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Ann Thorac Surg 1995;59:1200-1203
© 1995 The Society of Thoracic Surgeons

Operation for Type B Aortic Dissection: Introduction of Left Heart Bypass

Department of Cardiovascular Surgery, The Heart Institute of Japan, Tokyo Women's Medical College, Tokyo, Japan

Accepted for publication February 6, 1995.

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Various support techniques for surgical treatment of type B aortic dissection have been used and recommended in many medical centers. In the last 21 years, 55 patients with type B aortic dissection underwent 65 operations including 10 reoperations, and 10 cases showed Marfan's syndrome. As circulatory support during operation, venoarterial bypass mainly was used until March 1987 (period I) and low-dose heparinized left heart bypass was applied since April 1987 (period II). Surgical results were compared among subgroups by the Kaplan-Meier actuarial method and Cox-Mantel statistical analysis. After the operation, early mortality was 27.3% in 33 patients in period I and 9.4% in 32 patients in period II (p = 0.06). The incidence of fatal hemorrhagic complications was decreased significantly by using the left heart bypass technique (p < 0.02). The 5-year actuarial survival of type B dissection was 60.6% in period I and 79.2% in period II (p = 0.07). These results suggest that surgical results of type B aortic dissection in this series might be improved with the introduction of left heart bypass and extended surgical procedures.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
See also page 1203.

Recently, surgical results of type B aortic dissection have been improving, and the early mortality after operation is about 10% or less at major medical centers [1–3]. However, various support techniques for this type of operation, such as simple cross-clamping [4, 5], open distal anastomosis [6, 7], passive shunt [8, 9], femoral venoarterial bypass [10, 11], and left heart bypass [1, 12, 13] are used and recommended in different centers.

We have applied several different techniques for surgical treatment of type B aortic dissection over 21 years [14, 15]. The aim of this study is to evaluate the change in surgical results of type B aortic dissection with the introduction of left heart bypass.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
From July 1972 to June 1993, 55 consecutive patients with Stanford type B aortic dissection were treated surgically at the Heart Institute of Japan, Tokyo Women's Medical College. Thirty-eight patients were men and 17 were women. The age of patients ranged from 23 to 69 years and averaged 48.3 ± 10.6 years. Nine of those patients received 10 reoperations; therefore, we had 65 surgical cases in this time period.

According to the Stanford classification of types of aortic dissection [16, 17], 65 cases showed type B dissection without involvement of the ascending aorta. With respect to the timing of operation, aortic dissection was defined as acute in patients who received surgical treatment within 14 days after the onset of symptoms. Four patients had acute type B dissection and 61 had chronic type B. Of the 65 patients, 10 patients (15.4%) had Marfan's syndrome.

All patients gave informed consent, and the institutional committee on human research approved the present study protocol.

Intraoperative Circulatory Support
Concerning the circulatory support during operation on aortic dissection, several types of assisted circulation have been used over the last 21 years [14, 15]. In patients with type B dissection, femoral venoarterial bypass with oxygenation mainly was used for the former 15 years and low-dose heparinized left heart bypass [13] with a centrifugal pump and heparin-coated tubes (Fig 1) was applied since April 1987.

View larger version (32K): [in this window] [in a new window]   Fig 1. . Low-dose heparinized left heart bypass with a centrifugal pump and heparin-coated tubes was applied since April 1987. During left heart bypass, the flow rate was maintained at 2.0 to 3.0 L/min and activated coagulation time was controlled to be about 200 seconds. (Ao = aorta; IVC = inferior vena cava; RA = right atrium.)

Operative Techniques
In patients with type B dissection, the distal aortic arch to descending thoracic aorta was exposed through a left posterolateral thoracotomy in the fourth or fifth intercostal space. For retroperitoneal exposure of the thoracoabdominal aorta, a left pararectal muscle incision was added, the left costal arch was disconnected, and the left hemidiaphragm was incised. Partial cardiopulmonary bypass with femoral arterial and venous cannulations mainly was used until March 1987. Since April 1987, low-dose heparinized left heart bypass with left atrial uptake was performed as circulatory support during cross-clamping of the descending aorta.

The descending aorta was incised longitudinally, and the intimal tear and aortic wall dissection were examined. The proximal aortic cuff just beneath the left subclavian artery was anastomosed to a tubular woven Dacron graft with reinforcement using double-layered Teflon felts. In the usual cases, the distal aortic cuff in the descending aorta was oversewn with double-layered Teflon felts and anastomosed to the tubular graft. Extended replacement of the thoracoabdominal aorta with reconstruction of its branches was indicated for type B dissection with involvement of the major abdominal branches [18, 19]. To avoid abdominal organ ischemia, arterial blood was perfused from small side tubes of the left heart bypass graft through balloon catheters in the major abdominal branches. By using segmental aortic cross-clamping, as many patent major intercostal arteries as possible were reconstructed during temporary occlusion of the arteries with small balloon catheters.

Follow-up and Statistical Analysis
The follow-up interval of 53 operative survivors was from 0.1 to 20.1 years with a mean follow-up of 7.1 years. The information on all patients was confirmed by contacting the patients or their primary physicians in January 1994. No patient was lost during this follow-up period.

Any postoperative death in the hospital after operation for aortic dissection was considered an early death. Regardless of the cause of death, all late deaths were counted for analysis of the follow-up data.

We divided the patients into two period subgroups of type B aortic dissection according to the circulatory support techniques. Period I is until March 1987, when femoral venoarterial bypass with oxygenation was mainly used, and period II is since April 1987, when the low-dose heparinized left heart bypass was introduced.

Statistical significance of the differences between categoric parameters were evaluated by ² contingency analysis. The average of continuous variables in each group was compared by analysis of variance and Student's t test. Postoperative survival was analyzed by the Kaplan-Meier actuarial method and compared among the subgroups by Cox-Mantel statistical analysis. A probability value less than 0.05 was considered to be statistically significant. Noted values are mean ± standard deviation.

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
In operation for type B dissection, extended surgical procedures involving thoracoabdominal aorta were carried out in 2 of 33 patients (6.1%) (2 early deaths) in period I and 17 of 32 patients (53.1%) (3 early deaths) in period II.

After operation for type B aortic dissection, 9 of 33 patients died in period I and 3 of 32 were lost in period II. Therefore, the early mortality of type B dissection decreased from 27.3% in period I to 9.4% in period II (p = 0.06).

Causes of early death are listed in Table 1. In type B aortic dissection, intraoperative bleeding and multiple organ failure due to massive bleeding and blood transfusion were major risk factors in period I, and no bleeding-related fatal complication was observed in period II. This difference in the incidence of bleeding-related complications was statistically significant between periods I and II (p < 0.02). In period II, early mortality mainly was related to preoperative shock and organ dysfunction. Spinal cord injury was observed in 2 of 33 patients (6.1%) in period I and in 1 of 32 patients (3.1%) in period II.

In each period subgroup, actuarial survival (including all deaths) after operation for type B dissection is shown in Figure 2. Actuarial survival rate 3 to 7 years after operation was 60.6% in period I and 79.2% in period II. The improvement between the two period subgroups was close to statistical significance (p = 0.07).

View larger version (23K): [in this window] [in a new window]   Fig 2. . Actuarial survival curves after operation for type B dissection. The 5-year actuarial survival was 60.6% in period I and 79.2% in period II, and the improvement between the two period subgroups was close to statistical significance (p = 0.07).

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment References

In operation on the descending aorta, fully heparinized partial cardiopulmonary bypass with femoral vein and femoral artery cannulations [2, 10] is used widely as an intraoperative circulatory support. However, massive bleeding is still one of the major causes of early death after these types of operation, especially for thoracoabdominal aortic aneurysms [18]. The present study indicated that the low-dose heparinized left heart bypass was effective to reduce the incidence of bleeding-related fatal complications. Heparin-coated cardiopulmonary bypass [11] also has been reported to have a low rate of postoperative revisions due to massive bleeding.

Since introduction of the low-dose heparinized left heart bypass, extended replacement of the thoracoabdominal aorta was indicated more for type B aortic dissection with dissection of major branches of the abdominal aorta. In spite of long and complicated graft replacements, hemostasis was easier and operation time was shorter with left heart bypass than with previous techniques [13]. Needless to say, recent advances in diagnostic tools, such as transesophageal echography, magnetic resonance imaging, and three-dimensional computed tomography and progress in surgical materials, artificial grafts, membrane oxygenators, and so forth have made significant improvements in surgical strategies and results. As cumulative effects of various factors, the early and late results after operation for type B aortic dissection in period II showed some trend of improvement as compared with those in period I.

In conclusion, overall surgical results of type B aortic dissection in this series appeared to be improved with the introduction of left heart bypass and extended surgical procedures.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Address reprint requests to Dr Kitamura, Department of Cardiovascular Surgery, The Heart Institute of Japan, Tokyo Women's Medical College, 8-1 Kawada-cho, Shinjuku-ku, Tokyo 162, Japan.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kitamura, M. Articles by Koyanagi, H. Search for Related Content PubMed PubMed Citation Articles by Kitamura, M. Articles by Koyanagi, H.