Cryopreserved Allograft Valves Research Articles

Transplantation of cryopreserved human heart valves in Europe: 30years of banking in Brussels and future perspectives.

For over 30 years, our TE has processed, controlled for quality and distributed cryopreserved allograft valves for human application. We present a review of this activity and future perspectives of cardiovascular tissue banking. The donor age and medical/behavioral history are in compliance with the regulations of the EUMS. Allograft morphology and function are evaluated in a class A cleanroom. Tests for viral/bacterial infection, histological control of structure/infection/malignancy and control-rate cryopreservation are performed. A total of 7562 hearts were sent to our TE, whereas 7290 valves (pulmonary, aortic and mitral) were transplanted. The donations increased over time: 1934, 2566 and 3062 hearts were donated during the first, second and third decades (increases of 32.7 and 19.3% during the second and third decades). Likewise, there was a significant increase in transplantations with 2050, 2550 and 2690 valves implanted during the first, second and third decades (24.4 and 5.5% increase during the second and third decades). A total of 4475 pulmonary (61.4%), 2760 aortic (37.9%) and 55 mitral valves (0.7%) were transplanted. Outstanding long-term results in adults and evidence of immune-related deterioration of allografts in neonates and infants were demonstrated. Decellularization was suggested as a solution. One hundred pulmonary and 180 aortic valves were sent for transplantation after decellularization for the ESPOIR and ARISE clinical trials and beyond. The donation and transplantation activity increased progressively. Although cryopreserved valves represent the best substitute for diseased valves, accelerated failure appears after implantation in neonates and infants. The implementation of new technologies, such as decellularization, as a standard procedure for treatment of allograft valves will offer further improvements in allograft quality and increase of durability.

Interstage evaluation of homograft-valved right ventricle to pulmonary artery conduits for palliation of hypoplastic left heart syndrome

ObjectivePalliation of hypoplastic left heart syndrome with a standard nonvalved right ventricle to pulmonary artery conduit results in an inefficient circulation in part due to diastolic regurgitation. A composite right ventricle pulmonary artery conduit with a homograft valve has a hypothetical advantage of reducing regurgitation, but may differ in the propensity for stenosis because of valve remodeling. MethodsThis retrospective cohort study included 130 patients with hypoplastic left heart syndrome who underwent a modified stage 1 procedure with a right ventricle to pulmonary artery conduit from 2002 to 2015. A composite valved conduit (cryopreserved homograft valve anastomosed to a polytetrafluoroethylene tube) was placed in 100 patients (47 aortic, 32 pulmonary, 13 femoral/saphenous vein, 8 unknown), and a nonvalved conduit was used in 30 patients. Echocardiographic functional parameters were evaluated before and after stage 1 palliation and before the bidirectional Glenn procedure, and interstage interventions were assessed. ResultsOn competing risk analysis, survival over time was better in the valved conduit group (P = .040), but this difference was no longer significant after adjustment for surgical era. There was no significant difference between groups in the cumulative incidence of bidirectional Glenn completion (P = .15). Patients with a valved conduit underwent more interventions for conduit obstruction in the interstage period, but this difference did not reach significance (P = .16). There were no differences between groups in echocardiographic parameters of right ventricle function at baseline or pre-Glenn. ConclusionsIn this cohort of patients with hypoplastic left heart syndrome, inclusion of a valved right ventricle to pulmonary artery conduit was not associated with any difference in survival on adjusted analysis and did not confer an identifiable benefit on right ventricle function.

How to choose the best available homograft to reconstruct the right ventricular outflow tract

How to choose the best available homograft to reconstruct the right ventricular outflow tract

Belgian and European Experience with the European Homograft Bank (EHB) Cryopreserved Allograft Valves.-Assessment of a 20 Year Activity

European Homograft Bank (EHB) has been selecting, preparing, storing and distributing the cryopreserved allograft valves in Belgium and some other European Countries since 1989. It was established in 1988 by a pathologist and the cardiac and vascular surgeons from Belgian and other European centres as an inter-university, international nonprofit association. Due to its neutral behavior and very high quality criteria, European Homograft Bank became one of the prominent heart valve banks in Europe and wider. It collaborates with the transplant coordination in donor selection as well as with the huge network of the implanting surgeons in Belgium and other European Countries. The EHB responsible discusses with the implanting surgeon the allograft selection on basis of the indication and the patients state of emergency.A total of 8.911 donor heart valves have been evaluated in EHB during the last 20 years. After selection, 5.258 allograft valves (1.996 aortic, 3.189 pulmonary and 73 mitral) were cryopreserved and stored in vapors of liquid nitrogen between 6 weeks and 5 years. A total of 4.516 allograft valves (1.391 aortic, 2.620 pulmonary and 48 mitral) were implanted in the left or right ventricular outflow tract for replacement of the diseased aortic or pulmonary valve and for mitral or tricuspid valve replacement or repair. In 1.380 cases the allograft valves were used for right ventricular outflow tract reconstruction as part of the Ross-procedure, whereas in 668 cases the allograft valve served for replacement of the aortic valve for endocarditis. The most important indications for use of cryopreserved allograft valves were: important cardiac and valve malformation in children, female patients of child-bearing age with diseased cardiac valves, cases with contra-indication for anti-coagulation and the patients with severe endocarditis with septal or annular abscesses. Although the number of the donation increased by year, the available allograft valves in stock are still insufficient to respond to all the surgeons’ request for different indications.

Expression of A and B Blood Group Antigens on Cryopreserved Homografts

The contribution of ABO blood group mismatching on the rate of cardiac homograft failure is uncertain. It has been shown that there is lack of expression of A and B blood group antigens on fresh and cryopreserved homograft valves. However, expression of these antigens on the homograft vessel conduit has not been reported. Unused portions of cryopreserved pulmonary artery homografts (n = 16) were immunohistochemically stained and examined for expression of endothelial cell marker CD31 and A and B blood group antigens. The staining pattern for each antigen was described. Comparison of homograft donor blood group (as determined by immunostaining) to the blood group reported by the homograft supplier was made. Staining of CD31 and A and B blood group antigens was poor on the luminal surface (tunica intima) of the homograft conduit but strong in the vaso vasorum of the tunica media and adventitia. Homograft donor blood group was consistent with the reported donor blood group in 15 of 16 specimens (4 group A, 3 group B, 8 group O). In one specimen (reported as group O), we detected strong expression of CD31 and A antigen on the endothelium of the vaso vasorum. Cryopreserved homografts strongly express A and B blood group antigens on well-preserved endothelial surfaces of the medial and adventitial vaso vasorum. The significance of this finding with regard to the immunologic response to mismatched ABO blood group antigens and homograft longevity is uncertain.

Bioprosthetic Valves and Laudable Inflammation?

In this issue of Circulation , Dr Manji and colleagues1 from the University of Alberta (Canada) report a series of animal experiments designed to test the mythic role of gluteraldehyde in preventing recognition of bioprosthetic heart valve antigenicity with subsequent rejection and failure. Gluteraldehyde–cross-linked xenograft tissues (initially porcine) have been used in the manufacturing of stented (and now stentless) heart valves since 1970. Original theories for the clinical efficacy of gluteraldehyde were based on its ability to irreversibly cross-link collagen and thus to increase mechanical strength and durability over fresh untanned cardiovascular tissues. Porcine valve leaflets, bovine pericardium, equine pericardium, and bovine jugular vein, among other structures, have been treated this way for clinical applications. Since its introduction, however, limitations and unexpected consequences of gluteraldehyde and similar chemical treatments have been recognized clinically. As pointed out by the authors, durability is quite variable, tending to be better in older patients whereas younger patients suffer early deterioration, calcification, and fibrocalcific failure.2,3 The good news has been that the failures tend to be progressive rather than catastrophic, leading to semielective reoperations. Additionally, the xenograft bioprostheses have been extremely helpful in avoiding warfarin in the very young and the very old, reducing the risk of thromboembolism. The traditional explanation for the fibrocalcific degeneration of the nonvital gluteraldehyde-treated bioprosthetic heart valves has been a combination of physical and chemical effects leading to calcification and a fixation of the structural proteins that prevent protein recycling and renewal. Mechanical theories of fatigue-induced wear resulting in calcification have been proposed, especially along the flexion lines of the cusps. Others have proposed that the gluteraldehyde has serendipitously “masked” the antigenicity of xenograft proteins, retained cells, and cellular debris, thus prolonging the period to calcification. This well-designed series of studies buttresses other studies demonstrating that gluteraldehyde fixation …

Are allografts the biologic valve of choice for aortic valve replacement in nonelderly patients? Comparison of explantation for structural valve deterioration of allograft and pericardial prostheses

To compare explantation for structural valve deterioration in nonelderly patients after aortic valve replacement with stented bovine pericardial and cryopreserved allograft valves. From 1981 to 1985, 478 patients received pericardial prostheses during premarket approval; from 1987 to 2000, 744 patients received cryopreserved allografts. Mean age of patients receiving allografts was 49 +/- 12 years, and that of those receiving pericardial prostheses was 65 +/- 11 years; pericardial valves were used in 138 patients younger than age 60. Mean follow-up was 15 +/- 5.1 years for pericardial valves (4674 patient-years of follow-up) and 5.6 +/- 3.1 years for allografts (3892 patient years of follow-up). Multivariable hazard function methodology, age-group stratification, and propensity matching were used to compare age-specific explantation for structural valve deterioration. Ninety-five pericardial valves and 46 allografts were explanted, and structural valve deterioration was the mechanism of failure in 74% and 59%, respectively. The risk of structural valve deterioration increased with younger age at implantation for both allografts (P = .07) and pericardial valves (P < .0001), with a similar magnitude of effect in patients age 50 years or younger (P = .5), 50 to 60 years (P = .7), and greater than 60 years (P = .9) and in propensity-matched pairs (P = .2). Thus, pericardial valves were as durable as allografts at all adult ages. Structural valve deterioration is the most frequent cause of valve-related reoperation after both pericardial and allograft aortic valve replacement and is similarly age dependent, suggesting that pericardial valves may be appropriate for nonelderly as well as older persons.

Immunogenicity of decellularized cryopreserved allografts in pediatric cardiac surgery: comparison with standard cryopreserved allografts

Background Recognition of the immunogenicity of standard cryopreserved allografts has led to the development of new decellularized allografts (CryoValve SG; CryoLife, Inc, Kennesaw, Ga). This preliminary study examined the HLA antibody response to these decellularized allografts and compared it with the response to standard allograft material. Methods We prospectively measured the frequency of panel-reactive HLA class I (HLA-A, HLA-B, and HLA-C) and class II (HLA-DR/DQ) alloantibodies in 14 children (age 8.5 ± 7.9 years) receiving decellularized, cryopreserved allografts, including 6 undergoing allograft patch insertion and 8 with a valved pulmonary allograft. We compared them with 20 historical control subjects (age 1.7 ± 2.4 years) undergoing implantation of standard cryopreserved allografts, 8 with valves and 12 with allograft patch. All patients had panel-reactive antibody levels measured before and at 1, 3, and 12 months after the operation. HLA class I and class II panel-reactive antibody levels were determined with a sensitive flow cytometry technique. Results We found panel-reactive antibody levels in decellularized allografts to be elevated slightly from preoperative levels for both class I and class II antibodies at 1, 3, and 12 months ( P > .05). The panel-reactive antibody level for both class I and class II antibodies were significantly lower for decellularized allografts as compared to standard allografts. Functionally, the allografts were similar with decellularized valved grafts showing a peak echo-determined systolic gradient of 13 ± 15 mm Hg at 8 ± 2.6 months postoperatively as compared to a gradient of 24 ± 18 mm Hg measured 12 ± 6 months postoperatively in standard allografts ( P = .11). Conclusions Decellularized grafts elicited significantly lower levels of class I and class II HLA antibody formation at 1, 3, and 12 months after implantation than did standard cryopreserved allografts. Early hemodynamic function of decellularized grafts was similar to that of standard cryopreserved allograft valves. Further experience is necessary to determine whether the reduced immunogenicity of decellularized allografts will truly allow tissue ingrowth and improved long-term durability in patients.

Decellularized pulmonary homograft (SynerGraft) for reconstruction of the right ventricular outflow tract: first clinical experience.

Cryopreserved homograft valve conduits have been used to reconstruct the right and left ventricular outflow tract. Long-term studies have shown homograft degeneration and calcification, and it has been postulated that immunological mediated phenomena in a manner similar to that seen in chronic rejection may contribute to the degeneration process. The development of a decellularized, non-glutaraldehyde-fixed valve conduit creates a non-immunogenic connective tissue matrix for autologous recellularization by host cells. The aim of the study was to characterize the clinical and hemodynamic pattern in human implants of the novel decellularized pulmonary homografts (SynerGraft). Reconstruction of the right ventricular outflow tract was performed in 17 patients: 15 patients with aortic valve disease and the Ross procedure, and two patients with redo procedures following Fallot tetralogy and severe pulmonary regurgitation. Patients with the Ross procedure with standard cryopreserved homografts as neopulmonic conduits served as controls. Within the follow-up over six months morphological and hemodynamic parameters were characterized by echocardiography: maximal and mean pressure gradient across the right and left ventricular outflow tract, their effective orifice areas, determination of neopulmonic and neoaortic regurgitation. One patient died six weeks following surgical treatment due to non-valve related end-stage cardiopulmonary failure; all patients were free of valve-related complications during the follow-up period. The matched Ross patients showed a gradual but significant increase of both the maximal and mean pressure gradient across the right ventricular outflow tract (Delta P max 5.5+/-2.5 to 11.4+/-6.4 mmHg, p=0.002; Delta P mean 3.0+/-1.3 to 6.2+/-3.9 mmHg, p=0.003), whereas in the SynerGraft group increase of pressure gradients were measurable but did not reach statistical significance (Delta P max 7.1+/-3.7 to 10.1+/-3.9 mmHg, p=0.11; Delta P mean 3.6+/-1.6 to 5.5+/-2.3 mmHg, p=0.12). The pulmonary effective orifice areas decreased in the control group from 1.74+/-0.33 to 1.18+/-0.36 cm(2)/m(2) (p=0.001). Within the SynerGraft group time dependent reduction of the orifice area was significantly less (1.51+/-0.37 to 1.25+/-0.26 cm(2)/m(2); p=0.08). Up to six months after implantation reconstruction of the right ventricular outflow tract with decellularized homografts was safe, stable, and the morphological and hemodynamic features are promising.

Short-term result of aortic valve replacement with cryopreserved homograft valve in the University of Tokyo Tissue Bank.

The short-term results after aortic root replacement with 11 cryopreserved aortic homografts was examined. Since 1998, the University of Tokyo Tissue Bank has supplied 11 aortic homograft valves. Nine of the recipients were male, and the average age was 51.2 years. Nine out of 11 patients had suffered from a serious condition of native or prosthetic valve infectious endocarditis. All of the patients underwent aortic root replacement, and the blood type between the patient and the homograft was matched in 8 of the patients. Only 1 patient died (9.1%) in the short-term due to sepsis. The preoperative degree of aortic valve regurgitation in all of the cases was third or fourth while the regurgitation disappeared after the operation in all of them. Thinking of the serious condition of our cases preoperatively, the 9.1% operative mortality was quite acceptable. Long-term follow-up is necessary to estimate the quality of the homografts.

Surgical management of acute aortic root endocarditis with viable homograft: 13-year experience.

Cryopreserved homograft valves have been used for acute infective aortic root endocarditis with great success but it is compounded by its availability in all sizes. The long-term clinical results of geometric mismatched homografts are not well defined and addressed. Over a 15-year period (April 1986-June 2001), 816 patients presented with active infective endocarditis. One hundred and eighty-two of the patients aged between 9 and 78 years (mean: 51.0 +/- 1.13 years) consisting of 142 males and 40 females received homograft aortic valves. One hundred and ten patients were in NYHA functional class III and 72 in class IV and in cardiogenic shock. Of the patients, 2.7% suffered from septic embolism. One hundred and twenty-four (68.1%) patients presented with periannular abscesses and 58 (31.9%) with no abscess while 107 native valve (NVE) and 75 prosthetic valve (PVE) endocarditis were diagnosed preoperatively by transesophageal echocardiography (TEE) and confirmed intraoperatively. Freehand subcoronary implantation (FSCI) was used in 106 patients and root replacement in 76 patients. The operative death was 8.5% and for patients in NYHA functional class IV and in cardiogenic shock was 14.5%. Late mortality rate was 7.9%. Patient survival after discharge from hospital at 1 year was 97% and at 10 years was 91%, respectively. Thirty-one (22.1%) patients underwent reoperation after 1.7 years (mean) with two deaths (6.4%). Early (< or = 60 days) and late reinfection rate was 2.7 and 3.6%, respectively. Freedom from reoperation for matched and undersized homografts at 10-13 years was 85 and 55%, respectively. The univariate model identified undersized homograft (P=0.002), FSCI (P=0.09) and reinfection (P=0.0001) as independent risk factors for developing early and late valve dysfunction resulting in reoperation and homograft explant. Early aggressive valve replacement with homograft for active infective aortic root endocarditis with periannular abscesses is more successful than delayed last resort surgery. Homografts exhibit excellent clinical performance and durability with a low rate of reinfection, if properly inserted. Undersized homograft is an incremental risk factor for early and late reoperation.

Characterization of Ultrastructural Damage of Valves Cryopreserved under Standard Conditions

Cryopreserved allograft valves are increasingly being used as valvular replacements. This study was conducted to characterize the ultrastructural damage on the allograft valves obtained by a current standard protocol of valve procurement, antibiotic exposure, and cryopreservation, as a basis for future studies on allograft valve preservation. Materials used were seven aortic and seven pulmonary fresh porcine valves, which were cryopreserved according to the requirements of the American and European Associations of Tissue Banks. The samples were ramdomly assigned into four groups: (1) fresh, untreated; (2) fresh, treated with antibiotics for 24 h.; (3) treated with antibiotics and exposed to dimethyl sulfoxide (without freezing); and (4) treated with antibiotics, exposed to dimethyl sulfoxide, and then cryopreserved and stored until the study. All tissue samples were processed simultaneously for routine light microscopy and transmission electron microscopy. Fresh-untreated, antibiotic-treated, and dimethyl sulfoxide-exposed valves showed adequate preservation of cellular components. However, after cryopreservation significant damage was observed in fibroblasts with signs of apoptotic cellular injury. Our observation suggests that apoptosis occurs during valve processing. This apoptotic process may be related to various factors, including chemical injury or hypoxia.

The Failure Modes of Biological Prosthetic Heart Valves

Bioprosthetic heart valves have been used since the 1960s, starting with the use of homograft aortic valves obtained from human cadavers. Today prosthetic heart valves are used widely, and bioprostheses account for close to 40% of all heart-valve replacements. Although most bioprosthesis are still stented porcine aortic valves, the introduction of stentless valves and the increasing use of cryopreserved homograft valves has led to an upsurge of interest in bioprosthesis. There have been significant changes in the handling and fixation of porcine aortic valves; however, their modes of failure remain virtually unchanged, although many bioprosthetic valves now last for considerably longer periods. This article reviews the modes of failure of bioprosthetic heart valves.

Invited commentary

Invited commentary

Transpecies heart valve transplant: advanced studies of a bioengineered xeno-autograft

Background. Tissue engineering approaches utilizing biomechanically suitable cell-conductive matrixes should extend xenograft heart valve performance, durability, and growth potential to an extent presently attained only by the pulmonary autograft. To test this hypothesis, we developed an acellular, unfixed porcine aortic valve-based construct. The performance of this valve has been evaluated in vitro under simulated aortic conditions, as a pulmonary valve replacement in sheep, and in aortic and pulmonary valve replacement in humans. Methods. SynerGraft porcine heart valves (CryoLife Inc, Kennesaw, GA) were constructed from porcine noncoronary aortic valve cusp units consisting of aorta, noncoronary aortic leaflet, and attached anterior mitral leaflet (AML). After treatment to remove all histologically demonstrable leaflet cells and substantially reduce porcine cell-related immunoreactivity, three valve cusps were matched and sewn to form a symmetrical root utilizing the AML remnants as the inflow conduit. SynerGraft valves were evaluated by in vitro hydrodynamics, and by in vivo implants in the right ventricular outflow tract of weanling sheep for up to 336 days. Cryopreserved allograft valves served as control valves in both in vitro and in vivo evaluations. Valves were also implanted as aortic valve replacements in humans. Results. In vitro pulsatile flow testing of the SynerGraft porcine valves demonstrated excellent valve function with large effective orifice areas and low gradients equivalent to a normal human aortic valve. Implants in sheep right ventricular outflow tracts showed stable leaflets with up to 80% of matrix recellularization with host fibroblasts and/or myofibroblasts, and with no leaflet calcification over 150 days, and minimal deposition at 336 days. Echocardiography studies showed normal hemodynamic performance during the implantation period. The human implants have proven functional for over 9 months. Conclusions. A unique heart valve construct has been engineered to achieve the equivalent of an autograft. Short-term durability of these novel implants demonstrates for the first time the possibility of an engineered autograft.

Factors Affecting Longevity of Homograft Valves Used in Right Ventricular Outflow Tract Reconstruction for Congenital Heart Disease

Background —Few studies have explored the long-term function of cryopreserved homograft valves used for reconstruction of the right ventricular tract (RVOT) in patients with congenital heart disease. Methods and Results —Among 205 patients receiving cryopreserved homografts for reconstruction of the RVOT between November 1985 and April 1999, the outcome of 220 homografts in 183 operative survivors was analyzed. There were 150 pulmonary and 70 aortic homografts used. Median age at implantation was 4.4 years (mean 6.9±7.6 years, range 3 days to 48 years). End points included (1) patient survival, (2) homograft failure (valve explant or late death), and (3) homograft dysfunction (homograft insufficiency or homograft stenosis). Survival was 88% at 10 years. Freedom from homograft failure was 74±4% at 5 years and 54±7% at 10 years. Univariable analysis identified younger age, longer donor warm ischemic time, valve Z value &lt;2, and previous procedure as risk factors for homograft failure and dysfunction. Aortic homograft type and extracardiac operative technique predicted homograft failure but not dysfunction. For patients ≤1 year of age, valve type did not predict failure or dysfunction. Multivariable analysis identified younger age and longer donor warm ischemic time as risk factors for homograft failure and dysfunction, whereas, Z value &lt;2 and aortic valve type predicted homograft valve failure. Conclusions —Homograft valves used for RVOT reconstruction provide effective intermediate palliation with excellent late survival. Factors that adversely affect graft longevity include younger age, longer donor warm ischemic time, smaller homograft size, use of aortic homograft in the older patient, and extracardiac operative technique.

Factors Affecting Longevity of Homograft Valves Used in Right Ventricular Outflow Tract Reconstruction for Congenital Heart Disease

Few studies have explored the long-term function of cryopreserved homograft valves used for reconstruction of the right ventricular tract (RVOT) in patients with congenital heart disease. Among 205 patients receiving cryopreserved homografts for reconstruction of the RVOT between November 1985 and April 1999, the outcome of 220 homografts in 183 operative survivors was analyzed. There were 150 pulmonary and 70 aortic homografts used. Median age at implantation was 4.4 years (mean 6.9+/-7.6 years, range 3 days to 48 years). End points included (1) patient survival, (2) homograft failure (valve explant or late death), and (3) homograft dysfunction (homograft insufficiency or homograft stenosis). Survival was 88% at 10 years. Freedom from homograft failure was 74+/-4% at 5 years and 54+/-7% at 10 years. Univariable analysis identified younger age, longer donor warm ischemic time, valve Z: value <2, and previous procedure as risk factors for homograft failure and dysfunction. Aortic homograft type and extracardiac operative technique predicted homograft failure but not dysfunction. For patients </=1 year of age, valve type did not predict failure or dysfunction. Multivariable analysis identified younger age and longer donor warm ischemic time as risk factors for homograft failure and dysfunction, whereas, Z: value <2 and aortic valve type predicted homograft valve failure. Homograft valves used for RVOT reconstruction provide effective intermediate palliation with excellent late survival. Factors that adversely affect graft longevity include younger age, longer donor warm ischemic time, smaller homograft size, use of aortic homograft in the older patient, and extracardiac operative technique.

Class I and class II anti-hla antibodies after implantation of cryopreserved allograft material in pediatric patients

Objectives: Very little is known regarding the immune response to cryopreserved allograft valves and patch material used in the surgical repair of congenital heart defects. Methods: We prospectively measured the frequency of panel reactive antibodies directed against HLA class I (HLA-A, B, and C) and class II (HLA-DR/DQ) alloantigens in 24 children receiving cryopreserved allografts. We compared them with results in 11 previously reported control patients. Sixteen of the study patients underwent placement of a valved conduit (11 pulmonic, 5 aortic) between the right ventricle and pulmonary arteries, 6 underwent patch angioplasty of stenotic vessels with cryopreserved pulmonary artery, and 2 underwent placement of a pulmonary monocusp patch. Study patients had panel reactive antibodies measured before, 1 month, 3 months, and 1 year after the operation. Results: With allograft implantation, panel reactive antibodies increased from 1.9% ± 5% before the operation to 62% ± 33% at 31 ± 8 days after the operation, 92% ± 15% at 3.3 ± 0.6 months after the operation, and 85% ± 18% at 1.1 ± 0.2 years after the operation. The control group showed no change in panel reactive antibodies, with a level of 1.6% ± 1% before the operation, 3.2% ± 1% 28 ± 5 days after the operation, and 1.7% ± 1% 2.7 ± 0.3 months after the operation. Class II antibodies (anti-HLA-DR/DQ) rose to 49% ± 35% at 30 ± 8 days and 70% ± 26% at 3.3 ± 0.6 months after the operation. Conclusions: Cryopreserved allograft material induces a marked response that involves both class I and class II anti-HLA antibodies within 3 months after operation in children. This alloantibody response may represent a form of “rejection,” may have implications for those who require subsequent cardiac transplantation, and may play a role in early allograft failure. (J Thorac Cardiovasc Surg 2000;119:324-30)

Cryopreserved homograft valves in the pulmonary position: Risk analysis for intermediate-term failure

Objective: The purpose of this study was to examine the durability of cryopreserved homografts used to replace the “pulmonary” valve and to identify factors associated with their late deterioration. Methods: We reviewed our entire experience (1985-1997) with 331 survivors in whom cryopreserved homograft valves (pulmonary, n = 304; aortic, n = 27) were used to reconstruct the pulmonary outflow tract. Median age was 14 years (range, 2 days–62 years). Operations included Ross operation (n = 259), tetralogy of Fallot (n = 41), truncus arteriosus (n = 14), Rastelli operation (n = 11), and others (n = 6). Median follow-up was 3.8 years (range, 0.2–11.2 years); late echographic follow-up was complete for 97% of patients. Homograft failure was defined as the need for explantation and valve-related death; homograft dysfunction was defined as a pulmonary insufficiency grade 3/4 or greater and a transvalvular gradient of 40 mm Hg or greater. Results: Homograft failure occurred in 9% (30 of 331 patients; Kaplan-Meier); freedom from failure was 82% ± 4% at 8 years. Homograft dysfunction occurred in 12% (39 of 331 patients), although freedom from dysfunction was 76% ± 4% at 8 years. For aortic homografts, this was 56% ± 11%, compared to 80% ± 4% for pulmonary homografts ( P = .003). For patients aged less than 3 years (n = 38), this was 51% ± 12%, compared with 87% ± 4% for older patients ( P = .0001). By multivariable analysis, younger age of homograft donors, non-Ross operation, and later year of operation were associated with homograft failure; younger age of homograft donors, later year of operation, and use of an aortic homograft were associated with homograft dysfunction. Conclusions: Homograft valves function satisfactorily in the pulmonary position at mid-term follow-up. The pulmonary homograft valve appears to be more durable than the aortic homograft valve in the pulmonary position. (J Thorac Cardiovasc Surg 1999;117:141-7)

Tissue chimerism in human cryopreserved homograft valve explants demonstrated by in situ hybridization

Background. The presence of viable cells may contribute to increased homograft valve durability. These cells may be of infiltrating recipient or persisting donor origin. In this study, in situ hybridization was used to assess the origin of cells in cryopreserved homograft valve explants. Methods. A total of 10 homografts with a donor–recipient gender mismatch were acquired from patients whose graft had been explanted at reoperation or at autopsy. The period of implantation varied from 14 days to 70 months. Frozen sections were made and alternately examined with hematoxylin and eosin staining and in situ hybridization. Male cells were distinguished from female using a biotinylated Y–chromosome-specific deoxyribonucleic acid probe. Results. No endothelial cells were found. Thirty percent of the leaflets showed large acellular zones and 30% were completely acellular. The homograft arterial wall was occupied by a vast majority of penetrating host fibroblasts in 80% of the studied specimens. Donor and recipient cells were coexistent in the wall in 60% of the studied specimens and in 50% of the leaflets. In 30% only host cells could be identified. Conclusions. This finding of tissue chimerism may lead to new insights in homograft pathology. The technique of in situ hybridization may provide an indispensable contribution in further homograft research.