The traditional definition of PCI success in coronary intervention varied according to whether a stent was placed. Since the vast majority of PCIs involve the placement of a stent, the angioplasty definition is less relevant. In the stent era, procedure success is generally defined as at least a 50 % reduction in diameter stenosis and ≤20 % residual stenosis [1]. This definition pre-supposes that the lesion has been crossed with a guidewire, guide support has been sufficient to deliver devices to dilate the lesion, and that the stent has been successfully deployed across it. For a transradial PCI, all of this requires that radial access was successfully achieved, the arm and chest arterial vasculature was negotiated, diagnostic catheters were advanced into the ascending aorta and cannulated the coronary arteries to provide adequate opacification during angiography, and the guide catheter successfully intubated the coronary artery ostium.

Many observational studies have compared radial approach with femoral approach, but selection bias and confounding hamper the validity of these data. In order to determine which of the two approaches are superior, randomization is key. The largest randomized trial comparing radial and femoral is the RIVAL trial, which randomized over 7000 patients with acute coronary syndrome (with or without ST-segment elevation) undergoing angiography or intervention to either radial access or femoral access [2]. PCI success, a secondary endpoint, was defined as partial or full, with full success defined as successful dilation of all attempted lesions with <50 % residual stenosis and TIMI 3 flow. There was no significant difference between the two approaches (radial 95.4 % vs. femoral 95.2 %, p = 0.83). While angiographic details of the PCI procedures are not available, 65.9–66.8 % of patients underwent PCI, which is consistent with the proportions seen in national registries [3]. This suggests that PCI was not likely deferred due to the access site chosen.

An important dimension to the concept of PCI success is that the definition does not take into account whether the procedure was ultimately completed using the initial arterial access site. Therefore, the issue of procedure success versus PCI success must take into account access site crossover from radial to another arterial site (most commonly the femoral artery). In this context, proficiency with transradial procedures is of paramount importance. The RIVAL Trial investigators were required to have some experience with transradial procedures in order to participate. The requirement was for at least 50 transradial procedures within the prior year, although many operators had significant proficiency, performing > 142 procedures annually [2]. Access site crossover occurred in 7.6 % of patients assigned to radial access and 2.0 % of patients assigned to femoral access [hazard ratio 3.82 (2.93–4.97); p < 0.0001]. At centers with the highest volumes, access site crossover was much lower (4.4 %), but still higher in the radial arm. These data demonstrate that transradial procedure success (as opposed to PCI success) exceeds 90 % when performed by experienced operators.

Ad hoc PCI is a PCI procedure performed subsequent to a diagnostic catheterization during the same cath lab visit. The incidence of ad hoc PCI in the large US-based National Cardiovascular Data Registry CathPCI registry is > 50 %, but this likely varies across different countries. The performance of transradial ad hoc PCI assumes that the diagnostic portion of the procedure was performed via radial access. Transradial ad hoc PCI is feasible for several reasons. First, the diagnostic catheterization will provide detail on arm and subclavian arterial anatomy, which may allow for easier seating of the guide catheter. Studies examining procedure times and radiation exposure have shown that increases associated with radial approach are generally limited to the diagnostic cath with no significant difference for PCI [1]. Second, as stated above, data from the RIVAL trial indicate no difference in the proportion of patients undergoing PCI between radial and femoral access, thus indicating that PCI was not deferred based on the initial access site. Finally, the learning curve for becoming proficient at transradial procedures is not steep – approximately 30–50 cases [4] – and is easily overcome by performing ad hoc PCI.

The term “radial first” means that every procedure is approached with intent to start and end the case with radial access. While this may seem straightforward for Type A lesions, the issue is whether this can be applied to more complex lesions like heavily calcified stenoses, bifurcation lesions, unprotected left main stenosis, or chronic total occlusions. Technical aspects of transradial PCI of each of these lesion subsets are described in detail in the following chapters. In summary, the radial approach offers few limitations since almost all lesions can be successfully treated through 6-French systems, which are readily accommodated by the radial artery in most patients. Larger bore guide catheters can be used with or without a sheath, if appropriate, to minimize radial artery trauma. Dedicated transradial 7.5-French sheathless guide catheters are commercially available [5]. These guides have outer diameters of 2.49 mm (compared with an outer diameter of 2.52 mm for 6-French sheaths), and their inner luminal diameter easily accommodates two stents simultaneously. They are introduced into the ascending aorta over a 0.035″ standard guidewire. A long tapered dilator facilitates entry through the skin. Procedure success for complex PCI is excellent with these guides, but radial artery occlusion rates may not be lower compared with the use of arterial sheaths [5]. From and colleagues have described a sheathless approach using standard 7-French and 8-French guide catheters [6]. A long (125 cm) 5 or 6-French diagnostic angiographic catheter is placed through a standard length 7 or 8-French guide to facilitate entry through the skin into the radial artery.