Relationship between coronary calcium and myocardial perfusion determined by ⁸²Rb PET-CT in patients referred for ischemia rule-out

Abstract

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Objectives: The integrated value of coronary calcium scoring added to myocardial perfusion assessment in hybrid imaging protocols remains poorly defined. We sought to determine the relationship between calcium burden, other risk factors, and tissue perfusion in an intermediate likelihood group of patients with chest pain. Methods: Rest/dipyridamole stress ⁸²Rb perfusion images and calcium scores (CCS) were obtained in 60 patients using a GE Discovery RX 16-slice PET-CT scanner. From perfusion images, summed rest, stress, and difference scores (SRS, SSS, SDS) were calculated using a 20-segment model. Absolute CCS was determined according to Agatston and age/gender/ethnicity-matched CCS percentiles were calculated using the MESA database. Results: SSS, SRS and SDS were abnormal (≥4) in 23, 16, and 13 patients, respectively. Mean CCS was 193.8±467.8 (range 0-2122) and mean CCS percentile was 46.7±41.7 (range 0-99). CCS correlated with age (r=0.485, p<0.001), was higher in diabetics (p=0.010), and tended to be higher in hypertensives (p=0.086). 9 patients (32.1%) with a CCS=0 had an abnormal perfusion PET study. Of those with a normal perfusion study, 9 (32.1%) had a CCS=0, 8 (22.2%) had a CCS percentile ≥75, and 3 (8.3%) had a CCS percentile ≥90. CCS correlated significantly with SSS (r=0.300, p=0.019) and SDS (r=0.290, p=0.024), but CCS percentile did not (r=0.126, p=0.387; and, r=0.148, p=0.306 for SSS and SDS, respectively). No difference was detected in SDS among those with CCS percentile ≥75 or ≥90 when compared to those in lesser percentiles (p=0.187 and p=0.167, respectively). Calcification was present in the LAD in 28/32 patients with CCS>0. There was a significant difference in SDS among those with ≤ 1 vs. >1 vessel calcified (mean±SD: 1.11±2.22 and 2.94±2.46, respectively; p=0.009). Conclusions: Increased coronary calcium burden and impaired tissue perfusion in cardiac PET-CT coexist in some but not all patients referred for the exclusion of CAD. Both modalities seem to provide complementary rather than competitive information. These data should stimulate further exploration of diagnostic/prognostic strategies which integrate calcium scores and myocardial perfusion.