AJR: CTA growth stagnates, SPECT going strong
Although coronary CT angiography (CTA) can be employed to stratify risk and expedite the work-up of chest pain patients, its utilization dropped in 2008, and the exam may be severely underutilized, according to a study published in the April issue of the American Journal of Roentgenology. The authors reported that SPECT myocardial perfusion imaging was used 44 times as often as coronary CTA.

Numerous studies have described the value of CTA and detailed its sensitivity, specificity, positive predictive value and negative predictive value. Furthermore, in 2006, a multidisciplinary task force composed of representatives of the American College of Cardiology, the American College of Radiology and other cardiovascular organizations developed appropriateness criteria for CTA. Still, critics have voiced concerns over the “exploding use” of coronary CTA.

Given the circumstances, David C. Levin, MD, of the Center for Research on the Utilization of Imaging Services at Thomas Jefferson University Hospital and Jefferson Medical College in Philadelphia, and colleagues sought to assess CTA utilization trends, determine its growth and compare the clinical role and costs of CTA with myocardial perfusion imaging (MPI).

The researchers leveraged data from the Medicare Part B Physician/Supplier Procedure Summary Master Files, tracking CTA utilization for 2006, 2007 and 2008 and MPI utilization from 1996 to 2008.

Levin and colleagues found that the CTA rate per 100,000 Medicare beneficiaries rose from 99 in 2006 to 210 in 2007 and then dropped to 193 in 2008. MPI increased from 4,758 per 100,000 in 1998 to a peak of 8,753 in 2006 before dipping to 8,467 in 2008, offered the researchers.

“The findings of this study are surprising in at least two respects,” wrote Levin.

First, CTA utilization did not follow the rapid growth patterns typical of new technology. Instead, use declined in 2008. Second, although CTA and MPI are somewhat complementary studies, MPI utilization far outpaces CTA. Levin and colleagues offered several possible explanations for the findings, such as:
  • Reduced availability of equipment and personnel required for CTA;
  • Unfavorable CTA reimbursement;
  • Cardiologists’ investment in in-office nuclear cameras;
  • Radiation concerns;
  • Required preauthorization for advanced imaging for commercially insured patients; and
  • More careful application of appropriateness criteria for CTA.

Levin and colleagues also reviewed the shortcomings of MPI, pointing out that a negative stress MPI study does not rule out the presence of coronary artery disease (CAD). In contrast, a negative coronary CTA study does rule out CAD. In addition, MPI does not detect mild to moderate CAD until lesions become flow-limiting, and severe triple-vessel CAD can produce false-negative results.

CTA also is associated with several limitations. Specifically, patients who are obese or present with rapid heart rates not responsive to beta blockers, arrhythmias or heavy calcification of the coronary arteries may not be good candidates for CTA.

The researchers outlined shortcomings of the standard clinical evaluation for suspected coronary artery disease. “Several studies have shown that even in groups of symptomatic patients who are thoroughly evaluated by experienced cardiologists (including use of stress imaging) and then referred for invasive coronary angiography (ICA), there are often errors made, especially false-positive clinical diagnoses of significant CAD,” wrote Levin et al, who added that studies suggest that “clinical evaluation of patients with suspected CAD, including the use of stress MPI, is not highly reliable and that many unnecessary ICAs are being performed.”

Levin and colleagues referred to several other studies that demonstrate the value of coronary CTA as an effective means of stratifying risk in patients being tested for CAD. Specifically, a study conducted by Min et al (J Am Coll Cardiol 2007; 50: 1161-1170) revealed a link between all-cause mortality and the severity of CAD as determined by CTA. Others explored the relationship between CTA results and adverse cardiac events and suggested that patients are at very low risk for adverse events in the 12 to 24 months following a finding of normal coronary arteries via CTA.

The researchers also considered the utility of CTA in the ED and pointed out that $6 billion to $8 billion is spent on subsequent hospitalizations and evaluations on acute chest pain patients that turn out to be negative. In addition, 2 to 8 percent of true acute coronary syndromes are missed, wrote Levin. The researchers added that coronary CTA can be employed to triage patients and reduce length of stay.

Levin and colleagues acknowledged several limitations to the study. The three years of CT data is somewhat slim, and the 2008 decline in CTA utilization may not indicate a trend. “[F]urther data will be needed in future years to draw any firm conclusions about the use of [coronary CTA],” they wrote.

The researchers concluded by reiterating the value of CTA as the primary noninvasive imaging test for many patients with suspected CAD as MPI is associated with both false-positive and false-negative results. “Coronary CTA can be of great assistance in determining who should be referred for ICA, with a proven very high negative predictive value,” suggested Levin and colleagues, who continued, “Our analysis of the literature suggests that ICA and MPI are procedures that may be overutilized and that coronary CTA is one that may be underutilized.” The researchers recommended greater utilization of coronary CTA to reduce ICA and better definitively determine the severity of disease in patients with suspected CAD.