CCTA & SPECT MPI go head-to-head

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Comparative effectiveness research provides a platform for evaluating the clinical performance and cost-effectiveness of cardiac CT and other cardiac imaging modalities. Source: U. Joseph Schoepf, MD

Small studies assessing the efficacy of coronary CT angiography (CCTA) to diagnose or rule out coronary artery disease (CAD) have been the staple reference standard for its adoption. But a new era of comparative-effectiveness research is unfolding as CCTA will be tested against other validated cardiac imaging modalities, in particular, SPECT myocardial perfusion imaging (MPI).

Where SPECT may falter
Despite a normal SPECT MPI study, the attending cardiologist at the Medical University of South Carolina in Charleston could have blamed his patient's persistent angina on acid reflux, but he suspected the nuclear stress study had missed something more serious.

The case was referred to radiologist U. Joseph Schoepf, MD, also the director of CT research and development. For this patient, CCTA revealed high-grade stenoses in three arteries. His condition was severe enough to require closer examination with invasive catheter angiography.

Three-vessel disease also explained the reason for a false-negative finding with nuclear imaging. SPECT MPI can easily identify perfusion deficits from one or two occluded vessels, but occlusions in three major vessels can produce balanced ischemia making the SPECT images appear normal.

Many clinical trials have confirmed the clinical efficacy of CCTA and SPECT over the years. Now, however, randomized controlled multicenter trials will directly compare their performances and cost-effectiveness—via so-called comparative-effectiveness research (CER).

Many cardiovascular imagers welcome these trials. Skepticism about CCTA runs high, including its overuse and use in inappropriate patients, despite evidence demonstrating the weaknesses of SPECT to accurately triage patients either to the more costly catheter angiography or remand them to optimal medical therapy.

Clinical trials also suggest CCTA could improve this troubling performance. Multicenter efficacy trials, such as CORE64 and ACCURACY, published in 2007 and 2008, respectively, have demonstrated that CCTA accurately detects or excludes significant CAD in patients scheduled for catheter angiography.

According to David Levin, MD, a professor of radiology at Philadelphia's Thomas Jefferson University Hospital, enough evidence has already been collected to show that 64-slice or higher CCTA improves patient care and saves billions of healthcare dollars. "Compared with SPECT MPI, CCTA can provide a superior method of weeding out patients who don't need catheterization," he says.

Competing modalities compared
Yet, for private insurers, efficacy trials don't consider the cost-effectiveness of emerging technologies. Many insurance plans raised the bar for granting reimbursement for advanced imaging tests such as CT after being badly burned by an explosion of diagnostic imaging utilization in the early and mid-2000s. The primary source for that growth was cardiovascular imaging.

"The watch word among payors is data," says Maurine Spillman-Dennis, senior director of economics and health policy at the American College of Radiology (ACR). "They want information. They want trials and outcomes data."

The clash between clinical- and cost-effectiveness has compelled medical researchers and healthcare policymakers to reconsider how medical technologies are assessed. Their consensus solution is CER. "We have done great work defining the test performance [of cardiac CT] in terms of accuracy," says Arthur E. Stillman, MD, PhD, director of cardiothoracic imaging at Emory University in Atlanta. "But we haven't done well in performing real comparative-effectiveness trials. That is the overarching issue on how to define which test might be done for a particular indication and what the costs might be."

Not everyone agrees. Critics have questioned whether public policies growing out of CER could lead to healthcare rationing—denying care if treatment is deemed not effective enough or too pricey. Public health advocates worry that trials won't consider the relationship between CT use and patient exposure to ionizing radiation. And SPECT camera designers fear the study designs will fail to account for innovations that are improving the speed and image resolution of new gamma camera designs.

Link to healthcare reform
Still, CER has been on the U.S. spotlight since