Small AAA: To treat or not to treat
Dr. Ouriel is a vascular surgeon and president and CEO of Syntactx.
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Small aneurysms should be left alone.
By Karl A. Illig, M.D.
The currently accepted recommendation to delay repair of abdominal aortic aneurysms until they reach 5-5.5 cm is based on the historical mortality and morbidity of open repair.1 Endovascular aneurysm repair (EVAR) has clearly been shown to reduce the risk of operation, perhaps by as much as two-thirds. Should we now change the threshold for aneurysm repair, especially if the patient is a candidate for EVAR?
There are many arguments to repair small aneurysms. However, the answer really depends upon empirical data. At least three major papers address this question. In the U.K. Small Aneurysm Trial, 1,090 patients with abdominal aortic aneurysms measuring 4.0-5.5 cm in diameter were randomized to undergo early elective open surgery versus ultrasonic surveillance.2 There was an early survival disadvantage for those undergoing open surgery, as expected, but the curves evened out at 3 years or so, and no survival advantage occurred in either group, obviously favoring observation alone. Similarly, the ADAM group, pursuing the same protocol in 1,136 U.S. veterans, found the same thing, despite a low operative mortality of 2.7%. No advantage to early open repair could be seen.3
What of the situation after endovascular repair? The PIVOTAL trial, the lead author of which wrote the accompanying commentary, randomly assigned 728 patients with aneurysms measuring 4.0-5.0 cm to early endovascular repair with the Medtronic device versus ultrasonic surveillance.4 Aneurysm rupture or aneurysm-related death occurred in only two patients in each group (0.6%). The authors appropriately concluded that surveillance alone was equally as efficacious as early endovascular repair for patients with small aneurysms.
Finally, what of the arguments that, by waiting until the aneurysm is larger, you lose the window of opportunity for endovascular repair? We recently explored this in a cohort of 221 patients undergoing preoperative CT scanning for aneurysms of all sizes.5 With receiver operator curve analysis, a cutoff of 5.7 cm best differentiated those who were endovascular candidates from those who were not. Put another way, the rate of endovascular suitability hovered right around 80% until the aneurysm reached 6 cm, at which point it dropped off. In other words, waiting until the aneurysm reaches 5.5 cm doesn’t reduce the chance that a patient will be a candidate for EVAR.
There are many arguments for early intervention in small aneurysms. The concept that EVAR is safer than the procedure originally used to make the recommendation to wait until 5.5 cm is a valid point. However, empiric data still do not show any benefit for either open or endovascular repair as opposed to surveillance at sizes smaller than this. The operative mortality difference is only a couple of percentage points or so, and long-term survival appears to be identical after the initial risk has passed. This 2% or 3% early survival benefit does not seem to impart any long-term advantage, and long-term survival does not seem to be impaired by being a bit conservative. Until data come along that definitively show benefit for early repair, current guidelines remain valid.
Dr. Illig is the director of vascular surgery at USF Health, Tampa.
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2. Lancet 1998; 352:1649-55.
3. NEJM 2002; 346 (19): 1437-44.
4. J Vasc Surg 2010; 51:1081-7.
5. J Vasc Surg 2010;52:873-7.
