An electrocardiogram (EKG) is a diagnostic test that records the electrical activity of the heart. The electrocardiogram is a noninvasive test. The heart's electrical activity is recorded by attaching small contact electrodes to the limbs and chest wall. This allows recording of electrical activity onto paper printed from the electrocardiograph machine.
The EKG is the test of choice for diagnosis of abnormal heart rhythms and also can be useful for identification of heart enlargement or drug effects on the heart. An EKG is often recorded during anesthesia. An EKG is indicated whenever a heart rhythm problem is suspected. Often an EKG will be recorded when a heart murmur is detected, when there is x-ray evidence of heart enlargement, or when cardiovascular symptoms such as fainting occur. There is no real contraindication to performing this test; however, it should be appreciated that a normal EKG does not exclude the possibility of heart disease. As with all tests, the EKG is not 100 percent accurate.
There are variants of the standard EKG. Oscilloscope EKGs are monitors that display the electrocardiogram trace on a screen. These are used for quick assessment of heart rhythm, for anesthetic monitoring, and in critical care settings. The Holter electrocardiogram is an ambulatory EKG that is tape-recorded for later playback. The pet wears the recording box for 24 hours and the electrocardiogram is recorded continuously during that period. This test is used in the evaluation of serious heart rhythm disturbances. An event monitor EKG is an owner-activated monitor that can be worn by the pet for many days. This type of monitor is used in pets affected by fainting or sudden collapse. When a spell is observed, the button is pushed and the EKG is recorded.
What Does an Electrocardiogram Reveal?
An electrocardiogram is used to reveal abnormalities of heart rate and electrical rhythm (arrhythmias). The EKG tells us about electrical problems of the heart, but not necessarily about heart enlargement, valve disease, or heart muscle problems. While the EKG can be a "screening test" for serious heart disease, it does not detect all heart problems. In fact, the EKG is actually a complementary examination to the stethoscope exam, chest X-ray, and echocardiogram (ultrasound). One also must appreciate that the routine electrocardiogram is about 1 to 2 minutes long. When there are sporadic electrical disturbances of the heart, these may not be detected by a routine exam. In such cases, a Holter or Event monitor EKG is needed to diagnose the problem.
