In a recent study published online in the Journal of the American College of Cardiology: Cardiovascular Interventions, a team from Mayo Clinic reports that the learning curve for transcatheter aortic valve implantation (TAVI) surgery is 30 procedures, with evidence of a plateau in operator proficiency after reaching that threshold. The study reviewed procedure times, radiation exposure, and contrast volumes for the first 44 patients treated at Mayo Clinic as part of the PARTNER (Placement of Aortic Transcatheter Valve) trial.
Groups and variables analyzed
Using data from both the PARTNER A (high-risk) and PARTNER B (inoperable) groups, study authors Allli et. al. grouped the 44 patients into chronological tertiles to measure differences in operator proficiency over time. Across the three groups, contrast volume dropped from 180 to 160 to 130 mL, while fluoroscopy time dropped from 26.1 to 17.2 to 14.3 minutes. Among other variables tracked, average time between valvuloplasty and deployment of the new valve decreased from 12 minutes in the first tertile to seven minutes in the third. Radiation dose also decreased by nearly 69% from the first tertile to the third.
The evidence of decreased radiation and fluoroscopy exposure from the early experiences at Mayo Clinic suggest that the TAVI procedure is much safer as operator experience increases, however vascular complication rates, length of hospital stay and mortality did not significantly change across time. The authors note that their trial was not designed to measure improvements in morbidity or mortality, and that further studies are required to confirm or alter the suggested 30-procedure learning curve based upon clinical outcomes.
Training is key to success
Because the TAVI procedure is incredibly complex and requires collaboration among a large team including interventionalists and cardiac surgeons, procedural training must continue to evolve as adoption increases following the FDA approval of the SAPIEN valve. The study authors suggest that rigorous training and proctorship will be necessary as more physicians adopt this procedure, and further stipulate that modes of TAVI training will continue to evolve to include simulators, industry-sponsored training, and dedicated interventional/ structural heart training programs.
The Mayo Clinic study is a retrospective, single-center analysis with a small sample size, and as such there may be some limitations to the utility of the resulting data. The authors also note that the study does not account for previous experience or comfort level of physicians performing TAVI or variation in local practices which may vary heavily by institution.
Concerns regarding volume dilution across programs
In an accompanying editorial in the same journal, Dr. Peter Block looks closer at the implications of the Mayo Clinic data. He calculates that, using the commonly assumed estimate of 25,000-30,000 procedures per year in the United States, there may be approximately 100 ‘high-volume’ sites each performing approximately 100 cases per year, and about 200 sites performing fewer. Because volumes will not be equally distributed among these sites, it is almost certain that there will be sites performing less than one case per week.
Looking to the future of TAVI, Block questions if such low volumes will be acceptable and safe given the new Mayo data. For some physicians, it means they may need more than a year to become proficient. Moreover, no studies have examined the threshold necessary for maintenance of proficiency which could be equally difficult for some to meet.
The FDA, Society of Thoracic Surgeons (STS) and American College of Cardiology (ACC) all support setting a limit to the number of U.S. centers which can perform TAVI based on minimum volume requirements and operator credentials. According to Block, this may create significant tension between the centers which meet these criteria and those which cannot.
Now that the FDA has approved the SAPIEN valve, centers must look beyond ensuring they are able to perform TAVI with appropriate facilities and staffing, but must concern themselves with being able to do it well, an entirely separate challenge, as pointed out by the Mayo Clinic study.
For information for members
For additional insight into this game-changing emerging therapy, including latest volume forecasts, expected reimbursement figures, and key program elements for centers considering offering transcatheter-based therapies, please see the Cardiovascular Roundtable’s recently-updated Transcatheter Valve Technology Briefing.