An imaging procedure that fuses two types of cardiac images appears to be an “excellent” long-term predictor of which patients will have a major adverse cardiac event, such as a heart attack or unstable angina requiring hospitalization, according to a new study in Radiology.
Invasive coronary angiography is the “gold standard” for determining a patient’s percentage of stenosis, or the narrowing of the arteries because of plaque. However, it’s not always a good predictor of heart attack risk because it doesn’t provide information on the blood flow into the heart, known as perfusion. It therefore can’t predict whether lesions in the artery were relevant to the dynamics of the blood flow.
“In lesions with less than 50 percent narrowing, one in five lesions still produce an ischemia (inadequate blood flow),” says study coauthor Philipp A. Kaufmann, MD, professor and chair of nuclear medicine and director of cardiac imaging at University Hospital Zurich in Switzerland, where the study was conducted.
The researchers examined whether hybrid imaging, performed by fusing coronary computed tomography angiography (CCTA) with nuclear stress testing by use of myocardial perfusion imaging with single photon emission tomography (SPECT) could provide more information of a heart’s anatomy and function in a non-invasive manner.
They reviewed 428 patients that had been referred to their hospital for suspected cardiac artery disease and ultimately ended up with 375 patients in their final study population. The patients underwent a CCTA test and a SPECT MRI nuclear scan. The researchers then combined the two images to view both stenosis and perfusion in the arteries using a commercially available software package for image analysis.
They also conducted follow up of the patients for as long as 10 years. During that time, 160 major adverse cardiac events occurred in 109 of the patients, including 45 deaths and 19 non-fatal heart attacks.
Patients with matched findings—stenosis of 50 percent or more on CCTA with evidence of ischemia on SPECT in the heart to which the blocked vessel was supplying blood—had more than five times the risk of adverse events (21.8 percent) than those with normal findings (2.4 percent).
Patients with unmatched findings, or evidence of ischemia but not in part of the heart being fed by the stenotic artery, had three times the risk (9 percent), showing that patients with abnormal CCTA findings are at higher risk despite normal perfusion findings.
The study indicates that hybrid imaging can improve treatment decision making and avoid unnecessary invasive angiographies, according to the study authors. They did note that using two images exposes the patient to more radiation; they hypothesized that algorithms could help lower the radiation amounts.
The researchers hope to run a clinical trial to show how hybrid imaging can positively affect patient outcomes.
“The strategy of direct referral to invasive coronary angiography without noninvasive imaging is obsolete,” Kaufmann says. “Even after documenting coronary artery disease with coronary CT angiography, we need further noninvasive evaluation before deciding upon revascularization versus medication.”
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