Ventricular Tachycardia in Dogs
Ventricular tachycardia (VT) is a potentially life-threatening disease of the heart that causes arrhythmia, an abnormally fast heartbeat. Ventricular tachycardia can degenerate into ventricular fibrillation, a condition in which the ventricles (the bottom two heart chambers) become disorganized, contracting chaotically. This state can result in asystole – a sudden lack of electrical activity in the heart – and sudden death. VT may be due to an underlying heart disease, a metabolic disease, or an electrolyte imbalance.
The heart is divided into four chambers: the two top chambers are called the atria (singular: atrium) and the bottom chambers are called the ventricles. The heart has an electrical conduction system that is responsible for controlling the heart rate. This electrical conduction system generates electrical impulses (waves), which propagate throughout the musculature of the heart, stimulating the heart's muscles to contract and push blood through the interior arteries and out into the body. Ventricular tachycardia is related to abnormal behavior in the ventricles.
Ventricular tachycardia may occur in structurally normal hearts, as hereditary arrhythmias, or may be a consequence of myocardial abnormalities associated with cardiomyopathy (heart muscle disease), significant valvular disease, or myocarditis (heart muscle inflammation). To date, there is no medical therapy available that is known to prevent sudden death in dogs afflicted with ventricular tachyarrhythmias.
Symptoms and Types
- Fainting (syncope)
- Exercise intolerance
- Sudden death
- May be without symptoms
- Increased heart rate
- Signs of congestive heart failure (CHF)
- Cardiomyopathy (disease of the heart muscle)
- Congenital defects (especially subaortic stenosis – narrowing of the aortic passage)
- Chronic valve disease
- Gastric dilation and volvulus (stomach turns and flips on itself)
- Traumatic inflammation of the heart
- Digitalis toxicity (heart medication)
- Cancer of the heart
- Myocarditis - inflammation of the heart muscle
- Pancreatitis - inflammation of the pancreas
If your dog is unstable, your doctor will apply treatment based on the symptoms before diagnosing the cause of the ventricular tachycardia. (See the treatment section below.) If your dog is stable, your veterinarian will begin with a complete physical exam of your dog. You will need to give a thorough history of your dog's health, onset of symptoms, and possible incidents that might have led to this condition. A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, a urinalysis and an electrolyte panel. The electrolyte panel will show if there is hypokalemia and hypomagnesemia. The bloodwork may show evidence of pancreatitis and hyperthyroidism.
An electrocardiogram (ECG, or EKG) recording can be used to examine the electrical currents in the heart muscles, and may reveal any abnormalities in cardiac electrical conduction (which underlies the heart’s ability to contract/beat), and an echocardiogram (ultrasound imaging for the heart) will be performed to check for structural heart disease. A long-term ambulatory (portable) electrocardiograph recording of the heart's electrical activity, using a Holter monitor, can be used for detecting temporary ventricular arrhythmias in patients with unexplained syncope or weakness. The Holter can be especially useful for animals, since it can be worn as a vest, allowing your dog freedom of normal movement, which, when taken into account with a diary kept (by the pet caretaker) while the monitor is being worn, can give your veterinarian a reference frame for when the heartbeat irregularities are most likely to occur.
If your dog is stable, electrolyte abnormalities will be corrected using fluid administration. Echocardiogram and use a 24-Holter to establish a true baseline of the arrhythmia quantity and quality.
If your dog is unstable (inactive and lying down, weak, or frequent fainting), immediate intravenous treatment in a hospital setting with continuous ECG monitoring may be required. Once the arrhythmia is controlled and your dog's blood pressure has stabilized, oral medication should be started. The medication will be based on your dog's overall health, and how well your dog is able to tolerate the episodes of VT and how frequently they occur. Medications may be given to suppress future episodes, and your dog's activity level will probably need to be minimized. A follow-up 24-hour Holter will be required to test the efficacy of the anti-arrhythmic medication.
Living and Management
Unfortunately, dogs with ventricular tachycardia will sometimes die suddenly. Exciting situations (i.e., those that cause the heart to speed up) will need to be avoided in order to avoid provoking a ventricular tachycardia episode. This appears to be especially true in regards to the Boxer breed. Your veterinarian will schedule subsequent follow-up appointments with you for your dog as necessary.