We found a 30-day mortality of nearly 2% among Medicare beneficiaries undergoing carotid stenting. Mortality rates for elderly patients in contemporary clinical trials and registries are closer to 1%.13,14,19
Although the higher mortality rates we identified are likely being driven to a large extent by an older and less selected population of patients, we identified an additional factor that may be contributing: limited operator experience with carotid stenting as the procedure has disseminated into routine clinical practice. Indeed, we found that fewer than 1 in 8 operators had annual operator volumes of 12 procedures or more during the study period. Furthermore, we noted that patients treated by very-low-volume operators and those treated early during a new operator’s experience had significantly higher 30-day risk-adjusted mortality.
Ensuring that physicians are adequately experienced to perform innovative and technically-complex procedures, like carotid stenting, is not a new challenge.20
It has been seen with several health technologies in the past, most notably following the introduction of laparascopic procedures in the late 1980s.21,22
Yet, ensuring expertise with carotid stenting also raises concerns that are particularly unique to this procedure. For example, carotid stenting is performed by specialists from diverse fields including cardiology, radiology and surgery. These physicians have widely varying clinical backgrounds and technical skills that make it hard to standardize educational programs. An expanded pool of physicians capable of performing it also may make carotid stenting more difficult to concentrate expertise among a few operators, especially given strong interest in the procedure by all 3 specialties. Of course, making policy decisions about restricting use of carotid stenting to highly-experienced operators is complicated and involves balancing safety concerns with the potential long-term harm of limiting access to an innovative procedure early on during its dissemination.
To a certain extent, the challenge of ensuring adequate expertise among operators has been widely recognized by professional organizations and regulators. For example, professional organizations representing the major specialties involved in carotid stenting have listed specific criteria to guide facilities in credentialing individual operators.6-8
These include minimum volume requirements suggested for operators, although specific thresholds vary across groups. The FDA has also encouraged educational initiatives, and in particular, the development of dedicated virtual simulation technologies.23,24
Recent work indicates these initiatives may minimize differences in outcomes between operators with different levels of experience.25
Yet the application of volume requirements in routine clinical practice, the quality of various educational initiatives, and the overall impact of both approaches on outcomes remain largely unknown.
In addition to differences in 30-day risk-adjusted mortality, we also found that failure to use embolic protection devices was more common among patients treated by low volume operators and earlier on during a new operator’s experiences. Although we did not have sufficient clinical or anatomic information to identify why an embolic protection device may not have been used in a particular patient, a failure to receive these devices is a potentially important process measure that needs to better understood. It could be that, as operators are gaining more skill with these devices, they are simultaneously and independently improving other procedural techniques that lead to better outcomes. However, it could also be that operators with more experience are better at selecting patients based on their suitability for embolic protection devices or even deferring carotid stenting when they cannot be used.
Our study should be interpreted in the context of the following limitations. We examined carotid stenting in elderly Medicare beneficiaries. While this age group represents approximately three-quarters of the patients undergoing the procedure in the United States, our results may not be generalizable to younger patients. This also means that our determination of operator experience underestimates “overall” experience for any individual operator, especially if their case-mix of Medicare beneficiaries differs substantially from other operators. As such, inferring a precise number of procedures that will be associated with better outcomes is not possible from this study. However, determining such a number may be less relevant than understanding the overall association between greater operator experience and outcomes with carotid stenting.
A second issue related to Medicare claims data is the potential for residual confounding, particularly given the minimal changes we found between unadjusted and adjusted odds ratios from our models. Because we were unable to account for several clinical and anatomic factors, it may be that patients who were treated by lower-volume operators or early during their operator’s experience are sicker or more complex in unmeasured ways than high-volume operators. While this limits the ability to draw causal inferences from our analysis, the association we identified does point toward the need for further studies to understand potential reasons why outcomes were consistently worse among less experienced operators. Related concerns with using Medicare data include their limited ability to assess additional outcomes of importance (e.g., stroke) or the procedure’s overall appropriateness relative to alternative treatments, such as carotid endarterectomy or even medical therapy.
Third, our analyses examining early versus late experiences with carotid stenting in new operators is likely to have included some operators who performed carotid stenting prior to the date of the initial national coverage decision by the CMS. Carotid stenting has been described dating back to the mid 1990s, although in the past its use was more limited. Yet we suspect that any misclassification of operators, if present, biased our findings toward the null. Finally, we examined the association between these 2 measures of operator experience and outcomes across a large number of physicians. Although our findings represent an “average” effect, studies of the “volume-outcome” relationship and performance improvement in other areas suggest that individual operators develop and maintain their skills at varying rates,26
and it is even possible that this relationship could vary based on their prior experiences with other endovascular procedures.
In conclusion, many physicians have begun performing carotid stenting in Medicare beneficiaries during recent years, although most operators appear to have developed limited experience with the procedure over time. This finding is important since risk-adjusted outcomes following the procedure are worse among very-low volume operators and early during an operator’s experience.