Arrhythmogenic Right Ventricular Cardiomyopathy (also termed “Boxer Cardiomyopathy”) is a heart disease primarily of Boxer dogs, that results in fainting (syncope), heart failure, and/or sudden death. It is a disease of the ventricle, which is the main pumping chamber of the heart. The right ventricle is primarily affected in most cases, but can affect the left or both ventricles in about 10% of cases.
In ARVC, the normal muscle tissue is replaced by fibrous or fatty tissue. This disturbs the electrical system of the heart, usually resulting in an irregular heartbeat (arrhythmia). These are called “ventricular premature complexes” (VPC’s). As the disease progresses, the VPC’s can become more frequent or sustained, in which case it is called “ventricular tachycardia”. This is a very rapid and dangerous heart arrhythmia, and can cause the heart to beat at rates over 300 per minute. This can result in fainting (called “syncope”) or even result in sudden death. The progressive infiltration of the heart by abnormal tissue can result in the muscle to become weak and enlarged, with inefficient and poor forward blood flow. Less blood is pumped forward with each heartbeat, meaning that more stays in the heart – leading to elevated pressure in the heart and body. When that pressure is high enough, it forces water out of the blood vessels. At that stage, it is called congestive heart failure (CHF), and can be fatal unless treated. The low forward “cardiac output” also may result in weakness, lethargy or collapse because the heart is too weak to effectively pump blood to the body.
The best current method of testing dogs is a Holter monitor. This is a device that records an ECG for 24 to 96 hours. As shown to the right, the device is about the size of a deck of cards, and has leads that are attached to electrodes placed on the dog’s chest. A vest is placed over the leads to ensure the leads are not removed accidentally (or intentionally!). Holter monitors are usually very well tolerated by most dogs (even cats can wear them), but the occasional dog will have issues with the vest. Another diagnostic option that has become available recently is a test for one of the genetic mutations thought to lead to ARVC. This requires a simple cheek swab. Unfortunately, there is no current test that is 100% accurate in diagnosing ARVC in all dogs; a veterinary cardiologist can help assess likelihood in each case.
Annual Holter monitoring, starting at 3 years of age, is the best way to screen for ARVC. This is the current recommendation for all Boxer dogs. This may allow identification of the disease prior to the onset of clinical signs (including sudden death). Unfortunately, there is no currently available test that is 100% accurate for diagnosis, and a positive result on a Holter monitor does not mean a Boxer will die of ARVC.
There are 3 clinical forms of ARVC. The first is the concealed form; this means there are no clinical signs of ARVC. In this form, the dog appears totally normal at home, but ECG/Holter analysis reveals substantial arrhythmias. The second is the overt form; this is characterized by signs of ARVC, including collapse, weakness, and/or fainting. The third, least common form is characterized by myocardial failure and signs of congestion. This form carries the worst prognosis. Your cardiologist can help determine which form is present, and the best treatment to pursue.
It is impossible to know for sure how long a dog with ARVC will live. ARVC may progress quickly, or cause sudden death at any stage. Conversely, a Boxer with ARVC may live years following diagnosis, and die of another disease process. Frequently, predictions are based on the form of ARVC (see paragraph above).
Sadly, one of the first signs of ARVC is sudden death. The most frequent initial sign, however, is collapse – called syncope. Dogs may appear to faint; they may become suddenly weak and wobbly, or lose consciousness altogether. Most commonly, they appear to totally recover after a brief period of time (<2-5 minutes). Less commonly, dogs may present with signs of congestive heart failure (CHF). These include fluid accumulation in the abdomen (swollen belly), or fluid in or around the lungs (breathing difficulty, coughing). The best way to know if your Boxer has ARVC is to diagnose it prior to the onset of clinical signs; this generally requires a Holter monitor evaluation (see “diagnosis” section above).
Treatment for this disease remains medical, primarily antiarrhythmic drugs. The most common drug used is Sotalol; other drugs may be added, or the drug may be changed based on the response. Therapy is intended to reduce clinical signs and reduce the risk of sudden death. A reduction in clinical signs is usually obvious (or not). There is no perfect way to judge the reduction in the risk of sudden death. A reduction in the amount and complexity of ventricular arrhythmias (on a Holter exam) is often used as a surrogate measure. If the myocardial failure form of ARVC is present, additional therapy for heart failure is indicated.
In humans, therapy for ARVC often involves implantation of a cardioverter-defibrillator. This is relatively expensive, and has not been successful in Boxers thus far. The devices are intended for humans, and often deliver inappropriate shocks to dogs – these are painful, and limit the tolerability of the device. Additional therapy includes omega-3 fatty acid supplementation, which may help reduce the frequency of arrhythmias. The lack of side effects render this an attractive therapeutic option, and is recommended in all cases of ARVC. Other therapy may be effective depending on the individual case, and should be discussed with the cardiologist.