HEALTH
KABOOM BOXERS
CKC Registered Breeder since 1995

HEART CONDITIONS

The two common heart conditions in the Boxer are SAS (Sub-Aortic Stenosis) and Cardiomyopathy (Boxer Cardiomyopathy/BCM, or more recently re-named Arrythmogenic Right Ventricular Cardiomyopathy/ARVC). Heart conditions are one of the top killers of Boxers, and breeders need to start screening their breeding dogs to protect the breed from becoming extinct in the years to come. Heart conditions are so prevelent in the breed now, if all affected Boxers were removed from breeding programs, the gene pool would be so limited that the breed would face other serious problems or even become extinct. Testing is a way of gathering as much information as possible in order to make an informed decision when it comes to the merging of bloodlines.

The Orthopedic Foundation for Animals (OFA) now offers databases for DNA screening for ARVC. Testing is done for a very reasonable cost of $60 via sending blood samples or cheek swabs to Washington State U.

SUB-AORTIC STENOSIS is a narrowing of the outflow tract from the left ventricle of the heart, below the aortic valve leading to the aorta. Comparatively, it is much like water flowing through a hose. As you make the hole at the end of the hose smaller (ie. place your thumb over the end), the speed with which the water leaves the hose increases in order to pass the same volume of water through a smaller opening. This would simulate a stricture such as is present with SAS. In order to push the same volume of water (or blood) out over a unit of time, the workload on the pump (heart muscle) increases. Over time, the muscle mass of the heart increases and additional problems can develop, including arrhythmias. These irregular heartbeats can result in insufficient blood flow to the heart muscle itself, and the brain. Sudden death can occur.

In recent studies by Dr. K. Meurs, an expert on canine cardiac disease, there have been several noteworthy findings, the first being that younger, more excitable dogs were more likely to have a high blood flow speed and a heart murmur. Secondly, it was found that an increased blood flow rate can be caused by stenosis itself, excitement, or pregnancy/heat.  Perhaps most importantly, non-Boxers in the study uniformly had larger aortas than Boxers. From that finding, it is now believed that Boxers are different than other breeds, which may explain the high incidence of SAS: many Boxer murmurs may be purely physiologic in nature because of their smaller aortas. Most of the information on SAS to date has been based on studies of Newfoundlands, so these new findings will be of great significance for understanding SAS in Boxers.

Diagnosis: Auscultation by board certified cardiologist, and subsequent OFA certification; Doppler ultrasound/Echocardiogram showing blood velocity (rate) of less than 2.5ml/sec. Previously, a rate of over 1.7ml/sec was cause for alarm, however, with new research done by Dr. Meurs, it is believed that a rate between 1.7 and 2.5ml/sec can be considered normal in BOXERS as long as there is no turbulence or fibrous ridge/ring detected on a color-flow Doppler echocardiogram. A fibrous ridge may or may not be noticeable on an ultrasound, but depending on if found during autopsy, it will confirm or disprove the presence of SAS.

BOXER CARDIOMYOPATHY (BCM), also known as Arrythmogenic Right Ventricular Cardiomyopathy (ARVC) is an electrical conduction disorder that is particular to Boxers, similar (but not identical) to Cardiomyopathy seen in Danes and Dobies. BCM/ARVC causes the heart to beat erratically (to have an arrhythmia) some, but not all, of the time. It is diagnosed with a 24-hour holter monitor machine, and now more recently, through DNA testing at Washington State University, in conjunction with OFA. An arrhythmia usually consists of Premature Ventricular Contractions (PVC's - also known as Ventricular Premature Complexes, or VPC's) that are heard as an extra beat or a skipped beat that does not have a corresponding pulse. To identify these the listener must have one hand on the stethoscope, holding it to the chest, and one hand feeling for a pulse at the femoral artery inside the hind leg. In a normally functioning heart, there is a pulse for every beat that is heard. A dog with PVC's will have episodes of an irregular (early or late) beat, with no pulse to push the blood through the system. The heart is beating, but not pumping the blood. "Runs" of PVC's (clusters of several in a row) cause the dog to faint, as the brain is receiving no oxygen (un-pumped blood) for several seconds. If the heart corrects itself to normal full functioning beats, the dog regains consciousness usually in a matter of seconds. Boxers generally show no symptoms until the disease is quite advanced. Early testing (starting at age 2 and at least every 2 years after that) is the only way to discover PVC's, but due to numerous "unknowns" in this disease that are being discovered through on-going research, one Holter test showing PVC's is not a definitive diagnosis, and breeders must be careful to not remove any dogs from a breeding program without multiple testing and careful evaluation of the overall quality of the affected dog. DNA testing is emerging as an alternative (or an add-on) to Holter monitor testing.

Diagnosis: DNA blood sample or cheek swab; or a Holter Monitor result showing PVC's; and after death, by a necropsy that shows fatty infiltration into the right ventricle. In more severely affected dogs, the fat may also infiltrate the left side of the heart and/or the septum.

Current treatment for ARVC consists of medication with Sotalol or Mexilitine/Atenolol, but treatment still may not reduce the risk of sudden death, even in those dogs that are showing symptoms such as fainting.

DILATED CARDIOMYOPATHY is a disease of the heart muscle in which inflammation and scarring cause enlargement (stretching, dilation) of the heart and dilation of the chambers. Eventually the muscle weakens (becomes over-stretched) and the dog develops congestive heart failure. It occurs most often in young to middle-aged males. The first indications are unexplained lethargy, weight loss, cough, exercise intolerance, and shortness of breath.

Cardiac arrhythmias may cause fainting. IN A SMALL NUMBER OF CASES, CARDIOMYOPATHY can be caused by prior infection (ie. Lyme disease), hypothyroidism, vaccination, or diseases such as cancer and diabetes. Sudden death can occur.

Both SAS and CM are inherited, and testing prior to breeding is advisable by Auscultation by a cardiologist (and if “clear” can be OFA certified), Holter Monitor (a 24-hour ECG/EKG for a prolonged sampling of the electrical activity of the heart) and/or Ultrasound (an in-depth detailed view of the heart to observe muscle wall thickness, blood flow and any valve irregularities – Echocardiogram or Colour-flow Doppler). An ECG/EKG is a 3-minute electrical test, and may not be long enough to pick up PVC's. X-rays can be useful when suspecting an enlarged heart (possible dilated cardiomyopathy).

Heart conditions are very common in the Boxer, and careful elimination of affected dogs from breeding programs will be crucial in preserving the breed.  

American Boxer Club - update on BCM/ARVC and SAS

MORE INFO ON HEART CONDITIONS

CAN VACCINES CAUSE CARDIOMYOPATHY?

CARDIOMYOPATHY - Wendy Wallner DVM

Familial Ventricular Arrythmia in Boxers - Kate Meurs

Orthopedic Foundation for Animals - Congenital Cardiac Disease


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