How do class 1b antiarrhythmic drugs help in treating ventricular fibrillation?

Sodium Channels: Sodium channels are responsible for the action potential, the depolarization of the heart. These drugs decrease the excitability of the heart because they interfere with the sodium channels. So it will help against ventricular fibrillation.

Weak: Class ib drugs work by blocking the rapid influx of sodium ions during the depolarization phase of the heart’s depolarization-repolarization cycle. This decreases the refractory period, which reduces the risk of arrhythmia. These are weak drugs that do not improve survival and are used only to treat symptoms if at all. They're rarely used in modern treatment.