What gross macroscopic features are characteristic of the necrotic stage of myocardial infarction?

During the necrotic stage of myocardial infarction, macroscopic examination reveals a pale/dull ischemic focus surrounded by a hyperemic (reddish) border. Progressive breakdown of cells and tissues occurs, along with a color change in the necrotic area of the heart muscle.

What microscopic features are characteristic of the necrotic stage of myocardial infarction?

In the necrotic stage, cardiomyocytes lose their nuclei and show signs of necrobiosis, such as karyolysis, cytoplasmic eosinophilia, and loss of cross-striations. Coagulative necrosis of the muscle tissue develops. On the second day, a distinct demarcation inflammatory rim with leukocytic infiltration forms around the focus, and by days 3–7, disintegration of dead myofibrils and their resorption by macrophages begin.

What early complications can develop during the necrotic stage of myocardial infarction?

The early period of myocardial infarction can be complicated by severe rhythm and conduction disturbances, acute heart failure manifesting as cardiac asthma and pulmonary edema, and cardiogenic shock. Dangerous morphological complications include myocardial rupture, acute cardiac aneurysm formation, rupture of a necrotic papillary muscle, interventricular septum perforation, and thromboembolic syndrome originating from fresh thrombotic masses on the endocardium.

What changes occur at the light microscopy level during the ischemic stage of myocardial infarction?

Light microscopy during the ischemic stage reveals myofibrillar alterations at the level of Z-discs, as well as swelling and fragmentation of cardiomyocytes. Glycogen depletion from the cell sarcoplasm is also noted.

How does the organization stage of myocardial infarction proceed at the tissue level?

The organization stage begins with the resorption of necrotic masses by segmented neutrophils and macrophages. By days 7–10, granulation tissue grows from the demarcation zone into the injury site, gradually replacing the necrotic zone. Subsequently, maturation of the granulation tissue occurs, transforming it into mature fibrous connective tissue and resulting in large focal post-infarction cardiosclerosis.

What compensatory mechanisms are triggered during the ischemic stage of myocardial infarction?

In response to a severe energy deficit in the intact myocardium, hyperplasia of intracellular structures is triggered, primarily mitochondria. Recombinational changes in mitochondria are activated to prevent worsening tissue hypoxia.

What are the main stages of myocardial infarction pathogenesis?

There are three stages: ischemic (prenecrotic), necrotic, and organization (scarring) stages.

Why does the intact myocardium suffer during a myocardial infarction?

The preserved myocardium takes on an increased workload due to the exclusion of the ischemic area. This causes an energy deficit, mitochondrial hyperfunction, destruction of their cristae, and the development of tissue hypoxia.

What is the role of collateral circulation?

With adequate collateral blood flow, ischemic changes in the peri-infarction zone are reversible. Inadequate blood supply leads to the progression of dystrophy into necrosis and an expansion of the lesion size.

Home › Pathology › Myocardial Infarction: Pathogenesis

Myocardial Infarction: Pathogenesis

Infarctus myocardii

For medical students2 min readUpdated 2026-10-10

Myocardial infarction is the necrosis of heart muscle resulting from an acute deficiency of coronary blood flow. The underlying process is ischemia, which progresses through several consecutive stages from reversible cellular changes to scar formation.

Main causeAcute myocardial ischemia due to absolute or relative blood flow deficiency

Prehospital mortalityAbout 30% within the first hour of the disease

Early ultrastructural shiftsSarcolemma damage, mitochondrial destruction, and sarcoplasmic edema

Stages of the processIschemic (prenecrotic), necrotic, and organization stages

Ultrastructural Changes in Ischemia

At the ultrastructural level, hypoxic injury to cardiomyocytes affects critical intracellular structures. Electron microscopy reveals:

Damage to the sarcolemma and plasma membrane.
Destruction of mitochondria and breakdown of their cristae.
Swelling of the sarcoplasmic reticulum and sarcoplasmic edema.
Disruption of intercalated discs.

At the light microscopy level, myofibrillar alterations involving Z-discs are visible.

Stages of Pathogenesis and the Role of Collaterals

The pathogenesis of infarctus myocardii develops dynamically and includes three key phases:

Ischemic (prenecrotic) stage — metabolic disorders escalate, energy deficiency develops, compensatory mechanisms are activated, and the fate of the peri-infarction zone is determined.
Necrotic stage — irreversible death of cardiomyocytes.
Organization stage — replacement of the necrotic area with connective tissue (scarring).

The fate of the injury zone largely depends on collateral circulation. If collateral blood flow is sufficient, ischemic damage in the peri-infarction zone may be reversible. With inadequate blood supply, dystrophic changes progress to necrosis, enlarging the lesion size.

Changes in Intact Myocardium and the "Vicious Circle"

The preserved (intact) myocardium assumes an increased workload due to the functional loss of the ischemic area. This leads to a series of interrelated shifts:

Energy deficiency arises because the baseline number of mitochondria only meets normal functional demands.
In response to increased workload, hyperplasia of intracellular structures is triggered—primarily mitochondria.
Mitochondrial hyperfunction leads to accelerated breakdown of their cristae, oxygen consumption becomes incomplete, and tissue hypoxia develops.

Tissue hypoxia increases alongside organelle destruction, creating the threat of a "vicious circle." Recombinational mitochondrial changes help prevent this outcome. In an optimal scenario, the body resolves the energy deficit, the patient survives the ischemic phase, and is followed by infarct organization and reparative hypertrophy.

Mnemonic

Three pillars of MI pathogenesis: Ischemia (reversible stage with battle for the peri-infarction zone) $ \rightarrow$ Necrosis (tissue death) $ \rightarrow$ Organization (scar).

Frequently asked questions

What gross macroscopic features are characteristic of the necrotic stage of myocardial infarction?: During the necrotic stage of myocardial infarction, macroscopic examination reveals a pale/dull ischemic focus surrounded by a hyperemic (reddish) border. Progressive breakdown of cells and tissues occurs, along with a color change in the necrotic area of the heart muscle.
What microscopic features are characteristic of the necrotic stage of myocardial infarction?: In the necrotic stage, cardiomyocytes lose their nuclei and show signs of necrobiosis, such as karyolysis, cytoplasmic eosinophilia, and loss of cross-striations. Coagulative necrosis of the muscle tissue develops. On the second day, a distinct demarcation inflammatory rim with leukocytic infiltration forms around the focus, and by days 3–7, disintegration of dead myofibrils and their resorption by macrophages begin.
What early complications can develop during the necrotic stage of myocardial infarction?: The early period of myocardial infarction can be complicated by severe rhythm and conduction disturbances, acute heart failure manifesting as cardiac asthma and pulmonary edema, and cardiogenic shock. Dangerous morphological complications include myocardial rupture, acute cardiac aneurysm formation, rupture of a necrotic papillary muscle, interventricular septum perforation, and thromboembolic syndrome originating from fresh thrombotic masses on the endocardium.
What changes occur at the light microscopy level during the ischemic stage of myocardial infarction?: Light microscopy during the ischemic stage reveals myofibrillar alterations at the level of Z-discs, as well as swelling and fragmentation of cardiomyocytes. Glycogen depletion from the cell sarcoplasm is also noted.
How does the organization stage of myocardial infarction proceed at the tissue level?: The organization stage begins with the resorption of necrotic masses by segmented neutrophils and macrophages. By days 7–10, granulation tissue grows from the demarcation zone into the injury site, gradually replacing the necrotic zone. Subsequently, maturation of the granulation tissue occurs, transforming it into mature fibrous connective tissue and resulting in large focal post-infarction cardiosclerosis.
What compensatory mechanisms are triggered during the ischemic stage of myocardial infarction?: In response to a severe energy deficit in the intact myocardium, hyperplasia of intracellular structures is triggered, primarily mitochondria. Recombinational changes in mitochondria are activated to prevent worsening tissue hypoxia.
What are the main stages of myocardial infarction pathogenesis?: There are three stages: ischemic (prenecrotic), necrotic, and organization (scarring) stages.
Why does the intact myocardium suffer during a myocardial infarction?: The preserved myocardium takes on an increased workload due to the exclusion of the ischemic area. This causes an energy deficit, mitochondrial hyperfunction, destruction of their cristae, and the development of tissue hypoxia.
What is the role of collateral circulation?: With adequate collateral blood flow, ischemic changes in the peri-infarction zone are reversible. Inadequate blood supply leads to the progression of dystrophy into necrosis and an expansion of the lesion size.

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