In ambulatory
(electrocardiography), a wearable device called a Holter monitor is used to record the electrical activity of the heart by means of electrodes attached to the chest. The monitor is usually worn for 24 hours or longer and detects intermittent arrhythmias (abnormal heart rates and rhythms). The wearer can press a button on the monitor to mark the recording whenever symptoms occur. The recording can later be analysed to see if the periods of arrhythmia coincide with the symptoms.