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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 hearts 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.

Its 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, it may be the result of a pulmonary embolism or a right ventricular infarction, or it can be from the backing up of blood from damage to the hearts left side. If there is 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 interstial 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 cardiomyapthy (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

Posted on June 28, 2003, 10:01, Last updated on March 4, 2009, 17:17 | Cardiovascular