We have two major heart problems in boxers;
Cardiomyopathy, which seems to be more prevalent in 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 middle aged to older dogs, now it is diagnosed on 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 free at a young age is not a guarantee not to develop the disease later....... It seems most vets agree that the way to diagnose Cardiomyopathy is to holter, since the main symptom (at least in the early stages, before the dog develops other clinical symptoms) is arrhythmia (irregular heart beats). The arrhythmia may not occur during the short EKG examination, so the chance of not diagnosing a (at the time slightly) affected animal is there. The EKG - examination will, though, diagnose those with a more advanced Cardio, and is therefore not a total waste......The recommendation in Canada is to Holter .....(please fill in when and how often, you know this better than I!)
The other heart problem in boxers is Aortic stenosis(AS), or Sub aortic stenosis - 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 which are not indicative of a heart disease. By the age of 1 year, these innocent puppy murmurs have mostly disappeared, and the aortic or sub-aortic stenosis has developed fully. This means that a grade heart murmur diagnosed at 6 months may or may not be a heart problem, but if the murmur is still there at 1 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 you measure is heart rate, rhythm, and alteration of the heart muscle; these rarely change in aortic stenosis - and not unless the condition is severe. The way to diagnose AS/SAS is auscultation by a cardiologist (listening to the heart with 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 Edinburg 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.
No methods are infallible, and of course, some affected animals will pass as normal - but they are few and far between (but of course 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 this due to AS /SAS later. The very few 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 is heart tested by a cardiologist at 1 year or older. Boxers with no murmur(0) or a slight murmur(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.
There are, of course other heart conditions that may affect boxers, and can give arrhythmias and murmurs, but if you have a boxer with a grade 2 or more heart murmurer, it is a 95 % chance that it has AS/SAS.
Both these conditions can give, as the first symptoms, sudden unexpected death or severe fainting episodes.
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