Cardiac Diagnostic Testing
An arrhythmia is an abnormality or disturbance in the rate or rhythm of a person’s heartbeat. Arrhythmia monitoring refers to tests physicians use to identify the type and the cause of irregular heart rhythms. Many arrhythmias occur infrequently, so to record the heart’s electrical activity under real-world conditions, physicians use continuous monitor recording, also called ambulatory electrocardiography.
Arrhythmia monitoring refers to tests physicians use to identify the type and the cause of irregular heart rhythms. These tests include electrocardiographic (ECG) testing and electrophysiology (EP) testing.
Arrhythmias are changes in the heart’s normal rate or rhythm and are classified by their location in the heart and by their speed or rhythm. An atrial or supraventricular arrhythmia occurs in 1 of the 2 upper chambers of the heart, the left or right atrium. Ventricular arrhythmias originate in the ventricles, the lower chambers of the heart, and can interfere with the heart’s ability to pump blood to the body.
One way that physicians monitor arrhythmias is by using ECG.
There are 3 forms of ECG testing, which are used to assess the heart’s electrical activity under different circumstances:
- Resting ECG
- ECG stress test
- Ambulatory ECG
Physicians also use EP testing to diagnose arrhythmias. EP testing examines the electrical function of the heart from inside the heart itself using catheters (thin, flexible tubes). Resting ECG, ECG stress tests, and EP testing typically are used for arrhythmias that occur frequently, and ambulatory ECG is used for infrequent arrhythmias.
ECG. Patients are instructed not to exercise strenuously just before ECG. Physicians may also check the patient’s medication regimen to see if he or she is taking certain drugs, such as muscle relaxants, that may interfere with test results.
EP testing. People scheduled for an EP test should not eat or drink anything for 8 to 12 hours before the test. People taking antiarrhythmic medications may be advised to stop taking them prior to an EP test, but other medications often may still be taken.
What to Expect
For frequent or constant arrhythmias, physicians perform a resting ECG or an ECG stress test in a physician’s office or a hospital. Approximately 10 to 15 electrodes are placed on the person’s chest, arms, and legs. For a resting ECG, the patient lies down during the test. For ECG stress test, patients walk on a treadmill for 5 to 15 minutes. For people who cannot exercise, the effects of exercise on the heart can be simulated with drugs.
During an EP test, physicians insert catheters into the coronary arteries to monitor the heart’s electrical function. The physician may also stimulate the heart with electricity to produce and observe the effects of an arrhythmia and map the site it comes from.
To monitor infrequent arrhythmias, the physician uses ambulatory ECG, or event recording. The patient wears portable ECG devices that record arrhythmic events while the patient is away from the physician’s office.
Ambulatory Monitoring Devices
Holter monitors. Holter monitors are worn for 1 to 3 days while the patient goes about normal tasks. The device uses between 3 to 7 electrodes that attach to the patient’s chest. Wires from the electrodes lead to a small battery-powered device that can be clipped onto a waistband or belt, or placed in a small carrying case and slung over a person’s shoulder. The device constantly monitors the heart and records the heart’s rhythms onto a slow-moving cassette tape or a computer disk.
Patients keep a diary of their activities, such as sleeping or eating, so that physicians can associate any arrhythmia with a specific activity. During Holter monitor testing, patients should avoid taking showers or baths and limit the use of small electrical devices, such as electric toothbrushes or razors.
Loop recorders. A loop recorder is also a portable device with electrodes that are worn continuously for an extended period of time. Like Holter monitors, electrodes on a person’s chest that are connected to the loop recorder enable constant monitoring of the heart’s electrical activity. But a loop recorder continues to record and re-record the heart’s activity in a loop. When a person notes arrhythmia symptoms, he or she saves the recording of the heart’s electrical activity before, during, and immediately after the event. The information can be kept or transmitted to the physician.
There are some special restrictions for patients wearing these monitors, such as not showering or bathing, and minimizing the use of electrical devices, such as electric shavers and electric toothbrushes.
In cases where the symptomatic events occur much less frequently, implantable loop recorders can be placed under the skin near the collarbone. The devices may be left in place for up to 18 months. Once an arrhythmia is detected, the recorder can be removed.
Most patients can resume normal activities following an ECG test. When the test is complete, the catheters are withdrawn, pressure is applied to the insertion point to control bleeding, and the person usually is asked to remain lying down for 4 to 6 hours. Within 8 hours, most people can often resume normal activity.
ECG and EP testing rarely cause complications. Very rarely during EP tests, some individuals experience serious rhythm abnormalities, including ventricular fibrillation.
Other potential complications include:
- Infection at the catheter insertion point
- Blood clots in the vein
- Perforation of the myocardium, the muscular tissue of the heart
- Phlebitis, an inflammation of the veins
- Stroke caused by an embolism, or blood clot
- Heart attack