Page 223 - Clinical Small Animal Internal Medicine

19 Management of Heart Failure 191

there are rare reports of hepatotoxicity. Initial dosage of common than with BB. Diltiazem also has mild vasodila-
VetBooks.ir carvedilol is 0.05–0.1 mg/kg BID and is slowly titrated tory properties and monitoring blood pressure and heart
rate is recommended.
upward over 4–8 weeks to a final target dose of 0.5–
Verapamil is rarely used in veterinary patients although
1.0 mg/kg BID. Metoprolol is a beta‐1‐specific antago-
nist that is metabolized by the liver. Target dose is it is commonly used in humans with HCM. One author
0.2–0.4 mg/kg BID and 0.4–1 mg/kg q24h for the sus- (SR) has seen benefit in feline HCM patients with severe
tained‐release preparation. In humans, studies suggest a left ventricular hypertrophy and dynamic left ventricular
benefit of sustained‐release formulations due to more outflow tract obstruction. Verapamil provides heart rate
stable blood levels. Sotalol is a nonselective BB with control in addition to supposed effects on diastolic func-
potassium channel‐blocking antiarrhythmic properties. tion. Gastrointestinal side effects are common when
It is primarily used as an antiarrhythmic agent in dogs using verapamil and can be minimized by administering
with DCM or arrhythmogenic right ventricular cardio- with food. In cats, verapamil has a starting dose of 1 mg/
myopathy and is dosed at 1–3 mg/kg BID in dogs and kg BID with upward titration based on clinical signs,
2 mg/kg BID in cats (see Chapter 20). heart rate, and blood pressure over 2–3 weeks to a maxi-
mal dose of 5 mg/kg BID, with a target heart rate between
Calcium Channel Blockers 120 and 160 bpm. Amlodipine will be discussed under
Diltiazem, amlodipine, and rarely verapamil are calcium the refractory treatment of congestive heart failure.
channel blockers (CCB) used in the management of
chronic heart failure. Differences in the three agents Antithrombotic Therapy
center around their propensity for cardiac effects on heart
rate and myocardial contractility versus peripheral effects Thromboembolism is a common risk factor in human
of smooth muscle relaxation and peripheral vasodilation. patients with chronic heart failure, especially in the pres-
Among the most commonly used CCB, amlodipine has ence of atrial fibrillation. In dogs, clinical systemic arte-
the greatest vasodilatory properties, followed by diltiazem rial thrombosis is uncommon while in cats, arterial
and then verapamil. Conversely, verapamil is a potent thromboembolism is a devastating clinical complication
negative cardiac chronotrope and negative inotrope, fol- of cardiomyopathy. The exact mechanism behind arte-
lowed by diltiazem and then amlodipine, the latter of rial thrombosis is complex and the most effective strat-
which has very little effect on cardiac myocardial tissue. egy to prevent and treat is unknown.
In dogs, the most common indication for diltiazem is Chronic oral agents commonly administered to reduce
for ventricular rate control in atrial fibrillation and is the risk of thrombosis are aspirin and clopidrogrel. Less
dosed at 0.5–1.5 mg/kg q8h (See Chapter 21) Sustained‐ commonly, warfarin or injectable unfractionated or low
release preparations (Cardizem® CD and Dilacor®) are molecular weight heparin are used. More recently, the use
dosed at 3 mg/kg BID in dogs. Diltiazem is often pre- of factor Xa inhibitors like rivaroxaban and apixaban has
scribed in cats with HCM with or without atrial fibrilla- been recommended for patients with recurrent emboli or
tion and including cats with left ventricular outflow tract poor tolerance to other antithrombotic agents. In one
obstruction. The authors use either diltiazem or atenolol study, clopidogrel was more effective than aspirin in pre-
in cats with severe HCM and echocardiographic evi- venting reoccurrence of thromboembolism in cats with a
dence of diastolic dysfunction. Diltiazem is typically previous history of thrombus. Antithrombotic agents are
added to the treatment regimen once the cat is receiving also empirically administered in cases with a perceived
furosemide, ACEI, and antithrombotic agents. In cases increased risk thromboembolism. These risk factors
of active CHF, the authors often delay initiation of CCB include the presence of an intracardiac thrombus, spon-
or BB until after the patient is stable on the aforemen- taneous echocardiographic contrast (“smoke”), severe left
tioned cardiac drugs to try to reduce the incidence of atrial dilation, protein‐losing nephropathies, hypopro-
adverse reactions, such as bradycardia or hypotension. teinemia, pulmonary hypertension, immune‐mediated
In cats, diltiazem is dosed at 7.5 mg/cat q8h. Sustained‐ hemolytic anemia or heartworm disease. For aspirin ther-
release diltiazem preparations are available (Cardizem apy, the authors utilize 20–81 mg/cat q72h in cats and
CD, 10 mg/kg q24h; Dilacor XR 30 mg/cat q12 h). 1–5 mg/kg q24h in dogs. Clopidrogrel is dosed at ¼ of a
Canine patients generally tolerate diltiazem while cats 75 mg tablet (18.75 mg) q24h in cats and 3–5 mg/kg q24h
have a higher incidence of gastrointestinal upset, loss of in dogs. Cats, in particular, often do not like the taste of
appetite, and hypersalivation. The authors recommend clopidrogel, which can lead to vomiting, hypersalivation,
administering diltiazem with food or encapsulating the anorexia, and difficulties in pill administration.
tablet in a gelatin capsule to hide the adverse taste from Antithrombotics agents can lead to adverse reactions
the cat. Diltiazem has some negative inotropic effects when used with corticosteroids or nonsteroidal antiin-
that can exacerbate signs of CHF, although this is less flammatory agents and might reduce the efficacy of