Seven-Year Clinical Outcomes of Successful Versus Failed Revascularization Using Drug-Eluting Stents for the Treatment of Coronary Chronic Total Occlusion

Abstract: Objectives. The aim of our study is to investigate the long-term, 7-year clinical outcomes of patients who received successful or failed revascularization using a drug-eluting stent (DES) for the treatment of chronic total occlusion (CTO). Background. The benefits of successful CTO revascularization remain unclear. Methods. In this prospective cohort study, a total of 377 consecutive CTO patients were divided according to successful (n = 253) or failed (n = 124) DES revascularization. We compared a composite index that consisted of death, myocardial infarction (MI), stroke, and target-vessel revascularization (TVR) at 7 years using propensity matching and inverse probability of treatment weighted (IPTW) analyses. Results. After a median follow-up period of 2561 days (interquartile range, 1533-2996 days), the successful-revascularization group demonstrated numerically lower incidence of the composite endpoint than the failed-revascularization group (26.5% vs 34.3%, respectively; log-rank P=.27). After IPTW adjustment, the risk of clinical outcomes (hazard ratio, 1.00; 95% confidence interval, 0.58–1.74; P=.99) was not statistically different between the groups. Propensity-score matching analysis (91 matched pairs) revealed similar outcomes (hazard ratio, 1.09; 95% confidence interval, 0.62-1.90; P=.77). Conclusions. Successful CTO revascularization does not demonstrate beneficial long-term clinical outcomes over 7 years compared with failed revascularization.

J INVASIVE CARDIOL 2016;28(6):229-236. Epub 2015 November 15.

Key words: chronic total occlusion, drug-eluting stent, high-risk PCI

Chronic total occlusion (CTO) of the coronary arteries develops in 18%-50% of patients with significant coronary artery disease who undergo coronary angiography,^1-3 and 3.8% of all percutaneous coronary interventions (PCIs) are performed for CTO.⁴ Improved techniques and the development of novel devices, such as drug-eluting stents (DESs), have improved the procedural success rate and long-term patency.^5-11 However, despite the higher probability of success, the potential for failure and disastrous complications remains relatively high. Meanwhile, medical therapies that employ appropriate risk factors have improved. For these reasons, it remains unclear if successful CTO recanalization is actually beneficial. Recently, several studies reported the clinical outcomes of CTO-PCI.^12-28 However, they differed in terms of various factors (eg, follow-up duration, CTO definitions) and yielded different conclusions. To address this controversy, the present retrospective cohort study was performed to determine the very long-term (7-year) safety and efficacy of performing PCI using DES implantation on patients with “true” CTO, which was defined as the presence of documented Thrombolysis in Myocardial Infarction (TIMI) grade-0 flow for ≥3 months. Accordingly, patients were divided according to the success of their CTO revascularization procedure using DES implantation, and their outcomes were examined. 

Methods

Study population and procedure. We enrolled 377 consecutive patients who underwent CTO-PCI between February 2003 and March 2006 at Presbyterian Medical Center and Kangbuk Samsung Hospital, a tertiary referral hospital located in Jeonju and Seoul, Korea. In all cases, patients underwent angiography and were screened for suitability to receive PCI. De novo true CTO was defined as a TIMI flow grade 0 on angiography that was estimated to have been present ≥3 months. CTO duration was estimated based on the patient’s clinical history at the time of their last myocardial infarction (MI) in the same target-vessel territory. Alternatively, CTO duration was estimated based on the gap between the current diagnosis and any diagnoses made after prior angiograms.^16,29 If there were no definite symptoms of total occlusion, at least two experienced interventional cardiologists diagnosed CTO according to morphology present on angiography (eg, degree of calcification, bridging collaterals, non-tapered stump, and/or angiographic filling from the collaterals). 

All CTO patients were offered the opportunity to receive PCI for revascularization after carefully following the recommended guidelines.³⁰ Thus, all patients were informed about both the possible adverse outcomes and potential benefits, thereby allowing them to truly provide informed consent. Imaging modalities were used to determine distal myocardial viability. The ultimate decision to perform CTO-PCI depended on several factors, including technical difficulty, likelihood of a successful outcome, extent of other coronary artery diseases, and amount of viable myocardium supplied by the CTO vessel. Basically, all patients were diagnosed with symptomatic angina, with or without positive results on functional stress tests (eg, treadmill test, myocardial perfusion imaging study).

Revascularization and DES implantation were performed using standard procedures. All patients received aspirin (200 mg loading dose followed by 100 or 200 mg/day indefinitely) and clopidogrel (300 or 600 mg loading dose followed by 75 mg/day for ≥12 months). In 253 patients, PCI successfully revascularized all target CTO lesions; altogether, these patients had 274 successfully treated CTO lesions (232 patients had 1 treated CTO lesion, while 21 patients had 2 treated CTO lesions). However, PCI was unsuccessful in the remaining 124 patients. To minimize the impact of any residual non-CTO lesions in patients with multivessel disease, the objective of PCI was to achieve the complete revascularization of all PCI-feasible non-CTO lesions; in other words, to restore TIMI grade-3 flow and <30% residual stenosis in the major epicardial coronary arteries and their major branches on visual assessment. In the failed-revascularization group, 74 non-CTO lesions in 57 patients were successfully treated, while 162 non-CTO lesions in 104 patients were successfully treated in the successful-revascularization group.

After the index procedure, all patients were administered optimal medical therapy to control their symptoms and improve prognosis. This included the comprehensive modification of risk factors, including blood pressure, glucose control, weight, nutrition, exercise, emotional stress, and smoking, which was provided as secondary prevention and cardiac rehabilitation therapy as recommended by the applicable guidelines.³¹ 

Study endpoints and definitions. The primary endpoint was a composite index that consisted of death, MI, stroke, and target-vessel revascularization (TVR) during the follow-up period. Individual incidences of death, MI, TVR, stroke, and stent thrombosis (ST) after DES implantation were the secondary endpoints.

All events were determined and clinically diagnosed by each patient’s physician and adjudicated by an independent group of clinicians. Death was defined as death from any cause. MI during the follow-up period was defined by increases in cardiac biomarkers with at least one value above the 99th percentile, along with at least one of the following: (1) ischemia symptoms; (2) new (or presumed new) significant ST-segment to T-wave (ST-T) changes or new left bundle-branch block; (3) development of pathological Q-waves on electrocardiography; (4) imaging evidence of new loss in the viable myocardium or new regional wall-motion abnormality; or (5) intracoronary thrombus on angiography or autopsy. 

Stroke, as indicated by the rapid onset of a focal or global neurological deficit due to appropriate signs or symptoms, was confirmed by a neurologist based on the neuroimaging results. Transient ischemic attack was not considered a stroke if the neurological deficits did not resolve within 24 hours. TVR was defined as the repeated revascularization of an index vessel with PCI or coronary artery bypass graft (CABG) surgery. Stent thrombosis was assessed according to the Academic Research Consortium (ARC) definitions³² and defined according to the timing of the event as early (0-30 days), late (31-365 days), or very late (>365 days). Definite stent thrombosis was defined as an angiographic or pathologically confirmed thrombus within the stent, along with the presence of clinical symptoms or objective signs suggestive of acute ischemia. Probable stent thrombosis was defined as unexplained death within the first 30 days after stent implantation or acute MI of the target-vessel territory without angiographic evidence. 

Data collection and follow-up. Clinical, procedural, operative, and outcome data were recorded in dedicated databases by independent research personnel. Patients received clinical follow-up examinations at 1, 4, 6, and 12 months, and yearly thereafter via office visits or telephone contact. To ensure the accurate assessment of the clinical endpoints, additional information was obtained using visits or telephone contact with living patients or their family members or by reviewing the medical records of other hospitals, as necessary. Data were carefully verified and adjudicated by an independent events committee that was blind to the CTO-PCI results.

To validate the complete follow-up data in terms of all-cause mortality, information about the vital status of each patient was obtained from the National Population Registry of the Korean National Statistical Office using the unique personal identification number of each patient. 

Statistical analysis. The continuous variables in both groups were compared using the t-test or Wilcoxon rank-sum test, and categorical variables were compared using χ² statistics or Fisher’s exact test, as appropriate. Cumulative probability and survival curves were constructed using Kaplan-Meier estimates and compared using the log-rank test. To estimate the effects of PCI success on primary and secondary outcomes, univariate and multivariate Cox proportional-hazards regression analyses were performed. All baseline characteristics in Tables 1 and 2 were tested using univariate analysis; variables with a P-value ≤.20 were included in the multivariate analysis. The final models were determined using backward stepwise elimination. 

To reduce the impact of selection bias and potential confounding in this observational study, we rigorously adjusted significant differences in the patient characteristics using weighted Cox proportional-hazards regression models, inverse probability of treatment weighting (IPTW), and robust standard errors. Here, the weights of the patients who received successful recanalization were inversed to 1 – propensity score, and the weights of the patients who received failed recanalization were inverse to the propensity score. Additionally, we performed propensity score-matching analyses. The propensity of the score-matched pairs was created by matching the group subjects on the logit of the propensity score using calipers with a width equal to 0.2 of the standard deviation of the logit of the propensity score. After propensity score-matching, the baseline covariates were compared between groups using the paired t-test or Wilcoxon signed-rank test for continuous variables, and the McNemar or marginal homogeneity test was used to compare categorical variables. Matching balance was assessed using standardized differences for each covariate. The estimated effects of treatment on clinical outcomes were determined using Cox regression models, and robust standard errors were used to account for the clustering of matched pairs. Survival curves of the propensity-matched cohort were constructed using Kaplan-Meier estimates and compared using the log-rank test. All data analyses were performed using SAS software version 9.1 (SAS Institute). A two-tailed P-value <.05 was considered statistically significant. 

Results

CTO incidence and treatment strategies. In total, 10,988 patients underwent coronary angiography at our hospital between February 2003 and March 2006. Of these, 955 patients (8.7%) had ≥1 CTO lesion. Of these, 377 (39.4%) were referred at physician’s discretion to undergo PCI. Of the remaining 578 CTO patients, 382 were managed using only medical therapy for various reasons, including inappropriate anatomy, patient or physician preference, distal lesion location, or comorbidities, and 196 patients underwent CABG due to coexisting multivessel stenosis (Figure 1).

Characteristics of the study patients. Of the 377 consecutive patients enrolled in this study, PCI was successful in 253 patients (67.1%) and failed in the remaining 124 (32.9%). Of the latter, 6 patients underwent urgent CABG during hospitalization after PCI failure due to severe, concordant coronary artery disease in another vessel. There were no serious procedure-related in-hospital deaths or major adverse events. 

Table 1 shows the baseline and angiographic characteristics of the enrolled patients. Compared with the failed-revascularization group, the successful-revascularization group was significantly younger and demonstrated a greater incidence of involvement of the left anterior descending artery and lower incidences of hyperlipidemia, renal failure, previous MI, and previous heart failure. In addition, the average CTO lesion length was longer in the failed-revascularization group (Table 2). Most patients (203 patients; 79.9%) received PCI with sirolimus-eluting stents. To minimize the effects of other non-CTO lesions, attempts were made to correct all suitable lesions using PCI. The incidences of non-target lesion intervention between the successful-revascularization group (41.1%) and failed-revascularization group (45.9%) were similar (P=.93).

Follow-up and long-term clinical outcomes. Over a median follow-up period of 2561 days (interquartile range [IQR], 1533-2996 days), 40 patients died, 10 developed MI, 13 developed stroke, and 41 underwent TVR due to progressive ongoing ischemia in the target coronary arteries. The successful-revascularization and failed-revascularization groups did not differ in terms of the overall incidence of the composite that included death, MI, stroke, or TVR over the 7-year follow-up period (26.5% vs 34.3%, respectively; log-rank P=.38 according to the Kaplan-Meier estimates) (Figure 2). In addition, the groups did not differ in terms of individual outcomes such as death, MI, TVR, or stroke.

IPTW analysis. After the data were adjusted using the IPTW method, there was still no significant association between PCI success and the composite outcome (adjusted hazard ratio [HR], 1.002; 95% confidence interval [CI], 0.577-1.741; P=.99), death (HR, 0.994; 95% CI, 0.474-2.081; P=.99), MI (HR, 0.529; 95% CI, 0.133-2.101; P=.36); TVR (HR, 0.871; 95% CI, 0.403-1.882; P=.72), or stroke (HR, 0.997; 95% CI, 0.139-7.129; P>.99) (Table 3, Figure 2)

Propensity-matched cohort. Table 3 shows the incidence of clinical outcomes in the two groups included in the propensity-matched cohort (91 matched pairs) over the 7-year follow-up period. A significant association between PCI success and primary endpoints was not observed (HR, 1.088; 95% CI, 0.621-1.905; P=.77). The two groups were also very comparable in terms of the incidences of individual events. 

Subsequent coronary artery bypass. Ten CABG surgeries were performed during the follow-up period, and the risk of subsequent CABG was higher in the failed-revascularization group (7 of 124 patients; 5.6%) vs the successful-revascularization group (3 of 216 patients; 1.2%) (P=.01). Of the 7 patients in the failed-revascularization group who underwent subsequent CABG procedures, 6 and 1 patient underwent CABG at 30 days or 2043 days after the index procedure, respectively. In contrast, the 3 patients in the successful-revascularization group underwent subsequent CABG at 160, 726, or 843 days after the index PCI, respectively.

Predictors of clinical outcomes. Multivariate analysis of the entire population revealed that the major determinants of the primary composite endpoint included left ventricular ejection fraction <40% (HR, 2.04; 95% CI, 1.08-3.83; P=.03), renal failure (HR, 2.63; 95% CI, 1.28-5.40; P=.01), and multiple CTOs (HR, 2.08; 95% CI, 1.17-3.69; P=.01). These three factors, along with age, also predicted mortality (HR, 1.12; 95% CI, 1.06-1.18; P<.001).

Stent thrombosis. Kaplan-Meier estimates revealed the incidence of definite or probable stent thrombosis to be 1.3% during the follow-up period. Four patients developed definite stent thrombosis (1 patient developed late thrombosis at 60 days, and 3 patients developed very late thrombosis at 1083, 2409, and 2642 days after the index PCI, respectively). 

Discussion

Several major findings emerged from this study. First, patients demonstrated similar long-term (7-year) clinical outcomes, regardless of successful or failed PCI. Second, left ventricular ejection fraction <40%, renal failure, and the presence of multiple CTOs were strong independent predictors of adverse outcomes. Third, the real incidence of CTO lesions in patients who received coronary angiography was 8.7%; of these, 39.4% underwent PCI in an attempt to revascularize their CTO(s). 

Several studies on the benefits of opening CTOs have reported conflicting results, which makes this procedure controversial. First, numerous studies report that patients who undergo successful CTO-PCI demonstrate lower mortality and cardiac event rates than patients who receive failed PCI.^12,14-21,33 However, most of these studies used diverse methods and definitions and focused primarily on the influence of successful PCI on mortality.^11,18,33 Moreover, several recent studies report that administering optimal medical therapy to patients with either stable or unstable CTO lesions is not inferior to successful CTO-PCI.^13,22,34 Small registry data suggest that medical therapy for failed CTO intervention may demonstrate outcomes comparable with successful CTO intervention.³⁴

This study examined 377 consecutive subjects and shows that opening CTO is not associated with long-term benefits through 7 years. To the best of our knowledge, the present study includes the longest follow-up duration of all published studies. Our findings suggest that medical treatments for patients with CTO lesions can be extrapolated to patients with true CTO. In addition, given that it is possible to achieve sufficient collateral flow if ischemic burden is well controlled, we hypothesize that the fate of patients with CTO lesions may be favorable, irrespective of revascularization.

In contrast to our current findings, several previous studies report that CTO success improves long-term outcomes.^{16,23-27,35,36} These differences may be due to several factors, including the enrolled study population, incidences of serious complications, revascularization of non-CTO lesions, and evolving medical treatments. In support of these findings, a large source of selection bias in the present study is that only 39% of patients with CTO lesions underwent CTO-PCI. Thus, the clinical outcomes of the remaining 61% of patients were not incorporated in our study. This bias may also apply to other studies to varying degrees, although here the incidence of PCI for CTO lesions is similar to a previously reported study.³ Moreover, it is possible that many patients with complex multivessel disease and CTO lesions were referred for CABG surgery, and thus were excluded from the present study cohort. This may have occurred in other studies to greater or lesser extent. It is also possible that our preprocedure and postprocedure management may explain why the failed-revascularization group demonstrated relatively favorable outcomes. In support of this, neither group differed in terms of TVR rates, even though the failed-revascularization group included 6 patients who required urgent CABG after failed CTO-PCI. In addition, there were no serious procedure-related complications in our study cohort. Finally, 12 of 124 patients with failed revascularization underwent subsequent revascularization with CABG or repeated revascularization. It is possible that subsequent coronary revascularization in patients with failed CTO-PCI may attenuate the possible long-term benefits of successful CTO-PCI. 

Because no randomized controlled trials comparing PCI vs medical therapy alone in patients with CTO lesions have been performed to date, and several studies report differences in the influence of PCI success on clinical outcomes, it remains unclear if successful CTO-PCI can improve outcomes. Another issue in CTO treatment is identifying patients who are most likely to demonstrate improved prognosis after CTO revascularization. Our current multivariate analysis showed that patients with a low ejection fraction, renal failure, or multiple CTOs were associated with worse outcomes. Therefore, a careful approach must be implemented in such high-risk patients. Our study underlines the importance of the ongoing need for further development of techniques and equipment to improve procedural success rates for CTO-PCI and large, randomized trials to demonstrate individualized risk assessment of CTO-PCI.

Study limitations. The present study has several limitations. First, it was a non-randomized, observational study and thus subject to the limitations inherent to this type of investigation. Indeed, our two study groups significantly differed in terms of baseline characteristics; thus, despite aggressive statistical adjustments, it remains unclear if our conclusion reflects the real effects of CTO-PCI or is related to hidden confounders. Moreover, there were too few patients to provide optimal statistical power. Second, uniform criteria for performing PCI on CTO lesions are unavailable, and therefore the decision was made by each attending physician. Thus, it may be difficult to extrapolate the observations and conclusions of the present study to CTO-PCI in general. Third, successfully intervening in the course of non-CTO lesions may have mitigated differences between groups. If there is sufficient collateral flow and preserved patency in the donor artery, the CTO is most likely stable. While our present investigation was designed to evaluate the impact of “true” CTOs on long-term clinical outcomes, we also attempted to revascularize any feasible non-CTO lesions, thus minimizing the impact of lesions in other vessels. The nature of the totality of disease and risk of progression would tend to equalize the outcome over time, even in CTO patients. Furthermore, we hypothesize that CTO-PCI failure is simply a marker of increased baseline complexity and the poorer outcomes seen in the failed group are related to the baseline burden of disease, rather than any effects of CTO-PCI. Fourth, we did not assess functional performance or subjective symptoms in our patients before or after the procedures were performed. Thus, we could not investigate the impact of recanalization on quality of life. Fifth, our data, which include an older CTO-PCI era, showed a relatively low success rate compared with the current CTO-PCI era; this factor could influence the clinical outcomes after successful or failed CTO-PCI. Finally, there is no information available regarding how myocardial territory viability affects the targeted lesions, which could affect final outcomes.

Conclusion

Over a 7-year follow-up period, patients who receive failed PCI to CTO lesions do not demonstrate any significant differences in terms of long-term clinical outcomes in comparison with patients who receive successful PCI. 

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From the ¹Division of Cardiology, Presbyterian Medical Center, Jeollabuk-do, Korea; ²Department of Applied Statistics, Gachon University, Gyeonggi-do, Korea; ³Division of Cardiology, Department of Internal Medicine, Kangbuk Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea; and ⁴the Division of Cardiology, Asan Medical Center, Ulsan University College of Medicine, Seoul, Korea. 

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein. 

Manuscript submitted June 11, 2015, provisional acceptance given June 26, 2015, final version accepted August 21, 2015.

Address for correspondence: Jong-Young Lee, MD, PhD, Division of Cardiology, Department of Internal Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea. Email: jyleeheart.lee@samsung.com