Volume 39, Issue 3 , Pages 266-270, March 2010
Natural History of Thoraco-abdominal Aneurysm in High-Risk Patients☆
Article Outline
- Abstract
- Introduction
- Patients and Methods
- Results
- Discussion
- Conflict of Interest/Funding
- Acknowledgements
- References
- Copyright
Abstract
Introduction
There is considerable interest in the role of novel endovascular techniques for the treatment of patients with complex aneurysms who are unsuitable for standard interventions. Knowledge of the natural history of these lesions, as well as other co-morbidities, is required in order that these techniques may be applied correctly in this high-risk group.
Method
This study reviews the outcome of patients deemed to be unfit for surgery following assessment under the Scottish National Thoraco-abdominal aneurysm service (TAAA) service (2002–2008).
Results
Of 216 patients assessed, 89 (41%) patients were considered to be unfit for intervention. The median (interquartile range, IQR) age of patients was 75 (70–80) years and there were 39 men (44%). Median (IQR) aneurysm size was 6 (5.6–7.0) cm. The median (IQR) follow-up time was 12 (7–26) months. There were 49 (55%) deaths during the follow-up period of which 23 (47%) cases were due to ruptured TAAA and 26 (53%) were not aneurysm-related. Comparing patients with aneurysms <6 cm (33 patients) with those aneurysms ≥6 cm (56 patients) there was no difference in aneurysm-related death (p = 0.32) or all-cause mortality (p = 0.147).
Conclusion
Aneurysm-related mortality amongst patients unsuitable for open TAAA surgery is considerable and evolving endovascular techniques may permit intervention in selected patients. However any intervention can only be justified if the patient's life expectancy is sufficient to allow benefit to accrue.
Keywords: Natural history, Thoraco-abdominal aortic aneurysm, Outcome
Introduction
The mortality associated with rupture of a thoraco-abdominal aortic aneurysm (TAAA) remains very high. In contrast, the outcomes for elective TAAA repair have improved in recent decades.1, 2 This improvement can be attributed to advances in operative technique as well as developments in pre-operative assessment and peri-operative care.3, 4 In particular, the ongoing development of endovascular techniques, including branched and fenestrated grafts, continues to challenge the indications and thresholds for operative intervention in patients with asymptomatic TAAA.5, 6, 7, 8, 9, 10
All interventions, whether open, endovascular or hybrid, are associated with significant risk. Therefore decision-making must weigh carefully the risk of rupture against the individual's estimated operative risk. The assessment of risk of aneurysm rupture is based largely on natural history data, which are limited currently.11, 12, 13, 14, 15, 16
In 1999 a National Service was established for the assessment and management of all patients with a TAAA in Scotland. Patients considered suitable for assessment for intervention are referred from both regional vascular units and district general hospitals. This study reports the outcome of patients who, after thorough assessment, were considered to be unfit for surgical repair, and were managed non-operatively.
Patients and Methods
Since the establishment of the Scottish National Thoraco-Abdominal Aortic Aneurysm Service, data have been collected prospectively in a clinical database. All patients assessed for suitability for intervention over a seven-year period (January 2002–December 2008) were identified from the database. Information from the database together with hospital records was used to gather demographic and clinical details.
All patients were assessed using a comprehensive investigation protocol that included routine blood tests (full blood count, electrolytes, liver function tests, coagulation profile), a chest radiograph, an electrocardiogram (ECG), pulmonary function tests and non-invasive cardiac stress testing (exercise ECG and/or stress echocardiogram). Percutaneous coronary angiography was used selectively. Computed Tomography (CT) angiography was used to determine the extent and morphology of the aneurysm, and the suitability of the aneurysm for open or endovascular surgical repair. In addition, the patient was reviewed by a multidisciplinary team comprising a consultant vascular surgeon, a vascular anaesthetist, an interventional radiologist and a cardiologist.
For those patients considered unfit for surgery following assessment, the reason for refusal was recorded. The patient's General Practitioner was telephoned at six-monthly intervals to obtain follow-up information and, where the patient was found to be deceased, the cause of death was established from death certificate data. Patients with an aneurysm <6 cm in maximum diameter were compared to those with an aneurysm ≥6 cm.
Statistical analysis was performed using SPSS for Windows Release 15.0.0. Univariate analyses between groups were determined by χ2 or Fisher's exact test for categorical variables. Kaplan–Meier survival curves were constructed and compared using a log rank test. P ≤ 0.05 was considered significant.
Results
Two hundred and sixteen patients were assessed by the TAAA service over the seven-year study period. Of these, 89 (41%) patients were found to be unsuitable for intervention following assessment. There were 39 men (44%) and the median (interquartile range, IQR) age was 75 (70–80) years. Table 1 summarises the baseline demographic data. The median (IQR) aneurysm diameter at referral was 6.0 (5.6–7.0) cm. Thirty-three (37%) patients had a TAAA <6 cm in maximum diameter and 56 (63%) had a TAAA ≥6 cm. Table 2 details the extent of the aneurysm for all of those assessed, for those operated upon and for those considered to be unsuitable for intervention.
Table 1. Patient demographics.
| Demographic | All patients (n = 89) | Aneurysm <6 cm (n = 33) | Aneurysm ≥6 cm (n = 56) |
|---|---|---|---|
| Age, median years (IQR) | 75 (70–80) | 74 (68–78) | 76 (71–80) |
| Male gender, n (%) | 39 (44%) | 13 (38%) | 26 (47%) |
| Max. aneurysm diameter, median cm (range) | 6.0 (5.0–10.0) | 5.5 (5.0–5.9) | 7.0 (6.0–10.0) |
Table 2. Aneurysm extent.
| Aneurysm type | Total assessed | Operated | Non-operated |
|---|---|---|---|
| Type I | 18 | 8 (44%) | 10 (56%) |
| Type II | 44 | 15 (34%) | 29 (66%) |
| Type III | 29 | 15 (52%) | 14 (48%) |
| Type IV/suprarenal | 99 | 66 (67%) | 33 (33%) |
| Type V | 1 | 1 (100%) | 0 (0%) |
| Descending thoracic | 25 | 22 (88%) | 3 (12%) |
| Total | 216 | 127 (59%) | 89 (41%) |
The reasons for patients being turned down for intervention are listed in Table 3. Many patients, 37/89 (42%), were considered to be unfit for surgery as a result of the presence of multiple (two or more) co-morbidities or global frailty.
Table 3. Reason being considered to be unsuitable for intervention.
| Reason for non-operative management | Number of patients (%) |
|---|---|
| Ischaemic heart disease | 22 (25%) |
| Respiratory disease | 11 (12%) |
| Renal impairment | 4 (4%) |
| Multiple co-morbidities/general frailty | 37 (42%) |
| AAA size borderline for intervention + moderate co-morbidity | 9 (10%) |
| Patient declined surgery | 4 (4%) |
| Aneurysm inoperable | 2 (2%) |
Follow-up was complete for all 89 (100%) patients. Median (IQ range) follow up was 12 (7–26) months. None of the 89 patients underwent a surgical or endovascular procedure during the follow-up period. During the follow-up period 49/89 (55%) patients died. Considering those patients who had died during the follow-up period 23/49 (47%) had a ruptured aneurysm whilst the remaining 26 patients (53%) died of a cause unrelated to their aneurysm. Further details of the cause of death are listed in Table 4.
Table 4. Cause of death.
| Cause of Death | All patients (%) (n = 89) | Aneurysm <6 cm (n = 33) | Aneurysm ≥6 cm (n = 56) |
|---|---|---|---|
| All-cause mortality | 49 (55) | 16 (48) | 33 (59) |
| Ruptured TAAA | 23 (26) | 6 (18) | 17 (30) |
| Non-aneurysm-related death | 26 (29) | 10 (30) | 16 (29) |
 Ischaemic heart disease | 6 | 4 | 2 |
| Respiratory (non-cancer) | 5 | 2 | 3 |
| Stroke | 2 | 1 | 1 |
| Malignancy | 6 | 2 | 4 |
| Gastrointestinal bleeding | 2 | 0 | 2 |
| Mesenteric ischaemia | 1 | 0 | 1 |
| Unknown/undetermined | 4 | 1 | 3 |
The overall survival for non-operated patients was 64% (SE 0.054) at 12 months and 52% (SE 0.061) at 24 months (Fig. 1). A comparison was made between the outcome of patients with an aneurysm <6 cm (33 patients) at the time of assessment and that of those with an aneurysm ≥6 cm (56 patients) (Fig. 2). At 12 months the survival of patients with aneurysms <6 cm was 71% (SE 0.083) and for patients with aneurysms ≥6 cm was 60% (SE 0.071). Over the entire study period there was no difference in survival between the two groups (p = 0.147) The incidence of aneurysm-related death (6/33 vs 17/56, p = 0.32) was similar for both groups.
Figure 1
Kaplan–Meier survival curve (all patients considered unsuitable for intervention).
Figure 2
Kaplan–Meier survival curve (comparison of survival of patients with aneurysms <6 cm compared to those with aneurysms ≥6 cm).
Discussion
Surgical repair of thoraco-abdominal aneurysms is associated with significant risk, but there are few contemporary studies of the natural history of TAAA from which to predicit the outcome of non-operative management. For 41% of the patients assessed for TAAA repair during the study period, the risks associated with surgery were considered to outweigh the risk of aneurysm rupture and these patients were turned down for surgical repair. Of those managed non-operatively, just over half died during the follow-up period, and, of those who died, nearly half had a ruptured aneurysm whilst the remaining deaths were thought to be unrelated to the aneurysm.
For infra-renal aneurysms, the results of the EVAR-2 trial suggest that there is no advantage of endovascular treatment over best medical therapy for patients considered to be unfit for open surgical repair.17 The situation for TAAA is somewhat different since open surgical repair is of a far greater magnitude than infra-renal aneurysm repair, with a particular risk of cardio-respiratory complications, renal failure, paraplegia and death.1, 2, 4, 18 The proportion of patients in this study assessed for TAAA surgery but turned down is approximately similar to that reported in the literature11 and is considerably higher than the proportion of those assessed for infra-renal aneurysm surgery in our institution.19 With half of deaths caused by aneurysm rupture, this study supports the idea that there exists a group of patients who are not fit for open surgical repair but, if their aneurysm could be repaired endovascularly with acceptable peri-procedural risk, would have a reasonable long term survival. It is clear from the fact that half of deaths are not aneurysm-related, that there will always be some patients who would gain no benefit from intervention due to their underlying co-morbidities. Thorough patient assessment and careful selection should continue to be used in parallel to evolving endovascular technologies.
This study reports the outcome of patients assessed and turned down for TAAA surgery and cannot be extrapolated reliably to the entire population of patients with TAAA. Furthermore, since the results come from a tertiary referral centre, this group has already been selected for referral from the patients' local hospital. There is evidence in the literature that the centralisation of services within high volume units achieves improved results.20 Due to the relative rarity of TAAA compared to infra-renal aneurysms, the number of patients in this study is necessarily small. This may explain in part the finding that there was no difference seen in the risk of aneurysm rupture or death for patients with TAAA <6 cm vs ≥6 cm which is out of keeping with the remainder of the literature.11, 15, 16 The United Kingdom has a low rate of post-mortem examinations and the limitations of using death certificate data are acknowledged. However the impossibility of conducting a large cohort study to look more accurately at the true natural history of TAAA justifies the use of these data.
Crawford et al. reported a series of TAAA with a 24% two-year survival in non-operated patients, of whom half died of a rupture.14 Other studies report lower mortality rates with a higher percentage of deaths being accounted for by ruptures.11, 15, 16 In a study of 1600 patients Elefteriades et al. observed that a patient with a TAAA of 6 cm had an annual risk of death of 10.8% and for the composite endpoint of rupture/dissection/death the annual risk was 14.1%.12
In conjunction with the present study these results support the aggressive approach to intervention for large TAAA in patients who have a reasonable operative risk. As endovascular techniques continue to develop and improve, some patients currently considered unfit for open surgical repair may be offered endovascular treatment. Whilst the potential benefits to be gained from less invasive techniques are evident, it must be recognised that, in these high-risk patients, any intervention can only be justified if the patient's life expectancy is sufficient to allow benefit to accrue.
Conflict of Interest/Funding
None.
Acknowledgements
We would like to thank our database manager Marion Livingstone for her contribution to this study. We also acknowledge the contribution of all of our colleagues involved with the Scottish National Thoraco-abdominal Aneurysm Service.
References
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☆ Presented at the XXIII Annual Meeting 3-6 September, 2009, European Society for Vascular Surgery, Oslo, Norway.
PII: S1078-5884(09)00663-7
doi:10.1016/j.ejvs.2009.12.023
© 2009 European Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.
Volume 39, Issue 3 , Pages 266-270, March 2010
