(Chest. 2003;124:989-995.)
© 2003
American College of Chest Physicians
Risk Factors for Descending Aortic Aneurysm Formation in Medium-Term Follow-up of Patients With Type A Aortic Dissection*
Chi-Hsiao Yeh, MD;
Min-Chi Chen, PhD;
Yi-Cheng Wu, MD;
Yao-Chang Wang, MD;
Jaw-Ji Chu, MD, FCCP and
Pyng Jing Lin, MD
* From the Division of Thoracic & Cardiovascular Surgery (Drs. Yeh, Wu, Wang, Chu, and Lin), Chang Gung Memorial Hospital, Taipei, Taiwan; and the Biostatistics Center and Department of Public Health (Dr. Chen), School of Medicine, Chang Gung University, Kweishan, Taiwan.
Correspondence to: Pyng Jing Lin, MD, Division of Thoracic & Cardiovascular Surgery, Chang Gung Memorial Hospital, 5 Fu-Hsing St, Kweishan, Taoyuan, Taiwan, 333; e-mail: L0688{at}cgmh.org.tw
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Abstract
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Background: After surgery to repair a type A aortic dissection, most late complications and mortality result from descending aorta-related problems. This study was performed to determine the risk factors leading to descending aortic aneurysm formation and late mortality in patients undergoing the type A aortic dissection operation.
Methods: The medical records of patients who survived the operation for type A aortic dissection between 1984 and 1998 were reviewed. There were 144 patients (95 men and 49 women), ranging in age from 24 to 78 years (mean age, 52 years). Most patients were acutely ill, 15 patients were in shock, and 54 patients had cardiac tamponade at the time of the surgical procedure. One hundred thirty-seven patients had ascending aortic replacement only, and of the other 6 patients 2 had hemiarch and 4 had total arch replacement using the elephant trunk technique. The aortic valve was replaced in 23 patients, resuspended in 100, and untouched in 21. Twenty-four risk factors were evaluated in statistical analyses for the prediction of descending aortic aneurysm formation and 3-year mortality. Risk factors were investigated using univariate and multiple logistic regression and survival analyses.
Results: The 3-year, 5-year, and 8-year cumulative survival rates were 96.2%, 89.1%, and 80.0%, respectively. The 3-year, 5-year, and 8-year cumulative survival rates, free from descending aortic aneurysm formation or descending aorta operation, were 74.7%, 58.6%, and 43.0%, respectively. Multivariate analysis confirmed that patent false lumen and initial descending aortic diameter were statistically significant risk factors for descending aortic aneurysm formation.
Conclusions: The medium-term survival rate of patients who received operations for type A aortic dissection was satisfactory, despite the high incidence of descending aortic aneurysm formation. The intimal entry site over the aortic arch that was resected during the first operation could decrease the patency rate of a false lumen over the descending aorta. In the absence of a patent false lumen over the descending aorta, the chance of descending aortic aneurysm formation or operation is lessened, and the late survival rate is increased.
Key Words: aortic dissection • descending aortic aneurysm • false lumen • reoperation
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Introduction
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The surgical therapy for type A aortic dissection consists mainly of replacing the ascending aorta, regardless of the extent of the pathologic process.1
Recent advances in preoperative diagnosis, surgical techniques, and postoperative surveillance have greatly improved the surgical outcome for patients with type A aortic dissection. Nevertheless, in a substantial number of patients, aneurysmal change of the residual dissected descending aorta occurred, which required a subsequent operation to repair the dissecting aneurysm. As a result, most late complications and mortality for type A aortic dissection were due to descending aorta-related complications.2
3
The long-term results of the type A aortic dissection depend largely on reducing complications related to the distal dissected aorta. Regular chest CT scan examinations and strict BP control have been recommended for all survivors. With all efforts, the postoperative survival rate in these patients declines in the first 3 years and reaches a plateau.1
4
Hence, the late mortality reported in this article is defined as death that occurred within 3 years after undergoing the operation. To predict the medium-term survival rate and the probability of descending aortic aneurysm formation after type A aortic dissection, the preoperative, perioperative, and postoperative variables have to be evaluated. In this study, we retrospectively reviewed the records of 144 surgical patients who had been regularly observed over 3 years to determine the risk factors for aneurysmal change after dissection of the descending aorta and for late mortality in the patients with type A aortic dissection.
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Patients and Methods
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Patients
Between October 1984 and April 1998, 193 consecutive patients with type A dissection were treated surgically at Chang Gung Memorial Hospital. Information gathered contemporaneously in our departmental database and supplemented as necessary from patient records and CT scans for 144 consecutive surviving patients who had survived at least for 3 months after receiving operations for type A aortic dissection at our institution were reviewed retrospectively. There were 95 men and 49 women whose ages ranged from 23 to 78 years (mean [± SD], 52 ± 12 years), and 40 patients (27.8%) were > 60 years of age at the time of surgery. Of the entire cohort, the indications for surgery were acute type A aortic dissection in 120 patients (83.3%), chronic type A aortic dissection with rupture in 9 patients (6.3%), and chronic type A dissection with aneurysm formation in 15 patients (10.4%). Only six patients in this series had Marfan syndrome.
As seen in Table 1
, the most common preoperative finding was a history of hypertension (66.7%), which was followed by a history of smoking (38.2%). Only seven patients (4.9%) were classified as having had DeBakey type II aortic dissections. Six patients (4.2%) who had previously undergone valvular surgery (none of them received aortic valve surgery) were operated on for chronic aortic dissection and aneurysm formation.
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Table 1.. Risk Factors Used for Descending Aorta Aneurysm Formation or Reoperation and Late Mortality in Patients After Type A Aortic Dissection Surgery*
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Surgical Technique
All operations were performed according to a standard method of cardiopulmonary bypass and deep hypothermic circulatory arrest. The intraoperative surgical techniques, including the methods of deep hypothermic circulatory arrest, retrograde cerebral perfusion, and perioperative management were identical for all patients and have been described in detail.5
Briefly, an arterial cannula was inserted through the right femoral artery, and venous cannulas were inserted through the right femoral vein and superior vena cava. Once cardiopulmonary bypass was established, systemic cooling was initiated to an average core temperature of 18 to 20°C (measured in the esophagus). The head is packed in ice to prevent warming of the CNS during circulatory arrest. The dissected ascending aorta was opened, then distal anastomosis or intraaortic graft implantation was performed during a hypothermic circulatory arrest in conjunction with a hypothermic retrograde cerebral perfusion. No aortic crossclamp was applied. The replacement technique for the exclusion method of the distal stump was the interpositioning of woven grafts with Teflon strip reinforcement. Gelatin-resorcin-formalin adhesive was not used. When the site of the intimal tear could not be identified, we simply replaced the ascending aorta.
Twenty-six patients (18.1%) underwent the operation without retrograde cerebral perfusion. After 1992, distal anastomosis was performed in 118 patients (81.9%) using hypothermic retrograde cerebral perfusion via the superior vena cava at a flow rate of 300 to 500 mL/min during hypothermic circulatory arrest. The ascending aorta of 108 patients (75.0%) was replaced using an exclusion, two-graft method. The remaining 36 patients (25.0%) underwent sutureless intraluminal graft implantation.
In addition to the ascending aorta replacement, other proximal repairs included resuspension of the aortic valve (123 patients; 85.4%), aortic valve replacement (21 patients; 14.6%), and the Bentall operation (12 patients; 8.3%). The transverse arch and proximal descending aorta were inspected carefully for tear sites in all patients. When an intimal tear was noted in the aortic arch, the tear was repaired, the proximal arch or hemiarch was replaced, or the total arch was replaced (6 patients; 4.2%) to obliterate the tear site in the arch. Coronary artery bypass grafting was the most common concomitant procedure and was performed in eight patients (5.6%). Other additional procedures such as mitral valve replacement were performed in 2.1% of the patients. The location of the tear was noted in the ascending aorta in only 65 patients (45.1%). Three patients (2.1%) had arch tears only, and 76 (52.8%) had multiple tears or no tears.
Postoperative Studies
In our department, all patients received a biannual serial CT scan and/or MRI and annual transthoracic echocardiography. Clinical follow-up information was added to recent outpatient records. The mean duration of follow-up was 58 ± 35 months. The daily measurement of systolic BP for each patient was reviewed and graded. Patients were coded as 1 if their average systolic BP was < 135 mm Hg, and as 2 if it exceeded 135 mm Hg. CT or MRI scans were employed in our hospital to serially measure the diameters of the isthmus of the aorta and descending aortic aneurysm (diameter > 55 mm) in every patient.
Statistical Analysis
The data were entered into a spreadsheet program (EXCEL; Microsoft; Redmond, WA) and analyzed using a statistical software package (SPSS, version 8.0; SPSS; Chicago, IL). A p value of < 0.05 was considered to be statistically significant. The 
2 test or Fisher exact test was employed to evaluate the relationship between the chance of reoperation/late mortality and the clinical variables (Table 1)
. The influence of various surgical factors on the possibilities of descending aortic aneurysm formation and late mortality were examined using multiple logistic regression (Tables 2
3
4
). Kaplan-Meier survival curves were used to determine the following: (1) whether the time prior to descending aortic aneurysm formation or reoperation at various intervals differs in all patients; and (2) whether the time of late mortality is distinguishable among all patients. The log-rank test was applied to compare the survival curves. The Cox proportional hazards model was applied to identify the risk factors that impacted survival (ie, time to aneurysm formation or reoperation and time of late mortality).
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Table 2.. Multivariate Analysis of Risk Factors Used for 3-Year Mortality Rate in Patients After Type A Aortic Dissection Surgery
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Table 3.. Multivariate Analysis of Risk Factors Used for Descending Aortic Aneurysm Formation or Reoperation in Patients After Type A Aortic Dissection Surgery
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Table 4.. Risk Factors Related to Patent False Lumen Over Descending Aorta in Patients After Type A Aortic Dissection Surgery Using Multivariate Logistic Analysis
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Results
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Late Mortality
The overall 3-year, 5-year, and 8-year survival rates were 96.2%, 89.1%, and 80.0%, respectively. Within the whole follow-up period, mortality occurred in patients who had undergone surgical repair of the descending aorta aneurysm or rupture (seven patients; 4.9%), ascending aorta reoperation-related complications (two patients; 1.4%), stroke (two patients; 1.4%), acute myocardial infarction (one patient; 0.7%), rupture of the aortic arch aneurysm (one patient; 0.7%), abdominal aortic aneurysm rupture (one patient; 0.7%), late sternal wound infection with sepsis (one patient; 0.7%), and other noncardiac conditions (three patients; 2.1%). As seen in Table 1
, univariate analyses showed the following two preoperative and two intraoperative risk factors to be statistically significant predictors of late mortality: diabetes; initial descending aorta diameter; acute dissection; and nonuse of the retrograde cerebral perfusion technique. Multiple logistic regression analysis identified the following two variables as independent predictors of late mortality: the use of the retrograde cerebral perfusion technique (odds ratio [OR], 0.0079; p = 0.0014) and final descending aorta diameter (OR, 1.06, p = 0.0079). As shown in Table 2
, the former predictor carried low risks of late mortality, and the latter carried high risks. The survival analysis also showed the nonuse of the retrograde cerebral perfusion technique was the only statistically significant factor (p = 0.0138 [log rank test]).
Descending Aorta Aneurysm Formation and Reoperation
Descending aortic aneurysm formation (diameter > 55 mm) was noted in 54 patients, 16 of whom underwent surgery to treat this condition. Although the rate of progression of descending aortic dilatation of > 5 mm every 6 months had been considered as an indication for surgery, all 16 patients were operated on because of a descending aortic aneurysm. As shown in Table 1 , univariate analysis revealed one preoperative risk factor, two intraoperative risk factors, and one postoperative risk factors, as follows: initial descending aorta diameter; nonuse of the retrograde cerebral perfusion technique; tear site at the ascending aorta only; and postoperative patent false lumen in the descending aorta. The different methods for repairing the ascending aorta were not associated with late descending aortic aneurysm formation. Logistic regression was applied to identify possible risk factors (Table 3)
. The two risk factors that were significantly related to the chance of descending aortic aneurysm formation were patent false lumen (OR, 13.28; p = 0.0002) and initial isthmus diameter (OR, 1.11; p = 0.0025) in the descending aorta, both of which carried high risks for descending aortic aneurysm formation or operation. The location of the initial tear sites (ie, ascending aorta, aortic arch, descending aorta, and multiple tear sites), tear management (ie, none, repair, or resection), and BP control during the follow-up period failed to affect descending aortic aneurysm formation. The Cox proportional model was used to examine the risk factors related to time to descending aortic aneurysm formation/reoperation after eliminating insignificant variables identified by the Kaplan-Meier analysis. As a result, patent false lumen was the only significant risk factor, with a hazard ratio of 11.77 for a 3-year increment.
Residual patent false lumen in the descending aorta was observed in 103 patients, and its risk factors were investigated (Table 4) . Using logistic regression, the following five significant factors were identified: the initial descending aorta diameter; male gender; tear site located in ascending aorta only; acute operation; and arch manipulation (total arch or hemiarch operation). The first three factors carried high risks for patent false lumen, while the other two carried low risks. For patients with patent false lumens in the descending aorta, the non-risk-adjusted, time-related rate of descending aortic aneurysm formation was significantly higher than that without adjustment (Fig 1
). Operations for descending aorta aneurysm were performed in 16 patients. Although there were > 16 patients who had the operation properly indicated, most patients opted for conservative management.
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Discussion
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Urgent surgical resection of the ascending aorta with graft replacement has dramatically altered the well-documented lethal natural history of untreated acute type A aortic dissection.2
However, the surgery per se carries a high risk of neurologic damage, and the survivors risk developing aorta-related complications from the failure of the proximal repair or failure at the distal aorta.3
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7
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For the early detection and prediction of late complications in those patients who survived the emergent operation, searching for the risk factors of aneurysm formation and late mortality is necessary. In this study, an unselected consecutive series of 144 patients who survived type A aortic dissection was analyzed to determine perioperative and postoperative risk factors for late mortality and descending aortic aneurysm formation.
Late Mortality
The following two variables were found to be statistically significant for late mortality in our patient population: using the retrograde cerebral perfusion technique; and the final descending aortic diameter. The best approach to protecting the brain during operations on the thoracic portion of the aorta, in which the arterial blood supply has to be interrupted temporarily, remains controversial.9
Surgeons at the Mount Sinai Hospital have used retrograde cerebral perfusion mainly to reduce embolization but have relied principally on antegrade cerebral perfusion as an adjunct to hypothermic retrograde cerebral perfusion when longer durations of hypothermic retrograde cerebral perfusion were anticipated.10
Herein, however, a modified retrograde cerebral perfusion technique, which was initially presented by Ueda et al,11
in conjunction with a moderate hypothermic circulatory arrest, were employed to protect our patients with aortic dissection from neurologic deficits. As was reported previously,5
12
13
retrograde cerebral perfusion effectively protects the brain from ischemic injury and extends the safe period of retrograde cerebral perfusion in the short term. Our results indicate that retrograde cerebral perfusion significantly extends the safe period of hypothermic circulatory arrest.5
The longest retrograde cerebral perfusion was 120 min, and the recipient regained clear consciousness without any neurologic deficits. Owing to retrograde cerebral perfusion, aortic operation can be performed in a calm, more deliberate fashion.5
Ehrlich et al1
reported that the duration of hypothermic circulatory arrest was not a risk factor for hospital death in a series of 107 patients. In this study, we further determined that using retrograde cerebral perfusion, which safely extended the duration of hypothermic circulatory arrest, afforded the surgeon enough time to examine and manipulate the tear sites over the aortic arch and proximal descending aorta. As shown in Table 4
, arch manipulation could obliterate the false lumen over the descending aorta, which plays an important role in determining whether the descending aorta becomes an aneurysm. By diminishing the incidence of aneurysm formation and by decreasing the diameter of the descending aorta, the late mortality rate might be reduced.
Another significant risk factor for late mortality is final descending aortic diameter. In our study, every 1-mm increase in the final descending aortic diameter increases the chance of late mortality 1.06-fold (Table 2)
. However, the only two significant risk factors for descending aneurysm formation (initial isthmus diameter and residual patent false lumen over the descending aorta) were related neither to our operative procedure (ie, inclusion or exclusion method) nor to postoperative BP control. Although many reports emphasized the need for continuing attention to adequate BP control and monitoring in all patients after the repair of type A aortic dissection, we could not demonstrate that strict BP control changed the rate of aneurysm formation.
Descending Aortic Aneurysm Formation or Operation
Several studies have advocated routine aortic arch replacement as a possible means with which to decrease distal aneurysm formation.8
14
15
16
However, Crawford et al17
have recommended replacing the arch only when it is aneurysmal, and when there is excessive enlargement and impending or actual rupture of the false channel. In addition, they recommended not treating the presence of a false lumen in the arch. In our study, the false lumen of the ascending aorta in all patients was obliterated completely. However, intimal tears in the aortic arch were repaired, resected, or untouched. For the deployment of intraluminal grafts, multiple mattress sutures with pledgets of Teflon felt were employed to repair all intimal tears in the aortic arch. On the basis of indications reported by Sabik et al,18
the exclusion method was used for hemiarch or total arch replacement when the intimal tear extended into the arch. Via multiple regression analysis, Haverich et al6
have demonstrated that primary intimal tear resection had no significant bearing on the likelihood either of late death or of subsequent reoperation. On the contrary, Miller et al9
have noted from the Stanford database that failure to resect an arch tear was associated with an increased risk of aorta-related reoperation. However, our results revealed that various treatments for intimal tears in the aortic arch failed to affect the medium-term result of aneurysm formation and reoperation of the descending aorta. In this study, the two significant risk factors for descending aortic aneurysm formation or operation were initial isthmus diameter and patent false lumen in the descending aorta, both of which carried high risks for this late complication. Furthermore, in patients with multiple entry sites along the entire aorta, eradication of the few accessible intimal tears on the ascending aorta and arch did not exclude the possibility of residual patent false lumen and descending aortic aneurysm formation. Only when all entry sites in the entire aorta were eradicated could the possibility of patent false lumen and aneurysm formation be precluded.
Patent False Lumen Over Descending Aorta
Most late complications and mortality from acute type I aortic dissection results from descending aorta-related complications.3
6
The incidence of postoperative residual patent false lumen has been reported to be relatively high.6
19
In a study of 108 patients, Appelbaum et al20
confirmed that although patients with acute dissection of the descending aorta had a similar initial mortality rate, whether treated medically or surgically, long-term survival was higher in the latter. Furthermore, they recommended that surgery at some stage was required for all dissections of the descending aorta.20
Surgical therapy includes resection of the intimal tear site, its replacement with an interposition graft, and obliteration of the distal false lumen via reestablishing normal flow through the interposition graft into the true lumen alone.21
With a mean follow-up period of 32 months, Turley et al19
discovered that, despite attempts to obliterate the false lumen, most patients had a persistent false lumen. Sabik et al18
reported that although the presence of a residual distal dissected aorta does not decrease late survival, it has a low risk of aneurysmal change and reoperation for a minimum of 10 years. However, in our investigation, freedom from aneurysmal change and reoperation differed significantly in patients with and without patent false lumen of the descending aorta. Moreover, patent false lumen is one of two significant risk factors of descending aortic aneurysm formation. The importance of this finding for those patients with residual patent false lumens is that the dissected descending aorta will eventually develop an aneurysm, which implies that their prospect for late survival is dismal.
Aortic arch replacement to treat an arch tear in a type A aortic dissection is controversial.17
19
22
23
Some authors believe that a postoperatively persistent patent false lumen is an inevitable result of the pathology. However, others have indicated that resection of the primary tear on the aortic arch could reduce the patency rate. With all operative methods performed herein, the patency rate of the false lumen in the descending aorta following aortic arch resection ranged between 47% and 100%. On the basis of our results, arch manipulation can decrease the patency rate of a false lumen in the descending aorta (OR, 0.093; p = 0.026). However, the various operative methods (ie, sutureless intraluminal graft or exclusion two-graft method) failed to influence the patency of the false lumen in the descending aorta.
Another interesting finding of our study is that, regardless of how strictly the postoperative BP was controlled, a patent false lumen in the untouched descending aorta with one or more entry sites persisted and aneurysm eventually developed in the descending aorta. Clearly, aggressive antihypertensive treatment is required in the immediate preoperative and postoperative period.24
However, herein, the effect of BP control on aneurysm formation was not significant.
In conclusion, this study confirms the following findings for patients with type A aortic dissections: (1) retrograde cerebral perfusion can safely and effectively extend the period of hypothermic circulatory arrest without midterm sequelae (this finding is supported by Lin et al5
; (2) intraluminal graft implantation and the use of exclusion do not influence the medium-term morbidity and mortality; (3) resection of intimal tears in the aortic arch can decrease the incidence of false lumen patency; (4) with patent false lumen of the descending aorta an aneurysm is almost assured; and (5) an enlarged descending aorta diameter implies a dismal mid-term outcome. Our current management for patients with type I aortic dissection is the use of the total arch or hemiarch resection to obliterate all tear sites from the isthmus to the ascending aorta.
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Footnotes
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Abbreviation: OR = odds ratio
Received for publication September 17, 2002.
Accepted for publication January 7, 2003.
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References
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- Ehrlich, MP, Ergin, A, McCullough, JN, et al (2000) Results of immediate surgical treatment of all acute type A dissections. Circulation 102,III-248-III-252
- Masuda, Y, Yamada, Z, Morooka, N, et al Prognosis of patients with medically treated aortic dissections. Circulation 1991;84,7-13
- De Bakey, ME, McCollum, CH, Crawford, ES, et al Dissection and dissecting aneurysms of the aorta: twenty year follow-up of five hundred twenty-seven patients treated surgically. Surgery 1982;92,1118-1133[ISI][Medline]
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- Lin, PJ, Chang, CH, Tan, PP, et al Prolonged retrograde cerebral perfusion in moderate hypothermia with retrograde cerebral perfusion: is brain ischemic? Circulation 1996;94,II-169-II-172
- Haverich, A, Miller, DC, Scott, WC, et al Acute and chronic aortic dissections: determinants of long-term outcome for operative survivors. Circulation 1985;72,II22-II34
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- Lin, PJ, Chang, CH, Tan, PP, et al Protection of the brain by retrograde cerebral perfusion during circulatory arrest. J Thorac Cardiovasc Surg 1994;108,969-974[Abstract/Free Full Text]
- Massimo, CG, Presenti, LF, Favi, PP, et al Excision of the aortic wall in the surgical treatment of acute type A aortic dissection. Ann Thorac Surg 1990;50,274-276[Abstract]
- Minale, C, Splittgerber, FH, Wendt, G, et al One-stage intrathoracic repair of extended aortic aneurysms. J Card Surg 1994;9,604-613[Medline]
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- Sabik, JF, Lytle, BW, Blackstone, EH, et al Long-term effectiveness of operations for ascending aortic dissections. J Thorac Cardiovasc Surg 2000;119,946-962[Abstract/Free Full Text]
- Turley, K, Ullyot, DJ, Godwin, JD, et al Repair of dissection of the thoracic aorta: evaluation of false lumen utilizing computed tomography J Thorac Cardiovasc Surg 1981;81,61-68[Abstract]
- Appelbaum, A, Karp, RB, Kirklin, JW Ascending vs descending aortic dissections. Ann Surg 1976;183,296-300[ISI][Medline]
- Reul, GJ, Jr, Cooley, DA, Hallman, GL, et al Dissection aneurysm of the descending aorta: improved surgical results in 91 patients. Arch Surg 1975;110,632-640[Abstract]
- Bachet, J, Giovanni, T, Goudot, B, et al Replacement of the transverse aortic arch during emergency operations for type A aortic dissection: report of 26 cases. J Thorac Cardiovasc Surg 1988;96,878-886[Abstract]
- Heinemann, M, Laas, J, Jurmann, M, et al Surgery extended into the aortic arch in acute type A dissection: indications, techniques, and results. Circulation 1991;84,25-30
- Wolfe, WG, Oldham, N, Rankin, JS, et al Surgical treatment of acute ascending aortic dissection. Ann Surg 1983;197,738-742[ISI][Medline]
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Abstract
Introduction
