Definition

A condition where the heart fails to adequately pump and circulate blood. It can result from either right side or left side ventricular failure or both. Failure of the heart’s ventricles results in blood backing up and congesting in the lungs, liver, abdomen and lower limbs.

Clinical Signs

May see any of the following:

• Tires more quickly.
• Inactive or sleeping more than usual.
• Weakness of the hind limbs not associated with arthritic conditions or neuropathies.
• Dry cough, bronchial wheeze, or moist lung sounds, making breathing labored. May prop up head to breathe easier.
• Enlarged abdomen, and / or swelling in limb(s) and feet , and / or weight gain may be seen due to fluid retention. *Note: the enlarged abdomen and swelling in limbs and feet is not commonly seen in rats with this condition.
• Little to no appetite.
• Cool, pale extremities (e.g., ears, feet, tail) due to poor circulation.
• A noticeable sign with CHF is cyanosis (a blue tinge due to poor oxygenation) of scrotum, toes and tip of tail. This is often a late sign.
• May show anxious behavior when breathing becomes harder (e.g., not willing to be held or stay in one place).
• Scant dark (concentrated) urine.
• Dilute Urine if kidney disease present.

It is important to note that respiratory infections (a common cause of disease in rats) may be caused by more than one organism and may, if not effectively treated, lead to CHF. It is therefore recommended to treat respiratory infections persistently and aggressively while determining, or treating for, CHF or Cardiomyopathy. In some cases a more intensive treatment regimen for respiratory infections may actually rule out a diagnosis of heart disease.

For more information regarding aggressive respiratory treatment modalities refer to the articles on Pneumonia and Mycoplasma.

Etiology

Heart failure is a syndrome rather than a disease. It occurs in response to the heart’s dysfunction in which other conditions or diseases have weakened or damaged the heart. Some factors which can lead to congestive heart failure are; dysrhythmias, cardiomyopathies (such as dilated, hypertrophic, and restrictive), systemic infections, respiratory infections, high ventricular output states, metabolic diseases, infiltrative diseases such as tumors, and diseases of the heart valves, to name a few.

The heart with its four chambers, two atria and two ventricles, is responsible for the transfer of blood coming from the venous system and into the arterial system. When the dysfunctioning heart fails it results in the inability to empty the venous system, or reduce delivery of blood to the pulmonary and arterial circulation.
Each of the heart’s chambers do not operate alone so any disruption or damage to one can affect the others.

Heart failure is often classified according to which side of the heart is affected, although failure of either side may occur independently or together.

In right sided heart failure, where right ventricular contractions are ineffective, the cause may be due to pulmonary embolism or right ventricular infarction, or as a result from the backing up of blood from damage to the hearts left side. If there is a backing up of blood into the right heart, the systemic veins become engorged, liver distention results, ascites (seen as enlarged abdomen) occurs and edema (swelling) of the limbs and feet may be seen.

With left heart failure, where there is a disturbance or a decrease in the contraction of the ventricle as usually seen in infarctions, or where there is disease of the valves, the ventricle is not able to empty blood and therefore can’t accept blood that is returning to it from the pulmonary veins of the lungs. This can result in Pulmonary edema where the fluid seeps out of the capillaries and into the interstitial spaces and alveoli of the lungs, or Pleural effusion when the lungs become engorged and fluid seeps out through the veins to collect in the pleural cavity.

As heart failure progresses the reduction in output by the heart results in certain adaptations to take place in the heart and systemically. The sympathetic nervous system increases activity to enhance myocardial contractility causing vasoconstriction. The cardiac blood volume is increased in order to stretch ventricular muscle fibers and increase ventricular contraction, and hypertrophy occurs in order to increase contractile tissue enabling contractility. However, as this condition continues the heart muscle becomes overstretched and the ability to contract declines.

Because rats are prone to chronic respiratory infections and complications thereof, dilated cardiomyopathy (enlarged heart), or hypertrophic cardiomyopathy (thickening of the ventricular wall) which leads to CHF may ultimately result.

While heart failure in rats cannot be cured, determining the underlying cause and treating appropriately can allow the rat to feel more comfortable and provide quality time.

Diagnostics

An x-ray can be taken to determine size, shape of heart, or presence of pulmonary vascular congestion (e.g., presence of Kerley B lines).
Early signs tend to reflect no change in the cardiac silhouette. Late sign may reflect increased cardiothoracic ratio.
*Note, however, that the presence of lung consolidation or Pleural Effusion may cause the borders to be too blurred making it difficult to adequately determine enlargement.

Lab draw for Electrolytes can reflect hyponatremia (low sodium) due to water retention.

Blood Chemistry may show an elevated BUN(blood, urea nitrogen) and Creatinine.

Urine studies may reflect metabolic acidosis or alkalosis. A specific gravity greater than or equal to normal shows excessive fluid intake, and a specific gravity less than or equal to normal can show decreased fluid intake; proteinuria and glucosuria.

Treatment

The following medications may be prescribed for CHF. Information on the use of these drugs can be found listed in the Rat Medication Guide.

• Lasix (a diuretic). May be used as a diagnostic tool to determine CHF (quicker acting than enalapril).
• Enalapril (or similar ACE inhibitor). May also be used as a diagnostic tool. *Note: results may take up to three days.
• Atenolol (or similar beta blocker).
• Digoxin/Cardoxin in dilated cardiomyopathy. *Note: use with extreme care if hypertrophic cardiomyopathy suspected.
• Pimobendan (in the same therapeutic class as digoxin, but is both a positive inotrope and vasodilator)
• Theophylline may be of some benefit as it is able to stimulate heart muscle giving it a slightly positive effect on heart strength, as well as, being able to relax smooth muscle allowing for bronchodilation making it easier to breathe in pulmonary congestion secondary to heart failure.

Oxygen may also be needed if symptoms are severe.

Nursing Care

• Provide one level cages to prevent difficulty to breathing from the exhaustion of climbing different levels.
• Ensure food and water is within easy reach.
• Monitor for weight gain, which indicates fluid retention.
• Prevent drafts or extreme temperature changes which increase workload of the heart.
• Monitor effectiveness of meds to see if there is improvement in condition. Medications may need to be adjusted or increased as disease progresses. If you see your rat’s condition worsening return to the vet for proper adjustment of medication.
• Provide for healthy adequate nutrition with reduced salt content. Including such supplements in the diet as, omega-3 oils in flax oil (25 mg/day), co-enzyme Q10 (10-30 mg/day), L-carnitine (25 mg/day), and taurine (50 mg/day) may be beneficial. ³

Outcomes

• Relief of heart failure symptoms
• Enhance heart’s performance
• Improve quality of life
• Emotional support for those having to consider euthanasia for their rat

Prevention

• Maintain a healthy cage environment.
• Ensure a healthy diet in order to prevent obesity.
• Ensure adequate treatment is provided for any illness.