Myocardial Flow Reserve measurement in SPECT: a strong predictor of lesions at invasive coronary angiography

Introduction: Myocardial blood flow (MBF) and flow reserve (MFR) measurement have been shown to improve diagnostic performances of coronary artery disease (CAD). Dedicated CZT cardiac cameras provide accurate evaluation of MBF and MFR. In this pilot study we correlated the results of SPECT MFR measurement with invasive coronary angiography (ICA) findings. Materials and Methods: We analyzed patients referred for dynamic myocardial perfusion imaging (MPI) for CAD screening between November 2018 and November 2020, prospectively included in the CFR-OR trial, and for whom coronary angiography was performed within 3 months. SPECT data were acquired on a CZT-based pinhole cardiac camera (Discovery NM530c GE Healthcare, Haïfa, Israël) using a stress (253 ± 10 MBq) / rest (507 ± 23 MBq) one-day Tc-99m-tetrofosmin protocol. Kinetic analysis was done with Corridor 4DM^TMsoftware using a 1-tissue-compartment model and converted to MBF using a previously determined extraction fraction correction. ICA was performed upon decision of the referring cardiologist and considered normal if no stenosis was found. The results of ICA were compared to global and regional MFR.

Results: 23 patients (12 male, 11 female) were analyzed. Mean global MFR was 1.9 ± 0.79. 5 patients had strictly normal ICA, 18 showed coronary plaques qualifying for high-risk patients and representing a total of 40 lesions on the 3 vessels. Considering those 18 pathological patients, 16 patients had impaired MFR (2 patients had global and regional MFR > 2, but their stenosis were moderate, <50%, with negative FFR); whereas only 4 patients had impaired visual MPI. Based on global MFR, and with a threshold of 2, sensitivity and specificity were respectively 83.3% and 100%, and Area Under Curve (AUC) was 0.94. Regarding regional MFR for the per-vessel analysis, using the same threshold of 2, sensitivity and specificity were respectively 85% and 62%, and AUC was 0.79.

Conclusions: Global MFR measured during MPI for CAD screening on CZT camera significantly enhances SPECT diagnostic performances and could be a safe exclusion or a strong motivation for asking an ICA.

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