What condition is characterized by a fixed cardiac output that can cause syncope due to its inability to fill vasculature?

Aortic stenosis is characterized by a narrowing of the aortic valve, which leads to a fixed cardiac output because the heart is unable to increase its stroke volume in response to increased demand. This condition can result in syncope, particularly during exertion, because the left ventricle struggles to eject blood effectively through the narrowed valve, leading to inadequate perfusion of the brain and other organs when physical demands rise.

In aortic stenosis, the compensatory mechanisms, such as increased heart rate or enhanced contractility, become insufficient over time as the left ventricle becomes hypertrophied and less compliant. Consequently, patients may experience dizziness or fainting spells due to transient drops in cerebral perfusion during increased physical activity or stress when the heart cannot adequately meet the metabolic demands of the body.

Other conditions, while related to cardiovascular issues, have different mechanisms or presentations. Pulmonary hypertension primarily involves elevated pressures in the pulmonary circulation, leading to right heart strain and failure. Eisenmenger syndrome is a long-term consequence of an unrepaired left-to-right shunt that eventually leads to right-to-left shunting and systemic cyanosis, rather than fixed cardiac output. Marfan syndrome is a connective tissue disorder that can affect cardiovascular structures, such as aortic