Closed loop catheter position in PDA
Right heart catheter is seen passing from the inferior vena cava into right ventricle through the right atrium. From the right ventricle the catheter passes into the pulmonary artery and then across the patent ductus arteriosus into the descending aorta. The position of the catheter in the descending aorta is confirmed fluroscopically by passing it below the level of the diaphragm. The pressure tracing and oxygen saturation of the blood withdrawn also help in differentiating it from a catheter position in the left pulmonary artery. The aortic pressure tracing will usually show a high pressure while the pulmonary artery tracing will be of lower amplitude. But this may be different in a person with severe pulmonary hypertension. In fact in this case the pulmonary artery pressures were systemic as the PDA was quite large. The oxygen saturation will be much higher in the aorta in case of left to right shunt, but can be lower if there is significant right to left shunting across the PDA. So the only definite way to differentiate the position in descending aorta from that in left pulmonary branch is passage of the catheter below the level of the left hemi-diaphragm.
The pattern of the loop is different between PDA and aortopulmonary window (AP window). Whereas it is a closed loop in PDA, it is an open loop in AP window. An open loop can also occur when the catheter passes from the right ventricle to aorta through a ventricular septal defect (VSD). PDA catheter position in lateral view is given below.
PDA catheter position in lateral view
The image in lateral view shows the right heart catheter passing through the patent ductus arteriosus into the descending aorta. The spine is visible on the right side of the screen. The right heart catheter coming through the inferior vena cava below the diaphragm is coursing anteriorly as it passes through the right atrium, right ventricle, right ventricular outflow tract and pulmonary artery. It curves posteriorly to enter the ductus arterious and the descending aorta, where it descends along the anterior border of the spine. The region of the catheter crossing the tracheal air column (transluscent) in front of the spine superiorly is the site of the patent ductus arteriosus.