Page 1026 - Cote clinical veterinary advisor dogs and cats 4th

506 Hypertrophic Cardiomyopathy

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atrial diameter > 16 mm in the cat denotes Acute General Treatment ○ ± Potassium supplement if serum K
left atrial enlargement, consistent with a more Acute decompensated CHF (p. 408): ≤ 3 mEq/L (dosage 2-4 mEq/CAT PO q
VetBooks.ir • Electrocardiogram (ECG): supraventricular or • Oxygen therapy in oxygen cage (p. 1146), • Anticoagulation for prevention of ATE
• Thoracocentesis if voluminous pleural effu-
8-12h)
advanced disease state.
sion (p. 1164)
ventricular premature complexes are possible.
○ Clopidogrel is a potent platelet inhibitor
Atrial fibrillation is possible but less common.
(18.75 mg/CAT PO q 24h), or
minimize stress
Left axis deviation (mean electrical axis, 0° to • Furosemide 1-4 mg/kg IV ○ One baby aspirin (81 mg ASA)/CAT or
−90°) or increased QRS amplitude > 1 mV • +/− Nitroglycerin 5 mg/CAT PO q 3 days, or
may indicate LVH, but substantial overlap • Concurrent fluid therapy is contraindicated. ○ Low-molecular-weight heparin (enoxapa-
exists among normal cats. • Avoid beta-blocker therapy during acute/ rin) 1.5 mg/kg SQ q 12h; pharmacoki-
• Clinicopathologic evaluation: CBC, serum critical CHF (unless severe tachyarrhythmia); netics and optimal dosing are still under
biochemistry profile, urinalysis unremarkable controversial whether to start after CHF investigation; if ATE has occurred or a
unless ATE (p 74). resolves thrombus or spontaneous contrast persists,
• Serum T 4 and systolic blood pressure: to q 12h dosing is changed to q 8h.
rule out secondary LVH Chronic Treatment ○ Combination anticoagulant therapy is
• Thoracic radiographs: often normal if no left Reduce SAM if moderate or severe: atenolol controversial but has been done in cats
atrial enlargement. Moderate or severe cases or diltiazem with persistent spontaneous echo contrast
may show evidence of left atrial enlargement • Atenolol 6.25-12.5 mg/CAT PO q 12-24h. or recurrent ATE.
and CHF (p. 408). Start at low dose (e.g., if asymptomatic, • Antiarrhythmic therapy if persistently rapid
• NT-pro-BNP (Cardiocare, IDEXX 6.25 mg/CAT PO q 12h), recheck in 1-2 supraventricular or ventricular tachycardia
Laboratories) often is markedly elevated weeks, and increase to 12.5 mg/CAT PO (pp. 96 and 1033)
in dyspneic cats with CHF (typically q 12h if heart rate (HR) remains > 170
> 200 pmol/L; sensitivity 90%-95%, beats/min and/or if SAM severity on Nutrition/Diet
specificity 85%-88%) and may be elevated echocardiogram is not improved. Do not Sodium restriction only if palatable and
in some asymptomatic cats with moderate increase atenolol if HR < 130 beats/min. only with CHF; goal is to minimize diuretic
to severe HCM (>100 pmol/L). Use of NT- • Diltiazem: less effective than atenolol in requirement
pro-BNP along with clinical information, reducing SAM and preventing tachycardia;
including thoracic radiographs, may improve fallen out of favor due to erratic drug levels Behavior/Exercise
accuracy in diagnosing heart failure (accuracy of sustained release format and thrice- Avoid encouraging intense physical activity
increased from 69% to 87% with knowledge daily dosing of standard form. Dosage of (e.g., laser pointer toy), which increases HR
about NT-pro-BNP). The point-of-care diltiazem (regular) 7.5 mg/CAT PO q 8h; and myocardial oxygen demand
NT-pro-BNP SNAP test may be useful to sustained-release diltiazem 30 mg/CAT PO
identify symptomatic cats with CHF and q 12-24h (Dilacor-XR) or 10 mg/kg PO q Drug Interactions
may be positive for cats with moderate 24h (Cardizem CD). • Diuretics and ACE inhibitors may exacerbate
to severe occult HCM (positive value is Benefit of antihypertrophic treatment for renal dysfunction.
> 100 pmol/L). moderate to severe LVH (wall thickness • Concurrent use of beta-blockers and calcium
> 7 mm) is unknown. channel blockers is generally contraindicated
Advanced or Confirmatory Testing • Atenolol or diltiazem as above; may reduce because they may cause bradycardia and
Tissue Doppler imaging (TDI) echocardiog- LVH in some cases but controversial hypotension.
raphy (pulsed-wave Doppler or color TDI) to • Angiotensin-converting enzyme (ACE)
identify diastolic dysfunction may be abnormal inhibitors or aldosterone antagonist (spi- Possible Complications
before development of LVH as an early finding ronolactone) not likely to be of benefit in • The three main complications of severe HCM
during screening for HCM in predisposed early compensated HCM are ATE (12%-17%), CHF (46% in one
breeds. Pimobendan may be beneficial in cats with study), and sudden death.
HCM and CHF, but it should be used with • Prerenal/renal azotemia and hypokalemia
TREATMENT caution in cats with SAM because it can worsen during treatment with diuretics
dynamic obstruction. • Cats receiving high doses of diuretics
Treatment Overview Chronic CHF (p. 409): furosemide and an may have mild to moderate azotemia but
• Treatment of CHF: reduce the accumulation ACE inhibitor are standard therapy. often maintain reasonable quality of life
of pleural effusion or pulmonary edema. • Chronic refractory CHF without requirement for concurrent fluid
• Antihypertrophic treatment in attempt to ○ Addition of second diuretic: spirono- administration.
reduce the concentric hypertrophy of the left lactone 1-2 mg/kg PO q 24h; potential • ACE inhibitors occasionally may cause
ventricle and decrease myocardial stiffness; risk of cutaneous drug reaction in Maine acute renal azotemia, which may reverse
unproven efficacy coon cats. Hydrochlorothiazide occasion- after discontinuation of the ACE inhibitor
• Reduce SAM if moderate or severe (pres- ally used in refractory CHF in cats: and supportive care.
sure gradient > 50 mm Hg), which reduces consider conservative dose of 0.5-1 mg/
the pressure overload of the left ventricle, kg PO q 24h, up-titrate to twice-daily Recommended Monitoring
reduces mitral regurgitation, and potentially dosage if necessary and azotemia is not • Baseline serum renal panel and urinalysis;
reduces concentric hypertrophy in severe prohibitive. repeat renal panel q 12-24h during acute
obstructions. ○ Consider switching from PO furosemide in-hospital CHF treatment.
• Antiarrhythmic treatment for severe tachyar- to torsemide (dosing not well defined in • Repeat renal panel 1-2 weeks after initiating
rhythmias such as ventricular tachycardia, cats; consider 10 of daily furosemide dose ACE inhibitor, and decrease or discontinue
1
supraventricular tachycardia, or atrial fibrillation divided for twice-daily dosing) ACE inhibitor (and reduce diuretic if
• Anticoagulant therapy in animals at high risk ○ Consider SQ administration (increased possible) if moderate to severe azotemia is
for ATE (spontaneous contrast, severe left bioavailability compared with oral) of present.
atrial dilation, or a left atrial thrombus seen furosemide 1-2 times/week if persistent • Thoracic radiographs to monitor CHF;
on echocardiogram) or in animals having CHF despite furosemide 3-4 mg/kg PO recheck radiographs q 2-4 months once
previously suffered ATE q 8h. stabilized.

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