Page 166 - Feline Cardiology

Chapter 11: Hypertrophic Cardiomyopathy 165

mental use is not indicated for treatment of HCM. cardiac events, and are less likely to become fluid over-
Positive inotropic agents such as digoxin or digitalis-like loaded compared to cats with left atrial dilation and/or
homeopathic therapies (hawthorne, compounds includ- heart failure. However, even cats with HCM and normal
ing strophanthus, foxglove, lily-of-the-valley, rhododen- left atrial size are at risk for fluid overload, since they
dron, oleander, milkweed) should not be given to cats have reduced left ventricular compliance and diastolic
with HCM, because they may worsen the severity of dysfunction. For specific protocols and details regarding
SAM and increase pressure overload to an already sedation and anesthesia of cats with HCM, see Chapter
hypertrophied left ventricle. Based on current knowl- 27.
edge, inodilators such as pimobendan are relatively con-
traindicated in cats with HCM unless there is end-stage COMPLICATIONS AND MONITORING
myocardial failure or possibly in refractory heart failure.
This relative contraindication may change with greater
research on the potential risk versus benefit analysis of Cardiomyopathies
inodilators in cats with HCM. Pimobendan is never a Key Points
substitute for an ACE inhibitor in cats with congestive
heart failure, and if indicated, it is given in addition to
standard therapy with furosemide and an ACE inhibitor. • Congestive heart failure, arterial thromboembolism,
and sudden cardiac death are the most common and
The use of long-acting corticosteroids, such as methyl- devastating clinical sequelae in cats with HCM
prednisolone acetate, is contraindicated in cats with • Prerenal azotemia and dehydration are common in heart
HCM, since it may significantly increase plasma- failure patients treated with furosemide ± an
circulating volume and may precipitate development of ACE inhibitor and are typically well tolerated unless
heart failure. severe.
• Mild functional azotemia is common following ACE
Considerations for General Anesthesia inhibitor therapy, and does not require altering
Cats with HCM may require anesthesia for routine pro- the therapeutic plan. Severe functional azotemia is
cedures (dental prophylaxis, dental extractions) or for addressed by stopping the ACE inhibitor, temporarily
diagnostic/therapeutic procedures of other more signifi- stopping the furosemide, and cautious fluid
diuresis.
cant systemic disease. The main concerns regarding • Supraventricular tachyarrhythmias such as atrial
anesthesia are minimizing fluid overload, avoidance of fibrillation or supraventricular tachycardia require
hypotension, and avoidance of pharmacologic agents treatment with either atenolol or diltiazem. Ventricular
that may worsen the severity of left ventricular outflow tachycardia should be treated with atenolol. Sotalol
tract obstruction in cats with SAM or exert proarrhyth- ± mexiletine may be used for refractory ventricular
mic effects. In a study of cats with congestive heart arrhythmias.
failure, the most common precipitating event was fluid • Monitoring of asymptomatic cats with HCM
administration (28%), followed by anesthesia/surgery includes repeat echocardiograms every 4–12 months
(25%) and recent corticosteroid administration (21%) depending on the severity and progression of the
(Rush et al. 2002). Ketamine was the most common disease. To evaluate for early heart failure, radiographs
anesthetic administered in 89% of anesthetized cats that should be obtained periodically (every 3–6 months)
developed CHF, but it was probably the most common in cats with significant left atrial dilation. These
recommendations must be balanced against the
anesthetic drug used in cats during the time of that patient’s anxiety and the client abilities in all cases
study. Ketamine increases heart rate and contractility, individually.
which may worsen left ventricular outflow tract obstruc- • Monitoring of cats with HCM and heart failure includes
tion in cats with significant SAM. Worsened SAM repeat thoracic radiographs and renal panels to assess
increases systolic left ventricular pressure and may clinical response and guide medical therapy. Thoracic
decrease myocardial perfusion and increase left ventric- ultrasound can be done to evaluate severity of pleural
ular filling pressure. Despite the “dogma” that cats with effusion and guide location for thoracocentesis. Targeted
heart disease should not be given ketamine, there is a repeat echocardiograms are done periodically (every
paucity of data detailing specific significant deleterious 3–6 months) to assess for presence of an intracardiac
cardiac effects. thrombus, or spontaneous contrast, and to evaluate
Cats with severe HCM and heart failure have a much myocardial function.
higher risk of adverse anesthetic or postanesthetic events • Systolic blood pressure and thyroxine levels should
be periodically evaluated in middle-aged to older cats
than cats with compensated heart disease, and elective that are at risk for developing systemic hypertension or
procedures should be avoided. However, cats with mild hyperthyroidism.
HCM and normal left atrial size have less risk of adverse