Which coronary artery is most often involved in myocardial infarction due to its supply to a large portion of the heart muscle?
Circumflex artery
Right coronary artery
Posterior descending artery
Left anterior descending artery
The Correct Answer is D
A. Circumflex artery:
The circumflex artery primarily supplies the lateral and posterior walls of the left ventricle and the left atrium. While occlusion can cause MI, it is less commonly involved than the LAD because it supplies a smaller portion of the myocardium in most individuals.
B. Right coronary artery:
The RCA supplies the right atrium, right ventricle, inferior left ventricle, and parts of the conduction system. While it can cause inferior MI when occluded, it is not the artery most frequently associated with large anterior infarctions.
C. Posterior descending artery:
The posterior descending artery (PDA) is a branch of either the RCA or circumflex depending on dominance. It supplies the inferior septum, but infarctions here are usually smaller than those caused by LAD occlusion.
D. Left anterior descending artery:
The LAD artery supplies the anterior wall of the left ventricle and the interventricular septum, which are critical for left ventricular contraction. Occlusion of the LAD is often called a “widowmaker MI” because it affects a large portion of the myocardium and is associated with high mortality.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
A. Blood flow decreases with increased blood pressure:
Increased blood pressure alone does not necessarily decrease flow; flow depends on pressure gradient and resistance.
B. Blood pressure increases as peripheral resistance increases:
Blood pressure is directly proportional to cardiac output and peripheral resistance (BP = CO × PR). Vasoconstriction increases resistance, raising arterial pressure, while vasodilation lowers it.
C. Peripheral resistance increases with decreased blood flow:
Resistance depends on vessel diameter and viscosity, not directly on blood flow.
D. Peripheral resistance decreases with increased blood pressure:
Peripheral resistance can remain constant or increase; increased blood pressure does not automatically decrease resistance.
Correct Answer is B
Explanation
A. Cardiac output remains unchanged as the heart compensates:
The heart has limited compensatory capacity. A significant LAD blockage reduces perfusion to the anterior wall and interventricular septum, impairing left ventricular contraction and reducing output.
B. There is decreased cardiac output due to impaired left ventricular function:
LAD blockage leads to ischemia of the left ventricle, reducing stroke volume and cardiac output. This can result in heart failure or cardiogenic shock if severe.
C. There is increased cardiac output due to compensatory mechanisms:
Compensatory mechanisms like increased heart rate may temporarily support output, but overall cardiac output declines due to impaired contractility.
D. Cardiac output increases initially, then decreases:
While compensatory mechanisms may attempt to maintain output, in acute LAD blockage, immediate decline in contractility dominates; initial increase is not typical.
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