Why is the HR increased with MS?

Why is the HR increased with MS?

• A. To compensate for reduced LV outflow
• B. To increase contractility
• C. To reduce LA pressure
• D. To decrease systemic vascular resistance

Answer: (A)

Mitral stenosis narrows the opening through which blood enters the left ventricle during diastole, so LV filling and thus stroke volume fall. To maintain cardiac output, the heart rate rises as a compensatory mechanism; increasing HR helps keep overall blood flow per minute despite the reduced amount of blood that reaches the ventricle each beat. This tachycardia is a response to the decreased LV inflow, trying to preserve forward flow through the stenotic valve. Other ideas—like boosting contractility, lowering left atrial pressure, or reducing systemic vascular resistance—don’t directly address the reduced filling that drives the need for a higher heart rate in mitral stenosis.

Mitral stenosis narrows the opening through which blood enters the left ventricle during diastole, so LV filling and thus stroke volume fall. To maintain cardiac output, the heart rate rises as a compensatory mechanism; increasing HR helps keep overall blood flow per minute despite the reduced amount of blood that reaches the ventricle each beat. This tachycardia is a response to the decreased LV inflow, trying to preserve forward flow through the stenotic valve. Other ideas—like boosting contractility, lowering left atrial pressure, or reducing systemic vascular resistance—don’t directly address the reduced filling that drives the need for a higher heart rate in mitral stenosis.