Cardiology - What lies beneath

‘Sparticus’, an 8 year old male Boxer, presented with a history of arrhythmia detected on routine examination. Underlying was something sinister, but it only showed itself in a handful of heartbeats every day.

Sparticus did not look in any way unwell when we first met him. Sparticus was reported to have always been a very healthy and outgoing dog. In fact, his owners had even brought him over from the US when immigrating to Australia. Little did they know that there was the possibility of Sparticus developing a breed-related heart condition that often does not show any abnormalities until the problem is advanced.

Sparticus had Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC), also known as Boxer Cardiomyopathy (BCM). In ARVC the electrical impulses are disturbed, most commonly causing ventricular premature complexes (VPCs). An animal with only occasional VPCs will not typically demonstrate any symptoms of heart disease. However, if multiple successive VPCs occur, the heart cannot produce a normal, effective contraction and there is an increased possibility of acute patient collapse. In the worst case, a prolonged run of VPCs can ultimately lead to complete cardiac arrest and death unless the heart resumes a normal pattern of contraction.

The best way to diagnose ARVC is to perform a 24 hour ECG (Holter monitor examination). 24 hour ECG technology has the ability to capture a handful of abnormal heart beats in upwards of 100 000 normal contractions during a 24 hour period. It does this by faithfully recording the electrical activity of the heart over an extended period and is extremely effective at identifying VPCs. The monitor is strapped to the torso and electrodes placed on the chest whilst the animal goes about its normal activities. The total number of beats, including the abnormal VPCs, is recorded and a vet can subsequently assess whether the patient requires medical management.

In Sparticus’ case, a Holter monitor examination was performed, demonstrating frequent VPCs and runs of rapid ventricular tachycardia. Sparticus now had a diagnosis and treatment could proceed.

An antiarrhythmic (Sotalol) was prescribed for Sparticus in an attempt to control the abnormal electrical activity and reduce the possibility of sudden death. A repeat 24 hour ECG was then performed approximately one month later to monitor the efficacy of the Sotalol and assess the requirements for additional therapy. If Sparticus were to show any clinical signs of exercise intolerance or collapse thereafter, the addition of Mexilitine would be considered.

Nearly a year on Sparticus is still being treated with Sotalol and has had no episodes of collapse or clinical signs which could be associated with the cardiac disease. A further repeat 24 hour ECG revealed a marked decrease in the number of ventricular premature complexes and no runs of ventricular tachycardia. As Sparticus is responding so well to the current dose of Sotalol he will continue on this medication indefinitely. Should medication be halted, he will again be at increased risk of sudden collapse and death, a situation his owners are keen to avoid!

Although his owner’s are aware of the risks of this disease, they continue to take each day as it comes and are happy to enjoy every moment with their very outgoing boxer, with the heart of a real gladiator.

24 hour ECG is available from the Southern Animal Referral Centre and allows us to monitor the arrhythmias hidden amongst over 100 000 beats...

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