the surgeon to correct the intra-cardiac defects due to the position of the right coronary artery.12
The increasing reports of ACM of the great arteries suggest that the anomaly may not be as rare as it is thought to be. More powerful imaging modalities such as CT angiography and magnetic resonance imaging are being used to diagnose ACM and therefore increasing reports of such cases are coming forward.
The authors wish to acknowledge Dr. Sohail Bungash for the intraoperative findings and Dr. Habiba Tasneem for supplying the preoperative echocardiographic data.
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Department of Paediatric Cardiology, National Institute of Cardiovascular Diseases, Karachi, Pakistan. Correspondence: Kalimuddin Aziz. Email: email@example.com
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|Publication:||Journal of Pakistan Medical Association|
|Date:||May 31, 2013|
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