Final answer:
Ventricular Fibrillation and Ventricular Tachycardia are potentially lethal cardiac arrhythmias, while Sinus Bradycardia is typically not lethal unless associated with serious symptoms.
Step-by-step explanation:
Potentially lethal cardiac arrhythmias include Ventricular Fibrillation and Ventricular Tachycardia. These arrhythmias are types of ventricular arrhythmias that can be life-threatening and may require immediate medical attention, such as defibrillation. Ventricular Fibrillation is particularly dangerous as it results in the heart beating in an uncontrolled manner, preventing it from effectively pumping blood, and can lead to brain death very quickly if not treated. On the other hand, Ventricular Tachycardia is a condition where the heart beats very rapidly, also posing significant risks. Sinus Bradycardia, although slower than normal heart rhythm, is not typically classified as lethal unless it leads to significant symptoms or hemodynamic instability.