The use of coronary CT angiography can be an effective gatekeeper to decrease the number of unnecessary cardiac catheterizations after mildly abnormal nuclear imaging exams, according to a study in this month’s issue of the Journal of Cardiovascular Computed Tomography.
Jerome L. Hines, MD, from the Illinois Vascular and Heart Institute, and colleagues retrospectively compared the rate of invasive coronary angiography before and after installation of a 64-slice CT scanner in patients referred for evaluation within six months after a mildly abnormal myocardial perfusion stress imaging (MPI) exam.
Case matching yielded 154 patients in each cohort.
Before implementation of CT, patients with mildly abnormal MPI were recommended for catheter angiography based on clinical evaluation. After implementation of CT, patients initially had clinical evaluation, and, when warranted, CT was obtained. Patients then were recommended for catheter angiography on finding either a 70 percent stenosis or a 50 percent to 70 percent stenosis on that correlated with the area of ischemia on MPI, according to the study.
Using a GE Healthcare LightSpeed VCT scanner, researchers set the tube voltage at 120 kV, and the current at 335–800 mA during 55 percent of the cardiac cycle (diastole) and a reduction of the current by 50 percent during the remaining time of the R-R interval.
Researchers found that 87 patients were referred for catheterization: 39 percent in the pre-CT cohort and 18 percent in the post-CT cohort. The number of these patients who underwent revascularization was not statistically significant: 14 percent versus 11 percent in the pre- and post-CT cohorts, respectively. Additionally, CT identified 53 patients with 50 percent to 70 percent stenosis, but only nine had a matching MPI deficit.
“Given the similar rate of revascularizations in both cohorts, we estimate that patients in the post-CT cohort were 86 percent less likely to receive invasive catheterization compared with patients in the pre-CT cohort,” the authors concluded.
They also pointed out that 15 patients found on CT to have total occlusion of bypass grafts also were spared catheter angiography.
Researchers found no clinical events in either cohort for patients not referred to catheter angiography during six months of follow-up.
In an accompanying commentary, Jason H. Cole, MD, from Cardiology Associates of Mobile in Alabama, called the study an important scientific contribution. He noted the 21 percent absolute reduction in the rate of referral to invasive angiography, with no significant change in percentage of patients undergoing revascularization.
Cole also praised the authors’ choice of clinical scenario, the mildly abnormal MPI test, as an important clinical case. “It seems quite authentic to the practitioner in the trenches who has to deal with this scenario every single day,” he wrote.