Download Occult Cardiomyopathy in Doberman Pinschers

Occult Cardiomyopathy in
Doberman Pinschers
Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)
BASIC INFORMATION
Description
Occult cardiomyopathy (OC) is a slowly progressive heart muscle disease that results in abnormal heart rhythms (arrhythmias)
in Doberman pinschers. Because it causes arrhythmias, often ventricular premature contractions (VPCs) and ventricular tachycardia (VT), it is also called arrhythmogenic cardiomyopathy.
Dobermans with OC may have no clinical signs for long periods,
which is why the disease is referred to as occult. Eventually the
dog develops arrhythmias and, later, dilated cardiomyopathy.
Causes
OC runs in families of Dobermans, so a genetic factor is involved.
It can be traced back to the original seven sires of Doberman lines
in the United States, three of which died suddenly when they were
middle-aged. The exact gene or genes causing OC have not yet been
identified, but it may be an autosomal dominant characteristic.
Clinical Signs
OC can start as early as 9-12 months of age, but most dogs are
between 2-4 years old. By 6 years of age, about 50% of Dobermans
have OC. Most dogs with OC have no symptoms. Their arrhythmias may be detected on a routine physical examination or on a
screening electrocardiogram (ECG) or Holter monitor study.
Dogs with more frequent VPCs or VT may have fainting episodes (syncope). About 30% of affected dogs die suddenly, without prior symptoms. Older dogs may have exercise intolerance.
Diagnostic Tests
Since OC is very prevalent in Dobermans, annual screening of
adult dogs often starts at 2-3 years of age, and may include a
24-hour Holter monitor and echocardiogram (heart ultrasound)
study. The likelihood of finding VPCs, VT, or echocardiographic
changes increases as the dog ages. Once arrhythmias have been
found, the only way to diagnose OC is to rule out all other causes
of ventricular arrhythmias. Routine laboratory tests, chest and
abdominal x-rays, thyroid hormone tests, an echocardiogram, and
possibly other tests may be recommended.
TREATMENT AND FOLLOW-UP
Treatment Options
If VT, severe VPCs, or fainting episodes are occurring, it may be
necessary to hospitalize your dog for treatment with intravenous
drugs. The more severe the arrhythmia, the greater the chance of
sudden death. Once your dog’s heart rhythm has been stabilized,
it can be managed on an outpatient basis with the use of several
different drugs, alone or in combination. Not every drug works in
every dog, so sometimes a dog must be switched from one drug to
another to control the ventricular arrhythmias.
• Oral drugs that are used for controlling ventricular arrhythmias caused by OC include the combination of mexiletine
and atenolol, mexiletine and carvedilol, sotalol, or mexiletine
alone.
• If these medications do not control the arrhythmia, then a combination of mexiletine and sotalol may be tried.
• Amiodarone is 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, antiarrhythmic drugs can make the
arrhythmia worse, so that the dog must be switched to another
medication. Amiodarone has multiple side effects, including liver
damage, decreased white blood cell counts, and damage to the thyroid gland.
Follow-up Care
Affected Dobermans 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. 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.
Echocardiograms may be done every 6-12 months to monitor for
evidence of dilated cardiomyopathy, which can follow OC.
Prognosis
Dobermans with infrequent VPCs that are feeling well usually
develop changes on their echocardiograms within 1 year. Within 2
years, their VPCs and heart changes often get worse, and 30-50%
of these dogs may die suddenly.
Dobermans with severe VPCs or VT that are well controlled
with medication can live up to 1 year or longer. No drug is 100%
effective in preventing sudden death. The better the arrhythmia is
controlled, the less likely it is that sudden death will occur. Holter
monitors provide the best way to evaluate how well the medications are controlling the arrhythmias.
If dilated cardiomyopathy develops, the dog’s life span is only
weeks to months (average, 3-4 months). Because OC has a genetic
basis and runs in families, it is wise not to breed dogs that have
the problem.
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