Case Studies In Small Animal
Cindy recovered reasonably well from anesthesia. She had isorhythmic AV dissociation for several hours while recovering but was clinically stable. Echocardiography was repeated the following day when she was fully recovered from anesthesia.
As opposed to the echocardiogram of the pulmonic valve taken before intervention, the pulmonic valve after has an orifice that has a readily demonstrable orifice in the echocardiogram above. RVOT - right ventricular outflow tract; PA - pulmonary artery; AO - aorta.
Although the color flow Doppler signal after valvuloplasty does not show laminar flow across the pulmonic valve, the abnormal signal appears to be primarily due to aliasing rather than turbulence. In addition, the signal is much wider in the region of the pulmonic valve than it was before valvuloplasty. RV - right ventricular cavity; AO - aorta; PA - main pulmonary artery.
As opposed to the systolic pressure gradient of approximately 210 mm Hg across the pulmonic valve region before valvuloplasty, the pressure gradient (PG) after is 43 mm Hg, a marked reduction. Pressure gradients between 30 and 50 mm Hg are common following successful balloon valvuloplasty. The pressure gradient almost never decreases to normal (less than 10 mm Hg). Interestingly, a flow signal out into the right ventricular outflow tract or pulmonary artery can be seen during atrial systole on the continuous wave tracing (upward arrow). This probably indicates forceful atrial contraction. Flow in diastole toward the transducer can be seen above the line (downward arrow) and is due to pulmonic regurgitation. It is low velocity indicating a normal, low diastolic pressure gradient across the pulmonic valve (normal early pulmonary artery diastolic pressure is around 10 mm Hg and normal right ventricular early diastolic pressure is 0 mm Hg making the pressure gradient 10 mm Hg and so the velocity is the square root of 2.5 [10 divided by 4] or 1.6 meters/second).
This color flow Doppler picture demonstrates pulmonic regurgitation. The frame is recorded in diastole and shows laminar flow in the pulmonary artery (PA) coming toward the transducer (red). When it reaches the pulmonic valve region it becomes aliased and projects into the right ventricle (RV). The pulmonic regurgitation appears worse than it did before the valvuloplasty since the size of the color jet is larger and is wider at its origin. However, since the pressure gradient is so low between the pulmonary artery and the right ventricle in systole, pulmonary regurgitation is almost never hemodynamically significant.
In addition to the above studies, another contrast echocardiogram was performed the day after valvuloplasty. It showed almost no bubbles traversing the patent foramen ovale. In addition, the dog appeared brighter. When the owner picked up the dog, it became very excited. Whereas before the intervention the dog became cyanotic and dyspneic, it was able to tolerate the excitement very well. When the owner was called the following day she was ecstatic. She claimed that the dog was "300% better" than before. She was able to play normally without fatigue, cyanosis, or dyspnea. The clinical improvement in this dog was almost certainly due a decrease in hypoxemia brought about by a decrease in right-to-left shunting across this dog's large patent foramen ovale. This decrease probably occurred because the amount of tricuspid regurgitation decreased once the pulmonic stenosis was relieved. Once the resistance to flow through the pulmonic valve decreased, flow would have increased into the pulmonary artery and would have decreased through the fixed resistance in the tricuspid valve. This is much like taking a river with two branches in which one branch has a dam with little flow and blowing up the dam. More flow goes through the branch with the blown-up dam and less goes through the other branch. The increase in pulmonary blood flow in this dog probably also improved systemic arterial oxygenation.
©Mark D. Kittleson, D.V.M., Ph.D. All rights reserved.