Page 153 - Feline Cardiology

152 Section D: Cardiomyopathies

of systolic anterior motion of the mitral valve is consis-
tent but not entirely specific for HCM. Systolic blood • Beta blockers (i.e., atenolol) or calcium channel blockers
pressure and thyroid level should be measured in all cats (i.e., diltiazem) are the most commonly used drugs in
with evidence of left ventricular hypertrophy to identify asymptomatic cats with HCM, and they may reduce
possible secondary causes of hypertrophy. A gray zone severity of hypertrophy.
exists for diagnosis of HCM, where there may be papil- • Beta blockers are more effective than calcium channel
blockers to reduce severity of systolic anterior motion
lary hypertrophy that is subjectively apparent, or inter- of the mitral valve and control heart rate to prevent
mediate wall thickness of 5.5–5.9 mm, and these cats are tachycardia.
typically classified as equivocal for HCM. The cardiac • Clinical evidence from placebo controlled, blinded
myosin binding protein C (MYBPC3) genetic screening clinical studies indicate that early use of angiotensin
Cardiomyopathies cats as a preliminary test, but false negatives exist since • Prophylactic anticoagulant therapy is indicated if there
test may be useful to evaluate Maine coon or Ragdoll
converting enzyme inhibitors or aldosterone antagonists
in cats with asymptomatic HCM and no heart failure is
not warranted.
there may be other causative genes yet to be identified
(see Chapter 28). A positive test indicates that the cat has
is echocardiographic evidence of spontaneous contrast
the genotypic abnormality that may lead to phenotypic
development of HCM, but some cats may be have the
thrombus. It is controversial whether cats without these
mutation and may not develop concentric hypertrophy. (i.e., red blood cell aggregation) or an intracardiac
The main uses of the test at this time are for breeding findings but with significant left atrial dilation should
programs to identify breeding animals that may have the be placed on prophylactic anticoagulation. Prophylactic
anticoagulant therapy is not necessary in cats with
mutation and for pet animals of these two breeds that mild HCM and normal left atrial size, except in the rare
may be at risk for developing the disease, which justifies incidence where such a cat has a history of confirmed
further, more comprehensive evaluations with an echo- ATE.
cardiogram. The MYBPC3 test is not useful at this time
in other breeds of cats, but over time additional muta-
tions are likely to be discovered in different breeds of
cats with familial HCM. Decision processes in treatment of
Diastolic dysfunction is often identified using tissue asymptomatic cats with HCM
Doppler imaging in cats with HCM, but it is not neces- Treatment of asymptomatic cats with HCM and without
sary to make the diagnosis. Diastolic dysfunction is not heart failure, thromboembolism, or significant arrhyth-
specific to HCM, and cats with other cardiac diseases mia is controversial and clinical data are limited. There
may also have diastolic dysfunction. are many factors involved in deciding whether treatment
HCM is definitively diagnosed by postmortem exami- is appropriate for individual asymptomatic cats (Table
nation and histopathologic evidence of myofiber disar- 11.1), and objective data are insufficient to make a defini-
ray of the left ventricular cardiomyocytes, as well as tive treatment recommendation for all asymptomatic
gross evidence of concentric left ventricular hypertro- cats with HCM. In addition, cats with mild nonprogres-
phy and increased cardiac mass. However, myofiber dis- sive HCM may live many years without deterioration and
array may be patchy with regional distribution, so it may may not require medical treatment. Finally, long-term
be missed in some cases. The reader is referred to the clinical benefit has not been evaluated, so at this time
Pathology subsection of the Etiology section for more there is a void in information regarding potential prolon-
detailed information on pathologic abnormalities seen gation in symptom free interval or survival benefit.
in cats with HCM. The decision of whether to treat asymptomatic cats
with HCM is typically based on the degree of concentric
TREATMENT hypertrophy, the severity of left ventricular outflow tract
obstruction in cats with systolic anterior motion of the
Treatment of Asymptomatic Cats
mitral valve, left atrial size, presence of tachyarrhyth-
mias, and the temperament of the cat and the client’s
wishes for giving lifelong oral medications. Most often,
Key Points
the choice of medications for asymptomatic cats is
whether to consider a beta blocker or a calcium channel
• There is significant controversy regarding when to blocker. According to the American College of Cardiology
initiate treatment, and what is the most appropriate Expert Consensus on HCM in people, there is debate
medical therapy in asymptomatic cats with HCM and no
heart failure. over whether treatment of asymptomatic patients actu-
ally prevents or delays development of symptoms and