© 2015 Wiley Periodicals, Inc.
648
DISEASES OF THE AORTA SURGICAL TECHNIQUE ___________________________________________________________
Extracellular Matrix Scaffold as a Tubular Graft for Ascending Aorta Aneurysm Repair Walid K. Abu Saleh, M.D.,* Odeaa Al Jabbari, M.D.,* Jane Grande-Allen, M.D.,y and Mahesh Ramchandani, M.D.* *Houston Methodist DeBakey Heart & Vascular Center, Houston Methodist Hospital, Houston, Texas; and yRice University, Bioscience Research Collaborative, Houston, Texas ABSTRACT Background: Although extracellular xenograft repair has produced encouraging results when applied to cardiac, valvular, and specific aortic defects, its employment as a tube graft to replace the ascending aorta has not been reported. We describe a patient who underwent resection and replacement of an infected ascending aortic graft with an extracellular matrix conduit. The patient did well, but 14 months later developed a pseudoaneurysm from the staple line used to construct the extracellular matrix conduit. Methods: The patient underwent a repeat sternotomy and removal of the graft. Because of the increased risk of graft failure, a homograft was felt to be more appropriate in this setting. Ultimately, we were unable to implant the homograft because it was too small for the aortic root; therefore we decided to construct a tubular graft from Cormatrix extracellular matrix (CorMatrix, Roswell, GA, USA). Fourteen months later, he presented with shortness of breath. Computed tomography scan revealed a 3.5 cm pseudoaneurysm of the ascending aorta. It appeared as if there was a disruption of the staple line in the extra cellular matrix graft. The plan was to replace it with a Dacron graft. Results: The Cormatrix graft material was removed and sent for culture and histological analysis. A 28-mm Gel weave graft (Terumo Cardiovascular Systems, Ann Arbor, MI, USA) was implanted. The patient tolerated the procedure well with good hemodynamics. Conclusions: Our experience suggests that the superior strength, handling characteristics, and resistance to infection make extra cellular matrix scaffold a possible alternative conduit to cryopreserved homografts. Applicability as an aortic conduit merits further investigation to better understand behavior of extra cellular matrix in this situation. doi: 10.1111/jocs.12583 (J Card Surg 2015;30:648–650) Extracellular matrix (ECM), derived from porcine small-intestine submucosa (SIS), presents some clear advantages over other materials. ECM has been shown to be angiogenic, chemotactic, and resistant to infection.1 We describe a patient who underwent resection and replacement of an infected ascending aortic graft with an extracellular matrix conduit. The patient did well, but 14 months later developed a pseudoaneurysm from the staple line used to construct the extracellular matrix conduit. PATIENT PROFILE A 64-year-old male had a history of type 2 diabetes, hypertension, coronary artery bypass (CABG) surgery.
Conflict of interest: The authors acknowledge no conflict of interest in the submission. Address for correspondence: Walid K. Abu Saleh, M.D., Houston Methodist Hospital, 6565 Fannin St., Houston, TX 77030. Fax: þ1-713790-2859; e-mail: [email protected]
In 2001, the patient presented with chest pain and shortness of breath. Upon evaluation, he had an ascending aortic aneurysm for which he underwent repair of the aneurysm and replacement of the ascending aorta. The patient presented with recurrent episodes of bacteremia attributed to multidrug resistant Pseudomonas in 2010. After an extensive workup, it was determined that the source of infection was the ascending aortic graft. The procedure was done on an institutional review board approved protocol and the patient gave full consent. The patient underwent a repeat sternotomy and removal of the graft. Because of the increased risk of graft failure, a homograft was felt to be more appropriate in this setting. Ultimately, we were unable to implant the homograft because it was too small for the aortic root; therefore, we decided to construct a tubular graft from CorMatrix ECM (CorMatrix, Roswell, GA, USA). The surgery was carried out under circulatory arrest via right axillary cannulation. Two sheets of CorMatrix
J CARD SURG 2015;30:648–650
ABU SALEH, ET AL. GRAFT FOR ASCENDING AORTA ANEURYSM REPAIR
were fixed along the lateral edges (via staples) around a 60 cc sized syringe to create a tubular graft; 3-0 prolene sutures were used for the Core Matrix anastomosis without any reinforcement. The procedure and the patient’s postoperative recovery were uneventful. Fourteen months later, he presented with shortness of breath. Computed tomography (CT) scan revealed a 3.5 cm pseudoaneurysm of the ascending aorta (Fig. 1). It appeared as if there was a disruption of the staple line in the ECM graft. The plan was to replace the ECM graft with a Dacron graft. The patient underwent the ascending aortic graft replacement. Arrest of circulation was achieved before the chest was entered to prevent fatal exsanguination, as the pseudoaneurysm was adhered to the underside of the sternum. After a careful dissection of the CorMatrix graft, the disruption of the staple line was evident. The proximal and distal anastomoses to the aorta were intact and well healed. There was no gross evidence of infection. The CorMatrix graft material was removed and sent for culture and histological analysis. A 28-mm Gel weave graft (Terumo Cardiovascular Systems, Ann Arbor, MI, USA) was implanted. The patient tolerated the procedure well with good hemodynamics and eventually was transferred to the regular surgical floor and was discharged. As part of our assessment, we performed a followup imaging study which included cardiac CT scan six months following the surgery, and there has been no evidence of this imaging study of any breakdown of the implanted graft and no recurrence of the pseudoaneurysm. HISTOLOGY REPORT The ECM explanted (Fig. 2) was compared to unused ECM material (control). Gross histological observation revealed little difference between the two samples with regard to diameter, cellularity, or organization in H&E stained cross-sections. Both explanted and
Figure 1. Computed tomographic scan showing a 3.5 cm pseudoaneurysm of the ascending aorta (arrow) 14 months after the CorMatrix tubular graft was implanted.
649
Figure 2. Explanted CorMatrix ECM Graft.
control ECM material were stained with Annexin V, cKit (C-19), and CD45 antibodies. Annexin V can target the loss of plasma membrane asymmetry. The anti-c-Kit antibody (C-19) was used to identify any cell phenotypes that invaded the tissue. The CD45 antibodies can identify the presence of pan-leukocytes and cellular changes or remodeling. After a detailed analysis, no significant differences between the two samples were found. Furthermore, we performed Verhoeff-Van Gieson (VVG) stain, which is used to identify and differentiate elastic fibers within tissue specimens (Fig. 3). After meticulous examination, no dissection, delamination, or breakdown of the material was noted in the patient sample. The patient sample appeared to be intact and organized in a single layer. MECHANICAL TESTING Rectangular segments were cut from the explanted patient and control ECM samples. Segments were cut according to their prior orientation as either circumferential or longitudinal. The width and thickness of each segment was measured in three positions and
Figure 3. Microscopic photograph of explanted specimen at 20 stained with Verhoeff-Van Gieson (VVG) elastin stain. No significant differences were observed.
650
ABU SALEH, ET AL. GRAFT FOR ASCENDING AORTA ANEURYSM REPAIR
J CARD SURG 2015;30:648–650
TABLE 1 Stress and Strain Parameters of Excised Tissue Sample Circumferential Longitudinal
Youngs Mod (MPa)
Extensibility
Yield Stress (MPa)
Yield Strain
Ultimate Stress (MPa)
Ultimate Strain
6.63356 12.9561
0.10537 0.10767
0.72838 1.6026
0.21688 0.23596
1.3936 2.223
0.37724 0.34635
averaged. The ends of each length of segment were affixed to balsa wood mounts with cyanoacrylate. The balsa wood mounts, with attached tissue, were clamped into the grips and the grip-to-grip distance was measured as the tissue gauge length. After preconditioning the segments for 10 cycles, the samples were pulled in tension until failure, at a rate of 0.15 mm/seconds, while time, load, and displacement were recorded. Stress and strain were calculated by dividing load and displacement by the cross-sectional area and gauge length, respectively. The elastic modulus (stiffness) was then calculated as the slope of the final linear portion of the stress–strain curve. The control ECM had an elastic modulus of 42.9 11.6 MPa. The elastic modulus of the explanted patient sample was 6.6 MPa in circumferential direction and 13.0 MPa in longitudinal direction (Table 1). These data indicate that the explanted CorMatrix is more susceptible to deformation. DISCUSSION The use of ECM in primary ascending aorta reconstruction is limited, but based on clinical experience and circumstances, we deemed it our best available option at the time. CorMatrix ECM has characteristics that makes it well suited for cardiac tissue and vascular repair. These include tensile strength, resistance to tearing and calcification, pliability, pro-hemostatic properties, ability to promote cellular and tissue infiltration, and the understanding that it does not induce an inflammatory cascade. Our patient was infection free 14 months following the CorMatrix graft implantation. The pseudoaneurysm of the ascending aorta developed at a disruption point along the stapled edges of the CorMatrix graft. We found that the graft was free of calcification, with no inflammatory changes along the graft. We view our case as a success in that we were able to employ the CorMatrix ECM as a graft for an extended period of time. However, we postulate that shear stress along the graft’s stapled edges caused displacement and the resulting pseudoaneurysm. Unexpectedly, our histological examination indicated no stem cell factor, no endothelial cell ingrowth, and almost identical morphology compared to a brand new CorMatrix sheet. This was contrary to the previous literature which described cellular remodeling postimplantation for arterial reconstruction.2 In our sample, there was trace vascular remodeling, but not enough to demarcate our patient sample as a fully infiltrated and transformed scaffold. We suspect that lack of cellular finding in our patient specimen may have been due to the location and tissue
explanted at the time of surgery. We have speculated that the reason that led to decellularization was that the specimen was maintained in normal saline for several days before microscopic examination and mechanical testing. Contrary to the aforementioned reports, which implanted CorMatrix in patch fashion, we created a tubular graft with the matrix material. Thus, our scaffold had a larger surface area free of contact with border points along the native aorta. The specimen was taken at the proximal point of aneurysm formation, and there may have been changes distally along the graft. In addition, the fact that a pseudoaneurysm formed suggests that the graft was displaced from native aortic tissue, which could have inhibited the matrix’s ability to infiltrate surrounding tissue cells. We also suspect that our securing technique (staples) played a vital role in the grafts durability, as the clinical outcome may have been different if the graft had been secured using hand sutures instead. We now would use prolene sutures to construct the tube as it has been used extensively for the implantation of CorMatrix in a patch configuration to reconstruct left ventricular aneurysms and also for reconstruction of the mitral valve and the aortic root. Our experience with the staples revealed an unforeseen problem that is the ability of the staples to literally cut through CorMatrix tissue. Finally, we have no ready explanation for the change in the modulus parameters. Although the strategy worked successfully in this patient, we do not feel that it provides enough support to use this routinely. Because of this, we have embarked on a series of animal experiments to implant tubular CorMatrix and better evaluate its performance in this position. CONCLUSION Our experience suggests that the superior strength, handling characteristics, and resistance to infection make ECM scaffold a possible alternative conduit to cryopreserved homografts. Applicability as an aortic conduit merits further investigation to better understand behavior of ECM in this situation. Long-term durability data are needed, particularly with regard to shear stress and ideal securing techniques when implanted as a primary graft in high pressure vascular systems. REFERENCES 1. Badylak SF: The extracellular matrix as a scaffold for tissue reconstruction. Semin Cell Dev Biol 2002;13(5):377–383. 2. Fallon A, Goodchild T, et al: Remodeling of extracellular matrix patch used for carotid artery repair. J Surg Res 175(1): e25–e34.
648
DISEASES OF THE AORTA SURGICAL TECHNIQUE ___________________________________________________________
Extracellular Matrix Scaffold as a Tubular Graft for Ascending Aorta Aneurysm Repair Walid K. Abu Saleh, M.D.,* Odeaa Al Jabbari, M.D.,* Jane Grande-Allen, M.D.,y and Mahesh Ramchandani, M.D.* *Houston Methodist DeBakey Heart & Vascular Center, Houston Methodist Hospital, Houston, Texas; and yRice University, Bioscience Research Collaborative, Houston, Texas ABSTRACT Background: Although extracellular xenograft repair has produced encouraging results when applied to cardiac, valvular, and specific aortic defects, its employment as a tube graft to replace the ascending aorta has not been reported. We describe a patient who underwent resection and replacement of an infected ascending aortic graft with an extracellular matrix conduit. The patient did well, but 14 months later developed a pseudoaneurysm from the staple line used to construct the extracellular matrix conduit. Methods: The patient underwent a repeat sternotomy and removal of the graft. Because of the increased risk of graft failure, a homograft was felt to be more appropriate in this setting. Ultimately, we were unable to implant the homograft because it was too small for the aortic root; therefore we decided to construct a tubular graft from Cormatrix extracellular matrix (CorMatrix, Roswell, GA, USA). Fourteen months later, he presented with shortness of breath. Computed tomography scan revealed a 3.5 cm pseudoaneurysm of the ascending aorta. It appeared as if there was a disruption of the staple line in the extra cellular matrix graft. The plan was to replace it with a Dacron graft. Results: The Cormatrix graft material was removed and sent for culture and histological analysis. A 28-mm Gel weave graft (Terumo Cardiovascular Systems, Ann Arbor, MI, USA) was implanted. The patient tolerated the procedure well with good hemodynamics. Conclusions: Our experience suggests that the superior strength, handling characteristics, and resistance to infection make extra cellular matrix scaffold a possible alternative conduit to cryopreserved homografts. Applicability as an aortic conduit merits further investigation to better understand behavior of extra cellular matrix in this situation. doi: 10.1111/jocs.12583 (J Card Surg 2015;30:648–650) Extracellular matrix (ECM), derived from porcine small-intestine submucosa (SIS), presents some clear advantages over other materials. ECM has been shown to be angiogenic, chemotactic, and resistant to infection.1 We describe a patient who underwent resection and replacement of an infected ascending aortic graft with an extracellular matrix conduit. The patient did well, but 14 months later developed a pseudoaneurysm from the staple line used to construct the extracellular matrix conduit. PATIENT PROFILE A 64-year-old male had a history of type 2 diabetes, hypertension, coronary artery bypass (CABG) surgery.
Conflict of interest: The authors acknowledge no conflict of interest in the submission. Address for correspondence: Walid K. Abu Saleh, M.D., Houston Methodist Hospital, 6565 Fannin St., Houston, TX 77030. Fax: þ1-713790-2859; e-mail: [email protected]
In 2001, the patient presented with chest pain and shortness of breath. Upon evaluation, he had an ascending aortic aneurysm for which he underwent repair of the aneurysm and replacement of the ascending aorta. The patient presented with recurrent episodes of bacteremia attributed to multidrug resistant Pseudomonas in 2010. After an extensive workup, it was determined that the source of infection was the ascending aortic graft. The procedure was done on an institutional review board approved protocol and the patient gave full consent. The patient underwent a repeat sternotomy and removal of the graft. Because of the increased risk of graft failure, a homograft was felt to be more appropriate in this setting. Ultimately, we were unable to implant the homograft because it was too small for the aortic root; therefore, we decided to construct a tubular graft from CorMatrix ECM (CorMatrix, Roswell, GA, USA). The surgery was carried out under circulatory arrest via right axillary cannulation. Two sheets of CorMatrix
J CARD SURG 2015;30:648–650
ABU SALEH, ET AL. GRAFT FOR ASCENDING AORTA ANEURYSM REPAIR
were fixed along the lateral edges (via staples) around a 60 cc sized syringe to create a tubular graft; 3-0 prolene sutures were used for the Core Matrix anastomosis without any reinforcement. The procedure and the patient’s postoperative recovery were uneventful. Fourteen months later, he presented with shortness of breath. Computed tomography (CT) scan revealed a 3.5 cm pseudoaneurysm of the ascending aorta (Fig. 1). It appeared as if there was a disruption of the staple line in the ECM graft. The plan was to replace the ECM graft with a Dacron graft. The patient underwent the ascending aortic graft replacement. Arrest of circulation was achieved before the chest was entered to prevent fatal exsanguination, as the pseudoaneurysm was adhered to the underside of the sternum. After a careful dissection of the CorMatrix graft, the disruption of the staple line was evident. The proximal and distal anastomoses to the aorta were intact and well healed. There was no gross evidence of infection. The CorMatrix graft material was removed and sent for culture and histological analysis. A 28-mm Gel weave graft (Terumo Cardiovascular Systems, Ann Arbor, MI, USA) was implanted. The patient tolerated the procedure well with good hemodynamics and eventually was transferred to the regular surgical floor and was discharged. As part of our assessment, we performed a followup imaging study which included cardiac CT scan six months following the surgery, and there has been no evidence of this imaging study of any breakdown of the implanted graft and no recurrence of the pseudoaneurysm. HISTOLOGY REPORT The ECM explanted (Fig. 2) was compared to unused ECM material (control). Gross histological observation revealed little difference between the two samples with regard to diameter, cellularity, or organization in H&E stained cross-sections. Both explanted and
Figure 1. Computed tomographic scan showing a 3.5 cm pseudoaneurysm of the ascending aorta (arrow) 14 months after the CorMatrix tubular graft was implanted.
649
Figure 2. Explanted CorMatrix ECM Graft.
control ECM material were stained with Annexin V, cKit (C-19), and CD45 antibodies. Annexin V can target the loss of plasma membrane asymmetry. The anti-c-Kit antibody (C-19) was used to identify any cell phenotypes that invaded the tissue. The CD45 antibodies can identify the presence of pan-leukocytes and cellular changes or remodeling. After a detailed analysis, no significant differences between the two samples were found. Furthermore, we performed Verhoeff-Van Gieson (VVG) stain, which is used to identify and differentiate elastic fibers within tissue specimens (Fig. 3). After meticulous examination, no dissection, delamination, or breakdown of the material was noted in the patient sample. The patient sample appeared to be intact and organized in a single layer. MECHANICAL TESTING Rectangular segments were cut from the explanted patient and control ECM samples. Segments were cut according to their prior orientation as either circumferential or longitudinal. The width and thickness of each segment was measured in three positions and
Figure 3. Microscopic photograph of explanted specimen at 20 stained with Verhoeff-Van Gieson (VVG) elastin stain. No significant differences were observed.
650
ABU SALEH, ET AL. GRAFT FOR ASCENDING AORTA ANEURYSM REPAIR
J CARD SURG 2015;30:648–650
TABLE 1 Stress and Strain Parameters of Excised Tissue Sample Circumferential Longitudinal
Youngs Mod (MPa)
Extensibility
Yield Stress (MPa)
Yield Strain
Ultimate Stress (MPa)
Ultimate Strain
6.63356 12.9561
0.10537 0.10767
0.72838 1.6026
0.21688 0.23596
1.3936 2.223
0.37724 0.34635
averaged. The ends of each length of segment were affixed to balsa wood mounts with cyanoacrylate. The balsa wood mounts, with attached tissue, were clamped into the grips and the grip-to-grip distance was measured as the tissue gauge length. After preconditioning the segments for 10 cycles, the samples were pulled in tension until failure, at a rate of 0.15 mm/seconds, while time, load, and displacement were recorded. Stress and strain were calculated by dividing load and displacement by the cross-sectional area and gauge length, respectively. The elastic modulus (stiffness) was then calculated as the slope of the final linear portion of the stress–strain curve. The control ECM had an elastic modulus of 42.9 11.6 MPa. The elastic modulus of the explanted patient sample was 6.6 MPa in circumferential direction and 13.0 MPa in longitudinal direction (Table 1). These data indicate that the explanted CorMatrix is more susceptible to deformation. DISCUSSION The use of ECM in primary ascending aorta reconstruction is limited, but based on clinical experience and circumstances, we deemed it our best available option at the time. CorMatrix ECM has characteristics that makes it well suited for cardiac tissue and vascular repair. These include tensile strength, resistance to tearing and calcification, pliability, pro-hemostatic properties, ability to promote cellular and tissue infiltration, and the understanding that it does not induce an inflammatory cascade. Our patient was infection free 14 months following the CorMatrix graft implantation. The pseudoaneurysm of the ascending aorta developed at a disruption point along the stapled edges of the CorMatrix graft. We found that the graft was free of calcification, with no inflammatory changes along the graft. We view our case as a success in that we were able to employ the CorMatrix ECM as a graft for an extended period of time. However, we postulate that shear stress along the graft’s stapled edges caused displacement and the resulting pseudoaneurysm. Unexpectedly, our histological examination indicated no stem cell factor, no endothelial cell ingrowth, and almost identical morphology compared to a brand new CorMatrix sheet. This was contrary to the previous literature which described cellular remodeling postimplantation for arterial reconstruction.2 In our sample, there was trace vascular remodeling, but not enough to demarcate our patient sample as a fully infiltrated and transformed scaffold. We suspect that lack of cellular finding in our patient specimen may have been due to the location and tissue
explanted at the time of surgery. We have speculated that the reason that led to decellularization was that the specimen was maintained in normal saline for several days before microscopic examination and mechanical testing. Contrary to the aforementioned reports, which implanted CorMatrix in patch fashion, we created a tubular graft with the matrix material. Thus, our scaffold had a larger surface area free of contact with border points along the native aorta. The specimen was taken at the proximal point of aneurysm formation, and there may have been changes distally along the graft. In addition, the fact that a pseudoaneurysm formed suggests that the graft was displaced from native aortic tissue, which could have inhibited the matrix’s ability to infiltrate surrounding tissue cells. We also suspect that our securing technique (staples) played a vital role in the grafts durability, as the clinical outcome may have been different if the graft had been secured using hand sutures instead. We now would use prolene sutures to construct the tube as it has been used extensively for the implantation of CorMatrix in a patch configuration to reconstruct left ventricular aneurysms and also for reconstruction of the mitral valve and the aortic root. Our experience with the staples revealed an unforeseen problem that is the ability of the staples to literally cut through CorMatrix tissue. Finally, we have no ready explanation for the change in the modulus parameters. Although the strategy worked successfully in this patient, we do not feel that it provides enough support to use this routinely. Because of this, we have embarked on a series of animal experiments to implant tubular CorMatrix and better evaluate its performance in this position. CONCLUSION Our experience suggests that the superior strength, handling characteristics, and resistance to infection make ECM scaffold a possible alternative conduit to cryopreserved homografts. Applicability as an aortic conduit merits further investigation to better understand behavior of ECM in this situation. Long-term durability data are needed, particularly with regard to shear stress and ideal securing techniques when implanted as a primary graft in high pressure vascular systems. REFERENCES 1. Badylak SF: The extracellular matrix as a scaffold for tissue reconstruction. Semin Cell Dev Biol 2002;13(5):377–383. 2. Fallon A, Goodchild T, et al: Remodeling of extracellular matrix patch used for carotid artery repair. J Surg Res 175(1): e25–e34.
