Objectives: Current methods for infarct size and microvascular obstruction (MVO) quantification by cardiac magnetic resonance (CMR) imaging rely on planimetry. This method is time-consuming. We sought to evaluate a direct assessment of MVO severity based on visual evaluation and to compare it to a reference method.
Methods: CMR was performed in 112 consecutive patients after reperfused myocardial infarction. MVO was estimated by direct visual assessment based on a three-grade severity scale (MVO 1, mild; MVO 2, moderate; MVO 3, severe) on late gadolinium-enhancement (LGE).
Results: MVO was present in 69 patients (61.6 %). Quantitative MVO extent significantly increased accordingly to visual MVO grading (p < 0.01). Correlation between visual grading and quantitative assessment was excellent (r = 0.92, IQR 0.88-0.95, p < 0.001). CMR inter- and intraobserver variability for visual MVO evaluation was low (κ = 0.93 and κ = 0.96, respectively), whereas quantitative MVO assessment suffered from moderate agreement (interobserver, bias = -0.81 ± 1.8 g LV; intraobserver, -0.83 ± 2.1 g LV). Visual evaluation was significantly faster than reference method (0.65 ± 0.37 vs. 10.2 ± 2.9 min, p < 0.0001).
Conclusions: MVO severity based on direct visual assessment on LGE images is feasible, rapid, reproducible and agrees very well with quantitative methods, with a very low inter- and intraobserver variability. Our approach could be used for routine evaluation in patients undergoing CMR after acute myocardial infarction.
Key points: • Microvascular obstruction direct visual evaluation is feasible, rapid and highly reproducible. • Microvascular obstruction direct visual evaluation correlates well with quantification by planimetry. • Microvascular obstruction or no-reflow phenomenon is determined on late gadolinium-enhanced images. • Cardiac MRI is useful for myocardial damage assessment after myocardial infarction.
Keywords: Magnetic resonance imaging; Myocardial infarction; Myocardial reperfusion; Myocardial reperfusion injury; No-reflow phenomenon.