Small metal sensors (electrodes or leads) are applied to the skin to record the electrical current generated by the heart with every contraction. The leads transmit this information to a machine that provides a graphic representation of the heart's electrical activity.
Purpose of the ECG
- To detect heart problems, including a recent or ongoing heart attack, abnormal heart rhythms (arrhythmias), lack of blood flow to the heart muscle, birth defects, abnormal position of the heart, coronary artery blockage, areas of damaged heart muscle (as from a prior heart attack), enlargement of the heart muscle, and inflammation of the sac surrounding the heart (pericarditis)
- To detect noncardiac conditions such as electrolyte imbalances and lung diseases
- To monitor recovery from a heart attack, progression of heart disease, or the effectiveness of certain heart medications or a pacemaker
- To rule out hidden heart disease in patients about to undergo surgery
Who Performs ECG
- A doctor, a nurse, or a technician.
Special Concerns about ECG
- Patients at high risk for dangerous arrhythmias may undergo a special ECG procedure called signal-averaged electrocardiography, in which the ECG is performed for 15 to 20 minutes and results over this period are averaged.
Before the ECG
- Tell your doctor if you take any heart medications, which may affect the results.
What You Experience
- You will disrobe and lie down on a table.
- ECG leads are attached to your chest, arms, and legs. A special gel may be applied to these areas to allow for better electrical conduction.
- The electrical impulses generated by your heart are transmitted through the leads to the ECG machine, which prints them as a series of waves (tracings) on a strip of paper. For the most accurate results, remain still, relaxed, and silent.
- The test usually takes 5 to 10 minutes.
Risks and Complications of ECG
After the ECG
- The leads are removed and any electrode gel is wiped away with a damp cloth.
- Results are determined by a doctor who examines the ECG tracings for abnormalities; sometimes a computer is used to help interpret the findings. (In some cases, ECG results may be transmitted over telephone lines to be evaluated at a diagnostic center or clinic.)
- If the ECG indicates an abnormality, additional tests—such as Holter monitoring, echocardiography, or electrophysiology studies—may be needed to establish a diagnosis.
- If the ECG reveals an ongoing heart attack, treatment to stabilize your condition is begun immediately.
- If results are normal, no further testing is usually needed. However, a normal resting ECG does not eliminate the possibility of heart disease. Further tests may still be needed.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media