Irregular contractions of the ventricles; may be fatal unless reversed.

• A. Atrial fibrillation
• B. Ventricular tachycardia
• C. Sinus tachycardia
• D. Ventricular fibrillation

Answer: (D)

Ventricular fibrillation is a life-threatening arrhythmia where the ventricles quiver in a chaotic, uncoordinated way. Because the ventricles aren’t contracting as a unit, they fail to pump blood effectively, so little or no blood reaches the brain and other organs. This creates a sudden risk of collapse and death if not reversed immediately, which is why the description says “irregular contractions of the ventricles; may be fatal unless reversed.”

Atrial fibrillation is irregular too, but the rhythm change starts in the atria, not the ventricles, and while it raises stroke risk, it isn’t the same immediate, complete loss of pumping as ventricular fibrillation. Sinus tachycardia is a fast but regular rhythm that originates in the normal pacemaker of the heart, not from the ventricles. Ventricular tachycardia is a rapid ventricular rhythm that can be dangerous and may deteriorate into ventricular fibrillation, but it is typically a fast, more organized rhythm rather than the chaotic quivering described here.