Page 19 - Feline Cardiology

Chapter 1: Heart Murmurs and Gallop Heart Sounds 9

scope is applied to the thorax and evaluate whether the
intensity of the murmur changes. These “false murmurs”
are easiest to produce at the heart base and likely repre-
sent compression of the great vessels in an animal with
a compliant chest wall.

Prevalence of Heart Murmurs Clinical Entities
Heart murmurs are a common finding in the general cat
population. Various screening studies have identified a
prevalence of heart murmurs in overtly healthy cats of
21% (blood donor candidates; n = 103) (Côté et al.
2004), 16% (privately owned cats; n = 103) (Paige et al.
2009), 27% (same privately owned cats after provoca-
tion, wherein the examiner quickly lifted the cat in the A
air twice) (Paige et al. 2009), and 34% (cats in shelters;
n = 199) (Wagner et al. 2010). No association between
heart murmurs and overt physical characteristics (coat
color, eye color, or breed) has been identified (Côté
et al. 2004). Echocardiography in these groups has
revealed structural heart disease in a substantial propor-
tion of cases: 16 (16%) of 103 seemingly healthy cats had
hypertrophic cardiomyopathy (HCM) in 1 study (5 with
a heart murmur, 11 without a heart murmur) (Paige et
al. 2009), and 18–62% of 92 cats (depending on criteria
used for defining ventricular wall thickness) had left
ventricular concentric hypertrophy in another study
(Wagner et al. 2010). B
The presence of a heart murmur does not confer a
diagnosis of a structural cardiac lesion. Between 25% Figure 1.3. Left lateral radiographs from a young cat (A) and
(Bonagura 2000) and 69% (Paige et al. 2009) of cats with from a middle-aged cat (B) showing the flattened cardiac angle
murmurs on physical examination have no echocardio- (yellow line), which can occur normally as cats age and which
can further concentrate normal and abnormal heart sounds in the
graphic evidence of heart disease, showing that no con- parasternal region in adult, older cats.
clusions can be drawn about the structure of a cat’s heart
based on the detection of a heart murmur. Moreover,
although they are a common finding, murmurs in list is formulated, further diagnostic tests such as tho-
cats can be challenging for many practitioners to evalu- racic radiography and/or echocardiography can help to
ate for several reasons. The rapid resting heart rate of establish a definitive diagnosis.
many cats (routinely > 200 beats/minute), particularly Although findings on physical examination may
when nervous at a veterinary hospital, can abbreviate the suggest the cause of a murmur, echocardiography is the
duration of murmurs to such a point that they are not only readily available way to identify the specific cause
auscultable. Making murmur characterization even of a murmur (and the type of heart disease, if heart
more difficult in cats is the close proximity of heart valve disease is present). However, echocardiography may not
areas on the thorax, so clear definition of valve areas is be feasible in all patients with murmurs, due to various
less certain in this species. Additionally the heart posi- constraints. In these individuals, a reasonable approach
tion in the thorax changes with age in cats resulting in is serial radiography. If the heart size is normal, hemo-
all valve areas becoming more parasternal in location dynamically significant structural heart disease is
(Figure 1.3). Despite these difficulties, characterizing unlikely and regular monitoring of heart size with this
murmurs by timing in the heart cycle and the point of modality is a reasonable alternative when echocardiog-
maximal intensity is a critical part of the physical exami- raphy is not available. For example, if the heart size is
nation and should be undertaken using the suggestions normal and remains normal over subsequent studies,
presented earlier in this chapter. This accurate charac- the patient is unlikely to benefit from cardiac medica-
terization of murmurs is crucial for the development of tions. It is important to remember that cardiac medica-
a thorough, specific differential diagnostic list, particu- tions are not instituted to treat murmurs, but to treat
larly in young animals. Once the differential diagnosis the underlying diseases that produce the murmurs.