Q waves and failed ST resolution: will intra-myocardial haemorrhage be a concern in reperfusing "late presenting" STEMIs?

Animal studies have demonstrated that intra-myocardial haemorrhage does not occur with STEMI unless myocardium is reperfused with blood. Managing late presenting STEMI is a challenge because reperfusion of non-viable myocardium will not salvage myocardium but potentially causes intra-myocardial haemorrhage which has negative connotations. In the infarct leads, there are pathologic Q waves of variable depth and width together with ST elevation. The latter often fails to resolve despite an angiographically successful primary PCI. This article reviews the literature of ST resolution after reperfusion therapy, recent mechanistic insights on intra-myocardial haemorrhage gleaned from cardiac MRI, the patho-physiology of STEMI including also findings from animal models, and the role of Q waves in characterising the evolution of STEMI towards its irreversible destiny. The MRI studies have correlated intra-myocardial haemorrhage with worse ventricular remodelling and worse outcome. A suggestion is made incorporating infarct-lead Q waves and time duration from symptom onset to discern whether late reperfusion attempts should be initiated or aborted. This suggestion should be confirmed through appropriate size randomized trials with mechanistic endpoints from serial MRI evaluations and, more importantly, with clinical endpoints on long-term outcome. Table 4 summarizes current STEMI guidelines for late-presenting patients and Fig. 5 suggests potential future alterations.