Geographic diversity in chronic total occlusion percutaneous coronary intervention: insights from the PROGRESS-CTO registry.

BACKGROUND: There is variability in clinical and lesion characteristics as well as techniques in chronic total occlusion (CTO) percutaneous coronary intervention (PCI). METHODS: We analyzed patient and lesion characteristics, techniques, and outcomes in 11 503 CTO-PCI procedures performed in North America (NA) and in the combined regions of Europe, Asia, and Africa from 2017 to 2023 as documented in the PROGRESS-CTO registry. RESULTS: Eight thousand four hundred seventy-nine (74%) procedures were performed in NA. Compared with non-NA patients, NA patients were older, with higher body mass index and higher prevalence of diabetes, hypertension, dyslipidemia, family history of coronary artery disease, prior history of PCI, coronary artery bypass graft surgery and heart failure, cerebrovascular disease, and peripheral arterial disease. Their CTOs were more complex, with higher J-CTO (2.56 ± 1.22 vs 1.81 ± 1.24; P less than .001) and PROGRESS-CTO (1.29 ± 1.01 vs 1.07 ± 0.95; P less than .001) scores, longer length, and higher prevalence of proximal cap ambiguity, blunt/no stump, moderate to severe calcification, and proximal tortuosity. Retrograde (31.0% vs 22.1%; P less than .001) and antegrade dissection and re-entry (ADR) (21.2% vs 9.2%; P less than .001) were more commonly used in NA centers, along with intravascular ultrasound (69.0% vs 10.1%; P less than .001). Procedure and fluoroscopy times were longer in NA, while contrast volume and radiation dose were lower. Technical (86.7% vs 86.8%; P > .90) and procedural (85.4% vs 85.8%; P = .70) success and in-hospital major adverse cardiovascular events (MACE) (1.9% vs 1.7%; P = .40) were similar in NA and non-NA centers. CONCLUSIONS: Compared with non-NA patients, NA patients undergoing CTO PCI have more comorbidities, higher CTO lesion complexity, are more likely to undergo treatment with retrograde and ADR, and have similar technical success and MACE.

Ranolazine in chronic total occlusion percutaneous coronary intervention.

Ranolazine is an anti-anginal medication given to patients with chronic angina and persistent symptoms despite medical therapy. We examined 11 491 chronic total occlusion (CTO) percutaneous coronary interventions (PCI) that were performed at 41 US and non-US centers between 2012 and 2023 in the PROGRESS-CTO Registry. Patients on ranolazine at baseline had more comorbidities, more complex lesions, lower procedural and technical success (based on univariable but not multivariable analysis), and higher incidence of major adverse cardiac events (MACE) (on both univariable and multivariable analysis).

Interventional cardiologists' perspectives and knowledge towards artificial intelligence.

BACKGROUND: Artificial intelligence (AI) is increasingly utilized in interventional cardiology (IC) and holds the potential to revolutionize the field. METHODS: We conducted a global, web-based, anonymous survey of IC fellows and attendings to assess the knowledge and perceptions of interventional cardiologists regarding AI use in IC. RESULTS: A total of 521 interventional cardiologists participated in the survey. The median age range of participants was 36 to 45 years, most (51.5%) practice in the United States, and 7.5% were women. Most (84.7%) could explain well or somehow knew what AI is about, and 63.7% were optimistic/very optimistic about AI in IC. However, 73.5% believed that physicians know too little about AI to use it on patients and most (46.1%) agreed that training will be necessary. Only 22.1% were currently implementing AI in their personal clinical practice, while 60.6% estimated implementation of AI in their practice the next 5 years. Most agreed that AI will increase diagnostic efficiency, diagnostic accuracy, treatment selection, and healthcare expenditure, and decrease medical errors. The most tried AI-powered tools were image analysis (57.3%), ECG analysis (61.7%), and AI-powered algorithms (45.9%). Interventional cardiologists practicing in academic hospitals were more likely to have AI tools currently implemented in their clinical practice and to use them, women had a higher likelihood of expressing concerns regarding AI, and younger interventional cardiologists were more optimistic about AI integration in IC. CONCLUSIONS: Our survey suggests a positive attitude of interventional cardiologists regarding AI implementation in the field of IC.

Update on chronic total occlusion percutaneous coronary intervention.

Chronic total occlusion (CTO) percutaneous coronary intervention (PCI) continues to evolve. This review summarizes recent publications categorized by outcomes, techniques, complications, and ongoing studies in this rapidly growing area.

Racial disparities in chronic total occlusion percutaneous coronary interventions: insights from the PROGRESS-CTO registry.

OBJECTIVES: There is limited data on race and outcomes of chronic total occlusion (CTO) percutaneous coronary intervention (PCI). The authors sought to evaluate CTO PCI techniques and outcomes in different racial groups. METHODS: We examined the baseline characteristics and procedural outcomes of 11 806 CTO PCIs performed at 44 US and non-US centers between 2012 and March 2023. In-hospital major adverse cardiac events (MACE) included death, myocardial infarction, repeat target-vessel revascularization, pericardiocentesis, cardiac surgery, and stroke prior to discharge. RESULTS: The most common racial group was White (84.5%), followed by Black (5.7%), "Other" (3.9%), Hispanic (2.9%), Asian (2.4%), and Native American (0.7%). There were significant differences in the baseline characteristics between different racial groups. When compared with non-White patients, the retrograde approach and antegrade dissection re-entry were more likely to be the successful crossing strategies in White patients without any significant differences in technical success (86.4% vs 86.4%; P = .93), procedural success (84.8% vs 85.0%; P = .79), and in-hospital MACE (2.0% vs 1.5%; P = .15) between the 2 groups. The technical success rate was significantly higher in the "Other" racial group (91.0% vs 86.4% in White, 86.9% in Asian, 84.5% in Black, 84.5% in Hispanic, and 83.3% in Native American; P = .03) without any significant differences in procedural success or in-hospital MACE rates between the groups. CONCLUSIONS: Despite differences in baseline characteristics and procedural techniques, the procedural success and in-hospital MACE of CTO PCI were not significantly different between most racial groups.

Use of plaque modification microcatheters during percutaneous coronary interventions for chronic total occlusion: insights from the PROGRESS-CTO Registry.

Plaque modification microcatheters (PM) (Tornus [Asahi] and Turnpike Gold [Teleflex]) are devices that are mainly used to modify the cap or lesion and maintain good support in chronic total occlusion (CTO) percutaneous coronary artery intervention (PCI). We evaluated the frequency of use and outcomes of plaque modification microcatheters in an international multicenter registry. Plaque modification microcatheters were utilized in 242 cases (1.6%: Tornus in 51% and Turnpike Gold in 49%) with decreasing frequency over time (P-for-trend: 0.007 and 0.035, respectively). Technical and procedural success and the incidence of major cardiac adverse events were similar with Tornus and Turnpike Gold use. PM are infrequently utilized in CTO-PCI and are associated with high success and acceptable complication rates.

Predictors of successful primary antegrade wiring in chronic total occlusion percutaneous coronary intervention.

BACKGROUND: Antegrade wiring is the most commonly used chronic total occlusion (CTO) crossing technique. METHODS: Using data from the PROGRESS CTO registry (Prospective Global Registry for the Study of Chronic Total Occlusion Intervention; Clinicaltrials.gov identifier: NCT02061436), we examined the clinical and angiographic characteristics and procedural outcomes of CTO percutaneous coronary interventions (PCIs) performed using a primary antegrade wiring strategy. RESULTS: Of the 13 563 CTO PCIs performed at 46 centers between 2012 and 2023, a primary antegrade wiring strategy was used in 11 332 (83.6%). Upon multivariable logistic regression analysis, proximal cap ambiguity (odds ratio [OR]: 0.52; 95% CI, 0.46-0.59), side branch at the proximal cap (OR: 0.85; 95% CI, 0.77-0.95), blunt/no stump (OR: 0.52; 95% CI: 0.47-0.59), increasing lesion length (OR [per 10 mm increase]: 0.79; 95% CI, 0.76-0.81), moderate to severe calcification (OR: 0.73; 95% CI, 0.66-0.81), moderate to severe proximal tortuosity (OR: 0.67; 95% CI, 0.59-0.75), bifurcation at the distal cap (OR: 0.66; 95% CI, 0.59-0.73), left anterior descending artery CTO (OR [vs right coronary artery]: 1.44; 95% CI, 1.28-1.62) and left circumflex CTO (OR [vs right coronary artery]: 1.22; 95% CI, 1.07-1.40), non-in-stent restenosis lesion (OR: 0.56; 95% CI, 0.49-0.65), and good distal landing zone (OR: 1.18; 95% CI, 1.06-1.32) were independently associated with primary antegrade wiring crossing success. CONCLUSIONS: The use of antegrade wiring as the initial strategy was high (83.6%) in our registry. We identified several parameters associated with primary antegrade wiring success.

Iso-osmolar vs low-osmolar contrast agents for coronary optical coherence tomography: a blinded prospective randomized controlled study.

BACKGROUND: The impact of contrast type on coronary optical coherence tomography (OCT) imaging has received limited research. METHODS: We conducted a blinded, prospective, single-center, randomized, controlled crossover study comparing iso-osmolar contrast media (IOCM) with low-osmolar contrast media (LOCM) in patients undergoing clinically indicated coronary OCT imaging. Patients were randomly assigned to undergo OCT imaging with either IOCM or LOCM as the initial contrast medium. Following a washout period, a second run of OCT imaging of the same coronary vessel was performed using the other contrast medium. RESULTS: A total of 62 patients were randomized to IOCM first (n = 31) or LOCM first (n = 31). Mean patient age was 65.9 ± 11.2 years and 74.2% were male, with high prevalence of dyslipidemia (82.3%) and prior myocardial infarction (41.9%). Percutaneous coronary intervention was performed in 60 cases (96.8%) and the left anterior descending artery was the most common target vessel (53.3%). The contrast volume used for OCT imaging was similar for IOCM and LOCM (8.0 [6.9, 9.0] mL vs 8.0 [6.7, 9.0] mL; P = .89), as was the length of clear OCT images (70.0 [62.8, 74.0] mm for IOCM vs 70.0 [64.0, 74.0] mm for LOCM; P = .65). Electrocardiographic changes were observed in 11 runs with IOCM (ventricular repolarization changes in 9 runs and premature ventricular contractions [PVCs] in 2 runs) vs 12 runs with LOCM (ventricular repolarization changes in 9 runs and PVCs in 3 runs). CONCLUSIONS: The use of IOCM in coronary OCT is associated with similar contrast volume and clear imaging length when compared with LOCM.

Emergency coronary artery bypass surgery after chronic total occlusion percutaneous coronary intervention: Insights from the PROGRESS-CTO registry.

BACKGROUND: Emergency coronary artery bypass surgery (eCABG) is a serious complication of chronic total occlusion (CTO) percutaneous coronary artery intervention (PCI). METHODS: We examined the incidence and outcomes eCABG among 14,512 CTO PCIs performed between 2012 and 2023 in a large multicenter registry. RESULTS: The incidence of eCABG was 0.12% (n = 17). Mean age was 68 ± 6 years and 69% of the patients were men. The most common reason for eCABG was coronary perforation (70.6%). eCABG patients had larger target vessel diameter (3.36 ± 0.50 vs. 2.90 ± 0.52; p = 0.003), were more likely to have moderate/severe calcification (85.7% vs. 45.8%; p = 0.006), side branch at the proximal cap (91.7% vs. 55.4%; p = 0.025), and balloon undilatable lesions (50% vs. 7.4%; p = 0.001) and to have undergone retrograde crossing (64.7% vs. 30.8%, p = 0.006). eCABG cases had lower technical (35.3% vs. 86.7%; p < 0.001) and procedural (35.3% vs. 86.7%; p < 0.001) success and higher in-hospital mortality (35.3% vs. 0.4%; p < 0.001), coronary perforation (70.6% vs. 4.6%; p < 0.001), pericardiocentesis (47.1% vs. 0.8%; p < 0.001), and major bleeding (11.8% vs. 0.5%; p < 0.001). CONCLUSIONS: The incidence of eCABG after CTO PCI was 0.12% and associated with high in-hospital mortality (35%). Coronary perforation was the most common reason for eCABG.

Validation of the J-Channel Score for retrograde channel crossing in the PROGRESS-CTO registry.

Successful collateral channel (CC) crossing is essential for the success of retrograde chronic total occlusion (CTO) percutaneous coronary intervention (PCI). Based on the Japanese CTO PCI expert registry, the J-Channel score was developed to predict CC crossing. We examined the performance of the J-Channel score in patients who underwent retrograde CTO-PCI at 31 centers between 2013-2023 as part of the Prospective Global Registry for the Study of CTO Intervention (PROGRESS-CTO). We observed an association between successful CC crossing and the J-Channel score, its predictive efficacy was modest for both wire and microcatheter crossing.

Burnout in cardiology: a narrative review.

The frequency of burnout is rising among cardiologists, affecting not only their well-being but also the quality of patient care. Computerization of practice, bureaucracy, excessive workload, lack of control/autonomy, hostile and hectic work environments, insufficient income, and work life imbalance are the main categories listed as contributing factors to cardiologists' burnout. Organization- and physician-directed interventions can be impactful; however, the effectiveness and feasibility of these interventions have rarely been assessed in cardiology. This review summarizes recent publications on burnout in cardiology, discusses the contributing factors and implications of burnout on physicians' health and patient safety, and explores possible interventions.

Radiation dose during contemporary percutaneous coronary interventions for chronic total occlusion: insights from the PROGRESS-CTO registry.

Chronic total occlusion (CTO) percutaneous coronary intervention (PCI) is associated with high radiation doses. In this manuscript, we examined the contemporary trends and determinants of radiation dose in the PROGRESS CTO (Prospective Global Registry for the Study of CTO Intervention; Clinicaltrials.gov identifier: NCT02061436) registry. Radiation dose during CTO PCI did not change significantly since 2020, highlighting the need for innovation and operator education to further maintain radiation safety.

Equipment entrapment/loss during chronic total occlusion percutaneous coronary intervention.

BACKGROUND: There is limited data on equipment loss or entrapment during chronic total occlusion (CTO) percutaneous coronary intervention (PCI). METHODS: We analyzed the baseline clinical and angiographic characteristics and outcomes of equipment loss/entrapment at 43 US and non-US centers between 2017 and 2023. RESULTS: Equipment loss/entrapment was reported in 40 (0.4%) of 10 719 cases during the study period. These included guidewire entrapment/fracture (n = 21), microcatheter entrapment/fracture (n = 11), stent loss (n = 8) and balloon entrapment/fracture/rupture (n = 5). The equipment loss/entrapment cases were more likely to have moderate to severe calcification, longer lesion length, higher J-CTO and PROGRESS-CTO complications scores, and use of the retrograde approach compared with the remaining cases. Retrieval was attempted in 71.4% of the guidewire, 90.9% of the microcatheter, 100% of the stent loss, and 100% of the balloon cases, and was successful in 26.7%, 30.0%, 50%, and 40% of the cases, respectively. Procedures complicated by equipment loss/entrapment had higher procedure and fluoroscopy time, contrast volume and patient air kerma radiation dose, lower procedural (60.0% vs 85.6%, P less than .001) and technical (75.0% vs 86.8%, P = .05) success, and higher incidence of major adverse cardiac events (MACE) (17.5% vs 1.8%, P less than .001), acute MI (7.5% vs 0.4%, P less than .001), emergency coronary artery bypass graft (CABG) (2.5% vs 0.1%, P = .03), perforation (20.0% vs 4.9%, P less than .001), and death (7.5% vs 0.4%, P less than .001). CONCLUSIONS: Equipment loss is a rare complication of CTO PCI; it is more common in complex CTOs and is associated with lower technical success and higher MACE.

Comparative Analysis of Polymer Versus Non-Polymer Jacketed Wires in Chronic Total Occlusion Percutaneous Coronary Intervention.

There is significant variation in wire utilization patterns for chronic total occlusion (CTO) percutaneous coronary intervention. This study aimed to compare the outcomes of polymer-jacketed wires (PJWs) versus non-PJWs in anterograde procedures. We analyzed clinical and angiographic characteristics, and procedural outcomes of 7,575 anterograde CTO percutaneous coronary interventions that were performed at 47 centers between 2012 and 2023. Cases in which PJWs were exclusively used were classified in the PJW group, whereas cases where at least one non-PJW was employed were classified in the non-PJW group. Study end points were as follows: technical success, coronary perforation, major adverse cardiac event. PJWs were exclusively used in 3,481 cases (46.0%). These cases had lower prevalence of proximal cap ambiguity, blunt stump, and moderate/severe calcification. They also had lower Japanese CTO (J-CTO), Prospective Global Registry for the Study of Chronic Total Occlusion (PROGRESS-CTO), and PROGRESS-CTO complications scores, higher technical success (94.3% vs 85.7%, p <0.001), and lower perforation rates (2.2% vs 3.2%, p = 0.013). Major adverse cardiac event rates did not differ between groups (1.3% vs 1.5%, p = 0.53). Exclusive use of PJWs was independently associated with higher technical success in both the multivariable (odds ratio [OR] 2.66, 95% confidence interval [CI] 2.13 to 3.36, p <0.001) and inverse probability of treatment weight analysis (OR 2.43, 95% CI 2.04 to 2.89, p <0.001). Exclusive use of PJWs was associated with lower risk of perforation in the multivariable analysis (OR 0.69, 95% CI 0.49 to 0.95, p = 0.02), and showed a similar trend in the inverse probability of treatment weight analysis (OR 0.77, 95% CI 0.57 to 1.04, p = 0.09). Exclusive use of PJWs is associated with higher technical success and lower perforation risk in this non-randomized series of patients.

Activated clotting time and outcomes of chronic total occlusion percutaneous coronary intervention: insights from the PROGRESS-CTO Registry.

BACKGROUND: The optimal range of activated clotting time (ACT) in chronic total occlusion (CTO) percutaneous coronary intervention (PCI) has received limited study. METHODS: We examined the association between ACT and in-hospital ischemic and bleeding outcomes in patients who underwent CTO PCI in the Prospective Global Registry for the Study of CTO Intervention. RESULTS: ACT values were available for 4377 patients who underwent CTO PCI between 2012 and 2023 at 29 centers. The mean ACT distribution was less than 250 seconds (19%), 250 to 349 seconds (50%), and greater than or equal to 350 seconds (31%). The incidence of ischemic events, bleeding events, and net adverse cardiovascular events (NACE) was 0.8%, 3.0%, and 3.8%, respectively. In multiple logistic regression analysis, increasing nadir ACT was associated with decreasing ischemic events (adjusted odds ratio [aOR] per 50-second increments: 0.69 [95% confidence interval (CI), 0.50-0.94; P=.017]; and increasing peak ACT was associated with increasing bleeding events (aOR per 50-second increments: 1.17 [95% CI ,1.01-1.36; P=.032]). A U-shaped association was seen between mean ACT and NACE, where restricted cubic spline analysis demonstrated that patients with a low ( less than 200 seconds) or high ( greater than 400 seconds) ACT had increasing NACE risk compared with an ACT of 200 to 400 seconds (aOR 2.06, 95% CI 1.18-3.62; P=.012). CONCLUSIONS: Among patients who underwent CTO PCI, mean ACT had a U-shaped relationship with NACE, where patients with a low ( less than 200 seconds) ACT (driven by ischemic events) or high ( greater than 400 seconds) ACT (driven by bleeding) had higher NACE compared with an ACT of 200 to 400 seconds.

Lesion complexity and procedural outcomes associated with ostial chronic total occlusions: Insights from the PROGRESS-CTO Registry.

OBJECTIVES: Ostial CTOs can be challenging to revascularize. We aim to describe the outcomes of ostial chronic total occlusion (CTO) percutaneous coronary intervention (PCI). METHODS: We examined the clinical and angiographic characteristics and procedural outcomes of 8788 CTO PCIs performed at 35 US and non-US centers between 2012 and 2022. In-hospital major adverse cardiac events (MACE) included death, myocardial infarction, urgent repeat target-vessel revascularization, tamponade requiring pericardiocentesis or surgery, and stroke. RESULTS: Ostial CTOs constituted 12% of all CTOs. Patients with ostial CTOs had higher J-CTO score (2.9 ± 1.2 vs 2.3 ± 1.3; P less than .01). Ostial CTO PCI had lower technical (82% vs. 86%; P less than .01) and procedural (81% vs. 85%; P less than .01) success rates compared with non-ostial CTO PCI. Ostial location was not independently associated with technical success (OR 1.03, CI 95% 0.83-1.29 P =.73). Ostial CTO PCI had a trend towards higher incidence of MACE (2.6% vs. 1.8%; P =.06), driven by higher incidence of in-hospital death (0.9% vs 0.3% P less than.01) and stroke (0.5% vs 0.1% P less than .01). Ostial lesions required more often use of the retrograde approach (30% vs 9%; P less than .01). Ostial CTO PCI required longer procedure time (149 [103,204] vs 110 [72,160] min; P less than .01) and higher air kerma radiation dose (2.3 [1.3, 3.6] vs 2.0 [1.1, 3.5] Gray; P less than .01). CONCLUSIONS: Ostial CTOs are associated with higher lesion complexity and lower technical and procedural success rates. CTO PCI of ostial lesions is associated with frequent need for retrograde crossing, higher incidence of death and stroke, longer procedure time and higher radiation dose.

Impact of coronary collaterals on the outcomes of chronic total occlusion percutaneous coronary intervention.

This study aims to evaluate the impact that the presence of interventional collaterals has on the outcomes of CTO PCI. We examined the clinical and angiographic characteristics and procedural outcomes of 11 205 patients who underwent 11 444 CTO PCIs at 45 US and non-US centers between 2012 and 2023.

Atrial fibrillation and chronic total occlusion percutaneous coronary intervention outcomes: insights from the Progress-CTO registry.

BACKGROUND: We examined the effect of atrial fibrillation on the outcomes of chronic total occlusion (CTO) percutaneous coronary intervention (PCI). METHODS: We examined the baseline characteristics and procedural outcomes of 9,166 CTO PCIs performed at 39 US and non-US centers between 2012 and 2023. RESULTS: Atrial fibrillation was present in 1122 (12%) patients. These patients were older and had a higher incidence of comorbidities, such as hypertension, dyslipidemia, heart failure, cerebrovascular disease, and peripheral arterial disease, lower left ventricular ejection fraction, and lower eGFR. Their CTOs were more likely to have moderate to severe calcification and longer lesion length. They also had higher mean J-CTO and PROGRESS-CTO complications (Acute MI, MACE, Mortality, Perforation, and Pericardiocentesis) scores. Patients with atrial fibrillation had higher prevalence of uncrossable and undilatable CTO lesions and required longer procedure (107 vs 119 min; P less than .001) and fluoroscopy (40 vs 43 min; P=.005) time. Technical success and MACE, including procedural/in-hospital bleeding, were similar in patients with and without atrial fibrillation. Although the crude incidence of MACE on follow-up (median 61 days) was significantly higher in patients with atrial fibrillation, the latter was not independently associated with adverse events on Cox proportional hazards analysis. CONCLUSIONS: Patients with atrial fibrillation undergoing CTO PCI are older, have more comorbidities, higher lesion complexity, and longer procedure time, but similar technical success and in-hospital MACE. They have higher MACE and mortality during follow-up, but the difference is not significant after adjusting for potential confounding variables.

Impact of target vessel on the procedural techniques and outcomes of chronic total occlusion percutaneous coronary intervention.

BACKGROUND: There is limited information on the impact of the target vessel on the procedural techniques and outcomes of chronic total occlusion (CTO) percutaneous coronary intervention (PCI). METHODS: We analyzed the baseline clinical and angiographic characteristics and procedural outcomes of 11,580 CTO PCIs performed between 2012 and 2022 at 44 centers. RESULTS: The most common CTO target vessel was the right coronary artery (RCA) (53.1%) followed by the left anterior descending artery (LAD) (26.0%) and the left circumflex artery (LCX) (19.8%). RCA CTOs were longer and more complex, with a higher Japanese CTO score compared with LAD or LCX CTOs. Technical success was higher among LAD (88.8%) lesions when compared with RCA (85.7%) or LCX (85.8%) lesions (P less than .001). The incidence of major adverse cardiovascular events (MACE) was overall 1.9% (n = 220) and was similar among target vessels (P=.916). There was a tendency toward more frequent utilization of the retrograde approach for more proximal occlusions in all 3 target vessels. When compared with all other RCA lesions combined, distal RCA lesions had higher technical success (87.7% vs 85.3%; P=.048). Technical success was similar between various locations of LAD CTOs (P=.704). First/second/third obtuse marginal branch had lower technical success when compared with all other LCX lesion locations (82.7% vs 86.8%; P=.014). There was no association between MACE and CTO location in all 3 target vessels. CONCLUSIONS: LAD CTO PCIs had higher technical and procedural success rates among target vessels. The incidence of MACE was similar among target vessels and among various locations within the target vessel.