RN Nursing · Health Assessment · Practice question
A patient with severe aortic stenosis is experiencing syncope upon exertion. Which mechanism explains this symptom?
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Compensatory tachycardia leading to decreased filling time.
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✓
Reduced cardiac output due to obstruction in the left ventricular outflow tract.
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Pulmonary hypertension leading to respiratory distress.
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Increased preload reducing myocardial oxygen supply.
Answer & explanation
Correct: Reduced cardiac output due to obstruction in the left ventricular outflow tract.
In severe aortic stenosis, the narrowed valve orifice creates a fixed obstruction to blood flow leaving the left ventricle. During exertion, the body demands increased cardiac output, but the stenotic valve prevents the ventricle from meeting that demand. The result is an inability to augment forward flow, causing a drop in systemic blood pressure and cerebral perfusion, which manifests as exertional syncope. The obstruction in the left ventricular outflow tract is therefore the central mechanism. Compensatory tachycardia does occur in cardiac disease and does shorten filling time, but tachycardia alone does not cause the exertional syncope characteristic of aortic stenosis — decreased stroke volume through a fixed obstruction is the key factor. Pulmonary hypertension can be a late complication of aortic stenosis but primarily causes dyspnea and right heart strain, not exertional syncope as a primary mechanism. Increased preload actually supports cardiac output rather than reducing myocardial oxygen supply; moreover, the classic symptom triad of aortic stenosis is syncope, angina, and heart failure — all traceable to impaired forward flow across the obstructed outflow tract. Recognizing this fixed-obstruction physiology is essential when caring for patients with valvular disease.
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