Problems outside the coronaries appear in cardiac CTA

Cardiac CT angiography holds the key to finding diseases outside of the coronary arteries - if, that is, diagnosticians are willing to look.

Research done at the University of Maryland School of Medicine found that cardiac CTA, performed after coronary artery bypass graft (CABG) surgery, revealed unsuspected and potentially significant findings.

Typically the only data examined following a cardiac CTA relates specifically to the coronary arteries, as physicians concentrate only on those questions that drove them to conduct the exam. One partial solution is to apply computer-aided diagnostics to look at pulmonary issues. The accuracy of lung CAD programs has been increasing steadily in recent years, but these programs usually do not work well with PACS. Another solution would be to interest clinicians in examining the data themselves.

The researchers deeply mined the cardiac CTA data because they were performing a lot of these exams, particularly following CABG to check the patency of grafts.

"We wondered how often we would find unrelated but clinically significant findings in the heart and lungs," said Dr. Charles White, director of thoracic imaging at the University of Maryland Medical Center. "We wanted to know the effect of using intravenous contrast and thinner slices on the prevalence of these findings."

What they found surprised them. Their study uncovered at least one unsuspected and potentially significant finding in 51 of 259 patients who had postoperative cardiac CTAs following CABG - an incidence of almost 20%. In the August issue of the American Journal of Roentgenology, White and colleagues report that 24 of these 51 patients had a cardiac finding such as intracardiac thrombus and 34 had a noncardiac finding such as pulmonary embolism, lung cancer, or pneumonia.

"One of the issues that we found somewhat surprising is the number of patients with pulmonary embolism who had undergone recent bypass grafting," he said. "It is reasonable to suspect that cardiac surgery patients who are often immobilized after their procedure might have these problems, but this connection is certainly not well known in the radiology community."

The researchers view the solution to this problem as more of a workflow issue than a technological one.

"The take-home message is that these examinations require physician interpreters who are trained to read the entire CT, not just the coronary vessels," White said.

A technological answer may appear in the near future. CAD systems for the lung have improved dramatically in sensitivity and specificity in recent years. In a study presented at the 2007 American Roentgen Ray Society meeting, Dr. Heidi Roberts, an associate professor of radiology at the University of Toronto, and colleagues found that CAD marked all 22 instances of pulmonary embolism on 100 consecutive CTA exams. Radiologists using CAD found an average of 2.6 false positives per case. More than 40% of false-positive marks were the type that can be easily dismissed, researchers said. Overall, the positive predictive value for CAD alone was 26%.

A limiting factor to the use of this technology is the lack of integration of lung CAD into PACS. This may be a problem that will go away in time, however, once this technology becomes better appreciated, and the need to look outside the coronary arteries following cardiac CTA is more widely recognized.