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Ann Thorac Surg 2005;79:790-794
© 2005 The Society of Thoracic Surgeons

Original article: Cardiovascular

Outcome of Medical and Surgical Treatment in Patients With Acute Type B Aortic Dissection

Ron-Bin Hsu, MDa,*, Yi-Lwun Ho, MDb, Robert J. Chen, MD, MPHa, Shoei-Shen Wang, MDa, Fang-Yue Lin, MDa, Shu-Hsun Chu, MDa

a Department of Surgery, Taipei, Taiwan, ROC
b Internal Medicine, National Taiwan University Hospital, National Taiwan University College of Medicine, Taipei, Taiwan, ROC

Accepted for publication July 23, 2004.

* Address reprint requests to Dr Hsu, National Taiwan University Hospital, No. 7, Chung-Shan S. Rd. Taipei, Taiwan 100, ROC; (E-mail: ronbin{at}ha.mc.ntu.edu.tw).


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 References
 
BACKGROUND: Optimal treatment of acute type B aortic dissection remain unclear. The aim of this study was to assess the clinical outcome of acute type B aortic dissection.

METHODS: In the last 8 years, 107 patients were admitted for acute type B aortic dissection. We medically treated patients at the time of onset with antihypertensives. Surgery was considered if there is intractable pain, uncontrolled hypertension, severe aortic branch malperfusion, or aneurysm expansion.

RESULTS: Twenty-nine patients had pleural effusion (27%), 9 patients had leg ischemia (8%), 5 patients had impending rupture, and 2 patients had aneurysm enlargement exceeding 60 mm on repeated imaging studies. A total of 16 patients (15%) underwent surgical intervention: 8 extra-anatomical bypass for leg ischemia, 1 in situ infrarenal aortoiliac bypass for distal aortic obstruction, and 7 thoracic aortic graft replacement. Of the 8 patients with extra-anatomic bypass, 3 patients died: 2 patients died of catastrophic aortic rupture 2 and 9 days after bypass, and 1 patient died of dissection progression to type A lesion 9 days after bypass. There was no in-hospital death in 92 medically treated patients. Follow-up was 92% complete. The mean follow-up duration was 36.1 months (range, 2 to 96 months). The 6-month, 1-year, and 5-year survival rates of all patients were 96.2 ± 1.9%, 95.2% ± 2.1%, and 95.2% ± 2.1%.

CONCLUSIONS: Medical treatment of acute type B aortic dissection produced good outcomes. Central aortic procedures such as aortic fenestration and endovascular stenting should be the preferred methods to treat patients with acute type B aortic dissection and leg ischemia because there was high risk of central aortic complications after extra-anatomic bypass.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 References
 
Previous studies have demonstrated that the prognosis of acute type B aortic dissection without major complications, such as impending rupture or aortic branch compromise, was acceptable with medical therapy alone [1, 2]. But the results of surgical intervention for complicated type B dissection were poor [3–10]. The aim of this study is to assess the clinical outcome of acute type B aortic dissection in a single center experience.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 References
 
Patients
Patients included were those presented to the emergency department within 2 weeks of the onset of their symptoms (chest pain or back pain). Patients with chronic dissection or iatrogenic dissection were excluded. Aortic branch compromise was defined by clinical abnormalities detected by clinical symptoms, physical examination, or imaging studies. The clinical evidence of aortic branch compromise in type B aortic dissection included leg ischemia, paraparesis/paraplegia, acute renal failure, and mesenteric ischemia (abdominal pain, tenderness, metabolic acidosis, or frank bowel ischemia confirmed at operation). It was further confirmed by imaging studies, either computed tomography or magnetic resonance imaging. Those patent aortic branches that were involved in the dissection process or were perfused from the false lumen were not considered as compromised aortic branches.

Medical Management
Patients were admitted to intensive care unit and treated with antihypertensives at the time of onset. Intravenous labetalol and nitroglycerin were given for keeping minimum systolic blood pressure below 140 mm Hg and to maintain appropriate urine output. Intramuscular meperidine was used to relieve pain. If there was no need of emergency operation, oral antihypertensives with ß-blockers, calcium-channel-blockers, angiotensin-converting enzyme inhibitors, or in combination were prescribed. Contrast computed tomography or magnetic resonance imaging was repeated while there was any evidence of complications, such as hematuria, decreased urine output, decreased pedal pulses, abdominal pain, drop of serum hemoglobin, and increased pleural effusion. Patients can be moved from intensive care unit 5 to 7 days after onset. Contrast computed tomography or magnetic resonance imaging was repeated 2 to 4 weeks after onset. Patients could go home 3 to 4 weeks after onset. Patients were followed by cardiologists or cardiac surgeons. Chest film was followed every 3 to 6 months and contrast computed tomography or magnetic resonance imaging was repeated if there was evidence of aneurysm progression.

Surgical Management
Surgery was considered if there was intractable pain, uncontrolled hypertension or serious aortic branch malperfusion. Patients complicated with leg ischemia were treated with extra-anatomic bypass, either axillofemoral or femorofemoral bypass. Intravenous heparin was used during the operation and was reversed with protamine after the operation. No anticoagulation was given thereafter and the blood pressure was controlled as described in medical management.

If there was evidence of impending rupture (intractable pain, uncontrolled hypertension or unstable vital signs), or the maximum diameter of dissected aorta exceeded 60 mm on repeated imaging studies, aortic graft replacement was performed. Through a posterolateral thoracotomy and with either partial (femorofemoral) cardiopulmonary bypass or total cardiopulmonary bypass and profound hypothermic circulatory arrest, a short segment of the dissected aorta containing the severe injury was replaced with a double velour-woven Hemashield Dacron graft. No anticoagulation was given thereafter and the blood pressure was controlled as described in medical management. Because of technical limitation, no endovascular procedure was performed for complicated acute type B dissection in our hospital.

Data Collection
Clinical data were obtained retrospectively through chart review, and current follow-up was obtained by telephone or written communication. The actuarial survival rate of patients was plotted by Kaplan-Meier method.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 References
 
Patients
Between January 1996 and December 2003, a total of 107 patients with acute Stanford type B aortic dissection were admitted to our institution. Eighty-two patients (76.6%) were male, and the mean age was 58.4 ± 14.7 years (range 22–95 years old). Ninety-three patients (86.9%) had a history of hypertension. Three patients had Marfan's syndrome. Thirteen patients (12.1%) had intramural hematoma at the time of onset. Among the 107 patients, 29 patients had pleural effusion (27%), 9 patients had leg ischemia (8%), 4 patients had impending rupture, and 1 patient had paraparesis. One patient had acute renal failure and 3 patients had renal infarction with preserved renal function. Two patients had dissection of superior mesenteric artery but no abdominal pain. Two patients, who were not Marfan's syndrome, had aneurysm enlargement to 65 and 70 mm on repeated imaging studies 14 and 30 days after the onset of type B dissection.

Surgery
A total of 16 patients (15%) underwent surgical intervention (Table 1): 8 patients underwent emergency extraanatomical bypass for leg ischemia, 1 patient underwent in situ infrarenal aortoiliac bypass for leg ischemia due to distal aortic bifurcation obstruction, and 7 patients underwent aortic graft replacement. The mean duration from the time of onset to surgery was 5.1 ± 8.3 days (range, 0 to 30 days). The operative mortality rate was 18.8%. Of the 8 patients with extraanatomic bypass (5 axillofemoral and 3 femorofemoral bypass), 3 patients died: 2 patients died of sudden aortic rupture 2 and 9 days after operation and 1 patient died of progression to type A dissection 9 days after operation. There was no in-hospital death in 7 patients with aortic graft replacement.


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  		Table 1. Patients Who Underwent Surgery
 
A 72-year-old male patient had a previous history of gastric carcinoma and infrarenal abdominal aortic aneurysm. He had acute type B aortic dissection from orifice of left subclavian artery to infrarenal abdominal aorta. The dissected abdominal aneurysm had accelerated enlargement from 60 to 70 mm 1 month after the onset. He successfully underwent aortic graft replacement of dissected abdominal aorta through thoracoabdominal approach. However, he died of stroke 7 months after operation.

Survival and Late Aortic Events
There were no in-hospital deaths in 92 medically treated patients. One patient died suddenly 1 month after discharge. Another patient underwent descending aortic grafting 5 years after discharge because of aneurysm enlargement. However, 9 patients were lost during follow-up. Follow-up was 92% complete. The mean follow-up duration was 36.1 months (range, 2 to 96 months). The 1-month, 6-month, 1-year, and 5-year survival rates of all patients were 97.2% ± 1.6%, 96.2% ± 1.9%, 95.2% ± 2.1%, and 95.2% ± 2.1% by Kaplan-Meier method (Fig 1). The 1-month, 6-month, 1-year, and 5-year survival rates of medically treated patients were 100%, 98.9% ± 1.1%, 98.9% ± 1.1%, and 98.9% ± 1.1%. The 1-month, 6-month, 1-year, and 5-year survival rates of surgically treated patients were 93.8% ± 6.1%, 81.3% ± 11.1%, 74.5% ± 11.1%, and 74.5% ± 11.1%.



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  		Fig 1. Actuarial survival curve of all patients (n = 107) with acute type B aortic dissection by Kaplan-Meier method.

 

   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
References
 
The clinical outcomes of patients with acute type B dissections continue to be debated [1, 2, 11–22]. The reported in-hospital mortality rates range from 3.8% to 14.6%. In a previous report of 384 patients with acute type B aortic dissection enrolled in the international registry of acute aortic dissection (IRAD) study [3], the in-hospital mortality rate was 12.8% and most deaths occurred within the first week. The in-hospital mortality rate was 32.1% in surgical patients and 9.6% in medically treated patients. Approximately two-thirds of the patients had initially presented elsewhere and were transferred to an IRAD center for further assessment and management. Genoni and colleagues [23] reported that the in-hospital mortality rate was 14.6%. Aortic rupture was present in 12%, and leg ischemia was present in 15% of their 130 patients. Umana and associates [12] also reported that the prognosis for patients with acute type B aortic dissection was bleak. Visceral ischemia was present in 27.5%, leg ischemia was present in 24.3%, and surgical intervention was performed in 35.4% of their 189 patients. Actuarial survival rates for their medically treated patients were 85% ± 4%, 71% ± 5%, 38% ± 6%, and 20% ± 6% at 1, 5, 10, and 15 years. However, Hata and coworkers [11], in a smaller series of 79 patients with acute type B aortic dissection, reported an extremely low in-hospital mortality rate because of a much lower incidence of complicated dissection. They reported that the in-hospital mortality rate was 3.8% and only 2 patients underwent emergency axillofemoral bypass for leg ischemia within 30 days after the onset of dissection. However, the rate of transferred cases was not mentioned.

Compared with the IRAD study [3], we had a lower rate of transferred cases (52.3% vs 64.4%), a lower rate of intervention cases (15% vs 27%), and a lower rate of compromise of iliac, mesenteric, or renal arteries (9% vs 22%). Compared to previous studies [3, 11, 23] published between 2002 and 2003 (Table 2), we and Hata had a much lower incidence of surgical intervention within 30 days after the onset of type B dissection and an improved in-hospital survival rate, especially in medically treated patients. It was assumed that the low in-hospital mortality rate in our series result from a referral bias present in previous studies. Only those patients with complicated dissection would be transferred to the medical center. Thus, a survey of national database will provide more correct information about medical and surgical treatment of acute type B aortic dissection.


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  		Table 2. Comparison of Characteristics of Patients With Acute Type B Aortic Dissection in Previous Reports Between 2002 and 2003
 
Optimal management of patients with acute type B dissections continued to be debated. Medical treatment was generally advocated for patients with acute type B aortic dissection without complications and surgery was reserved for patients with complicated dissection. In addition to central aortic complications, the dissection process might obstruct aortic branch ostia causing malperfusion and mortality [4, 6–10, 18–22]. Patients who had symptomatic aortic branch compromise had a significantly higher mortality rate than those who did not [1, 3]. In the IRAD study, 15% of all deaths were related to mesenteric ischemia. Optimal surgical management of such patients remained controversial with respect to both the techniques of intervention (open surgery or endovascular procedure) and the timing of surgical intervention. Some authors advocated consideration of early operation for selected patients with acute type B aortic dissection, irrespective of the presence or absence of complications [13–16]. Although aortic graft replacement was associated with low risk of in-hospital death, there was still high incidence of postoperative morbidity after early operation. In our 8 patients with aortic graft replacement (Table 1), 4 patients had at least one major postoperative complication. Because of an excellent clinical outcome of medical treatment in our patients, we recommended continued medical treatment in every case of acute type B aortic dissection without major complications.

There was still a controversy concerning the optimal surgical strategies for leg ischemia in patients with acute type B aortic dissection. Aortic grafting, aortic fenestration, or extraanatomic bypass can be selected to restore limb perfusion. Lauterbach and colleagues [10] reported that leg ischemia occurred in 11 of 86 patients (13%) with acute type B aortic dissection. Among patients with leg ischemia, 3 patients continued medical treatment with no surgical intervention and the pulse was restored spontaneously. One patient underwent descending aortic repair but the leg ended up with amputation. Six patients had open or endovascular aortic fenestration with good outcome. One patient had both aortic fenestration and aortofemoral bypass with good outcome. They concluded that aortic fenestration by either open or endovascular approach provided good results. But the result of extraanatomic bypass for leg ischemia remained unclear. In our 8 patients undergoing extra-anatomic bypass, 3 patients died of central aortic complications after bypass operation. It was possible that heparin use and fluctuating blood pressure during operation would increase the risk of central aortic complications and subsequent mortality. Central aortic procedures such as aortic fenestration and endovascular stenting should be the preferred methods to treat patients with acute type B aortic dissection and leg ischemia [4, 6, 10].

The study reviewed our 8-year experience with the treatment of acute type B aortic dissection. Like other previous reports, this study was limited by retrospective study and an inherent referral bias. However, this was first study demonstrating the risk of central aortic complication after extra-anatomic bypass.

In conclusion, medical treatment of acute type B aortic dissection produced good outcomes. Central aortic procedures such as aortic fenestration and endovascular stenting should be the preferred methods to treat patients with acute type B aortic dissection and leg ischemia because there was high risk of central aortic complications after extra-anatomic bypass.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 References
 

  1. Hagan PG, Nienaber CA, Isselbacher EM, et al. The international registry of acute aortic dissection (IRAD): new insights into an old disease JAMA 2000;283:897-903.[Abstract/Free Full Text]
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  11. Hata M, Shiono M, Inoue T, et al. Optimal treatment of type B acute aortic dissection: long-term medical follow-up results Ann Thorac Surg 2003;75:1781-1784.[Abstract/Free Full Text]
  12. Umana JP, Lai DT, Mitchell RS, et al. Is medical therapy still the optimal treatment strategy for patients with acute type B aortic dissections? J Thorac Cardiovasc Surg 2002;124:896-910.[Abstract/Free Full Text]
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