A clinician explains why tachycardia is poorly tolerated in mitral stenosis. Which single mechanism is responsible?

Answer: E. Tachycardia shortens diastole, reducing left ventricular filling across the narrowed valve

Tachycardia in mitral stenosis

In mitral stenosis the valve is narrowed, so blood must cross it during diastole.

Mechanism

• Tachycardia shortens diastole, reducing the time available for blood to flow across the narrowed valve into the left ventricle.
• This impairs left ventricular filling and raises left atrial pressure, worsening pulmonary congestion and risking pulmonary oedema.

Implications

• Avoid and treat tachycardia: good analgesia (epidural), treat anaemia/infection/fever, and shorten the second stage.
• This is why painful labour (with its catecholamine-driven tachycardia) is hazardous.

So shortened diastole reducing filling is the mechanism.