Study Raises Concerns About Noncompliance with EVAR Guidelines for AAA

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Over a 10-year period, clinicians performing endovascular aortic repair (EVAR) for abdominal aortic aneurysm (AAA) have strayed farther and farther from patient selection criteria according to device instructions, resulting in increasing rates of postprocedure aneurysm sac enlargement and potential rupture. Results from a study of over 10,000 EVAR patients were published online April 10, 2011, ahead of print in Circulation.

Researchers led by Andres Schanzer, MD, of the University of Massachusetts Medical School (Worcester, MA), analyzed pre- and postprocedure CT scans from 10,228 patients in a multicenter imaging database who underwent EVAR for AAA between January 1, 1999, and December 31, 2008. Baseline aortoiliac anatomic characteristics were reviewed for each patient. Although data pertaining to specific AAA endovascular devices were not available, morphological measurements were compared with both liberal and the most conservative published anatomic guidelines from the instructions for use from each manufacturer.

The goal was to determine the relationship between baseline anatomic characteristics and treatment failure and risk of rupture, represented by the incidence of aortic aneurism sac enlargement (defined as a growth of ≥ 5 mm in AAA maximal diameter from pre-EVAR to any post-EVAR CT scan).

Neither Conservative Nor Liberal

The average preoperative AAA maximum diameter was 54.8 mm, and more than half (59%) had an AAA maximum diameter less than the 55-mm threshold at which intervention is recommended over surveillance. The average AAA neck diameter was 32.1 mm, with a mean length of 20.7 mm and a mean angle of 36.9°. Instructions for use guidelines were compiled for 10 different devices from manufacturers including Guidant/Boston Scientific (Natick, MA), Medtronic (Minneapolis, MN), W.L. Gore (Newark, DE), Cook Medical (Bloomington, IN), and Endologix (Irvine, CA).

Over half of the patients (58.5%) were treated despite not meeting guidelines for conservative instructions for use, which included criteria such as: aortic neck angle less than 45° and aortic neck length at least 15 mm. In addition, almost a third of patients (31.1%) were treated outside the liberal instructions for use, which included criteria such as: aortic neck angle less than 60° and aortic neck length at least 10 mm. The last guidelines evaluated were time-dependent instructions for use, which reflected the most liberal criteria at different time points throughout the study. Over 4,500 patients (44.1%) were treated despite not meeting these criteria.

The proportion of patients treated outside the liberal and conservative guidelines remained constant over time, while patients treated outside the time-dependent criteria decreased over the 10-year study period, from 49.4% at the beginning to 32.6% at the end (P < 0.001).

Baseline characteristics also changed over time, as a liberalization occurred in terms of anatomic characteristics deemed suitable for EVAR (table 1).

Table 1. Baseline Characteristics for Patients Undergoing EVAR for AAA by Year

The incidence of AAA sac enlargement at 1, 2, and 5 years after EVAR was 3%, 17%, and 41%, respectively, with 30% of cases not manifesting until more than 3 years postprocedure. At 5 years, patients treated outside the instruction for use guidelines showed a higher incidence of AAA sac enlargement. This held true for both conservative (61.0% freedom from sac enlargement vs. 56.5% in patients treated within conservative guidelines; P < 0.001) and liberal criteria (59.1% vs. 57.5%; P < 0.001). In addition, patients treated after 2004 had worse freedom from sac enlargement rates compared with those treated earlier (38.4% vs. 74.3%; P < 0.001).

On multivariable analysis, independent predictors of AAA sac enlargement included endoleak (HR 2.70; 95% CI 2.4-3.04; P < 0.0001) and several of the same baseline characteristics that were liberalized over time:

• Patient age ≥ 80 (HR 1.32; 95% CI 1.03-1.75; P = 0.05)
• Aortic neck diameter > 32 mm (HR 2.07; 95% CI 1.46-2.92; P < 0.0001)
• Aortic neck angle > 60° (HR 1.96; 95% CI 1.63-2.37; P < 0.0001)
• Common iliac artery diameter > 20 mm (HR 1.46; 95% CI 1.21-1.76; P < 0.0001)

“In this multicenter patient population, compliance with published EVAR device [instruction for use] guidelines was low, and post-EVAR aneurysm sac enlargement was high, raising concern for long-term risk of aneurysm rupture,” the researchers conclude. “The liberalization in anatomic criteria deemed appropriate for EVAR, observed throughout the study period, was associated with worse outcomes. An improved understanding of these anatomic characteristics will ultimately improve the effectiveness and durability of EVAR to protect patients against AAA rupture.”

William A. Gray, MD, of Columbia University Medical Center (New York, NY), agreed with the major findings of the study, noting that “everything the authors said probably accurately reflects the practice of EVAR.”

A Clinical Context

However, there are other important considerations, he pointed out, including the fact that the data come from an imaging database, with no clinical information to provide context.

“It has to be individualized to the patient, and balanced with clinically relevant factors that unfortunately we don’t have here,” Dr. Gray explained. “I think what the authors say is true, and all their caveats are acceptable.” Nevertheless, he added, “there are certain patients for whom operative repair is a good idea, especially if they have bad anatomy, and they should be operated on. Alternatively, there are patients who aren’t [able to undergo] such great operations, and we have to accept there’s going to be a finite failure rate, but that may be their only reasonable option.”

For instance, for a 65-year old with a 5% operative risk who receives a suboptimal graft “that’d be an unsuccessful procedure,” Dr. Gray said.

“On the other hand, if you have an 85-year old with COPD and heart failure, and a 7-cm aneurysm, the aneurysm is going to kill him,” he said. “So you have to do something, and according to the authors, the patient has about a 90% chance of not having sac expansion. That’s not bad.”

Dr. Gray noted that while the results of the study were statistically significant, due mainly to the large numbers involved, the absolute differences over time were not as concerning. In addition, new devices are being developed to address particularly difficult anatomy, such as short and angulated aortic neck, Dr. Gray added, which should help with the more difficult cases.

But that does not take away from the strength of the findings, Dr. Gray acknowledged. “I will say we are working harder to fit devices into people who are borderline in terms of anatomy, and a lot of that has to do with people who are not great operative risks,” he said.

 

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Source:
Schanzer A, Greenberg RK, Hevelone N, et al. Predictors of abdominal aortic aneurysm sac enlargement after endovascular repair. Circulation. 2011;Epub ahead of print.

 

 

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