A 72-year-old woman is admitted with sudden hypotension, chest pain, and syncope five days after an anterior ST-elevation myocardial infarction treated medically. She rapidly deteriorates and develops signs of cardiogenic shock. The provider suspects free-wall myocardial rupture. Which of the following best explains the pathophysiologic mechanism responsible for this complication?
Progressive ventricular dilation from chronic volume overload leading to wall thinning
Acute coronary vasospasm causing recurrent ischemia and infarct extension
Structural weakening of the infarcted myocardium as necrotic myocytes are removed by phagocytes before collagen scar formation occurs
Compensatory hypertrophy of viable myocytes increasing wall stress
The Correct Answer is C
A. Progressive ventricular dilation from chronic volume overload leading to wall thinning: Chronic ventricular dilation can increase wall stress over time, but free-wall rupture is an acute complication that typically occurs within days of myocardial infarction due to localized structural failure, not gradual volume overload.
B. Acute coronary vasospasm causing recurrent ischemia and infarct extension: Coronary vasospasm may exacerbate ischemia, but it does not directly cause myocardial rupture. Free-wall rupture occurs because of mechanical weakness in the infarcted tissue rather than transient ischemic episodes.
C. Structural weakening of the infarcted myocardium as necrotic myocytes are removed by phagocytes before collagen scar formation occurs: After an infarction, inflammatory cells digest necrotic cardiomyocytes, leaving the infarcted region structurally weak. Collagen deposition and scar formation occur later. During this vulnerable period, increased wall stress can precipitate rupture, leading to sudden hypotension, cardiac tamponade, and cardiogenic shock.
D. Compensatory hypertrophy of viable myocytes increasing wall stress: While surviving myocytes may hypertrophy to compensate for lost contractile tissue, this adaptive change occurs over weeks to months and is not the immediate cause of acute free-wall rupture following myocardial infarction.
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Related Questions
Correct Answer is D
Explanation
A. Basophils:Basophils are circulating granulocytes involved in allergic reactions and parasitic infections. They release histamine and other mediators but do not form multinucleated giant cells or participate directly in granuloma formation in the lungs.
B. Endothelial cells:Endothelial cells line blood vessels and are involved in vascular permeability and inflammation. They do not differentiate into multinucleated giant cells and are not a source of granulomatous structures.
C. Eosinophils:Eosinophils are primarily involved in parasitic infections and allergic responses. While they may be present in some inflammatory infiltrates, they do not fuse to form the multinucleated giant cells seen in granulomatous lung disease.
D. Macrophages:Multinucleated giant cells in granulomas are derived from activated macrophages. These macrophages fuse in response to persistent antigens, such as Mycobacterium tuberculosisor fungi, and coordinate a chronic inflammatory response to contain pathogens that are difficult to eradicate.
E. Neutrophils:Neutrophils are the first responders in acute inflammation and are effective in phagocytosing bacteria. They do not fuse to form multinucleated giant cells, which are a hallmark of chronic granulomatous inflammation.
Correct Answer is A
Explanation
A. Valves are mostly acellular with limited blood supply, reducing the local inflammatory response and allowing bacterial growth:Native heart valves are composed primarily of connective tissue with very few cells and minimal vascularization. This acellularity and poor blood supply limit delivery of immune cells and antibodies, creating a site where circulating bacteria can adhere to damaged endothelium or preexisting vegetations and proliferate.
B. Valves are highly vascularized, promoting rapid bacterial dissemination:Heart valves are actually avascular. High vascularization would improve immune surveillance, making it less likely for bacteria to establish infection, which is the opposite of what occurs in infective endocarditis.
C. Valves contain abundant immune cells that trigger excessive inflammation:Valves contain very few resident immune cells. The lack of immune surveillance, rather than excessive inflammation, is the key factor that allows bacterial colonization in endocarditis.
D. Valves experience turbulent flow that mechanically damages leukocytes:Turbulent flow can cause endothelial damage, creating a nidus for bacterial adhesion, but it does not directly impair leukocyte function. The main reason bacteria proliferate is the acellular, poorly vascularized nature of valve tissue, not mechanical leukocyte damage.
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