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Ann Thorac Surg 1999;67:1922-1926
© 1999 The Society of Thoracic Surgeons

Surgical intervention criteria for thoracic aortic aneurysms: a study of growth rates and complications

^a Section of Cardiothoracic Surgery, Department of Surgery, Yale University School of Medicine, New Haven, Connecticut, USA
^b Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, Connecticut, USA

Address reprint requests to Dr Elefteriades, Section of Cardiothoracic Surgery, Yale University School of Medicine, 333 Cedar St, New Haven, CT 06510
e-mail: john_elefteriades{at}QM.yale.edu

Presented at the Aortic Surgery Symposium VI, April 30–May 1, 1998, New York, NY.

	Abstract

Top Abstract Introduction Patients and methods Results Discussion References

 
Background. Evidence regarding the behavior of thoracic aortic aneurysm (TAA) is limited. This study reviews our ongoing efforts to understand the factors influencing aortic growth rates and the complications of rupture and dissection in order to define scientifically sound criteria for surgical intervention.

Methods. Data from 370 patients with TAA treated at Yale University School of Medicine from January 1985 to June 1997 were analyzed. This computerized data base included 1063 imaging studies (magnetic resonance imaging, computed tomography, and echocardiography).

Results. The mean size of the thoracic aorta in these patients at initial presentation was 5.2 cm (range 3.5–10). The mean growth rate was 0.10 cm/year. Median size at the time of rupture or dissection was 5.9 cm for ascending and 7.2 cm for descending aneurysms. The incidence of dissection or rupture increased with aneurysm size. Multivariable regression analysis to isolate risk factors for acute dissection or rupture revealed that size 6.0 cm increased the probability of these devastating complications by 25.2% for ascending aneurysms (p = 0.006 compared with aneurysms 4.0–4.9 cm). For descending aneurysms 7.0 cm, risk of dissection or rupture was increased by 37.3% (p = 0.031).

Conclusions. If the median size at time of dissection or rupture had been used as the indication for intervention, half the patients would have suffered a devastating complication before surgery. Accordingly, a criterion lower than the median is appropriate. We recommend 5.5 cm as an acceptable size for elective resection of ascending aortic aneurysms because this operation can be performed with relatively low mortality. For aneurysms of the descending aorta, where perioperative complications are greater and the median size at the time of complication is larger, we recommend intervention at 6.5 cm.

	Introduction

Top Abstract Introduction Patients and methods Results Discussion References

 
Thoracic aortic aneurysms are critical conditions frequently requiring operative intervention in order to prevent rupture, dissection, and death [1]. The decision to operate on the thoracic aorta is relatively straightforward for patients without significant operative contraindications who present with very large, rapidly expanding, or symptomatic ascending or descending thoracic aortic aneurysms. However, determining whether surgery is indicated is more complex for asymptomatic patients with a gradually expanding, moderate-sized thoracic aorta. In deciding when to operate, the surgeon must consider both the benefits of resection and the operative risks: the ultimate objective is to select patients for whom the operative risks are justified. Current recommendations for surgical intervention have been based largely on clinical judgment, with a paucity of hard scientific and statistical data regarding appropriate size criteria.

Variation in the present management of patients with thoracic aortic aneurysms reflects existing limitations in the state of medical knowledge. Adding to this uncertainty are differences in the results of published studies that have endeavored to estimate growth rates of thoracic aortic aneurysms and to identify risk factors for complications. In addition, it is often difficult to evaluate the validity of the statistical evidence in a given study. The present report expands on an earlier study examining these issues [2], and includes a larger patient cohort and longer follow-up.

	Patients and methods

Top Abstract Introduction Patients and methods Results Discussion References

 
Study patients were identified through a computerized search of all patients undergoing magnetic resonance imaging (MRI), computed tomography (CT) scan, or echocardiography (ECHO) of the thoracic aorta at Yale-New Haven Hospital from January 1985 to June 1997. A search was also conducted to identify those patients who underwent aortic surgery, and autopsy records were examined for all patients who died from aortic disease during this time period. A hospital chart review was then conducted on every identified patient. The thoracic aorta was considered aneurysmal if it attained a maximal diameter 3.5 cm. Patients under 16 years of age were excluded.

The data base at the Yale Center for Thoracic Aortic Disease includes 1063 radiographic studies (371 CT scans, 223 MRI scans, and 469 ECHOs) performed on 370 patients with thoracic aortic aneurysms: 222 men and 148 women, with an average age of 62 years (range 16–92). Thirty-nine patients had Marfan’s syndrome. Among the 370 patients, a core group of 294 patients have had serial imaging studies: 201 with ascending aneurysms, 19 with arch aneurysms, 56 with descending aneurysms, and 18 with thoracoabdominal aneurysms. Serial information on aneurysm size was obtained in 109 patients who did not undergo aortic graft surgery. The period of follow-up ranged from 1 to 127 months, with a mean of 29.4 months.

Aneurysm growth rates
Growth rate estimates were obtained using a multivariable regression analysis described previously [3], in which aneurysm growth followed an exponential path. We also investigated potential risk factors associated with aneurysm growth, including chronic dissection, aneurysm size (< 4.0, 4–4.9, 5–5.9, and 6.0 cm), Marfan’s syndrome, aneurysm location (ascending or arch vs descending or thoracoabdominal), age, smoking history, hypertension (diastolic blood pressure > 95 mm Hg), and gender.

Complication rates
Multivariate logistic regression models were estimated to identify risk factors associated with complications. The logistic regression models relate occurrence of rupture or acute dissection to initial aneurysm size, aneurysm location (ascending or arch vs descending or thoracoabdominal), age, and gender. Separate models were estimated for subsamples of patients with ascending and arch, and descending and thoracoabdominal aortic aneurysms.

	Results

Top Abstract Introduction Patients and methods Results Discussion References

 
Growth rates
The exponential model assumed that aneurysm growth increases with initial size. For the average aneurysm size in our sample (5.2 cm), the annual growth rate was estimated to be 0.10 cm/year. The annual growth varied from 0.08 cm/year for small (4.0 cm) aneurysms to 0.16 cm/year for large (8.0 cm) aneurysms. The annual growth rates for patients suffering chronic dissections were significantly higher, ranging from 0.24 cm/year for small (4.0 cm) aneurysms to 0.48 cm/year for large (8.0 cm) aneurysms. The annual growth rate at 5.2 cm (sample mean) was also significantly higher for patients with chronic dissections (0.31 cm/year) compared with those individuals without chronic dissections (0.05 cm/year).

For those individuals who eventually underwent aortic replacement, the annual growth rate according to initial aneurysm size was higher (0.12 cm/year) than those who did not undergo surgery (0.10 cm/year). For ascending or arch aneurysms, the annual grow rate of 0.09 cm/year was lower than for descending aortic aneurysms (0.12 cm/year). These trends, however, were not statistically significant.

Complication rates
The incidence of acute dissection or rupture increases with larger aortic size. For aneurysms < 4 cm, the overall incidence of acute dissection or rupture was 8.8%; at 4.0–4.9 cm, it was 9.5%; at 5.0–5.9 cm, it was 17.8%, and at > 6 cm, it was 27.9%.

The median thoracic aortic size at the time of rupture or dissection differed according to aneurysm location: ascending or arch aneurysms ruptured or dissected at a median of 5.9 cm, whereas descending or thoracoabdominal aneurysms ruptured or dissected at a median diameter of 7.2 cm.

The results of a multivarible regression analysis predicting the probability of acute dissection or rupture of an ascending or arch aneurysm showed that the odds are 4.4 times greater for patients with aneurysms 6.0–6.9 cm than for patients with aneurysms 4.0–4.9 cm (p < 0.006). The corresponding regression analysis for descending or thoracoabdominal aneurysms shows that the odds of incurring a rupture or acute dissection are 14 times greater for patients with aneurysms 7.0–7.9 cm than for patients with aneurysms 4.0–4.9 cm (p < 0.03).

Figures 1 and 2 summarize the probability of rupture or acute dissection by initial aneurysm size : the probability of rupture or dissection is 25% higher in patients with ascending or arch aneurysms 6.0 cm (p < 0.006 relative to the 4.0–4.9-cm comparison group), and 37% higher in patients with descending aneurysms 7.0 cm (p < 0.03).

View larger version (12K): [in this window] [in a new window]   Fig 1. Regression analysis for the ascending aorta.

View larger version (12K): [in this window] [in a new window]   Fig 2. Regression analysis for the descending aorta.

	Discussion

Top Abstract Introduction Patients and methods Results Discussion References

Aneurysm size at time of dissection and rupture
Evidence from our series demonstrates a rising incidence of dissection or rupture with expanding aneurysm size. In our recent analysis [2], ascending aortic aneurysms ruptured or dissected at a median size of 6.0 cm, and descending aneurysms at 6.9 cm. The present study, with a larger cohort of patients, confirms these results, with ascending aneurysms rupturing or dissecting at a median size of 5.9 cm, and descending aneurysms at 7.2 cm.

Our data confirm that aortic rupture or dissection occurs at sizes smaller than those reported in early series (Table 2) [8,14] but similar to sizes in the 1994 report by Dapunt and associates [7]. Multivariate regression analysis to isolate risk factors for acute dissection or rupture revealed that a size between 6.0 and 6.9 cm means a 37% increase in the probability of these events for ascending aneurysms (p < 0.006), and an even greater increase, 43%, for descending aneurysms 7 cm (p < 0.003). Figures 1 and 2 depict graphically the risks for ascending and descending aneurysms, respectively. "Hinge points" in the risk of complication are strikingly apparent at 6 cm for the ascending aorta and at 7 cm for the descending aorta.

If the median size at the time of complication—in our series 6.0 cm for the ascending, and 7.2 cm for the descending aorta—had been used as the indication for elective surgical resection, half the patients would have suffered a devastating complication by the time of intervention. Accordingly, we propose that preemptive elective surgery be carried out at a size somewhat smaller than the median observed in unoperated patients at the time of rupture or dissection: at a diameter of 5.5 cm for ascending and 6.5 cm for descending aortic aneurysms. These proposed criteria allow intervention before the "hinge points" of increased incidence of rupture and dissection depicted in Figures 1 and 2.

These recommendations are supported by the results of our previous series [2], which demonstrated that elective surgery is much safer than emergency intervention. It is self-evident that age and coexisting disease may render aggressive surgical intervention inappropriate for some patients. In addition, the level of experience with these major surgical procedures at the treating medical center must be taken into account. These size criteria are proposed for elective aneurysm surgery in otherwise healthy patients cared for at experienced centers. Each patient must be evaluated independently, with the anticipated risks of operation (and especially paraplegia with descending aortic aneurysms) weighed against the estimated risk of rupture or dissection.

	References

Top Abstract Introduction Patients and methods Results Discussion References

 

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This Article Abstract Full Text (PDF) 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 Author home page(s): Graeme L. Hammond Gary S. Kopf Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Coady, M. A. Articles by Elefteriades, J. A. Search for Related Content PubMed PubMed Citation Articles by Coady, M. A. Articles by Elefteriades, J. A.