Which of the following devices is used to reverse cardiac arrhythmias?

An electrocardiograph (ECG or EKG) is used to monitor and record the electrical activity of the heart. While it provides valuable diagnostic information about heart rhythms, it does not have any therapeutic function to reverse arrhythmias. Instead, it helps healthcare providers understand the patient's heart condition.

A glucometer measures blood glucose levels and is primarily used for managing diabetes. It does not play any role in treating or reversing cardiac arrhythmias, as it is not related to heart function or rhythm.

A Holter monitor is a portable device worn by patients to continuously record the heart's electrical activity over 24 to 48 hours. It is useful for diagnosing arrhythmias but does not provide any treatment to reverse them. Its function is strictly observational, allowing for analysis of heart rhythms over time.

A pocket mask is a device used for providing rescue breaths during CPR. While it is important in the context of resuscitation, it does not have the capability to reverse arrhythmias. Its primary purpose is to facilitate ventilation when a person is not breathing.