Myocardial blush grade predicts myocardial and microvascular damage in ST-elevation myocardial infarction patients who underwent direct angioplasty

Background: Myocardial Blush Grade (MBG) has been established as an useful index of myocardial reperfusion in STEMI. However its pathological basis are still lacking. Recently contrast enhanced magnetic resonance imaging (ce-MRI) has been shown to describe myocardial tissue abnormalities produced by myocardial ischemia. The aim of this study was to investigate myocardial and microvascular abnormalities underlying the different patterns of MBG, using ce-MRI. Methods: 204 patients underwent direct angioplasty within 12 hours from STEMI were studied by ce-MRI. According to MBG patients were divided in three groups: group 1) MBG-0/1; group 2) MBG-2; group 3 MBG-3. At ce-MRI presence and extent of both myocardial necrosis (late hyperenhancement) and persistent microvascular obstruction (late hypoenhancement) were assessed on a 17-segment model. Myocardial necrosis was labelled as transmural if late-hyperenhancement extended to > 75% of the thickness of at least 2 contiguous segments. Results: MBG-0/1 occurred in 65 (31.9%), MBG-2 in 51 (25%), and MBG-3 in 88 (43.1%) patients. The baseline characteristics were similar among groups, except for pain-to-balloon time that was longer in MBG-0/1 (p = 0.02). After angioplasty TIMI-3 flow occurred in 74.6% of MBG-0/1, 96.2% of MBG 2, and 100% of MBG 3, respectively (p <0.0001). Transmural necrosis occurred in 76.9% of MBG-0/1, 62.7% of MBG-2, and 52.3% of MBG-3 respectively (p < 0.008), and involved 4.3±3.2, 3.3±3.1, and 2.2±2.6 myocardial segments in the three groups respectively (p < 0.0001). Persistent microvascular obstruction was occurred in 38.5% of MBG-0/1, 39.2% of MBG-2, and in 20.5% of MBG-3 patients respectively (p = 0.02), and involved 1.7±2.7, 1.4±2.0, and 0.5±1.2 myocardial segments respectively (p = 0.001). At multivariate analysis the extent of transmural necrosis resulted the only independent predictor of unsuccessful angiographic reperfusion (MBG 0/1): OR 1.16, CI 1.04 - 1.29, p = 0.005. Conclusions: Myocardial Blush Grade is related to the extent of both myocardial and microvascular damage. However, the extent of transmural necrosis is the only independent predictor of unsuccessful angiographic reperfusion.