Energy Crisis of Cardiomyocytes
The core pathogenesis is driven by acute coronary insufficiency spanning the ischemic period and the initial stage of reperfusion. The main issue is a total disruption of cellular energy supply, which develops via two primary pathways.
First is direct oxygen deprivation. Hypoxia causes inhibition of cellular respiration. Attempting to compensate for energy deficits, cells activate anaerobic glycolysis. However, this leads to massive lactate accumulation and the development of intracellular acidosis. The acidic environment, in turn, secondarily blocks glycolysis, depriving the cell of its final energy sources.
The second pathway is neurohumoral. Amidst the predominance of cholinergic influences, the activity of the enzyme phosphorylase drops sharply (it even begins to leak out of cells). This further inhibits glycolysis. The end result of both pathways is a catastrophic drop in ATP levels.
Chronology of Cell Death
Pathological changes in the heart muscle progress rapidly. Counting from the moment of vascular occlusion, the timeline unfolds as follows:
- First seconds: A steady decline in ATP concentration begins.
- 1–2 minutes: Contractile function ceases entirely, leading to akinesia of the ischemic area.
- About 10 minutes: ATP reserves drop to approximately 50% of baseline normal.
- About 20 minutes: Critical energy deficiency occurs — ATP levels drop by 90%.
- 20–40 minutes: The point of no return. Irreversible structural damage develops, culminating in the death of cardiomyocytes (necrosis).
Mechanisms of Cellular Injury
Cellular destruction during ischemia is not limited to energy starvation alone. Five primary mechanisms of injury are triggered:
- Intensification of LPO: A sharp surge in free-radical lipid peroxidation occurs.
- Activation of hydrolases: Dissolved, membrane-bound, and lysosomal enzymes become active, destroying the cell from within.
- Conformational changes: The spatial structure of vital macromolecules — proteins, phospholipids, and lipoproteins — is disrupted.
- Blockade of repair: De novo synthesis of components and resynthesis of damaged membranes are completely suppressed.
- Mechanical rupture: Due to cellular edema (hyperhydration), membranes stretch and tear.
These processes trigger a secondary biochemical cascade. Breakdown products (free fatty acids, lysophospholipids) accumulate in vast quantities and exert a powerful toxic, detergent effect on surviving structures.
Autonomic "Seesaw"
Myocardial ischemia is accompanied by prominent shifts in the autonomic nervous system, which are divided into two phases.
The initial phase is characterized by dominance of the sympathoadrenal system. The myocardial concentration of noradrenaline and, particularly, adrenaline rises sharply. Clinically, this manifests as tachycardia. Cardiac output briefly increases, although it typically begins to drop immediately after the onset of coronary insufficiency. Parasympathetic influences (acetylcholine) also rise but remain significantly lower than sympathetic ones.
Late stages (tens of minutes to hours later) proceed differently. Sympathetic activity wanes, and noradrenaline levels drop. The parasympathetic system comes to the forefront because acetylcholine concentrations remain high. During this period, the patient exhibits bradycardia, decreased cardiac output, and a reduced rate of heart muscle contraction and relaxation.