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Eur J Cardiothorac Surg 2005;27:801-806
© 2005 Elsevier Science NL
Department of Paediatric Cardiac Surgery, Diana, Princess of Wales Children's Hospital, Steelhouse Lane, Birmingham B4 6NH, UK
Received 10 September 2004; received in revised form 10 January 2005; accepted 17 January 2005.
* Corresponding author. Tel.: +44 121 333 9435; fax: +44 121 333 9441. (E-mail: william.brawn{at}bch.nhs.uk).
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Abstract |
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 Top Abstract 1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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Key Words: Heart defects • Congenital • Hypoplastic left heart syndrome • Shunts • Stenosis • Catheterisation
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1. Introduction |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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Although results of the Norwood procedure have improved dramatically over the past 20 years, the perioperative mortality and morbidity remains high. Operative techniques and intensive care management are constantly evolving and changing in an attempt to improve outcomes. One of the most important recent developments has been the emergence of the right ventricular-pulmonary artery (RV–PA) conduit as an alternative to the classical Blalock Taussig shunt as the source of pulmonary blood flow [2].
The potential benefits of the RV–PA conduit include more stable haemodynamics, higher diastolic pressure with improved coronary blood flow, predominately systolic pulmonary blood flow and potentially reduced interstage mortality [3–5]. These advantages have led us to adopt this modification as the standard procedure for HLHS in this unit since May 2001.
It has also been suggested that pulsatile flow through the RV–PA conduit may promote better pulmonary artery growth [3]. One of the fundamental aims of the multi-stage palliation is to ensure optimal pulmonary artery growth without any stenoses, so as to provide the best possible substrate for the Fontan procedure.
This study was undertaken to compare the size of the central pulmonary arteries following the stage I Norwood procedure using either a classical BT shunt or an RV–PA conduit in a consecutive series of infants with HLHS prior to conversion to Stage II. The aim was to determine whether the source of the pulmonary blood supply affected the size of the pulmonary arteries and the presence significance of shunt-related stenoses.
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2. Materials and methods |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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Of the 30 patients included in this study, 19 patients (63%) were male. Preoperative demographic data were broadly comparable between the two groups, as summarised in Table 1.
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In the classical group during the cooling phase, the pulmonary anastomosis of a modified Blalock–Taussig shunt was completed with a polytetrafluoroethylene (PTFE) tube conduit (GORE-TEX®, W.L. Gore & Associates (UK) Ltd. Livingston, Scotland) to the upper border of the right pulmonary artery. The proximal shunt anastomosis to the innominate artery was completed during the rewarming phase utilizing a side-biting clamp. A 3.5mm shunt was used in patients 
2.5kg (n=17) and a 3mm shunt was used in patients <2.5kg (n=1).
In the RV–PA group, an incision was made to the central pulmonary artery patch to which a pre-shaped polytetrafluoroethylene (PTFE) tube conduit (GORE-TEX®) was anastomosed using 8/0 monofilament suture. The conduit was cut to length and the proximal end anastomosed to a ventriculotomy in the distal infundibulum of the right ventricle using a 7/0 monofilament suture. A 5mm shunt was used in all patients 2.0kg (n=11) and a 4mm shunt was used in patients <2.0kg (n=1).
Cardiopulmonary bypass, cross-clamp and circulatory arrest times for the two techniques are shown in Table 2. Antegrade cerebral perfusion was introduced during the period of this study and used when the head-and neck vessels were of suitable size to accommodate the arterial cannula during arch reconstruction. During antegrade cerebral perfusion, bypass was recommenced at 1.2lmin–1m–2. The introduction of antegrade cerebral perfusion was made independently of the conversion to a modified Norwood procedure with a right ventricle–pulmonary artery conduit. However, only a small proportion of patients in the classical group (17%, n=3) received antegrade cerebral perfusion whereas it was used in all patients in the RV–PA group (100%, n=12; Table 2). Both groups of patients were commenced on heparin (10Ukg–1h–1) within several hours of their return to the intensive care unit and aspirin therapy (5mgkg–1) was initiated prior to ICU discharge.
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2.1. Data analysis
This study involved the retrospective review of all hospital records, operation notes, and echocardiographic and cardiac catheter data. Data have been examined by analysis of variance using a commercial statistical software package (SPSS for Windows, version 11, SPSS Inc, Chicago, IL, USA). Continuous variables are expressed as mean±standard deviation or median (range) and comparative univariate analyses have been made using the t-test, Mann–Whitney U-test or Wilcoxon signed rank test, as appropriate. Binomial or ordinal data are expressed as percentage and comparative univariate analyses have been made using the 
2 test or two-sided Fisher exact test. A probability value, P<0.05, was taken to represent a statistically significant difference between groups.
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3. Results |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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Twenty-four patients (80%) had central PA stenoses causing a 25% reduction in either the maximum indexed LPA or RPA diameter. There was no difference in the relative distribution (P=0.29); 16 patients (53%) had significant LPA stenosis and 20 patients (67%) had significant RPA stenosis. Overall, pulmonary artery stenoses caused a 33±16% reduction in the combined PA dimension.
Both surgical techniques were associated with central PA stenoses with comparable frequency. Significant stenoses were identified in 14 patients in the classical group (78%) and 10 patients in RV–PA group (83%; P=0.71). However, the stenoses were more severe in the RV–PA group, causing a maximum 42±16% reduction in PA dimension compared with the 28±14% reduction in the classical group (P<0.05).
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4. Discussion |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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The recent modification of the Norwood procedure incorporating an RV–PA conduit, originally described by Norwood et al. [13] and re-established by Kishimoto et al. [14] and subsequently Sano et al [2], represents a further development in the management of patients with HLHS. The principle advantage of the RV–PA conduit is that it abolishes the diastolic ‘runoff’ from the systemic to the pulmonary circulation, which characterises the modified BT shunt. This, in turn raises diastolic pressure and improves the coronary perfusion pressure [3–5]. Abolishing the diastolic ‘runoff’ may also establish a more reliable balance between the systemic and pulmonary circulations, in which systemic and coronary blood flow are less influenced by changes in the pulmonary vascular resistance [15]. A number of authors have reported more stable haemodynamics following the RV–PA conduit [2,3,14,15]]. This is likely to be particularly valuable in neonates at risk of high or dynamic pulmonary vascular resistance or patients with a small innominate artery.
Optimal pulmonary artery growth has long been recognised as crucial to a successful Fontan circulation [15]. Narrowing of the central pulmonary arteries and tubular hypoplasia of the left pulmonary artery are not uncommonly seen following the standard stage I Norwood, even when the site of the bifurcation is patched, as in this study (Fig. 1). It has been proposed that this may be due to the compressive effect of the Damus-type reconstruction of the aortic arch on the LPA or blood flow through the modified BT shunt being directed preferentially to the RPA [16–20]. These are very important lesions to correct at the stage II procedure as any mechanical obstruction to passive flow into the lungs carries significant morbidity.
It has been suggested that the RV–PA conduit technique may eliminate these problems and promote better growth of the central pulmonary arteries [3]. The results of this study illustrate that the central pulmonary arteries distal to the site of shunt insertion showed excellent development in those patients whose pulmonary blood supply was provided by a RV–PA conduit at the time of the Norwood stage I. The left pulmonary artery in particular appeared to benefit from this modification with a 33% increase in the maximum indexed LPA diameter compared to the classical Norwood group. Improved pulmonary blood flow does not explain why the RV–PA conduit promotes better growth of the central pulmonary arteries, as in our hands both the classical and RV–PA Norwood resulted in balanced circulations with no significant difference in Qp:Qs. A number of groups have demonstrated a lower Qp:Qs with the RV–PA conduit technique and it could be surmised that this reduced pulmonary blood flow would adversely affect pulmonary artery growth [2–5]. However, others have refuted this finding [3]. We propose that the more evenly balanced distribution of flow to the central pulmonary arteries by virtue of the more central distal shunt insertion site, is likely to result in improved central pulmonary artery growth. This improvement is particularly notable in the left pulmonary artery. By comparison, the blood flow in the modified BT shunt is in a more rightward orientation. The pulsatility or pulse pressure of flow may also have an impact on the improved pulmonary artery growth.
Significant stenoses were identified in both the classical Norwood and the RV–PA conduit group. These stenoses were typically within the central pulmonary arteries at the site of shunt insertion (Fig. 2). Nevertheless, the RV–PA conduit was associated with more severe stenoses than the modified BT shunt. This report suggests that the RV–PA conduit modification, in our hands at least, carries a significant risk of developing central pulmonary artery stenoses. The reasons for this are unclear. Every attempt is made at the time of the Norwood procedure to minimize the risk of stenosis development. The initial defect in the central pulmonary arteries is enlarged with a patch, a fine, non-irritant suture material (8/0 prolene) is used and the pulmonary arteries are mobilised to the hila bilaterally to reduce kinking and tension. Furthermore, the immediate postoperative and discharge echo data on these patients following stage I procedure suggests widely patent branch pulmonary arteries with saturation values equivalent to the control group. This would suggest that the problem develops during the first 3 postoperative months.
It is possible that, with growth of the infant, the conduit may impose tension on the pulmonary artery bifurcation causing it to be tented forward against the Damus reconstruction. Alternatively, it may be an intimal reaction to the pulsatility (i.e. pulse pressure), higher peak pressure or turbulent flow as the blood diverges into each branch PA. It is essential that central PA stenoses be treated at the time of the stage II procedure. It is envisaged that the stenoses that develop with the RV–PA conduit will necessitate more extensive mobilisation of the pulmonary arteries and more frequent patching of the central pulmonary arteries than the modified BT shunt, which will undoubtedly add to the complexity of the stage II operation. Nevertheless, this may yet be outweighed by the advantage gained with better growth of the central pulmonary arteries. The true value of these findings will only be apparent when these patients have gone through their stage II and III procedures and serial assessments of the pulmonary artery growth and development can be made. Provided these stenoses are aggressively managed at time of surgery the improvement in pulmonary artery growth may be maintained. Possible remedies to reduce or prevent the occurrence would be to allow more length in the shunt at the original operation, although this may lead to kinking and acute variations in pulmonary blood flow. A further option may be to reroute the conduit to the right of the aorta. This may reduce the tension on the pulmonary arteries behind the Damus and potentially allows easier access to any stenoses at the time of the second stage operation by reducing the need to mobilize the neo-aorta and left pulmonary artery.
There are a number of limitations to this study. Firstly, clinical details for the small number of patients involved were collected retrospectively and the control/comparison group was historical. However, this group consisted of the patients operated on immediately prior to, and during the introduction of the RV–PA conduit Norwood procedure. In addition, other surgical and anaesthetic techniques were unchanged with the exception of antegrade cerebral perfusion. Secondly, the RV–PA conduit group (RV–PA group) represented the very first patients to undergo this modification at The Birmingham Children's Hospital and results may improve as experience with the technique increases.
We have demonstrated that providing pulmonary blood flow in the Norwood operation by means of a RV–PA conduit is associated with considerably improved growth of the central pulmonary arteries. Although this has come at the expense of more severe stenoses of the pulmonary arteries in the region of the conduit insertion, we believe that the benefits obtained in pulmonary artery growth outweigh these when embarking on a Fontan type palliation.
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Appendix A. Conference discussion |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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Dr McGuirk: The original description of the modified Norwood procedure from the Birmingham group involved arch reconstruction using a direct anastomosis, i.e. without additional material. Our technique has since changed, a number of years ago, and currently, the aortic arch is reconstructed with a pulmonary homograft patch in all patients.
Dr B. Asfour (Sankt Augustin, Germany): While you place the right modified BT shunt, do you intentionally place it as far left to the midline as possible as we would recommend? Because in your image which you showed, it looked like the shunt was pretty far off to the right. In our experience, we very rarely see such hypolasia of LPA, so maybe this could be the reason and placement of the shut further to the left, the solution.
Dr McGuirk: That may well be true. Our BT shunt is placed at the distal innominate artery and runs directly down onto the right pulmonary artery.
Dr G. Ziemer (Tuebingen, Germany): Your group actually suggested to use for the RV-PA conduit not the way left to the neoaorta but to the right of the neoaorta because you had so many stenoses, but you didn't talk about it.
Dr McGuirk (Freiburg, Germany): That is very true. I think the general consensus amongst the published literature is that the modified Norwood procedure with a RV to PA conduit involves a conduit that passes to the left of the neo-aorta. As a result of our findings, as presented in this talk, we have modified this procedure and now use a RV to PA conduit that passes to the right of the neo-aorta. The results of this technique form part of the ongoing research within our department.
Dr Zimer: But you're still optimistic?
Dr McGuirk: Yes.
Dr C. Pizarro (Wilmington, Delaware, USA): Is this a consecutive series? Were these patients randomized?
Dr McGuirk: No. This study consisted of 30 consecutive patients and included the changeover from the classical Norwood procedure to the modified Norwood procedure with a RV to PA conduit.
Dr Pizarro: How did you decide where to measure the branch pulmonary artery? Obviously, you looked at the angiogram, but you must have chosen a particular segment to measure the branches and then made a comparison. Now, how do you choose that spot?
Dr McGuirk: We chose two measurements, which were the largest and the smallest diameter on the right and the left pulmonary artery out to the level of the first branch of the pulmonary arteries.
Dr Pizarro: How did you address the central PA stenosis?
Dr McGuirk: Do you mean in terms of whether the central PA stenosis affected the left or the right pulmonary artery?
Dr Pizarro: I mean at the time of the cavopulmonary connection you had to address that area where the conduit went in.
Dr McGuirk: Absolutely.
Dr Pizarro: So how do you deal with that?
Dr McGuirk: Our current practice is to fully mobilize the pulmonary arteries between the left and right hila and incorporate a further patch of pulmonary homograft to address any pulmonary artery stenoses that are present.
Mr V. Tsang (London, United Kingdom): I don't think your data answers your research question, if you allow me to say: "the Right Ventricle to Pulmonary Artery Conduit Stimulates Better Growth of the Central Pulmonary Arteries in Hypoplastic Left Heart Syndrome."
To answer that question, you need to have an ideal situation for both groups, that is, the systemic shunt does not distort your right PA, your central conduit does not distort your central bifurcation. Only on that basis you can say whether it is offering better growth because of the flow dynamics. You've got such a high incidence of central stenosis, so your data interpretation may be skewed by the surgical issue. Can you answer that?
Dr McGuirk: I think this is a difficult question. The literature would suggest that children with hypoplastic left heart syndrome are born with normal size pulmonary arteries. Children with hypoplastic left heart syndrome should have normal pulmonary arterial development provided there was adequate blood flow. We have demonstrated that the pulmonary artery dimensions at cardiac catheterization prior to the superior cavopulmonary shunt are different depending on whether they had a BT shunt or a RV-PA conduit.
If we normalize the data, w using Kirklin's algorithm, the patients in the RV to PA conduit group have normal size pulmonary arteries whereas the patients with a BT shunt have pulmonary arteries that are smaller than normal. I agree that there are limitations with this study. However, we have provided our entire experience, which therefore provides a true clinical representation.
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Acknowledgments |
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Footnotes |
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Presented at the joint 18th Annual Meeting of the European Association for Cardio-thoracic Surgery and the 12th Annual Meeting of the European Society of Thoracic Surgeons, Leipzig, Germany, September 12–15, 2004. |
References |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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