Which arrhythmia is considered the most dangerous?

Ventricular fibrillation is regarded as the most dangerous arrhythmia because it involves the rapid and chaotic electrical activity in the ventricles of the heart, leading to ineffective contractions. This results in the heart's inability to pump blood, causing a cessation of blood flow to vital organs. Without immediate intervention, such as defibrillation, ventricular fibrillation can lead to sudden cardiac arrest and death within minutes.

In contrast, while atrial fibrillation can increase the risk of stroke and may lead to heart failure over time, it is generally not immediately life-threatening. Ventricular tachycardia can also be serious and may lead to ventricular fibrillation if sustained, but it is often a more organized rhythm and might still allow the heart to pump effectively for a short period. Bradyarrhythmias can result in inadequate heart rates but usually do not elicit a rapid decline as seen in ventricular fibrillation. Therefore, the immediate life-threatening nature and the requirement for prompt resuscitation make ventricular fibrillation the most dangerous arrhythmia.