Remote Ischaemic Conditioning in Endovascular Recanalization for Proximal Anterior Circulation Occlusion Study

The aims of our study are to:

1. Demonstrate safety of remote ischaemic conditioning (RIC) in stroke patients;
2. Demonstrate practicality of the intervention (RIC);
3. Demonstrate the practicality of the study protocol and imaging modalities;
4. Determining appropriate and measurable end-points: e.g. cerebral infarct reduction (MRI), reduction of cerebral oedema, functional assessment and quality of life survey;
5. Provide preliminary data on likely effect size of the RIC intervention versus the sham procedure.

Background and Rationale:

Acute ischaemic stroke represents a significant cause of morbidity and mortality in the UK. It is estimated that 110,000 strokes occur in England each year, with an incidence of between 1-36/1000/year. Patients presenting with a proximal vessel occlusion in the anterior circulation have a particularly poor prognosis, with approximately 20% 90-day mortality and significant morbidity despite thrombolysis. Recently, endovascular recanalization with mechanical thrombectomy trials have brought about a paradigm shift in the optimal management of this high-risk group of patients; the interventional extraction of the occluding thrombus demonstrating significant benefits in MR-CLEAN(3), ESCAPE, EXTEND-IA (intra-arterial), SWIFT PRIME and REVASCAT (revascularisation) studies. Echoing primary percutaneous intervention in the management of ST-elevation myocardial infarction, endovascular recanalization represents rapid restoration of blood flow to the ischaemic cerebrum - with the promise of improved neurological salvage and functional outcome.

Reperfusion Injury:

Reperfusion is not, however, a benign process. Demonstrable in many organ systems including the brain (but studied most extensively in the heart), reperfusion leads to rapid restoration of intracellular pH, mitochondrial calcium overload and generation of reactive oxygen species - conditions that are prime for the opening of the mitochondrial permeability transition pore (mPTP). The mPTP, a large capacitance pore that forms on the inner mitochondrial membrane, leads to mitochondrial disruption and the release of proteins that trigger cell death. Therefore modifying conditions of reperfusion/ triggering cellular protection pathways are the key targets for optimising tissue salvage associated with reperfusion following any acute revascularisation intervention.

Remote ischaemic conditioning:

The brain has been demonstrated to share many of the cytoprotective signalling pathways found in other organs such as the heart, and like the heart, can be protected by ischaemic conditioning(6). Ischaemic conditioning can be either applied either directly to the organ, or more conveniently to a remote tissue (such as an arm, through inflation of a blood pressure cuff), either prior to, during or immediately following the restoration of blood flow to the ischaemic tissue (pre-, peri- and post-conditioning respectively). The remote conditioning stimulus leads to the activation of cellular survival kinases (termed the reperfusion injury salvage kinase (RISK) cascade) that in turn leads to inhibition of mPTP opening, and thus cell survival.

Ischaemic conditioning and neuro-protection:

While the phenomenon of ischaemic conditioning was first described and best characterised in the heart, it is well recognised that the ischaemic conditioning can result in cytoprotection across many mammalian organs, including the brain. Indeed, contemporaneous with the seminal myocardial preconditioning paper by Reimer, Murray and Jennings in the dog, Schurr et al demonstrated ischaemic preconditioning could also protect adult rat hippocampal slices against injurious anoxia/re-oxygenation. Ischaemic conditioning of neuronal tissue has subsequently been demonstrated to be triggered and mediated by similar receptor and downstream signalling pathways (e.g. G-protein coupled receptors, RISK pathway activation and suppression of cell death pathways), and that remote ischaemic conditioning is also effective at significantly attenuating the volume of cerebral necrosis in rat experimental models of acute right middle cerebral artery occlusion stroke (typically reducing infarct size by 40-60%). Similar results are observed in mouse (middle cerebral embolization, followed by thrombolysis with tissue-plasminogen activator) and in piglet, where the injurious effects of hypothermic circulatory arrest were attenuated, improving both functional and histological outcomes.

With building evidence of efficacy against cerebral ischaemia/reperfusion injury in the pre-clinical basic science studies, there is enthusiasm to translate these encouraging data into an effective clinical strategy for the management of acute stroke in man. A recent prospective, open-label, blinded outcome proof-of-concept study in Danish patients undertook ischaemic per-conditioning in patients presenting with an acute stroke syndrome. With the conditioning stimulus performed in the ambulance, the ischaemic stroke diagnosis was made/confirmed later in hospital. In patients with confirmed ischaemic stroke, they found patients in the intervention arm had a better functional status by National Institutes of Health Stroke Scale score on admission and an overall smaller infarct, but the study was overall neutral on the pre-specified primary endpoint (penumbral salvage, defined as the volume of the perfusion-diffusion mismatch not progressing to infarction after 1 month). There are useful lessons and observations to be made regarding the design of this trial that influences the design of the trial proposed within this application. First, thrombolysis does not guarantee re-canalisation of the culprit artery, and where restoration of blood flow does occur, the time of onset of reperfusion may be unpredictable. Thus, restoration of blood flow may either not have occurred, or when it had, may have occurred outside the protective time-frame of the remote ischaemic conditioning stimulus (classical conditioning has a protective "window" of typically just 2-3 hours).

Therefore, we are seeking to combine ischaemic conditioning with an effective endovascular re-canalisation procedure where the success and time of reperfusion are known. Second, in the Danish study, there would have been significant heterogeneity in aetiology of the presenting stroke symptoms that will include both anterior and posterior circulation occlusion and also small vessel disease. The pre-clinical efficacy of remote ischaemic conditioning is predominantly with models of anterior circulation occlusion and therefore, we have made this cohort of patients the focus of our study. And finally, there is emerging evidence that in order to ensure persistent infarct size reduction, it is critical to combine both initial ischaemic per-conditioning and subsequent post-conditioning to tackle both the acute reperfusion injury (the first 15 minutes of reperfusion) and the subsequent second phase of reperfusion injury (that occurs in the following hours and days). Thus our study is designed to combine both ischaemic per-conditioning and repeated post-conditioning over the following seven days to harvest the benefit of both conditioning strategies.

Interestingly, a Chinese study (RIC to both arms daily for 300 days after the initial stroke) was shown to be safe and effective. While this study had a different outcome to ours (attenuating the rate of stroke recurrence following the initial presentation), the efficacy of the RIC intervention nonetheless provides further encouragement that RIC may be an effective intervention in this group of patients.

In summary therefore, we are seeking to combine ischaemic conditioning with an effective endovascular re-canalisation procedure where the success and time of reperfusion are known, in a vascular territory that is known to benefit from RIC and are looking to combine both ischaemic per-conditioning and repeated post-conditioning over the following seven days to harvest the benefit of both conditioning strategies upon acute and inflammatory phases of reperfusion injury - encompassing the period over which peak cerebral oedema is typically observed.