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Posted By: Josh - Vet

The case of the fainting boxer

Genuine repeated episodes of fainting are not something we see that commonly in our patients, so when we do have an animal which is showing intermittent periods of unconsciousness, it can be very intriguing. Reg is a 7 year old Boxer who was brought in on a Monday afternoon after his owner had noticed 2 episodes of fainting during exercise that day.

Prior to this Reg had been fit and healthy and was showing no other symptoms, his appetite was good and his behaviour normal. Like most boxers he was very lively and friendly on examination. It is important in these cases to differentiate fainting (known medically as syncope) from possible seizures; on examination everything appeared normal with Reg and the episodes could have been nothing more than over exertion on a hot day. There are various other causes for fainting, including underlying illnesses and heart conditions, with perhaps the most interesting of these being narcolepsy - a neurological condition where animals spontaneously fall asleep often dozens of times a day! We decided however that we would monitor for now and if any more episodes occurred we would investigate.

Shortly after being seen Reg had another fainting episode that evening and was subsequently booked into the practice for investigations. Boxers, like all dogs, can develop heart conditions as they get older which have the potential to progress to heart failure, and it was this area we decided to investigate first. In most adult dogs heart failure is almost always caused by one of 2 conditions; Dilated Cardiomyopathy (DCM) or Mitral Valve disease (MVD). DCM tends to be seen in larger breeds of dog whereby the heart wall becomes weaker and contracts with less force and is therefore less able to pump blood around the body. MVD is seen more in small breed dogs, especially Cavalier King Charles Spaniels, and occurs as the valves separating the heart chambers degenerate and so blood occasionally flows backwards through the chambers.

In both of these cases the earlier the heart disease is picked up on and medications started, the longer the animals have to live normal lives.  The most common symptoms of heart conditions are a reduced tolerance for exercise, increased difficultly breathing, and development of a cough. Reg had the first of these signs, albeit intermittently. A heart scan was performed and an X-ray taken to determine the heart’s size and contractility – both were normal. Interestingly on the scan Reg’s heart would occasionally speed up from around 80 beats per minute often to over 250! This was clearly abnormal and so we opted to perform an E.C.G, which is the best method of assessing the reason behind such dramatic changes in heart rate. Whilst Reg’s heartbeat was normal for most of the time, it would occasionally have intermittent runs of what we call ventricular tachycardia – this is where the ventricle chambers of the heart beat at a very high rate for a short period of time. This all but confirmed a diagnosis. Reg had a condition known as Arrhythmogenic Right Ventricular Cardiomyopathy (quite the mouthful), otherwise known as Boxer Cardiomyopathy.

This condition almost exclusively occurs in Boxer dogs and is very different from the other 2 conditions discussed. The heart muscle, although appearing normal on scans and x-rays, becomes infiltrated by fatty tissue and therefore has a disruption in its electrical conduction, leading to the periods of very fast heart rates. When the rapid heart rates occur for more than 6-8 seconds, adequate blood flow to the brain is lost and fainting occurs. This explains the fainting episodes seen, and also why Reg was so normal in between the episodes as the majority of the time his heart was functioning normally.

Whilst there is no absolute cure for this condition, Reg is currently being managed on long term Beta blockers which act to reduce the frequency of his episodes. He is doing very well and is still as lively as ever.

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