Patients without known coronary artery disease (CAD) undergoing stress PET/CT myocardial perfusion imaging (MPI) should undergo a same-setting coronary artery calcium (CAC) study, as a significant number of these patients will have subclinical CAD, according to a study in the March/April issue of Journal of Nuclear Cardiology.
Kevin A. Bybee, MD, and colleagues from St. Luke's Mid-America Heart Institute in St. Louis, Mo., used their database to identify 760 consecutive patients with no CAD history, a normal clinically indicated rubidium (Rb)-82 PET/CT stress perfusion study, and a same-setting CAC scan.
They found that 64 percent of the patients had subclinical CAD based on an abnormal CAC score, which tallied as 47 percent of patients with a score greater than 100, 22 percent greater than 400 and 8 percent greater than 1,000.
Researchers found that 41 percent of patients with a CAC under 400 and 48 percent with a score greater than 400 had not been on statin therapy prior to the PET/CT. Likewise, 44 percent with scores less than 400 and 51 percent with scores greater than 400 had not been on aspirin therapy.
In patients not receiving statin therapy prior to the study, those with calcium were more likely to be initiated on statin therapy compared to those without CAC (20 vs. 11 percent). The univariate predictors of initiation or optimization of medical therapy for CAD were increasing amounts of coronary calcification by Agatston score, male gender, hypertension and post-stress left ventricular ejection fraction.
Researchers also found that while CAC was more prevalent in those with higher Framingham Risk Scores (FRS), a significant proportion of patients with intermediate and high FRS had little or no coronary calcification, while 57 percent of patients in the low FRS group had evidence of subclinical CAD based on the presence of coronary calcium.
"This observation is important as previously published reports have shown that CAC score data adds incremental prognostic information to the FRS and can subsequently refine cardiac risk estimates within FRS risk categories, especially in those within the intermediate FRS category," the authors wrote.
Bybee et al said they prefer to scan patients using PET rather than SPECT when they are referred for pharmacologic stress myocardial perfusion imaging (MPI) because PET offers a higher diagnostic accuracy.
They noted that many patients had prognostically significant amounts of CAC, which increases the risk of ischemic cardiac events in the intermediate and long term. They concluded, "Our findings support the concept that patients without known CAD undergoing stress PET/CT MPI should undergo a same-setting coronary calcification study."
But they also suggested that patients with normal stress SPECT or stress echo exams "be considered" for CAC testing.