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Ann Thorac Surg 2008;85:2079-2084. doi:10.1016/j.athoracsur.2008.01.098
© 2008 The Society of Thoracic Surgeons
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Original Articles: Pediatric Cardiac

Melbourne Shunt Promotes Growth of Diminutive Central Pulmonary Arteries in Patients With Pulmonary Atresia, Ventricular Septal Defect, and Systemic-to-Pulmonary Collateral Arteries

Muhammad A. Mumtaz, MDa,*, Geoffrey Rosenthal, MD, PhDb, Athar Qureshi, MDb, Lourdes Prieto, MDb, Tamar Preminger, MDb, Richard Lorber, MDb, Larry Latson, MDb, Brian W. Duncan, MDa

a Department of Pediatric and Congenital Heart Surgery, Cleveland Clinic, The Children's Hospital, Cleveland, Ohio
b Department of Pediatric Cardiology, Cleveland Clinic, The Children's Hospital, Cleveland, Ohio

Accepted for publication January 28, 2008.

* Address correspondence to Dr Mumtaz, Cleveland Clinic, M-41, 9500 Euclid Ave, Cleveland, OH 44195 (Email: mumtazm{at}ccf.org).

Presented at the Forty-third Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Jan 29–31, 2007.


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 Discussion
 References
 
Background: We manage patients with pulmonary atresia, ventricular septal defect, major systemic-to-pulmonary collateral arteries, and diminutive central pulmonary arteries with a staged approach. The first procedure is a central end-to-side aortopulmonary shunt (Melbourne shunt) intended to cause growth and development of the central pulmonary arteries. We subsequently measured central pulmonary artery growth after Melbourne shunt.

Methods: Forty consecutive patients were followed after Melbourne shunt. The maximum pulmonary artery diameter was measured at the time of surgery and at subsequent catheterizations or surgery.

Results: Median pulmonary artery size at surgery was 2 mm. The median pulmonary artery diameter was 5.5 mm at first assessment (median, 6.35 months) and 7 mm at most recent assessment (19.7 months). Mean modified Nakata index increased from 27 mm2/m2 at surgery to 138 mm2/m2 at first assessment, and 176 mm2/m2 at final assessment. There was one acute shunt failure from anastomotic stenosis. Thirteen patients (32.5%) required 21 percutaneous interventions. There were 4 deaths during a median follow-up of 68 months. At the time of complete repair (n = 25) all patients required pulmonary artery augmentation, and 8 are in various stages of palliation. The remaining patients are considered not reparable owing to irreversible pulmonary hypertension (n = 4) or have required fenestration of ventricular septal defect after complete repair (n = 2).

Conclusions: Melbourne shunt promotes modest growth of central pulmonary arteries leading to complete repair in the majority of patients. There is considerable need for further interventions in these patients to augment the size of the pulmonary arteries.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 Discussion
 References
 
Pulmonary atresia and ventricular septal defect with major systemic-to-pulmonary collateral arteries (PA/VSD/MAPCAs) has a subgroup with diminutive central pulmonary arteries (PAs). Management in this group is controversial, with some centers advocating repair with right ventricular outflow tract patch [1–4], whereas others advocate a central end-to-side shunt between the main PA and aorta [5–7]. This shunt was first described by Dr Mee's group [8] from Melbourne, Australia, and is termed the Melbourne shunt at our institution. We describe here our results of the Melbourne shunt with focus on PA growth.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 Discussion
 References
 
Patient Selection
This study was approved by the Cleveland Clinic institutional review board, and the need for individual parents' approval was waived. We identified 40 consecutive patients who underwent Melbourne shunt from December 1993 to November 2005. These 40 patients include 2 patients who had a Melbourne shunt performed outside of our institution with subsequent management by us. Maximum branch PA diameter was measured at the time of surgery and at subsequent catheterizations. Patients were selected for Melbourne shunt if they had PA/VSD/MAPCAs with diminutive but continuous PAs typically less than 3 mm in size. Twenty-six of these patients have been reported in a previous series [5]. During the study period a total of 85 patients with PA/VSD/MAPCAs were treated at our institution.

Surgical Technique
Our surgical technique has been described previously [5, 8]. If the Melbourne shunt was the only procedure to be performed, it was performed through a median sternotomy. A left thoracotomy was used if left-sided unifocalization was performed at the same time. In either case, cardiopulmonary bypass was not required except in 1 patient with severe hypoxia as a result of an inadvertent right mainstem intubation. The diminutive main PA was transected after controlling the branch PAs with soft clamps. A side-biting clamp was applied to the left posterior surface of the ascending aorta, and a spatulated anastomosis was performed between the filleted end of the main PA and the posterior leftward aspect of the ascending aorta (Fig 1).


Figure 1
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  		Fig 1. Melbourne shunt: side-biting clamp controls the ascending aorta; soft clamps control the branch pulmonary arteries. Inset demonstrates the completed shunt with the pulmonary artery anastomosed to the posterior and left lateral aspect of the ascending aorta close to the sinotubular junction. Reprinted with the permission of The Cleveland Clinic Foundation [5].

 
Data Collection
Data were collected retrospectively from the patients' medical records. Branch PA size was measured at the time of Melbourne shunt either by direct assessment at the time of surgery or from catheterization before Melbourne shunt or by a preoperative echocardiogram. Subsequent branch PA size was measured at the first cardiac catheterization after Melbourne shunt. This was available in 34 of the 40 total patients. The most recent branch PA size was measured at the most recent cardiac catheterization or at the time of final repair. These data were available in 31 patients. Four patients had no further assessment of the Melbourne shunt: 1 patient died, 1 patient required takedown of the Melbourne shunt owing to anastomotic narrowing, and 1 patient was lost to follow-up. One patient is currently awaiting further palliation. This study was approved by the institutional review board of the Cleveland Clinic.

Modified Nakata Index
The mean modified Nakata index (MNI) was calculated using the following formula: Maximum right pulmonary artery cross sectional area in mm2 + maximum left pulmonary artery cross sectional area in mm2/body surface area in m2 = MNI in mm2/m2 (branch PA area indexed to body surface area) [9].


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 Discussion
 References
 
Surgical data are summarized in Table 1. The median age was 4 months (range, 1 to 65 months), and the median weight was 5.25 kg (range, 2.6 to 17.8 kg) at the time of Melbourne shunt. Left thoracotomy was performed in 8 patients to perform Melbourne shunt along with left unifocalization. Median sternotomy was performed in 32 patients.


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  		Table 1 Surgical Data
 
Pulmonary Artery Growth
Median branch PA diameter at the time of Melbourne shunt was 2 mm (range, 0.5 to 5.5 mm). This increased to a median of 5.5 mm (range, 1 to 11 mm) at a median of 6.35 months (range, 1.3 to 60 months) after surgery. The branch PA diameter at the most recent assessment was 7 mm (range, 4 to 14 mm) at a median of 19.7 months (range, 8 to 59 months) after surgery (Figs 2, 3). Go The mean modified Nakata index (MMNI) was 26.6 mm2/m2 at the time of the Melbourne shunt. This increased to 138.2 mm2/m2 at a median of 6.35 months after surgery and to 175.9 mm2/m2 at a median of 19.7 months after initial surgery (Fig 4). The median increase in PA diameter was 3 mm (range, 0 to 9.5 mm) at the first assessment and 4.5 mm (range, 1 to 10 mm) at the most recent assessment.


Figure 2
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  		Fig 2. Right pulmonary artery growth as a function of time.

 

Figure 3
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  		Fig 3. Left pulmonary artery growth as a function of time.

 

Figure 4
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  		Fig 4. Mean modified Nakata index as a function of time.

 
Complications and Mortality
One case of postoperative bleeding requiring reexploration and one wound infection occurred in 2 separate patients. There was one early and one late shunt takedown before complete repair. In 2 patients there was thrombotic occlusion of the right PA during late follow-up. There was 1 patient with congestive heart failure thought to be related to the Melbourne shunt requiring early unifocalization.

There were 2 hospital and 2 late deaths. Two cyanotic neonates died at 83 and 97 days after the Melbourne shunt of respiratory failure and sepsis, without undergoing any further palliation. One of these patients had multiple congenital anomalies including Turner's syndrome and scalp aplasia. Another cyanotic neonate with DiGeorge syndrome underwent Melbourne shunt at the age of 17 days. A successful staged left and right unifocalization was performed at the ages of 6 and 8 months, respectively. The patient died of respiratory failure and sepsis at 2 years of age. The fourth death was in a patient who underwent successful staged palliation and finally complete repair. The postoperative period was complicated by catastrophic bleeding resulting in cardiac arrest and severe brain damage. The patient died 21 months later of aspiration pneumonia.

Procedures on the Melbourne Shunt
Thirteen patients required 21 percutaneous procedures after the Melbourne shunt. Ten patients underwent 20 balloon dilatation procedures without stenting. Two patients had one MAPCA coiled in each patient, and 1 patient had a balloon dilatation as well as an MAPCA coiled. All patients underwent reconstruction of the branch PAs with fresh autologous pericardium at the time of complete repair.

Long Term Follow-Up and Complete Repair
Until the end of the study period, follow-up was available for a median period of 68 months (range, 0 to 148 months). In addition to the deaths (n = 4) and shunt takedowns (n = 2), 4 patients were deemed unreparable as a result of severe pulmonary hypertension. One patient had Alagille's syndrome and had extremely small distal vessels. One patient had severe distal branch PA stenoses. Two patients exhibited pulmonary hypertension after unifocalization procedures despite no branch PA stenoses. One of these patients had severe latex allergy that was recognized after repeated hospitalizations for respiratory failure. The second had fungal pneumonia requiring lobectomy and decortication. Twenty-five patients have undergone complete repair, and 2 of these have had the VSD fenestrated because of suprasystemic PA pressures after repair. After the Melbourne shunt, there was a median of 2 additional operations before complete repair. Seven patients are in various stages of palliation and are deemed good candidates for complete repair. One overseas patient has been lost to follow-up (Fig 5).


Figure 5
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  		Fig 5. Outcomes of patients with Melbourne shunt. (VSD = ventricular septal defect.)

 

   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
Discussion
 References
 
Management of PA/VSD/MAPCAs with diminutive PAs imposes a number of challenges. For successful complete repair, it is essential to encourage growth of the central PAs to optimize blood flow through the native pulmonary circulation and to provide an appropriate central circulation upon which to base unifocalized MAPCAs. Various strategies have been proposed in the literature to encourage native PA growth in PA/VSD/MAPCAs, including rehabilitation of the native PAs using forward flow through the right ventricle [1], and rehabilitation of the native PAs using a central shunt. In regard to management of MAPCAs, the surgical approach must be highly individualized based on the specific anatomic features that are present, including presence or absence of dual supply, and number of segments in the native circulation versus the number of segments supplied by the MAPCAs.

We report here our management of a subgroup of patients with PA/VSD/MAPCAs undergoing Melbourne shunt to encourage growth of the diminutive central PAs. This approach creates a central shunt between the diminutive main PA and the ascending aorta without the use of prosthetic material. This was first reported by Dr Mee's group in 1991 [8].

Pulmonary Artery Growth
In the present study, Melbourne shunt led to a median growth of 3.5 mm in approximately 6 months and 5 mm in approximately 19 months. The MMNI increased by 110 mm2/m2 at approximately 6 months and by 150 mm2/m2 at 19 months. In most patients, VSD closure may be safely performed when the MMNI reaches 150 mm2/m2 [1]. However, most of these patients require multiple procedures to fully rehabilitate the native and unifocalized pulmonary circulation [5, 10]. In the present study 13 patients required a total of 23 balloon interventions, and all patients required pericardial patch reconstruction of the PAs at the time of complete repair. Although balloon dilatation of the branch PAs is difficult after the Melbourne shunt owing to the need for a retrograde approach through the aorta, at our institution this approach was successful in all patients taken to the cardiac catheterization laboratory.

Management of Congestive Heart Failure
In patients with diminutive central PAs, heart failure is unusual after the Melbourne shunt as a result of pulmonary blood flow through the native circulation. However, large MAPCAs may be the cause of heart failure in these patients. Our approach is to control MAPCA flow by performing early unifocalization.

Complete Repair
We have previously reported a 61% rate of complete repair using a staged approach in the management of a cohort of patients with PA/VSD/MAPCAs who had a variety of sizes of the central PAs [5]. Interestingly in the challenging group of patients in the present study who possessed diminutive PAs, the rate of repair was no different (60%). Although there were no early deaths, 4 patients died before complete repair and another 4 are not deemed to be candidates for VSD closure, emphasizing the difficulties in managing this group of patients.

Individualized Approach
The anatomic complexity in patients with PA/VSD/MAPCAs in general requires an individualized approach. Those with diminutive central PAs are approached at our center with a Melbourne shunt as the first procedure. If the patient has large MAPCAs on the left side that need to be addressed at the same time, the Melbourne shunt and concomitant left-sided unifocalization may be conveniently performed through a left thoracotomy. If an isolated Melbourne shunt is required, our preferred approach is through a median sternotomy without the use of cardiopulmonary bypass. As we have previously described, in patients with relatively well-balanced circulation, staged unifocalizations are performed at 6-month intervals before complete repair at 15 to 18 months. This approach can be modified if the patient experiences significant congestive heart failure or cyanosis. Eventually the decision to proceed with complete repair is made with an assessment of central PA growth, number of bronchopulmonary segments in continuity with the central pulmonary circulation, and the ratio of pulmonary to systemic blood flow.

Conclusion
Melbourne shunt promoted sufficient growth of the central PAs to allow complete repair in 61% of the patients in the present study. There is considerable need for further interventions in these patients to augment the size of the central PAs. Although substantial increase in the MMNI was seen in the majority of these patients, we routinely augment the branch PAs with fresh autologous pericardium at the time of complete repair.


   Discussion
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Discussion
References
 
DR FRANK A. PIGULA (Boston, MA): Thank you for your presentation. I have a question.

One alternative strategy in terms of establishing blood flow into these very small pulmonary arteries is the right ventricle–to–pulmonary artery conduit that can be performed in very young babies with very small central pulmonary arteries.

In your data, most of your patients were older. I think your average age was 4 months. What do you do with the neonate who's prostaglandin-dependent?

And a corollary and secondary question is you made not much mention of how you handled the aortopulmonary collaterals, and what do you do with those?

DR MUMTAZ: Thank you, Dr Pigula.

In answer to your first question, I personally have no experience in observation or any follow-up of patients who have undergone RVOT (right ventricular outflow tract) patch, which is an alternate strategy for dealing with pulmonary atresia, VSD (ventricular septal defects), and MAPCAs (major systemic-to-pulmonary collateral arteries).

During literature review for this particular abnormality in this paper, I came across a number of things, and I'll quote Dr Paul Ebert, which I think still stands true maybe 27 years later. In commenting on a paper of Dr Piehler in 1980 at the AATS (American Association for Thoracic Surgery) he commented, "The physiologic question regarding the benefit of transannular patching as a palliative procedure as compared to either some type of central shunt still is unanswered as the incompetent pulmonary valve does produce regurgitation into the right ventricle and clearly increases the ventricular work."

An additional comment by Dr Kirklin who was moderating that session states, "Our experience leads us to agree that under some circumstances, palliative transannular patching is optimum therapy in this situation. We disagree that the situation is as simple as Dr Piehler had suggested."

DR PIGULA: Well, I was really referring to homograft insertion. It's very hard with very small central pulmonary arteries to use the transannular patch.

In any event, how did you handle the aortopulmonary collaterals or how are they handled?

DR MUMTAZ: In answer to your second question about the MAPCAs, our philosophy is to unifocalize all MAPCAs. The MAPCAs that are supplying a segment that has dual circulation have been ligated if they are very difficult to transfer. And in subsequent cardiac catheterizations, these MAPCAs are balloon dilated if they are stenosed.

DR RICHARD A. JONAS (Washington, DC): I want to congratulate you on these excellent results with what I consider to be a technically difficult operation.

I have to say I've been referred a number of patients who have had this shunt, and the consistent problem has been kinking at the origin of the right pulmonary artery. And I've wondered if it's not just technical but perhaps related to differential growth of the aorta that stretches the right pulmonary artery over time.

So do you have some technical tricks that allow you to avoid this problem? You only saw it in 2 patients.

And can you tell us about the differential growth of the right pulmonary artery versus the left pulmonary artery? Thank you.

DR MUMTAZ: Dr Jonas, it certainly is a privilege, and I'm humbled by your question. I've certainly learned a lot from your teachings and from your writings.

In answer to your question, I will refer to what I've learned from Dr Mee, and we did not find in this paper and during this research that there was any differential growth between the right or left pulmonary artery. As I'm sure the audience is aware, the right pulmonary artery usually is a little bit larger than the left pulmonary artery.

The technical pearl that Dr Mee gave me was that the origin of the Melbourne shunt needs to be more posterior than what you think. And some of the anastomotic takedowns, there are at least two in which the RPA (right pulmonary artery) was thrombosed, and that was exactly the problem where the surgeon did not consider that the aorta is enlarged and made the anastomosis too anterior than leftward and posterior.

That's the only thing I can think of. Short of those two thrombotic complications after the Melbourne shunt, the other pulmonary arteries, when they were properly done, there was no difference in the RPA or the LPA (left pulmonary artery) growth.

DR HILLEL LAKS (Los Angeles, CA): I congratulate you also on your excellent paper.

We have some experience with this type of central shunt and had quite a few patients that developed excessive pulmonary blood flow. You mentioned the patients in failure, but how many of these patients would you say had a Qp/Qs (ratio of pulmonary to systemic blood flow) of greater than 2:1 once they got older?

Our alternative method for treating these patients is to do a connection between the right ventricle and pulmonary artery using a transannular pericardial patch, which can be done without the use of cardiopulmonary bypass.

The issue that you raised in your quotation of Dr Ebert about some kind of volume overload from regurgitation really is not a factor when you're dealing with 2-mm pulmonary arteries and is really not a big problem when you have a controlled pulmonary blood flow, which one can easily do with this technique. It has the advantage of being able to clamp the PA (pulmonary artery) below the ductus, and therefore, bypass is not necessary as well as the blood flow for the other collaterals.

And one also can control the size of the orifice in the right ventricle, and out of about 30 patients who we've done, of whom about half are 1 to 2 months of age, the opening into the right ventricle can be reopened by stenting, and you get no distortion or kinking of pulmonary arteries because the whole pulmonary artery remains intact. So I suggest that as an alternative method.

Could you comment on the number of patients that had excessive flow?

DR MUMTAZ: I don't have catheter-based data on Qp/Qs; however, the median preprocedure saturations in these patients were 70%, and their median postprocedure saturations were 80%. There was 1 patient who was in congestive heart failure that required prolonged intubation, and I did include that in the morbidity. However, that patient had large MAPCAs on one side. And the only change that we had to do was that instead of waiting 4 to 6 months, which is our normal routine to wait for the next stage of unifocalization, we took him for unifocalization after 2 weeks.

DR CHRISTOPHER J. KNOTT-CRAIG (Birmingham, AL): When you do the Melbourne shunt, do you use a punch to create a hole in the aorta or do you just make a slit in the aorta?

DR MUMTAZ: We take a small button out.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Discussion
 References
 

  1. Metras D, Chetaille P, Kreitmann B, Fraisse A, Ghez O, Riberi A. Pulmonary atresia with ventricular septal defect, extremely hypoplastic pulmonary arteries, major aorto-pulmonary collaterals Eur J Cardiothorac Surg 2001;20:590-597.[Abstract/Free Full Text]
  2. Freedom RM, Pongiglione G, Williams WG, Trusler GA, Rowe RD. Palliative right ventricular outflow tract construction for patients with pulmonary atresia, ventricular septal defect, and hypoplastic pulmonary arteries J Thorac Cardiovasc Surg 1983;86:24-36.[Abstract]
  3. Pagani FD, Cheatham JP, Beekman 3rd RH, Lloyd TR, Mosca RS, Bove EL. The management of tetralogy of Fallot with pulmonary atresia and diminutive pulmonary arteries J Thorac Cardiovasc Surg 1995;110:1521-1533.[Abstract/Free Full Text]
  4. Marshall AC, Love BA, Lang P, et al. Staged repair of tetralogy of Fallot and diminutive pulmonary arteries with a fenestrated ventricular septal defect patch J Thorac Cardiovasc Surg 2003;126:1427-1433.[Abstract/Free Full Text]
  5. Duncan BW, Mee RB, Prieto LR, et al. Staged repair of tetralogy of Fallot with pulmonary atresia and major aortopulmonary collateral arteries J Thorac Cardiovasc Surg 2003;126:694-702.[Abstract/Free Full Text]
  6. Rodefeld MD, Reddy VM, Thompson LD, et al. Surgical creation of aortopulmonary window in selected patients with pulmonary atresia with poorly developed aortopulmonary collaterals and hypoplastic pulmonary arteries J Thorac Cardiovasc Surg 2002;123:1147-1154.[Abstract/Free Full Text]
  7. Iyer KS, Mee RB. Staged repair of pulmonary atresia with ventricular septal defect and major systemic to pulmonary artery collaterals Ann Thorac Surg 1991;51:65-72.[Abstract]
  8. Watterson KG, Wilkinson JL, Karl TR, Mee RB. Very small pulmonary arteries: central end-to-side shunt Ann Thorac Surg 1991;52:1132-1137.[Abstract]
  9. Nakata S, Imai Y, Takanashi Y, et al. A new method for the quantitative standardization of cross-sectional areas of the pulmonary arteries in congenital heart diseases with decreased pulmonary blood flow J Thorac Cardiovasc Surg 1984;88:610-619.[Abstract]
  10. Rome JJ, Mayer JE, Castaneda AR, Lock JE. Tetralogy of Fallot with pulmonary atresia: rehabilitation of diminutive pulmonary arteries Circulation 1993;88:1691-1698.[Abstract/Free Full Text]




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