Formulas Identify Best Patients for AAA Repair

BY MITCHEL L. ZOLER

PHILADELPHIA -- Some patients with abdominal aortic aneurysms are simply too sick to safely undergo aneurysm repair, be it by open surgery or with an endovascular procedure. Evidence is now starting to accumulate on how to identify patients for whom aneurysm repair is too risky.

New data suggest that only a small percentage of patients, perhaps less than 3%, fall into the high-risk group that shouldn't undergo repair of an abdominal aortic aneurysm (AAA). And new findings also indicate that, contrary to prior belief, it's the fittest patients who gain the biggest advantage from undergoing an endovascular aneurysm repair (EVAR) instead of open surgery.

"The trend is toward the fitter the patient, the more EVAR may benefit over open repair," Dr. Roger M. Greenhalgh said at the Vascular Annual Meeting, sponsored by the Society for Vascular Surgery.

"At the other end, in extremely unfit patients, you eventually get to a point where the unfitness is so great that EVAR won't help at all," added Dr. Greenhalgh, professor of surgery and head of vascular surgery at Imperial College, London.

"It's an important finding that outcomes [from AAA repair] may be related to fitness, and it's sensible to use a scoring method to assess fitness."

One formula for measuring preoperative fitness was derived empirically by looking at all of the AAA repair patients in the more than 41 million patients of the Medicare data set from 2000-2004. In this group were 39,792 patients who underwent an elective, first-time AAA repair using EVAR. Overall in this group, the rate of death during the first 30 days after treatment was 1.73%, said Dr. K. Craig Kent, chief of vascular surgery at New York-Presbyterian Hospital.

EVAR use rose over the 5 years examined, from 1,500 patients in 2000 to 12,000 in 2004. And the 30-day mortality rate was cut in half, from 2.5% in 2000 to 1.25% in 2004. Based on a multivariate analysis that assessed the role of a variety of comorbidities in 30-day mortality, Dr. Kent and his associates calculated a preliminary scoring system to assess the risk of perioperative death that a patient faces from EVAR.

Renal failure emerged as the single most important comorbidity, scoring five points in the system Dr. Kent presented. (See box.) When this comorbidity scoring system was applied to the Medicare cohort, they found that scores could be associated with specific perioperative mortality rates. (See box.) Finally, Dr. Kent and his associates selected a representative high-risk score of 9, linked with a 9.3% risk of death, to determine how many of the Medicare patients met or exceeded this arbitrarily selected high-risk threshold.

The researchers found that 2.3% of the more than 39,000 patients in the group studied had a score of 9 or more. The remaining 97.7% of the AAA patients in the group had a lower score and hence they had a lower risk of 30-day death.

Until now, "we had thought that high-risk patients might be 20%-30%" of all patients with an AAA, Dr. Kent said.

A different approach to risk assessment was tested by Dr. Greenhalgh and his associates based upon using data they had collected on patients in the landmark EVAR trial 1 (Lancet 2005;365:2179-86) and EVAR trial 2 (Lancet 2005;365:2187-92).

The EVAR trial 1 randomized nearly 1,100 patients to EVAR or open surgical repair; EVAR trial 2 included 338 patients judged unfit for open surgery who were then randomized to EVAR or to no repair.

The risk assessment tool that Dr. Greenhalgh and his colleauges used was a modified form of a previously reported scoring system that had been developed to assess the perioperative mortality in those patients undergoing vascular surgery by researchers at Erasmus Medical Center, Rotterdam, Netherlands (Arch. Intern. Med. 2005;165:898-904).

The modified Rotterdam formula is called the customized probability index (CPI), and it uses seven clinical characteristics: renal dysfunction (defined as a serum creatinine level of 2 mg/dL or greater) adds 16 points, uncontrolled heart failure adds 14 points, ischemic heart disease adds 13 points, hypertension adds 7 points, and chronic pulmonary disease (defined as a forced expiratory volume of less than 60% of predicted) also adds 7 points. Treatment with either of two medications was considered to cut the mortality risk and therefore subtracts points. Treatment with a ?-blocker subtracts 15 points, and treatment with a statin pares 10 points off the total.

The result is a CPI point total that can range from -25 to +57, said Louise C. Brown, a statistician who works with Dr. Greenhalgh at Imperial College.

When the researchers applied the CPI to 1,174 patients in EVAR trial 1 studies, they found that 47% fell into a category with good fitness for surgery, having a CPI score ranging from -25 to 0. Another 26% had a moderate CPI score of 1-10, and 27% had poor fitness, with a score ranging from 11 to 36. The average CPI score for all patients in EVAR trial 1 was 3.7, and it was 10.1 for those in EVAR trial 2.

The London team then analyzed the 30-day operative mortality rates for patients in the three fitness categories based on whether the patients had been treated with EVAR or open surgery.

Patients with good fitness were 83% less likely to die when they underwent EVAR, compared with open surgery, a statistically significant difference.

Patients with moderate fitness had an 11% drop in mortality with EVAR, compared with open surgery, and poor fitness patients had a 53% reduced mortality, but a test for any differences across all the fitness ranges did not show any strongly significant results.

All-cause mortality during 5 years after surgery was roughly similar between the EVAR and open surgery groups for all three fitness subgroups.

Although aneurysm-related deaths during 5-year follow-up were reduced by 52% in patients repaired by EVAR in the good fitness group, there was little evidence of difference across the fitness spectrum.

In short, the analysis showed that there was no fitness group for which open surgery was shown to be superior to EVAR, but that there was some evidence that EVAR may be a better option for those patients who were most fit for AAA repair, Dr. Greenhalgh said. In addition, "there is a small but potentially definable group of patients for whom open surgery is not possible [because of the high risk that surgery poses], and EVAR will not save the day."

"I agree that there is a small fraction of patients who should not get EVAR. For patients with this level of risk, the best thing is to do nothing," commented Dr. Gregorio A. Sicard, professor of surgery and chief of vascular surgery at Washington University in St. Louis.

He also noted that a formal system for assessing a patient's fitness for AAA repair was better than current practice, which is to just rely on physicians' opinions. A scoring system would also give physicians guidance on how to improve a patient's fitness for AAA repair by, for example, improving control of heart failure or hypertension, Dr. Sicard said in an interview.