Cardiac Arrhythmias and the Role of cTnI in Horses

While some arrhythmias in horses are benign and pose no significant health risks, others can
severely impact performance and, in some cases, become life-threatening. Accurate diagnosis and management are especially critical in performance horses, where cardiac efficiency directly affects athletic ability.

Unlike humans, where vascular disease can lead to heart attacks, such conditions are rare in horses. Instead, horses are more commonly affected by cardiac rhythm abnormalities (arrhythmias). The most frequent arrhythmia observed is atrial fibrillation, which can impair heart function but is often manageable.

More serious are ventricular arrhythmias—abnormal heart rhythms originating from the ventricles—which can lead to severe cardiac complications. Horses with myocardial toxicities often experience these arrhythmias, but because they tend to be intermittent, detection can be challenging.

In human medicine, cardiac damage is assessed using cardiac troponin-I (cTnI), a regulatory protein released into the bloodstream when myocardial (heart muscle) cells are damaged. cTnI is highly specific to cardiac muscle and plays a crucial role in heart contraction. Elevated plasma cTnI levels are widely used to diagnose and assess the severity of myocardial damage, particularly in coronary artery disease (commonly associated with heart attacks).

Since equine cTnI is structurally similar to human cTnI, diagnostic methods developed for humans have been adapted for use in horses. 

Researchers, led by Jonathan Foreman, at the University of Illinois Veterinary Teaching Hospital, conducted a study to establish reference values for cTnI in healthy horses, using a human chemiluminescence assay. They then compared these values to cTnI levels in horses with diagnosed cardiac disease, confirmed through electrocardiography (ECG) and ultrasonography. All full report of the work is published in Animals.

The researchers found that horses with atrial fibrillation sometimes showed mildly elevated cTnI levels, occasionally falling outside the normal reference range.

On the other hand, horses with ventricular arrhythmias had a 10-fold higher median cTnI concentration compared to those with atrial fibrillation.

These results suggest that measuring plasma cTnI levels could be a valuable diagnostic tool in horses with suspected ventricular premature contractions or ventricular tachycardia. The findings support the use of cTnI assays in equine medicine to detect and monitor cardiac disease, improving early diagnosis and management of potentially serious conditions.

For more details, see:

Jonathan H Foreman, Brett S Tennent-Brown,  Mark A Oyama,  D David Sisson. 

Plasma Cardiac Troponin-I Concentration in Normal Horses and in Horses with Cardiac Abnormalities

Animals (Basel) (2025);15(1):92. 

doi: 10.3390/ani15010092