Clinical Examination of Farm Animals - CYF MEDICAL DISTRIBUTION

CHAPTER 6
Figure 6.4 Position of the tricuspid (T)
heart valve. See also Fig. 6.3.
Figure 6.5 Positions of the cardiac valves looking down into the heart from
above: P, pulmonary;A, aortic;T, tricuspid; B, bicuspid or mitral valve.
horizontally back from the shoulder joint and a line
drawn vertically up from the elbow joint.
Abnormal heart sounds
Adventitious sounds – cardiac murmurs – are sounds
which are superimposed over the normal heart
sounds. They may be so loud that they mask normal
heart sounds or so quiet that they are overlooked in a
noisy environment. Murmurs are mostly caused by
leakage of blood through closed but incompetent
valves, or through congenital orifices between the
chambers of the heart. Other murmurs are caused by
the presence and movement of fluid within the pericardium.
It is important to detect, by careful auscultation
over a series of cardiac cycles, the nature and
location of any cardiac abnormality which is causing
the murmur. Small defects can produce quite loud
murmurs. Murmurs are most likely to be heard in
systole when blood within the heart is under the
greatest pressure. It is important to be sure that
audible murmurs are arising from the heart and not
from the respiratory system. Friction rubs caused by
pleural adhesions may be mistaken for abnormal
heart sounds. Brief blockage of the nostrils will eliminate
respiratory but not cardiac sounds.
Murmurs may be classified according to the part of
the cardiac cycle over which they can be heard. Apansystolic
murmur extends over the whole period of systole.
Such a murmur may be heard in cases where
there is incompetence of an atrioventricular valve.
Diastolic murmurs are less common but may be audible,
for example, where there is incompetence of the
aortic valve: this allows blood to leak back into the
heart with a resultant murmur when the valve is
closed. In cases of patent ductus arteriosus (PDA) the
murmur, which is of varying intensity, extends over
the whole cardiac cycle.
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