Page 16 - Feline Cardiology

6 Section A: Clinical Entities

R are usually associated with turbulent or high-velocity
blood flow in the heart or great vessels. A quiet environ-
ment is essential for successful auscultation. Extraneous
Clinical Entities ECG Q S T difficult in some cats. Restraining the animal near a sink
P
sounds, such as purring, can make auscultation very
with slowly running water or placing a cotton ball
soaked with isopropyl alcohol near the cat’s face can
sometimes be useful to make the cat stop purring.
Occasionally, breath sounds or fur rubbing against the
Phono
S 3 S 4 stethoscope can be mistaken for sounds originating
S 2
S 1 from the heart. Careful auscultation while watching the
S 1 Split S 2
cat’s breathing pattern can be useful to differentiate
heart sounds from breath sounds.
Phono
Location and Characterization
S 2
S 2
S 1 of Heart Sounds
Split S 1
Systolic click It is very important that complete auscultation is per-
formed in order to identify all abnormal sounds and
Figure 1.1. Illustration of relationships between the electrocar- rhythms. A simple approach is to auscult the left heart
diogram (ECG) and timing of heart sounds.
base, medial to the triceps musculature (which is the
region of the aortic and pulmonic valve areas) and the
Box 1.1. Anatomy of the stethoscope left apex (which is the mitral valve area). The right heart
base and apex should also be ausculted. The right apex
A good stethoscope should have comfortable earpieces that is the area over the tricuspid valve area and tricuspid
angle slightly toward the examiner’s chin to direct sounds regurgitation is usually loudest in this region. Murmurs
down the ear canals. The chest piece should be capable of associated with ventricular septal defects are usually
detecting high-frequency (normal heart sounds and most
murmurs) or low-frequency sounds (S 3 and S 4 ). When the bell loudest at the right heart base but often radiate ventrally
is placed gently against the skin, it accentuates low-frequency to the sternum. In cats, cardiac murmurs of many origins
sounds, but this capacity is lost if the bell is placed too firmly are often loudest over the parasternal region because of
against the skin because the stretched skin acts as a dia- the cardiac positioning in this species, particularly as
phragm. When the diaphragm side of the chest piece is placed cats age and a greater amount of contact occurs between
against the chest wall, it tends to minimize the low-frequency the sternum and the heart. Therefore auscultation along
sounds and accentuates high-frequency sounds (such as the the left and right parasternum is crucial for a complete
normal heart sounds, S 1 and S 2 ). Some chest pieces are ca- assessment. In cats, systolic murmurs loudest at the left
pable of acting as both a bell and a diaphragm depending apex are most often due to systolic anterior motion of
on how firmly they are placed against the chest wall. Such the mitral valve (SAM; most often seen with hypertro-
a stethoscope design is actually intended for human cardiol- phic obstructive cardiomyopathy). Murmurs caused by
ogy. It may be suboptimal in most cats (exception: Sphynx) congenital cardiac malformations are much less common
because the haircoat interferes with the dual diaphragm-bell
function. Stethoscope chest pieces/heads come in a variety than those caused by myocardial disease because of the
of sizes. The pediatric size is advantageous for more specific distribution of congenital versus myocardial disease in
sound localization in cats; it is often difficult to localize a mur- this species. In one echocardiographic survey of 92 cats
mur’s point of maximal intensity to the heart base or apex in shelters, 18–62% had left ventricular concentric
with an adult size chest piece in small animals. hypertrophy but none had a congenital cardiac lesion
(Wagner et al. 2010), and in over 400 cats presented to
a referral hospital for another study, the ratio of cats
The stethoscope diaphragm is optimal for hearing with myocardial disease to cats with congenital heart
higher frequency sounds such as the normal first and defects was approximately 23:1 (Ettinger 2010). Systolic
second heart sounds. Abnormal heart sounds can be murmurs that are loudest at the left heart base may be
defined as either transient (brief in duration) such as caused by SAM, congenital aortic stenosis, incompletely
split heart sounds or gallop sounds (S 3 or S 4 ), or of ausculted patent ductus arteriosus, or physiologic
longer duration (e.g., most murmurs). Gallop sounds (benign) murmurs. A common cause of physiologic
are low-frequency, diastolic sounds heard best with the murmurs in cats is mild, dynamic right ventricular
bell of the stethoscope (see Box 1.1). Cardiac murmurs outflow tract obstruction, which can produce a systolic