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BioGlue®: A Protective Barrier After Pericardiotomy Nai Dong Wang, M.D.∗ , Donald B. Doty, M.D.,∗ John R. Doty, M.D.,∗ Umit Yuksel, Ph.D.,† and Robert Flinner, M.D.‡ ∗

Division of Cardiovascular and Thoracic Surgery, LDS Hospital, Salt Lake City, Utah; †Cyrolife, Inc., Kennesaw, Georgia; and ‡Department of Pathology, LDS Hospital, Salt Lake City, Utah

ABSTRACT Background: Repeat operation on the heart composes about 20% of procedures in contemporary practice of cardiac surgery. A sheet of material providing a barrier against cardiac adhesion to the sternum would be desirable. Methods: Anterior pericardiectomy was performed in rats. BioGlue® milled to a 0.4 mm sheet was applied to the anterior surface of the heart in 16 rats; Surgicel® plus liquid BioGlue® in seven; Surgicel alone in three; and nothing (control) in eight. The operative site was reexamined for gross evidence of adhesion, scarring, and residual BioGlue® 1, 3, and 6 months later. Results: There was formation of a loose connective tissue barrier containing blood vessels without scar formation in all animals treated with milled BioGlue® . Surgicel® plus BioGlue® resulted in a barrier containing more denser connective tissue with collagen fibers. Surgicel® alone resulted in a similar barrier. No barrier formed in the control experiments. Conclusions: A sheet of milled BioGlue® applied over the surface of the heart but not attached to it after partial pericardiectomy has been shown to stimulate formation of a loose connective tissue barrier containing blood vessels. This barrier is unique compared to dense fibrous scar which usually forms after opening the pericardium for cardiac operations. doi: 10.1111/j.1540-8191.2007.00410.x (J Card Surg

2007;22:295-299) Repeat operation on the heart composes approximately 20% of open heart operations in contemporary practice of cardiac surgery. More than one reoperation may be required in some patients, with each operation presenting more difficulty and risk. The initial pericardiotomy drains the pericardial cavity of its natural fluid. Manual manipulation of the heart during surgery and retained blood or clot in the pericardial sac precipitates the formation of fibrous adhesion of the heart to the pericardial sac. After the operation it may not be possible to completely close the pericardial sac anteriorly due to cardiac dilation, presence of aortocoronary bypass grafts, or excision of a portion of the pericardium for a reconstructive operation. This exposes the anterior surface of the heart to adhesion to the posterior aspect of the sternum and chest wall. Reoperation via reentry sternotomy with the heart attached to the sternum is difficult and hazardous. A sheet of material that could substitute for the anterior pericardium would provide a barrier against adhesion to the sternum after cardiac surgery. Various materials, mostly prosthetic, have been tried with variable results. BioGlue® (CryoLife, Inc., Kennesaw, GA) is a synthetic compound formed by mixing bovine albumin with glutaraldehyde. The aldehyde cross-links the protein molecules forming a semisolid, flexible material that can be milled to a sheet of any desired thickness, Address for correspondence: Donald B. Doty, M.D., 324 Tenth Ave. #184, Salt Lake City, Utah 84010. Fax: 801-408-1086; e-mail: ldddoty@ ihc.com Supported by a grant from Deseret Foundation, Intermountain Health Care, Salt Lake City, Utah.

with a thinner consistency being more flexible and conforming. The material is slowly biodegradable and does not elicit a significant inflammatory response. Our previous unpublished studies using BioGlue® indicate that the material is reabsorbed in six to 12 months when applied as adherent biological glue for the sealing of vascular anastomoses. The purpose of this experiment was to test milled BioGlue® sheet as a substitute for the absent pericardial sac after sternotomy. EXPERIMENTAL DESIGN AND METHODS Experiments were performed under auspices of LDS Hospital Institutional Animal Care and Use Committee (IACUC). Male Long Evans rats were anesthetized by intraperitoneal injection of pentobarbital, 0.06 mg/gm (body weight). Tracheostomy was performed and the animals placed on a ventilator. Under sterile conditions (shave, 1% iodine/alcohol skin preparation), a mid-line sternotomy was performed to expose the pericardial sac. The anterior aspect of the pericardial sac was excised. A control group of experiments was performed in which the pericardium was excised and the sac left open. The sternum was closed by suture and the remainder of the wound approximated. Air was aspirated from the thorax by needle on syringe. The animals were recovered according to established humane care. Butorphanol 0.5–2.0 mg/kg body weight was administered subcutaneously every four hours as necessary for one to two days for control of pain depending on activity of the animal. In the main experimental group, BioGlue® milled to a 0.4 mm sheet was used

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to cover the exposed heart after anterior pericardiectomy, attaching it to adjacent mediastinal tissues with a small amount of liquid, adhering BioGlue® . The heart, therefore, was moving freely beneath the bioprosthetic sheet. In another group of animals, Surgicel® moistened with normal saline was applied to the anterior surface of the heart after excision of the anterior pericardium. Liquid BioGlue® was applied to the Surgicel® in a thin layer. The BioGlue® spread uniformly over the Surgicel® (facilitated by the saline solution) forming an adherent covering of the heart. A final group of experiments was performed in which Surgicel® moistened with normal saline was applied directly to the exposed epicardium after anterior pericardiectomy. At intervals of one, three, and six months after operation, the animals were euthanized. The thorax was reopened and inspected for formation of adhesions. Adhesion formation was graded by gross examination as present or absent (yes/no). Remaining BioGlue® was determined as present or absent (yes/no) by examining for remnants of the product. Presence or absence of inflammation (yes/no) by gross examination was based on color of tissues. Presence or absence of hemorrhage (blood or clots) (yes/no) was determined by inspection of the operative site. The chest wall and heart were excised en bloc, fixed in 10% formalde-

Figure 1. Normal pericardium, rat. Shows thin layer of loose connective tissue and blood vessels.

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hyde, and sections taken. Histologic examination for presence and thickness of tissue barrier over the heart, the morphologic characteristics, and presence of residual BioGlue® was performed. Forty-seven experimental animals were used. One rat was sacrificed without operation to obtain an example of the normal pericardial sac. Twelve animals died on the day of operation of anesthetic, ventilation, or respirator complications. None of the deaths was related to use of BioGlue® , so these experiments were excluded from results analysis. There were eight animals in the control group of animals: one at one month, four at three months, and three at six months interval after pericardial excision. There were 16 animals in the BioGlue® milled sheet group: two at one month; seven at three months; and seven at six months. It was apparent that there was little change in the histology between three and six months, so the other test groups were examined at the three-month interval. There were seven animals in the Surgicel® plus liquid BioGlue® group: all were examined at three months. There were three animals in the Surgicel® -only group examined at three months. RESULTS Normal rat pericardium consists of a thin layer of loose connective tissue and blood vessels as demonstrated in Figure 1.

Figure 2. Control. Six months after excision of pericardial sac there is no adhesion formation or other tissue on the epicardium. Epicardial layer slightly detached from myocardium is fixation artifact.

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Figure 3. BioGlue® milled sheet, 1 month. A tissue barrier consisting of loose connective tissue and blood vessels has formed with loose attachment to the epicardium. The tissue barrier is thicker than normal pericardium.

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Control group: No adhesions and no formation of a tissue barrier were observed in any animal in the control group at one, three, or six months after excision of the anterior pericardial sac (Fig. 2). BioGlue® milled sheet group: At the one-month interval, there was formation of a tissue barrier over the heart consisting of loose connective tissue and blood vessels (Fig. 3). The new tissue was attached to the epicardium and was thicker than normal pericardium. At the three-month interval, the tissue barrier persisted and consisted of loose connective tissue and blood vessels (Fig. 4A). There was no formation of dense collagen tissue (scar). Gross examination of the heart showed a complete covering of the heart with the tissue barrier having many characteristics of a neopericardium except that it was attached loosely to the epicardium (Fig. 4B). There was a small residue of BioGlue® present in three of seven animals. At the six-month interval, findings were similar to those at three months with loose connective tissue and some blood vessels loosely adherent to the epicardium (Fig. 5). There was a small residue of BioGlue® present in four of seven animals. Thus, there was formation of a tissue barrier in all animals beginning as early as one month after operation. During the six-month observation period the barrier appeared to remain stable and showed no tendency to progress to scar. Surgicel ® plus liquid BioGlue® group: The seven animals in this group were all examined at three months. In six of seven experiments, there was formation of

Figure 4. (A). BioGlue® milled sheet, 3 months. The tissue barrier remains loose connective tissue and blood vessels. (B). BioGlue® milled sheet, 3 months. The heart is covered with the tissue barrier, which has characteristics of a neopericardium except that it is loosely attached to the epicardium.

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Figure 5. BioGlue® milled sheet, 6 months. The tissue barrier remains unchanged, showing loose connective tissue, blood vessels, and no progression to scar formation.

Figure 6. Surgicel ® and liquid BioGlue® , 3 months. The tissue barrier contains more collagen fibers and appears to be more densely connected to the epicardium.

a tissue barrier attached to the epicardium consisting of more denser connective tissue with collagen fibers (Fig. 6). Blood vessel formation was less compared to the BioGlue® milled sheet group. Surgicel ® group: A tissue barrier formed in two of three animals examined at the three-month interval. Histology was similar to findings in the Surgicel® /BioGlue® group with more denser fibrous tissue and apparent tighter adherence to the epicardium (Fig. 7).

satisfactory material has been identified. Walther and colleagues1 proposed use of a modified polysaccharide/glycerol membrane (CV Seprafilm, Genzyme, Cambridge, MA, USA) and reviewed various techniques used to decrease amount and tenacity of adhesions. They noted that CV Seprafilm was difficult to apply although with practice it became “easy.” Their wellannotated reference list represents the progress of investigations to 2004. Only polytetrafluoroethylene (PTFE) has been widely used in clinical practice and was found by Lahtinen and colleagues2 capable of minimizing retrosternal adhesion formation. PTFE, however, is a permanent implant, requiring fixation by suture to prevent migration, and may result in formation of a fibrous capsule around it. In our opinion, a biodegradable material would be more desirable than a permanent foreign body. Recent studies reported by Okuyama and colleagues3,4 used polyethylene glycol/polylactic acid film patch as a bioresorbable barrier to reduce adhesion formation between the epicardium and the pericardium or sternum in both rabbit and dog adhesion models. They hypothesized that prevention of adherence of the heart to the pericardium early after pericardiotomy would prevent the formation of dense scar adhesion later on the “scaffold” of early loose fibrous adhesions. Their experiments appeared to support the hypothesis. Iliopoulos and colleagues5 also reported that polylactide film reduced retrosternal and pericardial adhesions in adult

COMMENT Pericardiotomy during cardiac surgery inevitably results in adhesion between the pericardium and the epicardium. Adhesion of heart to anterior mediastinal tissues and the anterior chest wall may also occur. Mediastinal and intrapericardial adhesion is always worse when the pericardium is excised or left open following cardiac operation. Thus, most surgeons agree that closure of the pericardium is desirable. This may not be possible when the pericardium has been removed or there is any degree of cardiac distension or swelling. In some cases, adhesion of the heart to the healed sternotomy incision may be dense enough to present significant hazard or injury to the heart during reentry sternotomy. Pericardial substitutes and adhesion barriers have been pursued by several investigators but no uniformly

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an effort to stimulate adhesion formation. When bioabsoarbable cellulose mesh (Surgicel® ) combined with BioGlue® applied in liquid form was applied directly to the epicardium, the barrier formed but there was more fibrous connective tissue suggesting a more dense adhesion of the barrier to the heart. Surgicel® alone applied to the epicardium stimulates formation of a barrier similar to the combination of BioGlue® and Surgicel® . LIMITATIONS OF THE STUDY Rat was chosen as the experimental animal in this preliminary study because of cost, convenience in caging, and ease of maintenance after operation. Pericardial adhesions, however, do not appear to form after simple partial pericardiectomy in the rat, thus limiting inference regarding prevention of adhesion of the heart to remaining pericardium or to adjacent structures. On the other hand, since no adhesion formed in any control animal and a protective barrier formed in every BioGlue® test animal, we observed an all or none phenomenon making statistical analysis unnecessary. CONCLUSION

Figure 7. Surgicel ® , 3 months. The tissue barrier contains collagen fibers and is more densely connected to the epicardium.

pigs. Bennett and colleagues6 used tissue adherent, inert hydrogel films sprayed onto the surface of the rabbit heart in an abrasion adhesion model to demonstrate formation of an adhesion barrier. Bio-Glue® is a tissue adhesive formed by the chemical reaction of mixing bovine serum albumin with glutaraldehyde. The substance so formed can be milled to form a sheet of any thickness. Flexibility of the material is related to the thickness of the material. Optimal thickness appears to be 0.4 mm for use as a pericardial substitute/adhesion barrier in terms of pliability and ease of use. We postulated that a barrier would form around the bioabsoarbable scaffold that would protect the heart by forming a neopericardium. This study demonstrates that the material is biodegradable and only a small amount of residue remains at three to six months. When applied in a position anterior to the heart but not attached to the epicardium, it stimulates formation of a barrier loosely attached to the epicardium that simulates a new pericardium histologically. This barrier forms in every case in the rat heart pericardial excision model. Such a barrier was not formed in any control experiment when the pericardium was simply excised. It should be noted that no trauma or abrasion was applied to the epicardium in

A sheet of BioGlue® applied over the surface of the heart but not attached to it after partial pericardiectomy has been shown to stimulate formation of a loose connective tissue barrier containing blood vessels. This barrier is unique compared to dense fibrous scar that forms naturally in species other than rat and to the barrier formed when BioGlue® combined with Surgicel® or Surgicel® alone is applied adherent to the heart. These findings encourage further exploration of the use of milled BioGlue® as a substitute for pericardium to cover the heart at the conclusion of cardiac surgery. REFERENCES 1. Walther T, Rastan A, Dahnert I, et al: A novel adhesion barrier facilitates reoperations in complex congenital cardiac surgery. J Thorac Cardiovasc Surg 2005;129:359-363. 2. Lahtinen J, Satta J, Lahde S, et al: Computed tomographic evaluation of retrosternal adhesions after pericardial substitution. Ann Thorac Surg 1998;65:1264-1268. 3. Okuyama N, Rodgers KE, Wang CY, et al: Prevention of retrosternal adhesion formation in a rabbit model using bioresorbable films of polyethylene glycol and polyactic acid. J Surg Res 1998;78:118-122. 4. Okuyama N, Wang CY, Rose EA, et al: Reduction of retrosternal and pericardial adhesions with rapidly resorbable polymer films. Ann Thorac Surg 1999;68:913-918. 5. Iliopoulos J, Cornwall GB, Evans RO, et al: Evaluation of a bioabsorable polylactide film in a large animal model for the reduction of retrosternal adhesions. J Surg Res 2004;118:144-153. 6. Bennett SL, Melanson DA, Torchiana DF, et al: Nextgeneration hydrogel films as tissue sealants and adhesion barriers. J Card Surg 2003;18:494-499.