Relation of myocardial blush grade to microvascular perfusion and myocardial infarct size after primary or rescue percutaneous coronary intervention.

Angiographic myocardial blush grade (MBG) is a potent predictor of long-term outcome after percutaneous treatment of myocardial infarction, yet little is known regarding the underlying pathophysiologic features. The relation between MBG and cardiovascular magnetic resonance (CMR)-defined amounts of necrosis and microvascular obstruction was examined in 27 patients. Another powerful prognostic indicator, ST-segment resolution>70%, was correlated with other predictors. Increasing MBG was associated (p=0.001) in a linear fashion (p<0.001) with less microvascular obstruction using CMR, whereas the inverse relation with amount of necrosis, although significant (p=0.043), was nonlinear (p=0.36). ST resolution was not correlated with either MBG or CMR parameters. In conclusion, MBG is mainly influenced by microvascular patency and is less dependent on the amount of muscle necrosis, and the common practice of including MBG 2 and 3 into a single "patent microcirculation" category might not be justified. Moreover, the mechanisms of ST resolution should be searched for at the cellular level.