Cardiology

The core mechanism involves the rupture of an unstable atherosclerotic plaque in the coronary artery. This triggers the coagulation cascade and the formation of a thrombus that causes sudden occlusion. Myocardial cells distal to the obstruction experience anaerobic metabolism, leading to lactic acid accumulation and intracellular edema. Within 20-40 minutes, irreversible cell death begins at the subendocardium...

The SA node exhibits automaticity due to the 'funny current' (If) mediated by HCN channels. These channels open during hyperpolarization, allowing a slow influx of sodium ions. Unlike ventricular myocytes, the depolarization phase (Phase 0) is primarily driven by the influx of Calcium ions through L-type calcium channels, rather than fast sodium channels. Repolarization (Phase 3) occurs as calcium channels close and potassium channels open.