PET-measured longitudinal flow gradient correlates with invasive fractional flow reserve in CAD patients

<span class="paragraphSection"><div class="boxTitle">Aims</div>We aimed to evaluate whether a PET-determined longitudinal decrease in myocardial blood flow (MBF) or gradient, assumed as a more specific flow parameter for epicardial resistance, correlates with invasively measured fractional flow reserve (FFR) in coronary artery disease (CAD) patients.<div class="boxTitle">Methods and Results</div>In 29 patients with suspected or known CAD, myocardial perfusion and MBF in mL/g/min was determined with ¹³N-ammonia PET/CT during regadenoson stimulation and at rest, and corresponding myocardial flow reserve (MFR = MBF stress/MBF rest) was calculated. MBF parameters were assessed in the myocardial region with stress-related perfusion defect and with stenosis ≥50% (Region 1), without defect but with stenosis ≥50% (Region 2), or without stenosis ≥50% (Region 3). Hyperaemic MBFs were significantly lower in the mid-distal than in the mid-left ventricular myocardium in Regions 1–3 [median and IQ range: 1.57 (1.24, 1.84) vs. 1.87 (1.61, 2.00), and 1.23 (1.11, 1.86) vs. 1.89 (1.80, 1.97), and 1.78 (1.48, 2.00) vs. 1.94 (1.84, 2.05) mL/g/min, <span style="font-style:italic;">P</span> < 0.0001]. Resulting longitudinal MBF gradient during hyperaemic flows was more pronounced in Region 2 than in Regions 1 and 3, respectively [−0.46 (−0.70, −0.10) vs. −0.17 (−0.29, −0.11) and −0.15 (−0.25, −0.09) mL/g/min, respectively, <span style="font-style:italic;">P</span> < 0.01]. There was a significant correlation between the hyperaemic longitudinal MBF gradient and FFR (<span style="font-style:italic;">r</span> = 0.95; <span style="font-style:italic;">P</span> < 0.0001), while this association was less pronounced for corresponding MFR (<span style="font-style:italic;">r</span> = 0.50; <span style="font-style:italic;">P</span> = 0.006).<div class="boxTitle">Conclusion</div>The observed close correlation between a longitudinal MBF gradient during hyperaemic flows and invasively measured FFR suggests the longitudinal flow gradient as an emerging non-invasive index of flow-limiting CAD.</span>

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