Dynamics of ultrastructural changes
The first hours and minutes of ischemia are accompanied by profound metabolic and structural shifts in the myocardium:
- After 5–15 minutes: microcirculation disorders, stromal edema, fatty and vacuolar dystrophy, as well as uneven myofibril overcontraction are recorded.
- After 30 minutes: glycogen completely disappears from muscle cells.
- After 2–4 hours: Krebs cycle enzyme activity drops, uncoupling of respiration and phosphorylation processes begins.
- After 4–6 hours: contraction-altered myofibrils predominate at the periphery of the ischemic zone, while in the center of the focus the number of relaxed fibers reaches 60% (this sign indicates irreversibility of damage).
Scarring stage and outcomes
The healing process of the necrosis zone proceeds in stages over several weeks:
- 2nd week: active formation of granulation tissue begins.
- 3rd week: the zone of dead myocardium is almost completely replaced by maturing granulations.
- 4th–6th weeks: granulation tissue transforms into mature connective tissue.
Complete organization of the infarction and myocardial adaptation are completed in 2–2.5 months. The main outcome is large-focal cardiosclerosis, which characterizes chronic coronary heart disease. Compensatory hypertrophy of muscle fibers develops in the surviving functioning myocardium.
Complications and chronic CHD
Myocardial infarction complications are subdivided into two periods:
- Early period: lasts up to 3 weeks.
- Late period: covers the segment from 4 weeks to 3 months.
Acute infarction can lead to acute heart failure with the development of pulmonary edema.
Chronic CHD is defined as chronic coronary circulatory insufficiency. Its key morphological manifestations:
- Diffuse small-focal cardiosclerosis.
- Large-focal post-infarction cardiosclerosis.
- Chronic cardiac aneurysm.
Briefly: answers to topical questions
What causes the development of atypical forms of myocardial infarction?
The provided study materials do not contain specific causes for the development of atypical forms of myocardial infarction, but it is indicated that such forms are observed in 2–10% of cases and present significant diagnostic difficulty because their clinical picture masks the true disease.
What macroscopic types of myocardial infarction exist by shape and color?
Based on the macroscopic picture, white (ischemic), red (hemorrhagic) infarction, and ischemic infarction with a hemorrhagic rim (mixed type) are distinguished. Myocardium is characterized by ischemic infarction with a hemorrhagic rim: the central zone is white and ischemic, while a wide zone of red-brown hemorrhages is located at the periphery. The shape of the infarction depends on angioarchitecture and the type of vascular branching: in the main type, it is triangular, cone-shaped, or wedge-shaped, while in the dispersive or mixed type, it is irregular.
Glycogen disappears in half an hour, Krebs enzymes in 2–4 hours, and 60% of relaxed fibers in the center of the ischemic zone mark the threshold of irreversible myocyte death.
Class and exam questions
How long does the ischemic stage of myocardial infarction last?
The ischemic stage lasts from 18 to 24 hours. During this period, primary ischemic injuries to the heart muscle develop.
Which sign indicates the irreversibility of ischemic damage in the center of the focus?
The irreversibility of damage is indicated by reaching 60% of relaxed fibers in the center of the ischemic focus (detected after 4–6 hours).
When is the complete organization of a myocardial infarction completed?
Complete organization of the infarction and adaptation to new conditions are completed 2–2.5 months after the onset of the disease.
What are the morphological manifestations of chronic CHD?
These include diffuse small-focal cardiosclerosis, large-focal post-infarction cardiosclerosis, and chronic cardiac aneurysm.
What else to study on this topic
- Pathophysiology of myocardial ischemia and necrosis
- Morphology of the necrotic stage of myocardial infarction
- Diagnostics of the ischemic stage of infarction
- Microscopic picture of maturing granulation tissue
- Clinical manifestations of atypical forms of myocardial infarction
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