Resting myocardial blood flow is impaired in hibernating myocardium: A magnetic resonance study of quantitative perfusion assessment

Background - Although impairment in perfusion reserve is well recognized in hibernating myocardium, there is substantial controversy as to whether resting myocardial blood flow (MBF) is reduced in such circumstances. Quantitative first-pass cardiovascular magnetic resonance (CMR) perfusion imaging allows absolute quantification of MBF. We hypothesized that MBF assessed at rest by quantitative CMR perfusion imaging is reduced in hibernating myocardium. Methods and Results - Twenty-seven patients with 1 or 2-vessel coronary disease and at least 1 dysfunctional myocardial segment undergoing PCI were studied with preprocedure, early (24 hours), and late (9 months) postprocedure CMR imaging. First-pass perfusion images at rest were acquired in 3 short-axis planes by use of a T1-weighted turboFLASH sequence. In each slice, MBF was determined for 8 myocardial segments in mL·min^-1·g^-1 by deconvolution of signal intensity curves with an arterial input function measured in the left ventricular blood pool. Cine MRI for assessment of global and segmental function and delayed enhancement MRI for detection of viability were also obtained. All coronary lesions were 80% to 95% stenosis in severity. Over all segments, mean MBF normalized by rate-pressure product ("corrected MBF") was 1.2±0.3 mL·min^-1·g ^-1·(mm Hg·bpm/10⁴)^-1 in segments without significant coronary stenosis and 0.7±0.2 mL·min ^-1·g^-1·(mm Hg·bpm/10 ⁴)^-1 in segments with coronary stenosis before PCI (mixed model controlling for slice and segment z=-23.9, P<0.001). Early after the procedure, the MBF was 1.2±0.2 mL·min^-1·g ^-1·(mm Hg·bpm/10⁴)^-1 in revascularized segments and 1.3±0.2 mL·min ^-1·g^-1·(mm Hg·bpm/10 ⁴)^-1 in nondiseased segments (z=-6.1, P<0.001). Late after PCI, the systolic wall thickening and end-diastolic wall thickness both increased significantly more (both P<0.001) in the myocardial segments subtended by severe coronary stenosis (8±17% to 40±19% and 6.5±1.1 to 9.3±2 mm, respectively) than in the myocardial segments supplied by nondiseased vessels. Mean MBF in dysfunctional segments with significantly improved contraction after revascularization was 0.8±0.2 mL·min^-1·g^-1·(mm Hg·bpm/ 10⁴)^-1 before PCI and 1.2±0.2 mL·min ^-1·g^-1·(mm Hg·bpm/10 ⁴)^-1 after PCI (z=2.0, P=0.04). Conclusions - CMR perfusion imaging detects impaired resting MBF in hibernating myocardial segments.