Heart Failure in Dogs

Chapter 147 Heart Failure in Dogs

Heart failure (HF) is a state wherein the cardiac output is inadequate to meet the perfusion needs of the metabolizing tissues and exercise capacity is limited. The causes of HF in dogs are diverse, but there are stereotypical cardiovascular and systemic responses to impaired cardiac function, regardless of cause. This chapter provides a brief overview of HF; considers the causes and diagnoses of HF in dogs; and reviews treatment plans for management of the cardiac failure patient. The clinical pharmacology and pathophysiologic rationale for drugs used in treatment of HF are detailed in Chapter 146. Management of HF in cats is discussed in the chapter “Cardiomyopathy” (Chapter 150).


Heart failure is a not a specific disease but a pathophysiologic disorder. Some of the key abnormalities of this condition are summarized below, and the pathophysiologic rationale for using particular cardiovascular drugs is summarized in Chapter 146. The reader is directed to other textbooks for a detailed review of pathophysiology of HF.


Next in this chapter we will consider the key causes of heart disease in dogs, as well as an overview of cardiac disease classification and applicable diagnostic studies. The following are salient points regarding cardiac diagnosis and the clinical workup.


Identifying the predominant form and cause of heart disease and classifying the pathophysiologic mechanism of cardiac failure allows the clinician to direct appropriate therapy and render a more accurate prognosis. Cardiac diagnoses can be classified in a number of ways.


Arrhythmia (dysrhythmia)—disorder of electrical impulse formation or conduction leading to an abnormal heart rate or rhythm.

Bradyarrhythmia—a cardiac arrhythmia characterized by a slow heart rate as with sinus bradycardia, sinus arrest, atrial standstill, or atrioventricular block.

Cardiac murmur: functional—a prolonged audible vibration associated with blood flow in the heart or great vessels but unrelated to structural heart disease (also termed physiologic or innocent murmur); functional murmurs are often caused by anemia, fever, thyrotoxicosis, elevated sympathetic tone, or protracted bradycardia.

Cardiac murmur: organic—audible vibration associated with abnormal blood flow in the heart or great vessels associated with structure disease; these murmurs typically indicate pathology affecting the heart valves or a congenital shunt.

Congestive heart failure—an advanced pathophysiologic state of heart failure characterized by renal sodium retention, elevated venous pressures, and fluid accumulation in the lung, subcutaneous tissues, or body cavities.

Contractility failure—a general mechanism of ventricular dysfunction; see myocardial failure.

Diastolic heart failure (diastolic dysfunction)—impairment of ventricular diastolic filling or distensibility as with concentric hypertrophy of the ventricle or pericardial disease; the ventricle must be filled by higher than normal filling (venous and atrial) pressures.

Heart failure—a pathophysiologic state caused by systolic or diastolic failure of the heart and characterized by neurohormonal activation and inadequate cardiac output relative to exercise and tissue perfusion demands.

Hemodynamic overload—a condition characterized by increased demand on the ventricle to pump a greater stroke volume or a higher pressure than normal; typically these are subdivided into volume overloads and pressure overloads (see the following).

Hypertension—elevated systemic arterial blood pressure; in dogs systolic values exceeding 160 mm Hg are suspicious and those >180 mm Hg are considered elevated

Hypotension—reduced systemic arterial blood pressure; when systolic ABP is <90 mm Hg, clinically significant hypotension is possible.

Myocardial failure—loss of ventricular myocardial contractility leading to systolic dysfunction as with dilated cardiomyopathy or chronic volume or pressure overload.

Pressure overload—condition wherein the ventricular systolic (pumping) pressure must be higher than normal to eject the stroke volume; usually associated with hypertension or obstruction to ejection as with aortic stenosis.

Pulmonary hypertension—elevated pulmonary arterial blood pressure generally caused by left-sided heart failure, pulmonary vascular or parenchymal disease, or marked increase in pulmonary blood flow (without concomitant decline in pulmonary vascular resistance).

Shock—an acute, life-threatening disorder characterized by diminished tissue perfusion, impaired oxygen delivery, altered metabolism, and tissue injury; various causes of shock include cardiogenic shock (from profound heart failure), hypovolemic shock (from fluid loss or hemorrhage), and distributive shock (excessive vasodilation secondary to sepsis, anaphylaxis, or spinal injury).

Shunting: left-to-right—abnormal flow of blood from the systemic to the pulmonary circulation as with ventricular septal defect or patent ductus arteriosus.

Shunting: right-to-right—abnormal flow of blood from the pulmonary to the systemic circulation as with tetralogy of Fallot or PDA with elevated pulmonary vascular resistance.

Sudden cardiac death—cardiac arrest due to asystole or ventricular fibrillation.

Syncope—sudden loss of consciousness and postural tone caused by reduced cardiac output, excessive vasodilation, or both.

Systolic heart failure (systolic dysfunction)—impairment of ventricular systolic pumping that limits stroke volume and cardiac output; typical of dilated cardiomyopathy, severe valvular heart diseases, and myocardial failure due to chronic volume or pressure overloads.

Tachyarrhythmia—a cardiac arrhythmia generally characterized by a fast heart rate, as with sinus tachycardia, atrial tachycardia/flutter/fibrillation, supraventricular re-entrant tachycardia, and ventricular tachycardia.

Valvular regurgitation—incompetency or insufficiency of the valve permitting backflow of blood during systole (mitral, tricuspid valves) or diastole (aortic, pulmonic valves).

Valvular stenosis—narrowing and obstruction to flow across a valve (or adjacent tissue) during systole (aortic, pulmonic valves) or diastole (mitral, tricuspid valves).

Volume overload—condition wherein the ventricular systolic (pumping) volume is higher than normal; usually associated with a left-to-right shunt, a regurgitant heart valve, or chronic bradycardia.


The most important causes of canine heart disease involve a limited number of acquired disorders and a handful of important congenital heart defects. These conditions, as well as usual diagnostic findings, are summarized in Table 147-4 and in other chapters across this section. The most important acquired cardiac disorders responsible for HF in dogs are:

The most important of the canine congenital heart defects include the following:

Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Heart Failure in Dogs

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