JAMA publication confirms utility of coronary CTA

Sixteen-slice CT angiography can rule out - but cannot conclusively identify - heart disease in patients, according to results to be published in tomorrow's issue of the Journal of the American Medical Association. The results establish a baseline for expectations regarding higher performance CTs, as their faster scan times could provide even better results.

For the time being, the results from the multicenter trial, to be reported in the July 26 issue of JAMA, definitively establish CTA as a useful tool in the assessment of patients suspected of having coronary disease. Lead author Dr. Mario J. Garcia, director of cardiac imaging at the Cleveland Clinic, said the results indicate that a negative finding on CTA virtually eliminates the possibility of significant coronary artery disease.

Of the eight indications for coronary CTA contained in the Model Local Coverage Determination for CT and CTA, intended for use by local Medicare carriers, three are met by 16-slice CTA, according to the study:

• as a tool to triage for invasive coronary angiography following a stress test that is equivocal or suspected to be inaccurate;

• to evaluate the cause of symptoms in patients with known coronary artery disease; and

• prior to noncoronary artery cardiac surgery.

A case can be made that the study results also point toward a fourth indication, coronary CTA to evaluate the cause of chest pain or dyspnea in patients with prior bypass surgery or intracoronary artery stent placement, because these patients have known coronary artery disease. But Philips executive Phil Prather said this might be pushing it a bit, as the study was not designed to assess patients with surgery or stents.

But at the very least, the study suggests that the glass is almost half-full for 16-slice CTA, when it comes to evaluating heart patients.

"It is certainly much fuller than before this publication," said Prather, director of global cardiac CT for Philips Medical Systems, which supplied the 16-slice devices used in the study. "Until now, we only had single-center experience."

Single-center studies, he noted, typically involve only qualitative comparisons to cardiac cath, whereas the findings of the Coronary Assessment by Computed Tomographic Scanning and Catheter Angiography (CATSCAN) study, as will be reported in JAMA, benchmark CTA results to cardiac cath quantitative coronary angiography.

The conclusions of the study are conservative. JAMA reviewers and editors required that any CTA segments that could not be assessed had to be classified as positive for statistical purposes, according to Prather. This led to the finding that CTA, as performed with a 16-slice detector, often leads to inconclusive or "false positive" results.

"We have seen in other single-center studies that nonassessable segments were thrown out when doing statistical analyses of sensitivity and specificity and negative and positive predictive value," he said. "That is why the results for specificity or positive predictive value are significantly lower (in this study) than in other studies."

The results will be of limited marketing use to Philips Medical Systems, which was the driver behind the CATSCAN studies, in regard to sales of its 16-slice scanners. Prather noted that the imaging community has moved on to scanners with more than twice the number of slices for coronary applications.

Data for the multicenter study were gathered from June 2004 through March 2005 with 238 patients undergoing evaluations at 11 centers in the U.S., Europe, Israel, Japan, and Argentina. Arguably, the results for cardiac applications would have been more relevant if the company had waited for the arrival of 64-slice scanners, as the shorter scan times (under 10 seconds for 64-slice CTs versus 25 to 40 seconds with 16-slice systems) substantially improves temporal resolution.

"But at some time you need to stop and draw a line in the sand and ask, 'Where are we?'" Prather said. "This trial, which holds for three of the eight indications for coronary CTA, serves as a foundation on which other studies can build."

Philips has no plans to engage in such studies, at least not at the 40- or 64-slice performance levels. Two such studies, supported separately by GE and Toshiba, are currently under way. But the CATSCAN trial sets the stage for the conclusions that might come from them.

"You certainly are not going to get any poorer (clinical) performance using a 40- or 64- channel system," Prather said.

It is an argument that he hopes will be well received by clinical sites considering the purchase of Philips super-premium CTs for coronary applications.