Response to Letter Regarding Article, “The Learning Curve for Transradial Percutaneous Coronary Intervention among Operators in the United States: A Study from the National Cardiovascular Data Registry”
Authors: Connie N. Hess, Eric D. Peterson, Megan L. Neely, David Dai, William B. Hillegass, Mitchell W. Krucoff, Michael A. Kutcher, John C. Messenger, Samir Pancholy, Robert N. Piana, Sunil V. Rao
Journal: Circulation (2015)

We thank Drs Azzalini and Ly for their interest in our work and for their comments. 1Access site crossover is certainly an important indicator of transradial percutaneous coronary intervention (TRI; PCI) success and operator proficiency.As acknowledged in our limitations, we could not account for this confounder, because it is not captured in the CathPCI Registry.The authors state in their letter that we "excluded cases where PCI was unlikely to be completed transradially and/or the postprocedural angiographic result was judged a priori to be potentially suboptimal," resulting in a "low" threshold for overcoming the TRI learning curve.To support their hypothesis, they cite the 89.7% of TRIs that were ad hoc.Several points merit discussion.First, we agree that operators may stage complex PCIs through the femoral approach, especially early in their radial learning curve.We intentionally excluded femoral cases, as they were not relevant to assessments of radial PCI proficiency.Second, although we demonstrate that technical proficiency continues to improve with greater operator experience, we were most interested in characterizing the early learning curve, since it is during this initial phase of learning to perform TRI that operators encounter the most difficulty and may give up the technique.Consequently, our 30-to 50-case range is meant to reflect the average threshold at which new radial operators appear to overcome the early learning curve.Third, PCIs may be staged for multiple reasons, including lesion complexity, renal insufficiency, and reimbursement, but the use of ad hoc PCI can also be influenced by provider practice patterns.A recent CathPCI Registry analysis reported that 85.7% of all PCIs in the United States are ad hoc, 2 suggesting that the slightly higher use (89.7%) in our analysis may reflect provider culture more than the selection of low complexity lesions for TRI.Furthermore, the complexity of TRIs (eg, high lesion complexity, bypass graft interventions) increased with operator experience.Therefore, although there is selection bias regarding which patients are chosen for TRI, these more complicated TRIs were included in our analysis and likely explain the continued learning curve after the initial threshold is surpassed.Fourth, we would argue that there should be provider selection bias in selecting less complex patients (eg, younger male patients undergoing elective PCI) for the radial approach early on to increase likelihood of procedure success, build operator confidence, and ensure continued use of radial, ultimately leading to greater operator proficiency, comfort, and willingness to attempt complex TRIs.Finally, although we quantify the overall threshold for overcoming the early learning curve for operators in our analysis, individual thresholds may vary, depending not only on operator proficiency (the focus of our analysis), but on additional factors like catheterization laboratory support and availability of TRI mentors.Regarding use of radial for STEMI, these patients comprised a small minority of our study population.We attempted subgroup analyses in this high-risk population, but were unsuccessful, due to small numbers and statistical limitations.Perhaps such analyses could be completed using data from countries where the radial approach is more prevalent.