There are 3 main forms of this:
1. Dilated (DCM)
2. Hypertrophic (HCM)
3. Restrictive (RCM)
Let's see what a normal feline heart looks like from the inside and out:
And how blood normally flows:
For all three of these, the primary way to diagnose and differentiate is through an ultrasound of the heart - also referred to as an echocardiogram. We'll also want to get a full blood panel: as a baseline before treating with medications, to make sure there are not OTHER problems too and to check a thyroid level (some cases of heart disease can be caused by hyperthyroidism).
In DCM, both ventricles dilate and become increasingly unable to effectively pump blood, resulting in heart failure. Think of them becoming like big floppy bags. The primary cause of this was determined to be taurine deficiency. Taurine is an amino acid that cats need to consume in their diets because unlike US they cannot make this from other amino acids. This was discovered in the 80's and therefore, diets were reformulated to meet the need and the incidence of this particular type of CM has gone down significantly. Cats with this type of CM have a very poor prognosis and may survive a few months. Though if caught early is reversible with proper nutritional supplementation.
In HCM, the left ventricle gets thick or hypertrophies. Here's a illustration to demonstrate this:
This is the most common type we see. As this progresses, this left chamber becomes stiff and is unable to relax enough to properly fill or to effectively pump blood, leading to a backward pressure problem - and eventually fluid in the lungs. There is a genetic link with this disease and it is still being studied but we know that there is a higher incidence in some breeds: Ragdolls, Himalayans, and Maine Coons. Still we see most of it in our Domestic Shorthairs (DSH) - the generic cats most of us have. Is that because we see more of them in numbers or is the disease truly higher in them? I don't know. It's been reported that 75% of cases are male.
Many times they are not clinical at all - they seem fine - until I listen and hear a murmur - typically along the sternal border (or breastbone area). I have also seen cats there were "fine" until they arrive at the hospital in a state of distress. What happened? They were "handling" the disease until they just couldn't anymore...these cases can suddenly decompensate. This signals a poor prognosis and we need to handle the cat very carefully. Xrays of the chest, while helpful, can be stressful enough to cause death. So we may want to put the cat in an oxygen chamber and give him some medications and let him chill!
Cats with HCM can live for years, depending on how severe things are (again we need the echo for this). There are different medications we can use to help the heart work better.
RCM is much rarer. As the name implies, the heart becomes "restricted" from functioning normally usually due to fibrosis or scarring in the heart muscle. This one is hard to diagnose even with an echo because it has a variety of appearances that are similar to the other ones AND it can occur WITH them.
Cats with any of the above heart muscle issues have a higher risk of developing blood clots in the chambers. Why? Well, the blood flow is not normal. Blood swirls around in the chamber and there is some back flow into the atria so it gives the blood a chance to clot and this can cause another problem called a "saddle thrombus." I'll touch on that tomorrow.
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