Canine valve disease is an idiopathic degenerative change of the heart valves and is common in older dogs, especially small breed dogs. There are 4 valves in the heart and the most commonly affected is the mitral valve. This valve separates the left ventricle (lower chamber) from the left atrium (upper chamber) and acts as a one way valve during heart contraction. If the valve thickens, it does not close adequately and allows for blood to flow backwards, referred to as "regurgitation". The regurgitation results in a murmur that can be heard with a stethoscope. The intensity or ‘loudness’ of the murmur can be graded from 1-6 (softest to loudest). The grade of the murmur does not necessarily equate to the severity of the valve lesions or overall heart size. Therefore, it is important to stage the heart changes once a murmur is identified.
Ultrasound images of a patient with mitral valve disease. The red arrow on the left shows a thickened valve. The image on the right displays color Doppler. The green color is abnormal and represents regurgitation through the thickened mitral valve.
There are often no symptoms early in the disease process. Over time, the heart may enlarge and predispose your dog to developing congestive heart failure (abnormal fluid retention). Signs associated with fluid retention include frequent coughing, heavy/labored breathing, an inability to rest or sleep comfortably, and fainting/collapse episodes.
Echocardiogram: The best way to evaluate the individual heart structures is to perform a heart ultrasound (echocardiogram). This allows the cardiologist to evaluate the valves, determine function, and assess blood flow using Doppler signals.
Radiographs (x-rays): X-rays are often used in combination with the ultrasound to further assess and characterize the stage of heart disease. This test provides useful information about the heart and lungs. This is the most sensitive test to diagnose fluid accumulation in the lungs.
X-rays from a patient with mitral valve regurgitation. The image on the left shows heart enlargement but no pulmonary edema (fluid in the lungs). The image on the right was taken 4 months later showing evidence of pulmonary edema (fluid appears white on an x-ray and is shown in the red circle).
Electrocardiogram (ECG): This may be an ancillary test used to assess the heart rhythm as some patients with heart enlargement develop secondary arrhythmias (abnormal heart beats).
Bloodwork: Baseline bloodwork to evaluate kidney function and electrolytes is typically done prior to starting cardiac medications. These values should also be monitored regularly while your dog is on treatment.
Valve disease is a lifelong disease and there are very few institutions that perform valve replacement surgery. Therefore, the goal for dogs with valve disease is to maintain a good quality of life for as long as possible using medical therapy. This may include medications to optimize heart function, manage fluid retention and control arrhythmias. The exact medications used will depend on the stage of your pet’s heart disease. Due to the progressive / dynamic nature of valve disease, and because no medications are without at least some side-effects, routine reevaluation of your pet is needed in order to provide optimal care.