Of the several factors affecting Boxer health, the one that is the easiest to deal with is the all too common lack of breeder education. The information available on many diseases is either confusing, conflicting, or incomplete. The MBHA believes that education is of the utmost importance in controlling and someday eradicating these diseases in the Boxer breed. A basic synopsis of the major problems in Boxers is given on this page, with links to detailed information following.
Boxer Arrythmic Cardiomyopathy
Aortic Stenosis (AS) is the second most common congenital heart defect in the dog (all breeds). Boxers have an odds ratio for developing the disease of 8.6 The mode of inheritance is unknown; some feel it is a simple recessive, others feel that it is caused by multiple genes. Regardless of how the disease is inherited, two unaffected dogs can produce affected puppies, and two affected dogs can produce unaffected puppies. AS is characterized by high-velocity, turbulent blood flow, which usually (although not always) produces a heart murmur.
Screening for AS is generally cardiac auscultation by a board-certified veterinary cardiologist. If a murmur is heard, a Doppler echocardiograph is performed to assess blood flow velocities and establish a definitive diagnosis. Velocities exceeding 2.0 m/sec are considered diagnostic for AS; velocities below 1.7 m/sec are considered normal. The 1.7 m/sec - 2.0 m/sec range is a "grey area" and is considered to be suggestive of mild AS when other supporting abnormalities (aortic regurgitation, sudden velocity acceleration, turbulent flow) are present. There have been cases of Boxers that were pronounced murmur-free upon auscultation, who upon Doppler were found to have blood flow velocities above 2.0 m/sec. It is due to these cases that some breeders feel that auscultation is not an adequate screening tool, and that all breeding stock should be Dopplered. (Most cardiologists would disagree with this.)
Mild to moderate cases of AS generally do not require medication - the dogs tend to lead a mostly normal life, although extremely vigorous exercise is sometimes to be avoided. Dogs with AS are also more prone to endocarditis, a bacterial infection of the heart, and so should be given a prophylactic round of antibiotics before undergoing any surgery or dental work. Dogs with severe AS are at an increased risk for sudden death within the first 2-3 years of life. Affected dogs of any level should not be bred.
Boxer Arrythmic Cardiomyopathy
Boxer Arrythmic Cardiomyopathy (BAC) - formerly known as Familial Ventricular Arrythmia (FVA), formerly known as Boxer Cardiomyopathy (BCM) - is an electrical conduction disorder of the heart, characterized by ventricular premature contractions (VPCs). BAC has been established as an autosomal (non-sex-linked) dominant trait. BAC affects males and females with equal frequency, it affects dogs of all ages, and the chances of developing BAC increases with age.
Traditional cardiac examinations and tests - auscultation, resting electrocardiograms (ECG), chest x-rays, and echocardiographs (cardiac ultrasounds) - are not adequate to screen a dog for BAC. The only accepted screening tool for BAC is a 24-hour ambulatory ECG (Holter monitor). Boxers with 50 or more VPCs in a 24-hour recording are considered affected with BAC, but many feel this number is much too high (in other breeds, 1 VPC is considered affected with cardiomyopathy). However, a reading of 0 VPCs at 2 years of age does not guarantee the same reading at 3 years of age, or 4 years, or 8 years - which is why repeated Holtering is necessary. Dr. Meurs, the cardiologist at Ohio State University who is conducting the largest study on BAC currently, recommends yearly Holters for breeding stock.
There has been success in controlling the arrythmias of BAC with the drug sotalol, a beta-blocker that functions as an anti-arrythmic. BAC may progress to congestive heart failure, but this is less common than the sudden death caused by arrythmia. In Dr. Meurs' study, 80% of the dogs enrolled had more than 1 VPC in 24 hours. 50% had greater than 10 VPCs, and 36% had greater than 50. At this point in time there is still not a set cut-off point at which a Boxer would automatically removed from a breeding program. It is up to the breeders to decide what their comfort level is, and to act accordingly. The pattern of VPCs may also play a role in the severity of BAC - whether the VPCs are isolated, or occur in pairs, triplets, or "runs" of four or more.
There is still much research to be done on BAC before any definitive protocols can be developed. To facilitate the collection of information, the OFA has set up a database for breeders to submit their Holter results. This database is voluntary, purely confidential, and the information will be released only to researchers (not to the public) and only with the approval of the American Boxer Club. MBHA members have agreed to submit their Holter results to this database to assist research into this disease.
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