The Veterinary Viewpoint

by Cecilie Stromstad, Boxerhaven, Norway
boxerhaven@BARUM.ONLINE.NO

We have two major heart problems in boxers - Cardiomyopathy (BCM), which seems to be more prevalent in the USA than in Europe, and Aortic Stenosis (AS) or Sub Aortic Stenosis (SAS), which seems to be more prevalent in Europe.

Cardiomyopathy is a disease of the heart muscle and will, if present, worsen with time. When this disease was first diagnosed in boxers, it was mainly in middle aged to older dogs. Now it is often diagnosed in young boxers as well. Since Cardiomyopathy is not something that is either there or not, it is important to examine the dogs more than once. Being clear at a young age is NOT a guarantee that the dog will not develop the disease later. It seems most vets agree that the way to diagnose Cardiomyopathy is with the use of a Holter monitor (a 24-hour EKG), since the main symptom (at least in the early stages, before the dog develops other clinical symptoms) is arrhythmia (irregular heartbeats). The arrhythmia may not occur during a short EKG examination, so the chance of not diagnosing a (at the time slightly) affected animal is there. The short EKG examination will diagnose those with a more advanced Cardio, though, and is therefore not a total waste.

The other heart problem in boxers is Aortic Stenosis (AS), or Sub Aortic Stenosis (SAS). This is a developmental defect, which is either there, or not. Even though it is not usually present at birth, it is considered congenital. The defect may take some time to develop, so a dog with no heart murmur at 8-10 weeks may have a severe heart murmur some months later. On the other hand, many puppies have "innocent" puppy murmurs that are not indicative of a heart disease. By the age of one year, these innocent puppy murmurs will have mostly disappeared, while the aortic or sub-aortic stenosis will have developed fully. This means that a grade 3 heart murmur diagnosed at six months may or may not be a heart problem; but if the murmur is still there at one year, it is a sign something is wrong. An EKG is not a good diagnostic tool when it comes to AS and SAS, because what the EKG measures is heart rate, rhythm and alteration of the heart muscle, and these rarely change in aortic stenosis, and not unless the condition is severe. The best way to diagnose AS/SAS is auscultation by a cardiologist (listening to the heart with a stethoscope). This method is very simple, and has proven to be the most reliable way to separate normal from affected animals.

There was a session in Edinburgh where several cardiologists from Britain and one from Sweden compared auscultation, color-doppler, and phonocardiogram, and the surprise was that the simplest method - auscultation - was the most reliable. [Editor’s note: I asked Cecilie if a phonocardiogram was what we in the US call an echocardiogram. Her reply: No - a phonocardiogram is a device to record the sound from the heart. It is an old instrument used before we got all the modern stuff. It was used earlier as an aid to diagnose heart defects, and has had a renaissance now in SAS diagnostics - it is used in Sweden and Norway, not in Britain as far as I know. It lets you see how loud the murmur really is, and where it comes in relation to the heart beat. The sounds are "written" on a paper. It is really interesting to see!]

No methods are infallible and some affected animals will pass as normal, but they are few and far between (of course, those are the ones you will hear about!). So if your boxer is diagnosed free from pathologic heart murmurs at one year, it is unlikely that it will develop a murmur due to AS /SAS later. The very few dogs that fall outside of this do not indicate that the diagnostic tool is wrong, only that both the dog and the tester are living beings, and they can vary from day to day! The recommendation in Britain is that a boxer be heart tested by a cardiologist at one year or older. Boxers with no murmur (grade 0) or a slight murmur (grade 1) are considered normal and fit for breeding. Boxers with a grade 2 murmur are considered normal IF they pass the doppler testing. Boxers with a grade 3 or more murmur are considered to have AS/SAS, and should not be bred from.