Introduction

• Cause : underlying heart disease → either poor systolic function, poor diastolic function, volume overload, pressure overload, compliance failure or dysrhythmias → if severe enough → congestive heart failure syndrome (CHF).
• Signs : syndrome characterized by fluid retention. Left congestive heart failure leads to pulmonary edema, whereas right congestive heart failure leads to ascites, pleural effusion.
• Affected animal uses normal homeostatic mechanisms of cardiovascular system (activation of sympathetic nervous system and other neuroendocrine systems), to maintain blood pressure → detrimental in chronic cases → decreased cardiac function → progressive vicious cycle.
• Diagnosis : signs, radiography, echocardiography.
• Treatment : specific measures for underlying heart disease, control fluid retention, countering adverse neuroendocrine activation, correction of dysrhythmia (if present), improving systolic or diastolic function.
• Prognosis : guarded - only palliative treatment available, which may stabilize condition but reversal of disease process is unlikely.

Classifications

International Small Animal Cardiac Health Council System

• Class I: asymptomatic.
• Class IA: no evidence of compensation for underlying heart disease. (No volume overload or pressure overload detected radiographically or echocardiographically.)
• Class IB: clinical signs of compensation for underlying heart disease. (Volume overload or pressure overload detected radiographically or echocardiographically.)
• Class II: mild to moderate heart failure with clinical signs at rest or with mild exercise. Treatment required.
• Class III: advanced heart failure; clinical signs of severe congestive heart failure.
  • Class IIIA: home treatment possible.
  • Class IIIB: requires hospitalization.

American College of Internal Medicine (ACVIM) classification for heart disease and heart failure - adapted from human AHA/ACC

• Stage A: patient at risk of developing heart disease in the future, eg patient from breed with high predisposition for cardiac disease.
• Stage B: asymptomatic patients with evidence of structural heart disease, eg presence of murmur:
  • B1: with no evidence of cardiac remodeling (radiographically or echocardiographically).
  • B2: with evidence of cardiac remodeling.
• Stage C: patients with clinical signs of congestive heart failure (either past or present).
• Stage D: refractory heart failure. Patients showing clinical signs in spite of standard treatment for congestive heart failure.

Pathogenesis

Etiology

• Degenerative mitral valve disease Heart: mitral valve degenerative disease.
• Dilated cardiomyopathy Heart: dilated cardiomyopathy (DCM).
• Patent ductus arteriosus Patent ductus arteriosus.
• Ventricular septal defect Ventricular septal defect.
• Mitral dysplasia Atrioventricular valve dysplasia.
• Mitral stenosis (rare).

• Pericardial disease Pericardial disease.
• Degenerative tricuspid valve disease Endocardiosis: tricuspid valve.
• Tricuspid dysplasia Atrioventricular valve dysplasia , or stenosis.
• Pulmonic stenosis Pulmonic stenosis.
• Severe heartworm disease Canine cardiopulmonary dirofilariasis.
• Cor pulmonale (less common) Cor pulmonale.
• Cor triatriatum dexter (rare).

Specific

• Underlying heart disease.

Pathophysiology

• Systolic failure, eg due to dilated cardiomyopathy Heart: dilated cardiomyopathy (DCM).
• Diastolic failure, eg due to hypertrophic cardiomyopathy or pericardial disease Pericardial disease.
• Volume overload, eg due to mitral regurgitation Heart: mitral valve degenerative disease , tricuspid regurgitation Endocardiosis: tricuspid valve , patent ductus arteriosus Patent ductus arteriosus , ventricular septal defect Ventricular septal defect.
• Pressure overload, eg due to aortic stenosis Heart: aortic stenosis , severe systemic hypertension, pulmonic stenosis Pulmonic stenosis , pulmonary hypertension Pulmonary Arterial Hypertension (PHT). - rarely produces CHF unless severe and chronic.
• Dysrhythmias Heart: dysrhythmia : ventricular tachycardia Ventricular tachycardia , supraventricular tachycardia, atrial fibrillation Heart: atrial fibrillation , high grade second degree or third degree atrioventricular block (rare) Heart: second degree atrioventricular block Heart: 3rd degree atrioventricular block.

• Decreased cardiac output → decreased blood pressure → activate baroreceptors → reflex increased sympathetic activity/decreased vagal activity → increased heart rate, increased contractility and vasoconstriction → maintain blood pressure.
• Sympathetic activation and poor renal perfusion → activates renin-angiotensin-aldosterone system (RAAS) → further vasoconstriction, sodium and water retention → increased sympathetic outflow and release of vasopressin (antidiuretic hormone) → further vasoconstriction and water retention → increased venous pressures and eventually capillary pressures → extravasation of fluid into lungs (left-sided congestive heart failure), or abdomen (right-sided congestive heart failure).
• Increased venous pressure and volume = increased preload → structural changes in myocardial sarcomeres.

Timecourse

• Depends on underlying heart disease; most heart conditions (except cardiac tamponade), are progressive and eventually cannot be controlled.

Diagnosis

Treatment

Prevention

Outcomes