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.

How Is an Electrocardiogram Done?

Specialized equipment is required to obtain an EKG. The EKG is recorded with the pet either standing or lying on his right side. Conductive gel or alcohol is applied to the skin to better transmit the electrical activity of the heart to the EKG machine. Clip or plate electrodes are attached to the pet's limbs and sometimes to the chest wall. These are attached to thin lead cables that connect to the EKG machine. The position of each wire is important and the operator must follow guidelines carefully. The EKG machine is started and the electrical field generated by heart activity is recorded. The typical recording is 30 seconds to two minutes in duration. Once the recording is completed, the clips are removed and the EKG tracing evaluated. The traditional EKG machine is located in the clinic and results are immediately available. In some instances, the EKG machine is actually a transmitter that links by telephone to a remote EKG (trans-telephonic EKG). Results of this exam may take up to 24 hours. A Holter (tape recorded) EKG is sent to an analysis center and results may not be available until one week after receipt of the tape.

The routine electrocardiogram takes approximately 5 to 10 minutes to perform and interpret. Many veterinarians read the results immediately, but in some situations, your veterinarian may seek consultation with a cardiology specialist. This can be accomplished by faxing the EKG to the specialist or by transmitting the EKG using trans-telephonic equipment.

Is an Electrocardiogram Painful?

The EKG exam is noninvasive and is not painful. Some animals resent the clips or bands used to connect the EKG machine to the skin, but most do not seem to mind the procedure.

Is Sedation or Anesthesia Needed for an Electrocardiogram?

Neither sedation nor anesthesia is needed in most patients. Some pets resent the brief restraint needed for the examination and may need sedation. However, in general tranquilizers and sedatives should be avoided to reduce the drug influence on the heart.