Microvascular obstruction (MO) is a feature of 20–40% of reperfused acute ST-elevation myocardial infarction (STEMI), and confers adverse prognosis. Cardiovascular magnetic resonance (CMR) can visualise MO with high resolution and accuracy. MO may be detected by different CMR sequences: first pass perfusion (FPP), early gadolinium enhancement (EGE), and late gadolinium enhancement (LGE). FPP and EGE are more sensitive than LGE for the detection of MO. However, only MO by LGE has been shown to confer prognostic information. It is unclear whether these three methods detect separate pathologies, or whether differences in MO appearances merely reflect contrast distribution over time. We aimed to determine how appearances between these methods are related.Methods
60 patients underwent CMR at 3.0T within 3 days following reperfused first STEMI. MO imaging was performed at identically-planned basal, mid-ventricular and apical short-axis slices. FPP imaging was performed during administration of 0.1 mmol/kg Gd-DTPA contrast. 4 min after contrast administration, EGE imaging was performed, followed by LGE imaging at both 10 min and at 20 min. MO was identified as a dark core within infarcted myocardium. We compared area and transmural extent of MO for each method on a per-patient and a per-slice basis.Results
29 patients (48%) had MO. All patients with MO on LGE also had MO on FPP or EGE, whereas LGE at 10 min failed to detect MO in 9 patients (31%) with MO on FPP, and 8 patients (28%) on EGE. Of 13 patients with MO volume <5 ml on FPP, 12 (92%) had no MO visible on LGE at 20 min.Results
Average visible area of MO per slice decreased with time of measurement (p < 0.001 for trend, Figure 1). MO area by FPP and EGE correlated with LGE at 20 min (r = 0.80; p < 0.001 and r = 0.80; p < 0.001) but MO volume (per patient) by FPP and EGE was on average 236 and 200% larger than LGE. Decrease in MO volume over time correlated strongly with size of MO (r = 0.95, p < 0.01, Figure 2) and transmural extent of MO (r = 0.77, p < 0.01).Conclusions
The reduction in visible size of MO is proportional to extent of MO and time from contrast administration. The strong correlation with MO size and time suggests that the reduction in MO size between methods is explained by contrast diffusion into the MO zone, rather than differing clinical or imaging factors. Smaller areas of MO on EGE and FPP become undetectable on LGE, while larger areas are detectable but smaller on LGE. MO by LGE therefore identifies more extensive MO than FPP or EGE, possibly explaining its higher predictive value for adverse prognosis following STEMI.