Biomarker Results Interpretation

Interpretation of heart test results

These notes are from the forms that were signed by those having their dogs tested as part of the biomarker research project.

Biomarker tests Dilated cardiomyopathy in Dobermanns

Dilated cardiomyopathy (DCM) is a major cause of death in Dobermanns. It is known to have a genetic basis. As DCM is an acquired disease, which may not appear to later on in the dog’s life, perhaps towards the end of a breeding career, it is very difficult to identify whether a young dog will develop the disease or transmit this to his/her progeny. If a single gene caused the disease, and a genetic test was available, this would be the gold standard.

There is one genetic test, called PDK4, a gene on chromosome 14, identified in USA Dobermanns, and this test is commercially available. However, it does not explain all cases in the USA or in Europe. A different chromosome, chromosome 5, has been associated with the disease in European Dobermanns, again explaining only about 50% of the cases, but so far, this is not a commercially available test.

Echocardiography (echo; a heart ultrasound scan) is the most sensitive method of detecting the disease once the dog has developed it. Echocardiography may identify minor abnormalities several years before the disease is manifested. However, echocardiographic screening needs to be repeated on an annual basis in breeding Dobermanns, so this is time consuming and expensive. As Dobermanns may have abnormal heart rhythms as DCM is developing, a 24 hour ECG (called a Holter monitor) may identify these prior to development of echo evidence of the disease. This is also an expensive test which needs to be repeated annually. Recent evidence suggests that cardiac biomarkers may identify dogs at risk of developing DCM, and identify those dogs on which to focus the more expensive tests.

Echo screening DILATED CARDIOMYOPATHY (DCM) is an acquired heart muscle disease which occurs with high prevalence in Dobermanns (estimated as approximately 50 – 60%). The clinical phase of the disease may be just a few weeks or months, characterised by signs of congestive heart failure (for example coughing, shortness of breath, difficult breathing, marked lethargy and exercise intolerance). However, echocardiography (cardiac ultrasound exam) can identify evidence of DCM many months or even years before the clinical phase develops. This earlier phase is called occult or preclinical DCM. An even earlier phase may be identified (called equivocal) where there may be minor echocardiographic abnormalities, but the dog will need follow-up scans to see if these progress to preclinical or clinical DCM (often over may years).

To interpret the echocardiographic results in your Dobermann, the following information is provided.

These volumes, indexed to body surface area, are abnormal and consistent with DCM:

Some Dobermanns also have abnormal heart rhythm (cardiac arrhythmias) which can cause fainting (syncope) or even sudden death, and the arrhythmia may be important before onset of congestive heart failure, or any significant echocardiographic abnormality. Therefore the “gold standard” of screening currently includes BOTH echocardiography and 24 hour ambulatory ECG recording (called Holter monitoring).

References Summerfield, N.J., et al., Efficacy of pimobendan in the prevention of congestive heart failure or sudden death in Doberman Pinschers with preclinical dilated cardiomyopathy (the PROTECT Study). J Vet Intern Med, 2012. 26(6): p. 1337-1349. Wess, G., et al., Prevalence of dilated cardiomyopathy in Doberman Pinschers in various age groups. J Vet Intern Med, 2010. 24: p. 533-538. Wess, G., et al. Sue of Simpson’s method of disc to detect early echocardiographic changes in Doberman Pinschers with dilated cardiomyopathy. Vet Intern Med, 2010. 24: p.1069-1076.

Holter screening (Introductory paragraph same as for echo.) For reliable results, the Holter recording should have at least 20 hours of good quality recording.

• Dog’s heart rates can range considerably from very slow when asleep and very fast when exercising (e.g. often ranging between 30 to 220 beats a minute over a day). The average one minute heart rate over the recording period in a healthy, relaxed dog is usually 65 – 90 beats a minute. Dogs who are very stressed or who have heart disease may have a faster average heart rate than this.

• Dobermanns with early evidence of DCM or with clinical DCM often show increased numbers of abnormal heart complexes, called ventricular ectopic (or aberrant) complexes. These may be premature, interrupting the normal heart rhythm (ventricular premature complexes or VPCs). These can be single, or occur in pairs (couplets), triplets or short runs (salvos). If there is a run of abnormal beats, this is called ventricular tachycardia. Ventricular tachycardia episodes, if prolonged, can cause syncopal (fainting) episodes or even, if they deteriorate further, sudden death.

Couplets, triplets, salvos and runs of ventricular tachycardia are never normal.

We need to remember that other illnesses the dog may be suffering may also cause these ventricular ectopic complexes, so your dog may need other health tests.

• Occasionally, other premature beats may be detected, called supraventricular premature complexes, which come from the upper heart chambers. Runs of these are called supraventricular tachycardia (SVT). A small number of premature beats is not a concern, but SVT would be. SVT needs to be distinguished from a normal fast heart rate when the dog is exercising or very excited.

• It is very normal for the dog to have a number of episodes of slow heart rate (bradycardia). The episodes recorded are when the instantaneous heart rate is less than 45 beats a minute for more than 4 beats. Dropped beats and pauses, often up to about 5 seconds, are also normal in resting or sleeping dogs.

If your dog has abnormal Holter results, especially if there are runs of ventricular tachycardia noted, the owner and / or the primary veterinary surgeon should speak with the veterinary cardiologist about further investigations, and possible treatment, which will depend on the results from other test including echocardiography.

Reference Wess, G., et al., Prevalence of dilated cardiomyopathy in Doberman Pinschers in various age groups. J Vet Intern Med, 2010.