Cardiac Hybrid Imaging an Effective Tool for Predicting Heart Attacks

Cardiac hybrid imaging with CT and nuclear stress testing is an excellent long-term predictor of adverse cardiac events like heart attacks in patients being evaluated for coronary artery disease, according to a study in Radiology.

Coronary artery disease is a leading cause of death and disability worldwide. Invasive coronary angiography (ICA) is considered the gold standard for determining the percent of stenosis due to plaque in a coronary artery. However, the degree of stenosis on ICA is not always an accurate predictor of heart attack risk because it gives no information on perfusion. Ischemia is a potential danger to the patient.

“In lesions with less than 50 percent narrowing, one in five lesions still produce an ischemia,” said study coauthor Philipp A. Kaufmann, MD, professor and chair of nuclear medicine and director of cardiac imaging at University Hospital Zurich in Switzerland.

Cardiac hybrid imaging combines coronary CT angiography (CCTA) and myocardial perfusion imaging with single photon emission CT (SPECT) to provide information on both stenosis and perfusion. The approach has shown promise in studies focusing on short-term observations, but information is lacking on long-term outcomes.

Patients with Stenosis and Ischemia at Greater Risk for Cardiac Event

The research team looked at 428 patients who underwent hybrid imaging. During a median follow-up of 6.8 years, a total of 160 major adverse cardiac events, including 45 deaths, were observed in the final study population.

Patients with matched findings — stenosis of 50 percent or more on CCTA with evidence of ischemia on SPECT in the area of the heart to which the blocked vessel was supplying blood — had more than five times the risk of adverse events than those with normal findings. Patients with unmatched findings, or evidence of ischemia but not in the area of the heart being fed by the stenotic artery, had three times the risk. Major adverse cardiac event rates were 21.8 percent for matched findings and 9 percent for unmatched — considerably higher than the 2.4 percent rate for normal findings.

The study supports CCTA use for an initial, noninvasive evaluation of patients with known or suspected stable coronary artery disease. No additional imaging would be necessary if the results were normal. If a lesion was evident, then clinicians could employ a nuclear scan to assess ischemia and fuse results from both modalities to make a hybrid image.

“The strategy of direct referral to invasive coronary angiography without noninvasive imaging is obsolete,” Dr. Kaufmann said. “Even after documenting coronary artery disease with coronary CT angiography, we need further noninvasive evaluation before deciding upon revascularization versus medication.”

The researchers hope to investigate whether hybrid imaging can have a positive impact on patient outcomes. They are also looking at what they call “triple hybrid” imaging, which combines the CCTA/SPECT hybrid with information on coronary artery shear stress, which could help identify lesions that could impact ischemia in the future.