According to Janet Powell, Imperial College London, UK, the highest risk factors for rupture of abdominal aortic aneurysms (AAA) are female gender, smoking, increasing age and mean arterial pressure, but there are still few useful indicators of how to manage screen-detected aneurysms to stop them enlarging. Powell put forward this view during yesterday’s Abdominal Aortic Controversies Main Programme which explored epidemiology, indications and medical management of abdominal aortic aneurysms.

In trying to work out what makes aneurysms grow, Powell said that mostly the “mundane” cardiovascular risk factors have been looked at—alcohol, diet, obesity, smoking, medicines taken, exercise taken.

Turning to the existing and ongoing randomised trials that provide evidence for growth factors, Powell pointed out three trials already completed and without a positive result—AAA:STOP, PHAST and AORTA.

“Even in 2015, it is quite difficult to find information about trials because some trials still remain unregistered. Large epidemiological studies have mainly shown us about the risks for developing aneurysms, but the focus has been on baseline risk factors, not aneurysm progression,” she said.

Powell referred to RESCAN, a large international project primarily with the purpose of looking at optimal surveillance intervals for small aortic aneurysms, which was an individual patient data meta-analysis of small aneurysms, their growth and rupture in more than 15,000 persons.

“As we all know, growth rate increases with aortic diameter—just 1.34mm a year for the smallest aneurysms and 3.63mm when it comes to 5cm aneurysms—with exactly the same growth rate between men and women,” she pointed out.

When it comes to smoking, Powell maintained that the data are remarkably consistent that it increases aneurysm growth rate but that the effect is modest. Similarly, the effect of diabetes to slow or reduce the aneurysm growth rate is very consistent, but small.

“So we identified out of the available baseline data we had only two factors in these 15,000 patients that influenced growth rate and both effects were relatively modest—smoking increases, diabetes decreases. Cholesterol, blood pressure, statins, anti-hypertensive drugs and aspirin had no effect, and the year of enrolment [1985–2008] had absolutely no effect either. Disappointing,” Powell stated.

Rupture rates

Even though rupture of small aneurysms is not common, findings were more informative. RESCAN showed that the smallest of aneurysms take eight or more years before the risk of rupture is anything substantive, but as the diameter increases, so does the risk of rupture. But even for a 5cm aneurysm, it is more than year before risk of rupture exceeds 1%.

Powell pointed to some strong associations with factors that increase rupture rates. “Most notable, the fact that in women, there is fourfold increase in rupture rates vs. men. With smokers there is a twofold increase, with a far bigger effect on rupture than on growth. Mean arterial pressure increases growth rate, as does age. The older you are, the more likely your aneurysm is to rupture for any given diameter. So we cannot have any of this ageism, we need to treat aneurysms in older people too,” Powell maintained.

In the EVAR 2 trial, and subsequently reproduced in other papers, Powell observed that aortic neck length was associated with rupture and the shape of the aneurysm might have mattered, and a long neck was associated with relative protection from aneurysm rupture.

“Where are we in 2015? For rupture, there are some strong factors increasing risk: female gender, smoking (which we can do something about), increasing age, higher mean arterial pressures (we could have more effective blood pressure control), and the fact that a long aneurysm neck could just be protective. However, for growth, the effects that we have identified are modest: smoking, which increases it, and diabetes, which is protective,” Powell said.

She re-stressed that both of those growth effects are modest, adding that, “unfortunately this leaves us in a position that as yet we have few useful indicators of how to manage screen-detected aneurysms to stop them enlarging other than the old classic that was used for intermittent claudication—stop smoking and possibly keep walking.”