As of May 2017, in the OFA Borzoi Health Survey we see that of almost 1000 entries, only 6.6% report cardiovascular disorders. Of those, 2% were diagnosed with heart murmur, 1.6% congestive heart failure; 1.1% cardiomyopathy, 1% mitral valve defect, 0.9% other, 0.4% tricuspid valve defect, 0.3% degenerative valve disease, 0.2% sub aortic stenosis, and 0.2% patent ductus arteriosis. In the OFA Borzoi cardiac statistics it shows only 1.4% abnormal and 3.2% equivocal out of 1774 borzois tested (I am not including the Advanced Cardiac Registry at this time since the numbers included are too low for conclusions to be made).
Because Borzois are a relatively rare breed these percentages give researchers a clear signal that there are not large enough numbers of borzoi with specific heart disorders to allow an effective study. And yet we have all either experienced or heard of borzois who have dropped dead suddenly with no cause of death found on necropsy. Is this a sign that there is a significant cardiac problem in our breed? Frankly, we do not know for sure. The statistics provided above have been obtained using screening techniques that have an exceedingly low chance of identifying life threatening cardiac arrhythmias. Even an ECG strip may miss pathological arrhythmias because the heart rhythm is not sampled for a long enough time nor is it obtained during a dog's normal activity. So the answer is that we have no idea what type of cardiac arrhythmias are found in borzoi, how widespread they are, at what age do these arrhythmias peak (cause the greatest number of sudden deaths), how many borzoi may be affected, or if all types of cardiac arrhythmias found in the breed are pathological and can lead to sudden death or the development of dilated cardiomyopathy. We also have no idea if cardiac arrhythmias in borzois have any of the characteristics that suggest heritability.
In order to even begin to gain an understanding of this problem we need data, lots of data. This is where the information sharing price break for Holter rental comes in. By sharing your results, future cardiac health and results of any cardiac testing done through the dog's life, the dog's pedigree, and date of death (with cause of death, if the cardiac problem was the cause or suspected to be the cause) you can help us begin to understand the mystery that surrounds sudden death in borzois.
Another question that can be answered through the sharing of data is if any of the sudden deaths we see in borzoi are connected to dilated cardiomyopathy (DCM). In several breeds, cardiac arrhythmias that have the potential to cause sudden death occur for several years before DCM can be detected by other means. This can give breeders a longer period of warning that a dog may develop DCM than is possible without Holter testing. We do not know if borzois with very early DCM produce cardiac arrhythmias and if they do, we do not know either what type of arrhythmias they produce or how early these arrhythmias can be detected. By following borzois with arrhythmias over time, we will eventually gain a better understanding of how Holter testing can help breeders avoid breeding dogs who will later develop DCM, as well as help those diagnosed with early DCM live longer through early medical intervention. By sharing your dog's heart health information, you can help us look for ways to identify DCM at younger ages than is currently possible.