Ann Thorac Surg 1999;68:1586-1591
© 1999 The Society of Thoracic Surgeons
Original Articles
Is distal anastomosis only to the true channel in chronic type B aortic dissection justified?
Yutaka Okita, MDa,
Osamu Tagusari, MDa,
Kenji Minatoya, MDa,
Motomi Ando, MDa,
Soichiro Kitamura, MDa,
Nobuyuki Nakajima, MD, PhDa,
Shinichi Takamoto, MDa
a Department of Cardiovascular Surgery, National Cardiovascular Center, Osaka, Japan
Address reprint requests to Dr Okita, Department of Cardiovascular Surgery, National Cardiovascular Center, 5-7-1, Fujishirodai, Suita, Osaka, Japan 565
e-mail: yokita{at}ncvc.hsp.go.jp
Presented at the Thirty-fifth Annual Meeting of The Society of Thoracic Surgeons, San Antonio, TX, Jan 25–27, 1999.
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Abstract
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Background. We investigated long-term outcomes of the distal false lumen of the aorta and aortic branches after distal anastomosis of the graft only to the true lumen in chronic type B aortic dissection.
Methods. From November 1979 until June 1998, we treated 98 patients without Marfan syndrome who had chronic type B aortic dissection and underwent replacement of the descending aorta, 79 of whom had distal anastomosis to the true lumen only. The celiac artery originated from the false lumen in 11 patients, superior mesenteric artery in 5, right renal artery in 19, and left renal artery in 16.
Results. There were 12 (15.1%) early deaths. Spinal cord ischemia was detected in 5 patients. Postoperative follow-up was achieved in 67 patients, and 13 patients died. Postoperative survival at 10 years was 67.6% ± 7.1%. Eight patients had complete occlusion of the distal false lumen, 54 patients had occlusion of the false lumen down to the celiac artery, and 5 patients had a patent false lumen. Four patients required further replacement of the thoracoabdominal aorta.
Conclusions. In non-Marfan patients with chronic type B aortic dissection, the false lumen distal to the graft anastomosis was likely to be thrombosed when the graft was anastomosed to the true lumen only. Postoperative visceral circulation was not compromised, but spinal cord ischemia is a problem that remains to be solved.
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Introduction
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In chronic type B aortic dissection, the conventional technique of distal anastomosis to both true and false lumens creates risk of further enlargement of the residual distal false lumen. The aim of this study was to investigate long-term outcomes of the distal false lumen of the aorta and major aortic branches after distal anastomosis only to the true lumen in chronic type B aortic dissection.
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Patients and methods
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From November 1979 to June 1998, 119 patients with chronic type B aortic dissection had replacement of the descending aorta. Mean age at operation was 56.7 ± 7.8 years (range, 27 to 78 years). Seventy-nine patients had distal anastomosis only to the true lumen when distal re-entries of the dissection were confirmed by angiography or computed tomography. The other 40 patients consisted of 21 patients with Marfan syndrome, 10 patients who had previous fenestration of the abdominal aorta, and 9 patients with both renal arteries branched from the false lumen, who had distal anastomoses to both lumens. The main indication for operation was aneurysm size over 60 mm, except for patients with Marfan syndrome. Six patients had ruptured aneurysms.
For circulatory support, a temporary arterial bypass was used in 38 patients, left atrium–arterial bypass in 14, femoro-femoral bypass in 24, and deep hypothermic circulatory arrest in 38. Conventional surgical techniques consisted of exclusion of the initial entry with graft replacement of the enlarged portion of the aorta, and distal anastomosis to the true and false channels. In 79 patients, we used a distal anastomosis only to the true lumen and obliterated false channels when it was possible (Fig 1). The extent of replacement of the descending aorta was limited to the proximal one third of the descending aorta in 41 patients and to the middle of the descending aorta in 38 patients. No patients in these subsets had extensive replacement from the distal arch to the diaphragm.
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Fig 1. (Left) Chronic type B aortic dissection with multiple re-entries. (Middle) Conventional surgical techniques consisted of exclusion of the initial entry with graft replacement of the enlarged portion of the aorta and distal anastomoses to both true and false channels. (Right) Distal anastomosis only to the true lumen and obliterated false channels with or without a short elephant trunk inserted distally into the true lumen.
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Preoperatively, distal re-entries around the celiac axis were documented in 70 of 79 patients who had distal anastomosis to the true lumen only. Distal re-entries were demonstrated in only 11 of 19 patients who had distal anastomosis to both lumens (p = 0.0015). In 11 patients the celiac artery originated from the false lumen, 5 had the superior mesenteric artery from the false lumen, 17 had the right renal artery from the false lumen, and 15 had the left renal artery from the false lumen (Table 1). Spatial relation of the true lumen of the lower descending aorta to the vertebral column was analyzed (Fig 2). The true lumen of the thoracoabdominal aorta was located on the side facing the vertebral column in 66 patients, on the opposite side of the aorta in 7, and intermediate in 6.
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Fig 2. Spatial relationship of the true lumen of the lower descending aorta to the vertebral column. (Left) Facing the vertebrae; (middle), intermediate; (right), opposite the vertebrae.
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Statistical analysis was done by 
2 test, Student t test, and analysis of variance. Postoperative survival was analyzed using Kaplan-Meier method. Statistical significance was assumed at the p less than 0.05 level.
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Results
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There were 12 (15.1%) early deaths. Mean age of the deceased patients was 65.8 ± 6.4 years, and 3 had ruptured aneurysms. The causes of the early death were new aortic dissection in 4 patients (2 proximal and 2 distal), multiple organ failure in 4, respiratory problems in 3, perioperative stroke in 2, and mediastinitis secondary to intraoperative esophageal injury in 1.
Postoperative spinal cord ischemia was detected in 5 patients (Table 2). Two patients had the true lumen located opposite the vertebral column in the thoracoabdominal aorta, and the false lumen was occluded postoperatively. Intraoperative hemodynamic derangement was responsible for postoperative paraparesis in 2 patients. Other causes of paraplegia in 2 patients were attributed to a retrograde iatrogenic aortic dissection from the femoral cannulation in 1 and to new stenosis in the distal anastomotic suture line and resultant low perfusion distally in the other.
Postoperative patency of the visceral arteries was assessed by computed tomography or angiography (Table 3). None of the celiac and superior mesenteric arteries were occluded postoperatively in patients who had distal anastomosis to the true lumen. Five patients had postoperative occlusion of renal arteries; however, only 1 patient had new occlusion of the right renal artery after anastomosis of the true lumen.
Postoperative computed tomography showed that 8 patients had complete occlusion of the distal false lumen down to the infrarenal aorta, 44 patients had the false lumen occluded to the origin of the celiac artery, and 5 patients had a patent false lumen (Table 4). Most patients who had distal anastomosis of the true lumen had the false channels occluded in the descending aorta but not in the infrarenal aorta.
Other major morbidities consisted of transient liver dysfunction, such as elevated transaminase and bilirubin levels in 13 patients; renal dysfunction, which is serum creatinine over 3.0 mg/dL in 12; respiratory insufficiency in 10; postoperative bleeding which required reexploration in 8; gastrointestinal bleeding in 6; stroke in 2; and myocardial infarction in 1.
Postoperative follow-up was achieved in 67 patients, for 348 patient-years. Thirteen patients died. Causes of late deaths were malignancy in 5 patients, redo operation in 2, new aortic dissection in 2, stroke in 2, and myocardial infarction in 2. Postoperative 5- and 10-year survival of the patients who had distal anastomosis of the true lumen was 84.4% ± 5.7% and 67.6% ± 7.1%, respectively (Fig 3). These survival rates were low, compared with patients with distal fenestration, but statistically insignificant.
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Fig 3. Kaplan-Meier survival curve. Distal anastomosis to the true lumen only (closed circles) and distal anastomosis to the both lumens (open circles).
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Among the survivors, we analyzed time-related change of the diameter of the aorta at the diaphragm after replacement of the descending aorta. The 17 patients who had distal anastomoses of both true and false lumens (hatched line in Fig 4) were more likely to have more dilatation of the distal descending aorta (from 42.5 ± 5.8 mm to 52.6 ± 10.5 mm) than patients who had distal anastomosis of the true lumen (solid line, from 39.5 ± 6.8 mm to 43.6 ± 7.0 mm, p = 0.042). Patients with a patent false lumen (hatched line in Fig 5) had a higher risk of dilatation of the distal aorta (from 41.3 ± 6.1 mm to 53.2 ± 9.8 mm) than patients who had thrombosed false lumen (solid line, from 39.1 ± 7.2 mm to 42.8 ± 8.1 mm, p = 0.033). In 12 patients with thrombosis of the distal false lumen, progressive decrease in size of the aorta was noted. Patients who had distal anastomosis of the true lumen (solid line in Fig 6) had more freedom from the patent false lumen of the descending aorta than patients with distal fenestration (hatched line in Fig 6).
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Fig 4. Time-related changes in the diameter of the aorta at the diaphragm after replacement of the descending aorta. Distal anastomosis to the true lumen only (solid lines) and distal anastomosis to the both lumens (dotted lines).
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Fig 5. Time-related changes in the diameter of the aorta at the diaphragm after replacement of the descending aorta: thrombosis of the distal false lumen (solid lines) and patent distal false lumen (dotted lines).
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Fig 6. Freedom from patent false lumen in the distal descending aorta. Distal anastomosis to the true lumen only (closed circles) and distal anastomosis to the both lumens (open circles).
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With regard to the infrarenal abdominal aorta (Fig 7), patients who had aneurysms over 40 mm at the time of initial replacement of the descending aorta were more likely to develop progressive dilatation of the aneurysms (hatched line, from 42.1 ± 3.8 mm to 53.8 ± 8.5 mm) than patients who had aneurysms less than 40 mm (solid line, from 31.0 ± 3.5 mm to 39.5 ± 10.1 mm, p = 0.015).
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Fig 7. Time-related changes in the diameter of the infrarenal abdominal aorta after replacement of the descending aorta. Diameter of 40 mm or more (solid lines) or less than 40 mm (dashed lines) at the time of initial replacement of the descending aorta.
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Multiple operations were required in 12 patients. Four patients had redo operations because of proximal lesions. Of 4 patients who needed replacement of the thoracoabdominal aorta, 2 had patent false lumens and 2 had occluded false lumens. Three patients required replacement of the infrarenal aorta, and 1 patient had an extraanatomic bypass because of graft infection. Among patients with distal anastomosis of the true lumen, 2 patients required emergent operations for distal aorta rupture secondary to clamp injury. Freedom from reoperation on the distal aorta was lower in those patients than in patients who had distal fenestration (Fig 8).
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Fig 8. Freedom from aortic events in the distal descending aorta. Distal anastomosis to the true lumen only (closed circles) and distal anastomosis to both lumens (open circles).
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Comment
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Elective repair of chronic type B aortic dissection yielded better results than those obtained for emergency repairs of acute aortic dissection. Although early death rates have gradually declined, surgical results for chronic type B aortic dissection are somewhat worse than those for chronic type A aortic dissection. In the historical series of DeBakey and colleagues [1] in 1965 they reported a 19% early mortality rate, whereas in 1988 Crawford and colleagues [2] reported a 7.4% mortality rate for chronic type B dissection. Their analysis showed that the predictors of early postoperative death were older age, year of operation, extent of replacement, cardiac complications, reoperation for bleeding, paraplegia or paraparesis, and postoperative dialysis.
Long-term results for chronic type B dissection have been less encouraging. The 5-year survival rate has varied between 45% and 95%, decreasing to 50% or 60% after 10 years [2–6]. Ergin and associates [5] reported that total obliteration of the distal false lumen at primary repair improved event-free survival (85% at 5 years versus 63% with the distal false lumen patent). Crawford and colleagues [7] noted that residual aortic aneurysm was the principal determinant for reoperation. In their experience, freedom from reoperation was only 25% at 5 years in patients with a residual distal aneurysm compared with 90% in patients without aneurysm. Borst and associates (Borst HG, Jurmann MJ, Heineman MK, Laas J. Redo surgery after primary operation for acute and chronic aortic dissection [abstract]. International Symposium on Disease of the Aorta, February 24–26, 1992, Tokyo, Japan) reported that aneurysmal dilatation of the distal aortic segments was the indication for reoperation in 87.5% of cases after repair of chronic aortic dissection. Further replacement of the thoracoabdominal aortic segments adds additional risks for long-term results. Svensson and coworkers [8] reported that multivariate predictors of postoperative death after thoracoabdominal operation were older age, preoperative renal dysfunction, concurrent proximal aortic aneurysms, coronary artery disease, chronic pulmonary disease, and total aortic cross-clamp time. The incidence of paraplegia or paraparesis varied from 5% to 30%, and renal failure occurred in 10% to 20%. Cumulative survival after thoracoabdominal replacement further decreased to 40% to 60% compared with survival of descending aortic operations [9].
Conventional surgical techniques consisted of exclusion of the initial entry with graft replacement of the enlarged portion of the aorta, and distal anastomosis to the both true and false channels. However, this technique results in a patent distal false channel and carries a risk of the further operation for distal aortic segments. Our strategy for distal anastomosis in patients with chronic type B dissection was to anastomose a graft solely to the true lumen when significantly large distal re-entries were identified by angiography or computed tomography. Thrombosed false lumen in the distal aorta progressively decreased in diameter or grew more slowly compared with the diameter of the patent false lumen. This strategy carries some risk of obstruction of the major arterial branches. However, normally in aortic dissection, several re-entries of the intimal flap exist around the celiac axis. The false lumen of the distal descending aorta eventually occluded after replacement of the proximal descending aorta, with obliteration of the false lumen in most patients, but the false lumen around the celiac axis was patent except in 1 patient. The results of the present study provide supporting data for clinical application of the stented graft for chronic type B aortic dissection.
Multifactorial causes of postoperative spinal cord ischemia made prediction of spinal cord injury complicated [10–12]. Preoperative evaluation by angiography of blood supply to the spinal cord is time-consuming and unpredictable. A less invasive procedure, magnetic resonance imaging, has potential to detect the Adamkiewicz artery in the near future. We arbitrarily classified locations of the true channels of the lower descending aorta or thoracoabdominal aorta in relation to the vertebral column. When the true channel runs opposite to the vertebrae in the aorta, the intercostal arteries are likely to originate from the false lumen facing the vertebrae, and the resultant occlusion of the false lumen after proximal obliteration could promote spinal cord ischemia.
In chronic dissection with dilatation of the aorta, the paraceliac portion of the aorta is the predisposing site for aortic obstruction [13]. Major branches of the abdominal aorta are likely to be perfused from the false channel alone. Formation of mural thrombus in low-flow areas of either true lumen might ensue, there and in the false lumen as well. Under these circumstances, rerouting of blood into the true lumen after aortic repair could have unpredictable effects on visceral and lower-extremity perfusion [14]. Moreover, during thoracic aortic repair, retrograde perfusion of the aorta from the femoral cannula might not permit perfusion of vital organs, especially the heart and brain [15]. By preceding aortic fenestration with graft replacement of the abdominal aorta in patients with aortic obstruction, a secure cardiopulmonary bypass, even with retrograde perfusion through femoral arterial cannulation, is provided. Opening the blind channel by fenestration or resection of the intimal flap in the abdominal aorta provides hemodynamic relief [16].
In patients with chronic type B aortic dissection who do not have Marfan syndrome, the technique of anastomosing a graft only to the distal true channels and obliterating the false channel might prevent later replacement of the descending aorta and could prevent future dilatation of the thoracoabdominal aorta. However, careful assessment of the vasculatures of the spinal cord and visceral arteries is mandatory to prevent organ ischemia.
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References
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Abstract
Introduction
