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Ann Thorac Surg 2004;77:1711-1716
© 2004 The Society of Thoracic Surgeons

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Original article: cardiovascular

Medtronic freestyle valve for right ventricular reconstruction in pediatric ross operations

^a Department of Surgery and Pediatrics, University of Tennessee, Memphis, Tennessee, USA
^b Department of Cardiac Surgery, Rebro University Hospital, Zagreb, Croatia
^c Department of Pediatric Cardiac Surgery, National Heart Institute, Lima, Peru
^d International Children's Heart Foundation, Memphis, Tennessee, USA
^e Department of Pediatrics, University of Kentucky, Lexington, Kentucky, USA

Accepted for publication October 2, 2003.

^* Address reprint requests to Dr Novick, International Children's Heart Foundation, 1750 Madison, Suite 100, Memphis, TN 38104, USA
e-mail: ichfno{at}aol.com

	Abstract

Top Abstract Introduction Patients and methods Results Comment Limitations of the study Conclusions Acknowledgments References

 
BACKGROUND: The use of homograft conduits to reconstruct right ventricle (RV) to pulmonary artery (PA) connections is an essential component of the Ross operation. Homograft availability and cost may be problematic when considering the Ross operation. We elected in January 1998 to utilize commercially available xenografts as an alternative to homografts for RV/PA reconstruction in the pediatric Ross operation. Our early results using the Medtronic Freestyle valve (Medtronic, Minneapolis, MN) for RV/PA reconstruction are presented.

METHODS: We reviewed our database for all Ross operations performed on children since January 1998. A total of 16 patients were identified. Eleven children received a Medtronic Freestyle valve, 2 children received a homograft, and 3 children received another type of xenograft. Echocardiographic evaluation of all children who received the Medtronic Freestyle valve was performed at hospital discharge and at two subsequent outpatient evaluations.

RESULTS: The median peak instantaneous pressure gradient across the xenograft was 16 ± 9 mm Hg (immediately after surgery before hospital discharge); 22 ± 20 mm Hg at 23 ± 11 months (first postdischarge follow-up); and 27 ± 20 mm Hg at 35 ± 9 months (second postdischarge follow-up). Linear regression analysis revealed an increasing pressure gradient with time (R²-adjusted = 0.44, p < 0.0001). At the same three observation points, the xenograft annulus diameter decreased: 25 ± 1.2 mm; 19 ± 4.3 mm; and 20 ± 1.8 mm. Linear regression analysis revealed a decreasing annulus diameter with time (R²-adjusted = 0.41, p < 0.0001).

CONCLUSIONS: The Medtronic Freestyle valve provides a possible alternative to homografts for the reconstruction of the RV/PA connection in the pediatric Ross operation. Long-term follow-up is necessary to evaluate this xenograft as an alternative to the homograft.

	Introduction

Top Abstract Introduction Patients and methods Results Comment Limitations of the study Conclusions Acknowledgments References

 
The Ross operation is an excellent procedure for the treatment of aortic valve disease in children [1]. Freedom from autograft replacement, potential for growth and freedom from anticoagulation are reported as reasons for utilizing this approach in children. Currently, the ideal conduit for the reconstruction of right ventricle to pulmonary artery (RV/PA) continuity is a pulmonary valve allograft [2].

However, pulmonary valve allografts are unavailable in many areas of the world [3]. A number of xenograft and xenograft valve conduits have been proposed as substitutes for RV/PA reconstruction in children. Since 1998, we have used commercially available stentless xenografts or xenograft conduits when homografts were not available for RV/PA reconstruction when performing the pediatric Ross procedure. The purpose of this study is to report our early results using the Medtronic Freestyle valve (Medtronic, Minneapolis, MN) for RV/PA reconstruction in children operated on for left ventricular outflow tract obstruction using the Ross technique.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment Limitations of the study Conclusions Acknowledgments References

 
Patients
Beginning in January 1998, we used commercially available stentless xenograft valves or valve conduits to reconstruct RV/PA continuity in children undergoing the Ross operation when homografts were unavailable. All children who received a Ross procedure between January 1998 and December 2001 were identified in the database of the International Children's Heart Foundation (Memphis, TN). Confirmation of the procedure and valve conduit used for RV/PA reconstruction was obtained from the records of the referring physicians in the country where the surgery was performed (Zagreb, Croatia; Lima, Peru; and Belgrade, Yugoslavia).

Operative technique
The operative technique was the same for all patients and consisted of routine cardiopulmonary bypass utilizing bicaval venous cannulation. All operations were performed by one of the authors (W.M.N.). Moderate hypothermia (25°C) was employed and both blood and crystalloid cold cardioplegia were used as per local customs. Initial cardioplegic arrest was accomplished using antegrade delivery (30 mL · kg^–1) and maintenance was retrograde (15 mL · kg^–1). Maintenance cardioplegia was infused every 15 to 20 minutes. Topical ice slush was employed in all cases. The size of the xenograft used for RV/PA reconstruction was based upon the size of defect that resulted from the harvest of the pulmonary autograft. Commercially available valve sizers were used to estimate the right ventricular defect and the nearest size xenograft was prepared. The xenograft was anastomosed to the right ventricular outflow tract (RVOT) using continuous 3-0 Prolene (Ethicon, Somerville, NJ). All xenografts were extended distally with previously harvested autologous pericardium (Fig 1). The pulmonary artery/pericardial extension and the conduit/pericardial extension anastomoses were constructed using continuous 4-0 Prolene (Ethicon). Once the xenograft was seated in the RVOT, the cross-clamp was removed and the remaining anastomoses were constructed.

View larger version (36K): [in this window] [in a new window]   Fig 1. Operative diagrams of pericardial extension. (A) Construction of the pericardial extension with posterior row anastomosis. (B) Completed extension.

Statistical analysis
Data are presented as the median ± interquartile difference. Xenograft annulus diameter and peak-instantaneous pressure gradient at the three observations were compared (first versus second and second versus third) with one-way paired Student t test. The same measurements were additionally analyzed as a function of the continuous follow-up duration with linear regression modeling. This latter modeling accounts for variation in follow-up period, whereas the former statistical test does not. All Z-values are calculated based upon the body surface area (BSA) at the time of measurement.

	Results

Top Abstract Introduction Patients and methods Results Comment Limitations of the study Conclusions Acknowledgments References

 
Study group description
Sixteen patients underwent the Ross procedure. One patient died on postoperative day 1 (mortality rate 6.2%). Eleven patients received the Medtronic Freestyle valve, 2 received homografts, and 3 received other types of xenografts. Children receiving the Medtronic Freestyle valve define the study group (n = 10). The children ranged in age from 4.6 to 16.4 years (13.9 ± 2.1) and in weight from 19 to 68 kg (49 ± 14). Seven of the patients were male (70%). The pathology and previous interventions are listed in Table 1. The cardiopulmonary bypass time was 170 ± 58 minutes and the aortic cross-clamp time was 98 ± 14 minutes.

Xenograft Z-Values
The size of the Medtronic Freestyle valves implanted (Table 1) ranged from 23 to 27 mm (25 ± 1.2). All children received a valve that was significantly larger than the Z-value defined for the pulmonary valve based upon their BSA at time of implantation. The Z-values for the pulmonary valve of these children ranged from +4.5 to +9.7. At time of implantation, the Z-value for the valves was +6.8 ± 1.4. The Z-values at the subsequent first and second postdischarge observations were +1.15 ± 2.0 (p = 0.0002) and +2.5 ± 1.4 (p = 0.13), respectively.

Xenograft annulus diameter
The xenograft annulus diameter was 25 ± 1.2 mm at time of implantation as determined by the manufacture's nominal valve specification. Evaluation at the first postdischarge follow-up revealed an echocardiographic annulus size of 19 ± 4.3 mm (p = 0.0001). However, at second postdischarge evaluation, no further diminution was observed (20 ± 1.8 mm, p = 0.07). Linear regression analysis (Fig 2, A) revealed decreasing annulus diameter over the entire implantation to follow-up period (R²-adjusted = 0.41, p < 0.0001).

View larger version (11K): [in this window] [in a new window]   Fig 2. Postoperative annulus measurement and pressure gradient linear regression analysis of (A) xenograft annulus diameter (mm) versus postoperative follow-up interval (months) and (B) peak-instantaneous xenograft pressure gradient (torr). Cross markers = immediate postsurgical and predischarge evaluation; open markers = first postoperative evaluation; solid markers = second postoperative evaluation.

Xenograft insufficiency
Pulmonary insufficiency in the initial follow-up was mild or less in all children. One child progressed to moderate insufficiency in the second follow-up examination.

	Comment

Top Abstract Introduction Patients and methods Results Comment Limitations of the study Conclusions Acknowledgments References

 
The use of the Ross operation for the surgical management of aortic valve disease in children has become the method of choice at many institutions [4–6]. The procedure can be performed with low mortality and limited early morbidity in high volume pediatric centers [7]. Freedom from anticoagulation, potential for growth, autograft durability, and freedom from autograft reoperation are the reasons often cited for providing this procedure to children with left ventricular outflow tract obstruction involving the aortic valve. Excellent immediate and long-term results can be expected for the autograft [1], although some have cautioned using the procedure when aortic insufficiency is the predominant preoperative lesion [8].

The durability of homografts used in children for RV/PA reconstruction is limited. Conduit shrinkage has been shown to occur and is a leading reason for replacement [9, 10]. This shrinkage is frequently associated with a Z-value that is lower than the expected Z-value at re-replacement time. The influence of immunologic factors [11] may be responsible for the shrinkage observed in homografts in children. However, this etiology has been disputed as the cause of homograft failure in adults [12]. All valves in our series demonstrated some shrinkage, although not to the degree that resulted in a Z-value less than the expected Z-value at the time of echo-Doppler follow-up.

Despite the problems associated with longevity, the use of the pulmonary valve homograft is currently recommended for the reconstruction of the RV/PA connection [2]. Availability of these conduits is limited, however, and in many third world countries they are simply not available [13]. The lack of availability has prompted some centers to develop unique alternatives utilizing autologous tissue to reconstruct the right ventricular outflow tract [14, 15]. The performance of conduits in the RV/PA position can dictate the need for later reoperation and exposure to additional morbidity and mortality. A number of options for the reconstruction of RV/PA continuity in children have been proposed. Corno and associates [16] and Bové and colleagues [13] have both reported excellent results using the valved bovine jugular vein conduit for RV/PA reconstruction in children. Their results are encouraging; however, long-term follow-up data are needed.

Allen and colleagues [17] reported the use of a customized conduit of Gore-Tex (Flagstaff, AZ) and a bovine pericardial valve to reconstruct RV/PA continuity in 48 children with a variety of conditions. Intermediate follow-up at an average of 43 months showed that no significant valve conduit stenosis or regurgitation. The valve conduit was constructed during the cross-clamp. Thus, the ischemic time necessary to perform a Ross operation would be extended. Dittrich and colleagues [3] compared their results using commercially available xenograft conduits for RV/PA reconstruction and compared them with matched historical controls who had received homografts for RVOT reconstruction. In their series a total of six conduits required replacement for obstruction. Four of these six xenografts were explanted because of supravalvar obstruction. Pathologic examination of these explanted xenografts revealed an obstructive neointimal proliferation at the site of the distal anastomosis. The xenograft valve leaflets were noted to be free of this process and intact.

We have not observed supravalvar obstruction in our group of patients. Perhaps this is secondary to the use of autologous pericardium at the pulmonary artery anastomosis with our reconstruction approach. Aupecle and colleagues [18] reported their experience with xenograft conduits for RVOT reconstruction and found that by 2 years after implant the mean gradient had increased to 61 ± 29 mm Hg. These authors noted that the obstruction did not occur primarily at the distal or proximal anastomotic site, this finding was similar to our observations. Histologic examination of two of the explanted conduits revealed thickening and retraction of the valve leaflets and some calcifications in the conduit wall. Although we have not yet explanted any of the xenografts in our series we have noticed that the transconduit gradient that developed in the conduits usually occurred at the valve level; a finding similar to that reported by Aupecle and colleagues [18].

Marianeschi and colleagues [19] reported their experience with the Shelhigh porcine pulmonary valve conduit in a series of 25 patients ranging in age from infancy to young adulthood. Follow-up of these patients was available in 20 of 25 cases and only two conduits had been explanted. Fifteen of the 20 patients were assessed by echo-Doppler 12 months after implantation and the peak instantaneous Doppler velocity was only 2.17 ± 1.18 m/s. These results are similar to those found in our patients at the first follow-up time period. We did not observe a further increase in the gradient or decrease in the annulus size between the first follow-up and second follow-up time periods. However, Pearl and colleagues [20, 21] observed that when they evaluated their results with the Shelhigh porcine pulmonary valve conduit used in a series of neonates and small infants that actuarial conduit failure was 72% at 1 year. Conduit failure was defined as explanation. The histologic examination of the explanted valves in these two series was very different. Pearl found a marked pseudointimal peel formation in the conduit with involvement of the entire conduit complex, whereas Marianeschi found isolated thrombus in one case and fibrosis at the distal suture line in the other case. Although our series of patients clearly lies between these two series with respect to age, we have not observed any gradient except at the annular level, suggesting leaflet immobility rather than a diffuse process as noted in Pearls' study or distal suture line obstruction as in the report by Marianeschi.

Our choice of the Medtronic Freestyle valve for the reconstruction of the RV/PA connection in the Ross operation was based upon this valve's apparent durability when used in the aortic position in adults [22] and as a substitute for the homograft in the RVOT reconstruction in the Ross operation in adults [23]. Our use of the Medtronic Freestyle valve for the reconstruction of the RVOT in children is not unique. Chard and colleagues [24] reported their experience using the Medtronic Freestyle valve in the reconstruction of RV/PA continuity in a heterogeneous group of children. One conduit was replaced approximately 2.3 years postimplant for subconduit obstruction. They did note host tissue extending into one of the cusps of the valve, but the leaflets were noted to be mobile and without calcification. Echo-Doppler follow-up performed at a mean of 9 weeks postoperatively revealed no gradient greater than 20 mm Hg. This degree of obstruction is similar to that observed at our initial follow-up evaluation of 27 ± 20 months. We have 3 children with echo-Doppler gradient between 60 and 65 mm Hg. One child has undergone repeat catheterization and attempted valvuloplasty, which was unsuccessful and will be scheduled for conduit replacement in the future. The other 2 children will undergo cardiac catheterization and possible balloon valvuloplasty, in the near future. The remaining 6 children have a gradient less that 40 mm Hg and will continue to receive yearly echo-Doppler examinations.

	Limitations of the study

Top Abstract Introduction Patients and methods Results Comment Limitations of the study Conclusions Acknowledgments References

 
The small number of patients, the relatively short follow-up period, and the single surgeon bias limit this study. An additional limitation to this study could be the absence of echocardiographic measurement of the annulus diameter before discharge. We used the manufacturers stated valve size to determine Z-values of the implanted valves and the annulus size.

	Conclusions

Top Abstract Introduction Patients and methods Results Comment Limitations of the study Conclusions Acknowledgments References

 
The Medtronic Freestyle valve provides a possible alternative to the use of homografts for the reconstruction of the RVOT in children undergoing the Ross procedure. The availability of this valve and the option for a customized smaller size should allow for RVOT reconstruction in many countries where homograft cost and availability prohibit their routine use.

	Acknowledgments

Top Abstract Introduction Patients and methods Results Comment Limitations of the study Conclusions Acknowledgments References

 
Support was provided by the Paul Nemir, Jr, MD, Endowed Chair in International Child Health at the University of Tennessee-Memphis and the International Children's Heart Foundation. The authors extend their appreciation to Christy Ripley for the preparation of this manuscript and to Nestor Sandoval, MD, for the artistic rendition of the procedure.

	References

Top Abstract Introduction Patients and methods Results Comment Limitations of the study Conclusions Acknowledgments References

 

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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 Author home page(s): William M. Novick Darko Anic Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Novick, W. M. Articles by Di Sessa, T. G. Search for Related Content PubMed PubMed Citation Articles by Novick, W. M. Articles by Di Sessa, T. G. Related Collections Congenital - acyanotic