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Inherited Ventricular Tachycardia in the Dog
Sudden
Death in German Shepherd Dogs
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Ventricular
arrhythmia
Ventricular
arrhythmia is one of the most common cardiac arrhythmias seen in
dogs. In most cases there is either a structural abnormality
within the heart such as the change in cardiac muscle structure which
occurs in cardiomyopathy, or there is a systemic problem affecting the
heart's performance (e.g. septicaemia). Some dogs are born with
an inherited predisposition to sudden death
caused by arrhythmias (irregular heartbeat), including the wildly
racing heart beats called tachycardia. The dogs run, jump and fetch
with the best of them. Only when they lie down and go into REM (rapid
eye movement) sleep do the potentially fatal arrhythmias begin. Some
arrhythmia-affected dogs "outgrow" the problem.
The irregular
rhythm is usually detected during routine physical examination in young
dogs from four to twelve months of age. No sex predilition has
been recorded. Most dogs are outwardly normal before they die suddenly
and there is usually no history of exercise intolerance or fainting.
Most dogs appear outwardly normal before they die suddenly. Death most
often occurs between the age of four to eight months, and often during
sleep or a resting period after exercise.
In North America, a
syndrome of inherited sudden cardiac arrest and death has been reported
to occur in German Shepherd Dogs. Genetic inheritance has been
confirmed but the precise mechanism has not.
ECG
abnormalities
ECG and Holter
monitoring findings vary from one dog to another. A few
supraventricular premature complexes, frequent ventricular bigeminy,
ventricular couplets and periods of ventricular tachycardia have all
been reported.
Postmortem
examination
Routine
post-mortem examination has failed to confirm the final cause of death
or the underlying cause. It is assumed that the dogs die eventually
from ventricular fibrillation.
Treatment
50% of the dogs
with increased ventricular contraction rate (tachycardia) will die
suddenly within the first year of life.
Intravenous
antiarrhythmic drugs (lidocaine and procainamide) are effective drugs
for controlling arrhythmias and are recommended in these dogs, but more
studies need to be performed.
Breeding
Breeding from
lines of affected dogs is not recommended.
