A 32-year-old woman with moderate mitral stenosis is well compensated until she develops rapid atrial fibrillation with a ventricular rate of 140 bpm, after which she develops acute pulmonary oedema. The dominant haemodynamic reason for her decompensation is:

• A Loss of the atrial contribution to left ventricular filling across the stenosed valve
• B Irregular rhythm causing cyclic underfilling of the right ventricle
• C Loss of atrial contraction increasing pulmonary venous capacitance
• D Tachycardia shortening diastole, reducing the time available for left atrial emptying across the mitral valve ✓

Explanation

Mitral stenosis creates a fixed obstruction, so left ventricular filling depends on a long diastolic filling period and a transmitral gradient. Tachycardia shortens diastole disproportionately, sharply reducing the time for atrial emptying, raising left atrial pressure, and precipitating pulmonary congestion. Loss of the atrial kick (option A) contributes perhaps 20 to 30 percent of filling in normal hearts but matters far less than the shortened diastolic time in stenosis.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.