Heart Block or Conduction Delay (Right Bundle) in Cats

By PetMD Editorial on Mar. 19, 2010

Right Bundle Branch Block (RBBB) in Cats


Right Bundle Branch Block (RBBB) is a heart defect in the electrical conduction system in which the right ventricle (one of the cat's four heart chambers) is not directly activated by the electric impulses through the right bundle branch. RBBB may be complete or partial in nature; however, it is not as frequent as left anterior fascicular block.


Symptoms and Types


Often, no specific symptoms are seen that can be attributed to RBB, only those that are related to the underlying disease causing the defect.




Although it may be present in normal cats, a right bundle branch block is more often associated with congenital (present at birth) heart disease(s). Other typical causes for the defect include:


  • Chronic valve disease with fibrosis
  • Heart surgery to correct cardiac defect
  • Injury involving heart
  • Tumor(s)
  • Parasitic infection (e.g., heartworms)
  • Cardiomyopathy
  • Formation of clot in blood vessel (thromboembolism)
  • Abnormally high levels of potassium (hyperkalemia), especially in cats with urethral obstruction




You will need to give a thorough history of your cat’s health, including the onset and nature of the symptoms, to your veterinarian. He or she will then perform a complete physical examination, as well a biochemistry profile, urinalysis, and complete blood count (CBC) -- the results of which are typically non-specific. However, biochemistry profile may show high levels of potassium.


RBBB is often only found accidentally, perhaps while performing an echocardiogram. In the case of this defect, he or she may identify structural defects in the heart and right-side enlargement. Thoracic and abdominal radiography, meanwhile, may show masses and other abnormalities. If heartworms are the underlying cause, they also may be identified in diagnostic procedures


Treatment is directed towards treating underlying cause.


Living and Management


This condition itself is not life-threatening and treating the underlying cause results in complete resolution of problem. However, if left untreated, RBBB can lead to more severe heart rhythm changes or even complete heart block.


You may be required to take your pet for regular follow-ups exams to evaluate the status of disease and the cat's response to treatment. No diet modifications are necessary, unless required to manage underlying condition.

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