Cardiac Electrical Failure in Dogs

Cardiac electrical failure in dogs is a breakdown in electrical signals within the chambers of the heart that can be very mild to severe. When the electrical impulses of transmission from the atria of the heart to the heart’s ventricles are interrupted, the dog’s heart health can be greatly affected. 

The canine heart, like the human heart, has four chambers that the blood flows within. The top chambers of the heart are the atria, and the bottom chambers are the ventricles. The right atrium contains the sinus node, or the sinoatrial node. These are the cells that create the electrical impulses that allow the heart to beat properly and efficiently. The electrical signal needs to flow from the sinus node to the ventricles, following a path. It also flows through the atrioventricular node, which is special tissue in the heart that conducts the electrical signals. All of this is what makes the heart beat correctly. When the signal fails to transmit properly, it can cause an irregular heartbeat, which is otherwise referred to as a “heart block”.

Cardiac electrical failure in dogs is referred to as “heart block” or “AV block” and is a condition in which the electrical impulses which control the heartbeat are abnormal, or in some cases, nonexistent.

Symptoms of heart block may be confused with other disorders, and it is imperative that a veterinarian is seen at the onset of any of the following clinical signs:

• Lethargy
• Slow heart rate
• Weakness
• Shortness of breath after exercising
• Tiredness

Types

There are three types of heart block or AV block. These three types are actually degrees of impairment; your dog may have a minor impairment in the transmission of electrical impulses or a more severe condition. The three types are:

• First-degree heart block - the electrical impulses move too slowly 
• Second-degree heart block – signals do not reach the ventricles properly, causing a delay
• Third-degree heart block, or complete heart block – the electrical signals do not flow from the upper to the lower chambers

There are several causes of this disorder, and since there are many causes, the veterinarian will need to rule out any differential diagnosis when the dog is being tested. The electrical signal deficit in the heart may not be a stand-alone disorder, and causes can include:

• Cardiac amyloidosis
• Myocarditis
• Cardiac lymphoma
• Leiomyoma
• Hyperkalemia
• Hypertrophic cardiomyopathy
• Borrelia spp
• Muscular dystrophy
• Mitral valve endocardiosis
• Polymyositis

If you suspect your dog may be having trouble with his heart, once you take him to the veterinarian you will be asked to explain all of his symptoms in detail. The veterinarian will want to find any underlying issues that may be causing the heart block (once it is diagnosed). The veterinarian will perform all tests such as a biochemistry profile, blood work, and any other test he feels necessary to determine any infections or other underlying disorders.

Once the basic tests are complete, the medical professional will perform an echocardiogram, or EKG. This will show the veterinarian a great deal of information, such as the electrical pulses in the heart and will show any unusual heart behavior. He will also use imaging techniques to get a closer look. Both of these tests will rule out many kinds of other heart disease.

Treatment will depend on the type of cardiac electrical failure in your dog. Usually, no aggressive treatment is necessary unless the heart block is a second or third-degree heart block. For second or third-degree heart block, the following device is used:

Pacemaker

A pacemaker controls irregular heart rhythm caused by heart block in dogs that are diagnosed with more severe degrees of this condition. Electrical waves, or pulses, are sent through the heart to promote regular beating of the heart and to keep the heart and dog’s health from deteriorating. This small device is inserted into the chest of the dog.

Disease-specific treatment

If the heart block is caused by a specific underlying disorder, the veterinarian will treat that disorder in conjunction with inserting a pacemaker (if a pacemaker is needed).

If your dog has heart block, the prognosis is good, especially for a mild degree. If your dog has a second-degree heart block and receives a pacemaker, prognosis is fair and guarded. Every dog is unique and every condition is different, and your veterinarian will explain your dog’s prognosis with the pacemaker. 

Regular veterinarian visits may be necessary to monitor the heart rhythm of your canine, with or without the pacemaker, and your veterinarian may want to keep abreast of the situation with regular echocardiograms. At home, if there are any specific changes to your loved one’s lifestyle with first or second-degree heart block, such as with diet and exercise, be sure to follow your medical professional’s instructions.

If your dog has third-degree heart block, the prognosis is poor; however, with very careful monitoring of him with the pacemaker and making sure he gets proper rest and follows the veterinarian’s guidelines in terms of diet and lifestyle, he may still be able to be with you for some time. Your veterinarian is the only individual that will be able to accurately communicate with you about your companion’s future.