They say the eyes are the windows to the soul. But when veterinarians want to see a cats heart – while its still beating inside the kitty, of course – they need a special kind of X-ray vision.
Theres electrocardiography or ECG (which used to be called EKG before humans learned to spell) and, yes, they do use X-rays to look at the heart (but the bill will say radiographs, just to be technical).
But the most interesting technique, which I recently stumbled on while making my rounds of the Cornell University Hospital for Animals, is echocardiography. Being the resident cat in the Cornell Feline Health Center does have its privileges, and one is being able to stick your head in the door when you hear the sound of a leaky faucet.
Sophisticated ultrasound exam
There on a clear plastic table, lying much more calmly than I would have under the
circumstances, was the cat that was the center of all this high-tech attention and the source of the curious sound. He was being examined with a gizmo called a Doppler color-flow ultra sound machine, and if his heart held any secrets, they were about to be revealed to the veterinary doctors.
Chest X-rays are surprisingly good for imaging soft tissue – they can show us the relative size and position of the heart and are still the best way to look at the lungs, for instance – and an ECG will reveal abnormalities in the rhythms of the heart, Mark Rishniw, BVSc, a veterinary cardiologist at the Cornell University College of Veterinary Medicine, had told me earlier. But when we want to see blood moving – which is what the heart is all about, after all – we need color-flow Doppler ultrasound. Healthy blood flow is laminar or smooth, he said. Turbulent flow, which the machine highlights with bright colors on the black-and-white picture of the beating heart, is a sign that heart valves arent working properly, theres a leak somewhere, or theres a narrowing of the outlets from the heart.
A treatment plan
It all started with a murmur – a Grade III murmur, to be precise – when the one-and-a-half-year-old cat on the table was just six months of age. On a scale of I to VI, a Grade III is not the loudest, but it was worth investigating in a young cat. This chap had been diagnosed with hypertrophic cardiomyopathy (HCM, see CatWatch, October 2001) and systolic anterior motion of the mitral valve, or SAM. The blood from his lungs had a difficult time entering his heart and, at times, leaving the heart to reach the rest of his body. He would become short of breath with the least little exercise and his pulse would race more than 230 beats a minute.
The treatment for the feline was a beta-blocker drug, atenolol (the same medication used by humans with high blood pressure and other cardiac aliments), administered by a very caring human companion twice a day in a dab of flavored kitty toothpaste (which, unlike humans toothpaste, is safe to swallow and is a pretty good trick for pilling us persnickety patients). Now, a year later, the cat was back to see if he could get off the beta-blocker and leave the pills for middle-aged, high-blood-pressured humans who really need them.
What goes wrong?
Heart murmurs are not unusual as cats grow older, says Dr. Rishniw, a board certified internist and cardiologist. Very often they are what we call innocent murmurs without any serious, underlying disease. But just listening to the heart doesnt tell us enough. Further evaluation is usually required.
Then he threw out some terms to make an old (but healthy, really) cats heart flutter: Things like bacterial endocarditis, a leaky valve condition that starts with a bacterial infection; or pericardial effusion, the build-up of fluid in that membrane sac around the heart that is usually associated with FIP (feline infectious peritonitis); and hypertrophic cardiomyopathy, the disease that thickens the heart muscles so they cannot flex properly. The last one mainly affects Maine Coons, Siamese, and Persians, none of which I am. But then he said it can run in the family among American shorthairs, and is even seen in regular garden-variety kitties! Gulp!
Then theres congestive heart failure, when fluid builds up in the lungs or the chest cavity or even the belly, he added, and some conditions connected with hyperthyroidism, but by then I wasnt concentrating. Surely, Doc, a little open-heart surgery will fix these problems, yes?
Not really, Dr. Rishniw told me. The cats heart is so small that for various reasons most surgical repairs are all but impossible. The good news, he said, is that many feline heart diseases can be managed with medicine. Diuretics can reduce the fluid load, for example. Beta-blockers such as atenolol can slow the heart and allow it to relax and fill more completely.
If hyperthyroidism is the cause of the heart condition, then correcting the thyroid disease – either with medication, surgery, or radioiodine – usually restores the heart problems. Taurine-deficient cardiomyopathies can be treated with – guess what? Yep, taurine – although now that taurine is added to cat foods, that disease is much more rare. And calcium-channel blockers do a nice job of promoting muscle relaxation in HCM, according to Dr. Rishniw.
What about congenital heart defects of the heart? Actually, Dr. Rishniw said, cats usually tolerate this form of heart disease better than do dogs – and better than most people.
The people running the fancy echocardiography machine, meanwhile, were busy with their tolerant feline patient (who did not need to be sedated for the painless procedure). Doppler color-flow ultrasounds are mostly found in big, regional veterinary medical centers rather than in local veterinary practices (which may have basic ultrasound machines), and this cat was getting all the bells-and-whistles worth. The pie-slice-shaped image of the beating heart on the monitor was so vivid that even I could tell – with a few clues from the operator – which way the blood was flowing. Interesting images were stored in a computer for further analysis, ECG readings could be made and displayed on the monitor at the same time, and of course the thing printed out still photos of echocardiograms to show friends and family.
Oh, about the leaky faucet noise? That really was the sound of the cats blood surging through the heart. Depending on what part of the cats ticker was being examined, some places produced a rhythmic gushing sound and others, a sort of plop, plop. Absolutely amazing!
There was good news for the patient, too. No sign of SAM (systolic anterior motion of the mitral valve). The cat could stop taking the beta-blocker drug but not abruptly, the cardiologist advised. Better to wean him from the drug that had been controlling his heart rate. That way, if the dog with whom he shares his home suddenly jumped out from around a corner, the frightened felines heart wouldnt race off the chart.
In other words, take it easy. Shouldnt be too tough for us cats to comply with that prescription, eh?