Holter monitors, event recorders and insertable loop recorders are devices to record a person's heart rhythm over an extended period of time. Abnormalities of the heart rhythm tend to be paroxysmal and more often than not, do not occur while the patient is in the doctor's office being examined. When a patient complains of symptoms that sound like they are due to an abnormal or erratic heart rhythm, it is important to record the rhythm electrocardiographically.

There are many different types of abnormal heart rhythms. Some don't require any treatment. For those that do, the type of abnormal heart rhythm must be known in order to select the proper treatment. What works for one type of abnormal heart rhythm may be ineffective or dangerous for other types of abnormal heart rhythms. Finally, in some people, the monitor shows that heart rhythm was normal when the symptoms occurred. Then, the doctor knows that another cause for the symptoms must be sought.

A holter monitor is generally worn for 24 hours but it can be worn for longer periods of time if needed. ECG electrodes are attached to the patient's chest and are attached by wires to a small recording device which hangs by a small shoulder strap. This records a continuous ECG on a magnetic tape. The patient is also asked to keep a diary, noting the time of activities and symptoms. At the end of the recording period, the patient returns to the doctor's office where the electrodes and monitor are removed. The tape is then analyzed and the recorded heart rhythm is correlated with any symptoms the patient recorded in the diary.

Many times, the symptoms occur rarely and it's hard to catch them even with a holter monitor. For these patients, an event monitor is used. This device is similar to a holter monitor but can be kept for weeks at a time. It continuously records the heart rhythm into a temporary memory The patient is instructed to press a button on the device when the symptoms occur. When the button is pressed, the recording for the preceding few seconds as well as the subsequent few seconds is placed into a permanent memory. Otherwise, the remainder of the recordings in the temporary memory are discarded. The permanently stored recordings can be transmitted back to the doctors office over standard telephone lines for instant analysis.

For symptoms that occur even more rarely, such as once every six months, there is the insertable loop recorder. This is a small metal device, about 3/4 inch by 2 1/2 inches that is implanted under the skin in the chest using a local anesthetic. This functions just like the event monitor except that it can be left in indefinitely. The patient uses a hand help activator to tell the device to permanently store the heart rhythm when symptoms occur. The device can be "interrogated" through the skin to determine what the heart was doing when the symptoms occured. The device is removed when no longer needed.

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