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Abnormal Heart Rhythm in a Thoroughbred Gelding

The heart is one of the most vital organs when it comes to overall health and performance for the horse, let alone any other species.  If the heart stops, death quickly follows.  There are many cardiac conditions and arrhythmias that can affect the horse, but overall, they are not very common thankfully.  In this case of an 18 y.o TB gelding, an abnormal heart rhythm developed that quickly threatened his health and ability to perform. The success of the case was not through pharmaceutical intervention, but instead through dietary optimization and targeted herbal therapy.

Rocky a Horse with Abnormal Heart Rhythm

Rocky a Horse with Abnormal Heart Rhythm

Rocky is an 18 y.o TB gelding that has been owned by his owner since the age of 3, competing in low level Hunter competitions.  He was moved to a whole-food based diet at the age of 15, when his appetite had changed and his body condition changed.  Rocky’s owner had started to feed him alfalfa pellets, beet pulp, Flax seed, Renew Gold® and various Bio-Star® products targeting diet and nutrition. He was also fed whole oats in the winter and Chaffhaye with grass hay as a main forage source.  Rocky was also placed on the Cur-OST EQ Green formula as a preventative measure for inflammation by his owner, but had been discontinued in the recent past.  His body condition since starting the new diet has been around a 4.5 / 10.  Rocky spends most of his time outdoors, unless weather is poor. Overall, he seems to be doing well.

In the Beginning

In the fall of 2017, Rocky experienced a colic episode which left him admitted to the hospital for 5 days.  His colic was due to gas, which is very common.  In most of these cases, the horses are mildly uncomfortable and resolve quickly with pain medication, mineral oil by nasogastric tube, and some handwalking.  The average heart rate for a gas-colic is around 45-60 bpm.  The higher the heart rate, the more pain the patient generally is in and the more serious the cause of the colic.  Rocky was maintaining a heart rate of about 90-100 bpm, despite showing no overt signs of pain and ongoing evidence of colic.

An EKG (electrocardiogram) was performed to evaluate his heart rhythm, which indicated tachycardia (high heart rate) and an abnormal rhythm or beat of an irregular nature, with some ‘escape beats’ noted.  Evaluation of the EKG rhythm did not determine what type of arrhythmia was present, but it was suspected that he had AV-block.  This is a condition where nerve input to the upper (atria) and lower chambers (ventricles) is not coordinated.  There are a few different types of AV block that can develop in those horse, but to have it be a clinical problem is not very common.  In some horses, due to high level of fitness and low resting heart rates, it is not uncommon to find low grade AV block.  This is often quickly abolished or eliminated when the horse is put into light exercise.  It is also not uncommon to have some sedatives induce AV block in some patients, which resolves as the sedative agent wears off.

The veterinarians in charge of Rocky’s care had started him on a course of antibiotics and a non-steroidal pain medication, as the cause of the elevated heart rate was unknown.  The blood work that was submitted had indicated no abnormal values of concern.  While on the NSAID medication, it appeared that Rocky’s heart rate stabilized, returning back to a normal level.  When the medication was discontinued, his heart rate would climb again.  In most cases, this would raise the question of pain being present and likewise influencing the heart rate.  However, in Rocky’s case, a pain source could not be localized.  He was eating, drinking, producing normal feces and normal gastrointestinal motility patterns.  It was puzzling.

Rocky was discharged to his owner with directions to continue the antibiotics.  While at home, he appeared clinically to be fine, but the owner would still hear 1-2 abnormal heart beats while at rest when listening to his heart with a stethoscope.  His heart rate has remained normal, but the concern was that the abnormal heart rhythm was still present.  Considering this, Rocky’s owner was advised not to exercise him.  As a result, his owner was concerned about his ability to return to training and competition, as well as long-term health implications.

Rocky’s owner had reached out to Secondvet, to gain another viewpoint on the situation.  After review of the medical records and EKG readout, I felt that the abnormal rhythm was due to AV block.  The pattern fit as did the fact that he continued to demonstrate a few ‘escape beats’ or abnormal beats at home while at rest.  However, the AV block condition generally does not fit with an elevated heart rate. Could there have been two problems?  The ultimate question would be regarding if this was a normal condition for Rocky or was it a new problem?

Looking back on his history, there was no indication of poor performance or stamina related issues.  His owner did note that in the early part of 2017, he did have a fever episode which left him with a diminished appetite.  The attending veterinarian performed a physical examination with the only concerning findings being an elevated body temperature.  All of the lab work and physical exam findings were normal otherwise.  Rocky was treated for a viral infection of unknown cause using NSAIDs as the primary medication to keep the fever under control.  After a couple of days, his fever was resolved and his appetite had returned.  There as no notation of an abnormal heart rhythm at the time of that examination.

Rocky was also seen in July 2017 for a mild colic episode.  Again, he was managed with pain medication.  All of this laboratory and physical exam findings were normal. There was no mention of an abnormal heart rhythm at this time.

So, the question remains as to whether the AV block is relatively ‘new’, it has been there for some time, or maybe something was being done in the past that was keeping it under control?

It is quite possible that the viral infection may have created myocarditis, which would be inflammation of the heart muscle tissue.  This could result in ongoing arrhythmia problems potentially, but I would expect possible indications by the July colic examination.

The other possibility would be that the AV block has been there the whole time, but now just being diagnosed.  The only flaw in that theory is that if the AV block was present continuously, we would expect that it would be detected on the physical examination with the viral episode.

The final possibility is that the AV block has been present for quite some time, unrelated to the viral episode or the colic, but was being controlled during one period and not the other.   Is it possible that Rocky had an abnormal heart rhythm (AV-block) for years or months.

So many questions!

Finding Answers and Clues to the Arrhythmia

It is hard to completely determine from the history how and when the AV block heart condition developed.  As we dig deeper into Rocky’s history, especially paying attention to the diet and supplement regimen, one thing becomes clear.  The whole-food diet had been a part of his regimen for the last 3 years with most supplements remaining consistent.  However, the Cur-OST EQ Green formula became a part of Rocky’s regimen in February 2017 and was discontinued around August of 2017.  Could this have played a role?

The entire situation was discussed with Rocky’s owner.  The main concerns revolved around the ability to return to full work.  The attending veterinarians had recommended a period of rest and were unable to determine if training could be restarted.  I had asked the owner to monitor his heart rate before and after light exercise with her veterinarian’s guidance.  His heart rate at rest averaged around 40 bpm with 1-2 irregular beats, but were quickly abolished with light exercise, obtaining an average heart rate of 65 bpm.  Rocky appeared to have good energy and was willing to work.  This fit into a suspicion of AV block.

I recommended to Rocky’s owner to restart the Cur-OST EQ Green formula, dosing twice daily for 14 days, then once daily in addition to his current supplement regimen and diet.  A light exercise regimen was put into place with his owner monitoring his heart rate before and after exercise.  The owner noted that in that 2 week period, his energy levels greatly improved and he was very active.  After reducing the dose to once daily, she noticed a reduction in his energy and less overall vigor.  The dose was then increased back to the loading dose originally recommended, to which Rocky responded rapidly.

Over the next 2 months, with monitored exercise, Rocky’s heart rate and rhythm have returned to normal with no evidence of abnormal or ‘escape beats’ while at rest or when exercised.  There have been no noted episodes of tachycardia or generalized discomfort.

What Happened to the Abnormal Rhythm?

There are several factors at play in Rocky’s situation.  In order to look at the variables, we need to go back through his history.  Originally, the owner had noted that Rocky was becoming an easy-keeper type, but then seemed to shift to the opposite spectrum.  His owner began to notice that his weight was dropping and he required more food to maintain weight.  This change is what prompted his owner to make a shift in his diet, moving to whole-foods.  This shift in body composition is not uncommon, but signals a stress response in the horse, often reflecting in a dysfunctional gastrointestinal tract.  Stress and GI function go hand in hand.  Was there something that created  stress response in Rocky?  To this day, we do not know, but I suspected that he had some underlying gastrointestinal problems.  All prior blood work was normal and with that we can determine that there was no organ dysfunction outside of the GI tract.

The gastrointestinal tract is linked back to health and immune function.  It is often linked to systemic or whole-body inflammation additionally.  When we look at Rocky’s not so distant past, he had two reported incidences of colic, both gas, in the past year.  One of which resulted in hospitalization.  This is a sign that there is a lack of balance in the GI tract and coincides with our suspicions mentioned above. There was also the fever episode, which may have been viral, and could indicate a compromised or stressed immune response.  Again, linking us back to possible inflammation and gastrointestinal dysfunction on some level.

In terms of the AV block and heart rhythm, this is more complex.  AV block is generally not associated with an elevated heart rate, but more often the rate is very low.  Thus, it is not uncommon to see the AV block pattern in highly fit athletes at rest, when their heart rates are very low.  It is also not uncommon to see after sedation, in some horses, due to the impact of the sedative medication on the heart rate. I suspect the elevated heart rate (tachycardia) was due to stress when in the hospital, more so than pain or a pure cardiac condition.  The tachycardia and AV block were likely separate.

The exact cause of AV block is not known and there are several forms that are present.  We tend to consider it ‘normal’ in highly tuned athletes, but is it really normal?  Just because we find it often in those athletes, does it mean it is normal?  AV block is a disruption of nerve activity within the heart and can be serious in high degree levels.  AV block is associated with higher vagal tone and generally abolished with increased sympathetic tone.  This is all related to neurotransmitters and nerve conduction.  There are some medications that are used in humans and pets, but not often used in horses due to expense and ease of use.  Many cardiac conditions, including arrhythmias, are linked back to oxidative stress and inflammatory damage on a cellular level.  This damage can be to the cardiac cells or even the nerve cells transmitting signals.  This is common in some patients with Rheumatoid arthritis, as an example, in which case the inflammatory condition impacts cardiac health and conductivity.

In reality, the AV block could be associated with systemic inflammation secondary to possible underlying gastrointestinal dysfunction.  It could also be related potentially to an electrolyte imbalance or a nutrient deficiency, again secondary to the gastrointestinal dysfunction and poor absorption.  Either are plausible but hard to prove.

We do not know the period of time that the AV block was present for nor the cause.  My suspicion in Rocky’s case was that the AV block may have been present at least for the past year, but was abolished or improved with the administration of the Cur-OST EQ Green supplement.  While he was on the formula, there was no evidence of AV block, but the arrhythmia appeared during a period in which it was not used. Could there be a connection?  Placing him back on the formula was the only way to make a connection.  Given his response and improved cardiac rhythm after restarting the formula, it certainly does seem to have been a factor.  Was this positive response due to inflammation reduction, improved gastrointestinal function, stress modulation, or maybe a boost in nutrient provision via the formula?

Many cardiac and circulatory health problems are linked back to inflammation and oxidative stress damage on a cellular level.  There are many origins of this inflammatory response, being linked back to diet, environment, stress and some medications.  Given Rocky’s situation, my main concerns were over stress being a major factor in his life, creating inflammation and contributing to gastrointestinal dysfunction.  The EQ Green is a nice base formula for these types of cases, as it helps to balance the inflammatory response with high levels of a patented BCM-95 curcumin in combination with Boswellia 65% extract.  The formula also addresses the stress response with a concentrated Ashwaghanda extract and benefits digestion with Anise seed.  The formula also has a nice nutritive base through alfalfa and spirulina blue-green algae that aids cellular health on many levels.

At this time, Rocky is doing well and is returning back to work.  He appears to be enjoying his work and there are no reported abnormal heart rhythms at this time.  He continues to be on an induction dose of the Cur-OST EQ Green, which will likely reduce over time.  Some horses tend to have a higher inflammatory response that requires a higher level of supplementation.  In most, as the inflammation is managed, the required supplementation dose will reduce.

Here is to you Rocky and to your owner!  Job well done!

Author:  Tom Schell, D.V.M., CVCH, CHN

 

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