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Congestive Heart Failure

DEFINITIONS Most heart failure in cats is clinically identified as
backward failure (i.e., “wet”; congestive), versus forward
“low output” failure (i.e., “cold”), because the body pri-
Key Points oritizes maintenance of normal systolic blood pressure
over maintenance of normal capillary pressure. Since an
• Congestive heart failure is a clinical syndrome that overwhelming majority of cats with heart failure present
occurs secondary to severe heart disease of many with clinical signs of congestive heart failure (CHF)
causes, including those that cause severe diastolic rather than low output heart failure, the majority of the
dysfunction (e.g., hypertrophic cardiomyopathy or chapter will refer to CHF unless specifically stated as low
restrictive cardiomyopathy), systolic myocardial failure output heart failure. CHF may be left-sided (pulmonary
(e.g., dilated cardiomyopathy), or volume overload edema ± pleural effusion), right-sided (pleural effu-
secondary to valvular insufficiency or left to right sion ± ascites), or a combination of both (Figure 19.1).
shunting congenital heart diseases (e.g., ventricular Low output heart failure occurs when cardiac output is
septal defect).
• Backward heart failure consists of congestion and so severely decreased that there is poor tissue perfusion
edema. and arterial hypotension. It is uncommon in cats and is
• Forward heart failure (i.e., low output heart failure) often seen as a terminal event, unless precipitated by an
consists of low cardiac output, arterial hypotension, and acute transient tachycardia or bradycardia.
poor peripheral perfusion. CHF is the end result of severe cardiac disease;
• Left heart failure in cats is characterized by pulmonary however, many cats may have heart disease and never
edema and/or pleural effusion. develop heart failure. There are many diseases that can
• Right heart failure is characterized by pleural effusion lead to CHF in cats, and the majority cause diastolic
with or without ascites or mild pericardial effusion. heart failure (Figure 19.2). Diastolic heart failure is
caused by impaired diastolic filling that leads to elevated
diastolic filling pressure, in the face of normal systolic
function. The ventricles are able to contract normally,
INTRODUCTION
but they cannot normally accept the diastolic inflow of
Heart failure is a clinical syndrome caused by the inabil- blood within normal pressures (i.e., the heart is stiff or
ity of the heart to function within normal diastolic cannot relax), which leads to a backward transmission
filling pressures, which leads to congestion/edema (i.e., of elevated venous pressure to the capillary bed and
backward failure) or poor peripheral perfusion (i.e., ultimately leakage of fluid through the capillary wall to
forward heart failure) at rest or with exercise (Kittleson cause edema or effusion. Hypertrophic cardiomyopathy
1994). Previous definitions focused on the inability of (HCM), unclassified cardiomyopathy (UCM), and
the heart to pump, which is only one small fraction of restrictive cardiomyopathy (RCM) are all diseases that
the causes of heart failure in animals. Heart failure may cause diastolic dysfunction that may lead to CHF.
be a result of severe diastolic dysfunction, systolic myo- Systolic myocardial failure may lead to “pump” failure
cardial failure, or volume overload from valvular insuf- and subsequent increases in diastolic filling pressure.
ficiency or left to right shunting congenital heart diseases. Diseases causing systolic myocardial failure are less

Feline Cardiology, First Edition. Etienne Côté, Kristin A. MacDonald, Kathryn M. Meurs, Meg M. Sleeper.
© 2011 John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc.

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