Half of patients referred for invasive coronary angiography (ICA) for investigation of chest pain have angiographically non-obstructed coronary arteries (NOCAD). Index of microcirculatory resistance (IMR) is a useful tool for diagnosis of microvascular dysfunction (MVD) in patients with NOCAD but its use is limited due to its invasive nature. Adenosine stress CMR with myocardial perfusion mapping may have a role in the assessment of MVD as it allows for measurement of myocardial blood flow (MBF) at a pixelwise level.
To assess the performance of myocardial perfusion mapping for the diagnosis of MVD in patients with NOCAD.
Forty-four subjects (24 patients and 20 controls) underwent adenosine stress CMR with inline myocardial perfusion mapping at 1.5T using Gadgetron. The patients underwent ICA with measurement of fractional flow reserve (FFR) and IMR in all major epicardial vessels on the same day as the CMR. Perfusion maps were used to calculate global stress MBF and global myocardial perfusion reserve (MPR).
All patients had NOCAD (defined as FFR >0.80 in all epicardial vessels) and no subjects had visual perfusion defects on first pass stress perfusion images. Fifteen patients had evidence of MVD defined as IMR >25 in at least one epicardial vessel and 9 patients had normal coronary physiology (NCP). Patients with MVD had significantly lower stress MBF compared to those with NCP and controls (MVD 2.11±0.31ml/g/min vs NCP 2.70±0.53ml/g/min vs controls 3.21±0.64ml/g/min, p<0.001). Both patients with MVD and NCP had lower MPR and higher rest MBF compared to controls (MPR: MVD 2.35±0.90 vs NCP 2.52±0.51 vs controls 4.25±0.81; rest MBF: MVD 1.03±0.35ml/g/min vs NCP 1.17±0.26ml/g/min vs controls 0.80±0.21ml/g/min; both p<0.001). Global stress MBF <2.23ml/g/min was able to detect MVD with sensitivity 80% and specificity 97% (AUC 0.93, p<0.001) and was superior to global MPR (AUC 0.82, p<0.05 for comparison)).
Patients with MVD have impaired stress MBF and this can be accurately detected using CMR perfusion mapping. Adenosine stress CMR with perfusion mapping is a useful diagnostic tool for the assessment of patients with angina and NOCAD.