CTA can reduce need for stress tests and catheter angiograms
Coronary CT angiography (CCTA) can potentially reduce the need for further stress tests or cardiac catheterizations in the evaluation of low- to intermediate-risk patients with possible angina in an outpatient setting. Researchers at Walter Reed Army Medical Center have called for prospective studies to assess the overall cost effectiveness of this approach.

Researchers pointed out that less than 2 percent of all outpatient physician visits each year are chest pain patients and that the source of pain is coronary artery disease in less than 20 percent of cases. Yet, the multiple stress tests and unnecessary coronary angiographies that occur in this setting represent 10 percent of the $274 billion annual cost of cardiovascular services in the U.S.

Curved multiplanar reconstruction of the left anterior descending (LAD) artery (top) and right coronary artery (RCA) show the excellent pictures that CTA produces. Images of LAD and RCA show normal, patent coronary arteries in a 50-year-old man with chest pain and a non-diagnostic treadmill stress test. (Source for all images: Todd C. Villines, MD, Walter Reed Army Medical Center)  
Curved multiplanar reconstruction of the left anterior descending artery (LAD) shows a classic appearance of a mixed plaque (calcified and non-calcified) that, while not obstructive, is well visualized on CT in the proximal LAD.  
Patrick J. Devine, MD, and colleagues from both radiology and cardiology at Walter Reed compared a strategy that used CCTA with a pre-CCTA strategy in a study that appeared in the July/August issue of the Journal of Cardiovascular Computed Tomography

Researchers retrospectively identified 75 patients without known disease who had undergone CTA for the primary indication of possible angina. Two general cardiologists, blinded to the purpose of the study, reviewed the following information for each patient: subject age, nature of anginal symptom, known cardiac risk factors, calculated Framingham Risk Score, pretest probability of obstructive coronary artery disease as estimated by the Diamond–Forrester classification, and results of any previous ischemic evaluations.

The cardiologists were then asked to recommend their next single clinical course of action, excluding CCTA (pre-CCTA strategy). These choices included:
  • traditional coronary angiography
  • stress testing with imaging (myocardial perfusion study, stress echocardiography)
  • graded exercise treadmill test, or
  • no further functional or anatomic evaluation for angina needed.
Researchers found that a strategy using CCTA to evaluate patients with possible angina would have significantly reduced downstream resource utilization (defined as the need for further stress testing or cardiac catheterizations): 58 vs. 11. Furthermore, this strategy would have resulted in significantly fewer unnecessary cardiac catheterizations: 23 versus six.

In an accompanying editorial, Wm. Guy Weigold, MD, wrote that as a resident at Northwestern Memorial Hospital, “I often wondered how many patients we were sending home with undetected occult coronary atherosclerosis, and how many times we missed an opportunity to diagnose early coronary disease and to intervene.”

Weigold, now at the Washington Hospital Center in D.C., noted that “a better noninvasive test [than SPECT] would definitively diagnose or exclude coronary disease in the individual patient. Coronary CT angiography offers this promise.”

Study co-author Todd C. Villines, MD, director of clinical operations and co-director of cardiac CT at Walter Reed, told Cardiovascular Business News that they use CCTA in accordance with the 2006 Appropriateness Guidelines developed jointly by several organizations including the American College of Cardiology and the Society of Cardiovascular Computed Tomography.

“The majority of these low- to intermediate-risk patients in our study were referred to CCTA due to either non-diagnostic stress tests or ongoing worrisome symptoms despite a normal stress test,” Villines said. “This was done to avoid invasive catheterization given the non-convincing nature of their symptoms, the stress test abnormality, or both.”

Villines added that this is a common indication for CCTA at his institution.

Addressing the radiation exposure, Villines said they now employ very low doses of radiation in many of these patients by using lower tube voltages (100 kV) and prospectively triggered acquisition.

CT exams were performed with the Lightspeed VCT (GE Healthcare), and the contrast medium was either Visipaque (GE) or Isovue (Bracco Diagnostics).

There are a number of trials ongoing to evaluate the effect of CT on patient outcomes and cost in low-intermediate risk patients. These include CT-STAT, CT-EXTRA and CT-PRIME looking at chest pain patients.