An electrocardiogram (EKG or ECG) is a recording of the heart’s electrical activity as a graph or series of wave lines on a moving strip of paper. This gives the physician important information about the heart. For example, it can show the heart's rate and rhythm. It can also detect decreased blood flow (cardiac ischemia), enlargement (hypertrophy) of the heart, or the presence of either current or past heart attacks.
EKGs are noninvasive, quick, safe, painless and inexpensive tests that are routinely done if a heart condition is suspected. Depending on what the results show, in combination with the patient’s medical history and a physical exam, the physician may order further tests or a combination of medications and lifestyle changes.
Patients may receive an EKG as part of a physical exam in a hospital, clinic or doctor’s office, but the test can be performed almost anywhere.
About electrocardiograms (EKGs)
An electrocardiogram (EKG or ECG) is a recording of the heart’s electrical activity as a graph or series of wave lines on a moving strip of paper or video monitor. The test measures the size, timing and character of the electrical impulses traveling through the heart. This allows the physician to evaluate the heart’s rate, rhythm and certain cardiac problems.
Electrical activity that is fast, slow or otherwise abnormal can suggest various heart irregularities, disease and damage. For example, an EKG may be able to show whether a patient’s heart muscle was damaged as a result of a heart attack.
An EKG is routinely used when heart disease or damage is suspected in a patient. For example, the patient may be experiencing symptoms such as:
Angina(chest pain) resulting from the heart not getting enough oxygen
Strong, fast or otherwise irregular heartbeat (palpitations)
Abnormal, fast or slow heart rhythms (arrhythmias such as atrial fibrillation)
Shortness of breath (dyspnea)
Lightheadedness or loss of consciousness (syncope)
The patient’s first EKG (a baseline EKG) will be compared with EKGs taken in the future, if they become necessary (e.g., after a heart attack).
Conditions diagnosed using electrocardiograms
A physician can use EKGs in the diagnosis of a wide variety of abnormalities and diseases, such as:
Coronary artery disease. A disease in which blood flow to the heart and body is restricted due to hardening of the arteries (atherosclerosis).
Heart attack, either previous or current. The EKG is an essential investigation for diagnosis of heart attack. Initial findings may determine which patient requires emergency cardiac catheterization and angioplasty or administration of thrombolysis.
Arrhythmias. Abnormally fast (tachycardias) or abnormally slow (bradycardias) heart rhythms. For example, the EKG may help the physician detect heart block – abnormally slow heart rhythms due to either the partial or complete loss of electrical communication between the upper chambers (atria) and lower chambers (ventricles) of the heart. A pacemaker may be required as part of treatment. If the arrhythmia only occurs occasionally, the patient may be asked to wear a portable ECG called an event monitor, or Holter monitor. This device allows physicians to gather information about the heart's function over a prolonged period.
Atrial fibrillation. A condition in which the upper chambers of the heart beat abnormally fast and may cause blood clots.
Cardiac hypertrophy. An enlarged or thickened heart muscle. Recent studies have shown benefit in EKGs to help distinguish between benign, physiological heart enlargement (e.g., from sustained, intense exercise – “athlete’s heart”) and pathological enlargement (from significant heart disease).
Cardiomyopathy. A disease in which the heart muscle functions improperly due to a variety of conditions.
Pericarditis. Inflammation of the pericardium – a thin, fluid–filled sac surrounding the heart.
Long QT syndrome. A disorder of the heart’s electrical system, which could lead to fainting (syncope) or sudden cardiac death.
Myocarditis. Inflammation of the heart muscle due to viral or bacterial infection.
Certain congenital heart defects. Heart defects that someone is born with, such as Wolff-Parkinson-White syndrome.
Many people with coronary artery disease, heart valve disease or heart muscle disease will eventually show abnormal EKG readings. However, many EKGs are performed when the patient is at rest, which means certain abnormalities that occur during periods of stress may not show up. Because it is very common to see this false-negative result (e.g., the EKG does not find the damage or abnormality that is really present), a normal EKG is not enough to rule out suspected heart disease.
In some instances, patients may be asked to exercise lightly in conjunction with the EKG. This is called a stress test. It is used to evaluate the function of the heart under more strenuous conditions. If the patient is unable to exercise, they may be given drugs that stimulate the heart to beat more rapidly.
Before, during and after electrocardiograms
Patients should wear comfortable clothing that can be easily removed from the waist up. There is no need to limit eating or drinking before the electrocardiogram (EKG), and the test can be scheduled for any time of day. The test may be done in the physician’s office, a hospital or a clinic.
It is important for the physician to have a patient's complete medical history, including any medications that the patient is taking. Certain medications can affect the result of an EKG.
EKGs are noninvasive, quick, safe and painless. After removing clothing and jewelry from the waist up, the patient will be instructed to lie down. A nurse or technician will clean a series of small areas on the patient’s chest, arms and legs. The technician will apply gel to these areas. Ten or 12 small pads or metal devices (electrodes) are then attached to those clean areas of the skin and connected by wires to the electrocardiograph machine.
The electrodes record only the electricity that passes naturally through the heart. Electricity does not pass from the pads to the patient.
The technician will enter the patient’s information into a computer (e.g., name, age, sex, date). The patient will be asked to lie perfectly still for up to several minutes while resting-heart activity is measured and recorded. Each electrode produces a “tracing” or “lead” of a particular area of the heart and its activity.
Part of the evaluation may include an exercise stress test. This test requires the patient to either walk on a treadmill at varying speeds and elevations, or ride a stationary bicycle, to measure the heart’s activity during physical activity.
EKG results should be immediate. In some cases, the test may be done outside the physician’s office and results transmitted via phone line back to either the physician or another diagnostic center for evaluation. Transtelephonic monitoring, for the purpose of assessing the heart rhythm, can detect abnormal heart rhythms (arrhythmias) that occur when the patient is not in the physician’s office.
Depending upon the results, further treatment may or may not be necessary. If damage or a problem is found, usually a combination of medications and risk-reducing lifestyle changes is prescribed.
Abnormal EKG results will likely result in further testing. This may include imaging studies, such as chest x-ray, echocardiograms, magnetic resonance imaging (MRI) or computed tomography(CAT scan), or nuclear imaging studies that use specialized tracer chemicals to evaluate the heart's health. In some cases, EKGs may be combined with imaging studies, allowing the physician to carefully time the images of the heart to different phases of the heartbeat. This is called a gated study. More invasive testing, including coronary angiogram and electrophysiology studies, may also be recommended. The nature of the follow-up testing depends on what disease is suspected.
If abnormalities are not detected at the physician’s office, then the patient may be asked to wear a Holter monitor, a portable tape recorder that records the heart’s rhythm, usually over a 24-hour period.
Understanding P, QRS and T waves
The heart's electrical system is quite complex. Electrical rhythms begin as impulses emitted from the sinoatrial node, also known as the heart’s “natural pacemaker.” The impulse then travels across a specific route, or pathway, through the upper chambers of the heart (atria), causing them to contract in unison. After moving through the atria, the impulses reach the atrioventricular (AV) node, which rests between the upper and lower chambers of the heart. There, the signals are reorganized before being transmitted into the lower chambers of the heart, the ventricles, along special bundle of electrical-conducting tissue.
Once the impulses reach the ventricles, they serve as a set of instructions, causing the chambers to contract in a routine and consistent manner. If rhythms are interrupted, delayed or sent down the wrong path, the heartbeat may become abnormal, too fast or too slow. These rhythms are detected by an EKG.
The EKG breaks down each heartbeat into a series of electrical waves that give important information about the heart. Three distinct waves are displayed: the P wave, the QRS complex and the T wave. The P wave is associated with activity in the heart’s upper chambers (atria). The QRS complex and the T wave reflect activity in the lower chambers (ventricles). These three waves are critical in diagnosing a wide variety of heart-related conditions.
Questions for your doctor
Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to an electrocardiogram (EKG):
Do I need an EKG? Why?
What will an EKG be able to tell you about my health? What will it tell you about my heart?
How long will it take to perform the EKG?
What does the test involve?
Will the EKG be painful in any way?
What type of results do you expect from my EKG?
Do I need to make any special preparations for the test?
Am I currently taking any medications that might interfere with the EKG results?
What type of conditions could an EKG potentially identify?
Heart attack, either previous or current. The EKG is an essential investigation for diagnosis of heart attack. Initial findings may determine which patient requires emergency cardiac catheterization and angioplasty or administration of thrombolysis.
