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For the left coronary artery, catheters with a smaller curve will point upward and selectively engage to left anterior descending (LAD) and a larger curve will selectively engage and provide better support for the circumflex. The tip of Amplatz Left (AL) guides tend to point downward and are useful to selectively engage the circumflex in situations where there is a short or absent left main.

The shape of the guide catheter is an important component of the backup or support system that allows delivery of devices to the target lesion. Changing the guide catheter to improve support in the middle of a procedure can be problematic, and therefore careful consideration of guide support prior to intervention is critical. It is also important to appreciate that selection of a guide with optimal backup may obviate the need for stiffer wires or balloons, with a corresponding reduction in cost and procedure time. Although Judkins Left (JL) curves are commonly used for diagnostic intervention, these guide shapes provide less support than “backup” guides which provide contralateral aortic wall support such as the XB, EBU‐, or Q‐type curves. Because of the secondary curve on the JL, the tip may jump out of the coronary ostium when resistance is encountered. XB/EBU/Q/ Voda or similar curves provide comparatively more support with minimally increased risk of damage to the coronary ostia. AL curves are required in certain situations, but should only be used by experienced operators in view of the increased risk of iatrogenic dissection. Techniques to obtain support other than the passive support allowed by the guide catheter shape are discussed later in this chapter.

Shapes for commonly used guide catheters for the left coronary system are shown in Figure 5.1. The curve sizes of different shapes have been largely standardized and the comparable curve sizes used most commonly are shown in Table 5.3.

Figure 5.1 Shapes of a selection of guide catheters for the left coronary system.

Table 5.3 Comparability of curve sizes for different shapes of left sided guide catheters.

	AL (Amplatz) Curve	CLS or XB Curve	JL (Judkins Left) Curve	Q Curve	VL (Voda Left) Curve
Normal	AL 1 or 1.5	XB 4.0 or 3.5	JL 4	Q 4	VL 4
Dilated	AL 2 or 3.0	XB 4.0 or 4.5	JL 4.5	Q 4.5	VL 5
Narrow	AL 0.75	XB 3.0 or 3.5	JL 3.5	Q 3.5	VL 3