Page 120 - Feline Cardiology

Chapter 11: Hypertrophic Cardiomyopathy 119

evaluate for the potential for concurrent diseases that et al. 2003). Benign murmurs due to DRVOTO are typi-
may potentiate or negatively impact cardiac disease, cally soft, with a grade III or less, although there is a
such as diseases causing dehydration, clinical abnor- significant overlap between benign (innocent) murmurs
malities consistent with hyperthyroidism or renal failure, and murmurs due to SAM of the mitral valve in cats
or other systemic diseases that may influence treatment with HCM. Both benign murmurs due to DRVOTO and
decisions and monitoring for heart disease. pathologic murmurs caused by SAM are dynamic and
increase in intensity as the heart rate increases, so the
PHYSICAL EXAMINATION dynamic component is not a useful characteristic to dis-
tinguish murmur etiology. Presence of a murmur is very
• The most common auscultation abnormality is a insensitive (31–42%) for diagnosis of cardiomyopathy
systolic murmur (36–72% of cats), followed by a gallop in asymptomatic healthy cats, so auscultation alone is
heart sound (33%). Historically, only a small number not an adequate screening test (Paige et al. 2009; Wagner
of HCM cats (5%) were described as having normal et al. 2010). However, the presence of ≥III/VI holosys- Cardiomyopathies
heart sounds, although more recent echocardiographic tolic murmur has higher sensitivity (61%) for presence
screening studies of overtly healthy cats reported that of HCM in healthy cats (Wagner et al. 2010). In conclu-
a majority (up to 69%) of cats with HCM did not have a sion, the presence of a heart murmur justifies diagnostic
heart murmur on auscultation. imaging, ideally with echocardiography but possibly
• Dyspnea is the most common clinical abnormality in cats with serial thoracic radiography.
with heart failure. Dyspnea was present in 36% of cats
with HCM in one study. A gallop heart sound is the second most common
auscultation abnormality, and is present in approxi-
mately 1/3 of cats with HCM. A gallop heart sound is
A systolic murmur is the most common abnormality less common (33% of cats) than a murmur in cats with
on physical examination, and is present in 47–72% of HCM (Ferasin et al. 2003). A gallop consists of an extra
cats with HCM examined in a referral hospital setting heart sound (either S 3 or S 4 heart sounds) due to the
(Ferasin et al. 2003; Rush et al. 2002). Prevalence of a reverberation of the ventricular walls during early or late
murmur may be higher in these patients than in the diastolic filling when the ventricle is stiff or enlarged due
general population of cats screened for HCM, as they to cardiac disease or increased preload (see Chapter 1).
were likely referred for evaluation of a murmur. There A gallop is not an abnormal heart rhythm, although
was a lower occurrence (31%) of a murmur in clinically popular nomenclature often describes it as a gallop
healthy cats in the general population that were diag- rhythm. An S 3 heart sound occurs when there is rapid
nosed with HCM during echocardiographic screening passive filling into a stiff, hypertrophied ventricle, which
(Paige et al. 2009). Most often the systolic murmur is creates the extra heart sound. Other causes of an S 3
caused by left ventricular outflow tract obstruction gallop include marked increase in volume of blood
(LVOT), which is typically due to systolic anterior entering the ventricle in early diastole, which may be
motion (SAM) of the mitral valve and less commonly present in cats with diseases causing volume overload.
by a narrowed LVOT due to basilar septal hypertrophy. An S 4 heart sound occurs during atrial systole when the
LVOT obstructions create a dynamic holosystolic left atrium is ejecting the remaining 20% of stroke volume
parasternal murmur that typically increases in intensity into a noncompliant left ventricle. A gallop is not spe-
as the heart rate increases. Cats with SAM of the mitral cific for HCM and may be heard when there are other
valve have higher murmur grades than cats without heart diseases present, anemia, fluid overload, or hyper-
dynamic left ventricular outflow tract obstruction (Rush thyroidism. In fact, gallop heart sounds are more com-
et al. 2002). In cats with SAM of the mitral valve, the monly ausculted in cats with dilated cardiomyopathy
murmur grade does not predict the severity of the (79% of cats) than in cats with other cardiomyopathies
disease, including extent of wall thickness or left atrial including HCM (Sisson et al. 1991). Other “extra” heart
dilation. Presence of a heart murmur is not diagnostic sounds that may be confused for gallop heart sounds
for HCM and murmurs can be heard as a benign finding include a split first or second heart sounds or a systolic
in cats with dynamic right ventricular outflow tract click (see Chapter 1).
obstruction (DRVOTO), which may be present in 25– Tachycardia is variably present in cats with HCM,
69% of healthy asymptomatic cats with heart murmurs including only 26% of cats in one study, so it is not likely
and echocardiographically normal hearts (see Chapter to be a useful diagnostic parameter (Ferasin et al. 2003).
1) (Paige et al. 2009; Wagner et al. 2010). Pathologic Heart rate is influenced by many factors including
murmurs may be associated with other heart diseases, environment and stress, so presence of tachycardia is
although murmurs are more common in cats with HCM not specific for any heart disease in cats. Heart rate of
compared to other feline cardiomyopathies (Ferasin cats in the hospital setting is often driven by increased