What is the impact of a blockage in the left anterior descending artery on cardiac output?
Cardiac output remains unchanged as the heart compensates
There is decreased cardiac output due to impaired left ventricular function
There is increased cardiac output due to compensatory mechanisms
Cardiac output increases initially, then decreases
The Correct Answer is B
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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Related Questions
Correct Answer is B
Explanation
A. Atrial contraction:
Atrial contraction occurs just before ventricular systole and contributes minimally to heart sounds. The “lub-dub” of S1 and S2 does not correspond to atrial contraction.
B. Closure of the aortic and pulmonic valves:
The S2 heart sound (“dub”) occurs during ventricular diastole when the aortic and pulmonic valves close. This sound indicates the end of systole and the beginning of ventricular relaxation. It is best heard at the base of the heart.
C. Rapid filling of the ventricles:
Rapid ventricular filling occurs in early diastole and does not produce a normal heart sound. An abnormal sound (S3) can be associated with heart failure.
D. Closure of the mitral and tricuspid valves:
The closure of the mitral and tricuspid valves produces the S1 sound (“lub”), which marks the beginning of ventricular systole. Confusing S1 and S2 can lead to misinterpretation of cardiac auscultation.
Correct Answer is C
Explanation
A. Coronary arteries are filled with blood during atrial contraction:
Coronary arteries are primarily perfused during diastole, not atrial contraction. During systole, contraction of the ventricles compresses the coronary vessels, reducing blood flow.
B. Coronary circulation occurs only during systole:
Coronary blood flow mostly occurs during diastole, because the myocardial contraction during systole compresses the coronary vessels, especially in the left ventricle.
C. Coronary veins return deoxygenated blood to the right atrium:
Coronary veins collect deoxygenated blood from the myocardium and empty it into the right atrium via the coronary sinus, completing the coronary circulation.
D. Coronary arteries supply deoxygenated blood to the heart muscle:
Coronary arteries supply oxygenated blood to the heart muscle, not deoxygenated blood.
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