Infarction pathophysiology
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Myocardial Infarction Pathophysiology: Ischemia, Cell Death, and Inflammation
Myocardial infarction (MI) occurs when blood flow to a part of the heart muscle is reduced or stopped, most often due to coronary artery disease (CAD) caused by atherosclerosis, thrombosis, or plaque erosion. This leads to oxygen deprivation (ischemia) and ultimately cardiac cell death if the blockage is prolonged 135. The process begins with metabolic and ionic disturbances in the affected heart tissue, resulting in rapid loss of contractile function and, if unresolved, a "wavefront" of cell death that spreads from the inner (subendocardial) to the outer (subepicardial) layers of the heart muscle 35.
Mechanisms of Cell Death: Apoptosis, Necrosis, and Necroptosis
Cell death in MI is triggered by both intrinsic and extrinsic pathways, with apoptosis (programmed cell death) and necrosis (uncontrolled cell death) being the primary mechanisms. Recent research also highlights the role of necroptosis, a regulated form of necrosis, in myocardial injury 235. Mitochondrial dysfunction is a key factor in these processes, leading to irreversible damage to heart cells .
Inflammatory Response and Scar Formation
The heart has very limited regenerative capacity, so the damaged area heals by forming scar tissue rather than regenerating new muscle. The healing process is initiated by an inflammatory cascade, triggered by molecules (alarmins) released from dying cells. Immune cells clear away dead tissue, and fibroblasts are activated to deposit extracellular matrix proteins, resulting in scar formation 23. This process is regulated by anti-inflammatory pathways and signaling molecules such as transforming growth factor-β .
Infarct Expansion, Extension, and Remodeling
After the initial injury, the affected area may undergo infarct expansion—thinning and stretching of the infarcted segment—which can lead to ventricular dilation, reduced heart function, and increased risk of complications like heart failure and aneurysm formation . Infarct extension refers to additional injury in the same vascular territory, often due to repeated episodes of reduced blood flow or rethrombosis . These changes contribute to adverse remodeling of the heart's structure and function 36.
Pathophysiology of Perioperative and Watershed Infarctions
Perioperative MI, which occurs around the time of surgery, is often caused by a mismatch between oxygen supply and demand (demand ischemia), rather than by acute plaque rupture and thrombosis 78. In contrast, watershed infarctions in the brain are typically due to hemodynamic impairment from carotid artery stenosis (internal watershed) or microembolic events (cortical watershed) .
Risk Factors and Triggers
Major risk factors for MI include age, male sex, family history, high cholesterol, smoking, hypertension, diabetes, obesity, and stress . Other triggers can include aortic dissection, drug misuse, and congenital heart abnormalities . In the perioperative setting, increased cardiac demand and pre-existing coronary disease are key contributors 78.
Reperfusion Injury and Cardioprotective Strategies
Restoring blood flow (reperfusion) is essential to limit infarct size, but it can also cause additional injury through oxidative stress and inflammation. Strategies such as ischemic preconditioning, postconditioning, and remote ischemic conditioning, as well as certain drugs, have shown promise in reducing reperfusion injury, though clinical results are still evolving 59.
Conclusion
The pathophysiology of infarction involves a complex interplay of vascular occlusion, ischemia, cell death, inflammation, and tissue remodeling. Understanding these mechanisms is crucial for developing effective prevention and treatment strategies to reduce the impact of MI and its complications 1235+5 MORE.
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Most relevant research papers on this topic
Pathophysiology of acute myocardial infarction, 1981.
Acute myocardial infarction pathophysiology involves platelet aggregability, coronary arterial spasm, and thromboxane A2 and prostacyclin, with spasm potentially initiating the infarction process in some cases.
The pathophysiology of acute myocardial infarction and strategies of protection beyond reperfusion: a continual challenge.
Remote ischaemic conditioning and certain drugs show potential in reducing infarct size in STEMI patients, but more research is needed to improve clinical outcomes.
Myocardial infarct expansion, infarct extension, and reinfarction: pathophysiologic concepts.
Infarct expansion occurs early in myocardial infarctions and leads to poorer exercise tolerance, more congestive heart failure symptoms, and increased early and late mortality.
Angiographic investigation of the pathophysiology of perioperative myocardial infarction
Demand ischemia is the predominant etiology of perioperative myocardial infarctions, potentially facilitating preoperative evaluation and management.
Pathophysiology of ST-segment elevation myocardial infarction: novel mechanisms and treatments.
Early detection, cardioprotection, and stem cell treatment show promise in reducing infarct size and improving outcomes in ST-segment elevation myocardial infarction patients.
The Pathophysiology of Watershed Infarction: A Three-Dimensional Time-of-Flight Magnetic Resonance Angiography Study.
Internal watershed infarcts are mainly caused by hemodynamic impairment related to carotid stenosis, while cortical watershed infarcts are mostly caused by microembolic mechanisms.
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