Many people have had an electrocardiogram, or EKG, at some point in their lives. Although it is one of the simplest medical tests to perform, it can give doctors a wealth of information, some of which could ultimately prove lifesaving. Many conditions can cause an abnormal EKG result. These range in severity from harmless to potentially life-threatening, such as a heart attack.
The heart contains a network of electrical tissue that conducts impulses to stimulate coordinated heart contractions. This system can malfunction at various places along its path and cause abnormalities in the heart rate, rhythm or both. These changes, called arrhythmias, show distinctive, abnormal patterns on an EKG.
Atrial fibrillation is the most common arrhythmia. It involves rapid, chaotic signaling in the upper chambers of the heart, leading to a fast and irregular heartbeat. Another of the many types of arrhythmia is bundle branch block, in which electrical impulses are hindered from traveling along a large group, or bundle, of electrical tissue. Heart block is another arrhythmia in which the electrical signal from the heart's upper chambers is blocked from reaching the lower chambers. The electrical tissue of the heart occasionally has a "hiccup," resulting in an isolated premature or abnormal beat. These can be detected on EKG but are usually harmless.
Decreased Blood Flow
Angina describes chest pain due to blockage of an artery supplying blood to the heart, depriving the tissue of needed oxygen. Angina may be brief and cause no lasting symptoms, or it may persist and ultimately result in the death of some heart muscle cells -- a heart attack. While a new heart attack can cause dramatic EKG abnormalities, more subtle changes can be seen when blood flow to the heart is reduced but not severely enough to cause a heart attack. If an EKG is done during of a bout of angina, it frequently shows these subtle abnormalities. Detecting these changes allows doctors to intervene and correct the blockage before a heart attack occurs.
Some disorders of the heart valves cause predictable abnormalities on an EKG, as can a variety of disorders that primarily affect the heart muscle itself. Congenital heart disease -- meaning a heart defect that is present since birth -- can cause various EKG abnormalities. Enlargement of the heart or specific chambers of the heart also cause EKG changes. A wide variety of conditions, ranging from certain infections to lupus, can inflame the heart muscle or its lining leading to characteristic EKG abnormalities. Even some lung diseases are known to cause unexpected EKG results.
Medications and Other Causes
Numerous medications can affect the electrical current in the heart and alter the appearance of an EKG test. Some speed up the heart rate and others slow it down. This is not necessarily a side effect as certain medicines are prescribed specifically to stimulates these effects. Some medications do not affect the heart rate but can cause changes in other components of the EKG reading. An abnormal blood potassium level -- either too high or too low -- can also alter the EKG. A very low body temperature, or hypothermia, is another condition that produces an abnormal EKG result.
Reviewed by: Tina M. St. John, M.D.
- Current Medical Diagnosis & Treatment 2014; Maxine A. Papadakis, M.D., et al.
- Circulation: AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram
- American Heart Journal: The Evaluation and Management of Drug Effects on Cardiac Conduction (PR and QRS Intervals) in Clinical Development
- ECG Notes: Interpretation and Management Guide, 2nd Edition; Shirley A. Jones
- Merck Manual Professional Version: Electrocardiography