Introduction

DORV is a rare condition and accounts for 1-1.5% of all congenital cardiac malformations ₁. The anatomical variations are classified on the basis of: 1) the relationship between the VSD and the great arteries; 2) the position of the great arteries in relation to each other at the valvular level; 3) the presence of additional malformations.

In accordance with the relationship between the VSD and great arteries, DORV (Fig1. upper panel) is classified as: 1) DORV with sub-aortic VSD; 2) DORV with sub-pulmonary VSD; 3) DORV with doubly-committed VSD; and 4) DORV with non-committed VSD.

Subpulmonary VSD is the most frequently encountered anomaly, wherein the great arteries are positioned side by side or when the aorta is anterior and right sided (an arterial arrangement observed in complete transposition of the great arteries). Depending on the degree of overriding of the pulmonary valve in the trabecular region of the ventricular septum, different anomalies can be encountered (Fig1. lower panel), ranging from double outlet to transposition of the great arteries. Some authors prefer to group these malformations under the umbrella term “Taussig-Bing Complex₂.

Although these “Taussig-Bing Complex” hearts may resemble each other physiologically, there are significant morphological differences₃. The objective of our case presentation is to highlight the morphological features of the heart described by Taussig and Bing so as to be able to distinguish it from the heart clinically described under the common umbrella term “ Taussig-Bing complex₄ “.

Figure 1

Figure 1: Upper panel shows sub types of Double outlet right ventricle. Lower panel shows different anomalies encountered depending on degree of overriding of the pulmonary valve in the trabacular region. (DORV- Double outlet right ventricle, TGA- Transposition of great arteries, Ao- Aorta, VIF- Ventriculoinfundibular fold, PA- Pulmonary artery, OS- Outlet septum, VSD- Ventricular septal defect, TSM- Trabacula septo-marginalis).

Case 1 (46/06)

Post mortem examination of heart was performed in a one year old female child, clinically diagnosed as case of Taussig-Bing anomaly with severe PAH. She underwent an arterial switch operation, transatrial closure of VSD (gore-tex patch) along with reconstruction of arch of aorta (using bovine pericardium) & PDA ligation.

Grossly, the heart was enlarged and weighted 45grams. Neopulmonary artery was posterior and to the right of reconstructed aorta. On opening, right atrial chamber was dilated and a suture mark was noted in the fossa ovalis. Right atrioventricular valve was tricuspid. A pledged suture mark was noted on the septal leaflet. Right ventricle showed two outlets -. one was a large VSD with extension to sub-neoaortic region (with two additional small muscular VSDs) and another was the neopulmonary artery with bicuspid valve. Infundibular region showed a band of muscle obstructing the right outflow tract. Reconstructed anterior aortic cusps were seen prolapsing through the VSD.

Right coronary artery & left anterior descending artery were seen arising from sinus 2 and the left circumflex artery from sinus 1. Mitral valve was slightly dysplastic. Fibrous continuity was noted between the reconstructed aortic valve and mitral valve. PDA was found clipped and ligated.

In view of the gross anatomical features, a diagnosis of “Taussig-Bing complex” was made. (D-TGA with patent foramen ovale, large VSD and a PDA)

Case 2 (91/08)

Post mortem examination of the heart was carried out on a one and half month old male child, diagnosed clinically as Taussig-Bing anomaly with aortic isthmus hypoplasia. He underwent an arterial switch operation with VSD closure by gore-tex patch and aortic isthmus augmentation with autologus pericardial patch.

On gross examination, the heart weighted 35 grams. Apex was rounded. Neopulmonary artery was posterior and to the right of reconstructed aortic root. Coarctation of aorta at the isthmic region was observed. On opening, right atrium showed suture marks in fossa ovalis. Right atrioventicular valve was tricuspid. Anterior papillary muscle originated from the ventricular surface of moderate band. Right ventricle showed two outlets – a VSD (patched with PTFE) and a neopulmonary artery which was bicuspid

Reconstructed aorta was tri-cuspid and in alignment with the VSD and right ventricle (more than 50%). No coronary ostia could be probed through. Long axis of outlet septum was in alignment with the interventricular septum.

Pulmonary valve was close to mitral valve with fibrous continuity. No ventriculo- infundibular fold was noted. Left ventricle was well formed and it predominantly drained through VSD by alignment. Passage through junction with reconstructed aortic valve was narrowed by a muscular ridge. Mitral valve was bicuspid with normal papillary position.

Based on these findings a diagnosis of “Taussig-Bing complex” was rendered. (D-TGA with large VSD and coarctation of aorta at isthmic region).

Discussion

Double outlet right ventricle (DORV) is a heterogeneous group of conus arterisosus malformations. In literature, there has been no consensus as to the definition of DORV. Lev and Anderson et al defined DORV as “All of one great artery and 50% or more of the other artery must arise from the right ventricle” or in other words “an anomaly in which two cusps & part of third of both the semi lunar valves arise from the right ventricle”. The basis for their hypothesis is that, during conus malrotation, changes in position of anterior portion of the muscular interventricular septum and differential conus absorption lead to such malposition of great artery relations₅. DORV was first described by Birmingham in 1983, where both great arteries (pulmonary and aorta) arose primarily from the morphologically right ventricle. Le Compte proposed changing the term DORV to ‘malposition of great arteries’. Neufeld opined that, although the presence of aorto-mitral discontinity and bilateral coni are important descriptors, they should not serve as absolute pre-requisites for the diagnosis of DORV₆. Lacour-Gayet proposed nomenclature for a unique subset of DORV as 200% depending on the degree of deviation of the posterior outlet towards the right ventricle₇.

Characteristic features of the first heart described by Taussig and Bing include 1) Origin of the aorta from right ventricle 2) Aorta to the right of the pulmonary artery (side by side) 3) Pulmonary artery in its approximate normal position and overriding a VSD 4) Muscular ridge (defined as outlet septum) separating the origin of the two great vessels₄.

Physiologically, this malformation is characterized by higher oxygen content in the pulmonary artery than in right ventricle and aorta. It is difficult to differentiate such hearts from incomplete (owing to biventricular origin of pulmonary artery) transposition with over-riding pulmonary artery having similar physiological abnormalities₃. In these cases, relationship of the two vessels to each other in normal anatomical position is of greater diagnostic relevance than biventricular origin of the pulmonary artery.

Some authors prefer to include all cases of juxta-pulmonary VSD with misalignment of infundibular septum under the rubric of Taussig-Bing complex, possibly because of common features necessitating similar surgical options₂. Strictly speaking, a bilateral infundibulum is a fundamental requisite for defining the Taussig-Bing heart₈. By definition, VSD should provide the only outlet for the other ventricle in DORV. Initial descriptions of DORV required that both great arteries arise completely from right ventricle, with no fibrous continuity between the mitral & semi lunar valves.₉

Angelini and associates favor an older definition – ‘transposition of great arteries’ (TGA). TGA is present when aortic valve and ascending aorta are anterior to pulmonary valve and main pulmonary artery. However, Van Praagh & Van Praagh have described “Posterior transposition” in 11% of autopsy-proved cases of TGA with dextrocardia₁₀.

In 1814, when John Richard Farre introduced the word “transposition of the aorta and pulmonary aorta” he referred to the presence of aorta above right ventricle, and pulmonary aorta above left ventricle. A more precise definition would therefore be DORV or TGA, but not ‘DORV and TGA’. Besides, the surgical implications of either diagnosis – DORV or TGA – can be very different and so it would be mandatory from a therapeutic standpoint that a specific diagnosis is rendered.

The true Taussig-Bing heart is a type of DORV, with double subarterial conus and mitropulmonary discontinuity₈. The pulmonary artery always arises entirely from the right ventricle, independent of size and location of the VSD, either close or distant from the sub-pulmonary conus. In conditions, where the pulmonary artery does not entirely arise from the right ventricle, the sub-pulmonary conus does not exist and the malformation must correctly be designated as a D-TGA, independent of the grade of pulmonary overriding₁₁.

The sagitally malpositioned infundibular septum is the cause for subaortic obstruction and also determines the location of VSD, which always related to trabecula septomarginalis (an extensive septal trabecula of the right ventricle), above, below or between the arms of the trabecula.

The heart, as described by Taussig and Bing is quite dissimilar from the D-TGA hearts with pulmonary overriding, a frequent source of confusion in literature. However, a thorough morphological examination combined with utilization of non-invasive diagnostic modalities like angiocardiography, echocardiography and cardiac catheterization, will aid in rendering a more accurate diagnosis.

We propose that the following points be considered in a Taussig–Bing Heart, 1) presence of ventricular septum/ shadow cast of the pulmonary conus of right ventricle in antero-posterior view on angiocardiogram 2) presence of wide vascular shadow with prominent pulmonary segment in postero-anterior view and aorta projected anteriorly upon left anterior oblique view on X-ray 3) step-up in oxygen content in the right ventricle / PA oxygen content higher than in the aorta 4) morphologically - presence of subpulmonic VSD (in supracristal region), presence of subarterial conus and mitro-pulmonary discontinuity (due to left sided ventriculo infundibular fold).

With clinico-pathological correlation, such hearts can be more accurately classified as DORV of “Taussig-Bing type”, since an alternative surgical option needs to be considered as opposed to the common arterial switch operation with closure of VSD. Other hearts could be collectively labeled “Taussig-Bing complex” with specific description of the morphological sub type.

Correspondence to

Frontier Life Line, International Center for Cardio Thoracic and Vascular Diseases. R-30-C Ambatture Industrial Estate Road, Mogappair Chennai-600101. INDIA Tel:+91444201 7575 Fax: +914426565150 Pathneel@gmail.com