Page 162 - Feline Cardiology

Chapter 11: Hypertrophic Cardiomyopathy 161

ration done. Sedation may be needed in anxious or heart failure, cats require lifelong furosemide therapy,
fractious cats. Typical sedation “cocktails” may include the only exception being congestive heart failure that
midazolam and an opioid, or low-dose acepromazine was triggered by a transient precipitating factor such as
(0.01 mg/kg) and an opioid. The opioid chosen depends intravenous fluid administration.
on the clinician’s personal preference; options include Often cats with HCM and heart failure are given a
hydromorphone (0.05–0.1 mg/kg parenterally) or butor- multitude of medications, including furosemide, an
phanol (0.1–0.4 mg/kg preferably IV using gentle ACE inhibitor, an anticoagulant, and possibly a negative
restraint). Many cats with an even temperament or with chronotrope. Since cats are often sensitive to side effects
significant dyspnea do not require sedation. A butterfly (i.e., lethargy, anorexia, vomiting) of multipharmacy
catheter (19 gauge is preferred by the authors), 3-way treatment, starting the two most important drugs and
stop cock, extension set, and a 30–60 ml syringe are then staggering the remainder over the next 7–10 days
attached. A sample of the pleural effusion should be is recommended. An ACE inhibitor may be started con-
submitted for fluid analysis and cytology (see Chapter 3). currently with furosemide in outpatient treatment of Cardiomyopathies
In cats stable enough to be treated at home, oral furo- heart failure. In cats that have been hospitalized and
semide is started at doses as low as 1 mg/kg PO q 24 hr given high doses of furosemide, the ACE inhibitor can
for mild heart failure, to higher doses of 2–3 mg/kg PO be postponed until they are home, eating and drinking,
q 8–12 h for moderate heart failure, and 3–4 mg/kg PO to lessen likelihood of significant azotemia. ACE inhibi-
q 8 h for severe or refractory heart failure (see Chapter tors may be given to cats with mild prerenal azotemia
10). Cats with significant heart failure that do not require secondary to diuretic therapy, but initially should be
hospitalization can be given an injection of furosemide postponed in cats with moderate to severe azotemia
(2–3 mg/kg) prior to discharge. Cats tend to be more (acute change from normal values to BUN >80 mg/dl
prone to dehydration, anorexia, and prerenal azotemia (28 mmol/l), creatinine >3 mg/dl (264 mmol/l)). A low
on furosemide therapy than dogs. Assessment of basal dose of the ACE inhibitor (preferentially benazepril to
renal function prior to furosemide and an ACE inhibitor avoid problems with sole renal elimination of the drug)
is necessary, including chemistry and urinalysis. The may be initially started in azotemic cats, and up-titrated
initial furosemide dose may be higher to clear the fluid, depending on the cat’s clinical status and whether azo-
and then tapered to the minimal effective dose depend- temia has significantly worsened (i.e., 50% increase in
ing on respiratory rate and character at home. Ideal azotemia in already azotemic animals) on a follow-up
respiratory rate is <40 breaths/min at rest in the home renal panel. In cases of worsened azotemia as described
environment, with normal respiratory effort. Owners above, the dose of the ACE inhibitor may need to be
should be trained on monitoring resting respiratory rate decreased or the drug discontinued.
and subjectively assess the respiratory effort twice a day When choosing the specific ACE inhibitor, cost of the
initially and then at least once a day, and a log should be medication, frequency of dosing, and route of elimina-
kept and reviewed by the doctor during phone follow- tion of the drug affect the decision. Enalapril is the most
ups and recheck evaluations. Cats with resting respira- commonly used ACE inhibitor in the United States and
tory rates of >40 at home often have ongoing congestive is entirely eliminated by the kidneys. The recommended
heart failure and may require a higher dose of furose- dose is 0.5 mg/kg PO q 12–24 h, and the smallest size
mide. A recheck is planned in 1–2 weeks for cats with tablet available is 2.5 mg. Benazepril is mainly metabo-
mild heart failure that respond well to treatment (nor- lized through the liver (85%), and pharmacokinetics are
malization of respiratory effort and rate and return of not altered in the face of renal dysfunction. The recom-
good appetite, in 24 hours or less), and in 3–7 days for mended dose of benazepril is 0.5 mg/kg PO q 24 hr, and
cats with more severe heart failure depending on clinical the smallest size available is 5 mg tablets (King et al.
response. If a 7-day recheck is unavailable or unaccept- 1999, 2003). Likewise, ramipril is mostly eliminated
able to the owner, a phone consultation and review of through the liver (87%) and is also a good choice for
the respiratory log and overall clinical status of the cat cats with known renal insufficiency. The recommended
is very helpful to identify whether the response to dose of ramipril is 0.5 mg/kg PO q 24 hr, and it is sup-
diuretic therapy is adequate. The main criteria of a good plied as 2.5 mg tablets (Coulet and Burgaud 2002).
clinical response to diuretic therapy is the normalization All ACE inhibitors exhibit a class effect of reducing
of resting respiratory rate and respiratory effort, return glomerular efferent arteriolar tone through reducing
of appetite, and return of normal or near-normal behav- angiotensin II. In some patients, there is excessive effer-
ior. Thoracic radiographs are essential to monitor for ent arteriolar vasodilation, leading to a moderate
presence of pulmonary edema or pleural effusion that decrease in glomerular filtration rate and development
would dictate increasing the furosemide dose. Once in of significant azotemia (i.e., functional azotemia). This