Ip between resting MBF and sector end-diastolic wall thickness. However, at stress, there was a negative correlation between the two ( = -0.047 ml/g/min per mm, 95 confidence interval [CI]: -0.057 to -0.038, P < 0.001) with similar falls in the endocardium and the epicardium ( = -0.048 ml/g/min per mm, 95 CI: -0.058 to -0.039, P < 0.001 and = -0.048 ml/ g/min per mm, 95 CI: -0.058 to -0.038, P < 0.001, respectively).Perfusion and late gadolinium enhancementAdenosine achieved hyperemia, with MBF rising significantly between rest and stress. When considering the most normal sectors in each of the patients, the mean MPRI was significantly lower in the severe versus non-severe patients for sectors as a whole and in endocardial subsectors, with a trend towards significance in the epicardium (Figure 4). When comparing the 16 segments in all the patients, MBF rose significantly with A-836339MedChemExpress A-836339 stress in whole sectors (1.22 ?0.34 ml/g/min rising to 2.22 ?0.76 ml/g/ min, P < 0.001) and in both endocardial and epicardial subsectors (1.25 ?0.35 ml/g/min rising to 2.00 ?0.76 ml/g/ min, P < 0.001; and 1.20 ?0.35 ml/g/min rising to 2.36 ?0.83 ml/g/min, P < 0.001, respectively). At rest, endocardialSegments with LGE were significantly associated with lower perfusion at rest (odds ratio [OR] per ml/g/min increase in MBF: 0.086, 95 CI: 0.078 to 0.095, P = 0.003). This relationship remained consistent at stress (OR: 0.086, 95 CI: 0.081 to 0.092, P < 0.001) and when examined in relation to MPRI (OR: 0.053, 95 CI 0.032 to 0.089, P = 0.015). Both rest and stress MBF appeared to be significantly lower in segments with LGE relative to those without (Figure 5A), resulting in a significant difference in MPRI between segments with and without LGE (MPRI: 1.80 ?0.74 versus 1.92 ?0.64, P < 0.001 respectively).Ismail et al. Journal of Cardiovascular Magnetic Resonance 2014, 16:49 http://jcmr-online.com/content/16/1/Page 7 ofFigure 5 Mean myocardial blood flow (MBF) in (A) segments and (B) regions of interest (ROI) with and without late gadolinium enhancement (LGE).However, these differences did not persist after adjusting for differences in wall thickness. ROI analysis on pixel-level perfusion maps revealed a similar, yet stronger trend of reduced MBF when comparing areas of LGE to remote areas free of LGE. This trend was observed for both rest and stress (Figure 5B). As a result, the MPRI was significantly lower in ROI with LGE than in remote areas (1.61 ?0.65 versus 1.92 ?0.54, P < 0.001).Discussion We found evidence of widespread microvascular dysfunction in a cohort of patients with HCM being studied with multiparametric CMR. To our knowledge, this is the first study to assess stress myocardial perfusion in HCM with CMR PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/27532042 using pixel-wise quantification techniques. This allowed us to examine perfusion abnormalities at an unprecedented level of detail. In a subset of patients, pixelwise analysis revealed regions with not only a blunted or inadequate hyperemic response to vasodilator stress, but evidence of severe microvascular dysfunction that is likely to result in ischemia, with stress MBF levels below those of rest perfusion. In keeping with earlier work, we found that resting endocardial MBF was significantly higher than epicardial MBF . This may reflect the higher systolic wall tensionand consequent higher metabolic requirements experienced by the endocardium [34,35]. However, this transmural gradient of perfusion reversed with vasodilator stress to the detrim.