Shape & Size

 1. Determinants of guide catheter choice.

Guide engagement should be atraumatic and result in coaxial alignment. The ascending aorta size, the location of the coronary ostium and the orientation of the proximal vessel determine the choice of the catheter.

2. Coaxial alignment.

The configuration of bends at the distal end of the guide catheter determines how the tip will engage with the coronary artery ostium.

Ideally, the catheter tip should be parallel to the orientation that the proximal segment of the vessel originates from the aorta, and is said to be coaxially aligned.

Coaxial alignment allows safer transmission of the force necessary to advance devices and equipment into the coronary artery as it minimises contact against the walls of the artery. Also, the reduced friction lessens the risk of vessel trauma and dissection.

In some cases, the anatomy of the ostial segment may require additional manipulation of the guide catheter in the aorta to achieve coaxial alignment. This manipulation is often referred to as ‘deep seating the guide’. However, excessive intubation of the coronary ostium may also damage the vessel.

3. Pressure problems after catheter engagement.

Pressure wave ventricularisation or damping may occur as the tip of the catheter is engaged. Damping is where both systolic and diastolic pressures fall and often indicates a significant stenosis at the ostium or that the guide catheter diameter is too large. It is a sign that gentle catheter manipulation is required to avoid dissection, or that an alternative guide shape and size is needed.