Veterinarians with a good ear can zero in on heart murmurs in horses, study shows

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Warmblood study in Germany shows the diagnostic ability of veterinarians armed with a stethoscope.
A warmblood study in Germany shows the diagnostic ability of veterinarians armed with a stethoscope.

Heart murmurs in horses are often picked up by veterinarians with a stethoscope, but which valve is causing the problem?

Researchers in Germany have shown that a stethoscope can work well to help veterinarians identify which valve is causing a heart murmur, after comparing the results from listening to the heart with echocardiographic findings.

Jakob Hövener and his fellow researchers with the Free University of Berlin said heart murmurs in horses can be of a physiological or pathological nature in horses. Physiological murmurs result from the large amount of blood and the high velocity of blood flow in the equine cardiovascular system. Pathological murmurs result from either stenosis – narrowing – or regurgitation of one of the heart valves.

Stenosis is rarely seen in horses and most pathological systolic or diastolic murmurs are caused by valvular regurgitations or congenital defects.

The study team, reporting in the journal Animals, said certain murmurs can usually be linked to specific valvular regurgitations. However, limited information exists about the accuracy of these broad rules in warmblood horses.

The main goal of this study was to link certain findings with the stethoscope to the results of the echocardiographic examinations, to determine whether there was agreement on the valve affected, as well as to find out if the loudness of the murmur coincided with the grade of regurgitation and presence of dimensional changes.

They used data gathered on 822 warmblood horses presented for cardiac examination in a large equine referral center in northern Germany.

The horses were presented because of either a clinical complaint such as poor performance or collapse, or because of a heart murmur or arrhythmia detected as an accidental finding.

The heart of each horse was thoroughly assessed by one of five experienced veterinary practitioners at the clinic using a stethoscope. In total, 653 of these examinations revealed one or more heart murmurs.

The most common findings with a stethoscope were left-sided systolic murmurs (68%) or left-sided diastolic murmurs (15%).

An echocardiographic examination was performed on 635 of these horses, revealing regurgitations of the mitral valve as the most common valvular regurgitation (77%), followed by regurgitations of the aortic valve (23%).

Thirty-one percent of the horses that underwent an echocardiographic examination displayed dimensional changes in one or more compartments of the heart, with the left atrium being most affected (21%), followed by the left ventricle (13%).

The researchers reported that agreement between the findings with the stethoscope and those of cardiac ultrasound was substantial if one or more murmurs and regurgitations were present. Agreement was almost perfect if only one murmur and one regurgitation were found.

The stethoscope was particularly well suited for detecting left-sided systolic and diastolic murmurs, with 87% of left-sided systolic murmurs being caused by a mitral valve regurgitation and 81% of left-sided diastolic murmurs originating from an aortic valve regurgitation.

“We found a fair agreement between the grade of regurgitation and the respective murmur,” the study team reported.

“Association was particularly good between mild regurgitations and low-grade murmurs, while differentiation between moderate to severe regurgitation based upon the loudness of the murmur was less reliable. Dimensional changes were usually linked to more severe regurgitations and higher-grade murmurs.

“Ultimately, we can say that cardiac auscultation is an integral part of any cardiac examination and very well suited to identify the cause of a murmur in case of left-sided isolated murmurs and mitral valve regurgitation and aortic valve regurgitation, which show an almost perfect agreement between auscultation and ultrasonography.”

They noted that if right-sided murmurs and more than one regurgitation are present, agreement is lower and the technique is less suited to identify the valvular regurgitation as being the cause of the murmur.

“The limiting factor in this case is that only the grade, timing and location were used to describe the murmur. If character could have been taken into account, a higher agreement may have been achieved.

“We could determine a fair agreement between the grade of the murmur and the severity of the regurgitation. This is particularly true for mild regurgitations.”

Accuracy, they said, is lower for moderate to high-grade regurgitations, with the murmur often being less loud than the severity of the corresponding valvular regurgitation may suggest, possibly introducing the risk of underestimating the risk of a grade 3 or 4 murmur.

“We also found that horses with cardiac dimensional changes have, on average, louder murmurs; however, this could also be due to the fact that dimensional changes are often accompanied by more severe regurgitations.

“In the case of aortic valve regurgitation and left ventricular enlargement, we can even say that there is no direct correlation between the grade of enlargement and the murmur intensity.

“To sum up, we can say that auscultation is very well suited for an approximate assessment of a cardiac disease, especially in rural equine practice or when transportation to an equine referral center is not possible or not wanted.

“However, if further sporting activities are desired, further diagnostics should be performed, especially in a moderate to loud murmur, a right-sided murmur, or multiple murmurs, as auscultation may be inaccurate in these cases.”

The study team comprised Hövener, Julie Pokar, Roswitha Merle and Heidrun Gehlen.
Hövener, J.; Pokar, J.; Merle, R.; Gehlen, H. Association between Cardiac Auscultation and Echocardiographic Findings in Warmblood Horses. Animals 2021, 11, 3463. https://doi.org/10.3390/ani11123463

The study, published under a Creative Commons License, can be read here

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