Holter and event monitors are used to record a patient’s ECG for a prolonged period of time on an outpatient basis. Called ambulatory monitoring, their purpose is to look for evidence of heart problems that come and go, and that are not apparent when a standard ECG is performed. Ambulatory monitoring is particularly useful in diagnosing heart arrhythmias and cardiac ischemia.
With the Holter monitor, electrode leads are applied to the skin (similar to the leads used in recording a standard ECG), and attached to a tape recorder. The patient is sent home and resumes normal activities while the tape recorder records a continuous ECG tracing for 24 or 48 hours.
Event recorders use a circular tape that stores only approximately 30 seconds of a patient’s heart rhythm.
At any given time while a patient is wearing them, event recorders will have the most recent 30 seconds of the patient’s ECG. When the patient experiences a symptom, he or she presses a button that freezes the recording, which is then transmitted by telephone to an interpreting center.