Page 194 - Small Animal Internal Medicine, 6th Edition

166 PART I Cardiovascular System Disorders

did not receive pimobendan (~4 months). Further clarifica-
BOX 8.1 tion regarding potential benefits of pimobendan on heart
VetBooks.ir Treatment Outline for Cats with failure progression, optimal management, and survival time
await results of prospective study. If pimobendan is elected
Hypertrophic Cardiomyopathy
cation is feasible, at the same initial dose as recommended
Severe, Acute Signs of Congestive Heart Failure* for a cat with CHF, the drug is given as soon as oral medi-
for dogs (0.2-0.3 mg/kg PO q12h). For most average-sized
Supplemental O 2
Minimize patient handling cats, this dose equates to one 1.25 mg chewable tablet twice
Furosemide (parenteral) daily. Cats with poor cardiac output or cardiogenic shock
Sedation (butorphanol) can receive pimobendan every 8 hours during initial stabi-
Thoracocentesis, if pleural effusion present lization, if needed. Cats with more severe cardiogenic shock
Pimobendan (±; see p. 69, caution if LV outflow may require IV dobutamine (usually given as a continuous
obstruction) ratet infusion (CRI) of 1-5 mcg/kg/min). Adverse effects
Antiarrhythmic therapy or heart rate control, if indicated † of dobutamine can include sinus tachycardia, ventricular
±Nitroglycerin (cutaneous)
±Dobutamine (if needed for cardiogenic shock) ectopy, and seizures; if these occur, the infusion rate is halved
Monitor: respiratory rate, HR and rhythm, arterial blood or discontinued.
pressure, renal function, serum electrolytes, etc. As respiratory distress resolves, furosemide can be con-
tinued at a reduced dose (≈1 mg/kg q8-12h). Once pulmo-
Mild to Moderate Signs of Congestive Heart Failure* nary edema is controlled, supplemental oxygen is withdrawn
Furosemide and the patient is transitioned to oral medications. The furo-
ACE inhibitor semide dose is gradually titrated downward to the lowest
Pimobendan (±; see p. 69, caution if LV outflow effective level. For example, a starting dose of 6.25 mg/cat
obstruction) q8-12h can be slowly reduced over days to weeks, depending
Antithrombotic prophylaxis (clopidogreal ± anticoagulant) ‡ on the cat’s response. Some cats do well with once daily or
Exercise restriction every other day dosing, whereas others require furosemide
Reduced-salt diet, if the cat will eat it
±β-blocker (e.g., atenolol) or diltiazem (see text) several times per day. If instituted, oral pimobendan is con-
tinued at the starting dose. Once initial acute respiratory
Refractory Congestive Heart Failure Management* distress has resolved and the cat is eating and drinking, ACEI
Furosemide (optimize dosage and frequency) therapy should be added. An ACEI usually is prescribed in
ACE inhibitor the hope of reducing neurohormonal activation and abnor-
Pimobendan (caution if severe LV outflow tract mal cardiac remodeling. Enalapril and benazepril are the
obstruction) agents used most often in cats, although others are available
Antithrombotic prophylaxis (clopidogrel ± anticoagulant) ‡ (see Chapter 3 and Table 3.3).
Thoracocentesis as needed The decision to use other drugs is influenced by echocar-
±Spironolactone diographic or other findings in the individual cat. β-blockers
±β-blocker or diltiazem offer several theoretical benefits for cats with HCM, although
±Additional antiarrhythmic drug therapy, if indicated
±Hydrochlorothiazide (closely monitor renal function/ clinical evidence for increased survival time is lacking, and
electrolytes) the possibility of a negative effect in cats with CHF exists.
Home monitoring of resting respiratory rate and effort Nevertheless, β-blockers can reduce heart rate (including
Dietary salt restriction, if accepted ventricular response rate in AF), reduce or resolve dynamic
Monitor renal function, electrolytes, etc. LV outflow obstruction, and suppress tachyarrhythmias.
Manage other medical problems (rule out Sympathetic inhibition also can reduce myocardial O 2
hyperthyroidism and hypertension if not done demand, which could be important in cats with myocardial
previously) ischemia or infarction. By inhibiting catecholamine-induced
myocyte damage, β-blockers might reduce myocardial fibro-
ACE, Angiotensin-converting enzyme; CHF, congestive heart failure; sis. Although β-blockers slow active myocardial relaxation,
HR, heart rate; IV, intravenous; LMWH, low-molecular-weight
heparin; LV, left ventricular. an increase in ventricular filling time from their heart rate
*See text, Box 3.1 (p. 62), and Chapter 3 for further details. lowering effect might outweigh this. If a β-blocker is used,
† See text, Table 4.2 (p. 90), and Chapter 4 for further details. the selective β-1 blocker, atenolol, is most commonly chosen.
‡ See Chapter 12 for further details. β-blockers, especially nonselective agents like propranolol,
are not recommended for cats in active CHF. Blockade of
have demonstrated that the drug is well tolerated in cats. bronchial β-2 receptors could exacerbate bronchospasm,
More recently, pimobendan has shown apparent long-term which might occur with pulmonary edema. Additionally, in
benefit and improved survival in “typical” HCM with normal cats with reduced myocardial contractility, the negative ino-
systolic function. In a retrospective case control study of cats tropic effect of β-blockers could promote acute CHF decom-
with HCM and CHF, cats that received pimobendan lived pensation. For cats receiving atenolol (or other β-blocker)
significantly longer (~21 months) compared with cats that before CHF, the drug could be continued or its dosage