Ettinger: Textbook of Veterinary Internal Medicine, 7th Edition Arrhythmias and Antiarrhythmic Therapy Nick A. Schroeder What is an arrhythmia?
An arrhythmia is a disturbance in the electrical activity of the heart. Dogs and cats may
have arrhythmias secondary to underlying cardiac disease or from non-cardiac causes.
Careful assessment of the heart by the veterinarian is necessary to determine any
potential causes and blood tests, radiographs (x-rays), electrocardiography (EKG), Holter monitoring (24 hour EKG), event monitoring echocardiography (ultrasound of
the heart) may be required to help identify any causes. If an arrhythmia causes an
animal to have serious problems by reducing blood flow or blood pressure, resulting in
an exacerbation of heart failure or causing syncope (fainting), then medication may be warranted to suppress these arrhythmias. Drugs used for such purposes are called
antiarrhythmics. Arrhythmias are broadly classified into those that cause excessively
slow or fast heart rates. Examples of those causing slow heart rates include
atrioventricular block (AV block) and sick sinus syndrome. These arrhythmias may ultimately require pacemaker implantation. Examples of fast arrhythmias include atrial
fibrillation (AF or "A-fib"), supraventricular tachycardia (SVT) and ventricular
tachycardias (VT or "V-tach"). A pet's normal reaction to heart failure is a fast heart rate
(sinus tachycardia), which alone can worsen the animal's condition, and antiarrhythmics may be prescribed to slow the heart rate, allow for better filling of the
heart's chambers and improve the heart's ability to function as a pump. What is the treatment for an arrhythmia?
A group of drugs called sodium-channel blockers can be used to treat certain arrhythmias. Most commonly, these are used to treat arrhythmias coming from the
lower portion of the heart such as ventricular tachycardia. Examples of these
medications for oral use at home include procainamide (Procan, Pronestyl,
mexiletine Mexitil) and disopyramide (Norpace). These drugs act specifically on diseased cells in the heart to increase the threshold to electrical excitement.
Another group of antiarrhythmics are called beta-blockers. These drugs can be used to
effectively lower high heart rates, and can help to slow the scarring that occurs in congestive heart failure. These drugs are commonly prescribed for animals with atrial
fibrillation and supraventricular tachyarrhythmias. Examples of beta-blockers include
propranolol (Inderal, atenolol (Tenormin), metoprolol (Toprol), carvedilol
(Coreg) and sotalol (Betapace). Beta-blockers can cause the heart to contract with less energy. Careful monitoring by the veterinarian is necessary to minimize side effects
such as low blood pressure, collapse and worsening of congestive heart failure.
Copyright 2010 by Saunders, an imprint of Elsevier Inc.
Potassium-channel blockers are a group of antiarrhythmics that act by reducing the
ability of the heart to initiate arrhythmias. Examples of these include amiodarone
(Cordarone) and sotalol (Betapace). They may be prescribed to treat certain arrhythmias including ventricular tachycardias. Ventricular tachycardia may be
associated with fainting, and sotalol may be prescribed for animals experiencing these
Calcium-channel blockers comprise yet another group of drugs with antiarrhythmic
activity. These medications can be useful for supraventricular tachycardias including
atrial fibrillation, and may be used in combination with other drugs to optimize their
effects. Examples of calcium-channel blockers include diltiazem (Dilacor, Cardizem) and verapamil (Isoptin, Calan, Veleran). Other calcium-channel blockers such as
amlodipine (Norvasc) selectively act on smooth muscle in the peripheral arteries and
are used to treat high blood pressure (hypertension).
All antiarrhythmics medications require careful monitoring by a veterinarian
experienced with their use. Any antiarrhythmic can predispose animals to arrhythmias
under certain circumstances, thus the benefits of their use must outweigh the risks of
administration. Your veterinarian may wish to use specific drugs. Some conditions have
been shown to respond best to a specific drug or combination of drugs. For this reason, one product may be superior to another under the known disease circumstances.
Copyright 2010 by Saunders, an imprint of Elsevier Inc.
The Circle of Life Laura Hoge, RYT, CMT is the owner of Peaceful Edge Yoga, LLC offering private yoga instruction, western and Thai massage to the Central/Northern NJ area since 2003. She currently teaches Thai massage within the Tao Mountain Network. Prior to her current profession, Laura worked as a New Jersey State Licensed Funeral Director and spent years helping clients process g
Ettinger: Textbook of Veterinary Internal