Heart Failure:

• The primary function of the cardiovascular system is to ensure an adequate circulation of blood so that nutrients are delivered, waste products are removed and a homeostatic milieu is maintained at the organ and cellular level.
• Inadequate circulation interferes with nutrient delivery, removal of waste product and ultimately leads to heart failure.
• Two functional units of cardiovascular system is heart (pump) and blood vessels and blood (circuit).
• Pump and circuit may fail independently of each other, giving rise to two forms of circulatory failure- heart failure and circuit failure
• In heart failure, heart is unable to pump required amount of blood required by cells and tissues whereas in circulatory failure, blood is unable to return to heart resulting decreased in blood volume.

Heart failure can result from:

• Defect in filling of heart
• Abnormality in generation and conduction of electrical wave or depolarization
• Abnormality in contractile function
• Excessive workload or combination of one or more abnormalities

Heart failure can be divided into 2 types; Acute heart failure and Chronic (Congestive) heart failure. Heart failure can be left-sided, right-sided or both.

Left sided heart failure: There is increase in pulmonary venous pressure, increase in left ventricular end diastolic pressure and mean left atrial pressure. This affects lungs resulting in interstitial edema in lungs, in severe case pulmonary edema and death.

Right sided heart failure: This type of failure causes increase in right ventricular end diastolic pressure, mean right atrial pressure and jugular venous pressure. Right sided heart failure affects liver resulting hepatomegaly, increase in pleural, pericardial and peritoneal fluid (ascites).

Acute Heart Failure:

• Acute cardiac failure results from a sudden stoppage of effective cardiac contraction, and may cause death even within minutes.
• It can occur when there is severe defect in filling, failure of heart as pump either due to tachycardia, bradycardia or arrhythmia and when there is sudden increase in workload.
• Catecholamines are responsible for severe tachyarrhythmias along with severe excitement enough to cause acute heart failure.

Etiology:

• Disorder of filling: pericardial tamponade due to rupture of atria and ventricle, aortic and pulmonary artery rupture
• Tachyarrhythmias: myocarditis, Nutritional deficiency myopathies, ingestion of poisonous plant, electrocution, lightning strikes
• Bradycardia: Iatrogenic, e.g. intravenous calcium gluconate or borogluconate administration, xylazine, tolazoline, concentrated solutions of potassium chloride
• Plant poisoning
• Increased workload: Rupture of aortic valve, acute anaphylaxis

Clinical Signs:

• Brain is first affected and signs are neurological in acute cases.
• Pallor is prominent sign due to reduced blood flow
• Respiratory distress due to pulmonary edema
• Dyspnoea, staggering and falling
• Death occurs within seconds or minutes of appearance of signs
• Incoordinate movement of limbs
• Deep asphyxia gaps follow death.
• Absence of palpable pulse, bradycardia
• Absence of heart sounds
• Horses during racing or training dies suddenly due to acute heart failure.
• In typical acute cases, engorgement of visceral veins may be observed grossly during necropsy examination if attack has lasted for minutes.
• There are no gross lesion characteristics of acute heart failure.

Treatment:

• Treatment is usually not possible or practical in large animals due to short course of disease.
• Deaths under anesthesia can be controlled through external or internal cardiac compression to some exent.
• Intracardiac injections of very small doses of epinephrine in conjunction with external cardiac compression by jumping up and down on the thorax with the knees can be tried, with occasional success.

Congestive Heart Failure (CHF):

• Congestive heart failure denotes failure of heart to pump blood effectively over period of time.
• Onset of disease is slow and lasts for longer time period.
• Congestive heart failure is characterized by congestion in circulation, either in pulmonary or systemic venous or both.
• Pulmonary circulation refers to left-sided heart failure and systemic circulation refers to right-sided heart failure.
• It is also defined as failure of cardiac output to meet the requirement of body with retention of excess sodium and fluids.

Etiology:

• Any disorder of pericardium, myocardium and endocardium which results in interference of blood flow
• Rupture of valve
• Myocarditis; bacterial, viral, parasitic or toxic
• Myocardial degeneration due to nutritional deficiency or toxic causes
• Cardiac defects; ventricular or atrial septal defects, tetralogy of Fallot, patent ductus arteriosus
• Pulmonary or systemic hypertension
• Pressure load due to obstruction in outflow
• Weakness in myocardium or inference in conduction system

Pathogenesis:

Clinical Signs:

CHF is manifested in two forms; left-sided failure and right-sided failure

Left-sided heart failure:

• There is increased pressure in lungs.
• Increased heart rate
• Increase in rate and depth of respiration with cough and crackles at base of lungs
• Severe dyspnoea and cyanosis in severe cases

Right-sided heart failure:

• Venous distension and subcutaneous edema
• Increased heart rate
• Superficial veins are engorged
• Subcutaneous edema in brisket region, under jaw and along ventral midline in ruminant
• Ascites- indicated by presence of abdominal fluid wave on ballottement with palpation and less frequently by presence of abdominal distension- pear shaped abdomen
• In horses, edema is prominent in pectoral region between front limbs, ventral abdominal wall, prepuce and limbs
• Liver is enlarged and palpable in ruminant in right costal arch with thickened and rounded edge.
• Respiration is deeper than normal and rate is increased.
• Reduced urine flow and concentrated urine with small amounts of protein
• Feces are normal at first but in later stage, diarrhoea may be present.
• Epistaxis may occur in horse

Necropsy Findings:

Left-sided failure:

• Pulmonary congestion and edema
• Heart failure cells (haemosiderin-laded macrophages) appear in alveolar spaces
• Brown induration of lungs

Right-sided failure:

• Liver size is increased and increased weight. On sectioning, nutmeg pattern is seen on liver; congested centre of liver lobules followed by paler fatty peripheral regions.
• Congestion and hypoxia of kidney
• Anasarca, ascites, Hydropericardium
• Enlarged and cyanotic spleen

Diagnosis:

• On basis of physical examination and clinical findings
• On basis of ECG findings; prolonged QRS or P wave

Treatment:

• CHF due to pericarditis should be treated by removing pericardial fluid and preventing its return.
• Animals should be kept at stall rest and provided sodium free diet.
• Diuretic treatment should be done; Furosemide is most commonly used in treatment of large animals. It should be administered intravenously @ 0.2-1.0 mg/kg, b. wt initially for horses. For cattle it should be administered @ 2.5-5.0 mg/kg, b.wt.
• Prednisolone- 20 mg orally may be effective in some cases.
• Digitalization; use of digitalis; cardiac glycosides to improve contractility of heart. Digitalis is administered intravenously @ 1.0-1.5 mg/100 kg initially followed by 0.5-0.75mg/100kg, every 24 hours in horse.
• In cattle, digitalis @ 2.2mg/100 kg initially followed by 0.34mg/100 kg every 4 hours.
• If treated animals are not eating, daily oral administration of KCl should be practiced. Cattle- 100g, Horses- 30g
• Oxygen therapy, if possible to relief from severe anoxia
• Sedatives or tranquilizing agents for reducing pain.