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Eur J Cardiothorac Surg 2004;26:359-366
© 2004 Elsevier Science NL

Effects of the patent false lumen on the long-term outcome of type B acute aortic dissection

^a Intensive and Coronary Care Unit, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603, Japan
^b First Department of Internal Medicine, Nippon Medical School, Tokyo, Japan
^c Department of Internal Medicine, Tsurumi University School of Dental Science, Kanagawa, Japan
^d Musashino Hospital, Tokyo, Japan
^e Second Department of Surgery, Nippon Medical School, Tokyo, Japan

Received 10 January 2004; received in revised form 12 March 2004; accepted 16 March 2004.

^* Corresponding author. Address: Intensive and Coronary Care Unit, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603, Japan. Tel.: +81-3-3822-2131x6823; fax: +81-3-5685-3069
e-mail: nejima-j{at}tsurumi-u.ac.jp

	Abstract

Top Abstract 1. Introduction 2. Methods 3. Results 4. Discussion References

 
Objective: To determine the most effective treatment, we performed a detailed comparative study of the clinical course of patients with type B aortic dissection with a patent or thrombosed false lumen who did not undergo surgery in the acute period. We examined the effect of patency of the false lumen on outcome. Methods: Computed tomography scans of 138 patients with type B acute aortic dissection were reviewed. Of 138 patients, 110 were medically treated and survived the acute period. We focused on the outcome of these 110 patients, 62 with medically treated thrombosed false lumen (thrombosed group) and 48 with medically treated patent false lumen (patent group). We investigated factors influencing outcome among the 110 patients. The follow-up period was up to 10 years after the onset of aortic dissection. The three study endpoints were death from any cause, dissection-related death (aortic rupture, perioperative death, or death due to organ ischemia), and a dissection-related event (aortic rupture or surgery). In the patent group, we investigated factors influencing long-term outcome. Results: Patency of the false lumen was an independent risk factor for dissection-related death (P=0.038, hazard ratio=5.6, confidence interval=1.1–28) and for a dissection-related event (P=0.000, hazard ratio=7.6, confidence interval=2.7–22) but not for death from any cause (P=0.769, hazard ratio=1.2, confidence interval=0.45–2.91). In the patent group, location of the most dilated aortic segment at the distal arch was an independent risk factor for dissection-related death (P=0.026, hazard ratio=13.6, confidence interval=1.4–135) and for a dissection-related event (P=0.048, hazard ratio=2.6, confidence interval=1.0–6.9). Conclusions: Patency of the false lumen is a strong independent prognostic factor for type B aortic dissection. Location of the most dilated aortic segment at the distal arch is a significant risk factor in the patients with a patent false lumen.

Key Words: Aortic dissection • Stanford type B • False lumen • Prognosis • Risk factor • Distal arch

	1. Introduction

Top Abstract 1. Introduction 2. Methods 3. Results 4. Discussion References

 
Surgical intervention is generally recommended for Stanford type A aortic dissection, and medical management is recommended for type B dissection [1]. Surgical repair of type B dissections is reserved for cases that are complicated by impending rupture, organ ischemia due to involvement of major branches of the aorta, propagation of the dissection, or continued pain [2,3]. The preference for conservative management of type B dissection derives from an apparently favorable prognosis in the acute period. However, more than a few patients with type B dissection, die of aortic rupture during the chronic period despite medical management [4,5]. In fact, the reported 1-, 5-, and 10-year survival rates of patients with medically treated type B dissection are 90–95, 75–90, and 30–55%, respectively; corresponding survival rates of patients with surgically treated type B dissection are 90–95, 65–80, and 50–55% [5–7]. These data are inclusive for both patients with a thrombosed false lumen and patients with a patent false lumen. Juvonen et al. report that the status of the false lumen is not associated with an increased risk of rupture [4], whereas other investigators report that patency of the false lumen is an important predictor of aortic rupture or an otherwise poor outcome [8–11]. However, there are few reports focusing on patency of the false lumen, particularly in type B dissection, in relation to long-term outcome, and the clinical significance of the patent false lumen has not been clearly defined. Thus, several clinically important questions have arisen: whether patency of the false lumen affects the outcome of type B patients, when the type of treatment should be determined, and how the patients who would benefit from surgical treatment can be identified. Accordingly, the primary goal of the present study was to determine the effect of false lumen patency on the long-term outcome of patients with type B aortic dissection. The second goal of this study was to clarify the prognostic factors in patients with a patent false lumen.

	2. Methods

Top Abstract 1. Introduction 2. Methods 3. Results 4. Discussion References

 
2.1. Study population
Between January 1981 and December 2000, 148 consecutive patients with acute type B aortic dissection were admitted to the Coronary and Intensive Care Unit at Nippon Medical School Hospital. Of these 148 patients, 138 had computed tomography (CT) scans available for review and were diagnosed with an accurate date of onset. Acute aortic dissection was diagnosed on the basis of acute chest and/or back pain and by CT evidence of an intimal flap. None of the 138 patients suffered cardiopulmonary arrest or underwent surgery prior to admission. No dissection was caused by a surgical procedure or cardiac catheterization. The short-term outcome in these 138 cases was investigated.

Of the 138 patients, 110 were treated medically and discharged without surgery. The 110 included 62 with a thrombosed false lumen (thrombosed group) and 48 with a patent false lumen (patent group) (Fig. 1) . Patency of the false lumen was assessed by contrast-enhanced CT performed on admission and supplemental diagnostic procedures including transesophageal ultrasonography and/or aortography. A patent false lumen was identified by opacification of at least a portion of the false lumen with contrast media. A thrombosed false lumen was identified by complete occlusion of the false lumen by a thrombus. These patients were followed up for up to 10 years to assess long-term outcome.

View larger version (16K): [in this window] [in a new window]   Fig. 1. One hundred thirty-eight patients were included in our study. Of these 138, 110 were treated medically and survived the acute period. We focused on the outcome of these 110 patients, who comprised 62 with a medically treated thrombosed false lumen (thrombosed group) and 48 with a medically treated patent false lumen (patent group).

2.3. Factors influencing long-term outcome
Follow-up data were obtained from outpatient medical records. Telephone interviews were used to obtain current information about patients who did not return to our hospital for outpatient care.

Long-term outcome was determined for all patients in May 2002. Patients we could not contact and whose survival or death could not be confirmed in May 2002 were considered ‘lost to follow-up’.

Long-term outcome was assessed on the basis of three endpoints: death from any cause, dissection-related death, and a dissection-related event. Dissection-related death included death by aortic rupture, perioperative death, and death due to organ ischemia. A dissection-related event included aortic rupture and/or surgery.

Seven factors were used to assess the effect of false lumen patency on the long-term outcome: patency of the false lumen, age, sex, systolic blood pressure prior to therapy, start of treatment within 24 h of onset, location of the most dilated aortic segment at the distal arch, and aortic diameter of more than 45 mm. Additionally, we compared outcome during the chronic period of the thrombosed group with that of the patent group in terms of the three endpoints.

2.4. Factors influencing long-term outcome in the patent group
A separate analysis of factors influencing long-term outcome was performed for the patent group with all of the original factors except patency of the false lumen. The effects of these factors on the three endpoints were evaluated.

2.5. Time of onset and outcome
To investigate the effect of the time of onset on outcome, we compared the outcome of the patients enrolled between 1981 and 1990 with that of the patients enrolled between 1991 and 2000.

2.6. Statistical analysis
All continuous variables are expressed as median values (25th and 75th percentile). Differences in values between the patent group and the thrombosed group were analyzed by Mann–Whitney U test. Differences in percentages were evaluated by Fisher's exact test. Cox proportional hazard model was applied for all 110 patients and only for the patent group to determine the independent effects of variables on death from any cause, on dissection-related death, and on dissection-related events. The percentages of patients free from death from any cause, dissection-related death, and dissection-related events were determined by the Kaplan–Meier method, and the event-free curves of the thrombosed and patent groups were compared by log-rank test. Moreover, dissection-related-event-free curves drawn with and without factors most affecting the prognosis of the patent group were compared by log-rank test. We used SPSS (Ver. 11.0) software for all statistical analyses.

	3. Results

Top Abstract 1. Introduction 2. Methods 3. Results 4. Discussion References

 
3.1. Patient characteristics
Baseline characteristics of the patent group and thrombosed group on admission are shown in Table 1. Patients in the patent group were significantly younger than those in the thrombosed group.

There were 22 (20%) censored cases including 7 cases lost to follow-up at 2 years, 58 (53%) censored cases including 8 lost to follow-up at 5 years, and 87 (79%) censored cases including 11 cases lost to follow-up at 10 years of follow-up.

3.4. Factors influencing long-term outcome
Factors influencing the long-term outcome of patients in 110 type B patients discharged without acute-phase surgery are shown in Table 3. Patency of the false lumen was shown to be an important, independent prognostic factor for type B aortic dissection.

View larger version (17K): [in this window] [in a new window]   Fig. 2. Dissection-related-death-free ratio of patients in the thrombosed group and that of patients in the patent group are compared by the Kaplan–Meier method and log-rank test. The number of patients at risk and the dissection-related-death-free ratio are shown for each follow-up point. The number of censored cases is indicated in parentheses. The incidence of dissection-related-death is higher in the patent group than in the thrombosed group (P=0.048).

View larger version (19K): [in this window] [in a new window]   Fig. 3. Death-from-any-cause-free ratio of patients in the thrombosed group and that of patients in the patent group are compared by the Kaplan–Meier method and log-rank test. The number of the patients at risk and the death-from-any-cause-free ratio are shown for each follow-up point. The number of censored cases is indicated in parentheses. A significant difference between the two groups was not found in terms of death from any cause.

View larger version (20K): [in this window] [in a new window]   Fig. 4. Dissection-related-event-free ratio in patients with the most dilated aortic segment located at the distal arch and in patients with the most dilated aortic segment located away from the arch are compared by the Kaplan–Meier method and log-rank test. The number of patients at risk and the dissection-related-event-free ratio are given for each follow-up point. The number of censored cases is indicated in parentheses. The incidence of dissection-related events is higher in patients with the most dilated aortic segment located at the distal arch than in those with the most dilated aortic segment located away from the distal arch (P=0.0065).

	4. Discussion

Top Abstract 1. Introduction 2. Methods 3. Results 4. Discussion References

 
The major finding of the present investigation is that patency of the false lumen is a strong independent risk factor for dissection-related death and a dissection-related event in the chronic period. Previous reports have suggested that patency of the false lumen affects the outcome of patients with aortic dissection [8–11]. Some of these studies, however, did not take the Stanford classification system, an established predictor of outcome, into consideration [8,9]. In other studies, the number of patients involved was rather small [10,11]. In contrast to these reports, Juvonen et al. [4] showed that patency did not predict rupture. Kozai et al. [12] insisted that patency affected survival rate but did not affect events in the chronic period.

The important clinical implication of our major finding is that the possibility of surgical repair in the chronic period should be considered for medically treated patients with a patent false lumen. In balancing the risk of aortic rupture, which is usually fatal, against the substantial risk associated with surgical repair, some investigators have favored elective surgery for patients with type B aortic dissection and a large aorta [5,11]. Because of the high incidence of complications [13], however, the need for surgical repair of chronic type B dissection should be assessed with extreme caution. Effect of surgery on the outcome remains to be investigated. Considering the risks of surgery, endovascular stent-graft placement [14,15], if indicated, could be an alternative intervention for high risk patients, although the number of patients in our study treated with a stent-graft was limited.

A policy favoring some intervention raises two questions: for whom, and when should elective surgery be applied? Previous studies have identified several factors, some controversial, to be considered: a history of chronic obstructive pulmonary disease, patient age, blood pressure control, size of the aorta, and patency of the false lumen, as predictors of outcome in chronic type B dissection. The location of the most dilated aortic segment is of considerable importance because aortic dilatation might develop from increased aortic wall stress at this segment. Our data confirmed that, with a patent false lumen, the most dilated aortic segment at the distal arch is associated with dissection-related death and a dissection-related event.

Appropriate timing of the surgical repair is essential, since surgical procedures in the acute period carry a substantial risk, but postponement of the surgery endangers the patient because of the increasing risk of rupture. To determine the optimal time for surgical repair, it is important to estimate the time to potential rupture. In this connection, we found that the events occurred during earlier follow-up period in the patent group. The incidence of dissection-related death seems to increase beyond 1 year till 5 years after onset (Fig. 2). This fact suggests that surgical procedures can be postponed somewhat to avoid the risk of acute-phase surgery, but some intervention including surgical repair should be considered around 1 year after onset. Contrary to the findings of the studies mentioned above, a considerable number of patients with a patent false lumen in our study survived for some time. The reason for the different outcome in our group is uncertain. This could be explained in part by the location of the most dilated aortic segment, as suggested in the present study. The quality of blood pressure control in the chronic period might be partly responsible for the outcome. Further long-term observation of event-free type B patients with a patent false lumen is necessary. Unknown factors not included in this study must have contributed to their status.

Although the number of study patients was relatively small and not a small number of patients were lost to follow-up, our data clearly indicate a better outcome for patients in the thrombosed group than in the patent group. Patency of the false lumen did not significantly affect death from any cause. One explanation is that 12 patients in the thrombosed group died of causes unrelated to dissection, whereas only four in the patent group died of unrelated causes. Another explanation is that patients in the thrombosed group were significantly older than those in the patent group.

In our study, the thrombosed type dissection was observed more frequently in the last decade (1991–2000) than in the prior decade (1981–1990). This might partly explain the difference, although not significant, in the follow-up period between these two groups. Moreover, this could have influenced the clinical outcome because of advances in medical treatment during the last 20 years. However, our analysis of the issue showed that outcomes were similar between the more recent and the earlier patients in the thrombosed group. Meanwhile, in the patent group, although prevalence of events including surgery and rupture was similar in the two periods, the number of surgeries increased and the number of ruptures decreased in the latter period in comparison to numbers in the earlier period. Thus, the relatively recent onset of the dissection does not explain the better outcome in the thrombosed group, and the lower prevalence of rupture in the patent group was possibly because surgical procedures were used preferentially in the latter period.

There were several limitations to the present investigation. First, it was not a prospective controlled randomized study. A potential bias exists because of the number of censored patients and the relatively small number of patients involved. Our observations clearly should be confirmed by a large, prospective randomized study. Second, we could not perform a detailed evaluation of other factors influencing the outcome of our patients such as pulmonary emphysema or the quality of blood pressure control during the follow-up period. Third, the diameter of the aorta immediately before rupture was not well assessed in the follow-up period, making it difficult to precisely determine the critical size for aortic rupture.

We conclude that patency of the false lumen is an independent predictor of dissection-related death and dissection-related events. The location of the most dilated aortic segment is of considerable importance as a factor in determining prognosis of type B dissection in the chronic period.

	Acknowledgments

 
We thank Takashi Itoh, PhD, Nobuo Hatori, MD, and Sadao Ishimura, PhD for their statistical suggestions. We thank Ms Kozue Kosuge, Ms Naoko Inayoshi, and Ms Manami Kanamori for their secretarial assistance in preparing this manuscript.

	Footnotes

 
Presented in part at the 29th Annual Meeting of the Japanese Society of Intensive Care Medicine, Tokyo, Japan, March 9, 2001.

	References

Top Abstract 1. Introduction 2. Methods 3. Results 4. Discussion References

 

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