Visiting Vet: A heart murmur can mean many things

But for Smurf, the news is good.

Little White Dogs are known to have full body tremors. —Nick Fewings

Smurf is a classic example of what veterinarians call an LWD. That’s a Little White Dog. He happens to be a Maltese–toy poodle cross, but LWDs can be any pup fitting the description: bichon frisé, West Highland white terrier, coton de Tulear, to name a few. LWDs are particularly famous among veterinarians for a weird condition literally called Little White Shaker Syndrome, in which LWDs suddenly develop whole body-tremors, especially when excited, stressed, or exercising. Little White Shaker Syndrome mostly affects dogs under 5 years old. It usually responds well to treatment with corticosteroids.

The disease has other names, including idiopathic or corticosteroid-responsive generalized tremor syndrome, since small dogs of other colors can also be affected. Most affected dogs improve quickly with medication, but may have recurrent episodes.

Luckily, Smurf doesn’t have Little White Shaker Syndrome. He does have a few minor issues common in older dogs. When he came for his annual exam, as he has done like clockwork for 12 years, I noticed mild lenticular sclerosis in his eyes. This is an aging change that gives a whitish, or bluish, hazy appearance to the lens. Owners often mistake it for cataracts, which can cause blindness, but lenticular sclerosis only causes minor visual impairment. “He may not be able to read the fine print in the newspaper,” is my usual reassurance. I guess I need to update that, since there are few of us left who actually read a newspaper.

I continued my exam, which I always do in the same order so I don’t forget anything. His teeth had moderate dental tartar, another common finding in little old dogs. Not enough to warrant an anesthetic dental procedure, I decided. His skin looked fine. Pink, but fine. LWDs, like people with fair complexions, tend to have sensitive skin, and more than their share of dermatological issues. Not Smurf. Time to check his heart. I grabbed my stethoscope. I listened once. Twice. One more time. Yup. Smurf had a heart murmur. I flipped back through all 12 years of exams. Nope. No mention of this previously. So Smurf had a NEW heart murmur. I listened to his lungs. I listened to both sides of his chest. I listened to several different areas … and was reassured. I’ll tell you why — but first, a few basic things about veterinary cardiology.

Most veterinarians grade heart murmurs on a scale from I to VI. In school, we used to say a Grade I murmur is one a professor can hear but a vet student can’t. Perhaps nowadays that would be considered politically incorrect, or oppressive to vet students? So here’s a PC version. A Grade I murmur is a low-intensity sound that can only be heard in a very quiet room. Grade II, III, and IV are progressively louder, and may be audible over larger areas of the chest. With a Grade V murmur, you can actually feel a vibration when you place your hand on the dog’s chest. This is called a precordial thrill … though no vet is ever thrilled to find it. A Grade VI murmur has the thrill, and you can hear the murmur, even before your stethoscope touches the body wall. Smurf had a Grade II murmur.

Although it is tempting to assume that a low-grade murmur means less severe cardiac disease than a louder one, this is not always true. However, in Smurf’s case, the fact that his murmur was only Grade II really was good news. Read on. The most likely cause of murmurs in small-breed dogs, white or otherwise, is myxomatous mitral valve disease (MMVD). That’s a mouthful. What happens in MMVD is that due to degenerative changes in the valve in the left side of the heart, there is leakage. Blood flows at a time when it shouldn’t, causing the murmur.

MMVD is very common in little dogs. Males are affected more often than females. Older dogs are at much higher risk than younger, except in Cavalier King Charles spaniels, who seem to get MMVD earlier than other dogs. Breeds who are predisposed (besides Cavaliers) include miniature and toy poodles, Maltese, Yorkies, Chihuahuas, Pomeranians, Pekingese — really, any small breed.

Often there are no clinical signs, and the murmur is discovered as an incidental finding at a routine exam. Unfortunately, MMVD can sometimes progress to congestive heart failure and/or pulmonary hypertension. Signs can range from very mild to severe, and may include coughing, especially at night, rapid or labored breathing, rapid heart rate, loss of exercise tolerance, poor appetite, weight loss, blue or pale gums, fainting, collapse, even sudden death.

So why was I reassured? Because studies indicate that Grade I or II murmurs in little old dogs are almost always associated with mild disease. In fact, 75 percent of little old dogs with MMVD will never develop serious heart problems. “If you want to get a baseline, we could take radiographs today and see if there is any heart enlargement,” I said. “Odds are around 90 percent that his films will be normal at this point.” Smurf’s family opted to hold off on testing for now. I advised them to call right away if he developed any symptoms, otherwise to have a recheck and possible x-ray in six to 12 months.

If we see heart enlargement on x-rays, I suggest owners see a cardiologist for an echocardiogram, and to get the benefit of a specialist’s expertise about treatment. Different cardiologists have different takes on when and what medications to use. There are still many unanswered questions as to whether giving various drugs before the onset of clinical signs will slow the progression of disease, or delay onset of heart failure.

Cardiology is an extremely complex field. Murmurs can range from “innocent” to imminently life-threatening. Listen to what your veterinarian advises. See the cardiologist if at all possible. Don’t assume every murmur can just be monitored like Smurf’s … but sometimes it’s a good thing to be a little old, little white dog.