Clinical meaning
The nurse managing MI must understand the temporal evolution of myocardial necrosis and its complications. Ischemic injury progresses through four histological phases: (1) Coagulative necrosis (0-4 hours): earliest changes with wavy myofibers and contraction band necrosis at the margins; (2) Acute inflammation (4-24 hours): neutrophil infiltration, interstitial edema, beginning of myocyte dissolution; (3) Granulation tissue (1-3 weeks): macrophage infiltration, neovascularization, fibroblast proliferation with collagen deposition; (4) Scar formation (3-6 weeks to months): dense fibrous scar replacing necrotic myocardium. Mechanical complications correspond to this timeline: papillary muscle rupture and VSD occur at day 3-7 when the infarcted tissue is softest (maximal necrosis before scar formation). Free wall rupture occurs at day 5-14 and presents with sudden PEA arrest and cardiac tamponade. Dressler syndrome (autoimmune pericarditis) occurs 2-10 weeks post-MI from antibodies against exposed cardiac antigens. Ventricular remodeling begins within hours: infarct expansion (thinning and dilation of the necrotic zone) followed by eccentric hypertrophy of non-infarcted segments. Neurohormonal activation (RAAS, sympathetic) drives progressive dilation. ACE inhibitors, beta-blockers, and aldosterone antagonists attenuate remodeling and improve survival. The nurse monitors for each complication within its expected timeframe, interprets hemodynamic parameters, and manages complex medication regimens.