New outlook on pericardial substitution after open heart operations

Recurrent Cardiac Constriction after Implantation of an Expanded Polytetrafluoroethylene Surgical Membrane

One of the challenges compounding the complexity of reoperative cardiac surgery is the surgical adhesion, which can be responsible for adverse intraoperative events. Implantation of a substitute neo-pericardium has become a frequently used solution, with currently rising numbers of reoperations. We report the case of a 38-year-old man who developed recurrent delayed cardiac constriction following the implantation of an expanded polytetrafluoroethylene neo-pericardium. Careful preoperative planning is recommended to plan the optimal method of pericardioplasty, taking into account the pros and cons of each available material.

Use of Pericardium for Cardiac Reconstruction Procedures in Acquired Heart Diseases-A Comprehensive Review

BACKGROUND

Reconstruction of cardiac structures has been the goal of many surgeons even before the advent of open-heart procedures with cardiopulmonary bypass. Unsatisfactory results with synthetic materials has switched the attention to biological tissues, among which pericardium, either autologous or of animal origin, has been widely used as patch material.

METHODS

We have reviewed the literature to assess the effective role of pericardial tissue in the correction of various acquired cardiac lesions. Particularly, special attention was given not only to established techniques but also to detect any peculiar and unusual application of pericardium.

RESULTS

Autologous pericardium is frequently used as patch material particularly when limited valvular lesions must be corrected, while xenograft pericardium appears particularly useful in patients with endocarditis and extensive destruction of the intracardiac structures by infection and abscesses. Pericardium is an extremely versatile material owing to its pliability and strength; however, it tends to calcify in the long term when in contact with blood, although stability of the repair is maintained in most cases.

CONCLUSIONS

Pericardium plays an important role in various cardiac and aortic pathologies. Tissues resistant to fibrosis and calcification to be used as patch material are the ideal solution for more successful cardiac reconstruction procedures and will hopefully be provided by the ongoing research.

Bioengineered tissue solutions for repair, correction and reconstruction in cardiovascular surgery

The treatment of cardiac alterations is still nowadays a dramatic issue in the cardiosurgical practice. Synthetic materials applied in this surgery have failed in their long-term therapeutic efficacy due to low biocompatibility and compliance, especially when used in contractile sites. In order to overcome these treatment pitfalls, novel solutions have been developed based on biological tissues. Patches in pericardium, small intestinal submucosa, as well as engineered tissues of myocardium, heart valves and blood vessels have undergone a large preclinical investigation in regenerative medicine studies. Clinical translation has been started or reached by several of these new bioengineered treatment alternatives. This review will describe the preclinical and clinical experiences realized so far with the application of biological tissues in cardiovascular surgery. It will depict the progressive steps realized in the evolution of this research, as well as it will point out the challenges yet to face in order to generate the ideal biomaterial for cardiovascular repair, corrective and reconstructive surgery.

An Absorbable Hydrogel Spray Reduces Postoperative Mediastinal Adhesions After Congenital Heart Surgery

BACKGROUND

Adhesions encountered during reoperative cardiac surgery can prolong operative time and increase operative risk. The purpose of this clinical study was to investigate the antiadhesion property of a synthetic bioabsorbable polymer spray after cardiac reoperations in infants.

METHODS

A prospective randomized double-blinded study was designed. Forty infants requiring staged cardiac operations were randomly allocated to a study group (n = 20) or a control group (n = 20). The appropriate volume of the polymer was sprayed onto the mediastinal surfaces before chest closure after the first surgical procedure in the study group. At reoperation, adhesions were evaluated by a blinded investigator following a 5-grade scoring system. Five predetermined anatomic areas were scored. Incision to extracorporeal circulation time was also analyzed.

RESULTS

In all, 40 subjects were enrolled into the study. Four babies died before the second operation. Three others were missed for reevaluation. The control group (n = 16) had longer incision to extracorporeal circulation time (38 ± 10 minutes) than the study group (n = 17; 23 ± 6 minutes; p < 0.001). The control subjects had significantly more severe adhesions than the study group at all five mediastinal areas: (1) retrosternal (p < 0.001); (2) base of the heart (large vessels [p < 0.05]); (3) right side (p < 0.01); (4) left side (p < 0.02); and (5) diaphragmatic side of the mediastinum (p < 0.001).

CONCLUSIONS

The use of synthetic bioabsorbable polymer sealant spray at the end of primary pediatric cardiac surgery reduces the intensity of mediastinal adhesions and the reentry time in infants undergoing repeat median sternotomy.

Limiting Pericardial Adhesions after Coronary Artery Bypass: Experimental Study

Retrosternal pericardial adhesion formation constitutes a major hazard during re-do coronary artery surgery. To determine whether an onlay parietal pleural flap over the internal thoracic artery bed would reduce pericardial adhesions after coronary artery grafting, 16 sheep underwent a median sternotomy and both internal thoracic arteries were harvested. On the randomly selected study side, a dissected pleural flap was used to cover the internal thoracic artery bed, the opposite side was left uncovered as a control. Half of the sheep were sacrificed at a median of 102 days (range, 93–109 days), the remainder at a median of 176 days (range, 165–183 days). Two independent observers blinded to the initial operation scored the degree of postoperative adhesions. There was a significant decrease in adhesion formation on the study side covered by the mobilized pleural flap, compared to the control side. There were no increases in pulmonary morbidity or sternotomy wound problems from raising the lateral pleural flap. This simple technique appears to be an effective method of preventing adhesion formation following coronary artery bypass grafting utilizing the internal thoracic artery.

European clinical experience with REPEL-CV®

The objective of the feasibility study was to gain European clinical experiences with REPEL-CV for reducing postoperative adhesions in pediatric patients undergoing cardiovascular surgery. The pediatric patient population included patients requiring staged cardiovascular sternotomy procedures where it was anticipated that the second sternotomy procedure would be performed 2-8 months subsequent to the initial procedure. At the time of the second sternotomy procedure, 13 out of 15 (86.7%) patients had no Grade 3 ('severe') adhesions. The mean percentage of the investigational surgical site with severe adhesions was 11%. There were five serious adverse events. All were anticipated (identified in the protocol and the investigator's brochure) and were considered by the investigators to be 'definitely not related' to the study device. Based on the incidence and extent of 'severe' adhesions and the safety profile for REPEL-CV as demonstrated in this study, the effectiveness and safety of REPEL-CV have been further demonstrated.

A review of the current status of pericardial closure following cardiac surgery

Some cardiac surgeons prefer to close the pericardium whenever possible following surgery, others specifically avoid this practice, and still others believe that neither alternative has any meaningful influence on clinical outcomes. Unfortunately, scientific evidence supporting either approach is scarce, making a consensus regarding best practice impossible. In this article, the known functions of the native intact pericardium are summarized, and the arguments for and against pericardial closure after surgery are examined. In addition, the techniques and materials that have been utilized for pericardial closure previously, as well as those that are currently being developed, are assessed.

Properties And Prevention of Adhesions Applications of Bioelastic Materials

The origins, syntheses, variable composition and physical properties of bioelastic materials are discussed. The latter includes their capacity to undergo inverse temperature transitions to increased order on raising the temperature and to be designable to interconvert free energies involving the intensive variables of mechanical force, temperature, pressure, chemical potential, electrochemical potential and light.

Bioelastic materials include analogues and other chemical variations of the viscoelastic polypeptide, poly(Val-Pro-Gly-Val-Gly), and cross-linked elastomeric matrices thereof. This parent material has been shown to be remarkably biocompatible; it can be minimally modified to vary the rate of hydrolytic breakdown; it can contain enzymatically reactive sites; and it can have cell attachment sites included which promote excellent cell adhesion, spreading and growth to confluence.

One specific application is in the prevention of postoperative adhesion. There are some 30,000,000 per year surgical procedures in this country and a large portion of these would benefit if a suitable material were available for preventing adhesions. Bioelastic materials have been tested in a contaminated peritoneal model, and promising preliminary studies have been carried out in the rabbit eye model for strabismus surgery. In the peritoneal model, 90% of the 29 control animals exhibited significant adhesions; whereas, only 20% of the 29 animals using gas sterilized matrices had significant adhesions. On the basis of this data, it appears that cross-linked poly(VPGVG) is an effective physical barrier to adhesion formation in a trauma model with resulting hemorrhage and contamination.

The potential use of bioelastic materials as a pericardial substitute following the more than 400,000 open heart surgeries per year in the U.S. is under development beginning with the use of bioelastic matrices to prevent adhesions to the total artificial heart being used as a bridge to heart transplantation such that the site will be less compromised when receiving the donor heart.

Bioresorbable adhesion barrier for reducing the severity of postoperative cardiac adhesions: Focus on REPEL-CV(®)

Treatment of a number of congenital heart defects often necessitates staged surgical intervention. In addition, substantial improvements in postoperative cardiac care and more liberal use of biological valve substitutes have resulted in many adult patients surviving to become potential candidates for reoperations to repair or replace valves or to undergo additional revascularization procedures. In all these scenarios, surgeons are confronted with cardiac adhesions, leading to an increased surgical risk. Thus, bioresorbable adhesion barriers had become of increasing interest because they are easy to use, and safe and effective. This review focuses on the mechanisms by which REPEL-CV^® prevents adhesive processes, as well as the development, design, and materials used, and also summarizes efficacy studies, clinical data, safety, and current role in therapy.

Assessment of the Efficacy of the Bio-Absorbable Oxidized Regenerated Cellulose for Prevention of Post-Operative Pericardial Adhesion in the Rabbit Model

Pericardial adhesions complicate re-operative cardiac surgery and several attempts have been made to reduce adhesion formation. The efficacy of bio-absorbable oxidized regenerated cellulose in preventing post-operative pericardial adhesions was evaluated in the present study. Forty New Zealand white rabbits were divided into four groups of 10. In all rabbits an area of pericardium (2 × 2 cm) was excised. The wound was left open in groups 1 and 2 but replaced with bio-absorbable oxidized regenerated cellulose in groups 3 and 4. Rabbits in groups 1 and 3 were killed 3 weeks after surgery and those in groups 2 and 4 were killed at 6 weeks. Groups 1 and 2 showed more severe pericardial adhesions, more fibrous reaction and increased visibility of coronary vessels than groups 3 and 4, although there was no difference in inflammation. Light microscopy showed a mesothelium-like cell layer in groups 3 and 4. It is concluded that bio-absorbable oxidized regenerated cellulose may be suitable in patients receiving staged cardiac surgery and in those with a high probability of re-operation.

Novel Anti-Adhesive Pericardial Substitute for Multistage Cardiac Surgery

Dense adhesions in the retrosternal space make reoperations difficult in the field of cardiovascular surgery. Several substitutes for pericardium have been employed to prevent dense adhesions forming, but they have been unsatisfactory because of peel formation, calcification, and infection. To overcome these drawbacks, a novel biodegradable pericardial substitute was developed from gelatin obtained from specific-pathogen-free porcine skin and a bioabsorbable polyester mesh, which persists while the adhesion reaction occurs in the retrosternal space. A clinical pilot study of this gelatin sheet was carried out in patients scheduled to receive multistage cardiac surgery. From February 2003 to July 2004, the material was used in 5 patients aged 0.4 to 3.0 years. There were no complications related to the gelatin sheet. The effectiveness of the material was evaluated when the sternum was reopened 1.4 ± 0.5 years later. It took 24.5 ± 6.0 min for the resternotomy, and all surgeons who participated in the surgery rated the effectiveness of the gelatin sheet as “good”. This anti-adhesive sheet prevented dense adhesions, suggesting that this material may be useful as a pericardial substitute for multistage pediatric cardiac surgery.

Postoperative Pericardial Adhesion Prevention Using Carbylan-SX in a Rabbit Model

INTRODUCTION

The presence of dense adhesions within the pericardial space complicates reoperative cardiac surgery. Prior attempts to reduce adhesion formation after primary cardiac surgery using medications or biomaterials have had variable success. Carbylan-SX (Carbylan Biosurgery Inc., Palo Alto, CA) is a hyaluronan-based biomaterial, which has been shown to be effective at reducing adhesions in a nonthoracic rat model. This study evaluates whether Carbylan-SX can effectively reduce postoperative adhesions within the pericardial cavity.

METHODS

Thirty-eight New Zealand white rabbits underwent a left lateral thoracotomy. A pericardiotomy was made and epicardial adhesions were induced on the anterior surface of the heart using a Dremel device (Racine, WI). The rabbits were divided into four groups: controls with abrasions only receiving no treatment (n=10), Carbylan-SX films (n=10), Carbylan-SX aerosolized hydrogel (n=10), and Seprafilm (n=8). The pericardial sac and chest were subsequently closed. Rabbits were sacrificed at a mean of 15 days. For histological analysis, each heart was divided into 12 separate 1 mm sections. Computer imaging software was used to measure the adhesion thickness and the mean of 12 random measurements for each animal was recorded and statistical analysis performed.

RESULTS

Histological analysis revealed all treatment groups to be significantly better than the control (2159 mum thickness, P<0.0001) at preventing adhesions. The Carbylan-SX film and Carbylan-SX aerosolized hydrogel both proved to be better at preventing adhesions than Seprafilm (Genzyme Corp., Cambridge, MA) with an average adhesion thickness of 454 and 577 microm, respectively, compared with 1319 microm for Seprafilm (P<0.0001 and P<0.0005, respectively). The Carbylan-SX film and Carbylan-SX aerosolized hydrogel were equally effective at preventing adhesion formation.

CONCLUSION

Carbylan-SX film and Carbylan-SX aerosolized crosslinkable hydrogel are equally effective methods of reducing postoperative pericardial adhesions within the pericardial cavity. Both the Carbylan-SX film and aerosolized hydrogel showed a significantly greater reduction in adhesions than Seprafilm. Clinical application of Carbylan-SX could have significant therapeutic implications in the future.

Mesothelium regeneration on acellular bovine pericardia loaded with an angiogenic agent (ginsenoside Rg1) successfully reduces postsurgical pericardial adhesions

OBJECTIVE

Our objective was to reduce postsurgical pericardial adhesions with porous acellular bovine pericardia loaded with ginsenoside Rg1, an angiogenic agent isolated from Panax ginseng (the Acellular/Rg1 patch).

METHODS

The acellular/Rg1 patch was used as a substitute to repair a defect created in the pericardium of a rabbit model. A commercially available expanded polytetrafluoroethylene patch, the cellular pericardium (the cellular patch), and the acellular pericardium without loading Rg1 (the acellular patch) were used as controls. The implanted samples were retrieved at 1 and 3 months after surgery (n = 5 per group at each time point).

RESULTS

It was found that each side of the implanted patch could be remesothelialized provided that regeneration of neo-tissue fibrils occurred initially on its surfaces. Because remesothelialization did not take place on the surfaces of the expanded polytetrafluoroethylene and cellular patches, moderate to severe adhesions to the lung and epicardium were clearly observed. As compared with the cellular patch, the acellular patch significantly reduced postsurgical pericardial adhesions, especially on its lung side, as a result of remesothelialization. In the presence of Rg1, a faster remesothelialization was observed on each side of the acellular/Rg1 patch. Therefore, the acellular/Rg1 patch was free of any adhesions to the lung; however, there was still a filmy adhesion to the epicardium observed in 3 of the 5 studied animals at 3 months after surgery, due to incomplete remesothelialization.

CONCLUSIONS

The acellular/Rg1 patch effectively repaired pericardial defects in rabbits and successfully reduced the formation of pericardial adhesions.

Prevention of Postoperative Pericardial Adhesions With a Novel Regenerative Collagen Sheet

BACKGROUND

Postoperative pericardial adhesions make a repeat sternotomy time-consuming and dangerous. The purpose of this study was to evaluate the efficacy of a new collagen pericardial substitute for preventing postoperative pericardial adhesions.

METHODS

Our absorbable substitute consists of three layers: a middle layer of aterocollagen between two layers of sodium hyaluronic acid and aterocollagen. In experiment 1 in this study, the patch, made of 9,000 filaments of aterocollagen fibers, (group 1; n = 5) was compared with a patch made of 6,000 filaments (group 2; n = 7), an expanded polytetrafluoroethylene sheet (group 3; n = 6), and a control group (group 4; n = 4). Subsequently, in experiment 2, the patch was examined at 4 weeks (n = 5), 12 weeks (n = 5), and 24 weeks (n = 4) after the operation by light microscopy and scanning electron microscopy.

RESULTS

The area of adhesion in group 1 was significantly less as compared with that in the other three groups, and the coronary vessels were clearly identifiable; on the other hand, all the animals in the control group showed moderate to severe adhesions, and the coronary vessels were completely obscured. In experiment 2, formation of a membranous tissue resembling the native pericardial membrane was observed in all animals, and the thickness of this membrane showed a marked increase by 24 weeks after the operation. Light microscopy and scanning electron microscopy also showed the formation of a mesothelium-like lining.

CONCLUSIONS

The new absorbable and regenerative collagen patch seemed to be biocompatible, and its use was associated with minimal adhesion formation and preserved coronary anatomy.

Closure of the Pericardium Using Synthetic Bioabsorbable Polymers

BACKGROUND

Pericardial substitutes are known to ensure safer resternotomy at reoperation. A synthetic sheet made from expanded-polytetrafluoroethylene (e-PTFE) has been most commonly used as a pericardial substitute. The e-PTFE sheet, however, can induce severe inflammatory reaction and diffuse fibrosis. This study was designed to investigate the absorption rate and tissue reaction associated with two absorbable pericardial substitutes: a gelatin sheet and L-lactic acid-epsilon-caprolactone copolymer (L-C copolymer). In addition, e-PTFE sheet and autologous pericardium were used as controls.

METHODS

Sixty dogs were divided into four groups of 15. In group A, a 3 x 3 cm segment of pericardium was excised, and the autologous pericardium was resutured. In group B, the pericardial defect was replaced with gelatin sheet. In group C, the defect was replaced with L-C copolymer sheet. In group D, the defect was replaced with e-PTFE sheet. For each group, the implanted membranes were retrieved at 2 weeks (n = 1), 4 weeks (n = 3), 12 weeks (n = 5), and 24 weeks (n = 6) after implantation.

RESULTS

The e-PTFE sheet produced severe adhesions to the heart and pleura and a more prominent inflammatory reaction, as compared with the gelatin sheet. The absorbable pericardial substitutes were completely absorbed by 24 weeks after implantation, and were replaced with fibrous membrane.

CONCLUSIONS

Gelatin sheet may involve less adhesion and a reduced inflammatory reaction compared with e-PTFE.

Postoperative adhesion formation and the use of adhesion preventing techniques in cardiac and general surgery

The formation of postoperative adhesions is an inevitable sequel to surgical intervention, and, as part of the healing process, they are often beneficial. Nevertheless, the presence of adhesions may impose postoperative and reoperative surgical problems. An overview of some of the attempts to overcome such problems is presented, and the research surrounding them is discussed.

Reduction of retrosternal and pericardial adhesions with rapidly resorbable polymer films

BACKGROUND

The formation of postoperative cardiac adhesions makes a repeat sternotomy time consuming and dangerous. Many attempts have been made to solve this problem by using either drugs to inhibit fibrinolytic activity or different types of pericardial substitutes. The results have not been satisfactory.

METHODS

The efficacy of bioresorbable film prototypes made of polyethylene glycol (EO) and polylactic acid (LA) (EO/LA = 1.5, 2.5, and 3.0) in the prevention of adhesions after cardiac operations in canine models was tested. After desiccation and abrasion of the epicardium, a transparent bioresorbable film was placed over the heart. The pericardium was closed to allow intrapericardial adhesions (n = 32) or left open and attached to the chest wall to induce retrosternal adhesions (n = 17). Postoperative recovery was similar among the groups. Retrosternal and pericardial adhesions were evaluated at necropsy 3 weeks later by assessing area, tenacity, and density of the adhesions.

RESULTS

In the control dogs, tenacious, dense adhesions were observed. In contrast, adhesion formation was reduced at all sites covered by the films. The bioresorbable films were efficacious in the reduction of adhesion formation between epicardium and pericardium or between epicardium and sternum after cardiac operation. The EO/LA 1.5 film most effectively prevented the early adhesions.

CONCLUSIONS

The bioresorbable films (EO/LA = 1.5, 2.5, and 3.0) significantly reduced adhesion formation, with EO/LA = 1.5 (Repel CV) being optimal. As the barrier was rapidly resorbed, the capsule formation induced by permanent barriers was avoided.

The effect of fibrin glue on inhibition of pericardial adhesions

The effect of fibrin glue on inhibition of pericardial adhesions was tested using 26 beagle dogs. Dacron patches were sutured to the heart and tincture of iodine was applied to promote adhesions. Fibrin glue (3 ml) was sprayed over the patches in 15 dogs (test group), and was not separated in the remaining 11 dogs (control group). All animals in the test group had minimal adhesions between the pericardium and the epicardium or patched region, and an accumulation of gelatinous material was found in the subpericardial space. Marked fibrosis and a poor demarcation of the subpericardial space were found in the control group. The adhesion score and the visibility of coronary anatomy in the test group were significantly better than in the control group. The tension strength in the test group was significantly less than in the control group. We concluded, therefore, that fibrin glue may also be useful as an adhesion inhibitor.

Increased levels of surgical adhesions in TGFbeta1 heterozygous mice

Adhesion formation and fibrosis represent a major complication of surgical intervention. Reducing the morbidity associated with adhesions requires an understanding of the mechanisms underlying their formation. Since increased levels of transforming growth factor-beta1 (TGFbeta1) have been associated with inflammation and adhesion production, we investigated the requirement of TGFbeta1 in peritoneal adhesion formation utilizing mice carrying a targeted disruption of the TGFbeta1 allele. Mice that were either wild-type (+/+), containing two normal alleles of TGFbeta1, or heterozygous (+/-) for the TGFbeta1 null allele received injections of magnesium silicate (talc), and the extent of abdominal adhesions was determined utilizing a standard grading score. Wild-type (+/+) animals had at least twofold more TGFbeta1 protein in peritoneal fluids at 2 h posttrauma compared to heterozygous (+/-) mice (727 vs. 243 pg TGFbeta1/mg protein by enzyme-linked immunosorbent assay (ELISA) in +/+ and +/- mice, respectively), and had significantly less scar and adhesion formation (p < .05) at 7 days posttrauma (1.8 +/- 0.8 vs. 3.4 +/- 1.4, graded from 0 to 5, in +/+ and +/- mice, respectively). These results demonstrate that haploid insufficiency in TGFbeta1 levels can lead to inappropriate matrix and adhesion production during inflammation, and together with previous studies suggest that any perturbation of normal TGFbeta1 levels can modulate the injury response that regulates the extent of adhesion formation.

Computed tomographic evaluation of retrosternal adhesions after pericardial substitution

BACKGROUND

Reoperative median sternotomy can result in cardiac injury and serious bleeding, with the rate ranging from 2% to 6%. Closure of the native pericardium can maintain a preventing plane of cleavage. In patients in whom primary pericardial closure is not possible, several substitutes have been tried with variable results. We conducted a prospective study to evaluate the clinical feasibility of polytetrafluoroethylene and polyglycolic acid patches as pericardial substitutes, using computed tomography for imaging the postoperative state of the retrosternal space.

METHODS

The basic population comprised 540 patients who were scheduled for coronary artery bypass grafting, and 52 of them who met the research criteria were chosen for computed tomographic evaluation after 5 years after the primary operation.

RESULTS

As a substitute, polytetrafluoroethylene seemed to be less adhesive to the posterior surface of the sternum. Total adhesion scores were also statistically significant (p < 0.001) to the advantage of polytetrafluoroethylene over polyglycolic acid as a pericardial substitute.

CONCLUSIONS

Polytetrafluoroethylene membrane seems to be capable of minimizing retrosternal adhesion formation and thus it may protect the heart during subsequent reoperative sternotomy.

Prevention of retrosternal adhesion formation in a rabbit model using bioresorbable films of polyethylene glycol and polylactic acid

The purpose of this study was to test the efficacy of three bioresorbable films of polyethylene glycol (EO) and polylactic acid (LA) (EO/LA = 1.5, 2.5, and 3.0) in the prevention of adhesion formation between the epicardium and the sternum (retrosternal adhesions) in a rabbit model. Retrosternal adhesions were generated by sternotomy, pericardiotomy, and abrasion of the anterior epicardium. The adhesion barrier was placed between the epicardium and the sternum and sutured to the edge of the pericardium. Epicardial adhesions were evaluated 14-20 days later by assessing the area of the epicardium covered by adhesions. In the control rabbits, tenacious adhesions were observed between sternum and the central portion of epicardium (portion exposed through the pericardiotomy) which were difficult to dissect. When a bioresorbable film was placed over the pericardium, adhesion formation at the central strip of the epicardium (area between the sternum and the epicardium exposed through the pericardium) could be reduced or prevented. At this site, the areas of adhesion formation were 0% (EO/LA = 1.5), 8.4 +/- 2.8% (EO/LA = 2.5), and 5.6 +/- 4.7% (EO/LA = 3.0) of the central strip, significantly less than that observed in the control group, 78.0 +/- 5.8% (P < 0.01). At the anterior left and right and posterior apex of the heart (sites where the film was not placed), there were no differences between control and treatment groups. The films were completely resorbed at the time of necropsy in group EO/LA = 2.5 and 3.0. Small pieces of film were observed in group EO/LA = 1.5. In conclusion, the bioresorbable films [EO/LA = 1.5 (REPEL-CV), 2.5, or 3.0] were efficacious in the reduction of retrosternal adhesions to the epicardium.

An inhibitor of cell proliferation associated with adhesion formation is suppressed by N,O-carboxymethyl chitosan

Surgical adhesions are a major cause of morbidity and mortality. The ideal barrier agent will both minimize adhesions and provide a milieu for the regeneration of the mesothelium lining of the abdominal and thoracic cavities. N,O-Carboxymethylchitosan (NOCC), a derivation of chitin that markedly reduces adhesions, may function to modulate intracellular signals such as growth factors and cytokines in the inflammatory exudate. Since transforming growth factor-beta is implicated in the fibrotic process, we investigated the possibility that NOCC's effects on adhesion formation reflects a modulation of TGF-beta activity. Using a biological assay for inhibition of cell proliferation to detect TGF-beta activity, we demonstrate that NOCC suppresses the levels of an inhibitor of cell proliferation released into serum and peritoneal exudates after cecal abrasion in the rat. However, this activity was distinct from known forms of TGF-beta as determined using both TGF-beta-neutralizing antisera and a TGF-beta-resistant cell proliferation assay. Thus at least one potential effect of NOCC involves a mechanism distinct from TGF-beta inhibition.

Effect of physical protection on the mesothelial integrity of the pericardium

BACKGROUND

Mesothelial integrity is essential for the prevention of pericardial adhesions. This study was performed to determine the effect of physical protection of the pericardium on mesothelial integrity.

METHODS

A pericardial biopsy specimen was obtained at the time of pericardiotomy (0 minutes) in 10 patients undergoing a cardiac operation for the first time. The left free edge of the pericardiotomy was plicated inward to protect the mesothelium. Biopsy specimens were obtained from the protected and unprotected pericardium at 45 and 90 minutes after the start of extracorporeal circulation. Mesothelial integrity and the local inflammatory response were then assessed and graded histologically.

RESULTS

The mesothelium was found to be present in the protected specimens at 0, 45, and 90 minutes, but it was found to be denuded in the unprotected specimens (p = 0.003 at 45 minutes; p = 0.004 at 90 minutes). Local inflammation was totally established in both the protected and unprotected specimens at 45 minutes.

CONCLUSIONS

Physical agents appear to be the main factor that is damaging to the pericardial mesothelium, and this is an important concept to be taken into consideration when designing a method to prevent pericardial adhesions.

Use of the glutaraldehyde-chitosan-treated porcine pericardium as a pericardial substitute

The efficacy of chitosan post-treatment of glutaraldehyde-treated porcine pericardial substitute for the prevention of postoperative epicardial reaction and adhesion formation in mongrel dogs has been assessed. Glutaraldehyde (0.625%)-treated porcine pericardium showed moderate to dense adhesions to the heart and other underlying organs with moderate to severe epicardial reaction. None to minimal epicardial reaction without adhesion was observed in glutaraldehyde-treated porcine pericardium post-treated with chitosan at 5 months. Presumably, chitosan post-treatment prevents the slow release of residual glutaraldehyde and reduces the toxicity of the glutaraldehyde-treated implants, minimizing the chance of adhesion formation and epicardial reaction.

Perioperative histologic and ultrastructural changes in the pericardium and adhesions

The presence of pericardial adhesions prolongs the operation time and increases the risk of serious damage to the heart and other major vascular structures during resternotomy. The reported incidence of such damage is 2% to 6%. Pericardial mesothelial cells exhibit fibrinolytic activity, and therefore have an actual or potential role in the breakdown of the fibrinous adhesions that serve as the initial scaffolding for the firm collagenous adhesions seen at reoperation. Ten patients undergoing primary cardiac procedures were studied to assess the morphologic changes that take place within the pericardium and to relate these to accompanying changes in the pericardial plasminogen activating activity. Samples were taken at 0, 75, and 135 minutes after pericardiotomy. Compared with samples obtained at the time of pericardiotomy, those taken at 75 and 135 minutes demonstrated a significant progression in the mesothelial cell damage (p < 0.01), together with increasing evidence of pericardial inflammation (p < 0.01). The findings from electron microscope studies confirmed and supplemented these findings. Furthermore, compared with its initial levels (median, 2.06 IU/cm2; range, 1.28 to 6.48 IU/cm2), the plasminogen activating activity of pericardial biopsy specimens was significantly reduced at 75 minutes (median, 0.64 IU/cm2; range, 0.12 to 2.44 IU/cm2; P < 0.05), with some recovery at 135 minutes (median, 1.45 IU/cm2; range, 0.12 to 4.39 IU/cm2; p = 0.059). This study has revealed that, during cardiac procedures, the pericardium undergoes inflammatory changes with concomitant damage to its mesothelium, together with a reduction in the pericardial mesothelial fibrinolytic potential.(ABSTRACT TRUNCATED AT 250 WORDS)

Fibrinolytic drugs prevent pericardial adhesions in the rabbit

Epicardial adhesions are believed to form secondarily to impaired pericardial fibrinolytic activity. This activity was reconstituted in a rabbit pericardial adhesion model with single doses of the fibrinolytic agents tissue plasminogen activator (t-PA), t-PA analog (Fb-Fb-CF), and streptokinase (SK), resulting in reductions in the extent and tenacity of adhesion formation. Adhesions of the median strip of the anterior cardiac surface were reduced in area from 89% (n = 22) in controls, to 28% (n = 5) by treatment with Fb-Fb-CF (0.94 mg), and to 49% (n = 7) by treatment with SK (93,750 IU). A modified fabric of oxidized regenerated cellulose (mTC7) used to deliver the agent to the cardiac surface did not interfere with the activity of these agents (Fb-Fb-CF 19%, n = 14; SK 33%, n = 7). t-PA (0.94 mg) was also found to reduce adhesion formation in combination with mTC7 (4%, n = 4), although the appearance of significant postoperative bruising and bleeding resulted in a decision to terminate the treatment of further animals with t-PA with and without mTC7. Postoperative bruising, bleeding, and swelling, to a lesser extent, were associated with SK and Fb-Fb-CF. Despite the efficacy of the these fibrinolytic drugs further work is required to assess their safety before they are used clinically.

Regeneration of pericardial tissue on absorbable polymer patches implanted into the pericardial sac. An immunohistochemical, ultrastructural and biochemical study in the sheep

A new absorbable polymer prepared from polyhydroxybutyrate (PHB) was inserted as a pericardial patch in sheep to serve as a temporary scaffold for regeneration of pericardial tissue. Postoperative adhesions were rare or absent. The present study focuses on characterization of the regenerated surface cells. The luminal surface of the regenerated tissue was covered with a complete layer of mesothelium-like cells which at light and scanning electron microscopy resembled those in native pericardium. Immunohistochemical stainings for cytokeratin and thrombomodulin were positive in these cells. Heparan sulfate proteoglycan was found in a basement-membrane-like structure beneath the surface cells, as in the normal pericardium. Transmission electron microscopy of the regenerated surface revealed cells with the characteristics of mesothelium. Prostacyclin production in the regenerated tissue was similar to that in native pericardium. The results indicate regeneration of a mesothelial layer with many of the important functions of native mesothelial cells. This may explain the presently and previously observed prevention of pericardial adhesions after cardiac surgery in this field. Clinical testing of PHB patches as pericardial substitutes is warranted in cardiac surgery when pericardial closure is desired.