Unidad Regiomontana de Diagnostico, Monterrey, N.L., México
 
Definition: Double-Outlet right ventricle is not a single malformation from a pathophysiologic point of view. The term refers only to the position of the great vessels that is found in association with ventricular septal defects, tetralogy of Fallot, transposition, and univentricular hearts. In double-outlet right ventricle, most of the aorta and pulmonary valve arise completely or almost completely from the right ventricle.
Abnormal development of the apical portion of the atrial septum, of the basal portion of the interventricular septum, and of the atrioventricular valves that depends on the development of endocardial cushions, is commonly referred to as endocardial cushion defects, atrioventricular canal defects, or atrioventricular septal defects. In the complete form the tricuspid and mitral valve are fused in a large single atrioventricular valve that opens above and bridges the two ventricles. This valve has an anterior and a posterior leaflet. This common atrioventricular valve may be incompetent, and systolic blood regurgitation from the ventricles to the atria may give rise to congestive heart failure.

Case report: A 16-year-old woman with no family history of malformations or genetic disorders attended the ultrasound unit at 23 weeks and had a routine anomaly examination. The following images were obtained during that examination.
 
Four chamber view in systole and diastole that shows a complete atrioventricular canal with a single AV valve, and the descending aorta displaced to the right.

Color Doppler of a complete atrioventricular canal that shows inflow through the central portion of the single AV valve, and regurgitation jet during ventricular systole

Dilatation and anterior displacement of ascending aorta, with small main pulmonary artery.

Dextroposition of ascending aorta, which is larger then the main pulmonary artery and is located more anteriorly.

Unidirectional anterograde flow through  main pulmonary artery and aortic arch. Pulmonary artery is small as a consequence of subpulmonary stenosis.

Incidence: Double-oulet right ventricle has an incidence of 0.32 per 10:000 live births.

Prevalence: In a recent study by Boudjemline et al., in a series of 337 cases of conotruncal heart disease, tetralogy of Fallot made 56% of these cases, vascular malposition 16%, coarctation with or without interruption of the aortic arch 14%, truncus arteriosus 9% and agenesis of the pulmonary valves 5%.

Etiology: Unknown.

Pathogenesis:  Double-Outlet right ventricle is due to an abnormal embryological development of the heart in which the normal rotational process of the conotruncal septum does not take place the way it should, and a lesser than 180-degree rotary motion is responsible for the dextroposition of the aortic artery, remaining in an anterior position in relation to the main pulmonary artery. Frequently, there is side-by-side relationship of the great arteries. When the associated ventricular septal defect is subaortic in location, subpulmonary obstruction with a small main pulmonary artery is common. In contrast, when the ventricular septal defect is subpulmonary, subaortic stenosis with small ascending aorta and hypoplastic aortic arch is common (the so-called Taussig-Bing malformation).

Sonographic findings: The linear alignment of the three vessels in the three vessels view is abnormal in most cases with double-outlet right ventricle, since ascending aorta tends to be located more anteriorly, which leads the sonographer to investigate the ventricular outflow tracts, finding the alignment of the aorta and pulmonary artery totally or predominantly from the right ventricle.

Differential diagnosis: Prenatal diagnosis of double-outlet right ventricle can be made reliably in the fetus, but differentiation from other conotruncal anomalies can be very difficult, especially with tetralogy of Fallot and transposition of great arteries with ventricular septal defect.

Associated anomalies: As opposed to other conotruncal malformations, extracardiac anomalies and/or chromosomal aberrations associated with fetal double-outlet right ventricle have frequently been found.

Prognosis: It depends on the anatomic type of double-outlet right ventricle and the associated anomalies. Because the fetal heart works as a common chamber where the blood is mixed and pumped, the presence of double-outlet right ventricle is not expected to be a cause of cardiac failure.

REFERENCES

S.J. Yoo, Y.H. Lee, E.S. Kim, H.M. Ryu, M.Y. Kim, H.K. Choi, K. S. Cho  and A. Kim. Three-vessel view of the fetal upper mediastinum: an easy means of detecting abnormalities of the ventricular outflow tracts and great arteries during obstetric screening. Ultrosound Obstet. Gynecol. 9 (1997) 173-182.

Fleischer AC. Manning FA, Jeanty P, Romero R, Sonography in Obstetrics and Gynecology. Principles and Practice. Sixth Edition 2001.

Brons JT, Van Geijn HP, Wladimiroff JW, et al. Prenatal ultrasound diagnosis of the Holt Oram syndrome. Prenat Diagn. 1988; 8:175.

Kleinman CS, Donnerstein RL, De Vore GR, et al. Fetal echocardiography for evaluation of in utero congestive heart failure: A technique for study of noninmune fetal hydrops. N Engl J Med. 1982; 306:568

Machado MV, Crawford DC, Anderson RH, et al. Atrioventricular septal defect in prenatal life. Br. Heart J. 1988; 59:352.