AAA: To Screen or Not to Screen?

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Source: TGlnaHRTcGVlZFZDVF9BQUEtU3RlbnQtVlIyMDExLTA5LTIzIDE2OjE2OjMx.jpg - AAA
Abdominal aortic aneurysms (AAAs) have very few warning signs or symptoms, making untreated patients ticking time bombs. In fact, 80 to 90 percent of patients with a ruptured AAA die before ever reaching the hospital. While most aneurysms are found incidentally during routine ultrasound exams, initiatives focusing on improving screening for patients most at risk for AAA have surfaced and protocols have emerged to help streamline care upon diagnosis.

In 2007, Congress passed the SAAAVE Act, a measure that allows patients entering Medicare to undergo one-time ultrasound screening for AAA. Because the disease is four times more common in men, screening is currently limited to men older than 65 years who have smoked at least 100 cigarettes during their lifetime, and patients with a family history of AAA. However, more than half of the existing AAA cases—approximately 569,000 cases—occur among patients ineligible to undergo screening under these criteria. Thus, is more screening necessary?

Get your ducks in a row

Harborview Medical Center in Seattle treats 30 to 40 ruptured aneurysms annually. Establishing a protocol was imperative to providing the best AAA care quickly, says Benjamin W. Starnes, MD, chief of vascular surgery at Harborview. First, the facility connected its PACS to outlying PACS at surrounding facilitates to enable the transfer of images. Now, Starnes and colleagues can view AAA patient images earlier and make the decision of how to treat the rupture, before the patient reaches the hospital.

In 2007, Harborview integrated the same AAA protocol that doctors from the Albany Medical Center in Albany, N.Y., instituted in 2002 (J Vasc Surg 2006;44:1-8). After the protocols were implemented, Albany's mortality rate was a mere 18 percent, significantly lower than the standard 32 to 70 percent mortality rate for open surgical repair.

A multidisciplinary approach to AAA that brings together vascular surgeons, emergency department physicians, anesthesiologists, operating room and radiology staff is vital to expediting AAA care. After the care team is formed, an emergent CT scan is performed on presenting AAA patients who are hemodynamically stable with blood pressure levels less than 80 mm Hg. The patient is then prepped under local anesthesia and kept awake after which an aortic occlusion balloon is placed under x-ray guidance. Patients are kept awake to maintain the patient's physiologic state, Starnes offers.

Physicians must then decide whether to treat patients with endovascular aneurysm repair (EVAR) or with surgery. While surgical repair remains the gold standard, it also has been linked to high mortality rates of 35 to 80 percent.

However, ample evidence has shown EVAR techniques may be less risky and improve complication rates. For example, one study showed that patients who underwent EVAR had a lower risk of death in the first 30 days after the procedure when compared with patients who underwent open repair, 0.2 versus 2.3 percent (JAMA 2009;302[14]:1535-1542).

While such protocols can decrease mortality, facility wide deployment may be difficult. A major challenge is attempting to change the mindset of providers and create a seamless transition from the ED to the operating room. "For example, it took time for the anesthesiologists at Harborview to become comfortable with keeping hypotensive patients with BPs equal to 80 mm Hg awake for a ruptured AAA repair," Starnes offers. "However, after a few of these cases, anesthesiologists realize that this technique saves lives."

Also, integrating protocols works. Prior to Harborview's protocols, "only 42 percent of our patients survived," says Starnes. Two years after the protocols were deployed, mortality dropped to 32 percent, the lowest in 30 years, he says. Thirty-day mortality rates dropped from 61.5 percent to 29 percent within the first six months.

Similarly, Alex S. Tretinyak, MD, and colleagues at the Minneapolis Heart Institute (MHI), who treat 10 to 15 AAA cases annually, instituted an AAA algorithm in 2008. "You have to compress the triage, transfer and plan for these patients in a very short period of time because they are very sick and require immediate treatment," says Tretinyak, a vascular surgeon at MHI.

In addition to creating a standard operating procedure to receive these patients, MHI took it a step further and went to 24 referring centers that transfer AAA patients to educate ED staff. MHI developed order sets (checklists for appropriate imaging, invasive monitoring, among others) to educate staff on what to look for when a possible AAA patient presents.

Waiting is the hardest part

Ruptured AAAs often result in death. While some argue that screening should be expanded to other patient populations—women and nonsmokers—others say that because only 1 percent of the patients screened for aneurysms require immediate repair, screening may not be necessary or cost effective.

B. Timothy Baxter, MD, of the University of Nebraska Medical Center in Omaha, says that nearly 80 to 90 percent of AAAs detected during routine ultrasound are too small for repair (5 cm or under). These small aneurysms grow on average 2.6 to 3.2 mm per year, requiring patients to undergo ultrasound every six months to gauge growth. It is not until the aneurysm grows to 5.5 cm in men and 5 cm in women that patients are eligible to undergo elective repair.

Kim et al found that early mortality benefit of ultrasonography screening for AAA was maintained long term, and that cost-effectiveness also improved (Ann Intern Med 2007;146[10]:699-706). After seven years of follow-up, cost effectiveness was estimated to be $19,500 per life-year gained based on AAA-related mortality and $7,600 per life-year gained based on all-cause death.

To expand screening to the target population, Kent et al from the Society for Vascular Surgery Screening Task Force developed a high-yield screening algorithm with hopes of better detection and management of the disease (J Vasc Surg 2010;52[3]:539-548). The algorithm looks at factors such as smoking duration, amount of cigarettes smoked and time elapsed since smoking cessation. The predictive scoring system uses criteria that also would identify aneurysms in women, nonsmokers and those under the age of 65.

"A scoring system that gives you the ability to pick up a greater number of patients with less screening and to detect AAAs among a broader population argues for fundamental changes to the current screening policy," says the study's author Giampaolo Greco, PhD, of the Mount Sinai School of Medicine in New York City.

What will the future bring?

There may be a component of AAA that is treatable: inflammation, Baxter says. AAA patients experience inflammation when protease breaks down tissues, which could be one of the culprits of aneurysms. These enzymes break down the aortic wall and drug therapies may be able to help block these proteases and halt inflammation, he suggests.

Baxter and his colleagues are currently examining how doxycycline can help slow the growth of an aneurysm. Already, a 36-patient randomized clinical trial studying the effects of a three-month doxycycline treatment (twice daily 100 mg dose) or placebo in patients with small asymptomatic AAA found that patients treated with the drug saw a reduction in plasma MMP-9 levels (J Vasc Surg 2002;36[1]:1-12). Only 21 percent of patients had elevated plasma MMP-9 after six months compared with 47 percent at baseline. Baxter called the results "exciting," but said clinical trials are necessary to prove these results.

Although less than 1 percent of patients screened for AAA have aneurysms that require immediate repair, expanding target populations could be necessary. In the future, a blood test to study biomarkers may help screen the disease, but until then the focus must shift to detecting the aneurysms that could harm patients down the road. Protocols that engage care teams when AAA strikes transform care and increase survival. More preventive screening and improved management can help to sidestep ruptures and avoid this silent killer.