Screening for HCM
Screening for hypertrophic cardiomyopathy (HCM) can currently only be performed by a veterinarian. Yet, with increasing numbers of breeders becoming proficient in the use of reproductive ultrasound, there is a growing interest in expanding their skills to heart scanning.
In the world of pregnancy scanning, a number of trained and experienced scanners work closely with their veterinarians. Some scan inside their local practice, and others scan independently, receiving referrals from their veterinarians and referring any concerning cases back in return. Most vets simply don’t have the time for performing detailed pregnancy scans in front of the owner, searching for the cutest views of the growing pups, gathering photos and video clips for them to take home and share. These animals are, after all, invariably fit and healthy, and not in need of veterinary care. Veterinarians are more than happy to outsource this work to somebody who specialises in it, freeing them up to spend their time and expertise with sick animals.
The purpose of this type of scan is simply to confirm pregnancy. It is not providing a diagnosis of any kind. Pathology may be found incidentally, or a pregnancy may be found to be abnormal, but this would prompt immediate referral to a veterinarian. Cardiac screening is a different scenario because the purpose of it is to rule pathology in or out, and this is precisely what a lay scanner would not have the qualifications or legal ability to do.
In the human world, a number of studies have demonstrated great success in training individuals with no prior cardiac experience to reproducibly obtain a limited number of views with a portable ultrasound machine, which can then be sent back to a cardiologist for interpretation. This has great benefit in less economically developed countries and rural locations, where access to a cardiologist may otherwise be impossible. In this way, entire villages can be screened for conditions such as rheumatic heart disease.
Access to a veterinary cardiologist may be easier in the United Kingdom than this (though not necessarily in the United States or Canada, where distances can be just as vast), but nevertheless, presents its own challenges particularly for animals that do not travel well or become very stressed outside of their home environment. Organisations such as ‘Hairless Hearts’ are attempting to address this challenge by bringing cat owners and veterinary cardiologists together on a set date and location for HCM screening, organising gatherings across the USA and UK which are usually open to all breeds (though Hairless Hearts themselves are dedicated to the sphynx). This uses the veterinarians’ time more efficiently, and drastically reduces the financial cost for the pet owners.
Another option would be to replicate the human model and utilise the equipment and training of existing canine and feline pregnancy scanners to assist with image collection. These individuals would have to be trained to obtain the required on-axis views, with strict quality control procedures in place and all images being processed through the Animal Ultrasound Association for auditing by a sonographer and a veterinarian. Considerable time and financial commitment would be needed on behalf of the scanners. Cardiac ultrasound machines are not cheap (starting at around £8000 for a new machine, with occasional deals on ex-demos such as this Edan U50 Colour Doppler system here), and training would be intensive, yet a similar model works very well in the United States for meat grading – even with equipment there priced at over $20,000 (£15,000), and an average training fee of $1200 + accommodation.
The key would be finding a local veterinarian who would be happy to interpret your images as either within normal limits or requiring referral – without this, a non-veterinarian could not advertise their cats or kittens as HCM screened. It could only be performed privately, for personal interest, and would have no validity or meaning beyond your own front door. Without diagnostic value, the financial and time investment would be likely to be too high for most people. Those in isolated communities (some of the islands, or in the rural United States or Canada) may be more likely to find a cooperative veterinarian, particularly in an equipment sharing arrangement (i.e. the breeder purchases a cardiac machine for use on her own animals, but the vet may also use this machine for her work).
Whilst performing a full cardiac scan is a highly involved process (for example, see ruling out hypertrophic obstructive cardiomyopathy with Doppler here), a screen – such as an HCM screen – can often involve just one or two 2D views, and utilise skills experienced pregnancy scanners have already perfected. It is easy to forget just how much skill probe manipulation involves, and it’s only when watching beginners attempt these things which we do as second nature – such as rotating the probe 90 degrees without moving it from place – that one begins to appreciate just how fine these movements are and how much training your brain has to go through to perfect it.
These skills are transferrable, and the most important measurement that veterinarians take for HCM is taken from just one image. The challenge with this image is making it on-axis and reproduceable every single time.
The heart is not a tubular structure like the intestines, but the left ventricle – the chamber that vets look at when assessing HCM – is bullet shaped, and has a long and a short axis, demonstrated below:
The below video will be replaced with a higher quality version shortly.
In the above video, I demonstrate the view that most vets will take their measurements from. I am demonstrating this on myself, but the appearance is very similar in a cat, the biggest difference being the heart rate. Below is an example from an animal (you’ll also notice how much clearer it is than on a human being sitting upright!):
In the human world, we take measurements in the long-axis, but most veterinary studies have been taken from the short axis, so this is what vets continue to use. The challenge is making sure you are cutting at the same point along the ventricle on every scan, and you can do this by looking for certain landmarks. The landmarks vets use are the papillary muscles and the beginning of the chordae, as they attach to these muscles. Just like when cutting through a gestation sac you wish to perform a gestational age calculation on, it’s important not to cut the ventricle obliquely, which is where your 90 degree rotation comes in. You can turn back to the long axis at any point, to make sure you are well aligned with the ventricle.
June 19, 2021
February 19, 2021