Which rhythm is considered shockable during a cardiac arrest?

Ventricular fibrillation is considered a shockable rhythm during a cardiac arrest because it involves disorganized electrical activity in the heart, preventing it from pumping blood effectively. This chaotic rhythm can lead to cardiac standstill and, ultimately, death if not treated promptly. The application of an electric shock through defibrillation can help to restore a normal rhythm by depolarizing the heart muscle, allowing for the re-establishment of a coordinated heartbeat and effective circulation.

In contrast, a sinus rhythm represents a normal heartbeat and does not require defibrillation, as it indicates that the heart is effectively functioning. Atrial fibrillation, although an abnormal rhythm, does not typically require immediate defibrillation and is often managed with medication or cardioversion instead, depending on the clinical scenario. Asystole, marked as a flatline on the ECG, indicates that there is no electrical activity in the heart that could benefit from defibrillation, which is why it is not considered shockable.