CMR image acquisition and analysis

CMR image acquisition was performed using a 1.5-Tesla scanner (Achieva, Philips Medical Systems, Best, The Netherlands) with 32-channel cardiac coils within 30 days after the index PCI, as previously described [18]. In brief, cine-CMR images were acquired with the scan protocol as follows: repetition time, 4.1 ms; echo time, 1.4 ms; slice thickness, 6 mm; flip angle, 55 degrees; field of view, 350 × 350 mm²; matrix size, 128 × 128; and number of 20 phases per cardiac cycle, 20. LV mass and volumes were calculated according to the Simpson’s rule. Late gadolinium enhancement (LGE) images were acquired 15 min after the injection of gadolinium contrast (0.10 mmol/kg) using inversion recovery prepared gradient echo sequences as follows: repetition time, 3.8 ms; echo time, 1.28 ms; slice thickness, 8 mm; flip angle, 15 degrees; field of view, 350 × 350 mm²; acquisition matrix, 200 × 175; and number of phases per cardiac cycle, 20. All CMR images were analyzed using a dedicated workstation (Virtual Place, AZE Ltd., Tokyo, Japan) by two independent investigators who were blinded to clinical, angiographic, and OCT data. The infarcted myocardium was quantified on the LGE images as myocardium with a signal intensity exceeding the mean signal intensity of the remote myocardium by ˃5 standard deviation (SD) by using a semi-automatic algorithm. The plane for flow measurement by phase contrast (PC) cine-CMR was positioned perpendicular to the coronary sinus (CS) at ≈1 to 2 cm from the ostium [19]. Velocity-encoded images were acquired using retrospective electrocardiographic gating during 15-second breath holds, and the imaging parameters were as follows: repetition time, 7.3 ms; echo time, 4.4 ms; slice thickness, 6 mm; flip angle, 10 degrees; field of view, 250 × 250 mm²; acquisition matrix, 128 × 128; number of phases per cardiac cycle, 20; and encoding, 200 cm/s. PC-CMR of the CS measurements was performed during maximal hyperemia and at rest. Maximal stable hyperemia was induced by intravenous adenosine triphosphate (160 μg/kg/min through a central vein). Coronary sinus flow (CSF) quantitative analyses by PC-CMR were performed in a blinded fashion using proprietary software (View Forum, Philips Medical Systems, Best, The Netherlands) by two independent investigators who were blinded to clinical, angiographic, and OCT data. CS contour was traced on the magnitude images throughout the cardiac cycle. CSF was quantified by integrating the flow rates from each cardiac cycle and multiplying them by the mean heart rate during the acquisition period. CSF quantifications were performed during maximal hyperemia and at rest. The resting CSF value was corrected using rate pressure products as follows: rate pressure product (RPP) = systolic blood pressure (mmHg) × heart rate (bpm); corrected CSF (mL/min) = (CSF/RPP) × 10,000; and corrected CSF (mL/min per g) = corrected CSF/LV mass (g) [19, 20]. G-CFR was evaluated by corrected CSF reserve, which was calculated as CSF during maximal hyperemia divided by corrected CSF at rest [18]. The reproducibility of G-CFR measurements was satisfactory for interobserver (intraclass correlation coefficient, 0.91) and intraobserver (intraclass correlation coefficient, 0.89).