Download Arrhythmogenic Right Ventricular/ Cardiomyopathy in Boxers

Arrhythmogenic Right Ventricular/
Cardiomyopathy in Boxers
Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)
BASIC INFORMATION
Description
Boxer cardiomyopathy is a disease of the heart muscle of boxers.
The condition causes abnormal heart rhythms (arrhythmias) that
arise in the right ventricle, the large chamber on the right side of
the heart. Because many people confuse this problem with dilated
cardiomyopathy, the disease has been given a new name, arrhythmogenic right ventricular cardiomyopathy (ARVC).
Causes
The heart muscle cells of affected boxers, mainly in the right ventricle, are replaced by fatty or fibrofatty scar tissue. Sometimes
these abnormal changes occur in the left ventricle also. These
changes cause arrhythmias, such as ventricular premature contractions (VPCs) and ventricular tachycardia (VT). (See the handout
on Ventricular Premature Contractions and Tachycardia.) The
overall heart size and function are normal in these dogs. Later in
the disease, however, some dogs develop dilated cardiomyopathy.
(See also the handout on Dilated Cardiomyopathy in Dogs.)
ARVC runs in families of boxers, and a genetic basis for the
heart changes is proposed, although the exact genes that cause this
defect have not yet been identified.
Clinical Signs
Most boxers with ARVC are clinically normal and show signs
only when the arrhythmias are severe. Sometimes arrhythmias
are found on routine physical examination or when an electrocardiogram (ECG) is run as a screening test. Some dogs have fainting episodes or die suddenly from severe ventricular arrhythmias.
Arrhythmias can develop at any age in these dogs.
Diagnostic Tests
In boxers with a family history of sudden death or ARVC, an
ECG or Holter monitoring is often done yearly. (See handout on
Electrocardiography.) The exact age at which screening ECGs
and Holter monitoring should be done is often based on the dog’s
family history.
If VPCs are detected and confirmed by ECG, the diagnosis of
ARVC is made by eliminating all other causes of these arrhythmias.
Since many problems can cause VPCs, extensive testing must be
done to rule out other diseases. Chest and abdominal x-rays and
laboratory tests (including thyroid tests and possibly titers for tickborne diseases and others) are often recommended. An echocardiogram (heart ultrasound) is done to rule out other heart diseases.
TREATMENT AND FOLLOW-UP
Treatment Options
If fainting episodes, VT, or severe VPCs are present, hospitalization is often needed to treat the arrhythmias with injectable medications. The more severe the arrhythmia, the higher the possibility
of sudden death.
Once the heart rhythm is stabilized, several different drugs or
drug combinations can be used orally. Not every drug works in
every dog, so changes may be needed in therapy to control the
ventricular arrhythmia.
• Oral drugs that may be used for the arrhythmias caused by
ARVC include sotalol, mexiletine, and a combination of mexiletine and atenolol.
• If these medications do not control the arrhythmia, then a combination of mexiletine and sotalol may be tried.
• Amiodarone may be used as a last resort and often requires
referral to a veterinary specialist for its administration.
Side effects of antiarrhythmic drugs include lethargy, anorexia,
vomiting, and diarrhea. The last three effects are more common
with mexiletine. Occasionally these drugs can make the arrhythmia worse, so that the dog must be switched to another medication. Amiodarone has multiple side effects, including liver damage
with elevated liver tests, decreased white blood cell counts, and
damage to the thyroid gland.
Follow-up Care
Affected boxers require frequent ECGs until their VT or VPCs
are controlled. Ideally, a Holter monitor is applied to dogs with
non–life-threatening arrhythmias to document the frequency of
the arrhythmias prior to treatment. Then another Holter recording
is done after the drug has reached adequate blood levels to judge
how effective it is in controlling the abnormal beats. Affected dogs
require antiarrhythmic therapy for the rest of their lives.
Prognosis
Boxers whose arrhythmias are well controlled with medications
can live a long time. No drug is 100% effective in preventing sudden death, however. Animals on medication can still die suddenly.
The better the arrhythmia is controlled, the less likely it is for sudden death to occur. Holter monitors provide the best way to evaluate how well the medication is controlling the arrhythmias.
Because this problem has a genetic basis and runs in families,
it is wise not to breed dogs that have ARVC.
IF SPECIAL INSTRUCTIONS HAVE BEEN ADDED, THEY WILL APPEAR ON THE LAST PAGE OF THE PRINTOUT.
Copyright © 2011 by Saunders, an imprint of Elsevier Inc. All rights reserved.