CARDIOLOGY

AFib Rate Could Offer Non-Invasive Predictor of Recurrent Arrythmia

By Adam Marcus

Noninvasive cardiac testing can accurately predict which horses are likely to experience relapses of atrial fibrillation (AFib) after treatment for the arrhythmia, researchers found.

As with humans, AFib is prevalent in equids—particularly larger breeds—affecting as many as 2.5% of animals, depending on the breed, and can significantly impair exercise tolerance. Although treatment with drugs and devices can correct the abnormal heart rhythm, relapse is common, occurring in as many as about 40% of cases. Predicting which animals are most at risk of relapse could help clinicians better manage atrial fibrillation, according to Rikke Buhl, DVM, PhD, a professor in the Department of Veterinary Clinical Sciences at the University of Copenhagen, in Denmark, and the first author of the new study.

One method for predicting relapse that has gained recent attention is the atrial fibrillation rate (AFR), which is obtained by surface electrocardiography (ECG). AFR is thought to reflect electrical remodeling in the heart. The higher rate of fibrillations per minute—expressed as the number of waves per minute (fpm)—the greater the remodeling.

For the new study, Dr. Buhl and her colleagues at institutions in the United States, Europe and Dubai sought to learn if AFR could be used to predict relapse of AFib in 195 horses. Of those, 74 received nasogastric administration of the drug quinidine, a standard therapy for AFib, and 121 received an intervention called transvenous electrical cardioversion (TVEC), an invasive procedure in which 2 catheters are introduced through a vein in the neck and positioned in the heart, and the organ is pulsed with electricity until normal sinus rhythm returns.

Of the animals treated with quinidine, 10 did not convert to sinus rhythm, and these horses had higher AFR than did the horses that responded successfully to the drug (383 vs. 351 fpm; P<0.01), according to the researchers. All but 1 horse that underwent TVEC successfully achieved normal sinus rhythm.

AFib is prevalent in equids.

“Horses with high AFR had a higher risk of getting AF again after a successful cardioversion to sinus rhythm,” Dr. Buhl told Modern Equine Vet. “Therefore, it seems that high AFR had a poor prognosis for keeping the heart in normal sinus rhythm. This can be helpful for the practicing vet as they can add this value to the other clinical parameters that assist in prognostication.”

The researchers noted that the TVEC group included more older, and especially Warmblood animals, which are known to be more prone to recurrent AFib and a higher prevalence of mitral regurgitation. “These factors may increase the complexity of AF and the atria becomes more remodeled. Whether this remodeling occurred before AF or as a consequence of AF is difficult to answer,” Dr. Buhl said.

At the moment, she added, ECG analysis occurs post-processing, but in the future the technology may evolve to calculate AFR instantaneously. “That would provide the clinician with information that can assist not only in treatment selection, but also for prognostication of the risk of AF recurrence,” she said.

For more information:

Buhl R, Hesselkilde EM, Carstensen H, et al. Atrial fibrillatory rate as predictor of recurrence of atrial fibrillation in horses treated medically or with electrical cardioversion. Equine Vet J. 2021 Dec. 27. https://doi.org/10.1111/evj.13551 https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.13551