Small Animal Clinical Pharmacology - CYF MEDICAL DISTRIBUTION

THERAPEUTIC APPROACH TO HEART FAILURE
Table 17.1 Causes of heart failure – pathophysiological
classification
Heart failure can occur as a result of:
• Primary reduction of myocardial contractility
– Dilated cardiomyopathy
– Taurine deficiency
– Chronic myocarditis (rare)
• Systolic mechanical overload
Pressure overloading
– Aortic stenosis and pulmonic stenosis (rare)
– Pulmonary hypertension
Volume overloading
– Chronic degenerative valve disease
– Mitral (rare) and tricuspid dysplasia ( relatively rare)
– Aortic or pulmonic insufficiency (rare)
– Congenital left-to-right shunts, e.g. patent ductus
arteriosus, ventricular septal defect (rare)
• Diastolic mechanical inhibition
Pericardial disorders, e.g. pericarditis, cardiac neoplasms
Ventricular myocardial disorders, e.g. feline hypertrophic and
restrictive cardiomyopathies (rare)
• Altered electrical function
Dysrhythmias
the goal of heart failure therapies is to relieve/reduce
clinical signs of backward heart failure, improve/preserve
clinical signs of forward heart failure and prolong
survival. Some medications work in more than one
category, enhancing their potential clinical utility. For
example, pimobendan reduces preload and afterload
through mixed arterial and venous dilation, augments
ventricular systolic function, may help palliate clinical
signs attributed to pulmonary artery hypertension and
have salutary effects on the maladaptive cytokine profile
in heart failure.
Table 17.2 contains an overview of cardiovascular
pharmacology. Agents are classified into categories
based on mechanism of action. Table 17.3 contains a
summary of cardiovascular medications used in the
management of common small animal heart disease and
is broken down by stage of disease, e.g. clinical versus
preclinical. Tables 17.4a and 17.4b provide an overview
of the common drugs and their indications in the
management of cardiac disease in dogs (17.4a) and cats
(17.4b).
Many drugs have more than one mechanism. For
example, spironolactone is an aldosterone antagonist
that acts as a potassium-sparing diuretic and a neuroendocrine
modulator. Enalapril is an angiotensin
converting enzyme (ACE) inhibitor with vasodilatory
and neuroendocrine modulation properties. For the
purpose of this chapter, an agent that has more than
one effect will be mentioned in every appropriate section
but the majority of the discussion and dosing recommendations
will be covered in the section that represents
its primary use. In addition, formulations and dose rates
are not included for agents that currently have little to
no clinical use in small animal veterinary medicine.
Therapeutic approach to backward heart
failure (WET)
Relieve clinical signs of congestion
1. Abdominocentesis (dog) and pleurocentesis (cat,
rarely dog) as required
2. Preload reduction
a. Plasma volume reduction
i. Diuretics such as furosemide,
hydrochlorothiazide, spironolactone
(especially right heart failure)
b. Venodilation
i. Nitroglycerine (topical), pimobendan
c. Dietary sodium restriction
3. Inhibition of the renin-angiotensin-aldosterone
system (RAAS)
a. ACE inhibitors such as enalapril or benazepril
b. Aldosterone antagonist such as spironolactone
4. Improve diastolic dysfunction if present
a. Feline hypertrophic cardiomyopathy
i. Calcium channel blocker such as diltiazem
Therapeutic approach to forward heart
failure (COLD)
Improve forward cardiac output
1. Afterload reduction
a. Contraindicated in feline obstructive
cardiomyopathy and canine subaortic
stenosis
i. ACE inhibitors, hydralazine, amlodipine,
pimobendan, Na nitroprusside (IV)
2. Augment systolic myocardial function in diseases
characterized by systolic myocardial dysfunction
a. Canine and feline dilated cardiomyopathy
(DCM)
b. Canine chronic valve disease (CVD)
i. Pimobendan, dobutamine (IV), digoxin
(weak inotrope)
3. Treat clinically important (hemodynamically
significant) arrhythmias
a. Tachyarrhythmias
i. Ventricular
Lidocaine (IV), procainamide, sotalol,
amiodarone
ii. Supraventricular (excluding sinus
tachycardia)
Digoxin, β-blocker, calcium channel
blocker, amiodarone, sotalol
b. Bradyarrhythmias
i. Pacemaker
381