A Holter monitor is a portable electrocardiogram (EKG) that monitors the electrical activity of an ambulatory (freely moving) patient’s heart for one to five days, 24 hours a day. The sensitive Holter monitor can be used to detect abnormal heart rhythms (arrhythmias) as well as cardiac ischemia – a usually temporary situation in which the heart is not getting enough oxygen-rich blood. Holter monitors may be especially useful to detect transient and short cardiac arrhythmias that might not be present during in-office EKG monitoring.

The device can also help to monitor pacemakers or evaluate how well medications are working, especially antiarrhythmics. Finally, Holter monitors or other forms of ambulatory EKG monitoring might be recommended for heart attack patients and patients with cardiomyopathy. The results of the Holter monitor may be compared to future results should further diagnosis or testing become necessary.

Holter monitors are important in the diagnosis and treatment of premature ventricular contractions, or PVCs. Research has shown that people who experience premature ventricular contractions are more likely to suffer from ventricular tachycardia and ventricular fibrillation. In these conditions, the ventricles beat too rapidly. Ventricular fibrillation is a medical emergency that requires rapid defibrillation to prevent sudden cardiac death. By detecting premature ventricular contractions with a Holter monitor, physicians are better able to design effective antiarrhythmic treatment programs, usually using various antiarrhythmic medications.

Holter monitors consist of electrodes that are attached to the chest of the patient. The electrodes are connected to a small unit that can be worn on a belt or over the shoulder using a shoulder strap. The unit records the data that the patient produces.   

After a patient is outfitted with a Holter monitor, he or she is sent home and instructed to go about usual daily activities while the heart’s electrical activity is recorded on a tape inside the machine. Patients are also told to keep a written diary of their activities and any physical symptoms they may have, such as palpitations (strong, fast or “galloping” heartbeat) or any chest pain. The diary is very helpful to the physician, who will match any written symptoms with the corresponding heart activity when evaluating the printout results.

In recent years, Holter technology has advanced and, in some cases, the devices are capable of transmitting their results over a telephone to the physician's office, called transtelephonic monitoring. Once transmitted, the results can be printed out as a standard EKG and interpreted. Although most of these transtelephonic devices are not equipped continuous monitoring, that option is sometimes available.