Degenerative valvular disease in older horses - DVM
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Degenerative valvular disease in older horses
Performance issues vary depending on stage, severity


"Quantification of the regurgitant jet on echo is based on the velocity of flow, distance it travels in the atria or into the ventricle and the percent of cross section of the valve that is involved," Sage explains.

"Prognosis for horses with MR is based on the duration, etiology and severity of the regurgitation, the extent of chamber enlargement, if any, myocardial contractility and clinical signs at the time of presentation," Sage says. "If the left atrium is normal size or the degree of left atrial and left ventricular enlargement is small and the regurgitation is mild to moderate, the regurgitation is likely to progress slowly over years, some without clinical significance."

If it progresses, horses with MR have a poor prognosis as the mitral regurgitation can lead to left heart failure.

Aortic regurgitation

Aortic regurgitation (AR) is most common in horses over 10 years of age. Reef states that "they range from 1-6/6". Both state that it is a holodiastolic decrescendo murmur with a point of maximal intensity in the left 4th intercostal space or "in the aortic valve area and radiate toward the cardiac apex." Aortic regurgitation murmurs often have a musical quality due to vibration of the valve leaflets.

According to Sage, most horses tolerate even severe aortic regurgitation well without clinical signs. Because most horses do not develop AR until they are middle aged (10+) and it usually progresses slowly, it rarely leads to congestive heart failure or death. Reef notes that in older horses, they may progress slowly, and they rarely cause significant concern for the health of the horse. Aortic valve prolapse also occurs in older horses, associated with regurgitation, but likewise remains unchanged or slowly progresses over several years.

Tricuspid regurgitation

Tricuspid regurgitation (TR) is defined by a holosystolic, band-shaped Grade 2/6 or louder, coarse with a point of maximal intensity at the right 4th intercostal space. Reef says they may be pansystolic, are coarse or blowing in quality with their point of maximal intensity at the right AV valve area radiating dorsally. Horses with tricuspid regurgitation rarely show clinical signs, and if it is mild to moderate, they do not show exercise intolerance, can perform maximally, and only display the cardiac murmur. Many of them do not have valvular lesions that can be detected by echocardiography. The majority of horses with tricuspid insufficiency have clinically insignificant to moderate tricuspid regurgitation and normal exercise tolerance, Reef says. With TR, most horses perform up to their owner's expectations without much concern.

Pulmonary regurgitation

Though more rarely to occur, pulmonary regurgitation murmurs are usually holodiastolic, decrescendo and are usually less intense than aortic regurgitation murmurs.

"They may range from grade 1-6/6, but most horses have a murmur that is grade 1-3/6, if it can be heard," Reef says. "It is more likely to be associated with congestive heart failure, with a poor to grave prognosis for life, about 3-6 months with supportive therapy."

How does DVD affect horse performance?

"A lot of them (murmurs) in their early findings are found to be trivial to mild," says Woodfield. They progress very slowly to the point where they need to be checked every couple of years or every several years. This is especially true if they have not changed much to where the owners are still getting good use from the horse without any consequence. As they start to progress, dependent on the intended use of the horse, any horse that has some symptoms associated with its heart disease are probably taken out of athletic use. Valve disease in an endurance horse is probably going to show up sooner than in the backyard horse, especially one that is ridden on a limited basis. When the exercise regimen is more intense, you're more apt to pick up the signs, or the horse is more apt to show exercise intolerance than a horse that's mildly worked. The more strenuous the exercise, the more apt the horse will be unable to perform at its peak. "The biggest question for the horse rider is: What risk is it to me to be on a horse with cardiac disease?" Woodfield says.

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Source: DVM360 MAGAZINE,
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