Infarction: Pathophysiology, Classification, and Clinical Consequences

Infarction is necrosis of tissue due to prolonged ischemia (inadequate blood supply). It results from arterial occlusion (thrombosis, embolism), venous obstruction, or hypoperfusion (shock).

Pathophysiologic Sequence

1. Blood flow interruption → O₂/nutrient deprivation.
2. Switch to anaerobic glycolysis → ATP depletion → failure of Na⁺/K⁺-ATPase → cellular edema.
3. Calcium influx → enzyme activation (proteases, lipases, endonucleases).
4. Mitochondrial permeability transition → cytochrome c release → apoptosis/necrosis.
5. Inflammatory response: neutrophil infiltration, cytokine release, phagocytosis of debris.
6. Healing: Granulation tissue → fibrosis (scar) — except CNS (gliosis) and myocardium (fibrous scar, no regeneration).

Classification by Organ

Infarct Morphology

• Anemic (white): Solid organs (heart, kidney, spleen) — limited collateral flow.
• Hemorrhagic (red): Loose tissues (lung, intestine, testis) or reperfusion — dual blood supply, venous congestion.

Clinical Consequences

Depend on organ, size, location, collateral circulation, and host reserve. Range from silent (microinfarcts) to fatal (massive MI, PE, mesenteric infarction). Timely reperfusion (thrombolysis, PCI, thrombectomy) salvages penumbra.

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Infarct Type	Vessel / Territory	Key Features
Myocardial Infarction (MI)	Coronary artery	STEMI (transmural) vs. NSTEMI (subendocardial); troponin ↑; ECG changes
Cerebral Infarction (Ischemic Stroke)	Internal carotid / vertebral / circle of Willis branches	Territorial (MCA, ACA, PCA) or lacunar; NIHSS; thrombolysis/thrombectomy window
Pulmonary Infarction	Pulmonary artery branch (PE)	Hemorrhagic, pleural-based wedge; pleuritic pain, hemoptysis
Renal Infarction	Renal artery / segmental	Flank pain, hematuria, AKI; often from cardiac embolus
Splenic Infarction	Splenic artery	LUQ pain, fever; sickle cell, emboli, vasculitis
Mesenteric / Bowel Infarction	SMA, IMA, SMV	Pain out of proportion, lactic acidosis; surgical emergency
Limb Infarction	Peripheral artery / embolus	Pain, pallor, pulseless, paresthesia, paralysis (6 P's)