Cardiology

Matters of the heart

By Adam Marcus

Using a stethoscope can rule out low-grade heart murmurs in most cases, but echocardiography is required in animals with more than a soft, faint murmur, new research shows.

The study, published in the Journal of Veterinary Cardiology, found that auscultation by itself cannot reliably determine the severity of mitral valve regurgitation (MR) or stage valve disease—making echocardiography essential for horses with signs of a significant cardiac condition.

“A more severe MR grade might be present in a low-grade murmur. So, in case the horse is showing clinical signs, it is advised to perform a cardiac exam even with a murmur grade less than or equal to 2/6,” said Marie Demeyere, PhD, of the Equine Cardioteam at Ghent University in Belgium, who led the research. “When a murmur is detected during a pre-purchase examination, an echocardiographic exam should be performed, even when the left-sided systolic murmur grade is ≤2/6, to make sure nothing clinically relevant is causing the murmur and the potential buyer can make an informed decision on whether to buy the horse.”

In the retrospective study, Dr. Demeyere and her colleagues compared auscultation and echocardiography readings in 151 horses: 50 were healthy or had evidence of trivial mitral regurgitation, 58 had mild MR, 36 had moderate MR, and 7 had severe valve problems.

The intensity and duration of left-sided systolic murmurs showed a fairly weak but positive correlation with MR severity (P<0.001 for both), and duration of a left-sided systolic murmur also showed a positive correlation with the duration of the jet on ultrasound (P<0.001). The researchers found the strongest agreement between a murmur grade of 2/6 or lower and trivial or mild MR.

That result confirms the 2014 recommendations from the American College of Veterinary Internal Medicine for referring horses for electrocardiography when the degree of the left-sided systolic murmur is 3/6 or greater, because the associated regurgitation might be clinically relevant J Vet Intern Med. 2024;28: 749-761.

“Severe MR is a rare finding in horses,” Dr. Demeyere said. “In case a high-grade murmur is detected in the field, it is advised to refer the horse for a comprehensive echocardiographic exam to determine the origin of the murmur.”

In cases of severe MR, she and her colleagues recommend echocardiography every 6 or 12 months, as well as regular checks of the animal’s heart rhythm at the stable. “This can also be done using the Polar H10 combined with the Equifib app developed by the Equine Cardioteam Ghent,” she said.

Some horses with mild MR can develop high-grade heart murmurs despite no obvious structural anomalies of the mitral valves or remodeling of the heart. “In these horses, a less frequent re-examination, such as every 1 or 2 years, is often deemed sufficient to follow up on potential changes in chamber size,” she said.

The study found that left atrial contractile function, measured by tissue Doppler imaging (TDI), did not decline with MR severity, as has been shown in dogs and humans, whereas the left atrial (LA) fractional area did change.

“The fact that the findings are different with the different measurement techniques probably has to do with measurement variability,” Dr. Demeyere said. TDI, which measures the speed of the heart contracting, is highly sensitive to changes in heart rate and subtle differences in the imaging plane, she said.

“Even though TDI did not show significant results in this study, this does not mean that it has limited prognostic value in horses. Longitudinal follow-up studies are needed to fully determine the prognostic value of TDI in horses,” she said.

In a particularly interesting finding, murmurs were classified more frequently as “crescendo”—increasing in intensity from halfway into systole until the end of systole—than jets classified as crescendo by echocardiography.

“This can probably be explained by more strict criteria used to classify a jet as crescendo using echocardiography,” Dr. Demeyere said. The trend raises the question of whether training should put more emphasis on distinguishing pitch from loudness. Such a change “would definitely be valuable … as many veterinarians are not aware of these 2 different characteristics, making them mistakenly interpret a higher pitch as a louder murmur,” she said.

She noted that thorough auscultation is time-consuming, “and it is very important to perform this in a quiet environment, which can be challenging in practice.”

“The reason we put a lot of emphasis on the difference between a mid-to-late crescendo murmur and a murmur that holds the same intensity through systole is that we hypothesize that horses with a crescendo MR jet on ultrasound, associated with a mid-to-late crescendo murmur, might progress slower and less over time compared with horses with a holosystolic MR jet, associated with a murmur with a constant intensity through systole,” she added. “However, we are currently analyzing long-term follow-up data to confirm this hypothesis.” MeV

FOR MORE INFORMATION
Demeyere M, Dufourni A, Verhaeghe L-M, et al. Auscultatory findings and left atrial function as indicators of mitral valve regurgitation severity in horses. J Vet Cardiol. 2026;S1760-2734(26)00070-6.