Which cardiac condition commonly causes syncope related to reduced cardiac output?

Which cardiac condition commonly causes syncope related to reduced cardiac output?

• A. Hypertrophic cardiomyopathy.
• B. Aortic stenosis.
• C. Chronic bronchitis.
• D. Pulmonary embolism.

Answer: (B)

Syncope related to reduced cardiac output often happens when the brain doesn’t receive enough blood during times of higher demand. Aortic stenosis creates a fixed obstruction to the left ventricle’s outflow, so during exercise the heart can’t increase forward stroke volume. The result is a drop in systemic blood pressure and cerebral perfusion, leading to fainting. This pattern—exertional collapse from an inability to raise cardiac output due to a fixed outflow block—is the classic scenario. While hypertrophic cardiomyopathy can also cause syncope, it’s usually due to dynamic obstruction of the outflow tract and sometimes arrhythmias, not a fixed reduction in forward flow. Chronic bronchitis is a lung condition and isn’t a primary cause of syncope from reduced cardiac output, and pulmonary embolism causes syncope mainly from acute hemodynamic failure rather than a steady, exertional decline in cardiac output.

Syncope related to reduced cardiac output often happens when the brain doesn’t receive enough blood during times of higher demand. Aortic stenosis creates a fixed obstruction to the left ventricle’s outflow, so during exercise the heart can’t increase forward stroke volume. The result is a drop in systemic blood pressure and cerebral perfusion, leading to fainting. This pattern—exertional collapse from an inability to raise cardiac output due to a fixed outflow block—is the classic scenario. While hypertrophic cardiomyopathy can also cause syncope, it’s usually due to dynamic obstruction of the outflow tract and sometimes arrhythmias, not a fixed reduction in forward flow. Chronic bronchitis is a lung condition and isn’t a primary cause of syncope from reduced cardiac output, and pulmonary embolism causes syncope mainly from acute hemodynamic failure rather than a steady, exertional decline in cardiac output.