What is the defining characteristic of cardiac arrest?

The defining characteristic of cardiac arrest is the complete stopping of heart activity. Cardiac arrest occurs when the heart unexpectedly stops beating effectively, leading to a cessation of blood flow to the body's organs and tissues. This is a critical condition that requires immediate medical attention, such as CPR and defibrillation, to prevent irreversible damage or death.

In the context of the other choices, slow heart rate, rapid heart rate, and heart palpitations do not accurately describe cardiac arrest. A slow heart rate (bradycardia) and a rapid heart rate (tachycardia) can be associated with various cardiac conditions but do not signify the absence of heart activity. Heart palpitations involve an awareness of heartbeat irregularities, which can occur when the heart is still functioning, albeit possibly ineffectively. In contrast, the absence of all heart activity clearly delineates cardiac arrest, highlighting the urgency and critical nature of the condition.