Ischemia and Infarction covers ischemia and infarction for INI CET (AIIMS PG).
Ischemia: Inadequate blood supply to an organ or tissue (oxygen + nutrient deprivation).
Causes:
- Arterial occlusion: Atherosclerosis, thrombosis, embolism, vasospasm
- Hypoperfusion: Shock, heart failure
- Venous obstruction: Outflow impairment (DVT, SVC syndrome)
Ischemia vs Hypoxia:
- Hypoxia: Reduced oxygen tension in blood/tissues
- Ischemia: Reduced blood flow — both oxygen AND nutrient supply are compromised; more damaging because waste products accumulate
Ischemic Time Sensitivity:
- Brain: Most sensitive — irreversible damage in 4–6 minutes
- Heart (myocardium): Irreversible in 20–30 minutes (wavefront of necrosis — subendocardium most vulnerable)
- Skeletal muscle: Can tolerate several hours
Infarction: Area of tissue necrosis caused by ischemia.
Types of Infarction:
- Pale (White) Infarct: Solid organs with end-arterial blood supply — kidney, spleen, heart; wedge-shaped with pale center
- Red (Hemorrhagic) Infarct:
- Dual blood supply (lung — bronchial artery + pulmonary artery)
- Loose tissue (brain — loose neuropil)
- Venous occlusion (mesenteric veins, testicular torsion)
- Reperfusion after ischemia (hemorrhage into necrotic tissue)
Myocardial Infarction (MI):
- Transmural (STEMI): Full thickness necrosis — from complete coronary occlusion
- Subendocardial (NSTEMI): Inner 1/3 to 2/3 of wall — from prolonged hypoperfusion or incomplete occlusion
- Temporal Evolution (gross morphology):
- 0–4h: No visible changes
- 4–12h: Dark mottling, wavy fibers
- 12–24h: Yellow-tan softening, early coagulative necrosis
- 1–3 days: Coagulative necrosis, neutrophil infiltration begins
- 3–7 days: Macrophage infiltration, early granulation tissue at margins
- 1–3 weeks: Granulation tissue, removal of necrotic debris
- Weeks to months: Dense scar formation (collagenous scar)
⚡ Exam Tip for INI CET (AIIMS PG): ECG changes in MI:
- STEMI: ST elevation in leads overlying infarcted area
- NSTEMI: ST depression or T-wave inversion (no ST elevation) Troponin I/T: rises within 3–4 hours, peaks at 24h, remains elevated for 7–10 days.