Learning Curve for New CTO Operators: Some Reassurances, Some Caveats

New CTO PCI operators face steep challenges, but also appear to accrue important technical skills over time that contribute to procedural success, according to a large national cohort study of the learning curve. While major adverse events appeared to be stable for most operators during this process, patient characteristics increased in complexity with experience, while bleeding rates also increased in a small, but persistent manner.

“I think if you look at the overall data, what stands out to me is that it is a safe procedure,” said lead study author Michael N. Young, MD (Dartmouth-Hitchcock Medical Center, Lebanon, NH), in an interview with TCTMD. But Young added that the trend toward higher rates of bleeding cannot be ignored.

“It goes back to the take-home message, which is that we should be cognizant that these are high-risk procedures and that we need to be sure that we don't compromise patient safety in attempts, well intentioned though they may be, to open up an artery and relieve angina,” Young noted.

In an accompanying editorial, David R. Holmes Jr, MD, and Gregory W. Barsness, MD (both Mayo Clinic, Rochester MN), say the information gleaned from new operators as they learn their way through CTO procedures “is essential for developing strategies to provide care for this large group of patients.”

Change in Patients With Accruing Experience

For the study, published online August 16, 2019, ahead of print in Circulation: Cardiovascular Interventions, Young and colleagues looked at 70,916 cases performed by 7,251 new operators from July 2009 through 2015. “New” CTO operators were those with a history of fewer than 10 cases per year from the time of their first CTO intervention. However, included in the cohort were 148 so-called “rapid adopters,” who performed more than 20 CTO PCI cases in their first year.

Overall, CTO procedural success was 61.4% and this improved with increasing case experience. Compared with the first 10 case experiences, total CTO PCI cases beyond 50 were associated with more cardiovascular comorbidities, including hypertension, dyslipidemia, cerebrovascular disease, previous MI, and previous interventions. Additionally, lesion lengths increased from an average of 20 mm in cases 1 to 10 to 32 mm when total case load exceeded 50, and lesion crossing was more frequent.

“The complexion of the patients changed and the data reflect that,” Young observed. “Perhaps operators, as they were accruing experience, are taking on more complex lesions, and or more complex patients and . . . become more fluent with procedures and feel like they are surmounting that learning curve.”

The number of elective versus urgent CTO cases also changed as new operators gained experience. Whereas only about 55% of most operator’s first 10 cases were elective, that number increased to 70.5% once they had performed 50 cases and more. Similarly, urgent cases decreased from 41.7% to 29.4%.

“What I'm gathering from the data is that early on in the experience, maybe these new operators are doing more ad hoc procedures, and as they become more experienced and as they do more cases, they may be less inclined to take on higher risk or challenging lesions ad hoc and instead stage them so that they can optimize the chance for success,” Young said.

Other procedural factors affected by increasing case volume were fluoroscopy time and contrast volume, both of which showed linear increases.

Composite MACE occurred at a rate of 4.2% among all new operators, and in-hospital mortality was 0.6%. Looking at the rates of those outcomes by operator case volume, MACE rates averaged 4.5% in the first 10 cases, 3.8% in cases 11 to 50, and 4.3% beyond 50 cases (P < 0.0001 for all comparisons). Similarly, in-hospital mortality occurred at a rate of 0.7% in the first 10 cases, 0.5% in cases 11 to 50, and 0.7% beyond 50 cases (P = 0.02 for all comparisons).

When rapid adopters were analyzed alongside the group as a whole, their overall outcomes were similar.  

Learning Curve Steep But Important

As CTO PCI volume surpassed case number 12, the risk for bleeding increased for every five additional cases (OR 1.010; P <0.0001). Major bleeding, perforation, and cardiac tamponade also occurred more often with greater case experience.

“Although the authors suggest that major bleeding, perforation, and tamponade were uncommon, the numbers suggest otherwise, with major procedure-related complications as high or higher among the more complex cases performed by more experienced operators, including bleeding in 7.6%, perforation in 2.3%, and tamponade in 1.2% of cases in the highest volume operator stratum,” Holmes and Barsness observe.

But Young and colleagues, by way of explanation, point to the complex nature of the patient population, and note that there was no corresponding increase in mortality or MACE.

Still, Holmes and Barsness say the study provides more evidence of “a steep learning curve among new CTO operators” that is “reflected in the distinct skill set required for hybrid antegrade and retrograde approaches, dual access-site management, and complication recognition and management,” they write. “There is even a novel vocabulary and unique toolset that requires initial mastery and ongoing review. Most important, perhaps, is knowing where to start and when to stop.”

Holmes and Barsness add that aspects of learning among CTO operators, such as developing “strategic awareness to plan for success” and being able to modify their approach to suit any situation and morphologic subtype, are important not only for optimizing individual patient outcomes, but also for advancing the entire field itself.