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Interact CardioVasc Thorac Surg 2009;8:211-215. doi:10.1510/icvts.2008.187963 © 2009 European Association of Cardio-Thoracic Surgery
Impact of 3-mm Blalock–Taussig shunt in neonates and infants with a functionally single ventricle
a Department of Cardiovascular Surgery, Kanagawa Children's Medical Center, 2-138-4 Mutsukawa, Minami-ku, Yokohama, Kanagawa 232-8555, Japan Received 9 July 2008; received in revised form 16 October 2008; accepted 23 October 2008
*Corresponding author. Tel.: +81-45-711-2351; fax: +81-45-721-3324.
Functionally single ventricle (f-SV) is susceptible to volume overload. Atrioventricular valve regurgitation (AVVR) tends to develop and ventricular function deteriorates due to excessive pulmonary blood flow following modified Blalock–Taussig shunt (mBTS). On the other hand, a small caliber graft has risks of early obstruction and poor growth of pulmonary vascular beds. We assessed the effect of mBTS with a 3-mm graft to circumvent volume overload in f-SV on achievement of the right heart bypass. Eleven neonates and infants with f-SV at the median age of 24 days underwent mBTS using a 3-mm graft between August 2004 and June 2007. There were no early deaths, but there was one late death. All survivors achieved bidirectional cavopulmonary shunt (BCPS) at 4.2 months after mBTS. Cardiac catheterization demonstrated sufficient growth of the pulmonary artery (pulmonary artery index, 268±98 cm2/m2), low pulmonary vascular resistance (1.4±0.9 U·m2). The AVVR remained mild or less. Ventricular end-diastolic volume and ejection fraction were 171±61% of the normal value and 64±6%, respectively. We conclude that a 3-mm mBTS was useful in preventing f-SV from volume overload and was effective for growing good pulmonary vasculature and achieving a right heart bypass.
Key Words: Congenital heart disease; Blalock–Taussig shunt; Single ventricle; Fontan
Functionally single ventricle is susceptible to volume overload. Excessive pulmonary flow through a large Blalock–Taussig shunt (BTS) may worsen atrioventricular valve regurgitation (AVVR) and can thus lead to ventricular dysfunction [1–3]. On the other hand, BTS with a small graft may develop shunt occlusion in an early stage and lead to poor growth of pulmonary vascular beds. As a consequence, patients would fail to be good candidates for right heart bypass operation [4, 5]. Recent improvements in the Norwood operation, however, have demonstrated that a 3-mm graft is useful in maintaining ventricular function and thus achieving a right heart bypass operation in patients with hypoplastic left heart syndrome [6, 7]. There was also a report showing no significant differences in size of shunt in pulmonary artery (PA) growth [8]. These facts encouraged us to consider a 3-mm graft for non-open heart palliation in patients with a functionally single ventricle. No studies have focused on the usefulness and effectiveness of BTS using a 3.0-mm graft, although several reports have used a 3.5-mm or larger graft. Therefore, in this study, we focused on a group with a 3.0-mm graft. The purpose of this study was to demonstrate the effectiveness of a 3-mm BTS on ventricular function and pulmonary vascular growth, and to assess the achievement of a right heart bypass operation.
2.1. Patients Eleven neonates and infants with functionally single ventricle underwent modified BTS using a 3-mm expanded polytetrafluoroethylene (ePTFE) graft at Kanagawa Children's Medical Center between August 2004 and June 2007. Preoperative characteristics of the patients are shown in Table 1. During the same period, 19 neonates and infants with functionally single ventricle underwent modified BTS as the first stage of a Fontan operation. A 3.0-mm shunt was used in 11 and a 3.5-mm in 8. Pulmonary arterial blood flow was dependent on the duct in 7 out of 11 patients and supplied by antegrade flow or major collateral arteries in the others.
2.2. Operative technique In seven patients, the chest was entered through a lateral thoracotomy at the opposite side of the aortic arch. Median sternotomy was also performed in four patients when the concomitant procedure was needed. The size of a graft to use was determined intra-operatively on the basis of anastomotic PA size first and proximal systemic artery size second. When the size of PA at its anastomotic site was >4 mm, we used a 3.0-mm graft. When it was <4 mm, we used a 3.5-mm graft. A 3-mm-ePTFE graft was interposed between the subclavian artery and the PA in nine patients. In two patients it was interposed between the carotid artery and the PA. The runoff of the PA was mainly dependent on the extent of the incision on the subclavian artery. When it was likely to have good runoff because the pulmonary artery was well grown, we incised the subclavian artery rather distally. In contrast, when the PA was small, we extended the incision partly onto the brachiocephalic artery. We made sure that the graft was anastomosed to the pulmonary artery as proximally as possible. Concomitantly, the pulmonary trunk was banded in one patient and ligated in one patient when major antegrade flow to the lungs was present. The duct was ligated in one patient (left-side shunt) and banded in two patients (median sternotomy in 1, left-side shunt in 1). The major aortopulmonary collateral arteries were ligated in one patient. 2.3. Postoperative management protocol Patients were deeply sedated and paralyzed for the first 24 h. The median duration of postoperative mechanical ventilatory support was three days. Oxygen was used in the early postoperative period depending on the presumed changes in pulmonary resistance after surgery. Anticoagulation therapy was started after the BTS procedure. Heparin infusion commenced immediately after bleeding was identified as minimal and continued for five days. Aspirin was initiated when starting oral feeding. The continuous data in this study are expressed as mean values±S.D. or as median values. Analyses were performed using SPSS software (Version 11.0J; SPSS Inc., Chicago, IL, USA). The probability of BCPS achievement was calculated using the Kaplan–Meier method.This study was approved by the Ethics Committee of the Kanagawa Children's Medical Center.
3.1. Fate of the duct and postoperative course To avoid excessive pulmonary blood flow after surgery, we administered prostaglandin preoperatively so that it would spontaneously close soon after creating the BTS. Therefore, we changed PGE1 to prostaglandin CD at one week before surgery. Echocardiogram showed that the size of the duct started to decrease between 6 and 24 h after discontinuing prostaglandin CD. Meanwhile, the blood flow through the graft started to increase during the same period. Thereafter, the duct was completely closed from 5 to 12 days after surgery in most patients. At discharge, median percutaneous oxygen saturation was 80% (70–90%). Echocardiogram at discharge revealed that AVVR was trivial, or none, in all patients. There were no instances of stenosis in the central pulmonary artery. There was a prolonged hospital stay in two patients; both of whom incurred acute graft thrombosis at 50 and 81 days after surgery, respectively; which was successfully treated by emergency catheter thrombolysis therapy. Both had a tendency for graft thrombosis. One had pulmonary atresia with intact ventricular septum associated with Protein-C deficiency characterized by hypercoagulability. A diagnosis of Protein-C deficiency was yet to be made when the graft was occluded. Another patient had a univentricular heart associated with both VATER association and bronchomalacia. High end-expiratory pressure was needed to avoid airway obstruction in the expiratory phase. The patient recovered from the event, but died of sepsis following respiratory infection at 96 days after modified BTS. 3.3. Achievement of right heart bypass Cardiac catheterization before BCPS is shown in Table 2. Atrioventricular valve regurgitation remained at a level of mild or less and the ventricular function was kept within the normal range with ejection fraction at 63±6%, ventricular end-diastolic volume of 186±71% of normal and ventricular end-diastolic pressure of 7±3 mmHg. Pulmonary angiography showed excellent growth of the PA without any stenosis (Fig. 1).
All survivors accomplished BCPS at 2.0–7.8 months (median, 4.0 months) after 3 mm BTS (Fig. 2) and one patient after another shunt, as mentioned above. The age at BCPS ranged from 3.0 to 10.0 months (median, 5.5 months). Concomitant procedures included TAPVD repair in two patients. At the follow-up after 7.6–41.6 months (median, 26.2 months), a Fontan operation with an extracardiac conduit had been performed in seven patients at the age from 15.0 to 25.3 months (median, 22.6 month) and the others were waiting for Fontan and were in a good hemodynamic state (Fig. 3).
Recent improvements in the Norwood operation have demonstrated that a rather small shunt is useful in reducing excessive volume load to the ventricle and the pulmonary beds in a functionally single ventricle. In this study, we demonstrated the successful application of a 3-mm shunt in patients with a functionally single ventricle with duct-dependent pulmonary circulation. We successfully achieved BCPS as the second stage in the staged Fontan strategy. 4.1. Graft size and the timing of the 2nd stage Ventricular function was maintained in a stable condition with minimum AVVR. The pulmonary artery grew well and the pulmonary vascular resistance was demonstrated to be low. We believe that a 3.0-mm BTS avoided volume overload by obliterating excessive pulmonary blood flow and thus maintained ventricular function at a reasonable level. On the other hand, even a 3-mm graft was large enough for the PA to grow adequately to attain right heart bypass. As a result, the second stage of a right heart bypass was successfully undertaken in a reasonable period in most of our patients. It appears that the minimum pulmonary blood flow using a 3.0-mm graft gave maximum gain from the vascular beds and the ventricle.Obviously, a 3-mm BTS might not remain patent as long as a 3.5- or 4-mm shunt. Recent successful application of BCPS at an earlier age, however, could circumvent such limitations associated with a 3-mm BTS [9–13]. It has been demonstrated that the pulmonary-to-systemic flow ratio significantly increased after placement of the shunt and, therefore, the shunt provided significant volume overload to the ventricle. Therefore, we prefer earlier application of BCPS. Chang et al. [11] reported encouraging early results in terms of improved oxygenation with low morbidity and mortality in infants who underwent BCPS at an age ranging from 4.2 to 6.5 months old. Jaquiss et al. [10] revealed that early BCPS after Norwood operation did not show a significant increase in mortality compared with an older group of patients (4 months) although the rate of morbidity was higher in the younger group of patients. However, a lower age limit for BCPS does seem to exist. Reddy et al. [13] performed BCPS at an earlier age of between 0.8 and 6.0 months and recommended that BCPS should be deferred until the patient is at least two months old. We should mention several important points for managing patient care. First, prostaglandin E1 could be changed to Prostaglandin CD at about one week before surgery so that the duct can be reduced in size several hours after surgery. This may then prevent the ventricle from acute volume overload after BTS. Second, although the duct tended to close spontaneously several days after surgery in all our patients, we do not recommend ligating a duct during surgery since a 3.0-mm shunt seemed only marginally sufficient to maintain an adequate oxygen level in the immediate postoperative period when pulmonary resistance changes. In the case that underwent sternotomy, we preferred to interpose a graft between the carotid artery and the PA to control the graft flow with adjustment of length.A significant correlation between non-confluent PA and mortality in the heterotaxy syndrome has been reported [14]. There was no PA coarctation in our series of patients, which included heterotaxy syndrome in four patients. We paid careful attention to the possibility of pulmonary coarctation during these procedures as a matter of course. Anticoagulation therapy needs to be discussed. We used heparin infusion for five days after BTS and gave oral aspirin to all patients when starting oral feeding, and warfarin in some cases. Aspirin reduces the risks of morbidity and mortality from aorto-pulmonary artery shunts [7]. Warfarin therapy is problematic because it may be hard to correctly manage coagulation level in a small baby. Although the grafts were occluded in two patients, those might be exceptional, as one had undiagnosed coagulopathy and another had long-standing high airway pressure owing to bronchomalacia.
In creating the aortopulmonary shunt, we used the smallest BTS currently available, a 3-mm shunt, and assessed the clinical outcomes. We conclude that a 3-mm BTS successfully prevented the functionally single ventricle from volume overload, allowed the growth of pulmonary vascular beds and enabled the subsequent right heart bypass operation.
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Abstract
1. Introduction
