Atrioventricular Block, Complete (Third Degree) in Dogs
Complete, or third-degree, atrioventricular block is a cardiac condition observed in dogs wherein all electrical impulses originating from the sinoatrial (SA) node fail to pass through the atrioventricular (AV) node, resulting in independent and uncoordinated contractions of the atria and ventricles.
The heart’s electrical conduction system, spearheaded by the SA node, regulates the heart rate by generating electrical impulses that travel through the AV node into the ventricles, prompting the heart muscles to contract and pump blood throughout the body.
Certain breeds such as Cocker Spaniels, Pugs, and Dobermans are predisposed to heart defects that can lead to complete heart block. Additionally, this condition is more commonly observed in older dogs.
Symptoms and Types
- Weakness
- Coughing
- Difficulty breathing
- Inability to engage in routine exercise
- Slow heart rate (bradycardia)
- Fainting
Causes
- Congenital heart defects present at birth
- Idiopathic fibrosis, which is scarring of heart tissue of unknown origin
- Inflammation of the heart (myocarditis)
- Inflammation of the lining of the heart (endocarditis)
- Infiltration of the heart muscle by abnormal substances or cancer (such as amyloidosis or neoplasia)
- Drug toxicity, such as from digitalis
- Electrolyte imbalances
- Heart attack (myocardial infarction)
- Lyme disease
- Chagas’ Disease
Diagnosis
To diagnose complete atrioventricular block in your dog, provide your veterinarian with a detailed history of your dog’s health, including when symptoms started and their nature. Your veterinarian will conduct a comprehensive physical examination, along with tests including a biochemistry profile, urinalysis, and complete blood count (CBC). Elevated white blood cell counts in blood tests may indicate heart infections, while the biochemistry profile could reveal electrolyte imbalances.
Your veterinarian will also perform an electrocardiogram (ECG) to aid in the initial diagnosis. If abnormalities are detected on the ECG or if your dog shows symptoms of heart issues, further tests such as echocardiography and Doppler ultrasound may be conducted to assess cardiac function.
Treatment
Treatment for complete atrioventricular block aims to resolve the blockage of electrical impulses at the AV node. This is typically achieved through the use of a specialized device known as a pacemaker, which helps regulate the heart’s rhythm by addressing the conduction issues with electrical impulses. Chest x-rays are utilized to confirm the proper placement of the pacemaker. Both temporary and permanent pacemakers are available, and your veterinarian will advise on the most suitable option for your dog. Surgical correction of the blockage is also possible but tends to carry higher risks for the dog.
Living and Management
Living and managing a dog with a pacemaker implanted requires extra care and cage rest. Permanent pacemakers are typically surgically placed in a pocket under the skin. To secure the pacemaker and prevent movement, a bandage is applied over the surgical wound for three to five days. Since pacemakers are battery-operated, there’s a risk of malfunction, infection, displacement, or battery depletion, potentially causing a recurrence of complete atrioventricular block. Therefore, it’s crucial to restrict the dog’s movement and monitor for any concerning symptoms.
Depending on the severity of the underlying condition, dietary adjustments may be necessary. Regular visits to the veterinarian for ECG and chest radiography are essential to evaluate pacemaker function. Unfortunately, the long-term prognosis for dogs with complete atrioventricular block is typically very poor.