"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 (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 (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.
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
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.
Horse DVD treatment options