Case Studies In Small Animal

Cardiovascular Medicine

Home Up .    Radiographs ECG 2D Echo M-Mode Color Flow Doppler Diagnosis

Case 9

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This continuous wave Doppler tracing was recorded by placing the ultrasound beam across the jet through the mitral valve from the left apex to align the cursor parallel with flow. As can be seen in the upper left hand corner of the image, a peak systolic velocity (V) of 4.50 meters/second was obtained. The modified Bernoulli equation (4 times velocity squared) was used to calculate the pressure gradient (PG) across the mitral valve in systole. As seen on the frame, the measured velocity translated into a calculated pressure gradient of 81 mm Hg. This means the left ventricular pressure was 81 mm Hg higher than the left atrial pressure. In order to estimate this dog's left atrial pressure, a Doppler device (Park's Doppler unit) and an inflatable cuff were used to estimate "Bingo's" systemic systolic arterial blood pressure. It was 125 mm Hg. Peak systolic left ventricular pressure and peak systolic systemic arterial blood pressure should be almost the same since this dog had no evidence of aortic stenosis.

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This dog also had a mild leak across its tricuspid valve. The peak velocity of this jet was also measured and in this dog was 3.69 meters/second. This translated into a pressure gradient across the tricuspid valve of 54 mm Hg which means the right ventricular pressure was 54 mm Hg higher than the right atrial pressure. This dog was not in right heart failure and so we can assume that its right atrial pressure was normal (0 to 5 mm Hg). This means the right ventricular systolic pressure was around 55 mm Hg (54 mmHg + 1 mmHg). There was no evidence of pulmonic stenosis in this dog so whatever systolic pressure was present in the right ventricle must also be present in the pulmonary arteries. Normal systolic pulmonary artery pressure is around 25 mm Hg. Consequently, this dog had systolic pulmonary hypertension. Normal diastolic pulmonary artery pressure is around 5 to 15 mm Hg. At a reasonable heart rate, diastolic pressure in the left atrium and diastolic pulmonary artery pressure equilibrate. Since Bingo's systolic pulmonary artery pressure was increased approximately 30 mm Hg higher than normal, it is reasonable to assume that his diastolic pressure is increased a similar amount which would make it approximately 35 mm Hg (30 mmHg + 5 mmHg assuming the low end of normal diastolic pressure range). The pulmonary artery diastolic pressure should be the same as diastolic left atrial pressure. 

Taking all of these data together, it appears that Bingo has a left atrial pressure of approximately 45 mm Hg in systole and 35 mm Hg in diastole with a mean (average) left atrial pressure around 40 mm Hg. This is compatible with left atrial pressures measured directly in other dogs with the same disease that were in severe left heart failure. Please note that in this dog that the pulmonary hypertension was purely due to the left heart failure (not to any reflex pulmonary vasoconstriction as is often seen in humans) and that this mild degree of pulmonary hypertension did not result in any right heart enlargement (see the previous two-dimensional echocardiograms).  

 

 

Mark D. Kittleson, D.V.M., Ph.D. All rights reserved.