Basic Research in Cardiology (2022) 117:39 https://doi.org/10.1007/s00395-022-00947-2 MEETING REPORT Remote ischaemic conditioning: defining critical criteria for success—report from the 11th Hatter Cardiovascular Workshop R. M. Bell1 · M. Basalay1 · H. E. Bøtker2 · S. Beikoghli Kalkhoran1 · R. D. Carr1 · J. Cunningham3 · S. M. Davidson1 · T. J. England4 · S. Giesz1 · A. K. Ghosh1 · P. Golforoush1 · A. V. Gourine5 · D. J. Hausenloy1,6,7,8 · G. Heusch9 · B. Ibanez10,11,12 · P. Kleinbongard9 · S. Lecour13 · K. Lukhna13 · M. Ntsekhe13 · M. Ovize14 · A. D. Salama3 · G. Vilahur15 · J. M. Walker1 · D. M. Yellon1 Received: 3 August 2022 / Revised: 3 August 2022 / Accepted: 3 August 2022 / Published online: 15 August 2022 © The Author(s) 2022 Abstract The Hatter Cardiovascular Institute biennial workshop, originally scheduled for April 2020 but postponed for 2 years due to the Covid pandemic, was organised to debate and discuss the future of Remote Ischaemic Conditioning (RIC). This evolved from the large multicentre CONDI-2–ERIC–PPCI outcome study which demonstrated no additional benefit when using RIC in the setting of ST-elevation myocardial infarction (STEMI). The workshop discussed how conditioning has led to a significant and fundamental understanding of the mechanisms preventing cell death following ischaemia and reperfusion, and the key target cyto-protective pathways recruited by protective interventions, such as RIC. However, the obvious need to translate this protection to the clinical setting has not materialised largely due to the disconnect between preclinical and clinical studies. Discussion points included how to adapt preclinical animal studies to mirror the patient presenting with an acute myocardial infarction, as well as how to refine patient selection in clinical studies to account for co-morbidities and ongoing therapy. These latter scenarios can modify cytoprotective signalling and need to be taken into account to allow for a more robust outcome when powered appropriately. The workshop also discussed the potential for RIC in other disease settings including ischaemic stroke, cardio-oncology and COVID-19. The workshop, therefore, put forward specific clas- sifications which could help identify so-called responders vs. non-responders in both the preclinical and clinical settings. Keywords Ischaemia reperfusion injury · Remote ischaemic conditioning · Cardiovascular 9 * D. M. Yellon Institute for Pathophysiology, West German Heart d.yellon@ucl.ac.uk and Vascular Center, University of Duisburg-Essen, Duisburg, Germany 1 The Hatter Cardiovascular Institute, University College 10 Centro Nacional de Investigaciones Cardiovasculares London, 67 Chenies Mews, London WC1E 6HX, UK (CNIC), IIS-Fundación Jiménez Díaz University Hospital & 2 Aarhus University Hospital and Aarhus University, Aarhus, CIBERCV, Madrid, Spain Denmark 11 CIBER de Enfermedades Cardiovasculares (CIBERCV), 3 Royal Free Hospital, London, UK Madrid, Spain 4 12 Stroke, Division of Mental Health and Clinical IIS-Fundación Jiménez Díaz Hospital, Madrid, Spain Neurosciences, School of Medicine, University 13 University of Cape Town, Cape Town, South Africa of Nottingham, Nottingham, UK 14 5 INSERM U1060, CarMeN Laboratory, Université de Lyon, Centre for Cardiovascular and Metabolic Neuroscience, Groupement Hospitalier Est, Bâtiment B13, F‑69500 Bron, Neuroscience, Physiology and Pharmacology, University France College London, London, UK 15 6 Institut de Recerca de l’Hospital de la Santa Creu i Sant Pau, CVMD, Duke-NUS, Singapore, Singapore CIBERCV, Barcelona, Spain 7 National Heart Research Institute Singapore, National Heart Centre, Singapore, Singapore 8 Cardiovascular Research Center, College of Medical and Health Sciences, Asia University, Taichung City, Taiwan 13 Vol.:(0123456789) 39 Page 2 of 12 Basic Research in Cardiology (2022) 117:39 Background Is RIC simply an intervention that cannot be translated from animal studies into the clinical setting (despite Remote Ischaemic Conditioning (RIC) has been shown encouraging data from early phase clinical studies), or are consistently to be an effective experimental intervention we looking at the wrong target for intervention? Despite for the reduction of ischaemia–reperfusion injury in all these doubts, grant awarding bodies are still funding clini- organ systems and animal species that have been studied cal trials. This speaks volumes regarding the persisting to date. The phenomenon is not new. Przyklenk’s group clinical need to improve outcomes following ischaemic first described in the heart that non-injurious ischaemia in emergencies and the acknowledgement of the relevance one coronary artery territory (i.e., circumflex) would lead of reperfusion injury. However, is the continued study to protection in an adjacent coronary vascular bed (dis- of RIC an appropriate and ethical use of resources? This tal to the left anterior descending occlusion in this study) was the basic premise for the 11th Hatter Cardiovascular almost 30 years ago [78]. MacAllister’s group were the Research Workshop, recently held in South Africa. The first to demonstrate inter-organ RIC in humans [55] and latest research in RIC in various models, including heart, this observation has since been extended to reveal that kidney and the brain were discussed and debated and the practically any organ system put under ischaemic stress question of how best to target RIC, an intervention that leads to the upregulation of cytoprotective pathways in has been repeatedly demonstrated to be safe in the clinical remote visceral tissues [46, 57]. These prosurvival path- setting, addressed. A recurring theme arising in the discus- ways have been shown repeatedly to reduce cell death sions was on whether it was time to “get back to basics” and infarction in response to injurious ischaemic injury and to finally identify the complete and precise mecha- in models that replicate clinical syndromes, such as acute nism by which RIC works, or whether RIC is a “therapy myocardial infarction, acute ischaemic stroke and acute in need of re-targeting”. To this end, it may be useful to ischaemic kidney injury [20, 31]. Given the promise of define which are the critical criteria for successful induc- strong basic research, and indeed the promising data from tion of cardioprotection using RIC—a point that will be clinical proof-of-concept trials, there has been a strong elaborated below. desire to translate what had promised to be a robust, low- cost, non-pharmacological intervention to further improve patient outcomes. Back to basics: understanding remote ischaemic conditioning While gaps in knowledge belying RIC signalling were not Failure of translation felt to represent a significant obstacle to clinical translation, recent neutral clinical outcome trials will force the field to However, attempts at clinical translation thus far have redress these omissions. not realised the uniformly effective intervention that had been either anticipated or hoped for. In recent years, large How does remote ischaemic conditioning work? patient outcome trials looking at the efficacy of RIC in the context of primary percutaneous intervention and In the ~ 30 years since the first description of RIC, the field cardiac surgery have proven predominantly neutral [43]. has expanded significantly, leading to a far greater under- The same is true in the setting of renal transplantation, standing of both the mechanisms preventing cell death fol- although the results are somewhat more mixed. While lowing injurious ischaemia and subsequent reperfusion, and most trials in deceased donor transplantation showed no the key target cyto-protective pathways recruited by pro- benefit following RIC [59, 97], in some—but not all— tective interventions, such as RIC. However, there remain living-donor studies of efficacy, estimated glomerular fil- significant gaps in our scientific knowledge as to how RIC tration rate (GFR) was improved in those patients who recruits signalling from one tissue bed, such as a limb, to received RIC [1, 71, 91]. The critical question, therefore, result in protection in remote organs. This knowledge gap is “Why?” Why is there an apparent disconnect between in how RIC functions could be critical, since it could have positive animal models and neutral clinical trials? This led to vulnerabilities of this pathway being overlooked. For vexing clinical translational question has been the subject example, the potential for the interaction of co-morbidi- of previous discussions and debate [7, 20, 28, 42, 43, 49, ties and coincident medical interventions to interfere with 83] that have led to a number of recommendations and the effective recruitment of cytoprotective signalling [26, actions, but the question of the viability of RIC as a clini- 56]. Another outstanding question relates to whether RIC cal intervention in acute ischaemic emergencies remains. can potentially be used to limit ischaemic injury itself as opposed to reperfusion injury alone [6, 56]. 13 Basic Research in Cardiology (2022) 117:39 Page 3 of 12 39 Fig. 1  Four main categories of potential failure in the application of Remote Ischaemic Conditioning The current model of RIC signalling from the limb to under the nervous control). This was first demonstrated a remote internal organ suggest that this is via a neuro- by Redington’s group through the extraction of plasma humoral pathway (Fig. 1) [3, 57]. The neural pathway from conditioned subjects and perfusing this through a recruits afferent innervation of the peripheral tissue under- naïve heart, which demonstrated a significant reduction going RIC [75]. These sensory nerves are activated by in infarct size in the naïve heart as it did in the heart of the ischaemic stimulus, and recruit efferent activity of the the animal that directly received RIC [86]. Yellon’s group vagus nerve [68, 73]. Vagotomy at various levels leads to confirmed this and further demonstrated the co-depend- abrogation of cardioprotection induced by RIC [76]. Gou- ence of the neural and humoral pathways in the mecha- rine’s group found that RIC is abolished in the rat model nism of RIC [75]. However, the humoral component and by total subdiaphragmatic vagotomy, gastric vagotomy its source remain controversial, although it is thought to or sectioning of the posterior gastric branch. However, be a small molecule (of less than 12–14 kDa) [75]. Numer- the efficacy of RIC cardioprotection was unaffected by ous potential candidates have been suggested, e.g., the hepatic, celiac or anterior gastric vagal branch transection 3.3 kDa Glucagon-like peptide-1 (GLP-1) [4, 72] and the [67, 69]. Moreover, electrical stimulation of the posterior 18 kDa immunoregulatory glycoprotein, interleukin-1α, gastric branch of the vagus reduced infarct size, mimicking interleukin-10, Stromal-derived factor 1a, and nitrite [13, the effect of RIC [67]. Heusch’s group similarly found that 22, 80] (reviewed in [57, 90]). Protection in circulating vagotomy abrogated RIC, although in the pig, in contrast blood, however, is not only mediated by circulating soluble to the rat, splenic rather than posterior gastric vagotomy factors [19], but also by components mediated by blood abrogated RIC-induced protection [64]. In fact, in pigs the cells (e.g., platelets [79] and extracellular vesicles [92]), spleen is the central relay organ between the neuronal and which may mask relevant protective components intracel- humoral cardioprotective signalling pathways [44]. How- lularly or intravesicularly. As yet, however, there is not a ever, the nervous system involvement does not appear to definitive answer to the elusive question of the circulat- be limited to the direct effect of the vagal innervation on ing factor, particularly in man [50, 65], and yet, if this the myocardium. Instead, remote organ protection appears could be resolved, then we would be in a better position to require the release of a humoral factor (which could be to develop a biomarker of RIC signalling activation, to 13 39 Page 4 of 12 Basic Research in Cardiology (2022) 117:39 facilitate our understanding the impact of co-morbidity protocols in animal models, but multiple co-morbidities or upon RIC and how such problems in clinical translation indeed co-medications are rarely, if ever, fully investigated could be overcome. in animal models. In reality, the true model that we need to consider here is the human “model”, more specifically Are we giving the correct remote ischaemic the patient who commonly presents with an acute ischaemic conditioning stimulus? syndrome, with all the attendant co-morbidities, such as ath- erosclerosis, age, diabetes etc., that these patients inevitably Perhaps surprisingly, the duration of limb ischaemia, the present with. In retrospective analyses of the limited existing number of cycles required and even the pressure of the clinical data, there is less solid clinical evidence for an effect cuff used to occlude arterial blood supply to the limb have of co-morbidities and co-medications on cardioprotection. received limited attention [53, 81, 93]. The regimen that Evidence for an influence of co-medications comes from has been most widely deployed to date—that of three to studies using antiplatelet agents which can, in themselves, four cycles of 5-min ischaemia, using a standard blood pres- elicit cardioprotection thus limiting the potential for further sure cuff that is generally inflated to 200 mmHg (or alterna- protection [15, 98]. In addition, the anaesthetic, propofol has tively 20 mmHg above systolic blood pressure), appears to also been shown to abrogate RICs protection during cardio- have been arrived at almost empirically, although there are vascular surgery [56]. abundant studies that show this protocol to be effective in In terms of optimising RIC “dose” in humans, currently a variety of animal models. However, is this protocol best the only way a dose–response curve can currently be con- optimised for effectiveness in multi-morbid patients with a structed is through assessment of a clinical endpoint, such background polypharmacy? as infarct size as the biomarker of RIC efficacy. This is a Perhaps the closest we can currently come to addressing difficult and expensive way of optimising a RIC regimen that this question is to look at the data that have already been may require many iterations in many different populations published in the setting of both acute myocardial infarction of patients with differing co-morbidities to identify the ideal and ischaemic stroke. Several groups have undertaken a RIC protocol. It is possible that flow-mediated dilatation or meta-analysis of remote conditioning protocols in basic and heart-rate response could be used as a biomarker of an effec- clinical settings, with the aim of ascertaining their ability tive RIC application [55], but bedside acquisition of such to protect and whether any observation can be made with measurements requires considerable skill to perform well, respect to the ischaemic stimulus itself in these two disease with results open to interpretation bias. A blood biomarker settings [12, 49, 62, 94]. In the stroke model [94], the meta- would be preferable for the ease and consistency of measure- regression did not reveal any relationship between cycle ment—and perhaps a panel of biomarkers to enable us to not number or cycle duration, the number of limbs used simul- only demonstrate an activated vagal signalling arc, but also taneously in the application of RIC and the efficacy of RIC release of humoral mediator and downstream cytoprotec- to reduce cerebral ischaemic injury. RIC must be applied tive activity within the organ of interest itself. The perfused prior to or possibly shortly after the onset of reperfusion, rodent heart has been used as a bioassay for humoral cardio- since its efficacy rapidly diminishes the later it is applied protective factors released in human individuals undergoing after the onset of myocardial reperfusion [2]. In terms of RIC [50, 65]. the “dose” of RIC (the total duration of limb ischaemia applied), as long as the ischaemic conditioning durations Classifying failure of remote ischaemic conditioning were between 15 and 45 min (irrespective of cycle number protection used to achieve this), cerebral infarct volume was demon- strably reduced. However, it was not possible to assess the It would be very helpful to be able to identify the reasons interaction of age, gender or co-morbidity. In the myocar- for failure to protect against injurious ischaemia by RIC, and dial infarct model, there was also no association observed thereby identify likely responders and non-responders. As between various cycle lengths, with 10-min cycles being alluded to previously, patients are frequently multi-morbid equally effective as 5-min cycles. As has been discussed and are often on therapy that can modify cytoprotective at previous meetings and in numerous reviews, any one of signalling. these factors, and possibly all three, are important in consid- As discussed above, the timing and dose of the RIC inter- ering the efficacy of intervention [26, 37, 96]. vention is important for obtaining maximal cardioprotec- Yellon’s group showed that in some cases, co-morbidities tion. As such, inappropriate timing or insufficient dose may can be overcome through increasing the number of cycles of result in failure of RIC (Category 1a RIC protection failure, RIC (effectively increasing the “dose” of the conditioning Table 1). Classical cardiovascular risk factors, such as dia- stimulus) to overcome a weakening of fundamental cyto- betes, are well known to reduce neuronal signalling—the protective signalling cascade response to standard RIC neuropathy encountered in diabetes includes sensory nerve 13 Basic Research in Cardiology (2022) 117:39 Page 5 of 12 39 Table 1  Defining critical criteria and potential pitfalls for success Category Possible causes 1 Signalling failure (Co-morbidities) (a) Insufficient dose of RIC or inappropriate timing to initiate signal- ling (b) Failure of nociception afferent signalling (c) Failure of efferent vagal signalling (d) Failure of sufficient release of humoral factor (e) Failure of target organ to respond to humoral factor 2 Target organ already protected prior to RIC (e.g., Co-medications) (a) Presence of significant collateral flow reducing infarct development (b) Administration of co-medications that are themselves cardioprotec- tive (morphine, P­ 2Y12 inhibitors, propofol, statins etc.) 3 Study underpowered (Experimental design) (a) Duration of ischaemia insufficient to lead to a large enough infarct to detect a significant change in infarct size (b) Insufficient numbers per group to detect a significant difference 4 Target organ severely damaged (Study protocol design) Duration of ischaemia excessive, resulting in irreversible injury to the majority of the area at risk Possible explanations for the failure of RIC to demonstrate cardioprotection dysfunction and vagal autonomic dysfunction [52]—and this This may have been the case in the recent large multicen- may well result in failure of RIC (Category 1b&c, respec- tre CONDI-2–ERIC–PPCI study which demonstrated that tively, Table 1). Even non-traditional co-morbidities, such RIC was not able to improve clinical outcomes [33]. What as chronic renal impairment, leads to vagal dysfunction is more, it is interesting to note that the mortality from car- [84] that in turn is likely to result in category 1b or 1c RIC diovascular death in the control group was only 2.7%. This protection failure. Co-morbidities may impair release of the suggests that these clinical studies using patients in coun- humoral factor or result in the target organ not responding tries with well-established cardiac coronary care, are of such to the humoral factor, again resulting in failure of RIC (cat- low risk that additional therapy is unlikely to demonstrate egories 1d and 1e, respectively, Table 1). any further benefit in outcome. This is despite the fact that, The drugs used to manage co-morbidities (for example, outside of clinical studies, mortality rates for hospitalized HMG CoA reductase inhibitors for hypercholesterolaemia) STEMI patients in Europe remain in the region of 15–25% or the acute ischaemic syndrome itself (e.g., the use of [38], which demonstrates that there clearly remains a need ­P2Y12 receptor antagonists in acute ST-elevation myocardial for cardioprotective strategies, even if it is difficult to dem- infarction (STEMI)) are frequently found themselves to be onstrate in this population. A solution to this quandary may cardioprotective. We have previously discussed the so called be to undertake future studies using this low-cost interven- “success hypothesis” [7], whereby the success of optimal tion in developing countries, where presenting patients are medical management in cardiac ischaemia management in at significantly higher risk [10, 35, 47]. reducing mortality from acute coronary syndromes is likely Ovize’s group undertook an extensive, retrospective to cause coincident and largely unintended up-regulation of analysis of their CIRCUS study, which was a phase 3 study the same cyto-protective pathways that are utilised by RIC. designed to investigate the protective effect of cyclosporine, In other words, we are already pharmacologically condi- a cyclophilin-D inhibitor. In pre-clinical animal and early tioning our patients (Category 2b). If the aforementioned clinical proof-of-concept studies, cyclosporine had shown pharmacological cytoprotection is realised via the same great promise in reducing infarct size through inhibition of pathway as RIC, then RIC will not further up-regulate this the formation of the mitochondrial permeability transition protection. This has been demonstrated by Yellons’ group pore [30, 34, 77, 87]. Nevertheless, the CIRCUS study was in a simple study in which rats were given a similar cocktail ultimately neutral [18]. Due to short pain-to-balloon times of medications that are routinely administered to patients (i.e., the time between onset of symptoms and the percutane- presenting with a STEMI. The combination of an opiate, ous intervention to re-open the occluded vessel), infarct sizes a ­P2Y12 inhibitor, and heparin themselves reduced infarct were relatively small. This would imply a Category 3a RIC size equivalent to that seen following RIC alone, and RIC protection failure (Table 1). Nevertheless, it was infarct size was not able to add any further benefit to the drug combina- that appeared to have the greatest impact on the ability to tion. In such a scenario, the RIC cytoprotective signalling see a cytoprotective signal [9]. Interestingly, in their analy- is thus likely “to have reached a ceiling by the concomitant sis, hypertension, renal dysfunction, post-PCI TIMI flow drug therapy to which RIC itself could not further augment grade and treatment with beta-blockers or ACEI all had a [36]—a Category 2b RIC protection failure (Table 1). major influence on clinical outcomes without significantly 13 39 Page 6 of 12 Basic Research in Cardiology (2022) 117:39 affecting infarct size or adverse LV remodelling [9], which may not have fully masked a positive signal, detecting that led the authors to suggest that infarct size alone maybe poor positive signal within the background “noise” of the study surrogate for outcome. On the other hand, infarct size has becomes significantly harder and skews the assumptions of been correlated with outcome in large STEMI studies [88]. the original power calculations. Ibanez raised the possibility Interestingly the relationship between infarct size and long- of using an adaptive study design for clinical cardioprotec- term outcome has not to our knowledge been investigated tion studies to optimise and improve the robustness of clini- in animal studies [39]. cal trials [16]. Heusch and Kleinbongard emphasised that not only However, through better understanding of the modes of infarct size but also coronary microvascular obstruction is an RIC failure, it should be possible to construct a clinical trial important but possibly neglected endpoint of cardioprotec- that is not, from the outset, biased towards neutrality through tion [32, 40, 41, 70]), which carries prognostic information inappropriate patient selection. Both the Remote Ischaemic for patients´ outcome [23, 24]. Conditioning in STEMI Patients in Sub-Saharan AFRICA (RIC–AFRICA) Study (NCT04813159) and the RIP–high Optimising the design of future clinical trials study offers an opportunity to address this important distinc- tion by designing a study to intervene in patients who are at Given the multiple potential points of failure in the RIC high risk. In the former study, the majority of patients are mechanism of protection highlighted in Table 1, there are naïve to the medical therapies that are innately cardioprotec- numerous ways in which clinical trial design can go awry. tive—thus potentially avoiding a category 2b RIC protection Similarly, many of these issues are not reflected in the design failure. of fundamental science-based studies. This begs an impor- Yellons’ group revealed that in their proof-of-concept tant question: do we need more complex animal models to Mauritian ERIC–LYSIS Study (NCT02197117, a positive mimic clinically relevant models of disease and patient man- signal towards cardioprotection was seen, with a 32% reduc- agement, or should clinical trials be more reductive, apply- tion in area-under-the-curve troponin-T release [99]. This ing rigorous eligibility criteria, to select only those patients study gave some cautious optimism that in a high-risk group who closely reflect the animal models? The latter is likely to of patients, in which thrombolysis (not PPCI) was used, and be the most useful in establishing proof-of-efficacy, although in a patient group which had significant levels of diabetes there is a role for the former to gain a more comprehensive and other co-morbidities and given less co-medication, there understanding of the pitfalls of implementing RIC in the may yet be a need to manage patients throughout the world clinical setting. Gourine suggested that a possible means of in health care systems with limited resources. Therefore, stratifying or identifying responders would be to identify using a cheap and low risk intervention such as RIC may patients with preserved vagal autonomic function using heart yet prove beneficial. This will be tested in patients recruited rate variability analysis or cardiopulmonary exercise test- to the RIC Africa study who will be high risk, often with ing [45]. Heusch emphasized that vagal function is indeed signs of heart failure (Killip > 1), are very likely to present central to protection by RIC [45]. much later than found in well-developed medical systems in In retrospect, the large outcome studies performed thus the Western world [66]. This will avoid a Category 3 RIC far have not been designed to detect a reduction in I/R injury. protection failure, but such an approach carries with it a risk In all cases, studies have been designed to optimise recruit- of a Category 4 RIC protection failure, as these patients may ment through inclusion of all-comers. In most studies of present very late owing to long transit times to their local acute myocardial infarction, there was no stipulation of heart attack centre, and thus more likely to present with a minimum duration of chest pain, the site of coronary occlu- fully infarcted risk zone. In addition, thrombolysis rather sion, the presence of collateralisation, patient age, whether than primary percutaneous intervention is the revascularisa- patients were previously naïve of medical therapies and they tion modality of choice, and thus the timing and even suc- only documented the presence of co-morbidities. Thus, car- cess of re-canalisation of the culprit vessel will be unknown, dioprotection studies have tended to recruit older, multi-co- but this was also the case in the ERIC–LYSIS study. That morbid patients (thus with a high likelihood of a Category said, there may be benefits even in those patients, where 1 RIC protection failure); with short symptom-to-balloon vascular patency is achieved too late to salvage the ischae- times; distal, non-LAD, TIMI > 1 lesions; possibly with col- mic myocardium, albeit in preventing adverse remodelling lateralisations (high likelihood of Category 3 failure); and and arrhythmia. given full optimal medical therapy (high likelihood of Cat- The RIP–HIGH trial will also examine this hypothesis egory 2 failure). Another factor may be that approximately of whether RIC can protect in a high-risk patient group. 1/3 STEMI cases are caused by plaque erosion, which RIP–HIGH is a two-arm randomized controlled trial with typically results in smaller infarctions and fewer complica- an adaptive study design aiming to compare the impact of tions in the microvasculature [58]. While these limitations combined remote ischemic conditioning and local ischemic 13 Basic Research in Cardiology (2022) 117:39 Page 7 of 12 39 postconditioning vs. standard of care on clinical outcome in Sepsis is associated with an increase in cytokines similar high-risk STEMI patients undergoing primary percutaneous to that observed in patients diagnosed with COVID-19 [74]. coronary intervention (NCT04844931). This particular question is being investigated in a clinical study Another population where RIC may be ideally suited designed to ascertain whether RIC can reduce cytokine lev- is in acute ischaemic stroke [5]. Substantial strides have els and prevent deterioration to critical care in patients with been made in recent decades in the management of stroke, COVID-19, and we await the outcome of the clinical studies particularly with thrombolysis that has recently been fur- [21]. ther augmented by interventional radiology and arterial Another area discussed, which is becoming increasingly thrombectomy. While patients will typically have co-mor- relevant to cardiologists and oncologists alike, is the impact of bidities, in contrast to the cardiac field, ­P2Y12 inhibitors, cancer therapy (particularly chemotherapeutic agents, such as heparin and opiates are not routinely used, and statin usage the prototypical anthracycline) upon cardiac injury and the risk for primary prevention is relatively less commonly applied— for the late emergence of heart failure and iatrogenic cardio- thus potentially avoiding a Category 2b RIC conditioning myopathy. It is certainly clear that repeated cycles of anthra- failure. In this context, Remote Ischemic Conditioning in cyclines lead to an accumulative injury to the heart, often real- Patients With Acute Stroke Trial (RESIST)(NCT03481777) ised by the release of troponin (e.g., high-sensitivity cardiac [8] and Remote Ischaemic Conditioning After Stroke 3 Troponin-T [hs-TnT]). Of note, in some cases anthracycline (RECAST-3, ISRCTN63231313) led by England’s group, cardiotoxicity results in cardiac contractile impairment without are aiming to study RIC in the context of ischaemic stroke, death of cardiomyocytes. These cases might not be picked up including sub-studies that aims to investigate RIC in the by hs-Tn evaluation, and more sensitive modalities, such as context of mechanical thrombectomy. RECAST-3 builds cardiac magnetic resonance imaging or strain echocardiogra- on the success of RECAST and RECAST-2, both providing phy should also be considered. In fact, in some ways, anthracy- positive biomarker signals of RIC efficacy [25], and builds cline cardiotoxicity may be a more suitable target for RIC than on the positive preclinical animal model which has shown a STEMI, since the timing for the intervention of RIC is more reduced cerebral infarction with RIC [3]. convenient (i.e., it can be planned to occur immediately before Other organ systems could be similarly targeted, for the exposure to the toxic agent: anthracycline infusion), there which ischaemic emergencies are encountered or transient is no issue regarding the area at risk or coronary collateraliza- ischaemia can be anticipated (for example in surgery and tion extent. This has inspired studies of RIC in the setting of particularly in the handling of donor organs)—and it could anthracycline cardiotoxicity [14, 20, 29], to which we await be argued that it may be worth revisiting certain studies such the outcome with interest. The REmote iSchemic condItioning as the REPAIR Study (REmote preconditioning for Protec- in Lymphoma PatIents REceiving ANthraCyclinEs (RESIL- tion Against Ischaemia–Reperfusion in renal transplanta- IENCE) trial, NCT05223413, was discussed in detail. This is tion) [91] in the light of our improved understanding of how an EU-funded project that will enrol 600 patients at risk for best to design appropriate studies avoiding the categories anthracycline-induced cardiotoxicity and randomize them to seen in Table 1. weekly RIC or standard of care with a comprehensive, serial, cardiac magnetic resonance imaging evaluation. However, the mechanism of anthracycline-mediated myo- Novel targets for intervention cardial injury remains unclear, and how chemotherapy may potentially impact the generation of the RIC signal has also While the focus of large clinical trials to date has appropri- not been described [48, 89]. Moreover, hs-TnT may not be ately been on ischaemia and reperfusion injury, there are the ideal biomarker, as cardiac troponin T can be expressed other emerging fields in which RIC may potentially find a by non-cardiac muscle [82, 85, 95]. It was suggested that role. Discussion in this workshop covered a range of novel other markers of cardiac injury should, therefore, be consid- targets that may be amenable to RIC intervention. In this ered, such as cardiac myosin-C (c-MyC) [54], and the novel regard, Redington’s group recently demonstrated the ability biomarker of ischaemic injury, glycosylated apolipoprotein of RIC to improve cardiac output and organ function in the J [17] may provide further sensitive and specific markers of context of lipopolysaccharide-induced sepsis [51]. Optimis- myocardial injury. ing clinical outcomes in severely ill patients on the intensive care unit has been a holy grail for intensivists, and other groups have also seen similarly positive signs of positive Conclusions and the path forward outcomes. Whether RIC can prove to be a helpful interven- tion in the sedated, ventilated patient in all forms of sep- The workshop participants concluded that, although some sis, be it bacterial, viral or fungal, in in the management of aspects of RIC remain an enigma it is recognised as a pow- shock, remains to be seen. erful cytoprotective intervention in experimental models. 13 39 Page 8 of 12 Basic Research in Cardiology (2022) 117:39 Furthermore, it has led to remarkable advances in our should be possible to construct a study with the best chance understanding of the mechanisms and progression of cell of revealing a positive result when powered appropriately. death following lethal ischaemia and reperfusion and has provided novel insights into neuro-humoral signalling that Author contributions This article emerged from a group discussion by all the authors at the 11th Hatter Cardiovascular Workshop. RB, SMD appears to link different organ systems under conditions of and DY drafted the initial manuscript. All authors provided feedback stress. However, thus far at least, it has failed to translate and comments. into an effective clinical therapy. Applying RIC in modern clinical practice has proven Funding GH and PK were supported by the German Research Foun- considerably more difficult than expected—the reasons dation (CRC 1116 B8). SMD was supported by the British Heart Foundation (PG/19/51/34493, PG/21/10798) and Rosetrees Foun- for its failure have been widely discussed. One conclu- dation (Seedcorn2021\100092). GV was supported by grants PGC sion of those attending this workshop was the importance 2018–094025-B-I00, MCIN/AEI/10.13039/501100011033 and Fondo to return to basics: to fully define the whole RIC cyto- Europeo de Desarrollo Regional (FFEDER). DJH is supported by the protective signalling arc and to understand how co-mor- Duke-NUS Signature Research Programme funded by the Ministry of Health, Singapore Ministry of Health’s National Medical Research bidities and concomitant medical therapies may interfere Council under its Singapore Translational Research Investigator with RIC signalling and the downstream cytoprotective Award (MOH-STaR21jun-0003), Centre, Grant scheme (NMRC signalling in the organ itself. On that basis, we propose a CG21APR1006), and Collaborative Centre Grant scheme (NMRC/ simple scheme for breaking down and understanding how CG21APRC006). RIC protection signalling may be inhibited, and based on this understanding, ensure that future clinical trials are Declarations cognisant of these potential issues and patient inclusion/ Conflict of interest AVG is a founder and Chief Scientific Officer for exclusion criteria are developed to ensure that trials can Afferent Medical Solutions. DJH has received: consultant fees from be appropriately powered to provide a definitive answers Faraday Pharmaceuticals Inc. and Boehringer Ingelheim International to the question: is RIC a potentially useful clinical inter- GmbH; honoraria from Servier; and research funding from Astra Zen- vention, or should it remain an incredibly useful research eca and Merck Sharp & Dohme Corp. All other authors have no com- peting interests. tool in which to expand our knowledge of ischaemia and reperfusion injury. Open Access This article is licensed under a Creative Commons Attri- It is also clear that we need a fuller understanding of the bution 4.0 International License, which permits use, sharing, adapta- neuro-humoral signalling pathway and need for biomark- tion, distribution and reproduction in any medium or format, as long ers to measure activation of the RIC signalling pathway, so as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes that conditioning protocols can be optimised and potentially were made. The images or other third party material in this article are identify patients who are RIC responders, and those who included in the article's Creative Commons licence, unless indicated are not. otherwise in a credit line to the material. If material is not included in In pre-clinical studies, there are already excellent guide- the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will lines for the design and reporting of fundamental science need to obtain permission directly from the copyright holder. To view a studies, such as those advised in neuroprotection: the copy of this licence, visit http://​creat​iveco​mmons.​org/​licen​ses/​by/4.​0/. Stroke Treatment Academic Industry Roundtable (STAIR) guidelines [27], the 20/20 standards for translational stroke research [60] and RIGOR guidelines [61]. Similar guide- lines, called the IMproving Preclinical Assessment of Car- References dioprotective Therapies (IMPACT) criteria, have recently 1. Bang JY, Kim SG, Oh J, Kim SO, Go YJ, Hwang GS, Song JG been proposed for studies of cardioprotection [63]. 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