How does an implantable cardioverter-defibrillator (ICD) work?

An implantable cardioverter-defibrillator (ICD) primarily functions to continuously monitor the heart rhythm. When it detects life-threatening arrhythmias, such as ventricular tachycardia or ventricular fibrillation, the device delivers an electrical shock to restore a normal heart rhythm. This ability to distinguish between normal and dangerous heart rhythms is crucial for patient safety, particularly for those at high risk for sudden cardiac arrest.

In contrast, the other options do not accurately describe the primary function of an ICD. Increasing heart rate during emergencies may be a function of a pacemaker in certain situations but is not the main role of an ICD. Providing continuous medication is not a function of an ICD, as that would typically be managed through other means such as oral medications or infusion therapy. Lastly, while some ICDs can have pacing capabilities, their primary purpose is not to function solely as a pacemaker; that role is more specifically tied to devices designed for managing bradycardias. Thus, option B encapsulates the critical purpose of an ICD effectively.