Canadian Journal of Cardiology



      Positron emission tomography (PET) myocardial perfusion imaging (MPI) is a well-validated non-invasive imaging technique for the assessment of coronary artery disease (CAD). Amongst its many advantage, it permits quantitative, non-invasive assessment of myocardial blood flow (MBF) and myocardial flow reserve (MFR). While the diagnostic and prognostic value of MFR has been extensively validated in the general CAD population, only limited data is available when it comes to its prognostic value in patients with prior coronary artery bypass grafting (CABG). Our study aim was to evaluate if diminished MFR on 13N-Ammonia PET MPI is associated with increased risk of major adverse cardiovascular events (MACE) amongst patients with prior CABG.


      A retrospective study was performed at the Montréal University Hospital Centre (CHUM) between February 2018 and September 2020. Patients (n=62) with prior CABG (at least 3 months) who had an 13N-Ammonia PET/CT scan performed were included. The main endpoint was to evaluate if myocardial perfusion values were associated with increased risk of MACE. MACE was defined as death, re-infarction, repeat revascularization or hospitalization for heart failure. In patients with multiple MACE, only the first event was considered for analysis. Our cohort was subdivided in two groups: patients with MACE and patients without MACE. The main indications for performing PET MPI are displayed in the figure. Baseline characteristics (table) were comparable between both groups except for the number of graft (3.0 [2.0,3.0] vs. 3.0 [3.0,4.0], p=0.005). Risk factors were similar between both groups except for presence of chronic kidney disease (CKD) (11 (55%) vs. 10 (23.8%), p=0.02). There was no difference between both groups regarding drug regimen. In patients with MACE as compared to no-MACE, both global MFR (1.8 ± 0.5 vs. 2.1 ± 0.5, p=0.03, respectively) and the global stress MBF (1.2 [0.9,1.4] vs. 1.4 [1.1,1.8] mL/min/g, p=0.049, respectively) were significantly lower. Sum Stress Score was higher in the MACE group (2.5 [1.0,10.0] vs. 0.0 [0.0,3.5], p=0.04). Low left ventricular ejection fraction (LVEF) reserve had no prognostic value in our study (p=0.20).


      In patients with prior CABG, both reduced global MFR and global stress MBF were associated with increased risk of MACE. Therefore, PET MPI with flow quantification can help identifying patients at risk of MACE after CABG. Our findings need to be confirmed in a larger cohort of patients.
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