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Electrocardiogram (ECG or EKG)
An electrocardiogram is a recording of the electrical activity of the heart. The timing and duration of each electrical phase of the heartbeat is recorded in the ECG tracing. The ECG can provide clues to potential thickening of the heart muscle, structural abnormalities, evidence of heart attacks, heart rhythm abnormalities, inadequate blood and oxygen supply to the heart muscle, or enlargement of the heart's chambers--and at no risk to the patient and relatively little cost. In most cases, if the ECG indicates an abnormality, additional testing may be needed to confirm a diagnosis.
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In an ECG, the electrical activity of the heart is recorded by electrodes that are temporarily attached to the skin with sticky pads. The electrodes transmit the heart's electrical impulses to a device that records these impulses as wave-shaped lines, called a tracing, on a scrolling paper or a monitor. Different sections of the waves represent the various areas of the heart and can impart a lot of information. The main components of the ECG tracing are:
- The P wave, representing currents in the atria
- The QRS complex, representing currents in the ventricles
- The T wave, representing the electrical recovery period of the ventricles
An ECG can reveal the strength and duration of the electrical impulses in the heart. It also can show a deviation in the electrical firing sequence of the heart, which normally starts in the atria and proceeds to the ventricles.
The actual ECG reading takes only 30 to 60 seconds. The test requires no preparation on the part of the patient. Usually, 12 to 15 electrodes are attached to various parts of the body, including one on each arm and each leg and six across the chest. The remaining electrodes are attached at other sites in the chest, neck, and back. After the leads are attached, the readings are recorded. There is no discomfort associated with this test.
Other types of ECG used in the evaluation of cardiomyopathy include:
Continuous or Ambulatory ECG. A Holter monitor is a portable ECG device that makes a continuous, or ambulatory, recording of the heart's electrical activity during a patient's daily routine. Usually worn for 24 to 72 hours, the Holter monitor, which is the size of a small paperback novel or smaller, can detect intermittent heart rhythm irregularities.
Event monitor. For irregular heartbeats that occur sporadically, a small, portable ECG device is used to record the electrical activity of the heart. Ranging from the size of a small paperback novel down to a thin deck of cards, it can be clipped to the clothing and is equipped with electrodes that are readily attached to the chest with sticky pads when the patient experiences the symptoms of an irregular heart rhythm. When the symptoms develop, a push of a button begins the ECG recording. The events can be recorded or transmitted across telephone lines.
Exercise ECG. Also known as a stress test, this procedure assesses how well your heart is working. It can detect coronary circulatory problems and abnormalities related to insufficient blood and oxygen supply to the heart muscle. Rhythm abnormalities triggered by exercise may also be detected and used to identify exercise limits and develop an individual fitness program.
Minor preparations are required for an exercise test, usually involving diet restrictions. The exercise ECG is performed with the individual on a treadmill or stationary bike, so wear comfortable clothing and athletic shoes. The exercise portion of the test usually lasts five to 15 minutes, with the entire test lasting 30 to 40 minutes. The exertion level will increase gradually at regular intervals until the peak exertion level, as determined by the healthcare team, is met. Shortness of breath and sweating are normal, but be sure to tell the healthcare team if you experience chest pain, severe shortness of breath, dizziness, or leg cramps. The ECG readings are recorded continuously before, during, and after exercise. Changes in blood pressure and exercise capacity are also recorded.
Oxygen consumption may also be measured to determine how well the heart and lungs are working together. This involves wearing a nose clip that forces you to breathe through your mouth and a special mouthpiece that measures the amount of oxygen you breathe during exercise.
An exercise ECG carries a small risk because it involves increasing the workload of the heart. The chances of suffering heart problems during the test are remote, however. For instance, just 48 out of 10,000 people taking an exercise ECG experience a serious heart rhythm problem; 3.5 in 10,000 experience a heart attack. Moreover, the healthcare professionals administering the test are trained to diagnose and treat these kinds of complications appropriately and quickly.
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