Quantitative evaluation of coronary artery calcium and vascular function by hybrid rubidium-82 PET/CT imaging in heart transplanted patients

Aim/Introduction Cardiac myocardial perfusion imaging (MPI) by positron emission tomography (PET)/ computed tomography (CT) represents a noninvasive method used for an integrated measurement of myocardial blood flow (MBF), myocardial flow reserve (MFR) and coronary artery calcium (CAC) content. No study has investigated the relationship between coronary atherosclerotic burden and vascular function in heart transplanted patients. Thus, we assessed the relationship between CAC score, MBF and MFR in heart transplant patients undergoing hybrid 82Rb positron emission tomography (PET)/computed tomography (CT) imaging. Materials and Methods We enrolled a total of 100 (mean age 60±13 years) consecutive patients referred to hybrid 82Rb PET/CT myocardial perfusion imaging for evaluation of myocardial ischemia. CAC score was measured according to the Agatston method and patients were categorized into 4 groups (0, 0.01-99.9, 100-399.9, and ≥400). Baseline and hyperemic MBF were automatically quantified. MFR was calculated as the ratio of hyperemic to baseline MBF and it was considered reduced when <2. The Spearman correlation coefficient was assessed between continuous CAC score and MBF or MFR values. Univariable and multivariable logistic regression analyses were used to determine the variables associated with reduced MFR. Results Global CAC score showed a significant inverse correlation with hyperemic MBF (r=-0.28, P < .05) and MFR (r=-0.40, P < .001), while no correlation between CAC score and baseline MBF was found (P = 0.9). CAC score was zero in 71 (71%) patients, 0.1-99.9 in 8 (8%), 100-399.9 in 12 (12%), and ≥400 in 9 (9%). Global baseline MBF was comparable among the four groups of patients at different levels of CAC score (F = 0.040, P = 0.989). Whereas hyperemic MBF (F = 2.897) and MFR (F = 4.344) progressively decreased with increasing CAC levels (P for trend <0.05). Univariable analysis demonstrated that age, diabetes, and CAC score (all P < .05) were associated with reduced MFR. At multivariable logistic regression analysis only age and CAC score (both P < .05) were independently associated with reduced MFR. The addition of CAC score to clinical data, increased the global chi-square value for predicting reduced MFR from 18.79 to 25.66 (P < .01). Conclusion In heart transplanted patients there was an inverse relationship between CAC score and MFR. The evaluation of calcium content might be helpful for identifying patients with a reduced MFR, at high risk to develop cardiac allograft vasculopathy.MBF across CAC score categories MFR across CAC score categories