Lucy is a 12-year-old Shih Tzu, who was diagnosed with chronic cardiac valve disease last fall. This degenerative condition of the heart valves is the most common cardiac disease in dogs, typically occurring in middle-age to older animals, and particularly frequent in small breeds. As many as a third of all small to medium-size dogs over the age of 12 interesting years may be affected. What happens is that the valve between two chambers of the heart (the atrium and ventricle) becomes thickened and irregular, which ultimately results in regurgitation of blood in the wrong direction. On the left side of the heart, it’s called mitral valve insufficiency. On the right side, it’s the tricuspid valve. The first indication of cardiac valve disease is often heard, but not seen. You’ve brought Lambert, your little poodle, in for a physical. Your veterinarian is doing the usual routine. She puts her stethoscope on Lambert’s side but then pauses. She listens a little longer, then thoughtfully ruffles through his previous medical history. “Did I ever mention a heart murmur?” she asks.
Whether or not to work up an asymptomatic heart murmur, i.e., one in which the dog shows no clinical signs of disease, depends on several factors. Heart murmurs are graded on a scale from I to VI. We used to joke that a Grade I murmur is one that a vet student can’t hear. A Grade VI murmur vibrates so much you can actually feel it with your hand on the side of Lambert’s chest. If the murmur isn’t very loud, and Lambert seems healthy otherwise, this usually suggests the problem is not very serious. It never hurts to get baseline radiographs, maybe even an ultrasound, but you can discuss with your veterinarian whether these are necessary.
Lucy’s murmur had been present for several years, but was gradually getting louder, and now at a Grade IV. Radiographs revealed some heart enlargement, so her owner opted to consult a specialist, who could do a Doppler echocardiogram, which evaluates how blood flows through the heart chambers, valves, and blood vessels. Lucy was diagnosed with chronic mitral valve disease with severe atrial enlargement. She was started on medication that lowers blood pressure, thus reducing the workload on the heart, and her owner was told to watch for signs of congestive heart failure (CHF.)
CHF occurs when the affected side of the heart stops being able to pump well enough to do its job adequately. Blood pools in the failing portion of the heart, creating back pressure which then causes fluid to leak out into either the lungs (left-sided failure), the abdomen (right-sided failure), or both. This spring Lucy developed classic signs of left-sided CHF, which include weakness, lethargy, exercise intolerance, coughing (especially at night), and difficulty breathing. A second trip to the specialist and more radiographs showed increasing heart enlargement that was now pushing her windpipe upward. Called “dorsal tracheal elevation,” this is a common result of an enlarged heart and is occasionally thought to be a contributing factor to the cough seen in CHF. But more typically the cough is attributed to pulmonary edema, i.e., fluid buildup in the lungs. Lucy was started on additional medications, including a diuretic to draw the fluid out of her lungs, and another drug to help improve the contractility of her heart muscle.
The problem with CHF is that it can progress at any time. It can get worse gradually, or very suddenly. If your Lambert has been diagnosed with CHF, you may be asked to keep a log of his Sleeping Respiratory Rate (SRR). This is a great tool for owners to monitor their dogs’ condition at home, as it is a very sensitive indicator of pulmonary edema. You start by getting several baseline readings, counting how many breaths Lambert takes per minute when he is asleep in a room that is not too hot, not too cold, and when he has had no abnormal exercise or agitation recently. A normal dog should have a SRR of less than 30. If Lambert’s is higher than this, check in with your veterinarian. If it is 50 or more, you should call immediately. Well, first make sure he’s really asleep … and that he’s not in the middle of a dream. (Dogs occasionally chase rabbits, or cars, or cats, in their sleep, and breathe faster as a result.) An elevated SRR does not necessarily mean Lambert has pulmonary edema or CHF, as there are many other causes for rapid respiration, but a normal SRR means you can rest easy.
Now here’s why I started writing this article in the first place. A few weeks ago Lucy had a bad bout of coughing, and I was faced with one of most troublesome dilemmas in veterinary practice: how to distinguish cardiac disease from primary respiratory disease. This can be a lot harder than you would think. Was Lucy coughing because of progression of her congestive heart failure? Or was it something else? Like the insanely high pollen counts that have left half the Island humans hoarse or coughing? There are whole seminars devoted to helping veterinarians differentiate heart issues from lung issues, but the bottom line is that there is not always a quick, easy, and/or definitive way to know which we are dealing with.
Lucy’s latest chest radiographs didn’t resolve my predicament. It looked like there might be a little pulmonary edema, but I couldn’t say so unequivocally. She still had the dorsal tracheal elevation, of course, but it didn’t seem any worse, nor did the heart enlargement. I opted for what is euphemistically known as a “therapeutic trial,” increasing the dose of Lucy’s diuretic, and waiting to see if her cough improved … which thankfully it did, supporting my presumptive diagnosis of mild pulmonary edema secondary to chronic CHF. I advised the owner to once again keep a log of her SRR, and suggested that now might be a good time to schedule a recheck with the cardiologist.