The Subtle Signs of Heart Failure in Dogs
In the last couple of weeks, I have had a few cases of congestive heart failure. One was recently euthanized by my colleague, one seems to be improving with appropriate medications. The most common heart disease in dogs is mitral valve disease. Perhaps you have heard of a person who has had a valve replacement. If you can recall from high school biology (it’s a stretch for some), there are four chambers in the heart. The mitral valve is the valve that separates the left atrium from the left ventricle. The atria are the small chambers that receive blood, and the ventricles are the larger chambers that pump blood out of the heart. We always want forward flow of blood, from the veins into the heart, then from the ventricles to the body/lungs through the arteries. After the ventricles contract, during relaxation, blood moves from the atria through the atrioventricular valves (AV valves: mitral and tricuspid). When the ventricles contract the AV valves close and the blood moves out of the heart through the aortic or pulmonary valves. However, when you have valvular disease, the valves are leaky, and some of the blood leaks backwards into the atria. This turbulence and leaky valve causes a heart murmur, a swooshing sound that your veterinarian (or physician) can hear with their stethoscope. In an older dog, every heart murmur is significant. When I hear a newly diagnosed heart murmur in a dog, I launch into an educational spiel with owners. When I get a patient on recheck or wellness that was previously evaluated by another veterinarian, I make sure that the owner has received the information on what it means to have a heart murmur. Even if you as the pet owner have not been told of a heart murmur, please keep in mind that several dog breeds are predisposed to degenerative valvular heart disease. When you get a puppy of these breeds, you can already start planning for their future as a senior with heart disease. For example, if you have a Cavalier King Charles Spaniel - you may as well start monitoring for heart disease once they reach their adult years. Congestive heart failure is the sequela to that backward flow of blood. When the blood leaks into the left atrium through the mitral valve, the left atrium cannot hold all of the blood, so it starts to stretch like a balloon filling with water. The left atrium is receiving blood from the pulmonary vein after it visits the lungs for oxygen exchange, once the left atrium cannot hold any more blood, it starts to stretch the pulmonary veins, then once the pulmonary veins cannot stretch any longer, the serum or fluid part of blood starts to leak into the alveoli, the part of the lungs responsible for gas exchange. If your alveoli are filled with fluid instead of air, then you cannot exchange the appropriate level of oxygen. Dogs may be coughing, or clearing their throats. They may be wheezing or having difficulty breathing, maybe taking deeper breaths. Often in the early stages of heart failure, the signs are subtle. They are not themselves. They might be slowing down on walks. They might be sleeping more, or resting more. They might not want to eat like they used to. Owners start to think that these are signs that their dog is getting old, when in fact they just cannot get the oxygen to their tissues like they used to. Occasionally, dogs will appear to pass out, called syncope. While an ultrasound (echocardiogram) of the heart is the best way to diagnose mitral valve disease, an x-ray is the best way to diagnose congestive heart failure. Below are x-rays of the same patient taken 7 days apart. Day 1 is when the patient (a 12-year-old female spayed Shih Tzu) presented with some coughing, and Day 7 is after treatment with oral Furosemide to reduce the fluid in the lungs. For the veterinary students and new graduates, comparing the images side-by-side is the best way to evaluate whether your treatment is working. To the trained eye, on Day 1, the perihilar region and part of the caudal-dorsal lung lobes has an increase in radiopacity consistent with fluid/soft tissue opacity. Now look at those regions on Day 7. You can see that the caudal-dorsal region has more air opacity (more radiolucent) than the first image. After we take blood work on the patient to ensure that the diuretic medication is not contributing to kidney or electrolyte abnormalities, we know that the patient requires this diuretic long term to treat congestive heart failure, and the dose is likely appropriate, unless they relapse (start to show clinical signs again). There is a medication that can delay the onset of clinical signs in dogs with mitral valve disease. This medication is called Pimobendan. If you own a dog that was diagnosed with a heart murmur, have a discussion with your veterinarian about early diagnostics and treatment to prevent or delay congestive heart failure.