Is endovascular repair for small aneurysms justified?

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The question of endovascular treatment of small aneurysms (4.0-5.0cm) is one that the PIVOTAL (Positive Impact of endoVascular Options for Treating Aneurysm earLy) study in the US is seeking to answer. The PIVOTAL study is a multi-center, prospective, randomized trial and will enrol approximately 1,680 patients at 70 clinical centers. The study is ultimately looking to answer the question: At what aneurysm size does the risk of an endovascular procedure become less than the risk of observing the patient without definitive treatment?

Traditional AAA treatment has generally been recommended when a patient’s aneurysm reaches a diameter of between 5-6cm, since at this point the risk of rupture is believed to be greater than the risk of open surgical repair. However, the recent introduction of minimally-invasive, catheter-based endovascular technology has made it possible to treat aneurysms and prevent rupture with lower mortality and morbidity rates compared to open surgery. The results of the less-invasive PIVOTAL trial could alter thinking if the use of endovascular stent graft systems instead of open surgery proves positive in these patients.

In a recent presentation at the VIVA ’06 meeting, Dr Daniel Clair, Department of Vascular Surgery, Cleveland Clinic Foundation (CCF), outlined the reasons for undertaking such a study arguing that no data exists regarding the endovascular treatment of small aneurysms.

He began by stating that two previous studies, the UK Small Aneurysm Trial (UK SAT) and the ADAM trial both assessed surveillance vs. early open repair. The results from these studies, argued Clair, showed that whilst the UK SAT results indicated a clinical benefit for early open repair (but no overall difference in mean survival), the ADAM trial showed no benefit for early open repair. Therefore, the conclusion from these trials was that surveillance is justified for small aneurysms.

However, he stated that these trials demonstrated a similarity between early operative repair and surveillance, but cautioned, in the UK SAT the perioperative mortality rate was 5.4% (30-day immediate repair group) and 2,1% in ADAM. Therefore, Clair asked, “If a procedure could be performed with a low perioperative mortality rate, that procedure might be able to ‘beat’ surveillance of small aneurysms.” Moreover, he said that the results from these small aneurysm trials could not be extrapolated to endovascular repair.

Next, he listed reasons that would justify the repair of small aneurysms; a lower mortality rate overall and a lower perioperative mortality rate. If these are seen as justifiable reasons, then Clair argued that endovascular repair can be utilised to provide a lower perioperative mortality rate than open repair and greater long-term rupture protection than surveillance.

To demonstrate this point, Clair highlighted data from the CCF, EVAR-1, DREAM and New York State trials/studies, which indicated that endovascular repair of AAA has lower mortality and lower complication risks compared with open repair.

The endpoints of the PIVOTAL trial are rupture, aneurysm-related death, all-cause mortality and aneurysm-related mortality; the same endpoints tabulated from the published data from the ADAM and UK SAT trials, stated Clair. According to CCF data, the 3-year Kaplan-Meier estimates for the rate of rupture is 0.9, for aneurysm-related death 1.1% and the combined rate would be 2.1%. This contrasts with the observation data from UK SAT and ADAM that according to Clair showed combined rates of 6.9% (UK SAT), 3,3% (ADAM and an average of 5.1%.

In the PIVOTAL trial, half of the patients with aneurysms between 4-5cm will be randomly assigned to receive endovascular repair at the time of their diagnosis. The other half will be monitored with ultrasound every six months. Those in the surveillance group who develop symptoms or experience enlargement can be treated with either an open or endovascular repair procedure. The two groups will be observed for five years to track differences in outcomes as they relate to any aneurysm or aneurysm repair.

In conclusion, Clair said that whilst randomised trials have evaluated open surgery vs. surveillance for small aneurysms many patients ultimately come to surgery in surveillance groups as the anatomy worsens following increases in diameter. The lower morbidity and mortality rates associated with endografting are likely to result in a significant advantage, compared to open surgery. Moreover, the PIVOTAL trial could provide some much needed data regarding the status of women and whether they should be treated at 5cm or earlier. Therefore, Clair said that the current recommendations should be: randomisation if endovascular repair is possible, observation if it is not; and close monitoring in any surveillance programme.

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