Heart Impulse Block or Conduction Delay in Cats

A heart impulse block is a condition in which the electrical impulses that stimulate heart muscles and regulate heart function are not successfully transmitted. A conduction delay is a similar condition in which these impulses are delayed rather than completely blocked. These conditions disrupt cardiac function, causing issues with heart rate and circulation. Impulse blocks and conduction delays are generally a symptom of another condition affecting the heart. These issues can become very serious, potentially leading to heart failure or death. Medical treatment is necessary to diagnose and treat the condition properly.

Heart impulse blocks or conduction delays may present in cats or other companion animals without any discernable symptoms. It is also possible for the cat to only present symptoms related to the underlying cause of the issue rather than the block or delay. 

Symptoms include:

• Weakness or lethargy
• Fainting or collapse
• Poor exercise tolerance
• Difficulty breathing
• Panting
• Pale gums or mucous membranes
• Abnormal heart rhythm 
• Bradycardia, or slow heart rate
• Difficult to detect pulse
• Lack of appetite 
• Bloating or fluid accumulation 
• Congestive heart failure
• Sudden cardiac death

Types

Several types of heart impulse blocks and conduction delays exist. The type is determined by which portion of the heart is affected. Common types that can affect cats include:

• Left Bundle Branch Block (LBBB)
• Left Anterior Fascicular Block (LAFB)
• Right Bundle Branch Block (RBBB)
• Sinoatrial Block

A heart impulse block or conduction delay is generally a symptom of another condition. Cats and other companion animals can experience blocks and delays when heart problems occur. Some common causes of a heart impulse block or conduction delay include:

• Post-cardiac surgery
• Abnormal electrolyte levels
• Heart conditions and cardiac diseases
• Congenital heart defects
• Some cancers, especially heart tumors
• Cardiac trauma
• Fibrosis or scar tissue buildup in cardiac muscles
• Hardening or thickening of the arteries
• Certain parasitic infections, like heartworms
• Blood clots 
• Extremely high potassium levels
• Cardiac inflammation
• Toxicity or poisoning
• Certain medications
• Heart failure

To properly diagnose the type of block or delay your cat is experiencing and the underlying cause of the condition, your veterinarian will use multiple diagnostic techniques. Methods that focus on heart performance and blood work are most common, but additional testing may be necessary to determine why cardiac impulses are being blocked or delayed. Be prepared to discuss your pet’s full medical history and any observed symptoms, including those that may seem unrelated. Advise veterinary staff of any recent trauma or surgery as well. A full physical examination, blood draw, and urine collection will be completed for analysis. Blood work, including cell count, biochemistry profile, electrolyte balance, and testing for certain antibodies that could indicate infection will be conducted.

An electrocardiogram or EKG is the most common diagnostic method used to monitor cardiac performance and detect abnormalities. In some cases, the cat may be required to wear a mobile EKG or heart monitor at home to continue monitoring. Information from the mobile EKG will be downloaded at a follow-up appointment or potentially transmitted remotely. X-rays or other imaging techniques like ultrasound may be used to more closely observe the heart’s function and look for fibrosis, signs of trauma, abnormal development, or tumors. Once the type and cause are determined, proper treatment can begin.

Treatment for heart impulse block or conduction delay will vary depending on the diagnosed cause and the severity of the condition. In less severe cases, treatment is generally outpatient, although hospitalization may be required if symptoms are severe or with certain serious underlying causes like heart failure and various cancers. Some common treatments include:

Restricted Activity

Reducing the amount of activity takes pressure off the heart and circulatory system. This treatment is generally combined with medical treatments related to the cause diagnosed by veterinary staff. Although there is no risk associated with this form of treatment, it can be difficult to accomplish with more active animals. 

Intravenous (IV) Fluids 

Fluid therapy is often used in conjunction with other treatments to ensure proper hydration and deliver appropriate nutrients to your pet. This is especially common when symptoms like lethargy and lack of appetite are present. IV fluids are usually administered on an inpatient basis for a short timeframe. There is a very low risk associated with this treatment. 

Surgical Intervention 

Surgery to repair heart damage or remove issues like tumors may be necessary to treat your cat’s condition. Surgery involves anesthesia and will generally require hospitalization. Additional medical therapies may be used in conjunction with surgical procedures, including antibiotic medications and drugs used to treat pain and inflammation. Surgery carries more risk than other treatment methods. Your veterinarian will determine if the risk is necessary to treat your pet properly. 

Pacemaker Implantation 

Implanting a pacemaker to help control heart function is a common practice for more severe cases. Surgery is required to implant the device, and continued hospitalization may be necessary for observation during recovery. Routine follow-up visits may also be needed to ensure proper pacemaker function. The greatest risk associated with this treatment is the initial surgery to implant the device. 

The likelihood of recovery from an impulse block or conduction delay depends on the condition that caused the issue. In the event of toxicity, parasite infection, electrolyte imbalances, and other treatable conditions the prognosis is good. More serious causes are generally more difficult to treat, and recovery may not be possible. Cats that receive a pacemaker implant have a fair prognosis. To aid in your pet’s recovery, continue to restrict their activity. Make sure their food, water, and litter are kept nearby. Continue to monitor your pet for worsening or recurring symptoms. Follow all of your veterinarian’s instructions for care, including providing the proper dosing of medications and returning for follow-up visits.