An Eventer with Atrial Fibrillation

As seen in the April 2019 issue of Horse Deals.

Sophie, tell us a bit about your horse Raz and how he was diagnosed with Atrial Fibrillation. Raz is a sweet 14 year old Thoroughbred gelding who I’ve had for eight years. He’s a handy horse to have at jump club, and a bold eventer - he’s brought me a lot of joy whilst keeping me on my toes! Raz was diagnosed with AF after an irregularity was noticed whilst checking his vitals during a mild gas colic. I took him to the clinic for an ECG shortly after which confirmed his diagnosis.

Had you noticed any performance issues prior to him being diagnosed? Not particularly. Observations and indications post diagnosis align from occasions prior when he’s shown poor recovery, but his nature under saddle is uncompromising. He likes getting the job done and throws everything into it - it can be a little tricky to guide his enthusiasm sometimes so the diagnosis has been invaluable to ensure I can train to parameters of safety.

How did you work out a management plan for the condition and what was the plan? Our treatment options were limited due to his age and suspected length of time he’s had AF. However, he’s fit and otherwise shown no effect of the condition during work or competition, so the management priority was to have insight into what his heart was doing whilst I ride. The plan as such is to continually record his data i.e. average bpm and max bpm in a training journal, alongside the length of the training session and whether we flat worked, jumped etc. I make notes on the sessions day to day and identify trends, improvements and anomalies in the data as we progress. For example, I can observe that after two weeks gradual work after a spell, his average heart rate can come down by as much as 20bpm as his fitness improves, and his mindset is calmer from the continuity.

How has training and competing changed since the diagnosis? Without sounding cliche - I have to use the term ‘heightened awareness’ to describe changes to our regime. The work is similar in that we flat and jump and do grids or cross country school; but we now complete exercises with one eye on the monitor to stay in the optimum range. If the numbers climb too high or too quickly we take a quick walk break to get back into the correct zone. Alternatively, we even move exercise up a gear when it’s not challenging enough and the reading is low and steady - it’s all about staying in the heart rate zone that will constructively build his fitness.

Do you have any concerns about competing him with the condition? Not now that I have a visual on what’s happening on the inside. If anything it’s easier now because I can make a more informed decision about whether he is coping with a task or if he has the ability to do more. Should I feel his readings are becoming detrimental to his health whilst out competing I can simply stop and withdraw or retire, however, the point of having a management plan is not having to do this because I’ve prepared his fitness with one eye on the clock and can accurately gauge what he’s capable of.

What have you learnt since regularly using a heart rate monitor? It’s been fascinating to observe the connection between the horse’s engagement with his work and environment with his physical response. He might show no outward signs of stress, other than to eyeball something that’s bothering him - yet I can see his heart rate elevating on the watch, which tells me he’s in fact being very obedient and brave. Thanks to the watch giving me a heads up that he’s more unsure than he’s letting on, I can adjust my approach accordingly. So I guess I’ve learned not to take every behaviour at face value.

How is day to day life different with Raz now? Other than implementing a few practical things like applying the heart rate monitor and keeping his journal, things are much the same. I’ve always been conscious of adequate nutrition, and I ensure he’s topped up with electrolytes and blood building supplements when faced with the demands of travel and performance.

What are the future plans for Raz? To keep on keeping on! We’ll continue to buzz around low level events and showjumping. He’s a real war horse and so careful. Perhaps we’ll chase one more grade higher at some point, provided we can pursue it happily and healthily.

How could all riders use a heart rate monitor to improve their training? I think riders are already faced with so much guesswork when it comes to caring for and training their horses, that the opportunity to eliminate this variable and have a clear window into their horse’s progress is priceless. Being able to know when to push, when to rest and when to call it a day, is something that could benefit riders of all levels, and it’s a game changer being able to validate instinct with the facts.

What advice do you have for owners who are trying to manage a performance limiting condition in their horse? You need an excellent vet and you need to do your homework. My definition of homework is reading published research papers, not internet forums! An honest evaluation of the prognosis of any condition is the first step to navigating the condition, and trusting your vet and following their advice is the second. Being realistic about what you can manage both emotionally and financially is far better than becoming overwhelmed and putting strain on yourself or your horse. Know your limits and seek guidance when it’s required.

DR JENNIFER LUGTON
Dr Jennifer Lugton graduated from the University of Sydney in 2007 and has been working as an Equine Veterinarian since then in both Australia and the UK. She currently works in the Hawkesbury Area of Sydney, NSW.

How does an electrocardiogram work? An electrocardiogram, or more commonly known as an ECG, is a medical test that uses electrodes placed on the horse’s chest and limbs to measure and record the electrical activity generated by the heart as it contracts. The heart emits a spike of electrical discharge with each heartbeat. This is what causes the heart muscle to contract and pump the blood around the body. We record these spikes over a few minutes and then analyse the trace for any abnormalities. In a normal heart, each beat occurs at a regular interval and produces a repeatable spike of electrical activity.

When investigating the irregularity of Raz’s heartbeat, what did you find? Raz’s ECG confirmed our suspicions of Atrial Fibrillation (AF). AF is actually very easy to diagnose as it has a very distinguishing trace on the ECG machine. Firstly AF is defined as an ‘irregular irregularity’ of the heartbeat. While other conditions of the heart produce irregularities at regular intervals of the heart beat, e.g. missing every 3rd heart beat in 2nd degree AV block. AF produces a completely unpredictable and random trace with different intervals between each heartbeat. Secondly, in AF the atria fail to contract and instead quiver or fibrillate. So we see a very wavy baseline between the irregular spikes.

What are the dangers of this condition going undetected in performance horses? As AF prevents the normal contraction of the heart muscle, it reduces the amount of blood the heart can pump to the body. In a horse that is not exercising heavily, atrial fibrillation may go unnoticed. But in racehorses, for example, who operate at the maximum heart rates, the heart just can’t keep up with the oxygen demands of the body and their performance is affected. In worst possible cases, the stressed heart can go into a ventricular arrhythmias, which places the horse at risk of collpase or death.

What are the options for treatment or management? Three treatment options exist for AF.
1. Converting the arrhythmia with drugs, the most common drug being quinidine sulfate.
2. Electrical cardioversion.
3. Not treating the arrhythmia and leaving the horse in AF.
With the first two options, there is no data or studies that conclude that one is better than the other. It depends on the case and the vet’s experience. These are usually chosen for horses that are involved in more strenuous exercise, like racing or top level competition, or if they are young and it is the best long-term outcome. Both conversions can be fantastic as they fully restore the horse back to its previous performance level. However, there are also some known complications with both options, so I never force clients into conversion. It is also important to note that any horse with physical signs of heart disease are not candidates for conversion. So we have the 3rd option. Many horses doing low level work, perform very well in their jobs and show no symptoms of AF. This was the case for Raz, who has been competing successfully for years. The most important thing if choosing this option is to know as much as you can about your horse’s heart, and to make sure the heart rate is never dangerously high. This is the value of the heart rate monitor.

Why was quinidine too high risk for Raz’s case? The decision to not use the quinidine for Raz was made for a few reasons. As mentioned previously, he has been asymptomatic and happily competing for years. While the majority of cases of conversion using quinidine are successful, there is still a small risk of fatal complications of the procedure. And lastly, the success of conversion is reduced, and higher recurrence rates exist for horses that have had AF for longer than 4 months. This was highly likely to be the case for Raz.

What about Raz’s case makes him safe to continue in a low-level performance career? Healthy horses with a normal rhythm can have heart rates of 240 beats per minute, or even higher, during maximal exercise. Horses with AF, however, will have higher heart rates, as the heart is less efficient and has to work harder, so they will reach their maximum heart rate at a lower level of exercise. It is best to keep horses with AF below their maximum heart rates. Using the heart rate monitor makes it safe for Sophie, as she can back off the level of exercise the moment his heart rate approaches his maximum level. And it is also a great tool over the long term to make sure he is as fit as can be before entering into any competitions.

Does atrial fibrillation affect the life expectancy of a horse? AF, that is not complicated by cardiac disease, is more of a performance limiting condition than a life threatening one. Horses at rest, or who are ridden at low levels, have a normal life expectancy.

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