Association of Annual Operator Volume With the Outcomes of Chronic Total Occlusion Percutaneous Coronary Intervention

Abstract

Objectives. There are limited data on the association of operator volume with the outcomes of chronic total occlusion (CTO) percutaneous coronary intervention (PCI). Methods. We analyzed the association between operator volume and procedural outcomes of 7035 CTO-PCIs performed between 2012 and February 2021 at 30 centers. Results. The study population was divided into 3 groups based on annual operator CTO-PCI volume: low-volume operators (LVO: <30 cases/year; 39.7% of the cases); medium-volume operators (MVO: 30-60 cases/year; 25.7% of the cases); and high-volume operators (HVO: >60 cases/year; 34.6% of the cases). Mean patient age was 64.4 ± 10 years and 82% were men. Cases performed by HVOs were more complex, with higher J-CTO score compared with cases performed by MVOs and LVOs (2.72 ± 1.27 vs 2.39 ± 1.19 vs 2.12 ± 1.27, respectively; P<.001). Moderate/severe proximal vessel tortuosity (35% vs 23% vs 20%; P<.001) and proximal cap ambiguity (44% vs 34% vs 32%; P<.001) was also more common in the HVO group. Cases performed by HVOs had higher technical success rates (87.9% vs 86.9% vs 82.6%; P<.001), but also higher rates of periprocedural major cardiac adverse events compared with MVOs and LVOs (3.08% vs 2.71% vs 1.50%; P<.01). On multivariable analyses, HVOs and MVOs were associated with higher technical success. Conclusions. In a contemporary, multicenter registry, 40% of CTO-PCI cases are performed by LVOs performing <30 cases per year. Cases performed by HVOs were associated with higher technical and procedural success, but also higher periprocedural major complication rates, potentially due to higher lesion complexity.

Keywords: chronic total occlusion, clinical outcomes, operator volume, percutaneous coronary intervention

Chronic total occlusion (CTO) percutaneous coronary intervention (PCI) can currently be performed with high success and low complication rates at experienced centers,^1-4 but outcomes are less favorable at less-experienced centers.^5-8 The association between individual operator CTO-PCI volume and outcomes has received limited study.^5,8-11 Studies examining other types of complex PCI, such as left main (LM)-PCI, found operator experience to be independently associated with cardiac death.¹² Compared with other types of PCI, there is a significantly longer learning curve to become experienced in CTO-PCI, including different crossing strategies, the hybrid approach, use of intravascular imaging, microcatheters, and other equipment. Moreover, CTO-PCI carries increased risk of complications and is often learned through proctoring.¹¹ The EuroCTO Club requires >300 cases and ≥50 cases per year for operators to be included in its registry, but did not provide data to support the selection of these thresholds. Understanding the association between operator volume on the outcomes of CTO-PCI has important implications for credentialing and establishing centers of excellence.

Methods

We analyzed the baseline clinical and angiographic characteristics and procedural outcomes of 7035 CTO-PCIs performed between 2012 and April 2021 at 30 centers. The study’s graphical abstract is presented in Figure 1. Data collection was recorded in a dedicated online database (PROGRESS CTO: Prospective Global Registry for the Study of Chronic Total Occlusion Intervention; Clinicaltrials.gov identifier NCT02061436). Study data were collected and managed using REDCap (Research Electronic Data Capture) electronic data capture tools hosted at Minneapolis Heart Institute Foundation.^13,14 The study was approved by the institutional review board of each site.

Study definitions. Coronary CTOs were defined as coronary lesions with Thrombolysis in Myocardial Infarction (TIMI) grade 0 flow of at least 3-month duration. Estimation of the duration of occlusion was clinical, based on the first onset of angina, prior history of myocardial infarction (MI) in the target-vessel territory, or comparison with a prior angiogram. Calcification was assessed by angiography as mild (spots), moderate (involving ≤50% of the reference lesion diameter), or severe (involving >50% of the reference lesion diameter). Moderate proximal vessel tortuosity was defined as the presence of at least 2 bends >70° or 1 bend >90° and severe tortuosity as 2 bends >90° or 1 bend >120° in the CTO vessel. A retrograde procedure was defined as an attempt to cross the lesion through a collateral vessel or bypass graft supplying the target vessel distal to the lesion; otherwise, the intervention was classified as an antegrade-only procedure. Antegrade dissection/re-entry was defined as antegrade PCI during which a guidewire was intentionally introduced into the extraplaque space proximal to the lesion, or re-entry into the distal true lumen was attempted after intentional or inadvertent extraplaque guidewire crossing. Technical success was defined as successful CTO revascularization with achievement of <30% residual diameter stenosis within the treated segment and restoration of TIMI grade 3 antegrade flow. Procedural success was defined as achievement of technical success without any in-hospital major adverse cardiac event (MACE), which was defined as any of the following events prior to hospital discharge: death, MI, recurrent symptoms requiring urgent repeat target-vessel revascularization (TVR) with PCI or coronary artery bypass graft (CABG) surgery, tamponade requiring either pericardiocentesis or surgery, and stroke. Myocardial infarction was defined using the Third Universal Definition of Myocardial Infarction (type 4a MI).¹⁵ The Japanese-CTO (J-CTO) score was calculated as described by Morino et al,¹⁶ the PROGRESS-CTO score as described by Christopoulos et al,¹⁷ and the PROGRESS Complications score as described by Danek et al.¹⁸Low-volume operators (LVOs) were defined as operators performing <30 cases/year, medium volume operator (MVOs) were defined as operators performing 30-60 cases/year, and high-volume operators (HVOs) were defined as operators performing >60 cases/year.

Statistical analysis. Categorical variables are expressed as percentages and compared using Pearson’s Chi-square test. Continuous variables are presented as mean ± standard deviation or median (interquartile range [IQR]) unless otherwise specified and were compared using the 1-way analysis of variance (ANOVA) for normally distributed variables and the Kruskal-Wallis test for non-parametric variables, as appropriate. The effect of annual operator volume on technical success and periprocedural MACE was examined using univariable logistic regression; thereafter, multivariable adjustment was performed by entering variables exhibiting significant univariable association (P<.10) in the models. The cutoff of the optimal annual operator volume was calculated with receiver operating characteristic (ROC) curve and the Youden index. All statistical analyses were performed using JMP, version 13.0 (SAS Institute). A 2-sided P-value of <.05 was considered statistically significant.

Results

Of the 7035 CTOs, a total of 2794 cases (39.7%) were performed by LVOs, 1809 cases (25.7%) by MVOs, and 2432 cases (34.6%) by HVOs. The baseline clinical characteristics and angiographic characteristics of the study patients are summarized in Table 1 and Table 2, respectively. Mean patient age was 64.4 ± 10 years, 82% were men, 43% had diabetes mellitus, and approximately one-third had prior CABG (29%) and prior congestive heart failure (30%). Patients treated by the HVO group were more likely to have diabetes mellitus (47% vs 44% vs 39%; P<.001) and prior CABG (36% vs 31% vs 23%; P<.001) compared with patients in the MVO group and LVO group, respectively. Patients in the HVO group had lower left ventricular ejection fraction compared with the MVO and LVO groups (48 ± 13% vs 50 ± 12% vs 51 ± 13%, respectively; P<.001).

The most common CTO target vessel was the right coronary artery (52%), followed by the left anterior descending (26%) and left circumflex coronary artery (20%). Moderate or severe calcification was present in 42%, mean J-CTO score was 2.40 ± 1.28, and mean PROGRESS-CTO score was 1.14 ± 1.01. Compared with cases performed by MVOs and LVOs, cases performed by HVOs were more complex (reflected by higher J-CTO, PROGRESS-CTO, and PROGRESS-CTO Complications scores) and more likely to have moderate/severe calcification (34% vs 38% vs 53%; P < .001) and proximal cap ambiguity (32% vs 34% vs 44%; P < .001). Application of complex crossing strategies, such as retrograde (42% vs 36% vs 22%; P < .001) and antegrade dissection and re-entry (25% vs 30% vs 18%; P < .001), were more common in the HVO and MVO groups compared with the LVO group, respectively. Mechanical circulatory devices were also more commonly used in the HVO and MVO groups compared with the LVO group (2% vs 3% vs 9%, respectively; P < .001).

Procedural characteristics and outcomes are shown in Table 3. Overall technical and procedural success rates were 85.6% and 83.7%, respectively. The incidence of in-hospital MACE was 2.36%. The HVO group had a higher technical success rate (87.9% vs 86.9% vs 82.6%; P < .001) (Figure 2A), but also a higher MACE rate (3.08% vs 2.71% vs 1.50%; P<.01) (Figure 2B) compared with the MVO and LVO groups. Perforation rates were higher in the HVO and MVO groups compared with the LVO group (7.65% vs 4.98% vs 3.90%, respectively; P < .001); however, there was no difference regarding tamponade (0.99% vs 0.66% vs 0.57%; P =.20) and pericardiocentesis (1.23% vs 0.72% vs 0.82%; P =.16). Mortality was higher among HVO and

MVO groups compared with the LVO group (0.78% vs 0.55% vs 0.11%, respectively; P<.01). Procedures performed by LVOs were shorter (125 minutes [IQR, 75-184] vs 132 minutes [IQR, 85-205] vs 106 minutes [IQR, 70-150]; P<.001) and had lower air kerma radiation dose (2.34 Gy [IQR, 1.364.11] vs 2.38 Gy [IQR, 1.30-3.83] vs 1.89 Gy [IQR, 1.06-3.27]; P<.001) compared with the MVO and HVO groups. On multivariable analyses, HVOs and MVOs were associated with higher technical success (Figure 3). The MVO group was also associated with higher incidence of MACE compared with the LVO group (Figure 4). On ROC curve analysis, the optimal annual volume cutoff for technical success was 29 cases/year.

Discussion

The main finding of our study is that CTO-PCIs performed by HVOs were associated with higher technical and procedural success rates, but also higher major complication rates compared with MVOs and LVOs.

In our study, 39.7% of the procedures were performed by LVOs, defined as operators performing < 30 cases/year. The ROC-derived threshold for better technical success was 29 cases/year. A prior analysis from the National Cardiovascular Data Registry (NCDR) also demonstrated that higher CTO-PCI procedural volume was associated with higher procedural success rates (<5 cases/year = 53.1%; 5–10 cases/year = 62.1%; > 10 cases/year = 74.6%; P < .001), with a 5% increase in success for each 10 CTO-PCI procedures performed per year. Yet in 2013, only 8 operators performed 50 or more CTO-PCI cases/year.⁵ In another analysis from the NCDR, procedural success was higher with accrued experience, while inpatient mortality, MACE, and other complication rates remained low across all CTO case strata.⁸ An analysis from the Blue Cross Blue Shield of Michigan Cardiovascular Consortium registry in Michigan demonstrated a positive relationship between prior operator and site experience and procedural success rates of CTO-PCI (likelihood ratio test = 141.12; df=15; P < .001), but found no relationship between operator and site experience and MACE rate (likelihood ratio test = 19.12; df = 15; P = .21).⁶ In the present study, we also found higher MACE rates among HVOs, which could be due to higher complexity in the HVO group, more frequent use of retrograde and antegrade dissection and re-entry technique, and more frequent use of mechanical circulatory support devices. The retrograde approach is often needed in high-complexity lesions and is associated with higher major complication rates.¹⁹ Use of the retrograde approach is 1 of the 3 parameters included in the PROGRESS-CTO Complications score (patient age > 65 years, +3 points; lesion length ≥23 mm, +2 points; and use of the retrograde approach, +1 point).¹⁸ On multivariable analyses, the LVO group as compared with the MVO group was associated with lower MACE rate. The potential causes of the increased MACE rate in the HVO group require further study. In addition to higher lesion complexity, more experienced operators may attempt cases that are inherently more risky and sometimes in patients with multiple comorbidities; even with more experience, new equipment and advanced techniques may not be able to achieve success without complications. Clinical judgment is key for determining the risk-benefit ratio for each patient referred for CTO-PCI and making a decision together with the patient about whether or not to proceed with the procedure.

In the RECHARGE (REgistry of Crossboss and Hybrid procedures in FrAnce, the NetheRlands, BelGium and UnitEd Kingdom) registry, the average success of centers or operators performing >100 cases/year was significantly higher compared with lower-volume operators (91% in those performing > 100 cases/year vs 82% in those performing 50-100 cases/year vs 83% in those performing <50 cases/year; P < .001).²⁰ The EuroCTO Club requires an annual volume of 50 CTO-PCIs for participation in its registry and 100 CTO-PCIs for considering an operator to be expert.^21,22 It also recommends that centers and operators with fewer than 30 CTO procedures/year should refer their CTO patients to more experienced operators. To become an independent retrograde operator, they suggest a minimum of 50 retrograde procedures (25 as second operator and 25 as first under supervision) and that retrograde techniques should be performed by experienced operators (ie, those performing > 50 cases/year).^22,23

In an analysis of 1948 LM-PCI patients, Xu et al found that patients treated by experienced HVOs had significantly lower risk for cardiac death at short- and long-term follow-up, despite having more extensive and complex coronary artery disease at baseline; operator experience was independently associated with cardiac death after LM-PCI.¹² Our study shows a different relationship between procedural volume and outcomes; HVOs had higher success, but also higher complication rates, likely at least in part due to higher lesion complexity. This highlights the importance of careful patient selection for CTO-PCI and for applying judgment about when to apply higher-risk techniques (such as the retrograde approach). Proceeding with higher-risk techniques may be acceptable for some patients (for example, those with severe, life-threatening symptoms), but not others. Understanding when to stop is therefore critical for optimal CTO-PCI outcomes, as aiming for very high success is likely to significantly increase complications.

Study limitations. Limitations of this study are the observational design, the lack of clinical event adjudication, and performance of all procedures at high-volume, experienced PCI centers with more than 40 cases/centers entered in the registry, limiting the generalizability of our findings to centers with limited CTO-PCI experience.

Conclusion

In a contemporary, multicenter CTO-PCI registry, 40% of cases were performed by LVOs. Cases performed by HVOs were associated with higher technical and procedural success, but also higher major complication rates, which was likely due to higher angiographic complexity in this group.

Acknowledgments. Study data were collected and managed using Research Electronic Data Capture (REDCap) electronic data capture tools hosted at the Minneapolis Heart Institute Foundation (MHIF), Minneapolis, Minnesota. REDCap is a secure, web-based application designed to support data capture for research studies, providing: (1) an intuitive interface for validated data entry; (2) audit trails for tracking data manipulation and export procedures; (3) automated export procedures for seamless data downloads to common statistical packages; and (4) procedures for importing data from external sources.

From ¹Minneapolis Heart Institute and Minneapolis Heart Institute Foundation, Abbott Northwestern Hospital, Minneapolis, Minnesota; ²Red Cross Hospital of Athens, Athens, Greece; ³Henry Ford Hospital, Detroit, Michigan; ⁴Gagnon Cardiovascular Institute, Morristown Medical Center, New Jersey; ⁵Baylor Heart and Vascular Hospital, Dallas, Texas; ⁶Cleveland Clinic, Cleveland, Ohio; ⁷Massachusetts General Hospital, Boston, Massachusetts; ⁸University Hospitals, Case Western Reserve University, Cleveland, Ohio; ⁹VA San Diego Healthcare System and University of California San Diego, La Jolla, California; ¹⁰Acibadem Kocaeli Hospital, Izmit, Turkey; ¹¹Beth Israel Deaconess Medical Center, Boston, Massachusetts; ¹²St Boniface General Hospital, Winnipeg, Manitoba, Canada; ¹³Aswan Heart Centre, Magdi Yacoub Foundation, Aswan, Egypt; ¹⁴Meshalkin Novosibirsk Research Institute, Novosibirsk, Russia; ¹⁵Division of Invasive Cardiology, Department of Internal Medicine and Cardiology Center, University of Szeged, Szeged, Hungary; ¹⁶International Medical Center; Jeddah, Saudi Arabia; ¹⁷North Oaks Health System, Hammond, Louisiana; ¹⁸Memorial Bahcelievler Hospital, Istanbul, Turkey.

Funding: The authors are grateful for the generosity of our many philanthropic partners, including Drs Mary Ann and Donald A. Sens, Ms Dianne and Dr Cline Hickok, Ms Charlotte and Mr Jerry Golinvaux Family Fund, the Roehl Family Foundation, the Joseph Durda Foundation, Ms Wilma and Mr Dale Johnson, and our anonymous donors, for making this work possible at the Minneapolis Heart Institute Foundation’s Science Center for Coronary Artery Disease (CCAD).

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Alaswad: consulting fees from Terumo and Boston Scientific; consultant (non-financial) for Abbott Laboratories. Dr Karmpaliotis: honoraria from Abbott Vascular, Abiomed, and Boston Scientific; equity in Saranas, Soundbite, Traverse Vascular. Dr. Khatri: honoraria from Asahi Intecc; speaker and proctor for Abbott Vascular. Dr Jaffer: sponsored research from Canon USA, Siemens, Shockwave, Teleflex; institutional grants from Abbott Vascular, Boston Scientific, CSI, Philips, Asahi Intecc, and Biotronik; consultant for Boston Scientific, Siemens, Biotronik, Magenta Medical, IMDS, and Asahi Intecc; equity interest in Intravascular Imaging, DurVena; Massachusetts General Hospital has a patent licensing arrangement with Terumo, Canon USA, and Spectrawave (Dr Jaffer has the right to receive royalties). Dr Poommipanit: consultant for Asahi Intecc, Abbott Vascular. Dr Patel: member of the speakers bureau for AstraZeneca. Dr Yeh: grants and personal fees from Abbott Vascular, AstraZeneca, Medtronic, and Boston Scientific. Dr ElGuindy: consultancy and proctorship fees from Medtronic, Asahi Intecc, Boston Scientific, and Terumo. Dr Abi-Rafeh: proctor and speaker honoraria from Boston Scientific and Abbott Vascular. Dr Brilakis: consulting/speaker honoraria from Abbott Vascular, American Heart Association (associate editor, Circulation), Amgen, Asahi Intecc, Biotronik, Boston Scientific, Cardiovascular Innovations Foundation (Board of Directors), ControlRad, CSI, Elsevier, GE Healthcare, InfraRedx, Medicure, Medtronic, Opsens, Siemens, and Teleflex; research support from Regeneron; owner, Hippocrates LLC; shareholder in MHI Ventures, Cleerly Health. The remaining authors report no conflicts of interest regarding the content herein.

Manuscript accepted March 17, 2022.

Address for correspondence: Michalis Koutouzis, MD, Red Cross General Hospital, 1 Athanasaki St, 11526, Athens, Greece. Email: koutouzismike@yahoo.gr

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