Page 990 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Cardiovascular system 965

VetBooks.ir side of the thorax at the 5th or 6th intercostal space 8.2
(ICS), above the elbow. On the right side the car-
diac impulse is slightly further forward, lower and is
normally weaker than on the left. An intrathoracic Left
mass or cardiac enlargement should be suspected if
the apex beat is abnormally located. A cardiac thrill
is a palpable vibration through the thoracic wall sub-
sequent to an intense murmur. A
P
L
Cardiac auscultation
Cardiac auscultation should be the last part of the
cardiac examination. The heart rate and rhythm
should be evaluated and compared with those
determined during pulse palpation. Simultaneous
palpation and auscultation aids in determining
the presence of pulse deficits and in determining the
stage of cycle for cardiac murmurs. The entire car- R
diac area should be auscultated on both sides of the
thorax, with an emphasis on detecting the location
of both transient cardiac sounds and the location
and distribution of cardiac murmurs, should they
be present. Heart rate and rhythm and the intensity Right
of the transient heart sounds should be assessed.
Heart sounds may be muffled in obese animals or in
those with pleural effusion or diaphragmatic her- Fig. 8.2 Location of heart valves and area of
nia. The heart sounds, while muffled, often radiate auscultation for each valve. The pulmonic valve (P) is
widely if pleural effusion is present. Heart sounds auscultated well forward under the triceps muscle on
are often intensified in tachycardia, such as that the left side of the thorax in the area of the 3rd ICS.
associated with excitement and anaemia, and also The aortic valve (A) is auscultated well under the triceps
in thin animals. muscle on the left side of the thorax in the area of the
4th ICS just dorsal and caudal to the pulmonic valve.
Heart sounds The left atrioventricular (AV) valve (L) is auscultated
Two to four transient heart sounds are present in slightly under and just caudal to the triceps muscle on
the normal horse. The first and second heart sounds the left side of the thorax. The right AV valve (R) is
(S1 and S2) are present in all animals. S1 is associ- auscultated under the triceps muscle on the right side of
ated with the closure of the atrioventricular (AV) the thorax.
valves and the beginning of systole. S2 is associated
with closure of the semi-lunar valve and the end of
systole. While the presence of the other transients, Table 8.1 Location of heart valves
S3 and S4, is generally considered pathological in VALVE LOCATION HEART SOUNDS
small animals, these sounds are commonly detected
in the normal horse. In many horses the fourth Pulmonic Left 3rd ICS S2 loudest
heart sound, corresponding to atrial contraction, is Aortic Left 4th ICS S2 loudest
detected just before the first heart sound. The third Left atrioventricular Left 5th ICS S1 loudest
heart sound is also often present, corresponding to (mitral)
rapid ventricular filling, and follows S2. Valve loca- Right atrioventricular Right 3rd–4th ICS S1 loudest
tions and corresponding heart sounds are outlined in (tricuspid)
Fig. 8.2 and Table 8.1. ICS = intercostal space.