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Ann Thorac Surg 2001;71:S361-S364
© 2001 The Society of Thoracic Surgeons

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Autografts, allografts, and biological valves in children

Use of the Medtronic freestyle valve as a right ventricular to pulmonary artery conduit

^a The Children’s Hospital, Westmead, New South Wales, Australia
^b Princess Margaret Hospital for Children, Subiaco, Western Australia, Australia

Address reprint requests to Dr Chard, Children’s Hospital Medical Centre, Suite 8, Level 1, Hainsworth St, Westmead NSW 2145, Australia
e-mail: chardric{at}netspace.net.au

Presented at the VIII International Symposium on Cardiac Bioprostheses, Cancun, Mexico, Nov 3–5, 2000.

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. We have used the Medtronic Freestyle bioprosthesis as a right ventricular to pulmonary artery conduit recently in an attempt to overcome some of the problems associated with homografts and stented xenografts. The aim of this study was to review the performance of this prosthesis.

Methods. Prospectively collected data for patients having Freestyle bioprostheses implanted as a right ventricular to pulmonary artery conduit were reviewed to assess clinical outcome and echocardiographic results.

Results. Thirteen patients aged 13 days to 22.5 years (median, 7.9 years) underwent either primary repair (n = 5) or change of conduit (n = 8) using the Freestyle bioprosthesis. One neonate with truncus arteriosus died postoperatively of pulmonary hypertension. One conduit was explanted 27 months after repair of neonatal truncus arteriosus. There has been no incidence of significant prosthetic regurgitation, thromboembolism, or endocarditis at mean follow-up of 10.1 months (range, 2 weeks to 29 months).

Conclusions. The Medtronic Freestyle valve is a reliable pulmonary valve substitute in the short term. Early results justify continued clinical use of the device in this setting with close follow-up.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Right ventricular to pulmonary artery (RV-PA) conduits are frequently required for the correction of congenital cardiac defects in which there is obstruction to the right ventricular outflow tract. Unfortunately, the ideal conduit has not been found. Homografts have been used since 1966 for this indication [1]. However their limited availability, especially in smaller sizes, as well as finite durability, both for competence and obstruction, have prompted a search for alternative solutions. In 1973, stented porcine xenografts were first used as extracardiac conduits [2], but were soon found to calcify prematurely in children and require early replacement [3, 4].

The Medtronic Freestyle porcine aortic root bioprosthesis (Medtronic, Minneapolis, MN) has recently been used with good early and midterm results in adults in the aortic position [5]. Its stentless design and antimineralization treatment have resulted in favorable hemodynamic characteristics and freedom from structural valve degeneration to date, and has led to its use in the pulmonary position after the Ross operation [6]. However, its use as an RV-PA conduit in children has been questioned [7].

We have recently used this bioprosthesis as an RV-PA conduit in a small number of children, prompted by lack of available homografts in smaller sizes. We have also used Freestyle valves in cases of early homograft failure requiring replacement. We report our results out to 3 years with this device.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
Patients
Prospective data on all patients having Medtronic Freestyle valves implanted as an RV-PA conduit by 3 surgeons (D.R.A., R.B.C., G.R.N.) were collected. Thirteen patients were followed and are summarized in Table 1.

In constructing the conduit, the xenograft was trimmed distally to just above the porcine sinotubular junction. This outflow line was anastomosed to the host pulmonary artery confluence, often spatulating the latter to accommodate a deliberately oversized valve. If necessary, a hood (using either polytetrafluoroethylene or the excised distal end of the xenograft) was attached to the inflow polyester cloth covering of the Freestyle valve. The hood was then anastomosed to the right ventricle so that the completed conduit would lie without kinking and so that the valve component was as distal as possible to avoid compression and distortion once the sternum was closed.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
Indications for surgery
Thirteen patients received Freestyle valves as an RV-PA conduit. There were 2 boys and 11 girls. Median age was 7.9 years (range, 13 days to 22.5 years). Seven patients had truncus arteriosus (4 change of conduit, 3 primary repairs). Two of these patients also had their truncal valve replaced concomitantly using a Medtronic Freestyle valve for truncal incompetence. Three patients had pulmonary atresia and ventricular septal defect (1 change of conduit, 2 primary repairs—both had previous palliative operations). Two patients had tetralogy of Fallot (both change of conduit). One patient had change of conduit after previous Rastelli operation.

Size of conduits
Freestyle valve sizes used were 12 mm (n = 1), 14 mm (n = 1), 16 mm (n = 1), 19 mm (n = 1), 21 mm (n = 1), 23 mm (n = 6), and 25 mm (n = 2). The three smallest valves were custom made.

Complications
One patient died on postoperative day 8. This was a 13-day-old neonate (2,540 g) with truncus arteriosus undergoing primary repair. She had a 12-mm conduit implanted. Twelve hours postoperatively she had a pulmonary hypertensive crisis with cardiac arrest requiring open cardiac massage. An echocardiogram performed the next day did not identify any obstruction to the conduit. The chest was closed on day 7; however, she failed to recover and died of biventricular failure.

One other patient had significant bleeding, which had settled, and was reexplored on day 1. No surgical point of bleeding was found. The patient made an otherwise uneventful recovery.

Late follow-up
Follow-up is 100% complete for survivors. Mean follow-up for survivors is 10.1 months (range, 2 weeks to 29 months). Total cumulative follow-up is 10.1 patient-years. There has been no incidence of thromboembolism, prosthetic valve endocarditis, or late death.

One conduit was explanted. This was a child who had truncus arteriosus repair as a neonate using a 14-mm custom-made prosthesis. She exhibited obstruction at the right ventriculotomy site, just proximal to the conduit attachment. The conduit itself was unobstructed, but was electively replaced with a 22-mm homograft at age 2 years 4 months. The leaflets were noted to be quite mobile, although host tissue was evident extending onto the porcine left cusp (Fig 1). Radiographic examination of the explanted valve demonstrated absence of calcification in the valve leaflets. A small amount of calcification was evident at the inflow aspect of the valve.

View larger version (128K): [in this window] [in a new window]   Fig 1. Freestyle bioprosthesis explanted 27 months after correction of neonatal truncus arteriosus.

	Comment

Top Abstract Introduction Patients and methods Results Comment References

 
Our rationale for using the Medtronic Freestyle bioprosthesis as an RV-PA conduit came about because of lack of suitable homografts in neonates requiring truncus arteriosus repair. We continue to use homografts as extracardiac conduits when available. However, their limited availability, particularly in smaller sizes, is a worldwide problem. The Freestyle bioprosthesis offers several potential advantages over homografts. First, it is readily available and can be custom made to all sizes, including sizes for neonates. Second, its antimineralization treatment and physiologic fixation design process have the potential to mitigate against calcification and early structural valve degeneration. It has good hemodynamics, and is more compressible than a stented prosthesis (including the Hancock). The inflow is fixed by cloth, which may help with long-term competence, but does not allow the dilatation seen in pulmonary homografts and hence does not accommodate growth as well. This is only a problem in children. It may also have an advantage in high-pressure situations, such as pulmonary hypertension or unfavorable pulmonary artery anatomy, in which early homograft dilatation and incompetence are a problem.

The results of this small series suggest that the Freestyle valve is an acceptable alternative to homografts as an RV-PA conduit in selected patients. The early hemodynamic data suggest that this conduit does not become obstructed or regurgitant in the short term in the extracardiac position. In the first 3 years of using this bioprosthesis, we have not observed any valve-related thromboembolic events or endocarditis. The analysis of the explanted 14-mm valve demonstrates an encouraging freedom from significant degeneration at greater than 2 years after neonatal truncus arteriosus repair (Fig 1).

The longer-term durability of this conduit and whether it can replace the more traditional homograft remain unanswered questions. Data from a randomized study performed at the Royal Brompton Hospital [8] suggested that the rate of calcification in Freestyle valves was significantly lower than that of homografts when implanted as an aortic root replacement. This prospective study was conducted in patients aged 40 to 79 years and used electron beam computed tomography to quantify valve calcification. Assuming the same holds true for children, in whom structural degeneration is accelerated, the difference in rate of calcification may even be greater.

Using a piglet model, however, Schoof and colleagues [7] found that the Freestyle valve in the RV-PA position developed early degenerative changes. Prostheses at explantation showed large cuspal masses of collagen and fibrin causing severe stenosis. The authors concluded that the use of this valve for right ventricular outflow tract reconstruction could not be recommended. Although we did note a host tissue reaction that restricted leaflet movement in the one explanted valve studied, the gross cuspal pathologic changes and nodular masses observed in the piglet model were not evident in our case.

Homograft durability in children has been studied extensively [9–12]. Among risk factors for early failure that have been identified are young age [9, 10] and small size of homograft [11, 12]. In addition, homografts used at reoperation have been shown to fail earlier than those used at original operation [13]. These problems prompted us to use an alternative conduit in patient 12 (Table 1).

Limited homograft availability, however, remains the major limitation to the use of this conduit in most countries. Neonates usually require a 12- or 14-mm conduit, which is often unavailable as a homograft. This remains our primary indication for using the Freestyle valve as an RV-PA conduit.

The stented porcine xenograft is an alternative, but it has had mixed results [3, 4]. The results from Boston Children’s Hospital found that all heterografts used as right heart conduits required replacement within 10 years [14]. The metal ring in the Hancock conduit (Medtronic, Minneapolis, MN) can also cause problematic compression in smaller infants.

In conclusion, the Medtronic Freestyle bioprosthesis demonstrates the following characteristics that make it an acceptable alternative to homograft conduits: (1) availability in all sizes, (2) satisfactory early hemodynamic performance in the RV-PA position, (3) freedom from thromboembolism and endocarditis in the short term, and (4) freedom from calcification after greater than 2 years after implantation in neonates. Our current indications for choosing this prosthesis are when a suitable homograft valve is unavailable or when accelerated homograft degeneration occurs requiring conduit replacement. Longer follow-up is required to determine whether the late results of this promising conduit remain satisfactory.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

1. Ross D.N., Somerville J. Correction of pulmonary atresia with a homograft aortic valve. Lancet 1966;2:1446-1447.[Medline]
2. Bowman F.O., Jr, Hancock W.D., Malm J.R. A valve containing Dacron prosthesis. Its use in restoring pulmonary artery-right ventricular continuity. Arch Surg 1973;107:724-728.[Abstract/Free Full Text]
3. Bisset G.S., Schwartz D.C., Benzing G., Helmsworth J.A., Schreiber J.T., Kaplan S. Late results of reconstruction of right ventricular outflow tract with porcine xenografts in children. Ann Thorac Surg 1981;31:437-443.[Abstract]
4. Boyce S.W., Turley K., Yee E.S., Verrier E.D., Ebert P.A. The fate of the 12mm porcine valved conduit from the right ventricle to the pulmonary artery. A 10-year experience. J Thorac Cardiovasc Surg 1988;95:201-207.[Abstract]
5. Doty D.B., Cafferty A., Cartier P., et al. Aortic valve replacement with Medtronic Freestyle bioprosthesis: 5-year results. Semin Thorac Cardiovasc Surg 1999;11(Suppl 1):35-41.[Medline]
6. Konertz W., Sidiropoulos A., Hotz H., Borges A., Baumann G. Ross operation and right ventricular outflow tract reconstruction with stentless xenografts. J Heart Valve Dis 1996;5:418-420.[Medline]
7. Schoof P.H., Hazekamp M.G., van Krieken H.H., Huysmans H.A. Pulmonary root replacement with the Freestyle stentless aortic xenograft in growing pigs. Ann Thorac Surg 1998;65:1726-1729.[Abstract/Free Full Text]
8. Melina G., Rubens M.B., Birks E.J., Bizzari F., Khaghani A., Yacoub M.H. A quantitative study of calcium deposition in the aortic wall following Medtronic Freestyle compared with homograft aortic root replacement. A prospective randomised trial. J Heart Valve Dis 2000;9:97-103.[Medline]
9. Bando K., Danielson G.K., Schaff H.V., Mair D.D., Julsrud P.R., Puga F.J. Outcome of pulmonary and aortic homografts for right ventricular outflow tract reconstruction. J Thorac Cardiovasc Surg 1995;109:509-517.[Abstract/Free Full Text]
10. Hawkins J.A., Bailey W.W., Dillon T., Schwartz D.C. Midterm results with cryopreserved allograft valved conduits from the right ventricle to the pulmonary arteries. J Thorac Cardiovasc Surg 1992;104:910-916.[Abstract]
11. Razzouk A.J., Williams W.G., Cleveland D.C., et al. Surgical connections from ventricle to pulmonary artery. Comparison of four types of valved implants. Circulation 1992;86(Suppl 2):154-158.[Abstract/Free Full Text]
12. Schorn K., Yankah A.C., Alexi-Meskhishvili V., Weng Y., Lange P.E., Hetzer R. Risk factors for early degeneration of allografts in pulmonary circulation. Eur J Cardiothorac Surg 1997;11:62-69.[Abstract]
13. Stark J., Bull C., Stajevic M., Jothi M., Elliott M., de Leval M. Fate of subpulmonary homograft conduits: determinants of late failure. J Thorac Cardiovasc Surg 1998;115:506-514.[Abstract/Free Full Text]
14. Jonas R.A., Freed M.D., Mayer J.E., Jr, Castaneda A.R. Long-term follow-up of patients with synthetic right heart conduits. Circulation 1985;72(Suppl 2):77-83.

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Chard, R. B. Articles by Nunn, G. R. Search for Related Content PubMed PubMed Citation Articles by Chard, R. B. Articles by Nunn, G. R. Related Collections Valve disease