An experimental study of a new sutureless intraluminal graft with an elastic ring that can attach itself to the vessel wall

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1 An experimental study of a new sutureless intraluminal graft with an elastic ring that can attach itself to the vessel wall A preliminary report Masaru Matsumae, MD, Hatsuzo Uchida, MD, and Shigeru Teramoto, MD, Okayama, Japan A new sutureless intraluminal graft was developed with an elastic ring made of a flat spring. The diameter of the ring could be reversibly reduced by compression. The sutureless intraluminal graft with an elastic ring can attach itself to the vessel wall by elastic expansion of the ring. The elastic-ring graft was implanted in the descending thoracic aortas of nine dogs and was evaluated histologicauy and angiographically at different intervals from 18 to 150 days. No complication such as detachment of the ring, aortic rupture, stenosis, or aneurysmal dilatation was observed. With the new graft neither ligation nor posterior aortic wall dissection is necessary, and no anastomotic stenosis occurs. This graft is applicable even if the diameter of the aorta is small. Therefore the elastic-ring sutureless intraluminal graft promises theoretic advantages over sutureless methods that use tape ligation. (J VAse SURG 1988;8:38-44.) The sutureless intraluminal graft has been widely used in reconstruction of the thoracic and abdominal aorta. 14 It has the advantage of markedly reducing cross-clamp time and total blood loss. Recently we developed a new sutureless intraluminal graft with an elastic ring (SIGER) to eliminate the disadvantages of the older graft (i.e., the necessity of wide posterior aortic wall dissection and the difficulty in introducing a graft of suitable size and securing the tape around the ring). The SIGER can attach itself to the vessel wall by elastic expansion of the ring, which is made of a flat spring. The diameter of the ring is reduced by compression; this process is reversible because of the ring's elasticity. The SIGER is compressed to reduce the diameter and intraluminatly inserted into the aorta. Then it is enlarged at the target and attaches itself to the vessel wall by elastic expansion. The SIGER, which is expandable, self-adjustable, and stays without tape fixation at the required location, can be valuable for vascular surgery. From the Second Department of Surgery, Okayama University Medical School Reprint requests: Masaru Matsumae, MD, Division of Vascular Surgery, Hiroshima Teishin Hospital, Higashihakushirna-cho, Naka-ku, Hiroshima 730, Japan. MATERIAL AND METHODS Graft preparation. The elastic ring is made of a flat stainless steel spring measuring mm and 0.2 mm in thickness. The diameter of the ring is 13 mm with a part that overlaps approximately 4 mm before compression; the diameter can be reduced to 8 mm by compression of the ring, which increases the overlapping part to 13 ram. Rings are placed at both ends of knitted Dacron grafts of 10 or 12 mm diameter and are covered with the cuff of the grafts, which are turned over at both ends. When the overlapping part is pinched with forceps, the SIGER can be kept smaller in diameter; when the forceps is released, the graft can be allowed to expand to its original size (Figs. 1 and 2). The soft knitted Dacron covering does not change the behavior of elastic recoil of the ring. Animal study. The animal experiment was carried out on nine dogs placed under general anesthesia. Nine SIGERs with 18 rings were implanted in the descending thoracic aortas of the dogs. The SIGEK, reduced in diameter by pinching the overlapping part with forceps, was introduced into the aorta far enough so that the ring was fully covered with aortic wall, that is, overlap of aortic wall was at least 2 to 3 ram. At the target the forceps was released; the ring expanded to its original size and at- 38

2 Volume 8 Number 1 July 1988 Suturelcss intraluminal graft with elastic Hng 39 A B t } Overlap 4ram ~b 1 3mm 8mm C D 6 ForceDs O Fig. 1. Schematic drawing of elastic ring. A, Ring is made of flat spring, it overlaps by 4 ram, and its diameter is 13 mm before compression. B, Overlapping part is increased to 13 mm by compression and diameter is reduced to 8 mm. This process is reversible. C, Ring can be kept reduced in diameter by pinching overlap with forceps. D, Forceps is released and ring expands to its original size. tached itself to the vessel wall. No circular tie around the ring was applied (Fig. 3). Animal care complied with the "Principles of Laboratory Animal Care" and the "Guide for the Care and Use of Laboratory Animals" (NIH Publication No , revised 1978). RESULTS The SIGER was implanted in nine dogs, each weighing 9.5 to 11.5 kg. They were evaluated at different intervals from 18 to 150 days. Seven dogs were killed and two dogs died of pneumonia. No death occurred from complication of the SIGER, such as detachment of the ring or pseudoaneurysm formation (Table I). In this experiment the average aortic clamping time was 2 minutes 35 seconds; the clamp time did not exceed 3 minutes in any case. There was no marked bleeding from the anastomosis. Autopsy was done in nine dogs; aortography was performed in six dogs that were killed. Detachment, pseudoaneurysm, or rupture did 1 2 Fig. 2. Sutureless intralttminal graft with elastic ring. Elastic rings are placed at both ends of knitted Dacron graft 10 or 12 rrlm in diameter and are covered with graft cuff, which is turned over at both ends.

3 40 Matsumae, Uchida, and Teramoto,~ourn~ of VASCULAR SURGERY V ( <5 Fig. 3. Implantation procedure. SIGER is kept reduced in diaincter by pinching overlapping part with forceps and introduced into aortic lumen far enough so that ring is fully covered with aortic wall, that is, overlap of aortic wall is at least 2 to 3 mm. At target forceps is released, ring expands to original size, and it attaches itself to vessel wall. No circular tie around ring is made. Table I. Summary of follow-up and cause of death Follow-up period Dog No. (days) Cause of death 1 18 Killed 2 25 Pneumonia 3 30 Killed 4 41 Killed 5 55 Pneumonia 6 64 Killed 7 73 Killed 8 80 Killed Killed not occur (Fig. 4). The SIGER was satisfactorily attached to the host aortas at the ring in all cases, and the inner surface was almost all covered with neointima (Fig. 5). The thickness of elastic fiber was reduced to half by the cxpansion pressure of the ring. However, the reduction was uniform and neither amputation nor marked reduction of elastic fiber was observed (Fig. 6). Longitudinal section showed that 2 to 3 mm overlap of aortic wall was preserved (Fig. 6). This finding proved that no migration occurred because rings were fixed; the overlap of aortic wall was 2 to 3 ram. However, in the inner one third of the aortic wall compressed by the ring, the nuclei of smooth muscle cells disappeared (Fig. 7). The anastomotic line was smooth, showing no difference in level. All grafts were patent, and aortography showed neither stenosis or dilatation at anastomosis in the six cases examined. Other complications, such as rupture or pseudoaneurysm, were not observed (Fig. 8). DISCUSSION Since the first application of the suturcless intraluminal graft to dissecting aortic aneurysrn in 1978 by Durcau et al.s and Ablaza et al.7 6 it has been widely used in reconstruction of the thoracic and abdominal aorta. The graft has the following advantages: (1) Aortic clamp time is shortencd bccause no suturing is necessary and (2) there is no bleeding from the anastomosis because of fixation by the circular tic. However, it also has the following disadvantages: (1) The degcneration of the host aorta induced by tape fixation may cause migration of the ring or wall rupture of the aorta at the ring. (2) Wide dissection around the dorsal aspect of the aorta is necessary for tape fixation. (3) The predicted diameter of the graft is sometimes too large to be inserted into the aorta because of reduction of the aortic diameter by clamphag. (4) Stcnosis sometimes occurs at the anastomosis. (5) Tape fixation arotmd the ring is sometimes difficult because marked atherosclcrotic change of the aorta makes the position of the ring unclear. To eliminate these problems, wc developed the SIGER. The SIGER, reduced in diameter by compression, is intraluminally inserted into the aorta and attaches itself to the vessel wall by elastic expansion of the ring. Because the SIGER stays in position with elastic expansion, no ligation nor dorsal aortic wall dissection 1S necessary.

4 Volume 8 Number 1 July 1988 Sutureless intraluminalgraft with elagticring 41 Fig. 4. Macroscopic findings of resected specimens. Macroscopic examina,:ion showed neither aneurysmal change nor detachment of ring. A, 41 days; B, 55 days; C, 64 days; D, 80 days after implantation. Fig. 5. Macroscopic findings of internal lumen. All grafts were covered with neointima and anastomotic lines were smooth. No detachment of ring was observed. A, 41 days; B, 55 days; C, 64 days; D, 80 days after implantation. In this study, the ratio of the host aorta to ring was 0.70 to 0.92 (host aorta without clamping: 9 to 12 mm; ring before compression: l a ram) and no migration of the ring was observed. Self-fixation of the SIGER was quite stable in all cases. However, dctachmcnt of the ring can occur because self-fixation depends on the expansion pressure. However, rupture can occur where the expansion pressure exceeds the acceptable pressure that the vessel wall can tolerate. Histologic study revealed the partial disap-

5 42 Matsumae, Uchida, and Teramoto Journal ot VASCULAR SURGERY Fig. 6. Microscopic findings. Elastic lamella was stained black. Its thickness was reduced to half at ring. Neither amputation nor marked reduction of elastic fiber was observed. Overlap of 2 to 3 mm of aortic wall was preserved. A, distal end: 41 days; B, proximal end: 73 days; C, distal end: 73 days; D, distal end: 80 days after implantation. (Elastic-van Gieson stain; original magnification 1.) pearance of the nuclei of the smooth muscle cells under expansion pressure of the ring, and this degeneration of the aortic wall suggested the possibility of aortic rupture. Moreover, no rupture occurrcd and histologically the elastic fiber was not degraded. In this study, the elasticity of the ring was suitable for avoiding complication, such as detachment of the ring or rupture of the vessel wall, but the results do not suffice to prove that neither migration nor rupture may take place.

6 Volume 8 Number 1 July 1988 Sutureless intraluminal graft with elastic ring 43 Fig. 7. Longitudinal section of graft 41 days after implantation. In inner one third of aortic wall compressed by ring, nucleus of smooth muscle cells disappeared. (Hematoxylin-eosin stain; original magnification x 100.) The predicted diameter of the sutureless intraluminal graft is often too large to be inserted into the vessel in our previous study on this graft 7,8 because aortic clamping reduced the aortic diameter. In clinical cases, 9 the diameter of the graft that could be inserted was small and stenosis occurred after implantation. There is tittle possibility that the SIGER cannot be inserted into the aorta because its diameter can be reduced on insertion; in this study all SIGER implantation (18 rings inserted) could be performed without difficulty. With SIGER, the diameter could be adjusted with elastic expansion as the vessel expanded after unclamping; therefore no stenosis occurred at anastomosis. On aortography, no stenosis was observed at the anastomotic line. In our clinical experience with the sutureless intraluminal graft, the tape sometimes could not be secured around the ring because a marked atherosclerotic change of the aorta makes the position of the ring unclear. The SIGER eliminates this problem because it can stay in the required position by elastic expansion of the ring and no ligation of the ring with tape is necessary. As mentioned earlier, SIGER has the following advantages: (1) No ligation with tape is necessary. (2) Posterior aortic wall dissection is not necessary. (3) No anastomotic stenosis occurs. (4) This graft is applicable even if the diameter of the aorta is relatively small. The SIGER may be available for the peripheral reconstruction such as the branch oftrans- Fig. 8. Aortography showed neither stcnosis nor aneurysmal dilatation at anastomosis. A, 30 days; B, 41 days; C, 60 days; D, 80 days after implantation.

7 44 Matsumae, Uchida, and Teramoto )'ournai of VASCULAR SURGERY verse aortic arch or thoracoabdominal aortic aneurysm without creating stenosis. Further research is currently underway for clinical application of this new material. REFERENCES 1. Spagna PM, Lemole GM, Strong MD, Karmilowicz NP. Rigid intraluminal prosthesis for replacement of thoracic and abdominal aorta. Ann Thorac Surg 1985;39: Goddard MB, Lucas AR, Curletti EL, Cohn MS, Sadighi PJ. Sutureless intraluminal graft for repair of abdominal aortic aneurysm. Arch Surg 1985;120: Cave-Bigley DJ, Harris PL. Use of ringed intraluminal graft in the operative management of abdominal aortic aneurysm. Br J Surg 1985;72; Lemole GM, Strong MD, Spagna PM, Karmilowicz NP. Im- proved restdts for dissecting aneurysms, intraluminal sutureless prosthesis, J Thorac Cardiovasc Surg 1982;83: Dureau GV, Villard J, George M, Ddiry P, Froment JC, Clermont A. New surgical technique for the operative management of acute dissections of the ascending aorta. J Thorac Cardiovasc Surg 1978;76: Ablaza SG, Gosch SC, Grana VP. Use of ringed intraluminal graft in the surgical treatment of dissecting aneurysm of the thoracic aorta. J Thorac Cardiovasc Surg 1978;76: Uchida H, Sunagawa M, Shirakawa K. Fate of ringed intraluminal grafts in the thoracic aorta: experimental observations. Presented at the Fifteenth World Congress of the International Cardiovascular Surgery, Athens, Greece, Sept 6-10, Inada H. Experimental study of ringed vascular graft in dogs. Nippon Kyobu Geka Gakkai Zasshi 1981;29: Ninomiya J, Yamate N, Koizumi K. Study on surgical treatment of acute aortic dissections. J Jpn Soc Clin Surg 1984; 45: