Clinical meaning
The clinician managing MI must integrate molecular pathogenesis with evidence-based reperfusion strategies and comprehensive post-MI optimization. The Universal Definition of MI classifies five types: Type 1 (spontaneous MI from atherosclerotic plaque disruption), Type 2 (MI secondary to supply-demand mismatch from non-coronary causes), Type 3 (MI resulting in death before biomarkers obtained), Type 4 (MI related to PCI: 4a peri-procedural, 4b stent thrombosis, 4c restenosis), Type 5 (MI related to CABG). Type 1 MI involves plaque rupture (60-70%) or plaque erosion (30-40%) with subsequent thrombosis. Plaque erosion is increasingly recognized, particularly in younger women and smokers, and may warrant less aggressive antiplatelet therapy per emerging evidence (EROSION study). Reperfusion injury is a paradoxical consequence of successful reperfusion: restoration of blood flow to ischemic myocardium generates a burst of reactive oxygen species (superoxide, hydroxyl radicals), activates complement cascade, triggers neutrophil infiltration, causes calcium overload and hypercontracture (contraction band necrosis), and can produce microvascular obstruction (no-reflow phenomenon). Microvascular obstruction occurs in up to 50% of STEMI patients after primary PCI and predicts adverse remodeling. Ischemic postconditioning (brief cycles of ischemia/reperfusion during PCI) and remote ischemic conditioning (limb ischemia/reperfusion) have shown promise in reducing reperfusion injury. Post-MI remodeling is driven by neurohormonal activation: RAAS (angiotensin II and aldosterone promote fibrosis and hypertrophy), sympathetic nervous system (norepinephrine causes apoptosis and hypertrophy), and natriuretic peptides (BNP attempts compensatory vasodilation and diuresis). The PARADIGM-HF and PARADISE-MI trials established sacubitril/valsartan (ARNI) as superior to ACE inhibitor for HFrEF, though the PARADISE-MI trial showed only a non-significant trend in the acute MI setting.