Regadenoson, an investigational drug being tested in nuclear scans of the heart, appears to be a better option than a widely used, commercially available alternative, according to researchers in the RegEx study. Regadenoson, an investigational drug being tested in nuclear scans of the heart, appears to be safer, better tolerated and better able to deliver high-quality images than a widely used, commercially available alternative. Researchers in the RegEx study are also evaluating whether incorporating mild exercise into the scan protocol further boosts image quality.

"In nuclear cardiology, images are everything," said Dr. Gregory Thomas, a clinical associate professor of medicine at the University of California Irvine and director of nuclear cardiology at Mission Internal Medical Group, Mission Viejo, CA. "Exercise improves blood flow to the heart instead of the gut, resulting in better images."

Using radioactive tracers and drugs that cause the arteries to dilate, nuclear scanning is able to track blood flow throughout the heart muscle, in a test known as myocardial perfusion imaging (MPI).The RegEx trial is comparing an investigational vasodilator drug, regadenoson, against a commercially available alternative, adenosine. Regadenoson is both easier to administer than adenosine and more targeted to the arteries of the heart, a feature that is expected to minimize side effects.

The RegEx study involved 60 patients, all of whom had an adenosine scan while lying at rest on their back. Patients were then randomly assigned in a 2:1 ratio to regadenoson plus radioactive tracer (in preparation for nuclear scanning) or to matching placebos. All patients performed mild exercise. In the end, the randomization scheme resulted in 39 patients in the regadenoson-exercise-nuclear scanning group and 21 patients in the double placebo-exercise group.

Dr. Thomas and his colleagues found that regadenoson could be safely combined with exercise. In addition, patients reported greate acceptance of and fewer side effects with the regadenoson-exercise protocol than with the standard adenosine study. A full 70 per cent of patients rated the regadenoson-exercise protocol as much better or somewhat better than the resting adenosine study. In addition, when three experts evaluated side-by-side images, 26 per cent said the regadenoson images were of better quality; 74 per cent said image quality was similar with the two imaging protocols.

"Adenosine MPI is a very good test. And the use of regadenoson makes MPI even better," Dr. Thomas said.