Abstract & Commentary
Door-to-Balloon Time Isn’t Everything: Transradial Access in Primary PCI May be Worth the Delay
By Jeffrey Zimmet, MD, PhD
Associate Professor of Medicine, University of California, San Francisco, Director, Cardiac Catheterization Laboratory, San Francisco VA Medical Center
Source: Wimmer NJ, et al. Delay in reperfusion with transradial percutaneous coronary intervention for ST-elevation myocardial infarction: Might some delays be acceptable? Am Heart J 2014; April 7. [Epub ahead of print.]
The mortality benefit to percutaneous coronary intervention (PCI) is unquestioned when it comes to ST-elevation myocardial infarction (STEMI). Based on compelling observational data linking time to reperfusion with mortality, incentives have aligned strongly toward decreasing reperfusion times, with guidelines supporting door-to-balloon (D2B) times < 90 minutes in the United States and < 60 minutes in Europe. D2B time has become a central performance measure, with reimbursement and public reporting incentives aligning to drive down times. Despite D2B times decreasing steadily over recent years, however, concomitant gains in mortality have not been observed.
Transradial arterial access for PCI has likewise been steadily gaining ground worldwide, but considerable variability exists among countries, hospitals, and individual operators. In the United States in particular, penetration of transradial technique has been slow on the uptake, particularly in the realm of STEMI. This is despite growing evidence for a benefit to transradial access. In particular, the RIVAL and RIFLE-STEACS trials each reported a mortality benefit to transradial PCI, both for in-hospital and 30-day outcomes. Even for the experienced operators in these trials, however, there was at least a trend toward longer procedure times and crossover rates from radial to femoral of more than 5%. The time delay inherent to radial vs femoral access, especially in the hands of operators with lesser radial experience, establishes a significant barrier to the adoption of radial access for STEMI intervention.
In this study, Wimmer and colleagues present a model comparing radial with femoral strategies in primary PCI, where the primary outcome was 30-day mortality. They used published mortality data from the RIVAL and RIFLE-STEACS trials, along with published estimates of per-minute increases in mortality with delays in D2B time. They used their model to quantify the delay in D2B time with radial vs femoral access (the transradial delay) that would counterbalance the reported mortality benefit of the transradial approach. Notably, because these two studies were reported using the intention-to-treat principle, the pooled crossover rate (from radial to femoral) of 7.8% is inherent in the mortality estimates. In the base case, the full mortality benefit reported in the two published studies was assumed, along with the per-minute mortality penalty reported from the NCDR Cath PCI database. A separate analysis was performed using the higher mortality estimates from an older Medicare population.
The results are striking. In the base case, the authors estimate that a transradial delay of 83 minutes would be required to offset the full reported mortality benefit of transradial PCI from the two randomized trials. Because the magnitude of the mortality benefit seen in RIVAL and RIFLE has been questioned, the analysis was repeated using estimates of mortality benefit that were half and one-quarter of those reported. The break-even times for transradial delay for these cases were still significant, at 41.8 and 20.9 minutes. When the analysis was performed based on the higher per-minute mortality penalty reported in the Medicare population, a transradial delay of 61.5 minutes was found. Even combinations of the higher per-minute penalty with 50% or 75% lower transradial mortality benefit resulted in a significant time buffer, with 30.8 and 14.8 minutes of transradial delay associated with equivalent mortality. The authors concluded that substantial delays in transradial access are required to substantially reduce the mortality benefit observed with transradial PCI for STEMI in randomized trials. These results have significant implications for operators reluctant to use the transradial approach in primary PCI and D2B time standards.
This is a very thought-provoking analysis, but we should approach its interpretation with caution. The magnitude of the transradial mortality benefit estimated by the two available randomized, controlled trials (RCTs), as well as the ability to replicate these results in general practice, has been widely questioned. Indeed, the nearly 4% absolute mortality reduction reported in RIFLE is greater than what one would expect from the best-recognized advantage of transradial access, namely the reduction in access site bleeding. If we accept that a mortality advantage to transradial access is both plausible and true, however, we can start to look at the major barriers to adoption of transradial primary PCI. These barriers primarily include the higher crossover rate and likely delays in achieved D2B times with transradial access. In what we would consider the best case, assuming the full magnitude of mortality benefit estimated by the RCTs, the time delay required to offset the benefit of transradial access was calculated at an astounding 83 minutes. The inclusion of a series of sensitivity analyses with varying mortality benefit and crossover rates is especially compelling, with even the worst case resulting in a significant time buffer supporting radial access.
The intention here is not to argue for a radial approach for all settings and all operators. Guidelines from the Society for Cardiovascular Angiography and Intervention (SCAI) recommend that interventionalists first perform a minimum of 100 elective PCIs from the transradial approach and achieve a femoral crossover rate of < 4% before considering a foray into transradial primary PCI. Substantial delays must still be avoided, and teams must be prepared to cross over to femoral access should the need arise. Experienced operators who are considering a switch may be reassured by the concept that the inevitable prolonged procedure times may be counterbalanced by the mortality benefits of transradial PCI.
Realistically, however, the data from this paper will be small consolation if D2B times suffer, given that so much is currently tied to this data point. Given that incremental decreases in D2B times have not resulted in decreased mortality, this study provides an opportunity to reassess the D2B metric. Whether it makes sense to reduce the emphasis on reperfusion times to allow for consideration of other improvements in care, such as decreasing false STEMI activations and transradial access, remains to be seen.