Page 287 - Feline Cardiology
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294 Section G: Congestive Heart Failure
• Treatment of moderate (nonregenerative) anemia with used in cats with refractory heart failure, but it may
erythropoietin may lessen degree of volume overload lessen hypokalemia and reduce potential deleterious
to the heart and improve oxygen handling capacity. effects of aldosterone on the cardiovascular system.
• Pimobendan is a positive inotrope and balanced arte- Spironolactone is an extremely weak diuretic, so it
riolar and venous vasodilator and is used to treat should not be expected to significantly reduce the sever-
refractory heart failure in all etiologies except hyper- ity of edema or pleural effusion accumulation (Jeunesse
trophic cardiomyopathy. Treatment of refractory heart et al. 2007). In a study of Maine coon cats and Maine
failure secondary to HCM with pimobendan is con- coon crossbred cats with familial HCM, one-third of
troversial, with some positive anecdotal experience. cats treated with spironolactone developed severe ulcer-
ative dermatitis attributed to a cutaneous drug reaction,
Refractory heart failure patients are defined as suffering and other cardiologists have similar anecdotal reports in
from recurrent pulmonary edema or pleural effusion some Maine coon cats (MacDonald et al. 2008). Another
despite multidrug therapy including high dose furose- option for refractory heart failure is substituting 1 to 2
mide (3–4 mg/kg PO q 8 h) and an ACE inhibitor (see subcutaneous doses of furosemide a week for the oral
Table 19.1). These patients most commonly have been doses, since oral bioavailability of furosemide is only
undergoing chronic treatment for months to years and ∼50% and may be lower if GI edema, inappetence, or
other factors interfere with absorption. If palatable, a
have suffered relapses in heart failure that have responded
Congestive Heart Failure tinue to have a good quality of life in the owner’s opinion. limit sodium and water retention and should be tried.
low-salt diet (0.15–0.2 g sodium/1000 kcal) will help
to increases in diuretic doses. Typically these cats con-
Treatment of refractory heart failure is differentiated
However, any commercial diet is preferable to anorexia,
from terminal heart failure by subjective assessment: the
and the furosemide dose is then raised accordingly to
owner and the attending veterinarian agree that treat-
offset increased sodium intake. Pimobendan (0.25 mg/
ment and monitoring for improvement are humane and
failure from all etiologies except pressure overload or
justified based on the cat’s demeanor and medical status.
Eventually, refractory heart failure deteriorates into a kg PO q 12 h) may be added in cats with refractory heart
hypertrophic cardiomyopathy. Treatment of cats with
terminal state, when there is failure to respond to rescue/ HCM and heart failure with pimobendan is controver-
refractory treatments, and end-of-life decisions must be sial and may be contraindicated if there is significant left
discussed. ventricular outflow tract obstruction.
In cats with refractory heart failure, the first task is to
increase the furosemide dose to the maximal tolerable Other Loop Diuretics: Torsemide
dose, and the maximal oral effective dose above which Torsemide is a loop diuretic that has 10 times the potency
no further diuretic effect is achieved is generally consid- of furosemide. Although it is not typically used in clinical
ered to be 4 mg/kg orally every 8 hours. If heart failure medicine, there are several potential advantages over
continues to recur, addition of a second diuretic (hydro- furosemide. Torsemide has a longer acting diuretic effect,
chlorothiazide 0.5–1 mg/kg PO q 12 hr or torsemide with a peak effect in cats seen 4 hours after oral adminis-
0.1–0.3 mg/kg PO q 12 hr)provides additional diuresis tration (0.3 mg/kg) that persists for 12 hours, compared
by inhibiting sodium absorption distal to furosemide’s to only 6 hours of diuretic effect after oral administration
site of action. Cats receiving high dose furosemide and of furosemide (Uechi et al. 2003). Torsemide is nearly
hydrochlorothiazide (1–2 mg/kg PO q 12 h) are prone to completely absorbed from the gastrointestinal tract, and
developing significant dehydration and azotemia. The has a high bioavailability of 80–100% in dogs, compared
goal in these patients with advanced cardiac disease is to to approximately 50% bioavailability of furosemide in
balance some degree of dehydration and azotemia with dogs (Ghys et al. 1985). Another advantage of torsemide
reduced dyspnea and improved quality of life. Thiazide over furosemide is that it inhibits the secretion and
diuretics are 1/3 as potent as furosemide for urinary receptor-ligand binding of aldosterone (Uchida et al.
sodium excretion. They inhibit the sodium chloride 1992; Goodfriend et al. 1998). Torsemide, but not furose-
cotransporter in the distal convoluted tubule, down- mide, decreases myocardial fibrosis and collagen synthe-
stream from the site of action of loop diuretics, thus sis in people with heart failure, which may be due to its
exerting “sequential nephron blockade” (Brater 1998). inhibition of aldosterone (Lopez et al. 2004). Similarly,
In an experimental feline isolated kidney model, chloro- torsemide improves left ventricular diastolic function in
thiazide doubled the urinary excretion of sodium and heart failure patients to a greater extent than furosemide
increased urinary loss of water and potassium (De Lima and is associated with a lower mortality than furosemide
and Lockett 1961). Spironolactone (1–2 mg/kg PO q in people with heart failure (Yamato et al. 2003; Cosin et
12–24 h), an aldosterone antagonist, is uncommonly al. 2002). Currently, the authors consider adding torse-