Commotio Cordis is defined as:

• A. A direct blow to the chest during diastole causing a heart attack
• B. A direct blow to the chest during the heart's repolarization period
• C. A direct blow to the chest during the heart's depolarization period - possibly causing ventricular fibrillation
• D. A direct blow to the chest causing atrial fibrillation

Answer: (C)

The concept being tested is that commotio cordis happens when a blunt chest impact hits the heart at a moment in its electrical cycle when the ventricles are particularly vulnerable—during repolarization. This brief window, represented by the repolarization phase (the T wave on an ECG), can trigger a dangerous change in rhythm, most commonly ventricular fibrillation, even in a structurally normal heart.

A blow during repolarization disrupts the heart at its most susceptible moment, which is why this timing best explains why sudden collapse and a lethal arrhythmia can occur without underlying heart disease. If the impact occurred during depolarization, the heart is in contraction and the resulting disturbance would not explain the classic VF outcome seen in commotio cordis. A hit during diastole isn’t the mechanism for sudden cardiac death from chest trauma, and atrial fibrillation isn’t the characteristic lethal rhythm produced by this blunt-impact scenario.