Catheters can be placed into the jugular vein and the carotid artery percutaCatheterisation of the carotid artery is more easily performed with the animal anaesthetised; however, this may not be desirable, depending on the type of study which is being performed. Catheterisation of the jugular vein using the modified Seldinger technique is a relatively simple procedure. A needle or small catheter is placed in the vein, a small guide wire is passed through this and the needle or catheter is removed. A wide-bore dilator is then passed over the wire so that a much larger catheter can be inserted. The position of the catheter can be confirmed from the pressure trace, which has characteristic contours in the different chambers and great vessels, or by identification on fluoroscopy or echocardiography.
Pressure measurements are useful to identify the haemodynamic effects of disease. For example, raised pulmonary wedge pressures would be detected in an animal with severe MR and congestive heart failure; abnormally high right ventricular pressure might be detected in an animal with a large VSD or an outflow obstruction such as the pulmonary hypoplasia or valvular stenosis found in tetralogy of Fallot. However, the pressure changes are seldom specific for any one condition.
Oxygen tension measurements are useful in cases with shunts. With right to left shunts, there will be an abnormally low oxygen tension and high carbon dioxide level in the left side of the circulation at the level at which the shunt is occurring. With left to right shunts, there will be raised oxygen tension in the right side of the circulation. For example, an animal with significant flow through a VSD would have raised P02 in the RV. The extent of these changes is indicative of the severity of the shunt.