Your pet's heart works constantly. When your veterinarian wants to know how well it's working, one of the most useful tools available is the electrocardiogram, also called an ECG or EKG. The test is quick and painless, and it gives your vet important information about your dog's or cat's heart.
What is an Electrocardiogram?
An electrocardiogram records the electrical activity of the heart. Each heartbeat starts with a small electrical signal. That signal travels through the heart muscle in a set pattern and makes the chambers contract and pump blood through the body. An ECG detects these signals and shows them as a waveform on a monitor or printout, so your vet can see exactly how your pet's heart is beating.
How the Test Is Performed
The test is non-invasive and usually takes only a few minutes.
- Your pet typically lies gently on their right side, though some pets can be tested while standing or resting on their chest.
- Small sensors called electrodes are attached to the skin, usually near the elbows and knees. They may be soft clips or adhesive pads.
- A small amount of alcohol or conductive gel is applied so the sensors pick up a clear signal. Shaving is rarely needed.
- The machine records the heart's electrical activity while your pet stays calm and still.
The procedure doesn't hurt, and most pets don't need sedation. Many pets lie quietly while a team member or their owner comforts them. In some cases, the recording is sent to a board-certified veterinary cardiologist for expert review.
Why Is an ECG Performed?
Your veterinarian may recommend an ECG for several reasons:
- Abnormal heart rhythm or rate: The vet hears an irregular heartbeat, or a heart rate that is too fast or too slow, while listening with a stethoscope.
- Heart murmur: The vet wants more information about a murmur or suspected heart disease.
- Fainting or collapse: Episodes of fainting (syncope), collapse, or sudden weakness can be caused by rhythm problems.
- Exercise intolerance: The pet tires easily, coughs, breathes hard, or seems lethargic.
- Pre-anesthetic screening: This is especially common for senior pets or pets with known health concerns, to make sure anesthesia and surgery are as safe as possible.
- Monitoring during anesthesia: The ECG tracks the heart continuously throughout a procedure.
- Breed screening: Some breeds are prone to specific heart conditions, such as Boxers, Doberman Pinschers, Cavalier King Charles Spaniels, and Miniature Schnauzers. Cats are also prone to cardiomyopathy.
- Electrolyte imbalances: Conditions such as urinary blockage in cats, kidney disease, or Addison's disease can change potassium levels and disrupt the heart's rhythm.
- Trauma or serious illness: Rhythm problems can follow injuries such as being hit by a car, or illnesses such as bloat (GDV), severe infection, or toxin exposure.
- Monitoring treatment: The vet tracks known heart disease or checks how well heart medications are working.
What Do the Results Tell the Veterinarian?
An ECG tracing is made of a repeating pattern of waves. Each wave represents a specific stage of the heartbeat:
- P wave: The electrical signal spreading through the upper chambers of the heart (the atria).
- QRS complex: The signal spreading through the lower, main pumping chambers (the ventricles).
- T wave: The ventricles electrically "resetting" (repolarizing) before the next beat.
Your vet looks at the shape, size, and timing of these waves, and the spacing between them, to judge whether the heart's electrical system is working normally.
What Information Is Gained From the Test?
An ECG can give your veterinarian valuable information about several aspects of heart health.
Heart rate. The ECG measures exactly how fast the heart is beating. A rate that is too fast (tachycardia) or too slow (bradycardia) for your pet's species, size, and situation can point to an underlying problem.
Heart rhythm. This is where the ECG is most valuable. It is the best tool for identifying arrhythmias, which are abnormal heart rhythms, including:
- Premature beats: Extra beats that start in the atria or ventricles, such as ventricular premature complexes (VPCs).
- Atrial fibrillation: A rapid, chaotic rhythm often linked with enlargement of the heart.
- Ventricular tachycardia: A potentially dangerous fast rhythm that starts in the lower chambers.
- Heart block (AV block): A delay or interruption of the signal between the upper and lower chambers.
- Sick sinus syndrome: A problem with the heart's natural pacemaker, which can cause pauses and fainting.
Signs of heart enlargement. Changes in the size and shape of the waves may suggest that certain chambers are enlarged. An ECG can raise this suspicion, but it can't confirm it on its own.
Electrolyte and systemic problems. Characteristic ECG changes can show imbalances such as high potassium. Some of these imbalances are life-threatening and need emergency treatment.
Response to treatment. Repeat ECGs help your vet judge whether medications are controlling an arrhythmia and whether doses need adjusting.