Coronary CTA lacks certainty as ischemia indicator

Plaque buildup in the coronary arteries seen on 16- and 64-slice CT angiography does not always mean blood flow to the heart is restricted, according to research conducted at the Leiden University Medical Center in the Netherlands.

The results, scheduled to appear in the Dec. 19 edition of the Journal of the American College of Cardiology, demonstrate that half the patients with a 50% or more narrowing of the coronary arteries did not have ischemia, indicating that the narrowing of the coronary arteries did not substantially impair blood flow to the heart.

The findings indicate that the two imaging tests used in the research, CTA and myocardial perfusion imaging with SPECT, have different roles to play in assessing patients with a moderate risk of coronary artery disease.

"These two types of coronary imaging tests are clearly looking at different, yet complementary, aspects of coronary artery disease," said research leader Dr. Jeroen J. Bax, professor of cardiology at Leiden University Medical Center.

The study involved 114 patients with chest pain or risk factors for CAD but no prior history of the disease. They underwent both imaging procedures within 30 days of each other. CT scans were performed using 16- and 64-slice CT in 28 and 86 patients, respectively. SPECT was performed with a technetium-99m imaging agent under either exercise or pharmacologic stress. Invasive coronary angiography was performed in a subset of 58 patients, confirming previous study findings of the tight agreement between CT and invasive coronary angiography.

"This study has major implications for the management of patients in clinical practice," Bax said. "One possibility is to use CT to identify the presence and extent of plaques in the arteries and if atherosclerosis is shown to be present, then clinicians may proceed to use SPECT imaging to evaluate whether the patient has ischemia."

The study underscores the need for more research into the use of CTA as the medical community tries to understand how best to utilize the 64-slice scanners that have become generally available.

"The findings of this study add to the growing evidence that multislice CT detects coronary plaque but not ischemia. Thus, relying on this test alone for making decisions about coronary revascularization could result in unnecessary revascularization procedures and higher costs without clear benefits to patients," said Dr. Sharmila Dorbala, associate director of nuclear cardiology in the nuclear medicine division and a radiology instructor at Harvard.

Dorbala, who wrote about the evolving role of CTA in an editorial that will accompany publication of the Leiden University results, recommends exploring whether specific characteristics of plaque or of patient groups might indicate when stenoses are more likely to impair myocardial blood flow.

"Until then, the findings of this study reiterate the need to base decisions about coronary revascularization on objective evidence of the degree of ischemia and symptoms," Dorbala said, "not solely on the severity of coronary stenosis seen on CT."