When during the cardiac cycle is the heart most susceptible to commotio cordis?

The heart is most susceptible to commotio cordis during the upslope of the T-wave. Commotio cordis occurs when a blunt force to the chest leads to ventricular fibrillation, typically triggered by a precise timing of impact relative to the cardiac cycle.

During the upslope of the T-wave, the heart is in a vulnerable state where repolarization is occurring. This is critical because if a traumatic impact occurs during this phase, it can disrupt the electrical activity of the heart, leading to fatal arrhythmias like ventricular fibrillation. The timing of the impact is essential; it is during this particular period—when the cardiac myocytes are more susceptible to electrical disturbances—that a sudden impact can push the heart’s electrical activity into dysfunction.

The other phases of the cardiac cycle, such as during the downsloping of the T-wave, the downslope of the R-wave, or at the end of the QRS complex, do not carry the same risk. During these times, the heart is either repolarizing or contracting, making it less susceptible to the chaotic electrical disturbances that would lead to arrhythmias. Thus, the upslope of the T-wave represents the interval when the heart is most vulnerable, validating why this is