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Ann Thorac Surg 2002;73:444-448
© 2002 The Society of Thoracic Surgeons

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Original article: cardiovascular

Repair of the thoracic aorta by transaortic stent grafting (open stenting)

^a Department of Cardiovascular Surgery, Hiroshima City Asa Hospital, Hiroshima, Japan

Accepted for publication August 7, 2001.

* Address reprint requests to Dr Uchida, Department of Cardiovascular Surgery, Hiroshima City Asa Hospital, Kabe-minami, Asakita-Ku, Hiroshima-City, Hiroshima, 731-0223, Japan
e-mail: cvgeka{at}asa-hosp.city.hiroshima.jp

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. The late results of direct open stent grafting of the aortic arch for aortic arch repair have not been reported previously.

Methods. Between September 1997 and December 2000, 19 patients underwent open stent grafting with carotid artery bypass for thoracic arteriosclerotic aneurysms (TAA) of the distal aortic arch. In addition, 21 patients underwent open stent grafting with total aortic arch replacement for Stanford type A acute aortic dissection and 7 patients underwent stenting with carotid bypass for Stanford type B chronic aortic dissection.

Results. The early mortality rate was 11% for TAA, 10% for type A dissection, and 0% for type B dissection. Whereas none of the TAA or type A dissection required a second operation on the thoracic aorta, 1 TAA patient died 6 months postoperatively after sudden aortic rupture and 1 type B patient required descending aortic replacement because of ulceration caused by the stent graft at 11 months postoperatively. On follow-up computed tomography scan, in TAA patients, true aneurysms excluded by the stent graft showed early thrombosis, but the absorption of thrombosed aneurysms started from 1 to 6 months postoperatively and gradually progressed. In patients with type B chronic dissection, the false lumen showed early thrombosis and the true lumen was dilated at the central portion of the graft, which might increase turbulent flow by interaction with the stent. In patients with type A acute dissection, the false lumen showed both early thrombosis and early absorption.

Conclusions. Early and late results of open stenting are acceptable and follow-up computed tomography scan may be able to predict late results of open stenting.

	Introduction

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Surgical treatment of aortic aneurysm or dissection involving the aortic arch results in a high mortality rate and a high rate of complications [1, 2]. Total arch replacement with selective cerebral perfusion [3] and endovascular stent grafting through the femoral artery [4] are associated with lower rates of death and complications, but the results can be unsatisfactory. In an effort to improve the outcome, direct stenting of the aortic arch (open stent grafting) was proposed by Kato and colleagues [5]. This new method has been used recently as a less invasive operation for aortic arch disease. Open stent grafting may also be used for extensive primary repair of the thoracic aorta through median sternotomy alone, thus avoiding left thoracotomy. However, the midterm results of open stent grafting have not been reported yet. This study was performed to assess the midterm results and to predict the long-term results by measuring the diameter and shape of intrastent and extrastent grafts using follow-up computed tomography.

	Material and methods

Top Abstract Introduction Material and methods Results Comment References

 
Patients
Forty-seven patients (30 men and 17 women) underwent repair of the thoracic aorta using transaortic stenting (open stent grafting) between September 1997 and December 2000. The patients ranged in age from 47 to 82 years (mean 65 ± 8 years). Table 1 summarizes their preoperative characteristics.

View larger version (30K): [in this window] [in a new window]   Fig 1. Schema of open stenting in this series. The type 1 operation involved open stent grafting with subclavian artery bypass from the ascending aorta for thoracic arteriosclerotic aneurysms of the distal aortic arch or type B aortic dissection, whereas the type 2 operation involved open stent grafting with total aortic arch replacement for acute type A aortic dissection.

Procedure
A self-expanding Z-shaped stent with the tip 5 cm on the distal side was attached to a Dacron prosthesis with a diameter between 22 and 35 mm using 5-0 monofilament sutures. These stent grafts were prepared preoperatively for use in emergency operations.

In patients with TAA and type B dissection, the stent graft was set at 110% of the diameter of the distal descending aorta on preoperative helical CT scans and the diameter was verified by intraoperative transesophageal echocardiography.

In patients with type A dissection, the size of the stent graft was determined by intraoperative measurement using a ball-shaped sizer inserted into the true lumen of the descending aorta from the transverse incision under transesophageal echocardiography guidance. The length of the stent graft was determined by intraoperative measurement, taking into consideration the findings on preoperative aortography.

Operative techniques
The type 1 operation involved open stent grafting with left subclavian artery bypass from the ascending aorta, whereas the type 2 operation involved open stent grafting with total aortic arch replacement.

In both operations, median sternotomy was performed under general anesthesia. An arterial perfusion cannula was inserted into the femoral or right axillary artery in patients with acute type A aortic dissection and into the ascending aorta at a point that was safe according to intraoperative ultrasonic examination in patients with TAA or type B aortic dissection. The patient was cooled to a rectal temperature of 22°C by extracorporeal circulation and cardioprotection was provided by retrograde blood cardioplegia.

In the type 1 operation for TAA or type B dissection, selective cerebral perfusion was performed through direct cut down of a carotid artery when the rectal temperature fell to 25°C before circulatory arrest. Three balloon catheters were inserted into the brachiocephalic artery, the left common carotid artery, and the left subclavian artery for perfusion at rates of 300, 200, and 100 mL/min, respectively. To prevent cerebral embolism, the aortic arch was dissected after selective cerebral perfusion had been initiated. The aortic arch was transected at the predetermined proximal anastomotic line (usually before the origin of the left subclavian artery). A stent graft measuring 8 to 17 cm long that had previously been attached to a self-expanding Z-shaped stent with the tip 5 cm on the distal side was selected with a diameter 10% larger than that of the normal aorta. Then the stented graft was placed in a 30F introducer that was inserted into the descending aorta by the method of Kato and coworkers [5]. The graft was fixed in the descending aorta by expansion of the Z-stent, advanced to the dissection in the distal aortic arch, and then trimmed to fit. The left subclavian artery was dissected transversely at its proximal end, and the proximal stump was closed using 4-0 monofilament sutures. The adventitia of the aortic stump was covered with a 2-cm wide felt strip, and the stump was reinforced by a continuous 4-0 monofilament suture. Then the transected aortic arch was closed with a continuous 3-0 monofilament suture and a felt strip 2 cm wide. An 8-mm gelatin-sealed, woven Dacron prosthesis with a side branch was then anastomosed to the ascending aorta after the aortic cannula was removed. After restarting systemic perfusion from the ascending aorta through the side branch, the patient was rewarmed by using the extracorporeal circuit. Then a left subclavian artery bypass was performed and selective cerebral perfusion was stopped just before direct closure of the cut-down aortic incision.

In type 2 operations for type A dissection, a cross-clamp was applied to the distal part of the ascending aorta before circulatory arrest was initiated. The ascending aorta was dissected transversely at the proximal end, and then geratin-resolcin-formalin glue was injected into the false lumen in the proximal ascending aorta. After the patient was cooled to a rectal temperature of 22°C, total circulatory arrest was achieved. Then the clamp was removed and the aortic arch was incised longitudinally until immediately before the origin of the left subclavian artery. At this point, the aortic arch was dissected transversely. Three balloon catheters were inserted into the vessels supplying the brain, as in the type 1 operation. A ball-shaped sizer was inserted into the true lumen of the descending thoracic aorta from the transverse incision in the aortic arch, and then the exact diameter of the lumen was measured gently under transesophageal ultrasonic guidance. A synthetic graft from 8 to 15 cm long, which had previously been attached to a self-expanding Z-shaped stent with the tip 5 cm on the distal side, was selected with the same diameter as that of the normal aorta. Then the graft was placed in a 30F introducer according to Kato’s procedure and was fixed inside the true lumen of the descending aorta by expansion of the Z-stent. Subsequently, the free end of the graft was pulled to the transverse incisional line in the distal aortic arch and trimmed to fit. The aortic stump was covered with a felt strip measuring 2 cm wide, and the stump was reinforced by continuous 4-0 monofilament sutures. Next, a synthetic graft with four branches was anastomosed end-to-end to the stump of the distal aortic arch using continuous 3-0 monofilament sutures. After the third branch of the graft was anastomosed to the left subclavian artery, the patient was rewarmed using the extracorporeal circuit. Subsequently, the proximal graft was anastomosed to the stump of the ascending aorta. Finally, the left common carotid artery and the brachiocephalic artery were anastomosed to the respective branches of the graft.

Follow-up
The patients were followed up until March 2001 and follow-up was 100% complete. The mean follow-up period was 20 months (range 3 to 42 months). Computed tomography was performed at 1, 6, 12, and 24 months postoperatively to detect thrombosis or absorption of the descending aorta excluded by the stent graft. The intrastent graft diameter, extrastent graft diameter, and total aortic diameter were measured on follow-up CT scans and the ratio of each diameter to the diameter of the inserted graft was calculated (Fig 2). Each diameter was measured on the point of maximum diameter in the patients with TAA, and on the end point of distally placed stent graft in the patients with type A or type B dissection. With egg-shaped stent grafts, the diameter was measured on the short axis. Absorption of thrombosis was defined as occurring if the diameter of the thrombosed descending aorta decreased by more than 4 mm.

View larger version (148K): [in this window] [in a new window]   Fig 2. Graft diameter ratio. The intrastent graft diameter, extrastent graft diameter, and total aortic diameter were measured on follow-up computed tomography scans and the ratio of each diameter to the diameter of the inserted graft was calculated. Intragraft diameter ratio = a/diameter of stent graft; Extragraft diameter ratio = b/diameter of stent graft; Total aortic diameter ratio = c/diameter of stent graft.

	Results

Top Abstract Introduction Material and methods Results Comment References

Table 4 summarizes the postoperative late results. One TAA patient died 6 months postoperatively after sudden aortic rupture into the esophagus caused by distal minor endoleakage. This patient showed no absorption of the thrombosed aneurysm on follow-up CT at 3 months after operation. None of the type A patients was dead after a mean follow-up period of 20 months, whereas 1 type B patient died of a ruptured abdominal aortic aneurysm.

Results of follow-up computed tomography scanning
In TAA patients, the intragraft diameter ratio remained at more than 0.95 from 1 month postoperatively (Fig 3). The total aortic diameter ratio increased slightly or was unchanged at 1 month and then gradually decreased from 6 months postoperatively.

View larger version (36K): [in this window] [in a new window]   Fig 3. Graft diameter ratio on follow-up computed tomography scans. (A) Intragraft diameter ratio = intragraft diameter/diameter of stent graft. (B) Extragraft diameter ratio = extragraft diameter/diameter of stent graft. (C) Total aortic diameter ratio = aortic diameter/diameter of stent graft. (TAA = thoracic arteriosclerotic aneurysm of the distal aortic arch; pre-op = before operation; 1M = 1 month after operation; 6M = 6 months after operation; 1Y = 1 year after operation; 2Y = 2 years after operation.)

In type B patients, the intragraft diameter ratio was low preoperatively (0.6) because the false lumen compressed the true lumen. The ratio increased or was unchanged at 1 month and then gradually increased from 6 months onwards. Also, the extragraft diameter or total aortic diameter ratio decreased slightly or was unchanged at 1 month postoperatively and then decreased gradually from 6 months onwards.

Additional operations
Three TAA patients and 1 type A patient underwent subsequent Y grafting for preexisting abdominal aortic aneurysms. However, none of the TAA or type A patients required a second operation on the thoracic aorta. However, 1 type B patient required descending aortic replacement 11 months postoperatively because of ulceration caused by the stent graft.

	Comment

Top Abstract Introduction Material and methods Results Comment References

 
It has been reported that endovascular stent grafting is less invasive and achieves good midterm results [6, 7]. However, the limitations of transluminal endovascular stent grafting have been pointed out, and its role in the treatment of the aortic arch has not yet been established. Many thoracic arteriosclerotic aneurysms or entry sites of dissecting aneurysms occur frequently in the distal aortic arch and involve the cephalic vessels. As a result, transluminal endovascular stent grafting is difficult to adapt to the branched portion of the aortic arch because the proximal neck that is essential in transluminal endovascular stent grafting does not exist in this type of aneurysm or dissection. Direct open stent grafting obtains anastomosis on the distal anastomotic portion by substituting the expansile force of the stented graft for the suture and on the proximal anastomotic portion by suture, where it is hard to adapt the stent anastomosis [5]. Therefore, direct open stent grafting of the aortic arch has been performed recently as a less invasive operation for aortic arch aneurysms [5, 8–11]. In addition, open stent grafting could be used for extensive primary repair of the thoracic aorta through median sternotomy alone, avoiding left thoracotomy.

Kato and colleagues [5] reported good early results with the open stent grafting method. In particular, the postoperative recovery period was shortened by avoiding massive bleeding and pulmonary complications. However, the late results of open stent grafting have not been reported previously, such as whether the aneurysm disappears as a result of the stent graft or whether intimal damage is caused by the stent. This study not only provided such late results, but also predicted the long-term results by assessing the diameter and shape of the graft on follow-up CT scans.

In TAA patients, true aneurysms excluded by the stent graft showed early thrombosis, but the thrombosed aneurysms were not absorbed in the early postoperative period so complications related to compression by the aneurysm were not avoided. The absorption of thrombosed aneurysms started from 1 to 6 months postoperatively and gradually progressed. If the diameter of the completely thrombosed aneurysm has not decreased after 1 year, our results would suggest the existence of minor leakage that is not detected by enhanced CT or angiography.

In patients with type B "chronic" dissection, the false lumen showed early thrombosis, but the thrombosed lumen persisted in the early postoperative period, as was the case in TAA patients. In addition, the true lumen was dilated at the central portion of the graft, which might increase turbulent flow by interaction with the stent. Such flow may damage the intima of the true lumen and lead to ulceration in the midterm postoperative period.

In patients with type A "acute" dissection, the false lumen showed early thrombosis and early absorption. This result demonstrated that early stent grafting for acute dissection can maintain the normal diameter and blood flow of the true lumen and can completely exclude the false lumen. In addition, the true lumen was not dilated at the site of stenting, so there would be less turbulence caused by interaction with the stent. Thus, open stent grafting of the distal descending aorta with total arch replacement can allow extended thoracic aortic replacement from the ascending to descending aorta in patients with acute type A dissection.

	References

Top Abstract Introduction Material and methods Results Comment References

 

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