Bulboventricular foramen enlargement: an alternative surgical approach

Abstract

Bulboventricular foramen (BVF) enlargement is often required to enlarge a restrictive interventricular communication in patients with univentricular hearts (UVH) to prevent the development of systemic ventricular outflow tract obstruction (SVOTO). We describe an alternative surgical technique through the transected pulmonary artery without an atriotomy, ventriculotomy or aortotomy that was successfully performed in a patient with double inlet left ventricle (DILV) with malposed great arteries (MPGA) and a restrictive BVF.

Introduction

The bidirectional superior cavopulmonary anastomosis (BDG) is an accepted intermediate-stage palliation for patients with single ventricle physiology, prior to the final Fontan procedure. In patients with a restrictive interatrial communication, atrial septectomy is an integral component of this operation. We have previously described the technique of atrial septectomy through the transected cardiac end of the superior vena cava (SVC) during the BDG [1]. Obstruction to the systemic flow in patients undergoing staged palliation for single ventricle variants is detrimental to the Fontan circulation. In patients with a DLIV with ventriculoarterial discordance, the incidence of SVOTO due to a restrictive BVF is high [2]. In this report, we describe an alternative surgical approach for BVF enlargement that can be performed concomitantly with the BDG in a selected group of patients.

Case report

Informed consent was obtained from the parents of this patient to publish this case report and the institutional ethics committee waived the need for a formal approval provided the patient identity was not disclosed.

A 10-year-old male child presented with cyanosis and exertional dyspnea. On physical examination, he had central cyanosis (saturation on room air was 70%) with no features of congestive cardiac failure. Echocardiography revealed DILV and a hypoplastic right ventricle with malposed great arteries. The interatrial septum was intact and the interventricular communication represented by a BVF that was restrictive with a gradient 105 mmHg across it. In addition, there was mild to moderate left atrioventricular valve regurgitation (AVVR). Computerised tomographic (CT) angiography (Fig. 1) was performed which confirmed the diagnosis of DILV with malposed great arteries and a restrictive BVF (3 mm).

Fig. 1.

Preoperative CT angiography axial cut section showing 3-mm BVF. BVF, bulboventricular foramen

Surgical technique

Presence of an intact interatrial septum and restrictive BVF was confirmed intraoperatively by tranesophageal echocardiography (TEE) that was also used to assess the adequacy of the septectomy and BVF enlargement after termination of cardiopulmonary bypass (CPB). Presence of left AVVR was also confirmed. A 22-G needle was placed in the right internal jugular vein to assess the Glenn pressure following termination of CPB.

Surgical approach was via a median sternotomy. A needle that was placed in the main pulmonary artery (MPA) revealed the pulmonary artery pressure to be 17/9 (mean 12 mmHg). Juxtaposed atrial appendages were present. CPB was established after cannulating the aorta and the superior and inferior vena cavae with core cooling to 32 °C. The SVC was dissected and the azygous vein was divided. The MPA was looped after separating it from the aorta. Both pulmonary arteries were dissected and mobilised completely up to the hilum of both the lungs. Both the cavae were then snared and the aortic cross clamp was applied. Before starting the administration of cardioplegia, the SVC was divided at its cardiac end and a cardiotomy sucker was inserted through the cardiac to vent the heart. After delivering cardioplegia, a wide atrial septectomy was performed through the cardiac end of the SVC using the technique described by us earlier [1].

The MPA was divided just above the commissures. The pulmonary valve was found to be thickened with commissural fusion and excised. We considered the difficulty in enlarging a restrictive BVF through the atrium in view of the presence of juxtaposed atrial appendages. Hence, a decision to accomplish this via the pulmonary artery was taken (Fig. 2). With the help of two small retractors, the interventricular septum and the BVF were visualised. The latter measured only 4 mm. Using a sharp scissor, the anterior and leftward margin of the BVF was excised in an anteroinferior direction towards the cardiac apex and the resultant opening measured approximately 2.5 cm in size. Following this, the MPA and cardiac end of the SVC were closed in two layers and after routine de-airing manoeuvres, the aortic cross clamp was released. The BDG anastomosis was then completed in a standard fashion during the period of rewarming and the patient was weaned off CPB support on dobutamine (5mcg/kg/min). Post CPB, TEE revealed unrestricted flow across atrial septum and BVF (Fig. 3a–d). There was also decrease in left AVVR to mild, due to decrease in ventricular pressures following enlargement of the BVF. Glenn pressure as measured by a needle in the right internal jugular vein was 9 mmHg. Postoperative course was uneventful and patient was discharged on day 5. There were no arrhythmias or aortic or atrioventricular valve insufficiency.

Fig. 2.

Sketch diagram showing divided main pulmonary artery and transpulmonary approach to the BVF enlargement. BVF, bulboventricular foramen; MPA, main pulmonary artery

Fig. 3.

a Intraoperative TEE showing intact atrial septum. b Intraoperative TEE showing restrictive VSD (BVF) and hypoplastic RV, with moderate Left AVVR. c Intraoperative TEE post-surgery showing post atrial septectomy status. d Intraoperative TEE post-surgery showing enlarged BVF. BVF, bulboventricular foramen; IAS, interatrial septum; RV, right ventricle; LV, left ventricle; RA, right atrium; LA, left atrium

Discussion

BVF is defined as a communication between a dominant left ventricle and rudimentary right ventricle (a remnant of the bulbus cordis) in a functionally univentricular heart with transposed great arteries [3]. Restrictive BVF is an important cause of obstruction to the systemic outflow. This obstruction and its sequelae, ventricular hypertrophy and dysfunction, causing AVVR have been identified as incremental risk factors for poor outcome after the Fontan operation.

The major surgical approaches to the relief of BVF obstruction in patients with single left ventricle (LV) are the Damus Kaye-Stansel (DKS) procedure or direct BVF resection or a palliative arterial switch operation [4, 5]. Each strategy has its advantages and disadvantages.

Theoretical advantages of the DKS include better relief of outflow gradients, lower potential incidences of postoperative heart block and lower incidences of reoperation. Potential disadvantages of this approach include increased semilunar valvar insufficiency, causing increased volume overload and a technically more difficult operation. In our patient, a thickened and dysplastic pulmonary valve precluded a DKS which would otherwise be an obvious choice in a small infant with a normal pulmonary valve.

Several groups have advocated BVF enlargement as an alternative strategy for the management of single ventricle patients with SVOTO [5–8]. The BVF enlargement can be accomplished via the right atrium, right ventricle or via the aorta. However, each approach has its own disadvantage. Moreover, the intimate relationship of the BVF with the semilunar valves and atrioventricular valves (AVV) may disallow adequate enlargement thus leading to insufficient SVOTO relief or recurrence of obstruction. Transatrial approach and an atrial suture line may cause atrial arrhythmias post-operatively and the atrial suture line may increase formation of adhesions that may complicate a future Fontan completion. Transventricular approach carries the disadvantage of ventricular dysfunction, arrthymias and late aneurysm and may be difficult in situations where a major coronary artery is crossing the right ventricular outflow tract (RVOT) [4]. The transaortic approach carries the risk of damage to the aortic valve and due to the intimate relationship of the BVF with the semilunar valves may disallow adequate enlargement thus leading to insufficient SVOTO relief or recurrence of obstruction. Some [4] however favour the transaortic approach as the primary choice because it is familiar to surgeons accustomed to performing other forms of subaortic resection, anatomic orientation is easily preserved and it maintains the contractile integrity of the subaortic outlet.

Advantages associated with transpulmonary artery approach include avoidance of ventriculotomy and its associated complications, decreased risk of heart block, avoiding atrial suture line and atrial arrhythmia, decreased chance of right atrioventricular valve injury and avoidance of junctional ectopic tachycardia due to right AVV stretch. In addition, we were also able to accomplish pulmonary valve excision from the same route. Finally, BVF enlargement may result in a high incidence of complete heart block necessitating permanent pacemaker implantation [4, 6, 8]. But via transpulmonary approach, since the margins of BVF can be clearly seen, chances of heart block can be minimised by following the principles as advised by Anderson et al. [9]. However, this approach cannot be used in patients in whom the pulmonary outlet has already been closed by a prior staging procedure. In addition, enlargement of BVF is nearly impossible to accomplish through the MPA in a small infant because of limited access. Therefore, this technique is best used in selected patients who are older and unsuitable for a DKS.

Compliance with ethical standards

Statement of human rights/ethical approval

All procedures performed in this study were in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. For this study, formal consent was obtained.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Conflict of interest

The authors declare that they have no conflict of interest.