An infarct is a localized area of tissue death (necrosis) resulting from an interruption of blood supply. Blood delivers oxygen and nutrients to every cell. When tissue is deprived of this flow, the condition is termed ischemia. If deprivation is prolonged, the cells die due to sustained oxygen and nutrient starvation.
How Blockages Cause Tissue Death
The direct cause of an infarct is an occlusion, or blockage, within an artery supplying blood to a specific tissue region. Arterial blood carries the oxygen required for cellular respiration; without it, cells cannot produce the energy needed to survive. This oxygen deprivation triggers cellular injury and leads to necrosis.
These occlusions arise from two distinct mechanisms: thrombosis or embolism. A thrombosis involves the local formation of a blood clot (thrombus) directly within the artery, often where the vessel wall is damaged by plaque buildup.
An embolism occurs when a traveling mass (embolus) becomes lodged in an artery too narrow for it to pass through. This embolus is frequently a piece of a blood clot broken off from its origin elsewhere, such as the heart or a distant vein. Other materials, including fat globules, air bubbles, or fragments of plaque, can also act as emboli.
The Major Types of Infarcts
Infarcts are named based on the location of the tissue death. A Myocardial Infarction (heart attack) is the death of heart muscle (myocardium) when a coronary artery becomes blocked. The loss of heart muscle impairs the organ’s ability to pump blood efficiently, and damage depends on the size of the blocked artery.
Similarly, a Cerebral Infarction (ischemic stroke) involves the death of brain tissue. This is caused by the occlusion of an artery supplying the brain, leading to a rapid loss of neurological function in the area controlled by the deprived tissue.
The principle of infarction can affect any organ with an end-arterial circulation, where one artery is the sole source of blood to a region. A Renal Infarct, for example, is the death of kidney tissue, often caused by an embolus traveling from the heart to the renal artery. A Splenic Infarct involves tissue death in the spleen, an organ that filters blood and stores immune cells.
What Happens to Necrotic Tissue
Tissue cells that undergo necrosis following an infarct cannot be restored to their functional state. The body initiates a wound healing process to contain the damage and remove dead cellular debris. This begins with an inflammatory response, where specialized immune cells, such as neutrophils and macrophages, infiltrate the area to clear away the necrotic material.
Over the following days and weeks, the body replaces the lost tissue with a non-functional collagenous scar. Specialized cells called fibroblasts migrate into the infarct zone to synthesize and deposit large amounts of collagen. This collagen forms a dense, fibrous patch, known as fibrosis, which structurally stabilizes the injured area. For organs like the heart or brain, this scar tissue is problematic because it lacks the original tissue’s ability to perform its function, such as contracting or transmitting electrical signals.