The likelihood of rupture of untreated large abdominal aortic aneurysms (AAAs) in patients deemed unfit for elective repair is lower than that commonly cited in the literature, according to a meta-analysis published online February 4, 2015, ahead of print in the Journal of Vascular Surgery. Although the risk of dying from rupture remains high in this population, it is less than that from other causes.

After reviewing the medical literature through January 2014, investigators led by Christopher P. Twine, MD, of the Royal Gwent Hospital (Newport, Wales), pooled data from 11 studies—10 observational and 1 RCT—comprising 1,514 patients who had 347 ruptured AAAs. Only 3 of the studies were published within the past decade.

Autopsy to confirm cause of death was not routine in any study. However, 6 studies used the office of national statistics or an equivalent organization, and hospital records or databases maintained by the study coordinators were used in all cases. Two studies were heavily weighted toward male participants.

The judgment that patients were unfit for intervention was made by the surgeon alone in 4 studies, by the surgeon with selective opinion from an anesthesiologist or further investigations in 5 studies, and by combined physician and anesthesia assessment in 1 study (the method was unstated in 1 study). One trial used dynamic stress testing and 1 cardiopulmonary exercise testing to inform the decision.

The overall rupture incidence among the studies varied from 2.6% to 7.9% per year. According to the authors, the range likely reflects AAA size differences because studies with a greater proportion of smaller aneurysms had lower rupture rates; when rupture rates were stratified by AAA size, there was far less heterogeneity.

Rupture Risk Rises With Increasing AAA Size

The overall annual incidence of rupture in patients with an AAA > 5.5 cm was 5.3% (95% CI 3.1-7.5), but the rate was proportional to AAA length:

• 3.5% for 5.5-6.0 cm
• 4.1% for 6.1-7.0 cm
• 6.3% for > 7.0 cm

The rates are cumulative; hence, the 10-year risk of rupture in patients with a 7.5-cm AAA, for example, would be 63%.

Emergency repair was offered to 32% of patients unfit for elective AAA repair, and perioperative mortality in this group was 58%.

The mortality risk of a ruptured large AAA was less than half that from any other cause during the combined study periods (19% vs 42%; P < .001), and the difference persisted across AAA lengths (table 1).

“Rupture rates of large, untreated AAAs in patients unfit for surgical repair were lower than expected and appear to be decreasing with time,” the authors write. And even though less than one-third of patients with ruptures were offered intervention, 42% who did receive surgery survived the postoperative period.

Treatment Trends

The investigators point to “significant changes” in treatment since the early 1990s. “There is greater awareness and use of best medical therapy, including antiplatelet, statin, and risk factor modification therapy,” they say. “[In addition, a] shift has occurred toward the use of endovascular repair, which has a very low postoperative mortality and may even be performed percutaneously under local anesthetic. A combination of these factors may explain the trends observed over time.”

Debate continues about use of endovascular repair in medically unfit patients despite the finding of no survival benefit in EVAR 2, Dr. Twine and colleagues say, noting that the trial was plagued by a high rate of crossover between its arms.

Moreover, uncertainty about how many patients deemed unfit for open surgery receive endovascular aneurysm repair (EVAR) confounds interpretation of the current results and “means that they may only apply to the most ‘unfit’ patient. That the definition of ‘unfit’ has changed with EVAR and that rupture rates may have reduced as a result is also worth noting,” they say.

The authors acknowledge that the meta-analysis likely underestimates true rupture rates, for several reasons:

• Postmortem data were lacking
• Attrition was high in some trials
• Ruptured AAA may have been misdiagnosed
• Annual rate dilution in studies with longer follow-up because ruptures tended to occur early

Also potentially distorting the picture, use of risk-modifying medications or compliance checks was not reported. And few studies performed follow-up surveillance scans, so ruptures may have occurred at a larger AAA size than attributed.

Data Help Put Risk in Perspective

The findings mean that multidisciplinary teams that deny patients repair at 5.5 cm due to unfitness for surgery “can reassure patients that their risk of rupture, at 3.5% per year, is probably lower than they expect,” the authors write. “Continued surveillance and reconsidering repair if the aneurysm size increases may be worthwhile.”

In addition, the fact that attrition from non-AAA causes remains high in this group should also be factored in to any risk-benefit calculation, they say.

Moreover, refusal of elective repair does not necessarily preclude successful emergency repair, Dr. Twine and colleagues say, and “a frank discussion and documentation of this decision should be separate from denying the patient an elective repair.”

They conclude that “[l]arge, population-based data with good postmortem or hospital-based diagnosis of ruptured AAA [are] required for more robust reporting.”

Source:
Parkinson F, Ferguson S, Lewis P, et al. Rupture rates of untreated large abdominal aortic aneurysms in patients unfit for elective repair. J Vasc Surg. 2015;Epub ahead of print.

Related Stories:

• More Aggressive Treatment of Ruptured AAA in United States Reduces In-Hospital Mortality vs England
• Elective EVAR Not as Successful in Women as in Men
• Designation as ‘Unfit for Open Repair’ Predicts Worse EVAR Outcomes