Page 411 - Feline Cardiology

Chapter 29: Which Drug for Which Disease? 435

12h) could be beneficial in compensated state based CONGESTIVE HEART FAILURE
on asymptomatic human DCM, but unproven (and
dosage accuracy may be difficult). Diuretic level 1: mainstay of treatment, adequate in most
• Calcium-channel blocker: as for beta blocker; may be cases. Furosemide (acute crisis inpatient: 2–6 mg/mg IV
indicated if a severe supraventricular tachyarrhythmia as needed to produce improvement in respiratory signs,
coexists with DCM. then rapidly tapered as dictated by response; chronic
home treatment: 0.5–4 mg/kg PO q 8–24h, adjusted
Congestive heart failure: see below based on sodium intake, tractability/ease of pilling, and
Aortic thromboembolism: see below resolution of signs and stability, aiming for lowest effec-
Syncope: see “Arrhythmias,” below tive dose).
Diuretic level 2 (progressive heart failure): with
RESTRICTIVE/UNCLASSIFIED CARDIOMYOPATHY chronic furosemide treatment, diuretic resistance may
develop (e.g., increasing dosage but persistent edema/
Early (compensated) state is rarely identified, likely effusion, and evidence of lack of systemic diuretic
because the lesion of RCM/UCM is almost always silent effect [normal/disproportionately nonelevated BUN
(no murmur) and because its gradual progression elicits or serum creatinine, or urine specific gravity >1.025]).
adaptive mechanism that maintain a compensated state In these instances, furosemide may be replaced with
until severe signs of congestive heart failure, aortic torsemide (0.3 mg/kg PO q 24h, or divided q 12h) or
thromboembolism, or both, are evident. No specific hydrochlorothiazide.
treatment is recommended prior to the onset of clinical Diuretic level 3 (refractory heart failure): instead of,
signs. Anticoagulant therapy is indicated in cats with or in addition to, torsemide addition to furosemide, a
evidence of spontaneous echocardiographic contrast second diuretic may be added to treatment if chronic
(i.e., smoke and red blood cell aggregation), an intracar- furosemide is insufficient (patient experiences recurrent
diac thrombus, or may be considered in cats with mod- CHF). First, review possible sources of excess sodium
erate or severe atrial dilation. When congestive heart intake, mineralocorticoid sources, and unnecessary
failure is present:
stress/tachycardia, all of which should be controlled or
• Digoxin (0.01875–0.03125 mg/cat PO q 48h). abolished in conjunction with diuretic therapy. Some
Controversial. No conclusive benefit shown in feline cats do well with intermittent (2–3x/weekly) SQ injec-
RCM/UCM from digoxin. Mainly used for neurohor- tions of supplemental furosemide given by the owner at
monal, autonomic, and other benefits, since its ben- home.
efits for systolic function are not relevant in RCM/
UCM (disorder of diastolic dysfunction). May be • Spironolactone (1–2 mg/kg PO q 12h). May be con-
useful as a negative chronotropic agent via increased traindicated in cats due to severe ulcerative facial der-
vagal tone in cats with atrial fibrillation or other matitis in some cats; or
supraventricular tachyarrhythmias. Monitor for clini- • Hydrochlorothiazide (1–2 mg/kg PO q 12h), reduce
cal signs of toxicosis (vomiting, diarrhea, lethargy, by half when patient is stable and sodium intake is
inappetence). May assess serum levels, though no low.
known correlation to benefit or outcome in the cat
(used mainly to rule in/out toxicosis). Centesis: thoracentesis if pleural effusion shown to be
• Pimobendan (1.25 mg/cat PO q 12h). Controversial. sufficiently voluminous to be causing dyspnea.
Dosage extrapolated from canine studies (4–10 times ACE inhibitor: indicated concurrently with diuretics
higher than human dosage). Informally described in treatment for all disorders causing heart failure. With
11 cases of feline RCM (Sturgess et al. 2007). Risks HCM, improvement in echocardiographic parame-
associated with long-term treatment are unknown in ters and some clinical indicators (Amberger et al.
the cat, as are benefits. Benefits in heart failure patients 1999) but mild or insignificant in many cats (Fox
may be due to the balanced vasodilation (arterial and 2003, 2004). Which Rx?
venodilator) and positive lusitropy, as well as the Beta blocker: generally not initiated for the first time
positive inotropic effects. Off-label, and considered after the onset of congestive heart failure due to risk
investigational use. of excessive heart rate suppression. Exception: ectopic
tachycardias (rapid/frequent atrial or ventricular
Congestive heart failure: see below tachycardia). Beta blockade is maintained during
Aortic thromboembolism: see below CHF if patient was already receiving it prior to decom-
Syncope: see “Arrhythmias,” below pensation, except if heart rate is conspicuously low