Diagnosing Cardiac Arrhythmias in Horses on the Farm
Cardiac arrhythmias are tricky. While some of these heart rhythm irregularities are perfectly normal, in more severe cases they can indicate heart disease and/or cause horses to collapse. But what makes them especially complex is detecting them in the first place. Most of these heart rhythm irregularities are impossible to identify definitively with a stethoscope alone, especially in the resting horse, and owners rarely know if their horses are affected. Veterinarians can diagnose arrhythmias with an electrocardiograph (ECG) machine, but it’s impractical to carry these cumbersome instruments in their trucks. So what’s a vet to do on a farm call?

Bill Gilsenan, VMD, Dipl. ACVIM (LAIM), a practitioner at Rood & Riddle Equine Hospital, in Lexington, Kentucky, offered up an option at the 2017 American Association of Equine Practitioners convention, held Nov. 17-21 in San Antonio, Texas. He described a smartphone-based heart monitor veterinarians can use in the field.

The AliveCor Veterinary Heart Monitor is a handheld wireless portable ECG device that veterinarians can use to evaluate cardiac rhythm. Gilsenan described it as essentially an iPhone case with electrodes on it that transmits an ECG-compatible signal to a phone.

In 2013 Kraus et al. performed a study to validate the monitor in 46 dogs, 23 cats, and 18 horses. All horses’ heart rates were accurate and identical to those measured on a traditional ECG machine.

To use this device, said Gilsenan, the veterinarian must first download the app to his or her smartphone. Then, he or she wets the horse’s left girth area with isopropyl alcohol and places the monitor against the horse’s skin, behind the elbow at the girth, for about 30 to 60 seconds. Once the tracing (the transcript of cardiac events) is recorded, the veterinarian can view it on his or her smartphone, export it as a PDF, or e-mail it to a colleague for consultation. In his opinion, said Gilsenan, the ECG is best viewed as a PDF.

Now comes the hard part: interpretation. Because analyzing the results can be overwhelming, he recommended a five-step systematic approach:

  1. What is the heart rate, and does it compare it to what you hear with your stethoscope?
  2. Is the rhythm regular or irregular?
  3. Is there a P wave for every QRS complex? (Each heartbeat includes three components: the P wave, followed by the QRS complex, followed by a T wave. Normally, QRS complexes pair with P waves.)
  4. Is there a QRS complex for every P wave?
  5. Does the waveform’s shape suggest a normal heartbeat?

Overall, he said, the Veterinary Heart Monitor is an extremely useful means of diagnosing cardiac arrhythmias in the field. “It offers substantially more information to the ambulatory veterinarian, who is equipped with simply a stethoscope,” he says, “and can influence decisions to properly treat or refer affected patients.”

The app also stores a catalog of the user’s recorded ECGs.

Veterinarians can order the products online for just under $200, he said.

Gilsenan noted that AliveCor has produced a newer heart monitor model called Kardia Mobile that’s Bluetooth-compatible. It’s used in human medicine but has not yet been validated for veterinary species.