Case Studies In Small Animal
Stubs presented with clinical signs consistent with and radiographic evidence of left heart failure. The radiographs also showed cardiomegaly with a markedly enlarged left atrium that was particularly noticeable on the lateral view. In this view, the left mainstem bronchus was markedly elevated because of the enlarged left atrium, leaving the right mainstem bronchus ventral to it left counterpart. On the ECG there was evidence of left ventricular enlargement (increased R wave height of approximately 3 mV in lead 2). The echocardiograms clearly demonstrated that there were two combined problems - mitral stenosis and mitral regurgitation. The mitral stenosis could be discerned on the two-dimensional echocardiogram as restricted leaflet motion in diastole. It was further defined by observing a turbulent jet that started at the mitral valve region and flowed into the left ventricle in diastole on color flow Doppler echocardiography. The severity of the stenosis was quantified by measuring the peak blood velocity through the mitral valve orifice using a pulsed wave Doppler echocardiogram and translating the velocity into a pressure gradient using the modified Bernoulli equation. Instead of a normal pressure gradient that peaks at approximately 2 mmHg, the pressure gradient in this dog was 12 to 16 mmHg. This would be a very mild stenosis if it involved a semilunar valve in systole. In mitral stenosis this is at least a moderate gradient as it increases the left atrial pressure by 12 to 16 mmHg. Normal left atrial pressure is less than 10 mmHg. When the left atrial pressure increases to 20 mmHg, pulmonary edema starts to develop. When it reaches 30 mmHg, moderate edema is present and at 40 mmHg the edema is severe. The diastolic pressure gradient in this dog means its left atrial pressure was at least in 20 to 25 mmHg range in early diastole. Stubs also had mitral regurgitation. Both functional problems (i.e., mitral stenosis and mitral regurgitation) were due to a congenitally abnormal mitral valve which can be called mitral valve dysplasia. In addition there appeared to be a band of tissue beneath the mitral valve that may also have contributed to the stenosis.
It appeared that the mitral regurgitation in Stubs was severe. In most dogs with mild to moderate mitral regurgitation, the pressure gradient across the mitral valve is in the 80 to 120 mmHg range. That's because the left ventricle generates a normal pressure (e.g., 110 mmHg) and the left atrial pressure is normal or mildly increased (e.g., 10 to 20 mmHg). A pressure gradient of 100 mmHg means the flow velocity is 5 meters/second (square root of 100 divided by 4). In Stubs the flow velocity and the pressure gradient were markedly reduced. That means either the left ventricular systolic pressure was decreased (i.e., systemic hypotension) or the left atrial pressure was markedly increased. Since he had moderate to severe pulmonary edema, his mean left atrial pressure was probably around 30 mmHg. Peak left atrial pressure was almost assuredly higher than this and could easily have been 45 mmHg. The pressure gradient was 55 mmHg which would translate into a left ventricular systolic pressure of 100 mmHg which is on the low end of normal.
Discharge instructions to the owner
Four months later
Stubs owner indicated in a voice mail message that they hadn't changed his dose of medication and that he was doing very well.
Three years later
Amazingly, Stubs is still alive and doing very well. In a telephone conversation with his owner, she indicated that Stubs currently weighs 56 pounds, similar to his father who is 60 pounds. One of his brothers, however, weighs 80 pounds. According to his owner, Stubs has a body build similar to his father and so she doesn't believe he's underweight. Stubs exercise capabilities appear to be quite good. In the summer he swims every day. He loves to dig holes in the sand on the beach. When he was a puppy his owner always let all of his brothers out to play and then let Stubs out to play with them when they had settled down a bit. Now he seems to know his limits. He will play hard and then take a break for a while before going back at it again. Neither he nor his father are neutered so they challenge each other often and Stubs is able to hold his own. So in almost all ways Stubs has a normal life. He is still on the same medications he was on previously (Lasix 25 mg BID; lisinopril 10 mg BID; digoxin 0.375 mg SID) and his owners don't take him to higher elevation with them during the summer. Other than that, although he is still his owners "special child," he appears normal in all respects. His owner calls him her miracle dog and sent a picture (above) to prove it.
©Mark D. Kittleson, D.V.M., Ph.D. All rights reserved.