STRENGTHS AND LIMITATIONS OF THIS STUDY
-
This long-term follow-up of a randomised controlled trial with blinded outcome assessment helps fill the evidence gap regarding the sustained efficacy of remote ischaemic postconditioning.
-
Propensity score analysis using inverse probability of treatment weighting was employed to adjust for baseline confounding, enhancing the reliability of findings on functional outcomes and stroke/transient ischaemic attack recurrence.
-
The study was limited by reliance on telephone-based outcome assessment, which may introduce recall or reporting bias and by the small sample size, which precluded subgroup or sensitivity analyses.
Introduction
Stroke is a leading cause of mortality and disability with high recurrence rate, and ischaemic stroke accounting for 80% of all strokes.1 Despite intravenous thrombolysis (IVT) and endovascular thrombectomy in acute ischaemic stroke (AIS) have improved patient survival and functional outcomes,2 3 40–55% of these patients still experience poor functional outcomes (modified Rankin Scale score, mRS>2) at 90 days, mainly due to the narrow therapeutic window and the risk of induced ischaemia–reperfusion injury.4 5 Moreover, among patients who survived the initial 28 days after first stroke, the 5-year stroke recurrence rate was as high as 41%.6
In recent years, remote ischaemic conditioning (RIC) has emerged as a promising neuroprotective strategy aimed at enhancing brain tolerance to ischaemia and mitigating reperfusion injury. RIC involves brief, repetitive episodes of ischaemia and reperfusion applied to a limb, which can reduce infarct size, preserve blood-brain barrier integrity, attenuate post-stroke inflammation and stimulate endogenous angioneurogenesis.7–11 Our previous randomised, rater-blind study showed that the remote ischaemic postconditioning (RIPC) combined with IVT significantly improved favourable outcomes (mRS score 0–2) at 90 days in patients with AIS.12 The RICAMIS trial (Effect of Remote Ischaemic Conditioning vs Usual Care on Neurologic Function in Patients with Acute Moderate Ischaemic Stroke) further demonstrated that RIC improved outcomes in patients not receiving reperfusion therapy.13 In addition, accumulating evidence suggests that RIC is safe, feasible and well tolerated in various clinical settings.13–16 Although these findings are encouraging, some studies have reported inconsistent results, particularly regarding the short-term efficacy of RIC within 90 days.16–19 Moreover, evidence on its long-term impact remains limited,20 with very few studies exploring whether the benefits of repeated RIC during the acute phase of stroke can be sustained over time. Therefore, in this study, we aimed to evaluate the long-term effects (approximately 5 years) of RIPC combined with IVT on global disability in patients with AIS.
Materials and methods
Study design and population
This was a post-trial follow-up study, conducted as an exploratory and hypothesis-generating analysis, based on our previous randomised trial investigating the effect of RIPC combined with IVT in patients with AIS (ClinicalTrials.gov Identifier: NCT03218293).12 The study protocol was approved by the local ethics committee. All available patients from the prior trial cohort were included in this follow-up, and no additional sample size calculation was performed given its post hoc exploratory nature.
The details of the previous study, including patients, methods, design and procedures, have previously been published.12 Briefly, eligible patients had an independent daily living before stroke onset (mRS score ≤2) and a score of lower than 25 on the National Institutes of Health Stroke Scale (NIHSS), as well as being treated with IVT within 4.5 hours after onset of stroke. Between August 2017 and June 2018, a total of 68 patients with AIS who underwent IVT at the First Affiliated Hospital of Xi’an Jiaotong University were enrolled and randomised in a 1:1 ratio to the RIPC group (n=34) or the control group (n=34). Randomisation was based on the oddity of patient health card identification numbers.
Patients in the RIPC group received five cycles of cuff inflation (to 180 mm Hg for 5 min) followed by deflation (3 min) on both upper limbs using a portable device (IPC-906X; Beijing Renqiao Institute of Neuroscience, Beijing, China). RIPC was initiated within 3 hours after completion of IVT and administered two times a day throughout hospitalisation. The control group received standard post-stroke care without sham treatment. While treating physicians and nurses were unblinded to group allocation, all outcome assessors remained blinded.
Data collection
Patients completing the previous study were regularly followed-up in the outpatient department and invited to take part in this extended follow-up trial after providing oral informed consent. Post-trial data after discharge were collected in November 2022 via structured telephone interviews conducted by an experienced physician who was blinded to the original treatment allocation. All assessments were conducted by one single assessor. Nonetheless, the assessor has over 10 years of experience with stroke outcome evaluations, which helped minimise potential rating bias. All interviews were carried out in a private and confidential manner. Each interview lasted approximately 15–25 min, with an average duration of 20 min. Interviews were not recorded, but all responses were documented in real time using a standardised questionnaire (online supplemental material 1).
The interview began with a general inquiry: ‘How have you been doing since your discharge from the hospital after your stroke treatment?’ This was followed by specific, structured questions aligned with the research objectives, such as: ‘Have you experienced a recurrent stroke or TIA?’, ‘Do you have some symptoms, but they do not interfere with your daily activities (such as walking, dressing, eating, or personal hygiene)?’ or ‘Have you developed any new cardiovascular or thrombotic conditions such as atrial fibrillation, myocardial infarction, or deep vein thrombosis?’ Additional probing questions were asked when needed, such as: ‘When did that occur?’, ‘Was hospitalization required?’ or ‘What treatment did you receive?’.
Data collection continued until all predefined items were addressed and participants had no further relevant information to share. If participants were unable to recall certain information during the call, a follow-up interview was scheduled or permission was sought to access relevant medical records. The latest available laboratory results were also retrieved from hospital databases to supplement interview data when available.
Outcome measures
The primary outcome was the proportion of patients achieving a favourable functional outcome at the time of post-trial follow-up, defined as mRS score of 0 or 1, indicating no symptoms or no significant disability. Secondary outcomes included the proportion of patients achieving an independent outcome (mRS scores 0–2, representing functional independence in daily living), and incidence of all-cause mortality, first recurrent stroke/transient ischaemic attack (TIA) and other cardiovascular events. Recurrent stroke was determined by an adjudication committee and defined as sudden neurological dysfunction caused by brain, spinal cord or retinal injury as a result of infarction or haemorrhage. Only events occurring ≥21 days after the index stroke, or earlier if occurring in a clearly different vascular territory, were classified as recurrent strokes.21 TIA was defined as a transient episode of neurological dysfunction caused by focal brain, spinal cord or retinal ischaemia, with no acute infarction but high risk of early stroke and recovery of symptoms within 24 hours. Other cardiovascular events included myocardial infarction, pulmonary embolism, deep venous thrombosis and peripheral arteriopathy.
Statistical analysis
Analysis was performed on an intention-to-treat basis. Baseline clinical characteristics are presented as number and percentage, mean and SD or median and IQR, as appropriate.
In order to independently assess the treatment effect while accounting for potential imbalances due to the limited sample size, we performed a propensity score analysis using inverse probability of treatment weighting (IPTW). The propensity score was calculated through multivariable logistic regression using the values of the covariates in online supplemental table 1 (age at admission, NIHSS at admission, sex, hypertension, atrial fibrillation, diabetes mellitus, smoke, chronic heart disease). Covariates for the propensity score model were selected based on clinical relevance and potential association with treatment allocation or outcomes. Variables derived from laboratory findings at follow-up and duration of follow-up were excluded to avoid adjustment for post-treatment factors. Covariate balance after weighting was assessed using standardised mean differences, with values <0.1 indicating acceptable balance (online supplemental figure 1). Missing data for covariates used in the propensity score model were handled by multiple imputation using chained equations under the assumption of missing at random.
Binary outcomes (eg, mRS score at latest follow-up) were analysed using generalised linear models (GLM). The GLM with binomial distribution, and log and identity link functions generated risk ratio (RR) and risk difference (RD) with their 95% CIs, respectively. RR reflects the relative likelihood of an outcome between groups, while RD provides the absolute difference in event rates, which may be easier to interpret in clinical contexts. Time-to-event data (eg, first recurrent stroke/TIA and all-cause mortality), IPTW-weighted Kaplan-Meier survival curves and corresponding weighted log-rank tests were used to visualise and compare groups. For other time-to-event outcomes, IPTW-weighted Cox proportional hazards models were used to estimate HRs with 95% CIs. Both unadjusted and adjusted treatment effects weighted by IPTW were calculated. For all analyses, a two-sided value of p<0.05 was considered statistically significant. All statistical analysis was performed using R V.3.6.0.
Patient and public involvement
Patients or members of the public were not involved in the design, conduct, reporting or dissemination of this research.
Results
The original trial included 68 patients allocated either to the control group (n=34) or the RIPC group (n=32). 3 patients in the control group and 1 patient in the RIPC group were lost to follow-up, leading to 62 patients included in the current follow-up investigation for long-term outcomes (figure 1). The overall time interval from randomisation to latest follow-up was 4.8 years (more than 4.8 years in 67.2% of patients; IQR 4.6–5.1). The median follow-up length in the control group and RIPC group were 4.8 years (IQR 4.6–4.9) and 5.1 years (IQR 4.8–5.2).
Study profile. IV, intravenous; IV tPA, intravenous tissue plasminogen activator; RIPC, remote ischaemic postconditioning.
Baseline characteristics of the univariate analyses for RIPC and control group before and after IPTW adjustment are given in table 1 and online supplemental table 1. Before adjusting for IPTW, patients in the RIPC group had longer follow-up time than patients in the control group (5.1 years vs 4.8 years), and more likely to have lower latest systolic blood pressure (133 mm Hg vs 140 mm Hg). Sex, age, medical history and other laboratory findings at latest follow-up were comparable in two groups.
Demographic and clinical characteristics at baseline
Among the 62 patients with available data at the latest follow-up (median follow-up: 4.8 years in the control group (IQR 4.6–4.9) and 5.1 years in the RIPC group (IQR 4.8–5.2)), 9 out of 31 patients (29.0%) in the control group and 19 out of 31 patients (61.3%) in the RIPC group had a favourable outcome (defined as mRS score of 0–1) (unadjusted RR, 3.87; 95% CI 1.34 to 11.17; p=0.012 and unadjusted RD, 32.26; 95% CI 7.86 to 54.08; p=0.007) (table 2 and figure 2). IPTW
Distribution of modified Rankin Scale scores at long-term follow-up. Median follow-up duration was 4.8 years (IQR 4.6–5.1 years) from randomisation. Scores range from 0 to 6: 0=no symptoms; 1=symptoms without clinically significant disability; 2=slight disability; 3=moderate disability; 4=moderately severe disability; 5=severe disability; and 6=death. mRS, modified Rankin Scale; RIPC, remote ischaemic postconditioning.
The primary and secondary outcomes of long-term follow-up in patients treated with RIPC or control
-weighted GLM model confirmed that RIPC treatment was associated with an increased probability of favourable outcome after taking adjustment variables into account when compared with control group (IPTW-adjusted RR, 5.92; 95% CI 1.45 to 24.24; p=0.017 and IPTW-adjusted RD, 27.34; 95% CI 10.05 to 43.53; p=0.002). Before IPTW adjustment, there was no significant difference in the proportion of having an mRS score of 0–2 between the two groups (p=0.07, table 2). As expected, a significant effect of RIPC treatment (IPTW-adjusted RR, 5.88; 95% CI 1.07 to 32.29; p=0.047 and IPTW-adjusted RD, 19.55; 95% CI 2.14 to 36.18; p=0.025) was confirmed after IPTW-weighting (table 2).
The cumulative number of all-cause mortalities during the follow-up period (median follow-up: 4.8 years in the control group and 5.1 years in the RIPC group) was 9 (29.0%) in the control group and 6 (19.4%) in the RIPC group. There was no significant difference in the cumulative rate of all-cause mortality either before or after IPTW analysis (unadjusted RR, 0.59; 95% CI 0.18 to 1.91; p=0.376; IPTW-adjusted RR, 0.43; 95% CI 0.10 to 1.98; p=0.286). The findings were consistent if outcomes were analysed with the Cox model before and after IPTW adjustment (unadjusted RR, 0.56; 95% CI 0.20 to 1.58; p=0.272; IPTW-adjusted RR, 0.57; 95% CI 0.20 to 1.63; p=0.292; table 2 and online supplemental figure 2).
During the follow-up, 9.7% (3/31) of participants in the RIPC group and 29.0% (9/31) in the control group had stroke/TIA recurrence. As shown in table 2, there were no significant differences in overall stroke/TIA recurrence rates between the two groups, whether calculated by the unadjusted Cox model (HR, 0.29; 95% CI 0.08 to 1.06; p=0.061) or the IPTW-adjusted model (HR, 0.25; 95% CI 0.06 to 1.00; p=0.050, table 2). However, a landmark analysis highlighted differences in recurrence-free survival over time. A landmark analysis was further performed to assess recurrence-free survival over time. During the initial 12 months after randomisation, there was no evidence of difference in stroke/TIA recurrence-free survival between the two groups (IPTW-adjusted HR, 1.93; 95% CI 0.18 to 20.32, p=0.585 by log-rank test, figure 3). After 12 months, however, the RIPC group demonstrated significantly higher stroke/TIA recurrence-free survival compared with the control group (IPTW-adjusted HR, 0.06; 95% CI 0.01 to 0.49, p=0.009 by log-rank test, figure 3).
Kaplan-Meier (A) and landmark (B) analysis of stroke/TIA recurrence-free survival during the long-term follow-up period after randomisation. All the statistics were adjusted after inverse probability of treatment weighting. HR=HR ratio median follow-up duration was 4.8 years (IQR 4.6–5.1 years) from randomisation. RIPC, remote ischaemic postconditioning; TIA, transient ischaemic attack.
Discussion
This study revealed several points: first, after approximately 5-year follow-up, RIPC combined with IVT treatment in patients with AIS resulted in a higher proportion of patients with a favourable outcome (mRS score of 0 and 1). Second, the stroke/TIA recurrence-free survival was better in the RIPC group than in the control group during the long-term follow-up period.
Previous studies have shown that RIC as an adjunctive treatment for ischaemic stroke may significantly improve patient outcomes at 3 months.13 22 However, it remains unclear whether short-term application during the acute phase can improve the long-term outcomes of patients with AIS. We showed that the patients with favourable outcomes in the RIPC group were higher than the control group even a median of 4.8 years after IVT. Although the long-term follow-up results only showed a slightly lower proportion of mRS 0–1 in the RIPC group than originally reported results at 90 days (71.9% at 90 days vs 63.3% at long-term follow-up), the control group seemed to present a greater decline in proportion of favourable outcome (defined as mRS score of 0–1) at long-term follow-up (50.0% at 90 days vs 32.1% at long-term follow-up). It is in line with the report that the proportion of functional improvement is greatest in the first 3 months after stroke, with limited improvement thereafter.23 24 However, long-term follow-up studies have indicated that these early improvements may not be sustained over the long term.25 26 Meyer et al observed that patients’ functional and motor outcomes declined over time, returning to levels similar to those measured at 2 months post-stroke when followed-up at 5 years.25 At approximately 5 years after randomisation, improvements in functional outcomes were retained in the RIPC group compared with control group in our study, despite a decrease in the magnitude of recovery in both groups.
Previously reported 5-year cumulative stroke recurrence rates of 14%–26%27 were similar to the 29% recurrent rate in the control group and higher than the 9.7% rate in the RIPC group in our long-term follow-up study. A meta-analysis designed to assess the efficacy and safety of RICs, which included 17 randomized controlled trial (RCT) studies, found that chronic RIC significantly reduced stroke recurrence rates at the endpoint of each study.28 Similarly, two small clinical studies performed in patients with intracerebral artery stenosis (ICAS) suggested that repeated RIPC for 300 days and 180 days can significantly reduce the risk of recurrent stroke.29 30 In addition, a recent study evaluating the effect of RIC applied for more than 1 year showed that RIC was effective in reducing ischaemic stroke recurrence in patients with symptomatic ICAS with better adherence (defined as >50% of days).20 Considering the findings of these studies and our study, we are reasonable to speculate that repeated RIPC may have a tendency to improve stroke/TIA recurrent survivals over a long time.
In this study’s explorative analyses, no significant differences were observed in cumulative stroke/TIA recurrence rates between the two groups over the entire follow-up period. However, the lower occurrence of recurrent stroke/TIA in the RIPC group began to appear approximately 12 months after AIS. Although RIPC was applied only in the early post-stroke phase, its long-term benefits may result from sustained effects on modulation of inflammation, vascular remodelling and neuroprotection.31 Animal studies have demonstrated that transient RIPC can suppress microglial activation and reduce delayed neuronal apoptosis,32 suggesting prolonged neuroprotective effects beyond the intervention period. Moreover, RIC may stimulate endogenous angioneurogenesis. Previous animal-based studies found that RIPC can induce sustained neurological recovery and long-term neuroprotection by promote the angiogenesis and neurogenesis, but in the subacute stages of stroke the neuroprotective effect of RIPC was not obvious.10 Angiogenesis and neurogenesis begin within 4–7 days after cerebral ischaemia,33 and neural progenitor cells act as ‘mini-pumps’ that continually secrete growth factors and other mediators. It was not until 3 months after the stroke that RIPC-induced growth factor concentrations in mice brain were significantly higher than in controls.
There are several limitations in our study. First, follow-up assessments were conducted retrospectively and not at a specific point in each patient’s disease course, which may introduce a recall bias. Second, all functional outcome data were collected by telephone interviews, potentially leading to some inaccuracies. Lastly, due to limited sample size, no subgroup or sensitivity analyses were performed, as such analyses would be underpowered and potentially yield unstable estimates.
Despite these limitations, our study provides preliminary long-term evidence of RIPC’s potential benefit. Larger, double-blind, multicentre randomised trials, along with mechanistic studies, are needed to validate these findings and elucidate the biological underpinnings of RIPC in stroke recovery.
Conclusion
In this exploratory follow-up study, IVT combined with repeated RIPC during hospitalisation after AIS may have a long-term effect on improving functional recovery and preventing recurrent stroke/TIA. Some multicentre larger trials are essential to confirm these findings.
Data availability statement
Data are available upon reasonable request. Data are available upon reasonable request. Data are available from the corresponding author upon request and subject to ethical approval.
Ethics statements
Patient consent for publication
Ethics approval
This study involves human participants and was approved by Ethics Committee of The First Affiliated Hospital of Xi’an Jiaotong University, XJTU1AF2022LSK-407. Participants gave informed consent to participate in the study before taking part.
Acknowledgments
The authors thank Professor Ji Xunming and his team from the Department of Neurosurgery, Xuanwu Hospital, Capital Medical University, Beijing, China, for providing the RIPC devices.
