Impact of Coronary Chronic Total Occlusion on Long-term Clinical Outcome in Patients with Unprotected Left Main Disease Undergoing Percutaneous Coronary Intervention : Cardiology Discovery

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Special Issue for Coronary Bifurcation Lesions, Guest Editor, Shaoliang Chen: Original Articles

Impact of Coronary Chronic Total Occlusion on Long-term Clinical Outcome in Patients with Unprotected Left Main Disease Undergoing Percutaneous Coronary Intervention

Sheiban, Imad1,*; Figini, Filippo1; Gaspartto, Valeria1; Moretti, Claudio2; Leonardo, Filippo1; Chen, Shaoliang3; D’Ascenzo, Fabrizio4

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doi: 10.1097/CD9.0000000000000071
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Abstract

CLINICAL PERSPECTIVE

WHAT IS NEW?

  • The incidence of left main coronary artery (LMCA) disease is 4% to 8% among patients referred to coronary angiography, and it is often associated with coronary chronic total occlusion (CTO) of one of the major coronary arteries. CTO represents a frequent finding in these patients and is associated with poorer prognosis.
  • In patients with LMCA disease, successful revascularization of major coronary vessel CTO with underlying viable myocardium is associated with an improved prognosis and a significant reduction of mortality at long-term follow-up.

WHAT ARE THE CLINICAL IMPLICATIONS?

  • LMCA disease can result in unfavorable long-term outcomes if it is associated with multivessel disease and CTO, especially if CTO is not recanalized.
  • Successful CTO-percutaneous coronary intervention (PCI) is associated with a reduced risk of death, particularly in patients with viable myocardium in the territory supplied by the occluded vessel. Thus, an appropriate patient selection for PCI in this patient subset should be guided by detection of myocardial viability and specific operator experience in CTO procedures.

Introduction

Left main coronary artery (LMCA) disease is found in 4% to 8% of patients referred for coronary angiography.[1,2] The technical evolution in percutaneous coronary intervention (PCI), including appropriate patient selection, improvements in device technology, stenting techniques, intravascular imaging guidance for final optimization, and post-procedural medical therapy have all contributed to make PCI a safe and effective alternative to coronary artery bypass graft surgery for unprotected LMCA disease.[3–5] However, when LMCA disease is associated with chronic total occlusion (CTO), many operators are discouraged from performing PCI of the LMCA due to a potentially increased risk of life-threatening periprocedural complications. In patients with LMCA stenosis requiring revascularization, CTO of a major coronary artery is therefore a common cause for coronary artery bypass surgery referrals[6,7]; these patients are mostly excluded from randomized LMCA intervention trials.[8,9] In this context, CTO represents one of the most challenging forms of coronary artery disease.[10] Compared to non-CTO percutaneous interventions, CTO-PCI is more complex; it includes risky crossing techniques, multiple stenting, and partly overlapping stents. A proper selection of suitable patients and meticulous evaluation of the coronary anatomy are essential for these procedures. In appropriately selected cases, CTO revascularization may translate to significant clinical and even survival benefits.[11–13]

The prognostic benefits of CTO recanalization depend on the extent of coronary artery disease and the target vessel. It has been reported that successful recanalization of CTO of the left anterior descending (LAD) and left circumflex artery is associated with survival benefit.[14,15] However, CTO-PCI of the right coronary artery (RCA) is more commonly considered for symptom relief, and is unlikely to confer survival benefit.[15] RCA CTO has also been reported to be a significant predictor of mortality in patients undergoing PCI for unprotected LMCA disease.[1]

LMCA stenosis confer the worst prognosis among all coronary lesions, mainly because of the extensive myocardial volume that is exposed to risk during intervention.[16,17] The prognostic significance of concomitant LMCA disease and CTO is unknown, and data on the impact of successful CTO-PCI on long-term outcomes of patients with unprotected LMCA disease are lacking. We therefore sought to compare the outcomes among patients without CTO, patients with untreated CTO or unsuccessful CTO-PCI, and successful PCI in a cohort with unprotected LMCA disease; the patients underwent PCI at high-volume centers that performed both angioplasty and CTO procedures for LMCA disease. The findings were expected to guide clinical decision-making more appropriately.

Materials and methods

Study design and patient population

All consecutive patients with an angiographic diagnosis of stenosis (>50% diameter stenosed on coronary angiography) in the unprotected LMCA, who underwent PCI between July 2014 and December 2018, were retrospectively included in our study. The procedure during which the unprotected LMCA was treated was considered the index procedure; the CTO was either treated during the index procedure or in a later step. CTO was defined as complete occlusion (thrombolysis in myocardial infarction (TIMI) flow grade 0) lasting > 3 months. The patients were divided into 3 groups: group A without CTO, group B with untreated or unsuccessful percutaneous transluminal coronary angioplasty (PTCA) for CTO, and group C with successful PTCA for CTO.

The primary and secondary endpoints were further analyzed by dividing group C into 2 subgroups according to the presence or area of myocardial vitality in the region supplied by the occluded vessel; this was evaluated via scintigraphy or echo-stress tests. There were no exclusion criteria. Written informed consent for treatment and data analysis was obtained from all patients and the approval from Ethical Committee for Clinical Trials at Pederzoli Hospital and University of Turin was obtained for database review.

Interventional procedures and postintervention medications

Coronary angioplasty and stent implantation during index PCI were performed according to current practice and guidelines. The choice of devices, techniques (including the approach to bifurcation stenting, kissing balloon, proximal optimization technique, and postdilatation) and drug therapy (including glycoprotein Ⅱb/Ⅲa inhibitors) for the index procedure was at the discretion of the cardiologist. After the procedure, all patients were advised to continue aspirin lifelong with 75 mg clopidogrel for at least 6 to 12 months.

Endpoint definitions and follow-up

The primary endpoint of the study was long-term occurrence of death. The secondary endpoints were: (1) myocardial infarction (MI), (2) repeat percutaneous or surgical revascularization for significant restenosis in the previously stented segment, (3) stroke, and (4) stent thrombosis. The diagnosis of MI at follow-up was based on peak values of total creatine kinase (CK) (≥ 2-fold increase from the upper limit for normal and a concomitant increase in CK-MB over the upper limit of normal, and/or ratio of peak CK-MB/peak total CK ≥ 0.10 and/or CK-MB increases by ≥ 3 fold the normal upper limit). Stroke was defined as an acute neurological defect lasting longer than 24 hours. Stent thrombosis was determined according to the Academic Research Consortium consensus.[6] Successful PCI was determined by attainment of a TIMI flow grade of 2 or 3; flow grade 1 denoted unsuccessful PCI.

Data were obtained by direct visits, telephone interviews, and searches of institutional electronic databases or municipal civil registries, and inquiring referring physicians.

Statistical analysis

Continuous variables are expressed as means ± standard deviation and were compared by analysis of variance or the Gosset T test. Categorical variables are presented as counts and percentages, and were compared using the chi-square test. P values unadjusted for multiplicity are reported throughout, with statistical significance set at the 2-tailed level of 0.05. Non parsimonious logistic regression was used to build a propensity score which was incorporated into a Cox multivariable model. Statistical analyses were performed using SPSS version 12.0 (SPSS, Inc., Chicago, Illinois, USA).

Results

Baseline characteristics

Between July 2014 and December 2018, 578 patients underwent PCI for unprotected LMCA disease at Pederzoli Hospital and University of Turin were enrolled in this study. They were divided into 3 groups: 374 (65%) without CTO (group A), 108 (19%) with untreated or unsuccessfully treated (by PTCA) CTO (group B), and 96 (17%) with successful PTCA of the CTO (group C). In group B, PCI was not successful in 22 patients; it was not attempted or performed in the others.

Among the 204 patients with CTO, 104 (51 %) had RCA-CTO, 21 (10%) had LAD-CTO, and 79 (39%) had left circumflex artery CTO. The baseline characteristics are summarized in Table 1. Cardiovascular risk factors such as hypertension, dyslipidemia, and diabetes mellitus were common in all groups. A history of MI was more common in groups B and C (38% vs. 57% vs. 63% in groups A, B, and C, respectively; P = 0.01); more patients in group B had undergone previous surgical revascularization (12% vs. 31% vs. 17% in groups A, B, and C, respectively; P = 0.03). The baseline left ventricular ejection fraction (LVEF) was significantly higher in group A (0.51 ± 0.06 vs. 0.42 ± 0.07 vs. 0.43 ± 0.05 in groups A, B, and C, respectively; P = 0.048). There were no statistically significant differences between other baseline characteristics.

Table 1 - Demographics and clinical characteristics of 578 patients with LMCA disease underwent PCI.
Variables Patients without CTO (n = 374) Patients with CTO-untreated or with unsuccessful PTCA (n = 108) Patients with successful PTCA
(n = 96)
P
Age (years), mean ± SD 69 ± 5 67 ± 7 68 ± 4 0.65
Female, n (%) 104 (28) 16 (15) 17 (18) 0.56
Hypertension, n (%) 291 (78) 86 (80) 73 (76) 0.67
Diabetes, n (%) 119 (32) 32 (30) 28 (29) 0.941
Dyslipidemia, n (%) 265 (71) 81 (75) 70 (73) 0.742
Prior MI, n (%) 142 (38) 62 (57) 60 (63) 0.01
Prior PCI, n (%) 90 (24) 28 (26) 13 (14) 0.23
Prior CABG, n (%) 45 (12) 33 (31) 16 (17) 0.03
Indications to PTCA, n (%)
Silent ischemia 60 (16) 16 (15) 17 (18) 0.39
Stable angina 64 (17) 15 (14) 10 (11) 0.34
Unstable angina 157 (42) 49 (45) 39 (41) 0.57
 Non-ST and ST segment elevation  myocardial infarction 93 (25) 28 (26) 20 (21) 0.76
Left ventricular ejection fraction, mean ±SD 0.51 ± 0.06 0.42 ± 0.07 0.43 ± 0.05 0.048
CABG: Coronary artery bypass grafting; CTO: Chronic total occlusion; LMCA: Left main coronary artery; MI: Myocardial infarction; PCI: Percutaneous coronary intervention; PTCA: Percutaneous transluminal coronary angioplasty; SD: Standard deviation.

Angiographic and procedural characteristics

The angiographic and procedural characteristics are presented in Table 2. No statistically significant differences were observed among the 3 groups. There was a trend towards a slightly higher prevalence of left main bifurcation disease in groups B and C versus group A (79% and 83%, respectively, vs. 85%; P = 0.11). The total number of treated vessels (including vessels with or without CTO) was similar across all patients in groups A and C, while single vessel treatment was higher in group B (27%) versus 7% and 5% in groups A and C, respectively (P = 0.05). There were no differences among the 3 groups in terms of the SYNTAX score (25.0 ± 4.7 vs. 27.0 ± 5.8 vs. 28.0 ± 4.4 in groups A, B, and C, respectively; P = 0.67).

Table 2 - Anatomical and procedural characteristics of 578 patients with LMCA disease underwent PCI.
Variables Patients without CTO
(n = 374)
Patients with CTO-untreated or with unsuccessful PTCA
(n = 108)
Patients with CTO and successful PTCA
(n = 96)
P
Left main bifurcation disease, n (%) 295 (79) 90 (83) 82 (85) 0.11
Provisional stenting, n(%)*
 Crossover LMCA to LAD
 Crossover LMCA to LCX
230 (78)
157 (68)
73 (32)
72 (80)
51 (71)
21 (29)
67 (82)
49 (73)
18 (27)
0.16
Two-stent strategy, n (%)* 65 (22) 18 (20) 15 (18) 0.19
CTO location, n (%)
 LAD 0 12 (11) 9 (9)
 LCX 0 40 (37) 39 (41)
 RCA 0 56 (52) 48 (50)
Number of treated vessels, n (%)
 1 vessel 25 (7) 29 (27) 5 (5) 0.05
 2 vessel 292 (78) 79 (73) 76 (79) 0.21
 3 vessel 57 (15) 0 15 (16) 0.76
SYNTAX score, mean ± SD 25.0 ± 4.7 27.0 ± 5.8 28.0 ± 4.4 0.67
“–” indicates that the data is not available.
*The ratios were calculated with the number of patients with left main bifurcation disease. CTO: Chronic total occlusion; LAD: Left anterior descending artery; LCX: Left circumflex Artery; LMCA: Left main coronary artery; PCI: Percutaneous coronary intervention; PTCA: Percutaneous transluminal coronary angioplasty; RCA: Right coronary artery; SD: Standard deviation.

Table 3 shows the procedural interventions in patients with CTO. CTO-PCI was attempted in 118 of 204 (58%) patients with CTO. Successful CTO recanalization was obtained in 96 (81%) patients who underwent PCI. The pre-PTCA TIMI flow grade was similar between groups B and C (P = 0.63). Ninety three percent of patients with successful CTO had a post-PTCA TIMI flow grade of 3; 7% had a TIMI flow grade of 2. Failed recanalization occurred in 22 (19%) patients; CTO was not attempted in 86 patients (both in group B).

Table 3 - Procedural characteristics in patients who underwent CTO recanalization procedures.
Variables Patients with unsuccessful CTO PCI
(n = 22)
Patients with successful CTO PCI
(n = 96)
P
TIMI pre-PTCA, n (%) 0.63
 0 22 (100) 92 (96)
 1 0 4 (4)
TIMI post-PTCA, n (%) <0.001
 0 22 (100) 0
 1 0 0
 2 0 7 (7)
 3 0 89 (93)
Number of stents implanted in CTO, n 0 112 (1 or 2 stents/CTO)
Length of stent (mm), mean ± SD 28 ± 15
Intraortic balloon pump, n (%) 3 (14) 15 (16) 0.43
Inhibitors Ⅱb/Ⅲa, n (%) 2 (9) 6 (6) 0.98
“–” indicates that the data is not available. CTO: Chronic total occlusion; PCI: Percutaneous coronary intervention; PTCA: Percutaneous transluminal coronary angioplasty; SD: Standard deviation; TIMI: Thrombolysis in Myocardial Infarction.

Long-term outcomes

At a median follow-up of (1090 ± 279) days, there was a trend towards higher mortality in group B than in groups A or C (13% vs. 19 % vs. 14% in groups A, B, and C, respectively; P = 0.12). The frequency of noncardiac death was higher in group B than in groups A or C (4% vs. 7% vs. 4%; P = 0.26) [Table 4]. There were no significant differences between the groups in terms of individual components of the secondary endpoints, including incidence of MI, repeat revascularization, stroke, or stent thrombosis. The primary and secondary endpoints were further analyzed by dividing group C into 2 subgroups according to the presence or absence of necrotic tissue; the subgroups comprised 54 (56%) patients with successful PTCA having viability (subgroup C1) and 42 (44%) patients with successful PTCA not having viability (subgroup C2).

Table 4 - Long-term clinical outcomes of 578 patients with LMCA disease underwent PCI.
Variables Patients without CTO
(n = 374)
Patients with CTO-untreated or with unsuccessful PTCA
(n = 108)
Patients with CTO and successful PTCA
(n = 96)
P
Death 49 (13) 20 (19) 13 (14) 0.12
 Noncardiac death 16 (4) 8 (7) 4 (4) 0.26
 Cardiac Death 33 (9) 12 (11) 9 (9) 0.19
Myocardial infarction 28 (7) 7 (6) 5 (5) 0.76
TLR 21 (6) 4 (4) 6 (6) 0.11
 Re-PCI 19 (5) 3 (2) 5 (5)
 CABG 2 (1) 1 (1) 1 (1)
Stent thrombosis 16 (4) 5 (5) 8 (8) 0.34
 Definite 2 (1) 0 1 (1)
 Probable 4 (1) 1 (1) 2 (2)
 Possible 10 (3) 4 (4) 5 (5)
Stroke 5 (1) 2 (2) 2 (2) 0.81
Data are presented as n (%). CABG: Coronary artery bypass grafting; CTO: Chronic total occlusion; LMCA: Left main coronary artery; PCI: Percutaneous coronary intervention; PTCA: Percutaneous transluminal coronary angioplasty; TLR: Target lesion revascularization.

Among patients with CTO, there was a statistically significant higher mortality rate in group B and subgroup C2 (with previous homolateral necrosis) than in subgroup C1 (successful CTO-PCI without previous homolateral necrosis) (19% and 19% in group B and subgroup C2, respectively, vs. 9% in subgroup C1; P = 0.05). The incidence of noncardiac deaths was similar across all groups; however, the incidence of cardiac deaths was higher in group B and subgroup C2 than in subgroup C1 (11% and 14% in group B and subgroup C2, respectively, vs. 4% in subgroup C1; P = 0.01) [Table 5]. Interestingly, the baseline LVEF was similar across group B and subgroups C1 and C2. At 3-year follow-up, there was a significant improvement in the LVEF only in subgroup C1 [Figure 1]. The incidence of MI was similar between group B, subgroups C1 and C2 (6% vs. 6% vs. 5% P = 0.74). The repeat revascularization rate was higher in subgroup C2 than in group B or subgroup C1 (7% in subgroup C2 vs. 4% and 6% in group B and subgroup C1, respectively; P = 0.14); however, the difference was not statistically significant. There were 2 (2%), 1 (2%), and 1 (2%) events of stroke in group B, subgroup C1, and subgroup C2, respectively (P = 0.34) [Table 5].

Table 5 - Long-term clinical outcomes in patients with CTO.
Variables Patients with CTO- untreated or with unsuccessful CTO-PCI
(n = 108)
Patients with successful CTO-PCI without previous homolateral necrosis
(n = 54)
Patients with successful CTO-PCI with previous homolateral necrosis
(n = 42)
P
Death 20 (19) 5 (9) 8 (19) 0.05
 Noncardiac 8 (7) 3 (6) 2 (5) 0.35
 Cardiac 12 (11) 2 (4) 6 (14) 0.01
Myocardial infarction 7 (6) 3 (6) 2 (5) 0.74
TLR 4 (4) 3 (6) 3 (7) 0.14
 Re-PTCA 3 (3) 2 (4) 3 (7)
 CABG 1 (1) 1 (2) 0
Stent thrombosis 5 (5) 4 (7) 4 (10) 0.32
 Definite 0 0 1 (2)
 Probable 1 (1) 1(2) 1 (2)
 Possible 4 (4) 3 (6) 2 (5)
Stroke 2 (2) 1 (2) 1 (2) 0.34
Data are presented as n (%). CABG: Coronary artery bypass grafting; CTO: Chronic total occlusion; PCI: Percutaneous coronary intervention; PTCA: Percutaneous transluminal coronary angioplasty; TLR: Target lesion revascularization.

F1
Figure 1::
Changes in left ventricular ejection fraction at follow-up in patients with chronic total occlusion. *P = 0.05.

Finally, although there was no definitive thrombosis in group B and subgroup C1, it was observed in only 1 patient from subgroup C2. In addition, there were no statistically significant higher rates of probable or possible stent thrombosis among the groups [Table 5].

Multivariable analysis

Non parsimonious logistic regression was used to build a propensity score (Hosmer-Lemeshow goodness of fit test P= 0.67, with an area under the receiver operating characteristics curve value of 0.78), which was then incorporated into a Cox multivariable model. On multivariable analysis, single group treatment (patients without CTO, with untreated or unsuccessful CTO-PCI, and with successful CTO-PCI) was not an independent predictor of death.s

The propensity to undergo successful revascularization of CTO was associated with a reduced risk of death (P = 0.01; odds ratio: 0.75; 95% confidence interval: 0.62–0.87). The other independent predictor of death was the presence of previous necrosis in the territory of the occluded vessel (P = 0.04; odds ratio: 12; 95% confidence interval: 1–18).

Discussion

The major findings of the present study evaluating the impact of CTO-PCI on the long-term outcomes of patients with LMCA disease undergoing percutaneous revascularization were: (1) CTO represents a frequent finding among patients with multivessel disease associated with poorer prognosis, (2) in patients with LMCA disease, successful revascularization of major coronary vessel CTO with underlying viable myocardium is associated with an improved prognosis.

In patients with multivessel disease who undergo CTO-PCI, successful revascularization confers freedom from adverse events for a longer term than no or incomplete revascularization.[16,18–20] Valenti et al[16] reported that successful CTO-PCI conferred a 2-year survival benefit in patients with multivessel disease that was completely revascularized (91.6% ± 2.0% vs. 87.4% ± 2.9%; P = 0.025). The authors included a large cohort of patients who underwent CTO-PCI, but only a small percentage had LMCA disease. In our study, patients with LMCA disease who underwent successful CTO-PCI of a major coronary artery had a lower mortality rate compared to those with no or failed CTO-PCI; however, this difference did not reach statistical significance. On follow-up, differences in the incidence of major adverse cardiovascular events among the 3 groups were not statistically significant. Our data correlate well with those reported by Migliorini et al[5]; they retrospectively analyzed data from patients with LMCA disease who underwent PCI, to investigate whether RCA CTO was a significant predictor of mortality. The authors found the 6-month cardiac mortality rate in patients with successful RCA CTO-PCI was 8.6%; the corresponding rate in patients with untreated CTO or failed CTO-PCI was 16.3% (P = 0.3). They also found that the 3-year cardiac survival rate was significantly higher in patients without RCA CTO (76.4% ± 6.8% vs. 89.7% ± 2.7 %; P = 0.003). This study only reported on data pertaining to CTO in RCA, and no other coronary arteries. In the present study, LAD and left circumflex CTOs were included in addition to RCA CTOs. No significant differences were found in terms of the site of CTO; however, it is worth noting that all groups had few patients with LAD CTO.

Most importantly, the mortality rate differed between patients with and without vitality of the myocardial area supplied by the occluded vessel. In fact, our study showed that percutaneous revascularization of CTOs is an effective therapeutic approach for patients in whom the myocardium supplied by the CTO vessel is viable. Improvement of left ventricular function with a significant increase in the LVEF is likely to be the main determinant of survival benefit in patients with successful CTO recanalization and viable myocardium, as compared to those with untreated or failed CTO-PCI and viable myocardium.

Available data regarding the clinical impact of revascularization in patients with CTO and viable homolateral myocardium are lacking. In this context, Galassi et al[21] reported improvements of LVEF in patients with successful CTO-PCI and poor LV function. In a recent meta-analysis, Megaly et al[22] reported that successful CTO-PCI is associated with a significant improvement in LVEF and decrease in end-systolic volume; these may reflect the beneficial effect of CTO recanalization on left ventricular remodeling and possible improvement in survival.

The present study demonstrated significant improvement in global left ventricular function in patients without previous MI or with a viable myocardium in the area supplied by the occluded vessel. Yang et al[23] demonstrated that myocardial injuries are common in CTO territory, but those with non-viable myocardium represent a minority. Furthermore, transmural myocardial scars are associated with worse functional outcomes. It therefore appears evident that in patients with left ventricular dysfunction undergoing any myocardial revascularization, the improvement in left ventricular function (and possibly survival) is only achieved when viability is preserved.

The relationship between the LVEF and post-MI mortality following surgical or percutaneous revascularization in patients with LMCA disease has been investigated in a sub-study analysis of the EXCEL trial.[24] The analysis showed that the composite rate of death, stroke, or MI at 3-year follow-up was significantly higher in patients with impaired (<50%) versus preserved (≥50%) LVEF; this was driven by an increased rate of all-cause death in those with reduced LVEF. Improvement in left ventricular function after successful myocardial revascularization (independent of type of revascularization) can therefore translate to improved survival; revascularization can even have a major impact if the revascularized area is more extensive. In the present study, successful revascularization of the LMCA and other nonoccluded vessels and successful CTO-PCI of occluded major coronary vessels that supplied viable myocardium translated to improved survival.

Percutaneous treatment of LMCA disease associated with coronary CTO is more challenging and increases the complexity of disease. CTO-PCI is more complex and involves risky crossing techniques and multiple stenting; it also often requires overlapping stents.[25] Proper selection of suitable patients and meticulous evaluation increases the probabilities of success with CTO-PCI. Proper selection is essential because CTO revascularization harbors significant clinical and survival benefits in this patient subset. Unsuitable anatomy, low expected success rates, and a lack of experience in CTO-PCI procedures may necessitate the use of surgical revascularization.

Study limitations

This study has several critical limitations, including the retrospective nonrandomized design and the descriptive scope. This leaves ample room for bias in patient and management strategy selection. In addition, no blinded adjudication committee was set up; however, the risk of data acquisition and adjudication bias was kept to a minimum by relying on hard clinical endpoints and established definitions.

Conclusion

LMCA disease is associated with unfavorable long-term outcomes, particularly if associated with multivessel disease and CTO. Among patients undergoing PCI, successful CTO-PCI is associated with a reduced risk of death, particularly in those with viable myocardium in the territory supplied by the occluded vessel. In addition to viability, appropriate patient selection for PCI in this patient subset should be guided by specific operator experience in CTO procedures.

Funding

None.

Conflicts of interest

None.

Editor note: Shaoliang Chen is an associate editor of Cardiology Discovery. The article was subject to the journal’s standard procedures, with peer review handled independently of this editor and his research group.

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Keywords:

Percutaneous coronary interventions; Left main coronary artery disease; Coronary chronic total occlusion; Myocardial viability

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