Case Studies In Small Animal

Cardiovascular Medicine

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Case 7

Case Discussion

This dog had severe valvular pulmonic (pulmonary) stenosis and tricuspid valve dysplasia. She also had a patent foramen ovale (PFO). The severe pulmonic stenosis resulted in severe concentric hypertrophy of the right ventricle which is expected. In addition, this dog had severe endomyocardial fibrosis which is unusual. The hypertrophy and the fibrosis would combine to produce an increase in the diastolic pressure of the right ventricle. This would most likely result in the right atrial diastolic pressure being greater than the left atrial diastolic pressure and right-to-left shunting if a patent foramen ovale is present. This happens with some frequency but almost never results in clinically significant right-to-left shunting and hypoxemia. This dog also had tricuspid regurgitation. This results in an increase in systolic right atrial pressure and would be expected to exacerbate the right-to-left shunt as it did in this case.

Correction (partial or full) of the pulmonic stenosis would be expected to result in lesser tricuspid regurgitation (decreased force pushing blood back through the abnormal tricuspid valve) and so less right-to-left shunting. Over time, the decrease in the systolic pressure overload in the right ventricle might also result in lesser hypertrophy which would also lessen the right-to-left shunt. Consequently, balloon valvuloplasty was indicated in this dog. Luckily she had a valvular lesion that was amenable to valvuloplasty. If she had not been amenable, closure of the patent foramen ovale would have produced benefit by stopping the right-to-left shunting of blood. Surgical correction of the pulmonic stenosis may or may not be indicated in that situation. We have observed one other dog whose pulmonic regurgitation in combination with its stiff right ventricle resulted in right heart failure after its foramen ovale was closed and its pulmonic stenosis surgically corrected.

Balloon Valvuloplasty

This dog was anesthetized and its right jugular vein exposed. A 4 French balloon wedge catheter was passed down the jugular vein into the right heart. It was passed through the right ventricle into the main pulmonary artery. 

This schematic shows the catheter being advanced from the right atrium to a distal pulmonary artery with the normal pressure waveforms immediately above each position. On the far left, the balloon at the end of the catheter is inflated and the tip of the catheter is in the right atrium. The next drawing shows the catheter tip in the right ventricle (note that the systolic pressure increases and the diastolic pressure is the same as the right atrial pressure). Next the catheter has been advanced into the main pulmonary artery (note that the systolic pressure in the right ventricle and the pulmonary artery are the same while the pulmonary artery diastolic pressure is higher). On the far right, the catheter has been advanced with the balloon inflated to a distal pulmonary artery branch. Since the catheter port (opening) is beyond the balloon, the pressure that is recorded is actually pulmonary capillary pressure since blood flow to this branch is now occluded (note that the pulmonary capillary pressure is nearly the same as diastolic pulmonary artery pressure).

Pressure was recorded in the main pulmonary artery (peak systolic = 20 mm Hg) and then as the catheter was withdrawn from the pulmonary artery into the right ventricle (the opposite direction of catheter placement as in the schematic diagram above). The right ventricular peak systolic pressure was variable either due to catheter artifact or to mechanical alternans but was approximately 100 mm Hg higher than the pulmonary artery peak systolic pressure. This was much lower than the estimated pressure gradient of 210 mm Hg obtained with continuous wave Doppler when the dog was awake. This was most likely due to a decrease in blood flow across the stenotic pulmonic valve caused by anesthesia.

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Following this, a small guide wire was passed through the catheter and the catheter removed, leaving the guide wire in place. A 6 French balloon wedge catheter was then placed over this guide wire, back into the pulmonary artery. The small guide wire was removed and a larger guide wire placed in the same manner. The balloon wedge catheter was removed and a 6 French Tyshak low profile balloon valvuloplasty catheter was placed over the guide wire so that the balloon lay across the stenotic pulmonic valve. 

   

The image below to the left was taken after the balloon was partially inflated with saline and contrast agent. An indentation in the balloon can be seen in the region of the stenosis. The picture on the right shows the balloon fully inflated. The stenotic valve has been ripped open by the fully inflated balloon. A subsequent balloon inflation revealed no remaining indentation.

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The pressure gradient was measured immediately after balloon valvuloplasty using the same catheter. It showed that the pressure gradient had not changed. An echocardiogram, however, showed that the valvular region appeared to be more open and the infundibular muscle appeared to obliterate the right ventricular outflow tract in systole. A continuous wave Doppler of the region (below) taken about 30 minutes after the valvuloplasty revealed that the gradient was decreasing (55 mm Hg) and that the waveform had the characteristic shape of a dynamic stenosis in that it increased to a higher peak late in systole. All of this is characteristic of a "suicide" ventricle. When the stenosis is relieved in this situation, afterload is decreased which allows the ventricle to contract down to a smaller diameter. With the tremendous hypertrophy in the right ventricular outflow tract, this muscle is able to collapse down on itself and produce a dynamic or functional stenosis in late systole. In some cases this situation resolves on its own, like it appeared to be doing in this case. In other cases, beta blocker administration can alleviate the problem by decreasing the contractility of the myocardium in this region.

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