Department for Cardiac and Thoracic Vascular Surgery, University of Luebeck, Germany

Transcription

1 Fifty-Two Months Mean Follow Up of Decellularized SynerGraft -Treated Pulmonary Valve Allografts J. F. Matthias Bechtel, Ulrich Stierle, Hans-Hinrich Sievers Department for Cardiac and Thoracic Vascular Surgery, University of Luebeck, Germany Background and aim of the study: It has been reported previously that the use of a decellularized pulmonary allograft (SynerGraft; CryoLife Inc.) for right ventricular outflow tract reconstruction in adults is associated with reduced immunization. The implantation appeared to be safe, but was not associated with any detectable clinical or echocardiographic advantage. The study aim was to follow further the outcome of SynerGraft patients. Methods: Twenty-three adult patients (19 males, four females) each received a SynerGraft-allograft during a Ross procedure. A further 49 patients (37 males, 12 females) who underwent a Ross procedure using a conventional pulmonary allograft during the same period served as controls. Follow up examinations using transthoracic echocardiography in standard views was performed on a regular basis. The latest follow up was performed after a mean of 52 months. Results: Directly after implantation, there were no echocardiographic differences between the two groups, but with time the pressure gradients increased significantly (p <0.001) in both groups. At the latest follow up, pressure gradients were slightly higher across the SynerGraft-allograft valves than across conventional allografts (P max 18.2 ± 9.0 versus 14.0 ± 6.9 mmhg, respectively; p = 0.049). On regression analysis (considering pre- and intraoperative variables), SynerGraft-allograft was the only variable predicting the increase in pressure gradient from its postoperative value to that at follow up. However, no clinical differences were observed between the groups. Conclusion: The present results relate to the longest follow up on decellularized pulmonary SynerGraftallografts conducted to date. No reoperations were required after a mean follow up of 52 months, and the echocardiographic results were stable after the first postoperative year. Based on these data, the use of pulmonary SynerGraft-allograft valves in adults appears not to provide any advantage over conventional allografts, although further follow up is warranted before any final judgment is made regarding this new technology. The Journal of Heart Valve Disease 2008;17: The SynerGraft treatment is a proprietary (CryoLife, Kennesaw, GA, USA) antigen-reduction process that was developed to provide an acellular valve matrix for autologous recellularization (1). This decellularization process can be applied to both xenografts and allografts (2); in the case of allograft valves it was hypothesized that decellularization would reduce the immunological response against the implant, and that Presented at the Fourth Biennial Meeting of the Society for Heart Valve Disease, 15th-18th June 2007, New York, USA Address for correspondence: Prof. Dr. H.-H. Sievers, Klinik für Herz- und Thorakale Gefaesschirurgie, UK S-H, Campus Luebeck Ratzeburger Allee 160, Luebeck, Germany sievers@herzchirurgie-luebeck.de this in turn would have a positive impact on long-term durability (3). With regards to immunogenicity, it has been clearly demonstrated by several groups, including the present authors (4), that SynerGraft-treated allografts [SG-AG] elicit a diminished immune response (3,5-7). The valve function of SG-AGs was reported to be either normal (2,7) or not to differ from that of conventional allografts (3,4,6,8). One study conducted in children (n = 26) even reported a superior valve function for SG- AGs as compared to conventional allograft valves (9). However, during a mean follow up of 19 months this was not translated into significant differences with regards to the rate of reintervention (3.8% for SG-AG versus 7.7% for conventional; p = 0.98). In addition to the small patient numbers and non- Copyright by ICR Publishers 2008

2 J Heart Valve Dis SynerGraft: 52-month follow up 99 random designs, the main limitation of all hitherto published reports on SG-AGs has been the relatively short follow up (30 months for aortic SG-AGs (7); 19 months for pulmonary SG-AGs (9)), thus precluding the drawing of any conclusions on the long-term durability of the valves. Hence, the aim of our present study was to provide long-term follow up data for patients receiving a pulmonary SG-AG. Clinical material and methods Patients Between December 2000 and July 2002, a total of 23 adult patients (19 males, four females) each received a cryopreserved pulmonary valve SG-AG during a Ross procedure at the present authors institution. A pulmonary SG-AG was implanted in two additional patients during reoperation for right ventricular outflow tract (RVOT) reconstruction after the repair of tetralogy of Fallot. One of these patients died five weeks after surgery, for reasons unrelated to the SG- AG (10). The other Fallot-patient is currently alive and well, with echocardiographically documented function of her SG-AG deemed satisfactory (mean gradient 7.0 mmhg; trivial regurgitation). This patient was is not considered any further in this report in order to compare groups which did not differ surgically except for the implanted allograft. A control group comprised 49 patients (37 males, 12 females) who each underwent a Ross procedure at the authors institution during the above-stated interval and received a conventional cryopreserved pulmonary valve allograft. Operative technique All operations were performed via a median sternotomy with hypothermic (26 C) cardiopulmonary bypass and cold crystalloid or blood cardioplegia for myocardial protection. For the Ross procedure, the diseased aortic valve was excised first, after which the pulmonary autograft was harvested from the RVOT and implanted as an aortic valve substitute inside the aortic root, in the subcoronary position. Cryopreserved pulmonary allografts (either SG-AG or conventional) were then thawed and implanted into the RVOT. The distal suture line was made with 5-0 interrupted polypropylene sutures; a 4-0 continuous polypropylene suture was used for the proximal suture line. Data acquisition and echocardiographic measurements There were no perioperative deaths. All patients underwent an echocardiographic examination within the first week after surgery (baseline), with follow up visits being performed on an outpatient basis. The SG- AG patients were examined after three, six and 12 months, and at longer intervals thereafter. Initially, the control patients were not seen at regular intervals after surgery, but at later times were examined on a nearannual basis. Because of this variation in intervals at which the patient and control groups were examined, only the baseline and latest follow up visits were considered for comparison in this report. Informed consent was obtained from all patients before conducting the investigative procedures, all of which were performed according to institutional guidelines. Echocardiography was performed using a Sonos ultrasound system fitted with a 2.5 MHz ultrasound transducer (Agilent Technologies, Andover, MS, USA). The measurements performed included transvalvular flow velocity of the neo-aortic valve from the apical five-chamber view using continuous-wave Doppler, left ventricular outflow tract (LVOT) flow velocity using pulsed-wave Doppler, and LVOT diameter. Flow characteristics across the RVOT were measured by continuous-wave Doppler from the Table I: Preoperative and surgical characteristics of the patients. Parameter SynerGraft Control p-value Gender ratio (M:F) 19:4 37: Age (years) * 37.0 ± ± BSA (m 2 ) * 1.99 ± ± Preop. homograft diameter + (mm) * 25.2 ± ± Age of allograft donor (years) * 48.1 ± ± Cross-clamp time (min) * 171 ± ± ECC time (min) * 208 ± ± Transfusion of allogenic blood (n) 4 (17) 6 (12) 0.72 * Values are mean ± SD. + According to cryopreservation protocol. Values in parentheses are percentages. BSA: Body surface area ( weight in kg height in cm ); ECC: Extracorporeal circulation.

3 100 SynerGraft: 52-month follow up J Heart Valve Dis Table II: Results of the echocardiographic examinations. Parameter SynerGraft Control p-value Baseline echocardiography + P max (mmhg) * 6.2 ± ± P mean (mmhg) * 3.3 ± ± Regurgitation (n) 0.47 None/trivial 40 (85) 21 (91) Mild 7 (15) 2 (9) Moderate or higher 0 0 Follow up echocardiography Time since implantation (months) * 52 ± 9 53 ± P max (mmhg) * 18.2 ± ± P mean (mmhg) * 9.4 ± ± Regurgitation (n) 0.31 None/trivial 23 (100) 43 (96) Mild 0 2 (4) Moderate or higher 0 0 * Values are mean ± SD. + Within first week after implantation. Values in parentheses are percentages. left parasternal short-axis view. The peak and mean transvalvular pressure gradients were determined using the modified Bernoulli equation (Δp = 4v 2, where Δp is the pressure gradient, and v is the maximal flow across the valve). Color-flow Doppler was used to detect pulmonary regurgitation, the severity of which was assessed semiquantitatively on the basis of the length and width of the regurgitation jet and the distance it reached into the RVOT; regurgitation was graded as none, trivial, mild, moderate, or severe. Statistical analyses Categorical data were reported as total numbers and relative frequencies, and compared using Fisher s Exact test. Continuous data were presented as mean ± SD. Echocardiographic measurements were compared using paired and unpaired Mann-Whitney U-tests, while multiple comparisons were corrected for using Bonferoni s method. The determinants of the change between the baseline pressure gradient and that at latest follow up were explored using stepwise linear regression analysis. A p-value <0.05 was considered to be statistically significant. All analyses were performed using SPSS for Windows, version 9.0 (SPSS, Chicago, IL, USA). Results The main characteristics of the patients are listed in Table I. No significant differences were identified between the groups, except that the SG-AG patients were younger than the controls. Likewise, no intergroup differences were found in the echocardiographic data at baseline (Table II). The latest follow up examinations were performed at a mean of 52 months after implantation in SG-AG patients, and at 53 months in controls (p = 0.62). One reoperation (due to endocarditis) was required in the control group, but none in the SG-AG group (p = 0.46). No patient in either group suffered from angina pectoris (p = 1.00), and almost no patient had dyspnea (median NYHA class I in both groups, minimum-maximum class I-II in both groups; p = 0.60). At echocardiography, regurgitation was seen not to have changed over time (p = 0.35) and did not differ between the groups (Table II). However, the pressure gradients across the RVOT had significantly increased in both groups (p <0.001; Fig. 1). At latest follow up, the maximal pressure gradient was slightly, but significantly, higher in the SG-AG group compared to the controls (median 16.0 versus 13.5 mmhg, p = 0.049; see Table II), and the mean pressure gradient tended to be higher (median 8 versus 7 mmhg, p = 0.065; see Table II). The calculated increase in pressure gradient between baseline and the latest measurement (Δ FU-BL ) was significantly greater in the SG-AG group for the maximal pressure gradient (Δ FU-BL = 11.9 ± 8.5, median 10.6 mmhg versus 7.7 ± 6.6, median 6.7 mmhg in controls, p = 0.038), as well as for the mean pressure gradient (Δ FU-BL = 6.1 ± 4.8, median 5.4 mmhg versus 3.9 ± 3.8, median 2.4 mmhg in controls, p = 0.030). A stepwise linear regression analysis was performed in order to explore the determinants of Δ FU-BL. Group, age, duration of follow up, body surface area, allograft diameter,

4 J Heart Valve Dis and age of the allograft donor were entered into the model, whereupon only implantation of a SG-AG was found to be significant (p = for Δ FU-BL of the maximal pressure gradient, and p = for Δ FU-BL of the mean pressure gradient). The serial echocardiographic examinations in the SG- AG group showed that the main increase in pressure A SynerGraft: 52-month follow up 101 Figure 2: Maximal (P max ) and mean (P mean ) pressure gradient across pulmonary SynerGraft-treated allograft valves at various time points postoperatively. After correction for multiple testing, only the steep increases in pressure gradient from immediately postoperatively to 3 months (P max and P mean ), and from 3 to 6 months (P max ) were statistically significant. *, p <0.05. ns: Not significant. RVOT: Right ventricular outflow tract. B gradient occurred within the first year after surgery (Fig. 2). Thereafter, the pressure gradient remained stable up until the latest follow up. Only slight, non-significant changes occurred over time with regards to regurgitation across the SG-AGs (Fig. 3). Discussion Herein are provided details of the longest follow up of SynerGraft-treated decellularized valves published to date. It was observed that the pressure gradients Figure 1: A) Maximal (P max ) pressure gradient of SynerGraft-allografts (solid symbols and line) and conventional allografts (open symbols, dotted line) directly after surgery and at the time of latest follow up. A significant increase in P max was apparent in both groups (both p <0.001). At the latest follow up, P max was significantly higher across SynerGraft-allografts than across conventional allografts (p = 0.049). B) Same situation as in (A), but showing mean pressure gradient (P mean ). A significant increase in P mean was apparent in both groups (both p <0.001). At the latest follow-up, P mean tended to be higher across SynerGraft-allografts than conventional allografts (p = 0.065). RVOT: Right ventricular outflow tract. Figure 3: Regurgitation across pulmonary SynerGrafttreated allograft valves at various time points postoperatively. The percentage of patients with a given degree of regurgitation is depicted. There were no significant changes over time (p = 0.38).

5 102 SynerGraft: 52-month follow up across the pulmonary SG-AG increased during the first 12 months after implantation - as also occurs with conventional allografts - but they did not increase further for up to a mean follow up of 52 months. Taken together with the fact that no reoperations have yet been required, these findings provide some evidence of the durability of decellularized allografts up to a maximum of 71 months. In contrast, the pressure gradients across the SG-AGs were found to be slightly, but significantly, higher at the latest follow up than across conventional allografts. In the present study, all patients operated on during the same period as the SG-AG patients served as controls, the aim being to control for subtle differences in implantation technique that may have occurred with time. It is believed, therefore, that the present report provides the most objective and fairest comparison of SG-AG and conventional allografts to date. All other reports have utilized a shorter follow up, and had either no control group (5,7) or a poorly defined control group (3,4,6,8,9). In addition, although disturbing, the present finding of higher pressure gradients across the SG-AGs was not unique; indeed, in an analysis of 347 patients who underwent a Ross procedure at the present authors department, SG-AG implantation was found to be one of the predictors of allograft stenosis (defined as a mean pressure gradient 10 mmhg) (11). The other predictors identified included the number of RVOT-interventions and a younger patient age. In the present study, the implantation of a SG-AG was predictive of the increase in pressure gradient, even after adjustment for patient age and other factors that might potentially influence the pressure gradient. It is well known that an increase in the pressure gradients across pulmonary valve allografts occurs postoperatively, and that this increase mainly occurs within the first year (12-14). In an initial study conducted by the present authors group on SynerGraft treatment, no echocardiographic differences were observed between the SG-AGs and conventional allografts during the first six postoperative months (4). Unfortunately, the intervals during which echocardiographic studies were performed in controls were varied, and did not permit any direct comparison with the serial echocardiographies obtained in SG-AG patients. Thus, it was not clear whether there was a more intense early increase in the pressure gradient, or a slightly longer-lasting increase following the implantation of a SG-AG. The etiology of the uniformly observed increase in the pressure gradient across pulmonary allograft valves is unclear, and remains the subject of controversy. However, there is good evidence from experimental studies to suggest that allograft valves are rejected (15- J Heart Valve Dis 18), which was one of the main reasons behind the development of decellularized allografts. There is, however, only sparse clinical evidence for a destructive immunological process contributing to allograft failure (19-22), and indeed several other studies have found no such evidence (23-28). In fact, it is even unclear whether the observed increase in pressure gradient can be viewed as part of a rejection process. An alternative explanation for the observed increase in pressure gradient would be a non-specific inflammatory response (26), most likely caused by stretching of the allograft (14). It has been observed that the smallest diameter of the allograft valve/artery conduit is located very proximally in most patients (8), and that the transallograft pressure gradient can be reduced significantly within the first two years postoperatively by resection of the proximal muscle tissue and its replacement with a pericardial or Gore-Tex strip (29). The etiology of the increase in the pressure gradient, of course, cannot be determined from such data. In conclusion, the present study has provided the longest follow up of SynerGraft-treated decellularized allograft valves to date. No reoperations were required during a mean follow up of 52 months, and no further increases in pressure gradient across the SG-AGs were observed after about the first postoperative year. However, the pressure gradients were slightly (but significantly) higher than across conventional allografts. In a regression analysis considering both preoperative and intraoperative variables, SG-AG was the only variable predicting an increase in pressure gradient over the follow up period. The mechanism of this unexpected finding is unknown, and further follow up is mandatory before any final judgment can be made regarding the value of decellularizing allograft valves with the SynerGraft antigen reduction technology. At present, however, it appears that the use of pulmonary SynerGraft-allograft valves does not provide any major advantage over conventional allografts. Acknowledgements The authors are indebted to Katrin Meyer for organizing the outpatient visits, and for data management. References 1. O Brien MF, Goldstein S, Walsh S, et al. The SynerGraft valve: A new acellular (nonglutaraldehyde-fixed) tissue heart valve for autologous recellularization. First experimental studies before clinical implantation. Semin Thorac Cardiovasc Surg 1999;11(Suppl.1): Goldstein S, Clarke DR, Walsh SP, Black KS, O Brien MF. Transspecies heart valve transplant: Advanced studies of a bioengineered xeno-auto-

6 J Heart Valve Dis SynerGraft: 52-month follow up 103 graft. Ann Thorac Surg 2000;70: Elkins RC, Lane MM, Capps SB, McCue C, Dawson PE. Humoral immune response to allograft valve tissue pretreated with an antigen reduction process. Semin Thorac Cardiovasc Surg 2001;13(Suppl.1): Bechtel JFM, Müller-Steinhardt M, Schmidtke C, et al. Evaluation of the decellularized pulmonary valve homograft (SynerGraft TM ). J Heart Valve Dis 2003;12: Elkins RC, Dawson PE, Goldstein S, Walsh SP, Black KS. Decellularized human valve allografts. Ann Thorac Surg 2001;71:S428-S Hawkins JA, Hillmann ND, Lambert LM, et al. Immunogenicity of decellularized cryopreserved allografts in pediatric cardiac surgery: Comparison with standard cryopreserved allografts. J Thorac Cardiovasc Surg 2003;126: Zehr KJ, Yagubyan M, Connolly HM, Nelson SM, Schaff HV. Aortic root replacement with a novel decellularized cryopreserved aortic homograft: Postoperative immunoreactivity and early results. J Thorac Cardiovasc Surg 2005;130: Bechtel JFM, Gellisen J, Erasmi AW, et al. Mid-term findings on echocardiography and computed tomography after RVOT-reconstruction: Comparison of decellularized (SynerGraft) and conventional allografts. Eur J Cardiothorac Surg 2005;27: Tavakkol Z, Gelehrter S, Goldberg CS, et al. Superior durability of SynerGraft pulmonary allografts compared with standard cryopreserved allografts. Ann Thorac Surg 2005;80: Sayk F, Bos I, Schubert U, Wedel T, Sievers HH. Histopathologic findings in a novel decellularized pulmonary homograft: An autopsy study. Ann Thorac Surg 2005;79: Sievers HH, Hanke T, Stierle U, et al. A critical reappraisal of the Ross operation. Renaissance of the subcoronary implantation technique? Circulation 2006;114(Suppl.I):I504-I Ward KE, Elkins RC, Overholt ED, et al. Evaluation of cryopreserved homografts in the right ventricular outflow tract after the Ross procedure: Intermediate-term follow-up. J Heart Valve Dis 1997;6: Briand M, Pibarot P, Dumesnil JG, Cartier P. Midterm echocardiographic follow-up after the Ross operation. Circulation 2000;102(Suppl.III):III- 10-III Carr-White GS, Kilner PJ, Hon JKF, et al. Incidence, location, pathology, and significance of pulmonary homograft stenosis after the Ross operation. Circulation 2001;104(Suppl.I):I16-I Moustapha A, Ross DB, Bittira B, et al. Aortic valve grafts in the rat: Evidence for rejection. J Thorac Cardiovasc Surg 1997;114: Dor FJMF, Oei FBS, Vaessen LMB, et al. Frequencies of donor-reactive helper T-lymphocytes correlate with rejection of aortic valve allografts in rats. J Heart Valve Dis 2002;11: Legare JF, Lee TDG, Creaser K, Ross DB. T lymphocytes mediate leaflet destruction and allograft aortic valve failure in rats. Ann Thorac Surg 2000;70: Legare JF, Ross DB, Issekutz TB, et al. Prevention of allograft heart valve failure in a rat model. J Thorac Cardiovasc Surg 2001;122: Rajani B, Mee RB, Ratliff NB. Evidence for rejection of homograft cardiac valves in infants. J Thorac Cardiovasc Surg 1998;115: Baskett RJF, Nanton MA, Warren AE, Ross DB. Human leukocyte antigen-dr and ABO mismatch are associated with accelerated homograft failure in children: Implications for therapeutic interventions. J Thorac Cardiovasc Surg 2003;126: Dignan R, O Brien M, Hogan P, et al. Aortic valve allograft structural deterioration is associated with a subset of antibodies to human leucocyte antigens. J Heart Valve Dis 2003;12: Pompilio G, Polvani G, Piccolo G, et al. Six-year monitoring of the donor-specific immune response to cryopreserved aortic allograft valves: Implications with valve dysfunction. Ann Thorac Surg 2004;78: Smith JD, Ogino H, Hunt D, et al. Humoral immune response to human aortic valve homografts. Ann Thorac Surg 1995;60:S127-S Mitchell RN, Jonas RA, Schoen FJ. Pathology of explanted cryopreserved allograft heart valves: Comparison with aortic valves from orthotopic heart transplants. J Thorac Cardiovasc Surg 1998;115: Bechtel JFM, Bartels C, Schmidtke C, et al. Does histocompatibility affect homograft valve function after the Ross procedure? Circulation 2001;104(Suppl.I):I25-I Koolbergen DR, Hazekamp MG, de Heer E, et al. The pathology of fresh and cryopreserved homograft heart valves: An analysis of forty explanted homograft valves. J Thorac Cardiovasc Surg 2002;124: Jashari R, Daenen W, Meyns B, Vanderkelen A. Is ABO group incompatibility really the reason of accelerated failure of cryopreserved allografts in very young patients? Echography assessment of the European Homograft Bank (EHB) cryopreserved allografts used for reconstruction of the right ventricular outflow tract. Cell Tissue Bank 2004;5:

7 104 SynerGraft: 52-month follow up 28. Yap CH, Skillington PD, Matalanis G, et al. Anti- HLA antibodies after cryopreserved allograft valve implantation does not predict valve dysfunction at three-year follow up. J Heart Valve Dis 2006;15: Schmidtke C, Dahmen G, Graf B, Sievers HH. Pulmonary homograft muscle reduction to reduce the risk of homograft stenosis in the Ross procedure. J Thorac Cardiovasc Surg 2007;133: Meeting discussion J Heart Valve Dis DR. PASCAL M. DOHMEN (Berlin, Germany): Do you plan to exercise the patients to see if, under pressure or under exercise, there will be any differences between the groups? Also, how are the patients in general life? Are there any group differences in their physical capabilities? DR. MATTHIAS BECHTEL (Luebeck, Germany): Unfortunately, we do not have any such data. We did not perform formal quality of life examinations, but there is no clinical distinction between the patients. Both groups contain patients that we have to watch carefully because of high pressure gradients, and we may need occasionally to decide whether a reoperation is needed. In some cases we use exercise tests to make that decision, but we do not carry out exercise testing routinely, although it s a good idea.