Passage of larger guiding catheters up the radial artery is limited by absolute vessel size and arterial spasm. In a recent multicentre registry containing over 1900 transradial procedures the incidence of radial spasm was 2.7 %, with multiple puncture attempts and use of larger introducer sheaths (7F) being independent predictors of radial spasm.18 Intra-arterial vasodilators reduce the incidence of radial spasm although the optimal “spasmolytic” cocktail remains to be identified and their use in some patients may result in hypotension and bradycardia. The use of hydrophilic sheaths and catheters can also further reduce spasm.19
Spasm can also be minimised by gradual graded gentle dilatation by tapered introducers. If resistance is encountered when upsizing from a 5F catheter to a 6F guide and forearm angiography has excluded an anatomical variation such as a radial loop or accessory artery, often balloon assisted tracking is sufficient to allow the new catheter to pass. In this technique a coronary guidewire is passed into the guide and into the aortic root ((alongside the 0.035” wire) and a 2.0 mm monorail balloon inflated two-thirds in and one third exiting the guide to provide a soft rounded shoulder tip.20 In a male patient with a 7F sheath experiencing resistance to 7F guide passage the same technique using a 2.5 mm balloon is often successful. Another technique to provide a more tapered tip to facilitate guide passage is a mother-in-child configuration, so the guide is lead by a smaller diameter section, e.g. use of a 4F Judkins Right 4 (JR4) or multipurpose (MPA) inside a 6F guide (requires either a longer 4F diagnostic >110 cm or shorter 90 cm guide), or similarly a 5F JR4 or MPA inside a 7F guide.
An elegant innovative solution is the use of sheathless guiding catheters. These are commercially available (Asahi Intecc Co Ltd, Aichi) in 6.5F, 7.5F and 8.5F sizes with inner diameters (I.D.) identical to 6F, 7F and 8F guides respectively. The outer diameters (O.D.), however, are less than a standard 5F sheath for 6.5F sheathless, <6F sheath for 7.5F sheathless and <7F sheath for the 8.5F sheathless and can hence be anatomically accommodated in the majority of radial arteries. The same principle is employed by “home-made” sheathless guides using commercially available tapered introducers with standard guide catheters. This has the advantage of free choice of shape and manufacturer of guide. Introducers include the Shuttle (Cook Medical, Bloomington, USA), a carotid device: 5F Shuttle introducer in 7F guide; 6F Shuttle introducer in 8F guide. The use of sheathless guides requires specific expertise as the highly hydrophilic coating may increase catheter instability. An additional drawback is that use of 150 cm devices, such as microcatheters in retrograde cases, may require guide catheters less than 100 cm, especially in taller patients. Sheathless guides are not available in shorter lengths. However, to overcome this, the tapered introducers from the Asahi commercial sheathless guides can be used inside conventional 90 cm guides for the same purpose and when guide exchange is required.