What to expect when undergoing this test
By Richard N. Fogoros, MD
Medically reviewed by Yasmine S. Ali, MD, MSCI
The electrocardiogram, also referred to as EKG, ECG, or 12-lead ECG, is a non-invasive diagnostic test that evaluates your heart's electrical system to assess for heart disease. It uses flat metal electrodes placed on your chest to detect the electrical activity of your heart as it beats, which is then graphed.
Your healthcare provider can analyze the patterns to get a better understanding of your heart rate and heart rhythm, identify some types of structural heart disease, and evaluate cardiac efficiency.
Purpose of an EKG Test
An ECG detects your heart's electrical rhythm and produces what's known as a tracing, which looks like squiggly lines. This tracing consists of representations of several waves that recur with each heartbeat, about 60 to 100 times per minute. The wave pattern should have a consistent shape. If your waves are not consistent, or if they do not appear as standard waves, this is indicative of heart disease.
There are a variety of characteristic changes that occur with different heart problems, and your healthcare provider can look at your ECG wave patterns to see if they are suggestive of certain types of heart disease.
Many healthcare providers order an ECG as part of a yearly medical examination to screen for heart disease. This may apply to you if:
You have had heart disease or other heart problems in the past.
You have a medical condition that predisposes you to heart disease, such as hypertension, diabetes, high cholesterol, or inflammatory disease.
You have other significant risk factors for cardiac disease.1
Electrocardiography may also be recommended if you have signs or symptoms of heart disease, such as chest pain, shortness of breath, heart palpitations, lightheadedness, dizziness, or fainting spells. Likewise, if you have signs of a TIA or stroke, such as vision changes, numbness, weakness, or communication problems, you are also likely to need an ECG because some types of heart disease can cause a stroke.2
If you have heart disease, you may need periodic ECG testing to evaluate whether your disease is worsening and to monitor the treatment effects of your heart medications.
An ECG is also required prior to any type of heart surgery, including surgery for pacemaker placement. A pre-operative ECG is also needed before any surgical procedure that involves general anesthesia because heart disease increases the risk of adverse events from anesthesia. The screening also helps your anesthesiologists as they plan your anesthetic medications and surgical monitoring.
Conditions
There are a number of conditions that can be detected when your healthcare provider checks your pulse, such as tachycardia (rapid heart rate), bradycardia (slow heart rate), and arrhythmia (irregular heart rate). EKG wave patterns can verify these alterations in your heart rhythm, and certain changes in the shape of the waves provides information about the specific type of heart disease and which region in the heart is affected.
Limitations
The ECG is one of the most commonly used tests in medicine because it can screen for a large variety of cardiac conditions, the machines are readily available in most medical facilities, the test is simple to perform, safe, and relatively inexpensive.
That said, an ECG has its limitations:
The ECG reveals the heart rate and rhythm only during the few seconds it takes to record the tracing. If an arrhythmia (heart rhythm irregularity) occurs only intermittently, an ECG might not pick it up, and ambulatory monitoring may be required.
The ECG is often normal or nearly normal with many types of heart disease, such as coronary artery disease.
Sometimes, abnormalities that appear on the ECG turn out to have no medical significance after a thorough evaluation is done.
Risks and Contraindications
ECG is a safe test that does not cause health complications. There are no medical conditions associated with any risks or adverse effects from an ECG.
Before the ECG Test
If your healthcare provider or cardiologist orders an ECG, you generally do not need to have any special tests or procedures to prepare for it. In fact, you can have it right in the healthcare provider's office if there is available time, space, and equipment. Sometimes, depending on the reason for your ECG, your healthcare provider may ask you to stop taking some of your medications for a day or two before the test.
Timing
If you are having an ECG as part of a healthcare provider's visit, anticipate needing an extra 10 to 15 minutes for the test. If you are going to have a special visit for the ECG, you should expect it to take longer because of the registration and check-in process.
Location
Often, an ECG is done in the healthcare provider's office, sometimes in the same exam room where you are seeing the healthcare provider. Your healthcare provider's clinic may have a separate space where you may need to go to have your test.
What to Wear
You will need to change into a hospital gown so that electrodes can be placed on your chest. You may be asked to remove large necklaces or chains if they dangle or get in the way, but you do not need to worry about electrical interference from metal jewelry.
Food and Drink
You can eat or drink whatever you want prior to your test. If your healthcare provider is worried that you have an especially rapid heart rhythm, you may be asked to abstain from caffeine for six to 10 hours before the test.
Cost and Health Insurance
Generally, an ECG is covered by most health insurance plans, but there are always exceptions. If you are insured and concerned that your plan may not cover the test, or if you have a plan with minimal coverage, you might want to check your benefits in advance. As with many procedures, your plan may also require you to pay a copay, and you should be able to find out by calling the number on your insurance card.
What to Bring
When you go for your ECG, you should bring your test order form (if applicable), your health insurance card, a form of identification, and a method of payment.
During the Test
Your test will be performed by a healthcare provider, a nurse, or a technician.
Pre-Test
You will be asked to change into a hospital gown and lie down on an examination table.
Once in position, a total of 10 electrodes are attached with a sticky, but easy-to-remove adhesive. One electrode is placed on each arm and leg, and six on the chest.
Throughout the Test
Each electrode is a flat, coin-shaped plate with wires attached to the ECG machine, which looks like a computer. The electrodes detect electrical activity produced by the heart and transmit this information to the machine, where it is processed and saved electronically or printed out as an ECG tracing.
Readings will be taken for about five minutes. During this time, you will be asked to remain still, as movement can disrupt the pattern. There is no pain or discomfort associated with this test.
Post-Test
After the test, the electrodes are removed. If there is any sticky material remaining, it can be easily wiped off with an alcohol pad. You may experience some pulling of hair underneath the nodes, but generally, the technicians are very careful with taking them off.
You should not expect any side effects after an ECG, and there are no limitations on your activity.1
Rarely, the adhesive can cause allergic reactions or rashes, which may not be obvious until about 24 hours after the test. If you experience a rash in the area of the electrodes, call your healthcare provider.
Interpreting the ECG Results
The electrical signals generated from the electrodes are processed to obtain the heart’s electrical activity from 12 different angles, each of which shows a separate tracing. By examining any abnormalities on the ECG and which leads they are stemming from, your healthcare provider can get important clues about the status of the heart. Learning to read an ECG and recognize these patterns takes months of training and practice.
The Tracing
A tracing consists of repeated waves that have a standard shape. The waves have sections named the P wave, QRS complex, ST segment, and T wave. There is also a PR interval between the P wave and the QRS complex, and a QT interval between the QRS complex and the T wave.
Different conditions are associated with changes in the height, width, and length of these waves, and the intervals between them. A shortened QT interval, for example, can be a sign of elevated blood calcium levels.3
Your ECG report may have a description of the wave pattern but is unlikely to describe your heart condition in detail. Your healthcare provider needs to take your symptoms and medical history into account when determining whether or not you could have a heart condition.
Your healthcare provider will be able to explain your results to you. Among many things, an ECG can indicate:
Heart arrhythmias, such as premature ventricular complexes or atrial fibrillation
Whether you have conduction abnormalities, which result from issues regarding how the electrical impulse spreads across the heart (such as with a bundle branch block)
Signs of an ongoing or a prior myocardial infarction (heart attack)
Whether you have signs of severe coronary artery disease (CAD), such as stable angina or unstable angina
If your heart muscle has become abnormally thickened, as in hypertrophic cardiomyopathy
Signs of congenital electrical abnormalities, such as Brugada syndrome
Electrolyte imbalances, particularly elevated or decreased levels of potassium, calcium, or magnesium
Congenital (from birth) heart defects
Infections involving the heart, such as pericarditis, which is an infection of the protective tissue surrounding the heart
Follow-Up
While the ECG can make a clear diagnosis of some cardiac conditions, such as a cardiac arrhythmia, it is more often used as a screening test. Therefore, abnormalities seen on the ECG often need to be followed by a more definitive test in order to make a firm diagnosis.
For instance, If the ECG indicates possible coronary artery disease, a stress test or cardiac catheterization might be needed. If ventricular hypertrophy is seen, an echocardiogram is often needed to check for diseases such as aortic stenosis or other structural abnormalities.4
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