Page 282 - Feline Cardiology

Chapter 19: Congestive Heart Failure 289

treated with an ACE inhibitor. Thus, in cats receiving resistance develops. Palatability is often a challenge in
ACE inhibitors, one possible explanation for their lack cats more than dogs, so the primary nutritional goal is
of any detectable benefit on myocardial hypertrophy for the cat to maintain adequate caloric intake rather
even after daily treatment for 1 year is that the body than insistence of feeding exclusively a low-salt diet.
circumvents the pathway being blocked by the ACE Moderately salt-restricted commercial renal diets are
inhibitor (MacDonald et al. 2006). This important con- also often protein restricted, which is contraindicated in
sideration has led to an interest in angiotensin receptor patients with heart failure unless there is concurrent
blockers (ARBs). severe renal dysfunction. Choices of low-salt cardiac
Angiotensin receptor blockers (ARBs; e.g., losartan, diets include commercially available diets (e.g., Purina
candesartan, valsartan) block the type I receptor for CV or Hills H/D) or a home-cooked diet that has been
angiotensin II, which mediates deleterious processes of formulated and balanced by a veterinary nutritionist
angiotensin II including vasoconstriction, salt and water (balanceit.com, petdiets.com [fee involved], Strombeck:
retention, hypertrophic responses, and fibrosis. The Home-Prepared Dog and Cat Diets: The Healthful
main reason these drugs were developed were to treat Alternative. Wiley-Blackwell, 1999). Water softeners add
people who were intolerant to ACE inhibitors, typically salt to the water and should be avoided in animals with
those with ACE inhibitor induced cough (due to heart failure. Omega 3 fatty acids (40 mg/kg PO q 24 hr
increased bradykinin concentration). There appears to eicosapentaenoic acid, 25 mg/kg PO q 24 hr docosa-
be similar benefit of ARBs compared to ACE inhibitors hexaenoic acid) should be given to animals with pro-
for treatment of heart failure in people, but addition of gressive weight loss and cardiac cachexia, since their
ARBs to ACE inhibitors may actually have additive anti-inflammatory properties may lessen the deleterious
improvement in morbidity and mortality, as evidenced anabolic effects of pro-inflammatory cytokines (tumor Congestive Heart Failure
in the CHARM trial (Ravandi and Teo 2009; Pfeffer et necrosis factor-α and interleukin 1) (Freeman et al.
al. 2003). The benefit in reduction of all-cause mortality 1998).
and cardiovascular mortality, and reduction of risk of
hospitalizations for heart failure appears to be more pro- Additional medical therapies
nounced in patients with systolic myocardial failure, and Beta blocker therapy should be postponed in cats with
when isolating patients with diastolic heart failure, there HCM and congestive heart failure until the heart failure
is a reduction in risk of heart failure hospitalizations but is compensated, and it is debatable whether to be started
no difference in all-cause mortality or cardiovascular at all once heart failure occurs. This is because the body
mortality (Pfeffer et al. 2003 Yusuf et al. 2003). However, relies on an activated sympathetic nervous system to
only 20% of people in the diastolic heart failure group maintain cardiac function and blood pressure during
were also receiving an ACE inhibitor, which may have decompensated heart failure. Once the cat has stabilized
caused additive benefits. Addition of an ARB to ACE with no active heart failure and is normotensive, beta
inhibitor therapy may be associated with worsened azo- blocker therapy may be considered in particular HCM
temia in people, making it imperative to closely monitor cases. Beta-blockade is generally not initiated in HCM
renal status. No studies have evaluated ARBs in cats, and once heart failure has developed, but may be continued,
there are no studies evaluating basic pharmacokinetics possibly at a lower dose, in cats already given chronic
in cats. Losartan, although popular in human medicine, beta blocker therapy provided that they are not hypo-
is not metabolized into an active metabolite in the dog, tensive or bradycardic (see Chapter 11 for more discus-
limiting the use in this species, and there is no informa- sion). Beta blockers or calcium channel blockers may be
tion regarding its metabolism in cats. Other ARBs (val- necessary in cats with active heart failure if there is a
sartan, irbesartan) have been used in experimental significant tachyarrhythmia that worsens the hemody-
models of heart failure in dogs. At this point, since there namic status of the cat—for example, in a cat hospital-
is a void in basic information regarding pharmacologic ized for acute treatment of congestive heart failure that
properties of ARBs in cats and no safety data available, has improved dyspnea and clinical stabilization, but the
their use is not recommended for clinical feline patients. heart rate remains at 280 bpm (rather than an expected
heart rate of 150–220 bpm). Negative chronotropic
therapy should be considered, after evaluation by an
Additional Therapies for Chronic Congestive
Heart Failure ECG to characterize the arrhythmia. Diltiazem would be
the drug of choice for cats with active heart failure and
Diet severe supraventricular tachycardia or rapid atrial fibril-
A low-salt diet (<0.6 g/kcal) is not usually implemented lation, whereas injectable lidocaine, procainamide, or
at the initial diagnosis of heart failure, but may be esmolol may be used for acute treatment of life threaten-
helpful over time as heart failure progresses and diuretic ing ventricular tachyarrhythmias (see Chapter 18).