Electrocardiogram Ekg - Diagnosing Heart Disease: Heart Disease

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Electrocardiogram (EKG)

The single most useful test for detecting heart problems is the electrocardiogram (EKG). The EKG provides a picture of the electrical activity that regulates the heart's cycle of contraction and relaxation (see Figure 3). Every person with suspected or diagnosed coronary artery disease should have an EKG as part of an initial evaluation. And this test is likely to be repeated periodically to detect whether a heart attack occurred between examinations. (The abbreviation "EKG" comes from the German spelling of this word.)

Should you have an EKG every year? In many cases, the answer is "no," according to the U.S. Preventive Services Task Force, a group sponsored by the U.S. Department of Health and Human Services and composed of physicians and scientists from around the country. In guidelines released in 2004, the task force recommended against routine EKG screening in people at low risk for coronary artery disease, and decided that there was not enough evidence to take a position on routine screening even for people at high risk. That may seem odd, since an EKG can provide valuable information about the functioning of the heart. But the task force urges caution in the use of EKGs for two reasons. First, there is not yet evidence that routine screening actually improves long-term health outcomes. Second, the agency was concerned that EKGs provide too many "false-positive" tests, especially in women, leading to unnecessary additional tests, and too many "false-negative" tests, which miss abnormalities.

Figure 3: Electrical waves of the heart An EKG provides a tracing that corresponds with each phase of a heartbeat. Cardiac contractions begin when the sinoatrial (SA) node sends a wave of electrical impulses through both upper chambers of the heart, known as the atria (A). This activity can be seen on the EKG in the form of a blip, called the P wave (see highlighted area, below left). As the wave moves through the atrioventricular (AV) node and stimulates both lower chambers, or ventricles (B), it generates the QRS complex, the tallest segment of the tracing (see highlighted area, below center). Once the ventricles have contracted, the heart relaxes for a moment as it prepares to repeat the cycle (C). This last phase produces a gentle rise and fall in the tracing, known as the T wave (see highlighted area, below right).

This advice could change in the future, based on new evidence from clinical trials. In the meantime, discuss this issue with your doctor. An EKG is still valuable if it is used along with other diagnostic tools. As a general guideline, if you are middle-aged or elderly and have risk factors for a heart attack — such as high blood pressure, high LDL cholesterol, or diabetes — you should probably have the test every few years, even if you're feeling fine.

In the standard technique, you lie down as the technician applies four electrodes, or leads, to your skin — one on each arm and one on each leg — with a special paste or adhesive pads. These limb leads permit the recording of cardiac electrical activity from different angles. Six additional electrodes are usually placed across your chest (labeled V1 through V6) to detect activity at the front and left side of your heart. The routine electrocardiogram provides information from many different areas, enabling doctors to find the location of possible heart damage.

The EKG gives a reading, or tracing, of the electrical activity that occurs with each heartbeat. This simple, painless test reveals a lot about your heart. By evaluating the tracings of your heart's electrical activity, doctors can see whether your heartbeat is irregular (an arrhythmia), find out whether your heart is enlarged, or even detect the telltale signs of damage from an old heart attack. The EKG is crucial for evaluating chest pain. EKG abnormalities are often enough to enable emergency department physicians to establish a definitive diagnosis of heart attack.

Last updated:	May 03, 2007