Cardiology · Vascular Disease
The facts most likely to be tested
The response-to-injury hypothesis posits that endothelial dysfunction is the initiating event in atherogenesis, leading to increased permeability and leukocyte adhesion.
Low-density lipoprotein (LDL) particles undergo oxidation within the tunica intima, triggering the recruitment of monocytes that differentiate into macrophages.
Foam cells are lipid-laden macrophages that form the fatty streak, the earliest visible lesion of atherosclerosis.
Smooth muscle cell migration from the tunica media to the tunica intima is stimulated by platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF).
Stable plaques are characterized by a thick fibrous cap composed of collagen and smooth muscle cells, whereas unstable plaques have a thin cap and a large necrotic lipid core.
Plaque rupture and subsequent thrombosis are the primary mechanisms underlying acute coronary syndromes, ischemic stroke, and critical limb ischemia.
Smoking, hypertension, dyslipidemia, and diabetes mellitus are the most significant modifiable risk factors that accelerate the progression of atherosclerotic lesions.
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A 62-year-old male with a history of hypertension and tobacco use presents to the emergency department with crushing substernal chest pain radiating to the left jaw. His ECG shows ST-segment elevation in leads V2-V6. Coronary angiography reveals a thrombotic occlusion of the left anterior descending artery. Histopathology of the culprit lesion would most likely demonstrate a thin fibrous cap overlying a necrotic lipid core.
Which pathophysiological process is most responsible for the acute clinical presentation in this patient?
Plaque rupture and thrombosis
The patient's presentation of ST-elevation myocardial infarction is caused by the rupture of an unstable atherosclerotic plaque, which is characterized by a thin fibrous cap and a large lipid core, leading to acute thrombus formation.
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Etiology / Epidemiology
Driven by dyslipidemia, smoking, hypertension, and diabetes. Chronic inflammatory process of the arterial intima.
Clinical Manifestations
Often asymptomatic until critical stenosis. Presents as angina pectoris, claudication, or transient ischemic attack.
Diagnosis
Coronary angiography is the gold standard. LDL > 190 mg/dL warrants high-intensity statin therapy.
Treatment
Atorvastatin is first-line. Avoid grapefruit juice with statins. Lifestyle modification is mandatory.
Prognosis
Major risk for myocardial infarction and stroke. 70% stenosis is the threshold for clinical significance.
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Epidemiology & Etiology
Primary risk factors include smoking, hypertension, diabetes mellitus, and dyslipidemia. Age and male gender are non-modifiable risks. The process begins in childhood as fatty streaks.
Pertinent Anatomy
Affects large and medium-sized muscular arteries. Predilection for bifurcation points and areas of turbulent blood flow. Common sites include the carotid bulb, coronary arteries, and abdominal aorta.
Pathophysiology
Endothelial injury leads to LDL cholesterol deposition and oxidation in the intima. Monocytes migrate and transform into foam cells, forming the atheroma. Smooth muscle cell proliferation creates a fibrous cap; rupture leads to acute thrombosis.
Clinical Manifestations
Symptoms depend on the vascular bed: claudication in PAD, angina in CAD, and amaurosis fugax in carotid disease. Acute limb ischemia presents with the 6 Ps: pain, pallor, pulselessness, paresthesia, poikilothermia, and paralysis.
Diagnosis
Coronary angiography remains the gold standard for visualization. Carotid duplex ultrasound is the initial screening for carotid stenosis. Ankle-brachial index (ABI) < 0.9 is diagnostic for peripheral artery disease.
Treatment
High-intensity statins (Atorvastatin 40-80mg) are the cornerstone of therapy. Myopathy and rhabdomyolysis are rare but serious side effects. Add aspirin for antiplatelet prophylaxis in established disease.
Prognosis
Major complications include myocardial infarction, ischemic stroke, and aortic aneurysm. Aggressive risk factor modification can stabilize or regress plaques. LDL reduction is the primary target for secondary prevention.
Differential Diagnosis
Vasculitis: systemic symptoms and elevated ESR/CRP
Fibromuscular dysplasia: string-of-beads appearance in young women
Thromboangiitis obliterans: Buerger's disease in young smokers
Embolic disease: sudden onset without chronic claudication
Spasm: Prinzmetal angina with transient ST elevation