The introduction of new technologies often follows what has been termed the “hype cycle” that displays the key phases of how that technology is received by society . During this cycle, there is differential uptake of the new technology that has been termed the “technology adoption lifecycle” ( Fig. 1 ) that starts with innovators and early adopters, and then enters a “chasm” phase of limited or no adoption, followed by steep uptake by the early majority . While these concepts have primarily been applied to the information technology field, they may also relate to the introduction of new medical devices or procedures. For medical devices, the slope of these curves can be affected by a variety of factors including the robustness of clinical data supporting their use, the size and scope of the marketing campaign, and clinicians’ experience. On the other hand, for procedures, there is the added complexity of clinicians gaining the skills to perform the procedure competently – the so-called “learning curve.” The learning curve, which is the rate at which a person is gaining experience or learning new skills, has taken on increasing significance in the cardiovascular field over the past few years because of the introduction of new procedures such as transcatheter aortic valve replacement. In addition, renewed interest in procedures described decades ago, like transradial PCI, are also generating interest in understanding how to achieve procedural proficiency. In this issue of Cardiovascular Revascularization Medicine, Barbash and colleagues describe the learning curve of two operators for transradial PCI at a single high volume center and find that that curve is actually quite flat . That is, they were unable to define a period of time during the adoption of radial approach where procedural metrics like fluoroscopy time or contrast volume. These data provide important insights for the interventional cardiologist and challenge the long-held belief that the radial learning curve is a major impediment to its adoption.

The technology hype cycle and adoption life cycle plotted together. Displays the reception of new technology by society and/or users and the curve of technology adoption over time (From http://setandbma.wordpress.com/2012/05/28/technology-adoption-shift/ Accessed May 4, 2014).

Radial access for PCI falls under the rubric of “bleeding avoidance strategies,” which also include appropriate dosing of antithrombotics and use of targeted anticoagulants . Unlike pharmacological strategies, which depend largely on learning their dosing and administration, radial approach relies heavily on the catheterization laboratory nurses and technologists learning proper patient set up and recovery, and the cardiologist developing expertise with radial arterial access, traversing the arm and chest vasculature, engaging the coronary arteries, arterial hemostasis, and addressing complications. Studies indicate that the causes of transradial procedural failure can be categorized into failure of access, failure to successfully reach the ascending aorta with the catheter, and lack of guide catheter support for PCI . Proficiency with each of these aspects is essential to achieving the benefits of transradial angiography and intervention.

Until recently, the use of radial approach both worldwide and in the United States has largely been sporadic. While it seems logical to use the transradial approach for those at highest risk for access site bleeding, studies indicate exactly the opposite – radial access is used least in patients that have the most to gain . This “risk-treatment” paradox likely exists because the patients at highest risk for bleeding and vascular complications (elderly, females, short stature, low-body weight) are also at high risk for transradial procedural failure and operators may feel uncomfortable tackling cases where the probability of femoral bailout is high. This selective use of radial approach in low-risk cases not only leads to suboptimal care for high-risk patients, but also significantly limits an operator’s ability to become proficient.

Expertise with radial access is necessary in order to develop a “radial first” approach to reduce the risk-treatment paradox, realize the benefits of transradial PCI for patients, and make the procedure safer for operators. Large randomized trials and observational studies clearly point to the superiority of radial approach over femoral approach among centers and operators with the highest radial volumes. In the RIVAL Trial, which randomized over 7000 patients with acute coronary syndrome undergoing angiography or intervention to either radial or femoral access, the primary endpoint of 30-day death, myocardial infarction, stroke, or major bleeding was significantly lower among patients assigned to radial approach at centers in the highest tertile of radial volume. This was also true for the composite endpoint of death, MI, or stroke, and these centers had the lowest rates of access site crossover . Similarly, Gutierrez and colleagues examined the association between radial access and outcomes in the US Veterans Affairs Health System and found that radial approach was associated with a reduced post-procedure transfusion and mortality, but only at the highest radial volume centers . With respect to procedural metrics that reflect safety such as radiation exposure, a substudy from the RIVAL trial demonstrated longer fluoroscopy times and marginally higher air kerma with radial procedures. When stratified by center and operator radial volume however, the differences were significant only in the low volume centers and among low volume operators . Taken together, these data provide strong evidence that the volume of radial procedures has a direct relationship with the efficacy and safety of transradial PCI.

The process of becoming a high-volume radial operator involves the learning curve, which has been cited as a disadvantage of transradial procedures. The study by Barbash demonstrates that this is not as much of a barrier as previously thought, and a strength of their study is that access site crossovers to femoral access were also reported and demonstrated to be very low. Three important limitations of the study are that the details of the operators’ radial training are not reported, the center and individual operator PCI volumes are likely much higher than that of other institutions, and it is unclear the extent to which the radial experts in the practice provided proctoring during the learning phase. In addition, specific training of the catheterization laboratory nurses and technologists, which is essential to the success of a radial program, was not reported. While this may limit the generalization of the results, the study is consistent with two recent studies that corroborate a relatively flat learning curve for transradial PCI. Ball and colleagues examined data from a single high volume PCI center in Canada and found that procedural metrics such as procedure failure, number of guide catheters used, contrast volume, and fluoroscopy time approached a plateau after 50 cases . Similarly, in the only multicenter study to delineate the transradial learning curve, Hess used data from 54,561 radial PCI procedures performed at 704 sites by 942 operators and found that the slope of improvement in procedural metrics flattened beyond 30–50 cases . Beyond this threshold, the metrics continued to improve, and data suggest continued improvement in proficiency even among experienced operators . This shallow curve indicates that even lower volume operators may be able to overcome the learning curve by routinely using radial access in consecutive patients. In addition, few studies have assessed the contribution of experience with diagnostic angiography (without PCI), which may also serve to facilitate the learning curve. Whether operators have a shorter learning curve at institutions with prior radial experience is unknown. Introducing a new procedure or modality is usually associated with inertia and resistance. The learning curve of an operator championing radial approach at a “radial-naïve” institution may be quite different compared to that of an operator starting at an institution with well-established transradial policies, and surrounded by experienced radialists and technologists that can assist in case of difficulties and prevent access site crossovers and complications.

The use of radial access is likely entering the early majority phase of the technology adoption curve. While there are many forces contributing to this increased use, studies challenging long-held beliefs about the barriers to transradial procedures are likely playing a large role. Continued educational efforts by professional societies and proctoring are crucial in this context. The study by Barbash addresses one of the last obstacles to the adoption of radial access by demonstrating that the learning curve is surmountable. By using a “radial first” approach, interventional cardiologists can achieve the best outcomes and stay ahead of the curve.