Boxer Cardiomyopathy

About the Diagnosis

Boxer cardiomyopathy is a heart disease that affects the heart muscle tissue of some dogs of the boxer breed. Although boxers can begin to show outward symptoms (clinical signs) of this disease at any age, it is usually diagnosed in adult dogs.

The heart tissue is made up mainly of muscle cells. In the normal, healthy heart, the heartbeat is triggered by a normal, organized wave of electricity that travels through these muscle cells to cause the heart to contract. When the heart contracts, the blood within it is pumped to the rest of the body, providing oxygen and various nutrients. In the heart affected by boxer cardiomyopathy, the electrical pathway is occasionally abnormal, and therefore, the heartbeat is irregular (abnormal rhythm or arrhythmia). Boxers with this disease may have episodes of weakness that may or may not be triggered by excitement or exercise. Some boxers faint (syncope) when the heart begins to beat irregularly because it may beat so irregularly and so fast that the pumping action of the heart is compromised and not enough circulation reaches the brain to maintain consciousness. Between these episodes, the dog may appear healthy and comfortable. Much less commonly and as a more serious form of boxer cardiomyopathy, the heart muscle tissue may hamper the circulation such that fluid accumulates in the dog's lungs and causes breathing problems, or in the abdomen/belly.

The problem is recognized in the breed internationally, but not all boxers have cardiomyopathy. Some boxers have an abnormal heart rhythm but no symptoms; these may be carriers of the disease who go on to develop symptoms later in life. The diagnosis is serious, because any boxer with this disease has an increased risk of sudden cardiac death.

Diagnosis: Boxer cardiomyopathy may be suspected by your veterinarian based on the dog's history and symptoms, if any. A cardiac arrhythmia may or may not be present at the time of examination, and it is an electrocardiogram (ECG, EKG) that is the definitive test. For this test, small metal clips are gently attached to the dog's skin in several places as the dog rests quietly. These clips are attached to a machine that can convert the heart's electrical impulses to a graphic representation on paper; this is the same type of ECG/EKG as in human medicine. The abnormal heart rhythm that is characteristic of boxer cardiomyopathy is sporadic, however. Therefore an electrocardiogram performed in the clinic may or may not reveal the abnormality. If there is uncertainty, portable heart monitors (Holter monitor, cardiac event monitor) may be used for assessing the heartbeat over 24 hours or intermittently over several days, respectively. Finally, since many, many other disorders unrelated to boxer cardiomyopathy can cause irregularities in the heart rhythm, an accurate diagnosis usually requires further assessment (e.g., x-rays of the chest and abdomen, ultrasound of the abdomen and heart, blood tests), which can be tailored based on the veterinarian's initial findings.

Cause: The cause of boxer cardiomyopathy is unknown. The disease has been diagnosed more commonly in particular blood lines; therefore it may be genetically acquired by some dogs.

Living with the Diagnosis

A diagnosis of boxer cardiomyopathy carries a guarded prognosis because a sudden deterioration or even a fatal event is possible. Depending on the results of the diagnostic tests (see above), different drugs can be given. However, because the exact cause of this disease is not known, these drugs only treat symptoms and are not a cure. Despite taking drugs, the disease may continue to develop in some dogs, and the goal of treatment is to reduce the symptomatic episodes and to try to reduce the risk of life-threatening heartbeat irregularities. It may be necessary to give several drugs until one is found that helps your dog.

Boxers diagnosed with this disease should not be bred in order to avoid perpetuating the problem in offspring. If your boxer is involved in a breeding program, your veterinarian may recommend regular (perhaps annual) testing with a Holter monitor.

If possible, dogs diagnosed with boxer cardiomyopathy should avoid stressful situations or events that cause excitement. This can be a difficult task for owners, but common-sense attention to minimizing environmental triggers of excitement (without severely compromising quality of life) may reduce the risk of severe or even life-threatening complications.

Treatment

Drugs are available to help control an abnormal cardiac rhythm. Your veterinarian will prescribe drugs based on the results of the x-rays, ultrasound exam, and/or electrocardiogram. These drugs help some dogs but not others, and unfortunately some dogs continue to develop problems related to this diagnosis even after taking drugs. In such cases, other types of antiarrhythmic drugs may be used, or further testing may be recommended to ensure that another disease process is not to blame.

A few boxers with this disease have benefited from a nutritional supplement, L-carnitine, when it is given several times per day, but only with the dilated form of boxer cardiomyopathy (rare; requires cardiac ultrasound for diagnosis).

Each dog diagnosed with this disease requires a tailored treatment regimen that may need to be changed periodically, depending on the dog's response. Your veterinarian will determine the best plan for your pet.

DOs

• If your boxer has periods of weakness and/or fainting take him or her to your veterinarian or the animal emergency clinic immediately. Keep the dog as calm and comfortable as possible during the car ride.

• Give drugs exactly as directed.

• Talk to your veterinarian about having your boxer tested regularly for this disease, especially if involved in a breeding program.

DON'Ts

• Do not breed a boxer that is diagnosed with this disease.

• Do not assume that your boxer does not have this disease if no symptoms are evident.

• Do not stop giving a drug without talking to your veterinarian. Some drugs must be gradually decreased or serious side effects can result.

When to Call Your Veterinarian

• If your dog shows negative reactions to the drugs including weakness, anxiety or nervousness, vomiting, diarrhea, hives (bumps under the skin), constipation, seizures, etc.

• If you cannot return for a scheduled visit.