013 In patients with normal perfusion imaging, is there a relationship between calcium score and myocardial flow reserve?

Standard relative perfusion imaging may underestimate the true extent of disease and may be unable to detect atherosclerotic microvascular dysfunction. We have shown that noninvasive quantification of myocardial flow reserve (MFR) using cardiac positron emission tomography (cPET) has prognostic value independent of relative myocardial perfusion imaging (MPI) even when relative MPI is normal. Likewise the calcification in coronary arteries measured as the Agatston score (AS) on cardiac computed tomography (CCT) represents a valuable tool for stratification of patients with suspected coronary artery disease (CAD) and can be considered a quantifiable marker of disease. Our objective was to determine if an elevated AS predicted reductions in MFR in patients with normal MPI (i.e. a sum stress score (SSS) < 4) on cPET. We identified 101 patients (mean age = 60.9 +/−10.4; 52 males) without known CAD, who had a normal cPET MPI (sum stress score < 4) and also underwent a CCT within a six month period. Exclusion criteria included prior coronary artery bypass, percutaneous intervention, valvular disease, or permanent pacemaker. Patients were also categorized according to normal MFR (≥2.5 ml/min/g) or abnormal MFR (<2.5 ml/min/g). Spearman correlation showed a weak but significant inverse relationship between calcium score and MBF (r = −0.25; P = 0.01). When patients were divided into 3 groups based on AS (figure 1, group 1: 0 (n = 34); group 2: 1-400 (n = 38); group 3: >400 (n = 29)) there was a significant difference in MFR (3.30+/− 0.98; 2.84 +/− 0.85; 2.63 +/− 0.79, respectively; P = 0.02, ANOVA; P < 0.01 group 1 vs 3). A calcium score of 0 had a sensitivity of 32/37 (87%) and specificity of 29/64(45%) for predicting an abnormal MFR (< 2.5 ml/min/g). In patients with normal relative MPI, AS and MFR have a significant but weak negative correlation. Patients with low AS (= 0) have significantly higher MFR than those with high AS (> 400). In this population, AS was sensitive but not specific for reduced MFR. The wide variation in MFR at different levels of AS suggests that in patients with low risk relative MPI on cPET, AS and MBF provide different yet complimentary information. Larger prospective outcome studies are required to determine the incremental prognostic value of these parameters.