Fourteen-year experience with homovital homografts for aortic valve replacement

Tissue engineering therapy for cardiovascular disease

The present treatments for the loss or failure of cardiovascular function include organ transplantation, surgical reconstruction, mechanical or synthetic devices, or the administration of metabolic products. Although routinely used, these treatments are not without constraints and complications. The emerging and interdisciplinary field of tissue engineering has evolved to provide solutions to tissue creation and repair. Tissue engineering applies the principles of engineering, material science, and biology toward the development of biological substitutes that restore, maintain, or improve tissue function. Progress has been made in engineering the various components of the cardiovascular system, including blood vessels, heart valves, and cardiac muscle. Many pivotal studies have been performed in recent years that may support the move toward the widespread application of tissue-engineered therapy for cardiovascular diseases. The studies discussed include endothelial cell seeding of vascular grafts, tissue-engineered vascular conduits, generation of heart valve leaflets, cardiomyoplasty, genetic manipulation, and in vitro conditions for optimizing tissue-engineered cardiovascular constructs.

Immune and non-immune factors in cryopreserved tissues

BACKGROUND

Although cryopreserved tissues are used clinically, the effects of cryopreservation on antigenicity leading to immune and non-immune responses are not well known.

METHODS

We investigated the change of inflammatory effects of cryopreserved tissue by using spleen and aortic allografts from Class I antigen-disparate B6.C-H-2(bm1) (bm1; K(bm1), IA(b), D(b)), Class II antigen-disparate B6.C-H-2(bm12) (bm12; K(b), IA(bm12), D(b)) and Class I and Class II antigen-disparate (bm1 x bm12)F1 (K(bm1 x b), IA(b x bm12), D(b)) mice against C57BL/6 Cr Slc (B6; H-2(b)) mice. Cryopreservation was done in a programmed freezer and cryopreserved tissues were kept in the vapor phase of liquid nitrogen for 2 weeks and thawed at room temperature.

RESULTS

Cryopreserved B6 spleen cells expressed almost the same levels of Class I (K(b) and D(b)) and Class II (IA(b)) antigens as observed in fresh B6 spleen cells. Cryopreserved bm1 and bm12 spleen cells had the same stimulator activities in mixed-lymphocyte reaction (MLR) and cytotoxic T-lymphocyte (CTL) assays compared with fresh bm1 and bm12 spleen cells, respectively. To elucidate the effects of cryopreserved tissues on immune response of recipients, descending aortas of (bm1 x bm12)F1 mice were implanted into the right common carotid artery of B6 (H-2(b)) mice with the cuff technique and the reactivities of recipient B6 mice against Class I antigen-disparate bm1 antigens and Class II antigen-disparate bm12 antigens were examined 4 weeks after implantation. In both MLR and CTL assays against bm1 or bm12 antigens, anti-donor reactivities were augmented and there was no significant difference between B6 mice grafted with fresh aortic allografts and those grafted with cryopreserved ones. Histologic analysis showed that mild infiltration of mononuclear cells into the adventitia was observed in both fresh and cryopreserved aortic allografts. The fibrous change was observed more strongly in cryopreserved aortic allografts compared with fresh aortic allografts.

CONCLUSIONS

Cryopreservation has no effect on eliciting immune responses to Class I or Class II alloantigens, but has some effect on promoting fibrous change.

Quantification of haemodynamic performance of stented and stentless aortic bioprostheses and potential influence on survival

BACKGROUND

The goal of aortic valve replacement is relief of symptoms, optimisation of haemodynamics, regression of left ventricular mass and advancement of survival. The objective of this review article is to provide the evidence-to-date on the clinical performance of stented and stentless heterograft bioprostheses with regard to haemodynamics, durability and survival.

METHODS

The haemodynamic advantage of aortic valve replacement prostheses is judged on ability to minimise postoperative gradients and to optimise the normalisation of left ventricular mass and function. The most frequent cause of high postoperative gradients occurs when the effective prosthetic valve area is less than that of the normal human valve. The effective orifice area index (EOAI) of >/= 0.85 cm(2)/m(2) is considered optimal to prevent patient-prosthesis mismatch (PPM) at rest and exercise.

RESULTS

The stented bioprostheses contribute to obstructive non-physiological flow patterns whereas stentless bioprostheses provide laminar non-obstructive flow. The stentless bioprostheses have been shown to have larger effective orifice areas and lower gradients. Mismatch is decreased with stentless bioprostheses especially when prosthesis size is </=21 mm. Left ventricular mass (LVM) postoperatively has been shown to relate to baseline LVM index (LVMI) and PPM. The EOAI >0.8 cm(2)/m(2) provides the best long-term regression of LVM. It has been identified that a tendency for PPM in sizes 21 and 23 mm stented bioprostheses did not prevent adequate achievement of appropriate LVMI. Survival at 5 years favoured stentless over stented bioprostheses for patients <70 years, but not in patients >/= _70 years of age. The durability comparison of the stentless bioprostheses must wait until 10-15 years experience is achieved. There is preliminary evidence that uneven shear stress on the leaflet of a regurgitant stentless bioprosthesis can accelerate leaflet tears at the level of the commissures. Dilation of the aortic root and, particularly, the sinotubular junction, can cause progressive stentless valve insufficiency.

CONCLUSIONS

The long-term performance advantages or disadvantages of stentless bioprostheses compared to stented bioprostheses will require at least another 5-7 years of cumulative stentless bioprostheses experience. Surgeons can use an algorithm intraoperatively to prevent patient-prosthesis mismatch while choosing the optimal prosthesis.

Aortic valve disease with severe ventricular dysfunction: stentless valve for better recovery

BACKGROUND

Stentless bioprostheses and homografts show better hemodynamic profiles compared with conventional stented bioprostheses and mechanical valves. Few data are available on stentless aortic valve implantation for patients with severe left ventricular dysfunction. The aim of this retrospective study was to assess the potential benefits of stentless aortic valve implantation for patients undergoing isolated aortic valve replacement with left ventricular ejection fraction < or = 35%.

METHODS

From November 1988 through March 2000, 53 patients (45 men and 8 women, aged 64.2 +/- 15.2 years) with a LVEF < or = 35% (mean EF, 28.7 +/- 5.4%) underwent isolated, primary aortic valve replacement for chronic aortic valve disease. Twenty patients received stentless aortic valves and 33 patients received conventional stented bioprostheses and mechanical valves. Predictive factors for LVEF recovery at echocardiographic follow-up (36.2 +/- 32.1 months) were analyzed by simple and multiple regression analysis.

RESULTS

There were no significant differences between groups in early and late mortality. Stentless aortic valve implantation required a longer aortic cross-clamp time (p = 0.037). The stentless aortic valve group showed a better LVEF recovery (p = 0.016). Stentless aortic valves had a larger indexed effective orifice area compared with conventional stented bioprostheses and mechanical valves (p < 0.0001). A smaller indexed effective orifice area (p = 0.0008), chronic obstructive pulmonary disease (p = 0.015), and implantation of a conventional stented bioprosthesis or mechanical valve (p = 0.016) were related to reduced LVEF recovery by univariate analysis. A larger indexed effective orifice area (p = 0.024) was an independent predictive factor for a better LVEF recovery by multivariate analysis.

CONCLUSIONS

Stentless aortic valve implantation for patients with severe left ventricular dysfunction, even if technically more demanding, is a safe procedure that warrants a larger indexed effective orifice area leading to an enhanced LVEF recovery.

Tissue engineering of heart valves: formation of a three-dimensional tissue using porcine heart valve cells

Tissue engineering is a promising approach to obtaining lifetime durability of heart valves. The goal of this study was to develop a heart valve-like tissue and to compare the ultrastructure with normal valves. Myofibroblasts and endothelial cells were seeded on a type I collagen scaffold. The histologic organization and extracellular matrix were compared in light and electron micrographs. Radiolabeled proteoglycans were characterized by enzymatic degradation experiments. In tissue engineered specimens, cross sectional evaluation revealed that the scaffold (300 microm) was consistently infiltrated with myofibroblasts. Both sides were covered with a multicellular layer of myofibroblasts and overlaid by endothelial cells (50 microm). A newly formed extracellular matrix containing collagen fibrils and proteoglycans was found in the interstitial space. Collagen fibrils with a 60 nm banding pattern were found in both specimens. Small sized proteoglycans (65 nm) were associated and aligned at intervals of 60 nm with collagen fibrils. Large sized proteoglycans (180 nm) were located outside the collagen bundles in amorphous compartments of the extracellular matrix. The majority of glycosaminoglycans were chondroitin/dermatan sulfate, and a minority were heparan sulfate. The morphology and topography of cells and the organization of extracellular matrix in artificial tissues strongly resembles those of native valve tissues.

Construction of Autologous Human Heart Valves Based on an Acellular Allograft Matrix

Objective Tissue engineered heart valves based on polymeric or xenogeneic matrices have several disadvantages, such as instability of biodegradable polymeric scaffolds, unknown transfer of animal related infectious diseases, and xenogeneic rejection patterns. To overcome these limitations we developed tissue engineered heart valves based on human matrices reseeded with autologous cells.

Methods and Results Aortic (n=5) and pulmonary (n=6) human allografts were harvested from cadavers (6.2±3.1 hours after death) under sterile conditions. Homografts stored in Earle’s Medium 199 enriched with 100 IU/mL Penicillin-Streptomycin for 2 to 28 days (mean 7.3±10.2 days) showed partially preserved cellular viability (MTT assay) and morphological integrity of the extracellular matrix (H-E staining). For decellularization, valves were treated with Trypsin/EDTA resulting in cell-free scaffolds (DNA-assay) with preserved extracellular matrix (confocal microscopy). Primary human venous endothelial cells (HEC) were cultivated and labeled with carboxy-fluorescein diacetate-succinimidyl ester in vitro. After recellularization under fluid conditions, EC were detected on the luminal surfaces of the matrix. They appeared as a monolayer of positively labeled cells for PECAM-1, VE-cadherin and Flk-1. Reseeded EC on the acellular allograft scaffold exhibited high metabolic activity (MTT assay).

Conclusions Earle’s Medium 199 enriched with low concentration of antibiotics represents an excellent medium for long time preservation of extracellular matrix. After complete acellularization with Trypsin/EDTA, recellularization under shear stress conditions of the allogeneic scaffold results in the formation of a viable confluent HEC monolayer. These results represent a promising step toward the construction of autologous heart valves based on acellular human allograft matrix.

Aortic cusp extension valvuloplasty for rheumatic aortic valve disease: midterm results

BACKGROUND

The surgical management of rheumatic aortic insufficiency in the young remains problematic owing to the drawbacks of prosthetic valve replacement at this age. In young foreign patients, for whom long-term anticoagulation therapy is unavailable, we have used a glutaraldehyde preserved autologous pericardium cusp extension technique to repair rheumatic aortic valve insufficiencies resulting from cusp retractions.

METHODS

From September 1992 to December 2000, 89 consecutive patients with a mean age of 16 +/- 5 years underwent triple pericardial aortic cusp extension valvuloplasty. Eighty patients had pure aortic insufficiency, 9 had mixed aortic disease. Twenty-nine patients (33%) had isolated aortic valve disease and 60 patients (69%) had combined aortic and mitral valve disease with significant tricuspid valve disease in 21 (24%). Aortic repair consisted of free edge aortic cusp extension using three rectangular strips of glutaraldehyde stabilized autologous pericardium. Twenty-nine patients (33%) underwent an isolated aortic repair, 39 patients (44%) underwent combined aortic and mitral procedures (34 mitral repairs, 3 mitral homografts, and 2 prosthesis replacements), and 21 patients (23%) underwent a triple valve repair.

RESULTS

The hospital mortality was 2.2%. Primary failure of the aortic repair requiring immediate reoperation occurred in 2 patients. During follow-up (mean of 62 +/- 22 months) 1 patient died and 7 underwent redo valvular surgery. At 5 years the actuarial survival rate was 96.4%, and 92.1% of the patients were free from redo valvular surgery. At 7 years 90% of the patients were free from valve-related complications. Among the 76 patients free from redo valvular surgery at follow-up, 6 had deterioration of the repair resulting in grade II aortic and mitral insufficiencies.

CONCLUSIONS

Our midterm results of glutaraldehyde stabilized autologous pericardial aortic cusp extension are encouraging and suggest that this technique should be considered as a viable alternative palliative procedure in a young rheumatic population, allowing for growth of the annulus and delaying to a less critical period the need for the lifelong anticoagulation therapy required for a prosthetic mechanical valve.

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

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Primary aortic valve replacement with cryopreserved aortic allograft: an echocardiographic follow-up study of 570 patients

BACKGROUND

Despite the many advantages of an aortic allograft valve (AAV) over a prosthetic aortic valve, its durability is suboptimal. The aims of the present study were to document characteristic features of AAV dysfunction and to investigate factors influencing the development of such dysfunction.

METHODS AND RESULTS

A group of 570 patients (mean age, 48+/-16 years) with a cryopreserved AAV underwent a follow-up echocardiographic study (mean time after surgery, 6.8 years; range, 1.0 to 22.9 years). Significant AAV regurgitation was present in 14.7% of patients, and AAV stenosis was present in 3.2%. The root replacement subgroup had the smallest number of patients with significant AAV regurgitation (5.0%) compared with the subcoronary (23.0%) or the inclusion cylinder technique subgroup (14.7%). After 10 to 15 years after AAV replacement, grade > or =2 AAV dysfunction was present in 40% of patients in the subcoronary subgroup, but no significant dysfunction was observed in patients in the root replacement subgroup (P<0.001). Smaller host aortic annulus size in both subcoronary (coefficient, -0.145; P=0.013) and root replacement subgroups (coefficient, -0.249; P=0.011) was associated with more frequent AAV dysfunction (grade > or =2). In addition, significant AAV dysfunction was more frequent when patients were younger (coefficient, -0.020; P=0.015) in the subcoronary subgroup and the donor was older (coefficient, 0.054; P=0.019) in the root replacement subgroup.

CONCLUSIONS

The present study indicates that the root replacement technique is associated with less frequent AAV degeneration. Our findings should help in establishing more strict selection criteria for surgical replacement procedure type and patient/donor factors for AAV replacement and, therefore, could lead to improve AAV longevity.

Aortic allografts for left ventricular outflow tract replacement in children

Aortic allografts provide many advantages in children requiring left ventricular outflow tract (LVOT) reconstruction. The low risk of thromboembolic events and freedom from the requirement for anticoagulation are primary benefits. Additionally, excellent hemodynamic results are possible even in the presence of multilevel obstruction. The pulmonary autograft has become the favored approach in most pediatric centers, as the limited longevity of the aortic allograft has now become apparent. However, some children are not candidates for the pulmonary autograft. Thus, the aortic allograft remains a useful aortic valve substitute in children. Using standard aortic root replacement (ARR) or extended aortic root replacement (EARR) techniques, aortic allografts can be used in any circumstance. Young age and small size are predictive of shortened valve longevity and higher operative mortality compared with older children. Reoperation to replace a degenerated aortic allograft can be accomplished safely. Copyright 2000 by W.B. Saunders Company

Stentless bioprostheses in aortic root disease

INTRODUCTION

The availability of aortic homografts is steadily decreasing. In the meantime, stentless xenografts convey similar flow characteristics, and tissue preservation methods are improving durability. Initially, these valves were contraindicated in aortic roots with discrepancy between annulus and sinotubular junction or with extensive calcification or sepsis. With increasing experience stentless xenografts are now applied in a wide spectrum of aortic root disease.

METHODS

I reviewed our own experience with stentless aortic bioprosthesis for aortic valve replacement (AVR) and more taxing root problems. I used these valves in aortic aneurysm repair, acute Type A dissection, and for endocarditis with abcess formation. I studied valve hemodynamics, regression of left ventricular hypertrophy, and comparative survival with stented bioprostheses.

RESULTS

Stentless bioprostheses convey hemodynamic and possibly survival benefit through a low incidence of valve-related complications. They provide a useful alternative to aortic homografts in endocarditis, Type A dissection, and aortic aneurysm surgery.

CONCLUSIONS

Stentless bioprostheses are no longer confined to AVR alone. Experience supports the use of stentless bioprostheses where aortic homografts were previously applied. With availability in a wide range of sizes.

Clinical use of stentless aortic valves with standard and minimally invasive surgical techniques

The stentless porcine aortic valve prostheses have the potential to provide superior hemodynamic function and durability. Our institution was a trial site for the investigational device exemption (IDE) for 2 of the 3 stentless valve bioprostheses and has clinical experience in all 3 valves that are soon to be available. From July 1996 to January 2001, we have implanted 213 porcine stentless valves: the Toronto SPV (159), the Freestyle (20), and the Prima Plus (34) (current IDE). Fifty-five percent of these patients had concomitant coronary artery bypass graft procedures, 44% had isolated aortic valve replacements, and 3 patients required aortic valve and mitral valve procedures. Fifty-nine percent of the patients were men, 9% of procedures were reoperations, and 22% of patients were in New York Heart Association classification III or IV preoperatively. Extubation occurred within 5 hours for 52% of patients, median cardiothoracic intensive care unit length of stay was 1 day, and postoperative length of stay was 6 days. Reoperations for bleeding occurred in 5.3% of patients (0 in the past 12 months), atrial fibrillation in 28.2%, and permanent neurologic deficit in 1.9%. No patients required valve-related reoperations or had either sepsis or sternal infections. Operative mortality was 1.4%. We have also analyzed a subset of patients who had minimally invasive aortic valve replacement versus the standard approach and found no important differences in mortality (none), postoperative complications, cardiopulmonary bypass, or cross-clamp times. There was a trend towards earlier ambulation, less atrial fibrillation (15.8% v 24.1%), and earlier hospital discharge (5.6 days v 7.2 days). We conclude that excellent results were obtained with all 3 stentless aortic valve bioprostheses. Hospital events should be predictably low in elderly patients and those requiring concomitant procedures. Stentless aortic valve bioprostheses can be incorporated into regular cardiac surgical practice with the techniques described.

Electron beam tomography for cusp calcification in homograft versus Freestyle xenografts

BACKGROUND

We have previously shown, by means of electron beam tomography, the pattern of calcification of the aortic root wall of homografts and porcine xenografts after aortic root replacement. However, application of similar methods for cusp calcification raises specific problems that have not been addressed before.

METHODS

A new method for localizing and quantifying calcification of the aortic valve cusps has been evolved. Intravenous contrast-enhanced electron beam tomography was introduced to visualize the aortic cusps. This technique was applied to quantify cusp calcification in 37 patients after aortic root replacement with a homograft (group H) or a Medtronic Freestyle valve (group F) at set intervals between 6 months and 2 years. A calcification score in Hounsfield units (HU) and a calcified volume score in cubic millimeters were calculated.

RESULTS

The aortic leaflets were clearly visualized in all patients. The mean calcium score in the cusps was 28.8+/-64.4 HU in group F and 62.4+/-66.9 HU in group H (p = not significant). The mean calcified volume score was 327.0+/-425.9 mm3 in group F and 642.0+/-443.0 mm3 in group H (p = not significant).

CONCLUSIONS

Contrast enhancement electron beam tomography is a useful tool for quantification of calcium in the aortic valve leaflets. Our preliminary results show a tendency toward more calcification in the homografts. This needs to be studied further in a bigger cohort of patients followed up for longer periods.

Human tissue valves in aortic position: determinants of reoperation and valve regurgitation

BACKGROUND

Human tissue valves for aortic valve replacement have a limited durability that is influenced by interrelated determinants. Hierarchical linear modeling was used to analyze the relation between these determinants of durability and valve regurgitation measured by serial echocardiography.

METHODS AND RESULTS

In adult patients, 218 cryopreserved aortic allografts were implanted with the subcoronary (85) or the root replacement technique (133), and 81 patients had root replacement with a pulmonary autograft. Mean follow-up was 4.2 years (SD 2.7; range, 0 to 10.5). Patient age, operator experience with subcoronary implantation, and allograft diameter were independent predictors for reoperation. With repeated color Doppler echocardiography, the severity of aortic regurgitation was assessed by the jet length method and the jet diameter ratio. Multilevel hierarchical linear modeling was used to estimate initial aortic regurgitation (intercept), its change over time (slope), and the effect of 11 potential determinants of durability on aortic regurgitation. With the jet length method, the intercept was 0.94 grade and the slope was 0.11 grade per year. With the jet diameter ratio, the intercept was 0.34 and the annual increase was 0.01. Subcoronary implanted valves had more initial aortic regurgitation, but progression of aortic valve regurgitation did not differ from root replacement. At midterm follow-up, recipient age <40 years was the only independent predictor of aortic regurgitation.

CONCLUSIONS

Subcoronary implantation has a learning curve, resulting in more initial aortic regurgitation and early reoperation compared with root replacement. In both techniques, progression of aortic regurgitation over time is small but accelerated in young adults.

Risk factors for late pulmonary homograft stenosis after the Ross procedure

BACKGROUND

We reviewed our experience with the Ross procedure to identify the prevalence and predictors of late pulmonary homograft stenosis.

METHODS

Between June 1992 and December 1997, 109 consecutive patients (age 34.5 +/- 8.6 years) underwent the Ross procedure, with reconstruction of the right ventricular outflow tract with a cryopreserved pulmonary homograft (22 to 30 mm diameter). There was one early and one late death. Echocardiographic follow-up was available in 105 of 108 patients (97%), with a follow-up of 39 +/- 20 months. Homograft donor and preservation measurements and patient variables were subjected to multivariable analyses to identify independent predictors of late homograft performance.

RESULTS

The major physiopathologic finding was homograft stenosis. Peak systolic gradients across the homograft were 20 mm Hg or more in 30 of 105 patients (28.5%) and 40 mm Hg or more in 4 of 105 patients (3.8%). One patient required two re-replacements of her homograft for severe stenosis. Moderate or severe homograft insufficiency was noted in 10 of 105 patients (9.5%). The independent predictors of late pulmonary homograft stenosis were younger donor age (p = 0.03), shorter duration of cryopreservation (p = 0.01), and smaller homograft size (p = 0.06). Beating heart donor status, short homograft ischemic time, and other factors that have been shown to be associated with increased graft viability were associated with graft stenosis but did not reach statistical significance. However, mean gradients across the homograft were significantly related (p = 0.002) to the number of these risk factors in each patient.

CONCLUSIONS

Stenosis of the pulmonary homograft can be a significant problem following the Ross procedure, and was predicted by younger donor age and shorter duration of cryopreservation. These factors may be related to increased cellular viability, which might actually predispose to late homograft stenosis in a subgroup of patients.

Cell composition of the human pulmonary valve: a comparative study with the aortic valve--the VESALIO Project. Vitalitate Exornatum Succedaneum Aorticum labore Ingegnoso Obtinebitur

BACKGROUND

Cell populations present in human semilunar valves have not been investigated thoroughly. The aim of this study was to characterize the cell phenotypes in pulmonary valve leaflets (PVL) in comparison with aortic (AVL) valve leaflets.

METHODS

AVL and PVL were dissected from hearts (n = 4) harvested from transplanted patients. Leaflets were processed for immunocytochemistry analysis and Western blotting procedures using a panel of monoclonal antibodies specific for cytoskeletal/contractile antigens.

RESULTS

The fibrosa and the ventricularis layers of AVL had a higher cellularity than PVL. In PVL and AVL most cells were reactive for vimentin and nonmuscle (NM) myosin, though vimentin-positive cells were more abundant in AVL than in PVL. Sparse cells positive to anti-smooth muscle (SM) alpha-actin, calponin, and anti-SM myosin antibodies were found only at the outer edge of fibrosa. In Western blotting, AVL and PVL extracts were shown to be equally reactive for vimentin, SM alpha-actin, and NM myosin, whereas both valves were negative for SM myosin and SM22.

CONCLUSIONS

Three distinct cell phenotypes have been identified in both valves: fibroblasts, myofibroblasts, and fetal-type SM cells whose distribution is specifically related to the valve layers. Although PVL and AVL cell populations differ quantitatively, some minor qualitative differences exist for vimentin and NM myosin distribution. These data are essential for studies aimed at repopulating valve scaffolds by using tissue engineering technology.

Survival advantage of stentless aortic bioprostheses

BACKGROUND

Bioprostheses (BPs) are used to avoid anticoagulation after aortic valve replacement (AVR) in patients over 65 years of age. Stentless BPs offer established hemodynamic benefits. We sought to determine whether these advantages translate into improved survival.

METHODS

Between 1993 and 1997, follow-up data (for Food and Drug Administration submission) were collected prospectively for 160 consecutive, unselected hospital survivors who received the Freestyle valve (FS). Equivalent data were collected for 247 Carpentier-Edwards (CE) porcine xenograft patients. Detailed comparative statistical analysis was used to compare events and survival between the groups. Follow-up was 100% complete for the FS (5.2 years maximum; mean 3.2+/-1.0 years) group and 98% (7.2 years maximum; mean 3.8+/-2.0 years) for CE.

RESULTS

The groups were well matched in age (FS, 73+/-6 years; CE, 74+/-6 years), gender (FS, 58% male; CE, 62% male), ventricular function, and number of patients requiring coronary grafts (FS, 41%; CE, 37%). Actuarial survival at 5 years was 84% for FS versus 69% for CE (p = 0.023 Kaplan Meier, p = 0.009 Cox). Annual mortality rates were 3.6% for FS versus 7.1% for CE (p = 0.001). Thromboembolic rate was 0.8% per year for FS and 2.4% for CE (p = 0.024) without a difference in cardiac rhythm. Incidence of nonstructural dysfunction (paravalvular leak) was 0.2% for FS versus 1.3% for CE (p = 0.020).

CONCLUSIONS

By 5 years, the stentless valve patients had improved survival and reduced adverse events. Though differences in durability are yet to be proved, our findings support the use of stentless bioprostheses in this age group.

Predictors of outcome in severe, asymptomatic aortic stenosis

BACKGROUND

Whether to perform valve replacement in patients with asymptomatic but severe aortic stenosis is controversial. Therefore, we studied the natural history of this condition to identify predictors of outcome.

METHODS

During 1994, we identified 128 consecutive patients with asymptomatic, severe aortic stenosis (59 women and 69 men; mean [+/-SD] age, 60+/-18 years; aortic-jet velocity, 5.0+/-0.6 m per second). The patients were prospectively followed until 1998.

RESULTS

Follow-up information was available for 126 patients (98 percent) for a mean of 22+/-18 months. Event-free survival, with the end point defined as death (8 patients) or valve replacement necessitated by the development of symptoms (59 patients), was 67+/-5 percent at one year, 56+/-5 percent at two years, and 33+/-5 percent at four years. Five of the six deaths from cardiac disease were preceded by symptoms. According to multivariate analysis, only the extent of aortic-valve calcification was an independent predictor of outcome, whereas age, sex, and the presence or absence of coronary artery disease, hypertension, diabetes, and hypercholesterolemia were not. Event-free survival for patients with no or mild valvular calcification was 92+/-5 percent at one year, 84+/-8 percent at two years, and 75+/-9 percent at four years, as compared with 60+/-6 percent, 47+/-6 percent, and 20+/-5 percent, respectively, for those with moderate or severe calcification. The rate of progression of stenosis, as reflected by the aortic-jet velocity, was significantly higher in patients who had cardiac events (0.45+/-0.38 m per second per year) than those who did not have cardiac events (0.14+/-0.18 m per second per year, P<0.001), and the rate of progression of stenosis provided useful prognostic information. Of the patients with moderately or severely calcified aortic valves whose aortic-jet velocity increased by 0.3 m per second or more within one year, 79 percent underwent surgery or died within two years of the observed increase.

CONCLUSIONS

In asymptomatic patients with aortic stenosis, it appears to be relatively safe to delay surgery until symptoms develop. However, outcomes vary widely. The presence of moderate or severe valvular calcification, together with a rapid increase in aortic-jet velocity, identifies patients with a very poor prognosis. These patients should be considered for early valve replacement rather than have surgery delayed until symptoms develop.

Retrospective clinical analysis of stented vs. stentless porcine aortic bioprostheses

OBJECTIVE

The study was designed to compare hemodynamic performance, structural failure and survival of patients undergoing aortic valve replacement (AVR) with a composite aortic stented or stentless porcine bioprosthesis.

METHODS

From January 1990 to June 1999, the clinical data of 725 patients undergoing AVR with stented porcine aortic bioprosthesis were reviewed. We defined two groups of patients with similar clinical characteristics: 202 patients receiving aortic stented and 205 patients stentless valves. The two patients groups were similar in age, sex, valve lesion, valve size, preoperative New York Heart Association (NYHA) class status and follow-up.

RESULTS

The number of patients available for follow-up, excluding hospital and late mortality, reoperations and patients lost to follow-up, was 157 for the stented and 175 for the stentless group. There was a higher incidence of rheumatic heart disease in the stented (59%) vs. stentless group (44%), (P=0.003). Fewer patients had prior aortic bioprosthetic dysfunction in the stented (7.6%) compared to the stentless group (25%) (P<0.001). The mean intensive care unit stay, hospital mortality and late mortality were similar (P, NS). The total complication rate was higher in the stented (12%) than the stentless (3.4%)(P=0.005). Valve related death was higher in the stented (2.5%) than the stentless (0%) (P=0. 049). Postoperatively, the aortic effective orifice area (AEOA) was larger (P<0.001) and the transvalvular peak and mean gradients were lower in the stentless group (P<0.001). The leaflet tissue degeneration analysis was 8.0% in patients at risk for stented and 0. 6% for stentless (P=0.001). Actuarial analysis disclosed no statistical difference in patient survival between groups (P=0.18). Reoperations were less frequent in the stentless group (P=0.010).

CONCLUSIONS

Hemodynamic benefits in the stentless group were evident and expressed by larger AEOA, lower gradients, better left ventricular remodeling with significant decrease of the left ventricular mass. Lower complication rates, lower reoperation rates, less leaflet tissue degeneration, and lower valve related mortality rates were seen in the stentless group. A controlled clinical comparison trial with longer follow-up will be required to confirm these clinical and hemodynamic benefits.

Aortic Stenosis

Choice of the best surgical option for aortic stenosis (AS) must be individualized and requires discussion among patient, cardiologist, and surgeon to weigh the risks and benefits of different options. Mechanical valves have been preferred for young patients, for those with a life expectancy of more than 10 to 15 years, or for those who require anticoagulation. Bioprosthetic valves have been preferred for elderly patients, for patients with limited life expectancy, or for patients who are unable to be anticoagulated. Newer tissue valves (eg, the stentless porcine aortic bioprosthesis and homografts) as well as newer techniques (eg, the Ross procedure) have increased the number of available options and the complexity of the decision-making process.

Pre-transplantation testing: who, when and why?

An ever-widening range of human organs and tissues is being transplanted, limited currently only by the ingenuity of surgeons and immunologists to overcome the physical and immune barriers. Microbiologists are in danger of being left behind. Although the major infective risks of human organ transplantation are now well understood, many details remain controversial, and the special risks associated with tissue banking have received little attention until recently. What should we do? Are we making mountains out of molehills? Are there any data on which to base a rational decision? Topics covered include: bacteriology of cadaveric heart valve transplantation (why are valves not cultured and only dunked in antibiotic solution for 24h, whereas endocarditis gets treated for 4 weeks?); screening for tissue-born viruses (why does everyone persist with serology when genomic methods are so much better?); screening organ donors for CMV (surely we should use the optimally sensitive combination of methods?); peripheral blood stem cell transplants (should we culture these, and what do the positive results mean if we do?); donor sputum screening before heart-lung transplantation (does this aid the post-operative management of the recipient?). With active participation from the floor some areas of consensus were identified and topics worthy of scientific investigation in the future were highlighted.

Accelerated allograft degeneration after aortic valve endocarditis

Early calcification of aortic allografts is usually seen in children less than 3 years of age. We describe a case of a 22-year-old intravenous drug user who developed calcific aortic valve stenosis less than 3 years after an allograft root replacement for endocarditis.

Immune response following fresh arterial homograft replacement for aortoiliac graft infection

INTRODUCTION

this prospective study defines the immune response to fresh arterial homograft replacement for graft infection.

MATERIALS AND METHODS

ten patients who underwent ABO-compatible homograft transplantation were studied for anti-HLA antibody production, and CD3-CD4-CD8-positive lymphocytes subset. Immunological studies were performed preoperatively, and at early (1, 3, 7 days) and late (1, 3, 6, 12, 18, 24 months) follow-up. All patients received immunosuppressive treatment with cyclosporine (1-3 mg/kg/day). Abdominal CT scans were performed postoperatively at the 1, 6, 12, 18, 24 months follow-up.

RESULTS

preoperatively, antibodies could not be detected. Postoperatively, as from 1st month post-transplant, a progressive increase in % PRA was observed in all patients, up to the 12th month of follow-up. Subsequently, at 18 and 36 months, a progressive decrease in % PRA was detected. Data showed that the recipient antibodies were directed against donor-specific antigens. During the immediate postoperative period (1, 3, 7 days) CD3- and CD4-positive T lymphocytes slightly increased, whereas CD8 simultaneously decreased. Later, CD3 and CD4 progressively decreased and CD8 increased. Clinically, all patients were cured of infection at late follow-up. CT scans showed thickening of the aortic wall (range: 2.5-4.5 mm), with no signs of aneurysmal degeneration.

CONCLUSIONS

fresh arterial homografts are immunogenic. Implanted homografts induce a strong anti-HLA antibody response, similar to chronic rejection, in spite of immunosuppressive treatment.

Aortic valve replacement: is the stentless xenograft an alternative to the homograft? Midterm results

BACKGROUND

This study was performed to assess the midterm clinical results after aortic valve replacement (AVR) with stentless xenograft (SX) compared with cryopreserved aortic or pulmonary homografts (HX).

METHODS

In 139 patients (<60 years) undergoing elective AVR, 59 HX and 80 SX were inserted. All patients were followed clinically and by color flow Doppler echocardiography for 45+/-12 months (range 31-58 months).

RESULTS

There were 5 in-hospital deaths (3.5%): 4 HX and 1 SX (p = NS). The mean gradient was 6+/-2 mm Hg in HX versus 13+/-6 mm Hg in SX (p<0.001) and remained unchanged during follow-up. Actuarial survival (HX 77%, SX 80%), freedom from endocarditis (HX 91%, SX 99%), freedom from thromboembolic events (HX 98%, SX 90%), and freedom from reoperation (HX 98%, SX 100%) were comparable between groups after 58 months.

CONCLUSIONS

Despite slightly higher transvalvular gradients, the stentless aortic valve achieved excellent midterm results, when compared with homografts.

Cryopreserved aortic allografts for aortic root reconstruction: a single institution's experience

BACKGROUND

An evaluation of early and long-term results of aortic root replacement with cryopreserved aortic allografts and echocardiographic follow-up of allograft valve function was performed.

METHODS

From September 1989 through May 1998, 132 patients aged 17 to 77 years (mean, 50.8 +/- 14.8 years) underwent freestanding aortic root replacement with a cryopreserved aortic allograft. Eighty-six (65.1%) patients had New York Heart Association class III or IV functional status before operation, and 27 (20.5%) patients underwent emergency operation. Fifty-nine (44.7%) patients had undergone previous cardiac operations. The cause of aortic disease was acute endocarditis in 63 (47.7%) patients, healed endocarditis in 15 (11.3%), degenerative in 20 (15.2%), congenital in 20 (15.2%), failed prosthesis in 10 (7.6%) and rheumatic in 4 (3.0%). Follow-up was complete, with a mean of 42 months.

RESULTS

There were 12 hospital deaths (9.1%; 70% confidence limits [CL], 6.6% and 11.6%); 9 of them were operated on for active endocarditis (p = 0.062). Multivariate analysis determined age older than 65 years (p = 0.012) and emergency operation (p = 0.009) as independent risk factors for hospital mortality. During follow-up, 6 (5.0%; 70% CL, 3.0% and 7.0%) patients died. Cumulative survival rate for the entire group was 81.8% +/- 5.4% at 8 years. Freedom from reoperation for structural valve failure was 100%, freedom from reoperation for any cause was 96.3% +/- 1.8% at 8 years. Freedom from endocarditis at 8 years was 97.9% +/- 1.4%. Follow-up of allograft valve function showed no or trivial aortic regurgitation in 97% of patients and absence of stenosis of the allograft in 100%.

CONCLUSIONS

Aortic root replacement with cryopreserved aortic allografts can be performed with acceptable hospital mortality and long-term results. The durability of cryopreserved aortic allografts is good, and reoperation for structural valve failure is absent at 8 years.

Long-term survival and valve-related complications in young women with cardiac valve replacements

BACKGROUND

The type of cardiac valve replacement associated with the lowest health risks for young women who may undergo pregnancies is unknown. We investigated which valve type was associated with greatest patient and valve survival and the effect of pregnancy on valve loss.

METHODS AND RESULTS

In this retrospective study, all women 12 to 35 years old who underwent valve replacements between 1972 and 1992 at Greenlane Hospital were identified, and follow-up was available in 93%. The 232 women were followed up for 1499 patient-years. Ten-year survival of women with mechanical (n=178), bioprosthetic (n=73), and homograft (n=72) valves was 70% (95% CI, 59% to 83%), 84% (95% CI, 72% to 99%), and 96% (95% CI, 91% to 100%), P=0.002. After adjustment for confounding variables, the relative risk (RR) of death with mechanical compared with bioprosthetic valves was 2.17 (95% CI, 0.78 to 5.88). Thromboembolic events occurred in 45% of women with mechanical valves within 5 years, compared with 13% with bioprosthetic valves, P=0.0001. Valve loss at 10 years was higher in bioprosthetic valves [82% (95% CI, 62% to 92%)] than in mechanical [29% (95% CI, 17% to 39%)] or homograft [28% (95% CI, 12% to 41%)] valves, P=0.0001. Pregnancy was not associated with increased bioprosthetic (RR, 0.96; 95% CI, 0.68 to 1. 35), homograft (RR, 0.65; 95% CI, 0.37 to 1.13), or mechanical (RR, 0.54; 95% CI, 0.27 to 1.08) valve loss.

CONCLUSIONS

Although 10-year valve survival was greater with mechanical than bioprosthetic valves, mechanical valves may be associated with reduced patient survival in young women. Thromboembolic complications, often with long-term sequelae, were common with mechanical valves. Pregnancy did not increase structural deterioration or reduce survival of bioprosthetic valves.

Stentless xenograft aortic valves

Replacement of the diseased aortic valve represents one of the triumphs of cardiac surgery; however, the perfect valve substitute continues to elude surgeons after almost four decades of clinical experience. The characteristics of the ideal valve substitute include the following: central flow capacity, low transvalvular gradient, low thrombogenicity, durability, easy availability, resistance to infection, non-immunogenicity, and easy implantability. The pulmonary autograft first performed by Ross (Lancet 1967, 2:956-958) came closest to achieving these goals, but creates a double valve procedure for single valve disease. Aortic valve replacement (AVR) with homograft aortic valve was introduced by Ross in 1962 (Lancet 1962, 2:487) and Barratt-Boyes in 1964 (Thorax 1964, 19:131-150). Like the pulmonary autograft, homograft AVR results in an excellent hemodynamic outcome but suffers from limitations of graft availability, lack of durability, and difficulty with implantation. Mechanical valves and stented tissue valves allow "off the shelf" easy availability as well as easy implantability. These valves are unfortunately intrinsically obstructed to some extent because of the space occupied by the stent and sewing ring. Stent mounted tissue valves also continue to exhibit limited durability. Stentless xenograft aortic valves have been developed as a compromise between these ends of the valve spectrum to allow excellent hemodynamics and hopefully improved durability while allowing "off the shelf" availability in a variety of standard sizes. We examine the rationale for use of the stentless xenograft aortic valve, the clinical development of this valve, and the surgical techniques of implantation.

Primary aortic valve replacement with allografts over twenty-five years: valve-related and procedure-related determinants of outcome

OBJECTIVES

Allografts offer many advantages over prosthetic valves, but allograft durability varies considerably.

METHODS

From 1969 through 1993, 618 patients aged 15 to 84 years underwent their first aortic valve replacement with an aortic allograft. Concomitant surgery included aortic root tailoring (n = 58), replacement or tailoring of the ascending aorta (n = 56), and coronary artery bypass grafting (n = 87). Allograft implantation was done by means of a "freehand" subcoronary technique (n = 551) or total root replacement (n = 67). The allografts were antibiotic sterilized (n = 479), cryopreserved (n = 12), or viable (unprocessed, harvested from brain-dead multiorgan donors or heart transplant recipients, n = 127). Maximum follow-up was 27.1 years.

RESULTS

Thirty-day mortality was 5.0%, and crude survival was 67% and 35% at 10 and 20 years. Ten- and 20-year rates of freedom from complications were as follows: endocarditis, 93% and 89%; primary tissue failure, 62% and 18%; and redo aortic valve replacement, 81% and 35%. Multivariable Cox analyses identified several valve- and procedure-related determinants: rising allograft donor age and antibiotic-sterilized allograft for mortality; donor more than 10 years older than patient for endocarditis; rising donor age minus patient age, rising implantation time (from harvest to aortic valve replacement), and donor age more than 65 years for tissue failure; and rising donor age minus patient age, young patient age, rising implantation time, and subcoronary implantation preceded by aortic root tailoring for redo aortic valve replacement. Estimated 10- and 20-year rates of freedom from tissue failure for a 70-year-old patient with a viable valve from a 30-year-old donor and no other risk factors were 91% and 64%; the figures were 71% and 20% if the donor age was 65 years. The rates of freedom from tissue failure for a 30-year-old patient with a 30-year-old donor were 82% and 39%; the figures were 49% and 3% with a 65-year-old donor. Beneficial influences of a viable valve were largely covered by short harvest time (no delay for allografts from brain dead organ donors or heart transplant recipients) and short implantation time.

CONCLUSIONS

Primary allograft aortic valve replacement can give acceptable results for up to 25 years. The late results can be improved by the use of a viable allograft, by matching patient and donor age, and by more liberal use of free root replacement with re-implantation of the coronary arteries rather than tailoring the root to accommodate a subcoronary implantation.

Effect of HLA mismatching and antibody status on "homovital" aortic valve homograft performance

BACKGROUND

Recipients of "homovital" aortic valve homografts are known to produce specific antibodies to human leukocyte antigen (HLA) determinants present on the cellular compartment of the valve tissue; however, the clinical significance of these antibodies is unknown. Data from 182 patients receiving homovital aortic valve homografts has been analyzed to determine the impact of HLA disparity and HLA antibody production on survival and function of the homograft.

METHODS

Human leukocyte antigen mismatch data were available for 127 patients (mean follow-up, 6.02+/-0.26 years). Two patients were considered well matched for HLA A+B antigens (zero or one mismatch) compared with 125 poorly matched (two to four mismatches). Nine patients had a zero HLA-DR mismatch compared with 52 with one mismatch and 59 patients completely mismatched for DR antigens.

RESULTS

There was no significant association between the degree of HLA mismatch for either class I or class II antigens whether the loci were considered alone or in combination (ie, A, B, DR, AB, or ABDR mismatching) with markers of long-term valve function including patient mortality, reoperation, valve degeneration, valve stenosis, presence of regurgitation, and postoperative New York Heart Association class. One hundred thirty-six of 167 (82%) were found to have produced antibodies after operation (mean time after operation, 6.42+/-0.58 years). In 61 cases both antibody specificity and donor HLA typing was available. In 92% of these, the antibodies were of the IgG subclass and were specific for the HLA class I molecules of the donor. The presence of HLA antibodies was associated with an increase in the frequency of mild valve stenosis (not significant) compared with those patients who did not develop HLA antibodies (antibody negative = 9.7%; panel reactive antibodies <50% = 29.1%; and panel reactive antibodies >50% = 22.2%; not significant). There was also an increased prevalence of valve degeneration associated with HLA antibodies. The actuarial freedom from valve degeneration for the 35 HLA antibody-negative patients was 100% at 1, 5, and 10 years compared with 100% at 1 year, 97% at 5 years, and 92% at 10 years for 55 patients with panel reactivity less than 50%, and 98% at 1 year, 94% at 5 years, and 88% at 10 years for the 77 patients who were highly sensitized (not significant). There was no correlation with other markers of long-term valve function.

CONCLUSIONS

The influence of the immune response on valve function requires further studies involving large numbers of patients followed for a longer period of time. We believe prospective matching for HLA antigens is warranted to produce a well-matched cohort of patients for analysis and to reduce antibody sensitization, which would help to clarify this issue.

Effect of antibiotic pretreatment on immunogenicity of human heart valves and component cells

BACKGROUND

For many years valves have been sterilized with high-dose antibiotics before implantation, but now there is an increasing trend to using "homovital" valves, which have been exposed to very low dose antibiotics.

METHODS

To investigate the immunogenicity of valve tissue, before and after exposure to high- and low-dose antibiotics, peripheral blood mononuclear cells and human allogenic T cells were cocultured with antibiotic-treated valve discs, cultured valve endothelial cells, and fibroblasts. Proliferation was measured by uptake of thymidine labeled with hydrogen 3.

RESULTS

Untreated tissue pieces stimulate peripheral blood mononuclear cells (4,080+/-980 cpm) at day 0 with similar results after 1 day in Hank's balanced salt solution (4,272.4+/-1,307 cpm) reducing to 2,442+/-926 cpm after 3 days and 1,111+/-255 cpm after 5 days; antibiotic-treated pieces are less immunogenic after 1 (2,560+/-403 cpm), 3 (1,550+/-60 cpm), 5 (717+/-295 cpm), and 7 days (633+/-174 cpm) in homovital solution, whereas sterilized pieces are not immunogenic (184+/-96 cpm) after only 1 day in strong antibiotics. Histologic analysis showed that this corresponds to a reduction of class I and class II expression by human valve endothelial cells. Human valve endothelial cells but not fibroblasts are capable of causing direct stimulation of CD4+ T cells. However, human valve endothelial cells poorly stimulate CD4+ T cells after incubation in homovital solution for 24 hours.

CONCLUSIONS

This study shows that valve tissue is immunogenic and this immunogenicity is mediated mainly by endothelial cells. However, the immunostimulatory potential of the valve can be reduced by incubating the solution in an antibiotic cocktail.

Fluorescence activated cell sorting: a reliable method in tissue engineering of a bioprosthetic heart valve

BACKGROUND

Techniques of tissue engineering are used to seed human autologous cells in vitro on degradable mesh to create new functional tissue like a bioprosthetic heart valve. A precondition is subsequent seeding of native-valve-analogous pure endothelial and myofibroblast cell lines. The aim of this study is to find a safe method of isolating viable cell lines out of tissues from the operating room.

METHODS

Mixed cells from ascending aorta obtained from the operating room were incubated with an endothelial-specific fluorescent marker. The labeled cells were activated and sorted by flow cytometry. Isolated cell lines were cultured and thereafter square sheets of polymeric scaffold were seeded with myofibroblasts, followed by endothelial cells. The created tissue was stained with hematoxylin and eosin, van Gieson stain, and stains for factor VIII and CD34.

RESULTS

Control culture samples (n = 25) revealed vital uncontaminated endothelial and myofibroblast cell lines. Microscopy of the seeded meshes (n = 16) demonstrated a tissue-like structure. Van Gieson stain showed production of collagen. Endothelial cells formed a superficial monolayer, demonstrated by factor VIII and CD34; no invasive formation of capillaries was detectable.

CONCLUSIONS

These results demonstrate that fluorescence activated cell sorting is a reliable and safe method to gain pure vital autologous cell lines out of human mixed cells for subsequent seeding on degradable mesh and that those cells are active to form new tissue.

Endothelial prostacyclin (PGI-2) production of human and porcine valve allografts related to ischemic history

BACKGROUND

The significance of cellular viability in human valve allografts for functional clinical longevity continues to be debated. Meaningful tests for this biological entity are therefore in demand to quantify the relative merits of graft origin and procurement techniques. The valve leaflet endothelium is recognized as a particularly sensitive target to noxes and its continued ability to produce prostacyclin (PGI-2) after explantation has been suggested as indicating viability.

OBJECTIVE

Graft ischemic history and species differences were therefore studied in human and porcine valve leaflets by the measurement of endothelial prostacyclin production, post-explantational, basal and after stimulation with bradykinin.

METHODS

Four groups of aortic valve donors were established. Fresh human heart-beating donors (h-HBD), cadaveric human donors (h-NHBD) processed within 24 h, fresh porcine donors (p-HBD) and cadaveric porcine donors (p-NHBD) also processed within 24 h. Leaflets were separately incubated at 37 degrees C for successive periods of 30 min up to 5 h in Earle's Medium 199. After 240 min PGI-2 production was stimulated by 10 microM bradykinin. Postincubational release was stopped with indomethacin 10 microg/ml. Prostacyclin production was measured as 6-kPGF1a using an ELISA.

RESULTS

Initial PGI-2 production is significantly higher in porcine than in human grafts and in both species enhanced by previous warm ischemia. While baseline species differences disappear during progressive incubation, differences resulting from graft history are maintained. After PGI-2 stimulation species differences dominate again while ischemic history has no effect.

CONCLUSION

Ischemia and surgical manipulation are stimulators of endothelial PGI-2 production in both human and porcine allografts and, therefore, a correlation of this metabolic activity with cellular integrity may be misleading. Valid data are obtained only if the natural time-course and reaction to stimulation of PGI-2 production are duely recognized and species differences in the response to mechanical and ischemic stress are considered.

Tissue engineering of heart valves--human endothelial cell seeding of detergent acellularized porcine valves

OBJECTIVE

Tissue engineering of heart valves represents a new experimental concept to improve current modes of therapy in valvular heart disease. Drawbacks of glutaraldehyde fixed tissue valves or mechanical valves include the short durability or the need for life-long anticoagulation, respectively. Both have in common the inability to grow, which makes valvular heart disease especially problematic in children. The aim of this study was to develop a new methodology for a tissue engineered heart valve combining human cells and a xenogenic acellularized matrix.

METHODS

Porcine aortic valves were acellularized by deterging cell extraction using Triton without tanning. Endothelial cells were isolated in parallel from human saphenous veins and expanded in vitro. Specimens of the surface of the acellular matrix were seeded with endothelial cells. Analysis of acellularity was performed by light microscopy and scanning electron microscopy. Cell viability following seeding was assayed by fluorescence staining of viable cells.

RESULTS

The acellularization procedure resulted in an almost complete removal of the original cells while the 3D matrix was loosened at interfibrillar zones. However the 3D arrangement of the matrix fibers was grossly maintained. The porcine matrix could be seeded with in vitro expanded human endothelial cells and was maintained in culture for up to 3 days to document the formation of confluent cultures.

CONCLUSIONS

Porcine aortic valves can be almost completely acellularized by a non-tanning detergent extraction procedure. The xenogenic matrix was reseeded with human endothelial cells. This approach may eventually lead to the engineering of tissue heart valves repopulated with the patients own autologous cells.

Clinical and hemodynamic comparison of the Medtronic Freestyle and Toronto SPV stentless valves

The excellent hemodynamics of stentless valves have been observed by numerous investigators. With the recent release of the Toronto SPV (stentless porcine valve) and the Medtronic Freestyle stentless valves in North America, it is appropriate to now compare the clinical and hemodynamic performance of these devices. We analyzed the results of 995 patients who underwent aortic valve replacement (AVR) with either of the two valves; in all cases a subcoronary implant technique was used. There were important differences in the preoperative characteristics for the two groups: Medtronic Freestyle patients were notably older than the Toronto SPV patients (70.7+/-8.6 vs 61.8+/-11.1 years, p < 0.001) and were markedly more symptomatic (p < 0.0001). In the Toronto SPV group, most patients had New York Heart Association (NYHA) Class II (41.5%) or Class III (44.7%) symptoms preoperatively, while in the Freestyle group, 61.5% were in Class III and 12.5% were in Class IV. There were no notable differences in mortality or morbidity for the two groups. Both devices demonstrated a meaningful decrease in mean gradient and a corresponding increase in effective orifice area (EOA). Furthermore, the indexed EOA (EOA/body surface area [BSA]) was > 1cm2/m2 for all valves indicating there was no patient-prosthetic mismatch. There was a meaningful decrease in left ventricular (LV) mass as well as LV mass index (LVMI) for both devices up to 3 years postoperatively. Our data indicate that there were no differences in clinical outcome or hemodynamic performance of these two valves. Both devices offer excellent results with normalization of LV function.

Aortic valve replacement with stentless and stented porcine valves: a case-match study

OBJECTIVES

To assess the potential benefits of the hemodynamic superiority of stentless valves, we conducted a case-match study among patients who underwent aortic valve replacement with two types of porcine bioprostheses: the Toronto SPV and the stented Hancock II bioprosthesis.

METHODS

Preoperative clinical variables predictive of death after aortic valve replacement were determined by a stepwise logistic regression analysis in a series of 908 consecutive patients who received porcine aortic bioprostheses during a 14-year interval. Advanced age, New York Heart Association functional class IV, left ventricular ejection fraction of less than 30%, and coronary artery disease were independent predictors of death. On the basis of these four variables, 198 pairs of patients who survived aortic valve replacement with stentless and stented porcine valves were matched. The follow-up, truncated to the shortest interval for each matched pair, was 43 +/- 24 months for both groups.

RESULTS

At 8 years the actuarial survival was 91% +/- 4% for the Toronto SPV group and 69% +/- 8% for the Hancock II group (p = 0.006); the freedom from cardiac-related death was 95% +/- 4% for the Toronto SPV and 81% +/- 8% for the Hancock II (p = 0.01); the freedom from any valve-related complication was 81% +/- 5% for the Toronto SPV and 50% +/- 10% for the Hancock II (p = 0.008). A Cox proportional hazard model demonstrated a significant reduction in cardiac mortality rates and valve-related morbidity in patients who received the Toronto SPV bioprosthesis.

CONCLUSIONS

Although it is possible that confounding factors may have played a role in the clinical outcomes of this case-control study, the study suggests that aortic valve replacement with a stentless porcine valve enhances survival. This is believed to be due to the hemodynamic superiority of these valves.

Evaluation of prosthetic valve function and associated complications

Significant advances in imaging modalities have occurred to evaluate prosthetic valve function and associated complications. These developments involve predominantly the introduction of Doppler technology for the non-invasive determination of gradients and valve areas and TEE for an improved assessment of valve structure, function, and associated complications. The current role of cinefluoroscopy is mostly to complement TEE in the evaluation of motion of mechanical prosthetic valves in the aortic position. Cardiac catheterization is now rarely needed to assess valve function. Diagnosis of prosthetic valve obstruction can be performed in the majority of cases with transthoracic Doppler echocardiography. Differentiation of valve obstruction from normal valve function in small valves with high flow conditions, however, may be difficult. Because of this and the variability in normal valves among different prostheses, knowledge of the type and size of the implanted valve is essential. Patients and ultrasound laboratories are encouraged to seek and provide this information on a routine basis. Although transthoracic echocardiography is the main diagnostic modality for the serial evaluation of prosthetic valve function, it is important to recognize its limitations in assessing prosthetic mitral regurgitation and evaluating structural abnormalities of prosthetic valves. These are the situations in which TEE has the most impact. A summary of general indications of TEE in prosthetic valves is provided in Table 6. Finally, a baseline transthoracic Doppler study is essential in the overall follow-up and serial evaluation of valve function. For future comparisons, the best indices of valve functions are those obtained for patients as their own control, from a baseline Doppler echocardiographic study performed early after the operation.

Aortic allograft implantation techniques: pathomorphology and regurgitant jet patterns by Doppler echocardiographic studies

BACKGROUND

The diagnosis of allograft-specific pathology by echocardiography has important consequences for patient counseling and research. This study describes the pathomorphologic findings and color Doppler jet patterns in a consecutive series of patients after allograft placement with either the subcoronary implantation or root replacement technique.

METHODS

From 1987 to July 1996, the subcoronary allograft implantation technique and root replacement technique were used in 82 patients and 70 patients, respectively. These patients comprised the study group.

RESULTS

The incidence of paravalvular leaks and eccentric regurgitant jets was higher with subcoronary implantation (41%) than with root replacement (11%). Patients with a subcoronary implanted allograft had a higher incidence of eccentric jets.

CONCLUSIONS

These findings support the concept of preservation of valve geometry after root replacement, as allograft-specific pathomorphologic abnormalities and eccentric jets are more common after subcoronary implantation of allografts. Learning effects, however, cannot be excluded as the cause of these abnormalities.

Late results of a valve-preserving operation in patients with aneurysms of the ascending aorta and root

OBJECTIVES

There is still no agreement about the best method of dealing with malfunction of the aortic valve caused by aneurysm or dissection of the aortic root. The experience, rationale, and development of a valve-preserving technique introduced and used since 1979 is described.

METHODS

During this period 158 patients (78% of all patients undergoing resection of aneurysm of the ascending aorta) were operated on using this technique. Their ages ranged from 2 to 72 years (mean 46.6 years). Of the patients 107 were male and 51 were female. A total of 68 patients had skeletal manifestations of Marfan's syndrome. The original disease was chronic aneurysm of the ascending aorta or root in 92 (58.2%), chronic dissection in 17 (10.8%), and acute dissection in 49 (31%) patients. One hundred eleven additional procedures were performed in 84 patients. In all there were five early deaths (4.6% +/- 2%) in the 109 patients with chronic aneurysm and one death in the 103 patients operated on electively (0.97% +/- 0.9%). Actuarial survival for patients operated on for chronic aneurysm was 93.3%, 88.0%, 79.0%, and 57.9% at 1, 5, 10, and 15 years and 96.8%, 91.2%, 82.0%, and 60.0% for those operated on electively. Actuarial survival for patients operated on for acute dissection was 72.8%, 63.4%, and 53.3% at 1, 5, and 10 years. The probability of needing reoperation was 3.0% +/- 2%, 11% +/- 0.5%, and 11% +/- 0.5% at 1, 5, and 10 years. There were no instances of infective endocarditis or thromboembolic complications except in two patients operated on early in the series who had cusp extension. No anticoagulants were used. Echocardiography showed reduction in left ventricular end-systolic and end-diastolic dimensions, which was maintained. At the end of follow-up trivial or no aortic regurgitation was demonstrated in 63.6%, mild to moderate in 33.3%, and severe in 3%.

CONCLUSIONS

Valve-sparing operations are possible in a large proportion of patients with aneurysms of the ascending aorta and the medium and long-term results are encouraging.

Allograft heart valve viability and valve-processing variables

BACKGROUND

The impact of allograft valve viability on valve durability remains controversial. Analyses of our clinical results have demonstrated the superiority of the cryopreserved valve viable at the time of implantation over the 4 degrees C stored valve nonviable at the time of implantation. In this study, we quantitatively assessed the effects on viability of current and past valve-processing protocols at The Prince Charles Hospital.

METHODS

The viability of pulmonary valves was quantitatively analyzed by thin-layer autoradiography to assess the effects of donor type, antibiotics, and valve storage.

RESULTS

Control valve segments obtained from beating-heart donor valves had a higher initial viability (0.92+/-0.02) than nonbeating-heart donor valves (0.66+/-0.03). Cryopreservation after low-dose antibiotic sterilization significantly reduced viability to 50% to 60% of the control, and in the presence of amphotericin B, viability dropped further to 10% to 36% of the control. After 7 days' storage at 4 degrees C, viability was reduced to 2% of control and to 0% viability after 21 days.

CONCLUSIONS

For maximal preimplantation viability, valves should be procured as soon as possible after cessation of heart beat and should be cryopreserved if they are not to be clinically implanted within 1 to 2 days. Amphotericin B should not be used in conjunction with cryopreservation if viability is to be maximized.

Aortic valve homografts in adults: a clinical perspective

Aortic valve replacement is a lifesaving measure in patients with severe aortic valve disease. In the United States, the most commonly used prostheses are the mechanical and bioprosthetic valves. With mechanical valves, long-term anticoagulation is necessary because of high thrombogenic potential. Bioprosthetic valves have a relatively high incidence of structural failure, especially in younger patients. Aortic valve homografts, derived from human heart donors or autopsy material, provide an alternative to mechanical or animal valves. The advantages of the homograft in comparison with the mechanical prostheses are the low incidence of thromboembolism without anticoagulation and lower valvular gradients in smaller sizes. Homografts are relatively resistant to endocarditis and are the valve of choice during active endocarditis. Their major mode of failure has been aortic regurgitation; however, recent advances in preservation and operative techniques have decreased this problem. Whether implantation of an aortic valve homograft should be the procedure of choice in subsets of patients remains controversial. Herein we review the history, techniques, results, complications, and current indications for aortic valve homografts.

Mitral valve replacement with glutaraldehyde preserved aortic allografts

OBJECTIVE

To present long-term results after mitral valve replacement with stent mounted glutaraldehyde preserved aortic allografts in patients older than 15 years. The clinical support for this study was to combine the glutaraldehyde technique of biological tissue preservation with the advantages of allografts when compared to xenografts. This was demonstrated in previous studies using other methods of tissue processing.

METHODS

Between September 1984 and November 1994, 70 patients aged 16-77 years (mean 35.4 years) underwent mitral valve replacement with this preserved and mounted allograft. Of these, 40 patients (57.2%) were aged 16-35 years and 15 (21.4%) were 20 years old or younger; 46 (65.7%) were females and 24 (34.3%) males. Single mitral valve replacement was performed in 60 patients and 10 were also subjected to other combined cardiac procedures. Human aortic valves were obtained during routine autopsy, processed in glutaraldehyde and mounted into flexible stents, using the same technique as that used for porcine bioprostheses.

RESULTS

Hospital mortality was 1.4%. Total follow-up was 543.1 patient-years, corresponding to a mean follow-up of 7.9 years per patient. Echocardiography demonstrated a hemodynamic performance similar to porcine bioprostheses. Late mortality was 0.7 +/- 0.6% per patient-year and the causes were congestive heart failure in 2, prosthetic endocarditis in 1 and acute myocardial infarction in 1. The 12-year actuarial survival was 92.4 +/- 3.2%. The incidence of late complications was 5.2 +/- 1.2% per patient-year, including congestive heart failure, prosthetic endocarditis, periprosthetic leak, thromboembolic episodes, recurrence of rheumatic disease, coronary artery disease and allograft failure. Complications related to heart disease represented 2.8 +/- 0.6% and allobioprosthesis-related 2.4 +/- 0.5% per patient-year. The 12-year actuarial freedom from primary valve failure was 81.0 +/- 15.0%. The incidence of reoperations was 1.5 +/- 0.8% per patient-year and the main indication was prosthetic endocarditis. Other causes were periprosthetic leak, aortic insufficiency in the native aortic valve and allobioprosthesis dysfunction. Functional results demonstrated a significant improvement in patients clinical condition.

CONCLUSION

This 12-year follow-up shows a very low incidence of primary allograft failure for patients older than 15 years undergoing mitral valve replacement, and much superior than our results with porcine bioprosthesis in the same age group. This supports our assumption that this investigational valve represents a new advance in cardiac valve surgery.