When a SPECT myocardial perfusion study of a patient with persistent angina produced a normal result, the attending cardiologist at the Medical University of South Carolina in Charleston suspected the study had missed something more serious.
Three-vessel disease also explains the false negative nuclear imaging finding. SPECT MPI works physiologically to indirectly detect coronary artery disease by mapping the abnormal perfusion of blood from blocked arteries through the heart muscle and easily identifies perfusion deficits from one or two occluded vessels. But occlusions in three major vessels can produce balanced ischemia in the heart muscle making SPECT images appear normal—one of many reasons why Schoepf prefers CCTA, which allows clinicians to directly survey the coronary arteries for occlusion. "CT gives you a much more comprehensive picture of the patient's cardiovascular status," he says. Indeed, multiple clinical trials have confirmed the clinical efficacy of cardiac CT and SPECT MPI.
The next step is controlled randomized multi-center clinical trials to compare performance. Many cardiovascular imagers welcome upcoming comparative effectiveness trials designed to provide statistically valid head-to-head comparisons of the relative financial costs and clinical benefits of SPECT MPI, coronary CTA and other noninvasive cardiac imaging exams. Skepticism about cardiac CT runs high, despite evidence demonstrating the weaknesses of the imaging techniques that are suppose to identify patients who should be referred for cardiac catheterization and x-ray coronary angiography.
Multi-center efficacy trials, such as CORE64 and ACCURACY, published in 2007 and 2008, respectively, have demonstrated that CCTA accurately diagnoses significant coronary artery disease and can reliably rule out its presence and assess the risk of future myocardial infarction (MI) and cardiac death.
David Levin, MD, a professor of radiology at Philadelphia's Thomas Jefferson University Hospital, says enough evidence has already been collected to show that 64-slice or higher CCTA improves patient care and saves billions of healthcare dollars. "There is a better way than SPECT MPI to weed out patients who don't need catheterization. That way is coronary CTA."
Yet, efficacy trials don't consider the cost-effectiveness of emerging technologies. "The watch word among payors is data," offers Maurine Spillman-Dennis, senior director of economics and health policy at the American College of Radiology. "They want trials and outcomes data."
Competing modalities compared
The clash between clinical- and cost-effectiveness has compelled medical researchers and policymakers to reconsider how medical technologies are assessed. Their consensus solution is comparative effectiveness research (CER), a method for weighing the relative clinical and sometimes financial merits of competing medical technologies.
"We have done great work in terms of defining the test performance [of cardiac CT] in term of accuracy," says Arthur E. Stillman, MD, PhD, director of cardiothoracic imaging at Emory University in Atlanta. "But we haven't done well in doing real comparative effectiveness trials."
CER can potentially answer the practical questions clinicians and policymakers pose when weighing the relative merits of competing technologies, according to Pamela K. Woodard, MD, head of advanced cardiac imaging at Washington University School of Medicine, St. Louis. "It will establish what coronary CTA is good for," she said. "In which clinical instances does it lead to better outcomes and cost savings?"
Congress contracted with the Institute of Medicine to solicit public and scientific opinion to develop a list of 100 initial CER priority topics. Two cardiac imaging issues appeared on the priority list. One called for studies comparing the effectiveness of traditional risk stratification methods for coronary heart disease and noninvasive imaging. The other recommended trials comparing the effectiveness of CTA and conventional angiography for assessing coronary artery stenosis in patients with moderate risk of coronary artery disease.
|Status of Four CER Cardiac Imaging Trials|
RESCUE, a randomized trial involving 4,300 adult patients with stable angina treated