Fourteen-year experience with homovital homografts for aortic valve replacement

Cardiac crossroads: deciding between mechanical or bioprosthetic heart valve replacement

Nearly 15 million people in the United States suffer from either aortic or mitral valvular disease. For patients with severe and symptomatic valvular heart disease, valve replacement surgery improves morbidity and mortality outcomes. In 2009, 90,000 valve replacement surgeries were performed in the United States. This review evaluates the advantages and disadvantages of mechanical and bioprosthetic prosthetic heart valves as well as the factors for consideration in deciding the appropriate valve type for an individual patient. Although many caveats exist, the general recommendation is for patients younger than 60 to 65 years to receive mechanical valves due to the valve's longer durability and for patients older than 60 to 65 years to receive a bioprosthetic valve to avoid complications with anticoagulants. Situations that warrant special consideration include patient co-morbidities, the need for anticoagulation, and the potential for pregnancy. Once these characteristics have been considered, patients' values, anxieties, and expectations for their lifestyle and quality of life should be incorporated into final valve selection. Decision aids can be useful in integrating preferences in the valve decision. Finally, future directions in valve technology, anticoagulation, and medical decision-making are discussed.

Homograft implantation for aortic valve replacement since 15 years: results and follow-up

BACKGROUND

The use of homografts in aortic valve replacement is an alternative to other prostheses and has been established in our department for 15 years.

METHODS

Since 1992, 360 homografts (HG) have been implanted in adult patients (mean age 51.6 years, 72.8% male). Prospective follow-up was done on an annual basis.

RESULTS

Thirty-day mortality was 5.0% (n = 17); after 5, 10, and 15 years, survival was 88.3%, 84.6%, and 76.0%, respectively. Out of 39 late deaths, 11 were valve-related (10 HG infections, 1 aortic aneurysm). Freedom from reoperation was 99.4% 1 year after operation; after 5, 10, and 15 years it was 94.1%, 78.2%, and 67.3%, respectively. Indications for HG explantation were graft infections (n = 20), calcification (n = 16), regurgitation > grade II (n = 17), perforation (n = 8), and paravalvular leakage (n = 1). Eleven transitoric ischemic attacks, 2 strokes, and 1 cerebral bleeding event were recorded. In echocardiography, the transvalvular pressure gradient changed from 10.55 to 15.02 (P = .004), 19.9 mmHg (P = .056), and 37 mmHg (not applicable) after 5, 10, and 15 years, respectively. Mean HG regurgitation was grade 0.49 before discharge and increased to 1.0 (P < .001), 0.91, and 2.5 after 5, 10, and 15 years, respectively. Ejection fraction increased from 61.9% to 64% after 5 years and to 66% after 10 years (P = .021) and then decreased to 63.5% after 15 years.

CONCLUSIONS

Comparing HG with other valve prostheses, survival and graft durability seem to be confirmed. They are vulnerable to infections. The hemodynamic performance is good, and hemorrhagic or thrombo-embolic events are rare.

Long-term outcomes after autograft versus homograft aortic root replacement in adults with aortic valve disease: a randomised controlled trial

BACKGROUND

The ideal substitute for aortic valve replacement in patients with aortic valve disease is not known. Our hypothesis was that the regulatory and adaptive properties of a living valve substitute could improve the long-term outcomes in patients. We therefore compared these outcomes after autograft aortic root replacement (Ross procedure) versus homograft aortic root replacement in adults.

METHODS

Male and female patients (<69 years) requiring aortic valve surgery were randomly assigned in a one-to-one ratio to receive an autograft or a homograft aortic root replacement in one centre in the UK. The random allocation sequence was computer generated. Treatment was not masked. The primary endpoint was survival of patients at 10 years after surgery. This study is registered as an International Standard Randomised Controlled Trial, number ISRCTN03530985.

FINDINGS

228 patients were randomly assigned to receive an autograft or a homograft aortic root replacement. 12 patients were excluded because they were younger than 18 years; 108 in each group received the surgery they were assigned to and were analysed. There was one (<1%) perioperative death in the autograft group versus three (3%) in the homograft group (p=0.621). At 10 years, four patients died in the autograft group versus 15 in the homograft group. Actuarial survival at 10 years was 97% (SD 2) in the autograft group versus 83% (4) in the homograft group. Hazard ratio for death in the homograft group was 4.61 (95% CI 1.71-16.03; p=0.0060). Survival of patients in the autograft group was similar to that in an age-matched and sex-matched British population (96%).

INTERPRETATION

Our findings support the hypothesis that a living valve implanted in the aortic position can significantly improve the long-term outcomes in patients.

FUNDING

Funding Magdi Yacoub Institute.

Outcome of aortic homograft implantation in 24 cases of severe infective endocarditis

The objective of the study was to evaluate the results of treatment of severe aortic endocarditis with an aortic homograft (an aortic valve and root from a donor) in combination with antibiotic therapy. 24 patients with either aortic prosthetic valve endocarditis (n=16) or severe aortic native valve endocarditis (n=8) with destruction of 1 or more cusps, paravalvular abscess formation and/or cardiac fistulas caused by aggressive bacteria, underwent surgery in 1997-2006. Staphylococcal species were the most common pathogens followed by streptococci. Intravenous antibiotic therapy was started before surgery and continued for at least 4-6 weeks. Three patients with prosthetic valve endocarditis died within the first 24 h after surgery from heart failure. Two of these patients required an additional implantation of a mitral valve prosthesis. Five patients died from non-cardiac causes within 1-7 y of surgery. Within the follow-up period no patients had relapse of endocarditis, and only 1 episode of recurrent endocarditis in an intravenous drug abuser was registered. In conclusion, an aortic homograft in combination with intravenous antibiotics is an excellent option for treatment of severe aortic endocarditis.

Retained structural integrity of collagen and elastin within cryopreserved human heart valve tissue as detected by two-photon laser scanning confocal microscopy

Cryopreservation is commonly used for the long-term storage of heart valve allografts. Despite the excellent hemodynamic performance and durability of cryopreserved allografts, reports have questioned whether cryopreservation affects the valvular structural proteins, collagen and elastin. This study uses two-photon laser scanning confocal microscopy (LSCM) to evaluate the effect of cryopreservation on collagen and elastin integrity within the leaflet and conduit of aortic and pulmonary human heart valves. To permit pairwise comparisons of fresh and cryopreserved tissue, test valves were bisected longitudinally with one segment imaged fresh and the other imaged after cryopreservation and brief storage in liquid nitrogen. Collagen was detected by second harmonic generation (SHG) stimulation and elastin by autofluorescence excitation. Qualitative analysis of all resultant images indicated the maintenance of collagen and elastin structure within leaflet and conduit post-cryopreservation. Analysis of the optimized percent laser transmission (OPLT) required for full dynamic range imaging of collagen and elastin showed that OPLT observations were highly variable among both fresh and cryopreserved samples. Changes in donor-specific average OPLT in response to cryopreservation exhibited no consistent directional trend. The donor-aggregated results predominantly showed no statistically significant change in collagen and elastin average OPLT due to cryopreservation. Since OPLT has an inverse relationship with structural signal intensity, these results indicate that there was largely no statistical difference in collagen and elastin signal strength between fresh and cryopreserved tissue. Overall, this study indicates that the conventional cryopreservation of human heart valve allografts does not detrimentally affect their collagen and elastin structural integrity.

Aortic valve and/or aortic root replacement using an aortic homograft

Aortic valve replacement using the homograft valve has a special place in the cardiac surgical practice although it has never been widely used, in part due to the lack of tissue donors but also due to the perceived difficulty of the procedure compared with aortic valve replacement using prosthetic devices and concerns regarding homograft valve failure. The principal indication for aortic valve replacement using a homograft aortic valve is for active aortic valve endocarditis (native or prosthetic) with or without perivalvular tissue destruction (abscess cavity, fistula, detachment of the anterior mitral valve leaflet from the aortic annulus). Since the homograft tissue is pliable and adaptable, it can be used to repair defects in complex cases with root destruction. A second interesting application of homograft aortic valve is in the treatment of small aortic root (in which replacement with a small prosthetic valve would produce an unacceptable orifice ratio and ultimately affect long-term outcome) and left ventricular outflow tract obstruction when the homograft aortic valve can be combined to the Konno procedure. Homograft aortic valve can be used in these cases without sacrifying the pulmonary valve to be used as aortic valve substitute (for instance in adolescents and young adults who do not want to undergo a 'two-valve' procedure like the Ross-Konno procedure). The most frequent operation technique is the cylindrical aortic root replacement, performed in a similar way than the classical Bentall procedure. This technique is the most easiest one and performed more frequently than the subcoronary implantation, which is substantially more demanding. Results from centres that have significant experience with homograft valve surgery report equivalent survival data. The University of Alabama had an 87% survival at 5 years in a 10-year period from 1981 to 1991. Of those who underwent isolated aortic valve replacement with a homograft, there was 99% survival at 30 days and 94% survival at 8 years. In the Mayo Clinic series, 82% were alive at 8 years. Like all tissue valves, homograft aortic valves may fail. An understanding of the mechanisms of homograft valve failure and the way in which these mechanisms interact has important surgical implications. Homograft aortic valves may develop progressive regurgitation as a result of a change in the mechanical properties of the leaflets over time.

Long-term storage in liquid nitrogen does not affect cell viability in cardiac valve allografts

Liquid nitrogen is the most common medium used by tissue banks for the storage of cryopreserved heart valves. This study evaluates the effect of the length of storage on human cryopreserved heart valves. Human tissues (14 aortic and 13 pulmonary) were frozen in a controlled-rate freezer (1 degrees C/min) and stored in the liquid phase of a nitrogen tank for 9.1+/-1.6 years. The preservative solution was medium M199 containing 5% human serum albumin and 10% Me(2)SO. After thawing in a water bath at 42 degrees C, the cryoprotectant was removed. Then, fragments from vascular wall and leaflet were dissected. Explant cultures and histological studies were performed in order to assess cell viability and structural integrity. CD90 and CD31 expression was analysed in cultured cells using flow cytometry. Light microscopy, immunofluorescence staining and laser scanning confocal microscopy were used to evaluate cell viability and extracellular matrix components. Electron microscopy was used for ultrastructural study. Cell cultures could be obtained from all the specimens assayed. Cells grew from explants showing a fibroblastic phenotype. CD90 expression was common in cultured cells but a low percentage of cells expressed CD31. Histological results showed a good preservation estructure in both leaflets and vascular walls. Morphological features of cellular irreversible damage were very rare. No differences which could be due to length of allograft storage period were observed. We concluded that allografts stored in liquid nitrogen up to 13 years did not significantly undergo loss of cell viability other than that due to disinfection, freezing and thawing protocols.

Apoptosis in fresh and cryopreserved cardiac valves of pig samples

To analyse the influence of cold ischemic time (CIT) (2-24 h) and of cryopreservation (liquid phase) on the viability of the valvular fibroblasts and in the presence of apoptosis. Cardiac valves from 10 pigs were evaluated by anatomo-pathological study of the wall, muscle and leaflet. At the same time, the presence of cellular death due to apoptosis was investigated in two ways; directly on tissue by Apodetec system and by two-colour flow cytometry assay analyzing a suspension of fibroblast from valve leaflets using Anexina V and propidium iodure (PI). We established three groups of samples to compare different experimental conditions: 2 h of ischemia (group 1), 24 h of ischemia (group 2), and a programme of cryopreservation (-1 degrees C/min) after 2 h of ischemia, followed by storage in liquid nitrogen during a week and thawing was performed (group 3). The analysis of viabilities showed slight differences between all three groups. The results indicated CIT of 24 h undergoing more structural affectation than CIT of 2 h. Flow cytometry analysis did not show important differences between groups; however cryopreserved samples (group 3) slightly less viability and a higher percentage of death by apoptosis than group 1 and 2 using flow cytometry. Apoptosis was confirmed on tissue from all valves but mainly in samples of group 2 and group 3. In summary, the viability of the valves in the case of ischemic times of 2 h, 24 h or after cryopreservation/thawing differs slightly. The death of the cells is mainly mediated by necrosis and not by apoptosis.

Prosthetic heart valves: Types and echocardiographic evaluation

In the last five decades multiple different models of prosthetic valves have been developed. The purpose of this article is to provide a comprehensive source of information for the types and the echocardiographic evaluation of the prosthetic heart valves.

Endothelial cell fatty acid unsaturation mediates cold-induced oxidative stress

Ultraprofound hypothermia (< 5 degrees C) induces changes to cell membranes such as liquid-to-gel lipid transitions and oxidative stress that have a negative effect on membrane function and cell survival. We hypothesized that fatty acid substitution of endothelial cell lipids and alterations in their unsaturation would modify cell survival at 0 degrees C, a temperature commonly used during storage and transportation of isolated cells or tissues and organs used in transplantation. Confluent bovine aortic endothelial cells were treated with 18-carbon fatty acids (C18:0, C18:1n-9, C18:2n-6, or C18:3n-3), C20:5n-3 or C22:6n-3 (DHA), and then stored at 0 degrees C without fatty acid supplements. Storage of control cells caused the release of lactate dehydrogenase (LDH) and a threefold increase in lipid peroxidation (LPO) when compared to control cells not exposed to cold. Pre-treating cells with C18:0 decreased the unsaturation of cell lipids and reduced LDH release at 0 degrees C by 50%, but all mono- or poly-unsaturated fatty acids increased injury in a concentration-dependent manner and as the extent of fatty acid unsaturation increased. DHA-treatment increased cell fatty acid unsaturation and caused maximal injury at 0 degrees C, which was prevented by lipophilic antioxidants BHT or vitamin E, the iron chelator deferoxamine, and to a lesser extent by vitamin C. Furthermore, the cold-induced increase in LPO was reduced by C18:0, vitamin E, or DFO but enhanced by DHA. In conclusion, the findings implicate iron catalyzed free radicals and LPO as a predominant mechanism of endothelial cell injury at 0 degrees C, which may be reduced by increasing lipid saturation or treating cells with antioxidants.

Autografts, homografts, and xenografts: overview on stentless aortic valve surgery

Stentless valves, either human (autografts, homografts) or animal (porcine xenografts), were historically among the first substitutes to be used to replace the diseased aortic valve. Forty years after those pioneering days and 15 years after revival of such valves, stentless grafts have become a mainstay in aortic surgery. Although limitations associated with the use of autografts, homografts and xenografts remain, stentless valves have profoundly improved quality of life after aortic valve/root replacement. In addition, stentless surgery has greatly advanced the understanding of aortic root anatomy, physiology and pathology among surgeons.

Endothelial cell preservation at 10 degrees C minimizes catalytic iron, oxidative stress, and cold-induced injury

There is growing evidence that oxidative stress plays an important role in mediating the injury induced by hypothermia during the preservation of cells and tissues for clinical or research use. In cardiovascular allografts, endothelial cell loss or injury may lead to impaired control of vascular permeability and tone, thrombosis, and inflammation. We hypothesized that hypothermia-induced damage to the endothelium is linked to increases in intracellular catalytic iron pools and oxidative stress. In this study, bovine aortic endothelial cells and cell culture methods were used to model the response of the endothelium of cardiovascular tissues to hypothermia. Confluent cells were stored at 0 degrees C to 25 degrees C and cell damage was measured by lipid peroxidation (LPO) and lactate dehydrogenase release. Varying the bleomycin-detectible iron (BDI) in cells modulated cold-induced LPO and cell injury. In untreated cells, injury was highest at 0 degrees C and a minimum at 10 degrees C. A similar temperature-dependent trend was found in BDI levels and cell plating efficiencies. Arrhenius plots of cell killing and iron accumulation rates showed biphasic temperature dependence, with minima at 10 degrees C and matching activation energies above and below 10 degrees C. These findings imply that the mechanisms underlying the hypothermic increase in catalytic iron, oxidative stress, and cell killing are the same and that preservation of the endothelium may be optimized at temperatures above those routinely used.

Allograft semilunar cardiac valves processing and cryopreservation - morphology in scanning electron microscope

OBJECTIVE

The most important factors of long term clinical performance of biological heart valve prostheses are methods of processing and cryopreservation. That is why we decided to evaluate the impact of current Allograft Heart Valves (AHV) Bank protocol on valve tissue morphology. Scanning electron microscope (SEM) is a valuable tool for investigation of biological surfaces. In case of cardiac valves it is especially suitable for detection of fine changes in endothelial covering and underlying layers.

MATERIAL AND METHODS

"Fresh" aortic and pulmonary AHV samples, harvested from "heart-beating" cadaveric donors, were compared with (1) tissue from AHV obtained from non heart-beating donors, (2) samples stored in 4 degrees C saline for 24 h, (3) antibiotic treated tissue for 24 h at 37 degrees C and finally (4) cryopreserved valves, stored in liquid nitrogen (-196 degrees C) for 6-38 months. All samples were dissected, dried with hexamethyldisilazane (HMDS), gold coated, studied and photographed by SEM (Tesla BS 301).

RESULTS

Our alternative method of drying samples by the HMDS method proved to be suitable for thin membranes of human semilunar valves. We were able to detect early changes in the endothelium after harvesting, and denudation of the endothelial covering during preservation with and without freezing.

CONCLUSION

SEM (using HMDS drying) along with other methods may be helpful for the morphological control of processing, cryopreservation and liquid nitrogen storage of AHV. According to the current findings we have to avoid washing of AHV in saline after harvesting.

Fibronectin-hepatocyte growth factor enhances reendothelialization in tissue-engineered heart valve

BACKGROUND

To overcome the limitations of tissue-engineered heart valves, which require cell seeding before implantation, a growth factor for in situ recellularization may be an important strategy. We developed a new decellularized valve containing a fusion protein combined fibronectin and hepatocyte growth factor. Here, we tested the hypothesis that our valve might accelerate in situ recellularization by inducing the proliferation of endothelial cells.

METHODS

Porcine aortic valves were decellularized using detergent. Fibronectin-hepatocyte growth factor was introduced into the decellularized valves. The decellularized valves with fibronectin-hepatocyte growth factor were implanted into the pulmonary arterial trunk of dogs (F group: n = 15). As controls, decellularized valves without the growth factor (C group: n = 12), and with hepatocyte growth factor (H group: n = 12) were implanted in the same manner. Histologic examinations were performed 1 week and 1 month after implantation.

RESULTS

One week after implantation, endothelial cells partially covered the surface of the graft in the F group but not the C and H groups. Although the C and H groups had inadequate recellularization 1 month after implantation, the F group showed a monolayer of endothelial cells, underneath which were areas of additional cell layers, which were vimentin positive. Quantitative evaluation demonstrated the amount of vimentin in the F group was 71% of the native control, and it was much lower in the other groups (C, 2.8%; H, 16.8%) 1 month after implantation.

CONCLUSIONS

This study demonstrated that fibronectin-hepatocyte growth factor enhanced early in situ recellularization in decellularized valves.

In vivo recellularization of plain decellularized xenografts with specific cell characterization in the systemic circulation: histological and immunohistochemical study

Decellularized biological scaffolds have been used for the tissue engineering of heart valves with good results in the pulmonary circulation. However, little information is available on the recellularization of plain decellularized biological scaffolds in the systemic circulation. The aim of this study was to determine whether plain decellularized xenografts (PDXs) can recellularize with specific cell characterization in the systemic circulation. The xenogenic aortic valved conduit grafts of rabbits were implanted in the abdominal aorta of dogs after decellularization. The grafts were explanted at 4, 12, or 24 weeks after implantation for histological, immunohistochemical examination, scanning electron microscope, and Western blot analysis. Although the valvular structures were completely lost after implantation, supravalvular conduits showed normal shapes and endothelialization. The PDXs were repopulated with basic vascular cell components in approximate natural proportions without immunological responses. The PDXs had been recellularized with specific cell characterization in the systemic circulation.

Long-term results after aortic valve replacement with the Bravo 400 stentless xenograft

BACKGROUND

This study was undertaken to evaluate the long-term clinical and echocardiographic outcome after aortic valve replacement with the Bravo Cardiovascular Model 400 stentless xenograft.

METHODS

Between February 1992 and January 1994, 67 patients underwent aortic valve replacement with the Bravo 400 bioprosthesis. The valvular pathology was aortic stenosis in 36 patients (53.7%), aortic insufficiency in 17 patients (25.4%), and mixed lesion in 14 patients (20.9%). Mean follow-up time was 9.8 +/- 2.73 years and median follow-up time was 11 years. Cumulative follow-up time was 659 patients-years and was 94% complete.

RESULTS

No early deaths were observed. Overall survival estimates at 11 years were 74.71% +/- 5.47%. The actuarial freedom from valve-related death at 11 years was 91.04% +/- 3.84%; from cardiac-related death at 11 years it was 87.95% +/- 4.29%; and from noncardiac death at 11 years it was 85.14% +/- 4.58%. Eleven-year Kaplan-Meier survival of patients younger than 65 years was 90.91% +/- 6.13% versus 66.08% +/- 7.38% for older patients (p = 0.0307, log-rank test). The actuarial freedom from all valve-related morbidity and mortality at 11 years was 80.3% +/- 5.4%. The mean transvalvular gradient decreased significantly after aortic valve replacement with a corresponding increase in effective orifice area. Left ventricular mass index at 10-year follow-up was 68.5% of the preoperative value.

CONCLUSIONS

The Bravo Cardiovascular Model 400 stentless xenograft has provided good clinical and hemodynamic results up until 11 years of follow-up.

Early and mid–term results of the Shelhigh stentless bioprosthesis in patients with active infective endocarditis

AIMS

This study investigated the early and mid-term results following valve replacement with the new Shelhigh stentless bioprosthesis made entirely of biological material in patients with active infective endocarditis (AIE).

MATERIAL AND METHODS

Between 02/2000 and 12/2004, 164 patients (n = 122 men, mean age 59, 18-85 years) received implantation of an AIE Shelhigh stentless bioprosthesis in the aortic, mitral, tricuspid or pulmonary position. A total of 119 patients (72.6%) had native AIE and 45 (27.4%) prosthetic AIE. A large proportion of the patients reached the operating room in a condition of cardiac decompensation: 37 (22.6%) patients were intubated, 40 (24.4%) had protracted septic shock and 41 (25.0%) required intensive catecholamine treatment. Surgery was regarded as urgent in 94 patients (57.4%) and was performed as an emergency procedure in 70 (42.6%). The mean follow-up time is 1.5 +/- 0.11 years (range, 5 months to 5.2 years). Echocardiographic follow-up examinations were performed early postoperatively and after 12 months.

RESULTS

In terms of the operative indication, we found a highly significant difference in the survival rate between patients who were operated on urgently vs in an emergency. In patients who died within 30 days, the main cause of death was septic multiorgan failure (67.6%). Only three patients required reoperation due to reinfection of the Shelhigh bioprostheses; this represents a reinfection rate of 1.8% in relation to the whole cohort. The postoperative echocardiographic examinations showed the Shelhigh valves to have very good hemodynamics without relevant pressure gradients.

CONCLUSION

Our experience in the use of Shelhigh bioprostheses in patients with native and prosthetic endocarditis show the early and mid-term results, in particular the low reinfection rate and the good hemodynamics, to be comparable with the results achieved using homografts. Since these prostheses are readily available and their implantation straightforward, they are increasingly being used in patients with endocarditis. These promising results need to verified in the long term.

Homograft aortic valve replacement--the experience of one unit

BACKGROUND

Homograft valves offer advantages including avoidance of anticoagulation and less susceptibility to infection especially in the setting of endocarditis. However, there is concern about their durability and possible accelerated degeneration particularly in cases of second time replacement with homografts.

AIM

This study aimed to evaluate the pattern of homograft failure and the quality of life in patients after homograft implantation.

METHODS

Between 1990 and 1998, 58 patients underwent aortic valve replacement with a homograft (aortic homograft = 47, pulmonary homograft = 11). Evaluation was based on clinical and echocardiographic examination, patient questionnaires and explanted valve pathology. Survival and freedom from cardiac related death were expressed by actuarial methods.

RESULTS

Follow up ranged from 1 to 10 years (mean 5.5 years). Analysis of questionnaires revealed 60% of respondents to be in good performance status and 20% in moderate and 20% in poor performance status groups. Eleven patients (18.9%) required subsequent redo valve replacement after initial homograft insertion (pulmonary = 6, aortic = 5) due to either valve dehiscence (n=4) or valve degeneration (n=7). The mean interval of re-replacement was 5.4 years.

CONCLUSIONS

Pulmonary homografts have a high failure rate in the aortic position. Overall subjective and clinical improvement after surgery is less than expected for a "physiological" device. In the setting of low availability of homografts the use of off-the-shelf devices such as stentless xenografts may be preferable in most cardiac surgical units in the current era.

Prosthetic valve endocarditis

Prosthetic valve endocarditis is a catastrophic complication of cardiac valve replacement, associated with high mortality rates. Medical treatment is effective in a few instances of endocarditis involving the leaflets alone in bioprostheses. However, accurate diagnosis, better myocardial protection, and improved surgical strategies have led to better survival in patients undergoing surgery after failed conservative therapy. This comprehensive review addresses various issues involved in the management of this complication.

Asymptomatic Adult Patients With Aortic Stenosis: Should They Ever Have Aortic Valve Replacement?

Presently, conventional wisdom is that an asymptomatic patient, even with severe aortic stenosis (AS), can be followed medically. The basis for this recommendation is that sudden death as the first "symptom" in an asymptomatic patient is rare. Unfortunately, symptoms are subjective and can be ignored or explained away by both patient and physician, and once symptoms are recognized, sudden death accounts for at least one third of the deaths from AS in unoperated patients. There is evidence that once AS becomes severe, ischemia and fibrosis occur rapidly, setting up the possibility of heart failure and sudden death even after successful valve replacement. Aortic valve replacement should be performed before extensive fibrosis occurs. Multiple studies have shown that in severe AS, symptoms will occur rapidly when there is heavy valve calcification, an aortic valve area <0.8 cm, an annual rate of progression of aortic valve velocity of >/=0.3 m/sec, or a positive exercise stress test. These findings are excellent evidence that asymptomatic patients with severe AS and any of the above findings should be considered for aortic valve replacement.

Midterm Results After Aortic Valve Replacement With a Stentless Bioprosthesis Aortic Valve

BACKGROUND

It is suggested that a simplified implant model Cryolife-O'Brien (CryoLife International, Kennesaw, GA) offers less satisfactory outcome compared with standard stentless models. This study was conducted to prospectively evaluate the midterm results after aortic valve replacement with the Cryolife-O'Brien stentless bioprosthesis.

METHODS

In 1996, a prospective clinical trial using different stentless valves was initiated. From September 1996 through September 2002, 156 consecutive patients with a mean age of 74.5 years underwent aortic valve replacement with the Cryolife-O'Brien porcine stentless bioprosthesis. The predominant aortic valve lesion was stenosis in 128 and insufficiency in 28 cases. Patients have been followed from 2 to 72 months (mean, 42 months). Echocardiography was performed by one echocardiographer preoperatively, intraoperatively, postoperatively at discharge, 2 to 6 months later, and annually thereafter.

RESULTS

Sixty percent of patients received a valve 25 mm in diameter or larger; 39% had concomittant coronary bypass grafting. The 30-day operative mortality rate was 6.4%. Ten late nonvalve-related deaths have occurred. Severe aortic insufficiency caused by oversizing leads to early reoperation in 3 patients. The peak and mean systolic gradients decreased significantly during the first 12 months after implantation, p < 0.001, and the effective valve areas increased significantly during this time interval p < 0.001. At 5 years, ten patients have moderate aortic insufficiency. The actuarial survival at 5 years was 88 +/- 3%. The rate for freedom from endocarditis was 100% and for freedom from thromboembolic events was 94%.

CONCLUSIONS

Midterm results after aortic valve replacement with the Cryolife-O'Brien stentless bioprosthesis are encouraging. Good hemodynamics have been coupled with low rate of valve-related complications, thus representing a very good alternative to conventional stented bioprostheses.

Fresh and Cryopreserved Arterial Homografts: Immunological and Clinical Results

INTRODUCTION

This prospective study defined the immunological and clinical results after fresh and cryopreserved arterial homograft replacement due to graft infection.

MATERIALS AND METHODS

Thirty patients who underwent ABO-compatible homograft transplantation were studied for anti-human leukocyte antigen (HLA): antibody production and CD3- and CD4- versus CD8-positive lymphocyte subsets. Nine patients (30%) received immunosuppressive treatment with cyclosporine (1 to 3 mg/kg/d). Immunological studies were performed preoperatively, and early (1, 3, 7 days) and late (1, 3, 6, 12, 24, 36, 48 months) during follow-up. Abdominal computed tomography scans were performed postoperatively at 1, 6, 12, 24, 36, and 48 months of follow-up.

RESULTS

Preoperatively, antibodies were not detected. Postoperatively, a progressive increase in percent panel reactive antibodies was observed in all patients 1 month after the transplant. There were no difference between fresh and cryopreserved homografts. The antibody response among patients treated with cyclosporine was less pronounced and delayed. Recipient antibodies were directed against donor-specific antigens. During the immediate postoperative period (1, 3, 7 days) there was a slight increase in CD3- and CD4-positive T lymphocytes and a concomitant decrease in the CD8 subset. Later, CD3 and CD4 progressively decreased and the CD8 set increased. Clinically, no patients had signs of recurrent infection upon late follow-up. Four patients died (13%), but only one death was homograft-related (rupture of the graft). At 2-year follow-up, two patients showed stenotic lesions due to chronic rejection. Clinically, no differences were noted between fresh and cryopreserved homografts, or between patients treated with or without cyclosporine.

CONCLUSIONS

Fresh and cryopreserved arterial homografts are immunogenic; they induce a strong anti-HLA antibody response, similar to chronic rejection.

Which biologic valve should we select for the 45- to 65-year-old age group requiring aortic valve replacement?

OBJECTIVE

The diversity of biologic valves available to replace the aortic valve renders selection difficult for the 45- to 65-year-old patient. To evaluate and compare the results of biologic valves in the 45- to 65-year-old patient, we reviewed our experience (1991-2004).

METHODS

Three hundred thirty-two patients between 45 and 65 years old with isolated aortic valve disease had a biologic valve implanted: Freestyle valve in 140 patients, a homograft in 54 patients, a stented Mosaic or Perimount valve (stented xenograft) in 62 patients, and a Ross procedure in 76 patients.

RESULTS

Perioperative mortality was comparable for all groups (Freestyle, 2.1%; homograft, 3.7%; stented xenograft, 3.2%; Ross procedure, 1.3%; P = .8). Echocardiographically determined valve performance at discharge was significantly enhanced in the Ross procedure and homograft groups (indexed effective orifice area: Freestyle, 0.9 +/- 0.3 cm 2 /m 2 ; homograft, 1.3 +/- 0.3 cm 2 /m 2 ; stented xenograft, 0.8 +/- 0.2 cm 2 /m 2 ; Ross procedure, 1.4 +/- 0.4; P < .0001; mean gradient: Freestyle, 12.0 +/- 6.6 mm Hg; homograft, 7.4 +/- 4.0 mm Hg; stented xenograft, 15.4 +/- 5.4 mm Hg; Ross procedure, 4.6 +/- 3.2 mm Hg; P < .0001). For all yearly follow-up, freedom from New York Heart Association class III or IV was comparable and greater than 95% for all groups. At 7 years, cardiac survival (homograft, 96.3% +/- 3.7%; Ross procedure, 90.6% +/- 6.3%; stented xenograft, 86.0% +/- 10.3%; Freestyle, 89.2% +/- 10.8%; P = .7) and freedom from reoperation (Ross procedure, 98.5% +/- 1.4%; homograft, 90.6% +/- 5.7%; Freestyle, 88.0% +/- 4.9%; stented xenograft, 90.0% +/- 8.0%; P = .4) were comparable. Freedoms from significant bleeding events, valve-related neurologic events, or endocarditis were comparable and greater than 95% for all groups.

CONCLUSION

Type of aortic biologic valve for the 45- to 65-year-old patient does not affect midterm survival or valve-related morbidity. Thus the choice of biologic valve for the 45- to 65-year-old patient should be dictated by patient-surgeon preference, ease of implantation, and reoperation until longer comparative studies are available.

Tissue Engineering für Herzklappen und Gefäße

Current prosthetic substitutes for heart valves and blood vessels have numerous limitations such as limited durability (biological valves), susceptibility to infection, the necessity of lifelong anticoagulation therapy (prosthetic valves), and reduced patency in small-caliber grafts, for example. Tissue engineering using either polymers or decellularized native allogeneic or xenogenic heart valve/vascular matrices may provide the techniques to develop the ideal heart valve or vascular graft. The matrix scaffold serves as a basis on which seeded cells can organise and develop into the valve or vascular tissue prior to or following implantation. The scaffold is either degraded or metabolised during the formation and organisation of the newly generated matrix, leading to vital living tissue. This paper summarises current research and first clinical developments in the tissue engineering of heart valves and vascular grafts.

Fresh homografts obtained through a national organ-sharing programme for repair of congenital heart disease

Homografts have been used in congenital cardiac surgery for over 30 years. We utilized the resources of a national organ-sharing programme to obtain fresh homografts and report their use in correcting cardiac pathologies in 20 children between March 2001 and May 2003. In 16 patients, a valved conduit was used to form a connection between the pulmonary ventricle and the pulmonary artery. In three patients, a non-valved aortic conduit was used to form an extra-cardiac Fontan circulation and in one patient, non-valved pulmonary and aortic conduits were used to repair an infected aortic aneurysm. Three patients died following surgery. Survivors were followed up using echocardiography between 2 and 24 months post-surgery. Results demonstrate that, with the help of a national organ-sharing programme, the use of fresh homograft conduits is feasible in a paediatric patient population with reasonable waiting times.

Six-year monitoring of the donor-specific immune response to cryopreserved aortic allograft valves: Implications with valve dysfunction

BACKGROUND

The immune rejection has been anticipated as one of the major causes of allograft aortic valve (AAV) degeneration. The purpose of this study was to prospectively serially measure the magnitude and evolution of the recipient anti-HLA class I antibody response up to 6 years from AAV implant and to correlate serologic data with valve performance by means of a concurrent echocardiographic survey.

METHODS

Cryopreserved AAVs were obtained from multiorgan HLA-typed donors. Nineteen patients younger than 50 years (mean age, 43.3 +/- 8 years) were prospectively studied. After successful surgery, all AAV recipient underwent at 3 and 6 months and each year postoperatively (mean follow-up, 71.9 months) concomitant serum sample collection and two-dimensional transthoracic echocardiography. The presence of anti-HLA antibodies was tested against a panel of lymphocytes obtained from 30 blood donors.

RESULTS

Progressive structural valve deterioration was seen in 6 patients (31.5%) of whom 4 (21%) were reoperated. All pretransplant recipients sera were panel-reactive antibody negative. Seventeen patients (89.4%) demonstrated significant panel-reactive antibody levels, which peaked at 6 months postoperatively, declined from 6 to 24 months, and slowly decreased afterward. In 14 of 19 cases (73.6%) donor-specific HLA antibodies were identified. A strong immunization (6-year persistence of panel-reactive antibody > 70% and peak panel-reactive antibody > 80%) was detected in 31.5% and 36.8% of recipients, respectively. Strong immunization was found to be significantly associated with progressive structural deterioration.

CONCLUSIONS

The immune reaction after cryopreserved AAV implantation is a peculiar long-lasting response occurring in the majority of recipients younger than 50 years of age. An association between a sustained and pronounced immunization and an aggressive AAV degeneration was observed.

Cryopreserved arterial allografts for in situ reconstruction of infected arterial vessels

OBJECTIVE

To review our experience of using cryopreserved allografts for in situ reconstruction in the presence of infection involving the aorta, iliac or femoral arteries.

DESIGN

Retrospective clinical study.

METHODS

From 3/2000 to 8/2003 all patients with mycotic aneurysms or secondary infection following earlier prosthetic replacement were treated with cryopreserved human allografts. Forty-two patients, 39 (93%) with a prosthetic graft infection and 3 (7%) with a mycotic aneurysm of the abdominal aorta were treated. Six (14%) had aorto-enteric fistulas, 5 (12%) had ruptured aneurysms, and 2 also had vertebral destruction. The median follow-up time was 20 months (range 1-42 months).

RESULTS

Thirty-day mortality was 14%. Three patients died due to multi-organ failure, two patients died from hypovolaemic shock due to allograft rupture and one from rupture of the native aorta. The overall mortality was 24% (four additional patients). Graft patency was 100% at 30 days and 97% at follow up in the survivors. The mean actuarial survival time was 32 months (95% CI=27-37 months).

CONCLUSIONS

Cryopreserved allografts for the in situ reconstruction of infected arteries or grafts have acceptable intermediate results.

Allograft Aortic Valve Replacement in the Adult: A Review

Aortic valve replacement using an allograft has been used continuously for over 40 years. Its advantages are excellent haemodynamic function, low thrombogenicity, resistance to infection and avoidance of the complications of anticoagulation. The main concern is its long-term durability, with the high hazard phase for failure between 10 and 20 years. We have only recently been able to judge the true long-term behaviour of the contemporary allograft with two recently published series of patients having reached follow-up beyond 20 years in significant numbers. This review of allograft aortic valve replacement in the adult covers the areas of history, benefits, techniques of sterilisation and preservation, operative methods and outcomes.

Viability and histologic structure of porcine valves after cryopreservation

BACKGROUND

Increased awareness of the limitations of current cardiac valve substitutes has generated a renewed interest in the use of allograft valves. The effects of currently used preservation techniques on the viability of the valve leaflets and the longevity of the implantation however remain controversial. The objective of this study is to analyze the influence of ischemic time, sterilization methods with or without fungicides, and storage procedures on the viability of the valve leaflets and on the histologic structure of the arterial wall, valve leaflet, and myocardium.

METHODS

The tissue sources were hearts from 40 pigs with 1 hour of warm ischemic time. The aortic and pulmonary valves were dissected after 2 or 24 hours of cold ischemic time. They were stored in antibiotic solution for 20 hours at 4 degrees C with or without an antifungal agent. The samples were cryopreserved using a programmed temperature decrease method. After 1 week of storage in a liquid nitrogen tank, either in a gas or a liquid phase, the cardiac valves were slowly thawed and examined.

RESULTS

Pulmonary valves showed greater viability than aortic valves. Decreased cellular viability was observed independent of cold ischemic time, treatment with amphotericin B, or the storage method used. Treatment with or without amphotericin B had no influence on cellular viability. Conversely it was observed that there was greater cellular viability among those valves stored in a liquid phase. As far as the histologic structure of the valve is concerned we did not observe any influence either in the treatment with amphotericin B or the storage method used although it was observed that reduction of the cold ischemic time minimized histologic injury.

CONCLUSIONS

Optimization of preservation methods may decrease the negative effects of cryopreservation on cell viability and histologic structure of the valve.

Depopulated vena caval homograft: a new venous conduit

OBJECTIVE

Completion of the Fontan procedure is frequently performed by using an extracardiac conduit between the inferior vena cava and the pulmonary artery. Most centers use a polytetrafluoroethylene graft for the extracardiac conduit, and because re-endothelialization is unlikely, anticoagulation is used for a variable period. This study explores the use of an alternate large-caliber venous conduit.

METHODS

The superior vena cava was replaced in 8 minipigs with either a polytetrafluoroethylene interposition graft (2 pigs) or a depopulated (acellular), cryopreserved superior vena caval homograft (6 pigs). After 6 months, the animals were killed, and the grafts were examined for patency and histology, including immunostaining. No anticoagulation was used.

RESULTS

Polytetrafluoroethylene grafts have a cross-sectional luminal narrowing, ranging from 16% to 40%. Histology showed only partial intimal ingrowth, with excessive subendothelial fibrosis and early calcification. In contrast, the depopulated venous homografts showed minimal luminal narrowing, ranging from 2% to 9%. These grafts were completely repopulated by the recipient with an endothelial lining, which stained positively for factor VIII, and a subendothelial region appropriately recellularized by myofibroblasts, which stained positively for smooth muscle actin and procollagen. There was no evidence of an immune response to the venous homografts, as judged by staining for T-cell surface antigen, CD4, and CD8. Thrombus was not seen in any of the grafts.

CONCLUSION

Depopulated, cryopreserved vena caval homografts might be superior conduits for cavopulmonary connection during completion of the Fontan operation by using the extracardiac conduit technique.

Comparison of autograft and allograft aortic valve replacement in children

OBJECTIVE

This study was undertaken to compare the clinical and hemodynamic results following aortic valve replacement with a pulmonary valve autograft (Ross procedure) or an allograft valve in children.

METHODS

The records of 107 pediatric aortic valve replacements from 1994 through 2001 were reviewed, including 78 autografts and 25 allografts. Four mechanical aortic valve replacements performed during this period were excluded from analysis.

RESULTS

There were 3 perioperative deaths and 1 late death. Reoperations were required in 5 autograft recipients (with autograft preservation in 4) and in 3 allograft recipients (all requiring valve re-replacement). Seven-year survival (96% in both groups) and reoperation-free survival (88% in the autograft group; 73% in the allograft group, P =.5) were not significantly different. Serial echocardiographic studies showed that in the autograft group, left ventricular outflow tract maximal velocity (2.0-1.8 m/s, P =.02) and left ventricular thickness (10.1-8.4 mm, P <.0001) fell significantly. In the allograft group, maximal velocity (2.3-3.0 m/s, P =.03) increased significantly and left ventricular thickness (9.5-9.0 mm, P =.2) showed minimal change. Analysis according to preoperative physiology (aortic stenosis versus insufficiency), congenital cardiac anatomy, number or type of previous operations, age of patient, and use of balloon valvotomy did not predict outcomes.

CONCLUSIONS

Aortic valve replacement with either the autograft or allograft provides excellent clinical results in children during an intermediate duration of observation. The Ross procedure achieves a superior hemodynamic result, which may be clinically important with longer follow-up.