A Holter monitor is a portable, battery-powered electrocardiogram (ECG) device that a patient wears over 24 hours or more in order to continually monitor and record the heart’s electrical activity. The electrical impulses are picked up by electrodes attached to the skin. This is particularly useful for diagnosing arrhythmias that come and go, and may not be present during a single clinic visit.
The monitor itself, about the size of a large smartphone, can be worn or carried in several ways—commonly around the neck or waist. It is put on by a technician, and every heartbeat during the time that it is worn is analyzed and interpreted by a cardiologist.