Delayed primary arterial switch for a rare and unusual variant of transposition of great arteries with posterior aorta

Abstract

Though initially described in 1971 by Van Praagh, transposition of great arteries with posterior aorta is rarely reported in last two decades. Since the arrangement of great arteries appears like normally related great arteries, a careful echocardiographic evaluation is necessary in patients with clinical features of transposition of great arteries. In majority of cases with this anatomy, arterial switch operation can be performed without the need of Le Compte manoeuvre.

Introduction

Transposition of great arteries with posterior aorta is a very rare entity. As opposed to transposition of great arteries with anterior aorta, this condition can mimic transposition of great arteries with normally related great arteries. Hence, it poses a challenge for its antenatal detection. Postnatally, a detailed echocardiographic assessment is needed not only for diagnosis but for planning surgical treatment. We report such a case of transposition of great arteries with posterior transposition ¹ managed by late primary arterial switch procedure.

Case report

Three-month-old female patient weighing 4.3 kg presented to hospital with complaints of cyanosis and fast breathing. Her perinatal history was uneventful, and antenatal scans were reported to be normal. Symptoms were tachycardia and tachypnoea, and oxygen saturation was 72% on room air. Auscultation revealed narrow split-second heart sound and a pan systolic murmur. Her chest radiograph was unremarkable with normal pulmonary vascularity. Electrocardiogram showed normal sinus rhythm with prominent right ventricular forces. On echocardiogram, she was noted to have situs solitus, levocardia and viscero-atrial, atrioventricular concordance. The great arteries appeared to be normally related. However, detailed evaluation showed the pulmonary artery arising anteriorly and leftward and was arising from the posterior left ventricle with noticeable conal tissue. Aorta was seen arising posteriorly and rightwards from anterior right ventricle. There was tricuspid-aortic valve continuity. Thus, the diagnosis of transposition of great arteries with posterior aorta was confirmed. There was a small ventricular septal defect which was slightly overridden by aortic valve. Coronary arteries originated from facing sinuses with left anterior descending and right coronary artery from sinus 1 and circumflex artery from sinus 2. Coronary artery from sinus 1 had an origin at sinotubuar junction and appeared difficult for translocation for arterial switch operation. Pulmonary valve was doming in morphology with mild systolic flow acceleration. Left ventricle appeared semi-prepared with LV mass of 48 Gm/m². Preoperative cath was not done because the echo images were clear and demonstrative of the anatomy and left ventricle appeared semiprepared but adequate to take pressure after an arterial switch surgery.

A delayed primary arterial switch procedure was planned. After sternotomy on external inspection, the relation between aorta and the pulmonary artery appeared almost normal with pulmonary artery arising anteriorly and to the left of aorta. Coronary artery anatomy was confirmed as in the preoperative assessment. Standard cardiopulmonary bypass was established with aortic and bicaval cannulation with moderate hypothermia and antegrade cardioplegia (DelNido) was given through aortic root. The left heart was vented through right superior pulmonary vein. Aorta was transected above the sinotubular junction and the coronary buttons carefully harvested. The right coronary artery was mobilised of the epicardium for allowing easy transfer. Pulmonary artery was divided proximal to the confluence and the coronary buttons were translocated to the neoaortic root using the medial based trap door flap method and slightly rotating the coronary button from sinus 1 medially to prevent kinking. Neo pulmonary artery was reconstructed using a rectangular patch of autologous fresh pericardium and commissures suspended with suture. LeCompte manoeuvre was not performed. Neopulmonary artery was sutured to an extended incision on inferior aspect of the right pulmonary artery to move the PA confluence rightward to avoid angulation and torsion. Ventricular septal defect was closed through right atrium by direct closure using pledgeted sutures. Cardiac activity recovered in sinus rhythm after deairing and cross-clamp release with no discernible electrocardiographic changes. Patient was weaned off bypass with milrinone 0.5mcg/kg/min inotropic support. Primary chest closure done on table after hemostasis. Two doses of cardioplegia with DelNido (20 ml/kg) were used during surgery with a Cross clamp time and cardiopulmonary bypass time of 224 and 292 minutes, respectively. Post-operative period in intensive care unit was uneventful. Patient was extubated after 48 hours. Post-procedure echocardiogram was suggestive of minimal flow acceleration across neoaortic valve, unobstructed flow across neopulmonary valve and normal biventricular function. She was discharged on eighth post-operative day.

Discussion

Though the developmental aspects of transposition of great arteries are largely unknown, it is considered to be related to abnormal development, growth, absorption of distal infundibular conal septum during 30–34 days of fetal life. It is hypothesised that the abnormal development of subaortic conal septum (instead of subpulmonic conal septum) leads to rightward, anterior and superior protrusion of aortic valve placing it above developing right ventricle. At the same time, failure of development of subpulmonic infundibulum leads to posterior placement of pulmonary valve with fibrous continuity with mitral valve.

However in very rare scenarios instead of straight conal septum and parallel outflows, there can be spiral truncal septum which mimic normally related great arteries. In these cases, due to variation in conal growth aortic valve remains in continuity with atrioventricular valves. Subpulmonic conus though not completely normal protrudes pulmonary valve anteriorly and leftwards but in continuity with left ventricle. ² This entity can pose difficulty in antenatal diagnosis of transposition of great arteries owing to appearance like normally related great vessels. Postnatal detailed clinical evaluation and echocardiogram help in appropriate diagnosis and planning surgical intervention.

Arterial switch operation (Jatene procedure) is a standard and logical procedure for transposition with posterior aorta. In most of these cases, Le Compte manoeuvre is not required. ³ However, location and length of coronary arteries may pose an additional obstacle in this operation. Intraventricular rerouting with VSD creation and total resection of infundibular septum has been described by Ishibhashi et al. ⁴ Though this procedure is mentioned as successful, a concern of ventricular outflow obstruction and ventricular dysfunction remains in long-term follow-up. Hence, Jatene procedure remains the first choice of intervention in transposition with posterior aorta.