A horse’s cardiovascular system is a key component of his engine during exercise. Researchers know that some cardiac anomalies have little to no bearing on performance potential, while others can have a significant impact. But is it possible to assess a young horse’s performance abilities just by identifying an arrhythmia?

Linda Frellstedt, DVM, MSc, PhD, Dipl. ACVIM, and colleagues recently performed a study in which they evaluated whether the presence of a cardiac arrhythmia—along with its type and frequency—impacted whether young Standardbred horses remained in training and raced. Frellstedt, a senior lecturer in equine sports medicine at Massey University, in Palmerston North, New Zealand, shared the results at the 2016 American College of Veterinary Internal Medicine Forum, held June 8-11 in Denver, Colorado.

The researchers employed 50 Standardbreds (32 geldings, 16 fillies, and two colts) aged 2 to 4 years and evaluated them during training over a three-month period. For each evaluation, the team conducted resting and exercising electrocardiograms (imaging of the electrical conduction of the heart and the heart rhythm) and monitored the horses’ exercising speeds. Frellstedt and colleagues looked for anomalies or arrhythmias on the horses’ echocardiograms, including:

• Second-degree atrioventricular (AV) block, in which individual heartbeats are missed from time to time due to slowed electrical signals between the atria and ventricles;
• Premature ventricular contractions (PVCs), in which the horse has extra, abnormal heartbeats that begin in one of the heart’s two lower chambers (the ventricles);
• Premature supraventricular contractions (PSVCs), in which the horse has extra, abnormal heartbeats that begin in one of the heart’s two upper chambers (the atria); and
• Sinus arrhythmias (SA), a varied and inconsistent (speeds up or slows down without obvious reasons) heart rate.

The team evaluated 120 training sessions; 30 horses participated in three sessions, six horses completed two sessions, and 14 horses took part in one training session