Advantages of decellularized bovine pericardial scaffolds compared to glutaraldehyde fixed bovine pericardial patches demonstrated in a 180-day implant ovine study

Glutaraldehyde (GA)-fixed bovine pericardial patches remain the cardiovascular industry standard despite reports of degradation, thickening, inflammation, calcification and lack of tissue remodelling. Decellularization provides the opportunity to attenuate some of these immune-mediated processes. This study compared the mechanical and morphological integrity of bovine pericardium that is GA-fixated (Glycar® patches) or decellularized (BPS), using a proprietary protocol, following implantation in an ovine model. The impact of the processing methods on tissue strength and morphology was assessed prior to implantation. Pericardial patches were then implanted in the descending aorta and main pulmonary artery of juvenile sheep (n = 6 per group) for 180 days, and clinically evaluated using echocardiography. At explanation, patches were evaluated for strength, calcification and biological interaction. Histology demonstrated a wave-like appearance of well-separated collagen fibers for BPS scaffolds that provided pore sizes adequate to promote fibroblast infiltration. The collagen of the Glycar® patches showed loss of collagen fiber integrity, making the collagen densely compacted, contributing to insignificant recipient cell infiltration. The clinical performance of both groups was excellent, and echocardiography confirmed the absence of aneurysm formation, calcification and degeneration. Explanted Glycar® patches demonstrated cells in abundance within the fibrous encapsulation that separated the implant from the host tissue. More importantly, the fibrous encapsulation also contributed to patch thickening of both the explanted aorta and pulmonary patches. The decellularized pericardial scaffolds demonstrated recellularization, resistance to calcification, re-endothelialization and adequate strength after 180-day implantation. The proprietary decellularization protocol produced pericardial scaffolds that could be considered as an alternative to GA-fixed pericardial patches.

The sequential effects of a multifactorial detergent based decellularization process on bovine pericardium

Decellularization is a promising method for obtaining extracellular matrix scaffolds (ECM) to be used as replacement material in reconstructive procedures. The effectiveness of decellularization and the alterations to the ECM vary, depending on several factors, including the tissue source, composition and density. With an optimized decellularization process, decellularized scaffolds can preserve the spatial and temporal ECM microenvironment, which play an integral role in modulating cell migration, proliferation and differentiation. The exploration of a variety of decellularization protocols has led to mixed outcomes and comparisons between decellularization protocols could not attribute these differences to any single step in a multiple-step process. This study aimed to characterize the effects of each step of a multifactorial decellularization method on the scaffold structure and mechanical integrity of bovine pericardium. Each step of the decellularization process and the effect on the tissue was assessed using hematoxylin and eosin staining, electron microscopy, total protein, ECM protein and triglyceride quantification. The biomechanical properties were assessed using uniaxial tensile strength testing. Cell lysis occurred mainly during the detergent and alcohol steps. Collagen structural damage occurred during the detergent and alcohol steps, with no significant decreased in collagen concentration. No significant damage to elastin could be shown throughout the process, however glycosaminoglycans were significantly removed by detergent treatment. Triglycerides were removed mostly by the alcohol treatment. The strength of the pericardium decreased somewhat after each step of the protocol. It is important to characterize each decellularization protocol with regards to the decellularization efficiency and the effect on the ECM proteins structure and function to accurately evaluatein vivooutcomes.

Tissue engineered aortic valve

Several prostheses are available to replace degenerative diseased aortic valves with unique advantages and disadvantages. Bioprotheses show excellent hemodynamic behavior and low risk of thromboembolic complications, but are limited by tissue deterioration. Mechanical heart valves have extended durability, but permanent anticoagulation is mandatory. Tissue engineering created a new generation heart valve, which overcome limitations of biological and mechanical heart valves due to remodelling, regeneration and growth potential. Several publications are available in using tissue engineered heart valves in right ventricular outflow tract reconstruction. Limited experiences are available on these heart valves implanted into the systemic circulation. This overview shows the current state on the development of tissue engineered aortic heart valves.

Clinical results of implanted tissue engineered heart valves

Since the first heterotopic implantation of a biological heart valve in 1955 by Murray, bioprostheses have been steadily improved. For allografts different methods have been evaluated and modified to stabilize and preserve the available tissue. Xenografts were fixed to cross-link the connective tissue as well as prevent immunogenic reactions. Nevertheless, gluteraldehyde fixation leads to structural deterioration, which could only be partially reduced by different kinds of anti-mineralization treatment. Due to preservation and fixation, allografts and xenografts become non-viable bioprostheses with a lack of remodelling, regeneration and growth. Tissue engineering is a possible key to overcome these disadvantages as it will provide living tissue with remodelling, regeneration and growth potential. This overview will look at the key points to provide such tissue engineered heart valves by creating an appropriate scaffold where cells can grow, either in vitro or in vivo and remodel a neo-scaffold which will lead to a functional autologous heart valve, and show initial clinical results.

Substituição valvar cardíaca em ovinos – Descrição da técnica operatória e análise dos resultados

Visando avaliar um protocolo experimentalde pesquisa com próteses valvares cardíacas emovinos, as técnicas cirúrgicas de substituição valvarpulmonar, aórtica e mitral de 58 cirurgias cardíacas foramanalisadas. Através de procedimentos padronizadosos ovinos (idade 18 ± 7 semanas e o peso 30 ± 9.9kg) foram submetidos ao implante de próteses valvaresbiológicas. Quarenta animais receberam prótesesvalvares pulmonares, 14 animais receberam prótesesaórticas e quatro animais receberam próteses mitrais.O quarto espaço inter-costal foi considerado de eleiçãopara realização das três técnicas operatórias avaliadas.O método de circulação extracorpórea (CPB)por canulação da aorta descendente e do átrio direitofoi considerado rápido e seguro. O tempo de CPB durantea substituição valvar pulmonar foi de 34 ± 14minutos e a mortalidade 7,5%. A substituição valvaraórtica, com implante subcoronariano, teve tempo deCPB 119 ± 5 minutos e mortalidade de 57%. Durantea substituição valvar mitral o tempo de CPB foi 74 ±22 minutos e mortalidade 50%. A técnica de implantevalvar pulmonar foi muito eficiente, entretanto a altamortalidade das técnicas de implante valvar aórtico emitral, associadas à maior complexidade cirúrgica eelevado tempo de CPB, faz necessário refinamentostécnicos para melhorar o aproveitamento dos animaisnas cirurgias das valvas cardíadas esquerdas.

Barrier function of the gut and multiple organ dysfunction after cardiac surgery

We studied the influence of sequential involvement of the gastrointestinal (GI) tract on the development of multiple organ dysfunction (MOD) after cardiopulmonary bypass (CPB). One hundred and forty-six patients undergoing elective cardiac surgery were included in this prospective observational study. Standardized oral inert-sugar tests (sucrose, lactulose, mannitol, sucralose) were performed before and after CPB in different patients. Enzyme-linked immunosorbent assay of plasma levels of endotoxin core antibodies (EndoCAb) were performed peri-operatively. The functional mucosal surface was calculated from the amount of mannitol absorbed from the GI tract. Lower urine concentrations of absorbed mannitol were observed pre-operatively in patients developing MOD. In binary logistic regression this was an independent parameter. Decreased plasma concentrations of EndoCAb after surgery were seen in every patient, but were more significant in patients developing MOD. A reduced pre-operative functional mucosal surface may predict the early occurrence of MOD after surgery.

Is there a possibility for a glutaraldehyde-free porcine heart valve to grow?

OBJECTIVE

A challenging issue is to create a heart valve with growth and remodeling potential, which would be of great interest for congenital heart valve surgery. This study was performed to evaluate the growth and remodeling potentials of a decellularized heart valve.

METHODS

In 4 juvenile sheep (age 12 +/- 1 weeks) with a weight of 24.3 +/- 4.4 kg, a 17-mm diameter decellularized porcine valve was implanted as pulmonary valve replacement. Valve growth was evaluated by transthoracic echocardiography. At explantation, valves were evaluated by gross examination, light microscopy (hematoxylin and eosin, von Kossa, Sirius red, Weigert and Gomori staining), electron microscopy and immunohistochemistry. Atomic absorption spectrometry was performed to evaluate calcium content.

RESULTS

All animals showed fast recovery. The mean follow-up was 9.0 +/- 1.8 months. All sheep at least doubled their weight (54.3 +/- 9.2 kg). Echocardiography showed no regurgitation and a flow velocity of 0.7 +/- 0.1 m/s at the latest follow-up. The valve diameter increased from 17.6 +/- 0.5 to 27.5 +/- 2.1 mm (p < 0.018). Gross examination showed a similar wall thickness of the implanted valve and native pulmonary wall, with smooth and pliable leaflets. Histology showed a monolayer of endothelial cells, fibroblast ingrowth and production of new collagen. No calcification was seen at von Kossa staining, confirmed by low calcium content levels of the valve wall and leaflets at atomic absorption spectrometry.

CONCLUSIONS

This glutaraldehyde-free heart valve showed not only the absence of calcification, but also remodeling and growth potential.

Impact of Implantation Technique on Hemodynamic Results of the Pericarbon Freedom Stentless™ Valve

BACKGROUND

The Pericarbon Freedom stentless valve has shown excellent hemodynamic results in the midterm course. However, there is no information as to whether a continuous or interrupted suture technique at the inflow site has an impact on postoperative hemodynamics.

METHODS

139 patients were enrolled in a non-randomized, prospective matched trial. An interrupted suture line technique was used in 68 patients and a continuous suture line technique was used in 71 at the inflow site. Isolated valve replacement was performed in 70.4% of the continuous and 67.6% of the interrupted suture group. Pre- and postoperative hemodynamics and one-year follow-up were obtained by echocardiography and expressed as mean and peak gradients and grade of regurgitation.

RESULTS

No significant difference between continuous and interrupted suture techniques were noted with respect to mean (11.8 +/- 6.3 vs. 12.5 +/- 6.2 mm Hg, p = 0.251) and peak gradients (21.0 +/- 9.6 vs. 22.0 +/- 10.9 mm Hg, p = 0.292) as well as to the degree of regurgitation. Bypass and cross-clamping times decreased by 22.4 and 20.6 minutes, respectively, with the use of the continuous suture technique. One year follow-up showed a further, significant decrease of mean and peak gradients.

CONCLUSIONS

The Pericarbon Freedom stentless valve appears to offer excellent postoperative performance. The suture line technique at the inflow site does not result in any hemodynamic differences.

Results of a Decellularized Porcine Heart Valve Implanted into the Juvenile Sheep Model

Objective: This study was performed to evaluate the possibility of creating a glutaraldehyde-free porcine xenograft to improve long-term durability. Methods: A decellularized porcine pulmonary valve was implanted into the right ventricular outflow tract of 7 juvenile sheep. Valves were explanted after 3 months (n = 4) and 6 months (n = 3). Evaluation was performed by gross examination, radiography, histology (hematoxylin-eosin and Sirius red staining), and immunohistochemistry. Quantitative determination of calcium content was investigated by atomic absorption spectrometry. Results: All animals showed fast recovery without complications. At explantation, all decellularized valves showed smooth and pliable leaflets without evidence of thrombosis. The valve wall was also smooth and pliable without hardness. Light microscopy showed a monolayer of host endothelial cells covering the inner surface of the heart valves and repopulation of host fibroblasts into the deeper layers. Sirius red staining enabled visualization of the production of new collagen. Radiographic results showed an absence of calcification, confirmed by the low calcium levels (1.08 0.28 m g/g and 0.73 0.31 m g/g at 3 and 6 months, respectively) revealed by atomic absorption spectrometry. Conclusions: The results with the juvenile sheep model showed that decellularized heart valves are recellularized in vivo. Host endothelial cells form a monolayer on the inner surface of the valve matrix. Furthermore, host fibroblasts repopulate the valve matrix and produce collagen; thus, a remodeling potential can be expected.

Chirurgie der Herzinsuffizienz - Stellenwert der Computertomographie in der prä- und postoperativen Diagnostik

The treatment of advanced, drug resistant congestive heart failure gains in importance in the field of cardiac surgery. Cardiac imaging for preoperative assessment and follow-up focuses on the determination of ventricular volumes and function as well as on the detection of postoperative complications. Computed tomography (CT) is highly accurate irrespective of the individual patient's anatomic situation, has a low examiner dependence and short examination time, does not require an arterial vascular access and can be performed in patients with metal implants. CT is the modality of choice in the follow-up of heart transplants to detect extracardiac and cardiac complications including coronary calcifications as an early sign of transplant vasculopathy. In addition, CT visualizes the elements of mechanical assist devices and can identify their possible local cardiac and mediastinal complications. CT can detect fibrolipomatous involution of the mobilized muscle flap in dynamic cardiomyoplasty and can depict fibrous reactions along the epicardial mesh implant in passive cardiac containment. Further indications include assessment of typical local postoperative complications, such as intrathoracic infection and mediastinal bleeding, intracardiac thrombus formation or pericardial effusion. CT is routinely used for evaluating bypass patency but is limited in assessing associated valve defects since it does not visualize flow.

Visualization of the pulmonary valve using cine MR imaging

PURPOSE

To evaluate the capability of bright-blood cine MR to directly visualize the leaflets of the valve replacement in pulmonary position following Ross operation.

MATERIAL AND METHODS

Long and short axis views of the pulmonary valve were obtained in 10 normal subjects and 14 patients after Ross operation. Valve morphology and function were analyzed and signal-to-noise (SNR) and contrast-to-noise ratios (CNR) were calculated. Flow measurements were performed in the pulmonary trunk to assess pulmonary regurgitation.

RESULTS

In all subjects, tricuspid morphology of the pulmonary valve was visualized. SNR of the leaflets in normal subjects (9.8 +/- 3.0) and in patients after Ross operation (7.5 +/- 2.2) differed significantly from blood (12.6 +/- 3.2 and 11.3 +/- 2.5, respectively, p < 0.05). Valvular regurgitation was seen in 5 patients as an insufficient closure of the valve which was confirmed by flow measurements.

CONCLUSION

Cine MR enables in-plane visualization of the pulmonary valve and allows for functional and morphological evaluation in patients after pulmonary valve surgery.

Visualization of the pulmonary valve using cine MR imaging

PURPOSE

To evaluate the capability of bright-blood cine MR to directly visualize the leaflets of the valve replacement in pulmonary position following Ross operation.

MATERIAL AND METHODS

Long and short axis views of the pulmonary valve were obtained in 10 normal subjects and 14 patients after Ross operation. Valve morphology and function were analyzed and signal-to-noise (SNR) and contrast-to-noise ratios (CNR) were calculated. Flow measurements were performed in the pulmonary trunk to assess pulmonary regurgitation.

RESULTS

In all subjects, tricuspid morphology of the pulmonary valve was visualized. SNR of the leaflets in normal subjects (9.8 +/- 3.0) and in patients after Ross operation (7.5 +/- 2.2) differed significantly from blood (12.6 +/- 3.2 and 11.3 +/- 2.5, respectively, p < 0.05). Valvular regurgitation was seen in 5 patients as an insufficient closure of the valve which was confirmed by flow measurements.

CONCLUSION

Cine MR enables in-plane visualization of the pulmonary valve and allows for functional and morphological evaluation in patients after pulmonary valve surgery.

Reoperation in a Jehovah's Witness 22 years after aortic allograft reconstruction of the right ventricular outflow tract

We report the case of a 29-year-old male Jehovah's Witness who presented with hemolysis and right heart failure as a consequence of extreme calcification of an aortic valve-containing allograft and Dacron prosthesis that had been placed 22 years earlier to repair tetralogy of Fallot. Reoperation had been denied by several other centers, because of the patient's refusal to undergo blood transfusion. For 2 weeks preoperatively, we raised the patient's hemoglobin level by treating him with recombinant erythropoietin, oral iron, and folic acid. At surgery, under normothermic cardiopulmonary bypass, we replaced the aortic allograft in the right ventricular outflow tract with a cryopreserved pulmonary allograft, also containing a valve. The postoperative course was uneventful, and the patient was released from the hospital on the 13th postoperative day in excellent condition.

In vitro hydrodynamics of a decellularized pulmonary porcine valve, compared with a glutaraldehyde and polyurethane heart valve

BACKGROUND

Hydrodynamic performance of a decellularized pulmonary porcine valve was evaluated with a computer versatile pulse duplicator and compared to glutaraldehyde fixated stentless porcine bioprosthesis and a polyurethane heart valve.

METHODS

Decellularized pulmonary porcine matrices (Group I, n = 5) were treated chemically to become cell-free collagen matrices. The findings of this heart valve were compared with aortic glutaraldehyde treated porcine prostheses (Group II, n = 5) and polyurethane three leaflet valve prostheses (Group III, n = 1). Measurements were performed in 0.9% saline test fluid at room temperature. Measurements compared were closing time, closing volume, systemic pressure difference and energy losses. Each valve was measured 6 times with 70 beats/minute, a stroke volume of 70 ml corresponds to a cardiac output of 4.9 L/minute.

RESULTS

Group I and group III showed no significant differences between parameters. The measured closing time was significantly different (p < 0.001) between group I and II, respectively 24.333 and 53.600 ms and group II and III respectively 53.600 and 24.000. Difference in closing volume was significant (p < 0.05) between groups II and I respectively 3.67 and 0.68 ms and group II and III respectively 3.67 and 0.71. Systolic mean pressure gradient was 18.25 +/- 1.04 mm Hg in group II which was significantly different (p < 0.001) from groups I and III, respectively 10.65 +/- 0.29 mm Hg and 7.70 +/- 0.30 mm Hg.

CONCLUSIONS

Decellularized pulmonary porcine valves showed the same excellent performance as polyurethane valve prosthesis, which are superior to the investigated glutaraldehyde fixed xenograft.

Lack of calcification of tissue engineered heart valves in juvenile sheep

The presence of viable endothelial cells may support longer durability and the absence of calcification in valve prostheses. This study shows the development of a tissue engineered heart valve, constructed from viable autologous endothelial cells on an acellular matrix and its evaluation in juvenile sheep. In 3-month-old sheep (n = 8) a piece of vein was harvested to culture autologous endothelial cells. A porcine acellular matrix was reendothelialized and implanted in juvenile sheep as pulmonary interposition. The valves were explanted after 1 week, 3 and 6 months. Examination was performed by X-ray, light microscopy, and atomic absorption spectrometry. Reendothelialization mean rate was 10.3 x 10(5) cells/cm(2) with a mean endothelial cell viability of 95.5% (0.98 x 10(5) cells/cm(2)). X-ray examination showed no cusp calcification at 1 week, 3 and 6 months, which was confirmed by light microscopy. Immunostaining for factor VIII demonstrated colonization of viable mature autologous endothelial cells on the heart valve after the seeding process. The atomic absorption spectrometry showed no significant increase of the calcium content after 3 (P value >.1) and 6 months (P value >.1) compared with nonimplanted tissue engineered heart valves. The tissue engineered valve showed no cusp calcification in the juvenile sheep after 3 and 6 months.

Magnetic resonance imaging of stentless xenografts for reconstruction of right ventricular outflow tract

The objective was to overcome allograft shortage during the Ross operation; stentless xenografts were carefully evaluated for hemodynamic behavior and valve deterioration during medium term follow-up. Between January 10, 1994 and January 4, 1996 nine adult patients (age 31-51 years) underwent aortic valve replacement with an autologous pulmonary valve and right ventricular outflow tract reconstruction with the Edwards Prima or Medtronic Freestyle xenograft. One patient was dead early and one late, both from noncardiac reasons. Forty-eight to 66 months follow-up was available for 7 patients and was performed with physical examination in the outpatient clinic, transthoracic echocardiography (TTE), and magnetic resonance imaging (MRI). Two patients received 29-mm valves and the remaining 27-mm valves. No reoperation became necessary during follow-up. Preoperative left ventricular ejection fraction ranged from 20% to 84%, median 61%, mean 59% +/- 18%. At latest follow-up left ventricular ejection fraction was 49% to 70%, median 57%, mean 58% +/- 8%. TTE showed no calcification of the xenograft wall or cusps. MRI revealed good autograft function with no evidence of stenosis in any patient. Four patients showed no and three trivial regurgitation. Right ventricular outflow tract-stenosis could not be seen in any patient. Calculated gradients of the xenograft valves ranged from 2 to 6 mm Hg, median 3 mm Hg (mean 3.1 +/- 2.4 mm Hg) and calculated EOA ranged from 2.0 to 4.0 cm(2), median 2.8 cm(2). MRI supported these findings and showed pliable xenograft cusps in all patients. Right ventricular function was well preserved in all patients. In adult patients right ventricular outflow tract reconstruction with stentless xenografts can be performed safely and intermediate-term results are encouraging. During medium-term (5-7 years) follow-up no calcification or deterioration of valve function occurred with excellent hemodynamic behavior.

Influence of ischemic time and temperature on endothelial cell growth after transport

BACKGROUND

The preparation of tissue-engineered material is a complex procedure. The possibility to transport tissue between laboratories without losing endothelial cell (EC) function was examined.

METHODS

In 3 month old juvenile sheep (n = 6) a piece of vein (n = 14) was harvested and transported over 900 km to the tissue laboratory in Dulbecco's Modified Eagle's Medium (= DMEM). Vein material of each animal was transported at 4 degrees C (Group I, n = 6) and 25 degrees C (Group II, n = 8). EC growth potential was evaluated in function of the medium temperature and the ischemic time (between 8-24 hours). At the end of the first passage the EC of Group I and II were put together to save autologous serum of the sheep. After the 2nd passage the EC were cryopreserved at -80 degrees C to evaluate if EC viability would change.

RESULTS

The growth potential of hypothermic Group I was equal in 16.7% (n = 1), higher in 33.3% (n = 2) and lower in 50% (n = 3) than Group II which had the same ischemic time during transport. Increase in ischemic time up to 24 hours showed no decrease of growth potential. Cryopreservation had no significant influence on EC viability. Viability at the end of the second passage, after recultivation and at the end of the third passage was 97.4% +/- 1.52, 95.5% +/- 1.34 and 94.5% +/- 1.08 respectively.

CONCLUSIONS

In sheep there is no need to transport the EC at a temperature of 4 degrees C. Up to 24 hours growth potential and viability are maintained also at 25 degrees C.

A reliable test to detect impending pump failure during long-term support on the Novacor N100 Left Ventricular Assist System

The Durastudy is a new surveillance protocol to detect impending pump failure in Novacor N100 Left Ventricular Assist Systems implanted for the long term. Our patient, a 54-year-old man with a history of dilated cardiomyopathy and contraindications for heart transplantation, received a Novacor pump in May 1995 and did not experience sustainable ventricular recovery during the subsequent 3 years. After more than 3 years of support, symptoms of pump wear were detected in this patient, through application of the Durastudy protocol. This enabled us to electively exchange the pump at 3.8 years. Our patient remained in New York Heart Association functional class I until he died in July 1999 of causes unrelated to the pump, after some 1,514 days of support. This, we believe, still constitutes a world record.

Diagnosis and management of left ventricular assist device valve-endocarditis: LVAD valve replacement

A 57-year-old man who has been wearing a Novacor N100 left ventricular assist device (LVAD) for more than 3 years suffered from LVAD endocarditis. Only by immunoscintigraphic methods was it possible to localize the septic focus. After successful exchange of in- and outflow tract valves, the infection was eradicated. Microscopic investigation confirmed the scintigraphic findings: Gram-positive bacteria were found. The valves showed no gross degenerative lesions after more than 1,100 days of implantation. The patient is now doing well.

Tricuspid and pulmonary valve involvement in carcinoid disease

We report the case of a 62-year-old woman in whom carcinoid disease had been diagnosed 6 years earlier. She subsequently developed tricuspid and pulmonary valve disease. Both valves were incompetent and mildly stenotic. The tricuspid valve required surgery; the pulmonary vaive was explored but not treated. Valve surgery in patients with carcinoid disease is discussed in light of the prognosis of these patients, the timing of valvular lesion presentation, and the choice of prosthesis. The justification for multiple-valve procedures in such cases is also considered.