The heart murmur is heard usually when the blood starts to leak to the point that it generates some noise. Commonly in horses,
the murmurs of the defective valves are detected but have yet to result in significant clinical problems. From there, a decision
is made to do a further work up by ultrasound/echocardiogram to try to determine what impact it might be having on cardiac
function. In many cases, the DVD progresses slowly during many years. Echocardiography is necessary to diagnose the specifics
of the condition and to assess its severity.
"Valvular lesions and regurgitation occur frequently and depending on their severity may impair the horse's performance, compromise
him, or have no affects on his life expectancy," Reefs says.
Timing, duration, intensity, quality, pitch, shape, point of maximal intensity and radiation define murmers.
"Timing refers to the phase of the cardiac cycle in which it occurs (systolic, diastolic or continuous)," Reef explains. "The
duration is the period during which the murmur is detectable during the cardiac cycle (i.e. early, mid, late, or holo, or
pansystolic, or diastolic). The intensity grade 1-6/6 is determined by the quantity and velocity of blood flow through the
murmur's origin, the distance of this blood flow from the stethoscope and the acoustic properties of the interposed tissue.
The quality is harsh, coarse, rumbling, scratchy, musical, honking, or blowing, and may be high, medium or low-pitched. The
shape auscultated is determined by the phonocardiographic depletion of the intensity of the murmur over time. The radiation
is usually from the murmur's origin in the direction of the abnormal blood flow, and is determined by the murmur's intensity
and physical characteristics of the chest."
Heart murmurs are detected on a six-point grading system. "It's not totally subjective; it has objective criteria, though
the grading system is not correlated with severity of disease," Woodfield says. "It's how loud the murmur is more than anything.
Subjectively the way I tend to look at it, which applies a little bit better to owners, is a soft, moderate or loud murmur,
grades 1 and 2 as soft, 3 and 4 as moderate, 5 and 6 as loud." A Grade 1 murmur by definition is the first audible sound you
can hear that you call a murmur in an ideal environment, where you can barely detect a murmur with your stethoscope. Generally
speaking, a Grade 1 murmur is not that much of a health concern, but you can't always go by that. A grade 2 murmur can be
heard fairly easily, but one has to concentrate to make sure that it's there all the time. Three's and four's are fairly easily
heard murmurs. "I differentiate a 4 from a 5 is by definition," Woodfield explains. "A grade 5 murmur has what we call a 'palpable
thrill.' When you put your hand on the chest wall, the murmur is vibrating the chest wall, and it is a very loud murmur. To
me, a grade 4 is a loud murmur, which I think is probably a grade 5, but it is not vibrating the chest wall."