Gudrun Kunst

Remote Ischemic Preconditioning and Outcomes of Cardiac Surgery

BACKGROUNDnWhether remote ischemic preconditioning (transient ischemia and reperfusion of the arm) can improve clinical outcomes in patients undergoing coronary-artery bypass graft (CABG) surgery is not known. We investigated this question in a randomized trial.nnnMETHODSnWe conducted a multicenter, sham-controlled trial involving adults at increased surgical risk who were undergoing on-pump CABG (with or without valve surgery) with blood cardioplegia. After anesthesia induction and before surgical incision, patients were randomly assigned to remote ischemic preconditioning (four 5-minute inflations and deflations of a standard blood-pressure cuff on the upper arm) or sham conditioning (control group). Anesthetic management and perioperative care were not standardized. The combined primary end point was death from cardiovascular causes, nonfatal myocardial infarction, coronary revascularization, or stroke, assessed 12 months after randomization.nnnRESULTSnWe enrolled a total of 1612 patients (811 in the control group and 801 in the ischemic-preconditioning group) at 30 cardiac surgery centers in the United Kingdom. There was no significant difference in the cumulative incidence of the primary end point at 12 months between the patients in the remote ischemic preconditioning group and those in the control group (212 patients [26.5%] and 225 patients [27.7%], respectively; hazard ratio with ischemic preconditioning, 0.95; 95% confidence interval, 0.79 to 1.15; P=0.58). Furthermore, there were no significant between-group differences in either adverse events or the secondary end points of perioperative myocardial injury (assessed on the basis of the area under the curve for the high-sensitivity assay of serum troponin T at 72 hours), inotrope score (calculated from the maximum dose of the individual inotropic agents administered in the first 3 days after surgery), acute kidney injury, duration of stay in the intensive care unit and hospital, distance on the 6-minute walk test, and quality of life.nnnCONCLUSIONSnRemote ischemic preconditioning did not improve clinical outcomes in patients undergoing elective on-pump CABG with or without valve surgery. (Funded by the Efficacy and Mechanism Evaluation Program [a Medical Research Council and National Institute of Health Research partnership] and the British Heart Foundation; ERICCA ClinicalTrials.gov number, NCT01247545.).

Myosin Binding Protein C, a Phosphorylation-Dependent Force Regulator in Muscle That Controls the Attachment of Myosin Heads by Its Interaction With Myosin S2

Myosin binding protein C (MyBP-C) is one of the major sarcomeric proteins involved in the pathophysiology of familial hypertrophic cardiomyopathy (FHC). The cardiac isoform is tris-phosphorylated by cAMP-dependent protein kinase (cAPK) on beta-adrenergic stimulation at a conserved N-terminal domain (MyBP-C motif), suggesting a role in regulating positive inotropy mediated by cAPK. Recent data show that the MyBP-C motif binds to a conserved segment of sarcomeric myosin S2 in a phosphorylation-regulated way. Given that most MyBP-C mutations that cause FHC are predicted to result in N-terminal fragments of the protein, we investigated the specific effects of the MyBP-C motif on contractility and its modulation by cAPK phosphorylation. The diffusion of proteins into skinned fibers allows the investigation of effects of defined molecular regions of MyBP-C, because the endogenous MyBP-C is associated with few myosin heads. Furthermore, the effect of phosphorylation of cardiac MyBP-C can be studied in a defined unphosphorylated background in skeletal muscle fibers only. Triton skinned fibers were tested for maximal isometric force, Ca(2+)/force relation, rigor force, and stiffness in the absence and presence of the recombinant cardiac MyBP-C motif. The presence of unphosphorylated MyBP-C motif resulted in a significant (1) depression of Ca(2+)-activated maximal force with no effect on dynamic stiffness, (2) increase of the Ca(2+) sensitivity of active force (leftward shift of the Ca(2+)/force relation), (3) increase of maximal rigor force, and (4) an acceleration of rigor force and rigor stiffness development. Tris-phosphorylation of the MyBP-C motif by cAPK abolished these effects. This is the first demonstration that the S2 binding domain of MyBP-C is a modulator of contractility. The anchorage of the MyBP-C motif to the myosin filament is not needed for the observed effects, arguing that the mechanism of MyBP-C regulation is at least partly independent of a tether, in agreement with a modulation of the head-tail mobility. Soluble fragments occurring in FHC, lacking the spatial specificity, might therefore lead to altered contraction regulation without affecting sarcomere structure directly.

Remote intermittent ischemia before coronary artery bypass graft surgery: a strategy to reduce injury and inflammation?

Perioperative myocardial ischemia contributes to postoperative morbidity and mortality. Remote intermittent ischemia (RI) has been shown to benefit patients undergoing coronary artery bypass graft (CABG) surgery by decreasing postoperative cardiac troponin levels. In addition, there is evidence that volatile anesthetics may provide myocardial protection. In this prospective randomized controlled trial we tested the hypothesis that RI is cardioprotective under a strict anesthetic regime with volatile anesthesia until cardiopulmonary bypass (CPB). We also assessed whether RI modulates postoperative cytokine and growth factor concentrations. Fifty-four patients referred for elective CABG surgery without concomitant valve or aortic surgery were randomized to three 5-min cycles of left upper limb ischemia by cuff inflation (RI) or placebo without cuff inflation (Plac). All patients received the volatile anesthetic isoflurane (1.15–1.5xa0vol%) before CPB and the intravenous anesthetic propofol (3–4xa0mg/kg/h) thereafter until the end of surgery. Cardiac arrest during CPB was induced by intermittent cross-clamp fibrillation, or by blood cardioplegia. We excluded patients older than 85xa0years, with unstable angina, significant renal disease, and those taking sulfonylureas. Troponin I (cTnI) was measured preoperatively and after 6, 12, 24 and 48xa0h. In addition, brain natriuretic peptide (BNP), creatine kinase (CKMB) and a panel of cytokines and growth factors were analyzed perioperatively. Although cTnI, BNP and CKMB all increased post-CABG, there were no significant differences between RI and Plac groups; area under the curve for cTnI 189.4 (183.6) ng/mL/48xa0h and 183.0 (155.2) ng/mL/48xa0h mean (SD), pxa0=xa00.90, respectively, despite a tendency to a shorter (pxa0<xa00.07) cross-clamp time in the treatment group. Similarly, there were no differences between groups in the central venous concentrations of numerous cytokines and growth factors. In patients undergoing CABG surgery RI does not provide myocardial protection under a strict anesthetic regime with volatile anesthesia until CPB, and RI was not associated with changes in cytokines.

Effect of remote ischemic preconditioning on clinical outcomes in patients undergoing coronary artery bypass graft surgery (ERICCA): rationale and study design of a multi-centre randomized double-blinded controlled clinical trial.

BackgroundNovel cardioprotective strategies are required to improve clinical outcomes in high risk patients undergoing coronary artery bypass graft (CABG)xa0±xa0valve surgery. Remote ischemic preconditioning (RIC), in which brief episodes of non-lethal ischemia and reperfusion are applied to the arm or leg, has been demonstrated to reduce perioperative myocardial injury following CABGxa0±xa0valve surgery. Whether RIC can improve clinical outcomes in this setting is unknown and is investigated in the effect of remote ischemic preconditioning on clinical outcomes (ERICCA) trial in patients undergoing CABG surgery. (ClinicalTrials.gov Identifier: NCT01247545).MethodsThe ERICCA trial is a multicentre randomized double-blinded controlled clinical trial which will recruit 1,610 high-risk patients (Additive Euroscore ≥xa05) undergoing CABGxa0±xa0valve surgery using blood cardioplegia via 27 tertiary centres over 2xa0years. The primary combined endpoint will be cardiovascular death, non-fatal myocardial infarction, coronary revascularization and stroke at 1xa0year. Secondary endpoints will include peri-operative myocardial and acute kidney injury, intensive care unit and hospital stay, inotrope score, left ventricular ejection fraction, changes of quality of life and exercise tolerance. Patients will be randomized to receive after induction of anesthesia either RIC (4 cycles of 5xa0min inflation to 200xa0mmHg and 5xa0min deflation of a blood pressure cuff placed on the upper arm) or sham RIC (4 cycles of simulated inflations and deflations of the blood pressure cuff).ImplicationsThe findings from the ERICCA trial have the potential to demonstrate that RIC, a simple, non-invasive and virtually cost-free intervention, can improve clinical outcomes in higher-risk patients undergoing CABGxa0±xa0valve surgery.

Differential effects of bupivacaine on intracellular Ca2+: Regulation potential mechanisms of its myotoxicity

BACKGROUNDnBupivacaine produces skeletal muscle damage in clinical concentrations. It has been suggested that this may be caused by an increased intracellular level of [Ca2+]. Therefore, the aim of this study was to investigate direct intracellular effects of bupivacaine on Ca2+ release from the sarcoplasmic reticulum (SR), on Ca2+ uptake into the SR, and on Ca2+ sensitivity of the contractile proteins.nnnMETHODSnSaponin skinned muscle fibers from the extensor digitorum longus muscle of BALB/c mice were examined according to a standardized procedure described previously. For the assessment of effects on Ca2+ uptake and release from the SR, bupivacaine was added to the loading solution and the release solution, respectively. Force transients and force decays were monitored, and the position of the curve relating relative isometric force free [Ca2+] was evaluated in the presence or absence of bupivacaine.nnnRESULTSnBupivacaine induces Ca2+ release from the SR. In addition, the Ca2+ loading procedure is suppressed, resulting in smaller caffeine-induced force transients after loading in the presence of bupivacaine. The decay of caffeine-induced force transients is reduced by bupivacaine, and it also shifts [Ca2+]-force relation toward lower [Ca2+].nnnCONCLUSIONSnThese data reveal that bupivacaine does not only induce Ca2+ release from the SR, but also inhibits Ca2+ uptake by the SR, which is mainly regulated by SR Ca2+ adenosine triphosphatase activity. It also has a Ca2+ -sensitizing effect on the contractile proteins. These mechanisms result in increased intracellular [Ca2+] concentrations and may thus contribute to its pronounced skeletal muscle toxicity.

Activation of Myocardial Contraction by the N-Terminal Domains of Myosin Binding Protein-C

Myosin binding protein-C (MyBP-C) is a poorly understood component of the thick filament in striated muscle sarcomeres. Its C terminus binds tightly to myosin, whereas the N terminus contains binding sites for myosin S2 and possibly for the thin filament. To study the role of the N-terminal domains of cardiac MyBP-C (cMyBP-C), we added human N-terminal peptide fragments to human and rodent skinned ventricular myocytes. At concentrations >10 &mgr;mol/L, the N-terminal C0C2 peptide activated force production in the absence of calcium (pCa 9). Force at the optimal concentration (80 &mgr;mol/L) of C0C2 was ≈60% of that in maximal Ca2+ (pCa 4.5), but the rate constant of tension redevelopment (ktr) matched or exceeded (by up to 80%) that produced by Ca2+ alone. Experiments using different N-terminal peptides suggested that this activating effect of C0C2 resulted from binding by the pro/ala-rich C0-C1 linker region, rather than the terminal C0 domain. At a lower concentration (1 &mgr;mol/L), exogenous C0C2 strongly sensitized cardiac myofibrils to Ca2+ at a sarcomere length (SL) of 1.9 &mgr;m but had no significant effect at SL 2.3 &mgr;m. This differential effect caused the normal SL dependence of myofibrillar Ca2+ sensitivity to be reduced by 80% (mouse myocytes) or abolished (human myocytes) in 1 &mgr;mol/L C0C2. These results suggest that cMyBP-C provides a regulatory pathway by which the thick filament can influence the activation of the thin filament, separately from its regulation by Ca2+. Furthermore, the N-terminal region of cMyBP-C can influence the SL-tension (Frank–Starling) relationship in cardiac muscle.

Remote ischaemic preconditioning in coronary artery bypass surgery: a meta-analysis

Aim Randomised trials exploring remote ischaemic preconditioning (RIPC) in patients undergoing coronary artery bypass graft (CABG) surgery have yielded conflicting data regarding potential cardiovascular and renal protection, and are individually flawed by small sample size. Methods Three investigators independently searched the MEDLINE, EMBASE and Cochrane databases to identify randomised trials testing RIPC in patients undergoing CABG. Results Nine studies with 704 patients were included. Standardised mean difference of troponin I and T release showed a significant decrease (−0.36 (95% CI −0.62 to −0.09)). This difference held true after excluding the trials with cross-clamp fibrillation, the study with off-pump CABG and studies using a flurane as anaesthetic agent (−0.41 (95% CI −0.69 to −0.12), −0.38 (95% CI −0.70 to −0.07) and −0.37 (95% CI −0.63 to −0.12), respectively). A similar trend was also obtained for patients with multivessel disease (−0.41 (95% CI −0.73 to −0.08)). The trials evaluating postoperative creatinine reported a non-significant reduction (0.02 (95% CI −0.09 to 0.13)). Moreover, the length of in-hospital stay was not influenced by the kind of treatment (weighted mean difference 0.27 (95% CI −0.24 to 0.79)). Conclusion RIPC reduced the release of troponin in patients undergoing CABG. Larger randomised trials are needed to clarify the presence of a causal relationship between RIPC-induced troponin release and clinical adverse events.

The effect of cyclosporin-A on peri-operative myocardial injury in adult patients undergoing coronary artery bypass graft surgery: a randomised controlled clinical trial

Objective Cyclosporin-A (CsA) has been reported to reduce myocardial infarct size in both the experimental and clinical settings. This protective effect is dependent on its ability to prevent the opening of the mitochondrial permeability transition pore, a critical determinant of cell death in the setting of acute ischaemia-reperfusion injury. Whether CsA can reduce the extent of peri-operative myocardial injury (PMI) in patients undergoing coronary artery bypass graft (CABG) surgery is unknown, and is investigated in this randomised controlled clinical trial. Methods 78 adult patients undergoing elective CABG surgery were randomised to receive either an intravenous bolus of CsA (2.5u2005mg/kg) or placebo administered after induction of anaesthesia and prior to sternotomy. PMI was assessed by measuring serum cardiac enzymes, troponin T (cTnT) and CK-MB at 0, 6, 12, 24, 48 and 72u2005h after surgery. Results There was no significant difference in mean peak cTnT levels between control (n=43) and CsA treatment (n=40) patients (0.56±0.06u2005ng/mL with control vs 0.35±0.05u2005ng/mL with CsA; p=0.07). However, in higher-risk patients with longer cardiopulmonary bypass times, there was a significant reduction in PMI with CsA therapy (p=0.049), with a reduced postoperative cTnT rise by 0.03u2005ng/mL for every 10u2005min, when compared with control. Conclusions In patients with longer cardiopulmonary bypass times, a single intravenous bolus of CsA administered prior to CABG surgery reduced the extent of PMI.

Peri‐operative anaesthetic myocardial preconditioning and protection – cellular mechanisms and clinical relevance in cardiac anaesthesia

Preconditioning has been shown to reduce myocardial damage caused by ischaemia–reperfusion injury peri‐operatively. Volatile anaesthetic agents have the potential to provide myocardial protection by anaesthetic preconditioning and, in addition, they also mediate renal and cerebral protection. A number of proof‐of‐concept trials have confirmed that the experimental evidence can be translated into clinical practice with regard to postoperative markers of myocardial injury; however, this effect has not been ubiquitous. The clinical trials published to date have also been too small to investigate clinical outcome and mortality. Data from recent meta‐analyses in cardiac anaesthesia are also not conclusive regarding intra‐operative volatile anaesthesia. These inconclusive clinical results have led to great variability currently in the type of anaesthetic agent used during cardiac surgery. This review summarises experimentally proposed mechanisms of anaesthetic preconditioning, and assesses randomised controlled clinical trials in cardiac anaesthesia that have been aimed at translating experimental results into the clinical setting.

Cardiac myosin-binding protein C: a potential early biomarker of myocardial injury.

Cardiac troponins are released and cleared slowly after myocardial injury, complicating the diagnosis of early, and recurrent, acute myocardial infarction. Cardiac myosin-binding protein C (cMyC) is a similarly cardiac-restricted protein that may have different release/clearance kinetics. Using novel antibodies raised against the cardiac-specific N-terminus of cMyC, we used confocal microscopy, immunoblotting and immunoassay to document its location and release. In rodents, we demonstrate rapid release of cMyC using in vitro and in vivo models of acute myocardial infarction. In patients, with ST elevation myocardial infarction (STEMI, nxa0=xa020), undergoing therapeutic ablation of septal hypertrophy (TASH, nxa0=xa020) or having coronary artery bypass surgery (CABG, nxa0=xa020), serum was collected prospectively and frequently. cMyC appears in the serum as full-length and fragmented protein. Compared to cTnT measured using a contemporary high-sensitivity commercial assay, cMyC peaks earlier (STEMI, 9.3xa0±xa03.1 vs 11.8xa0±xa03.4xa0h, Pxa0<xa00.007; TASH, 9.7xa0±xa01.4 vs 21.6xa0±xa01.4xa0h, Pxa0<xa00.0001), accumulates more rapidly (during first 4xa0h after TASH, 25.8xa0±xa01.9 vs 4.0xa0±xa00.4xa0ng/L/min, Pxa0<xa00.0001) and disappears more rapidly (post-CABG, decay half-time 5.5xa0±xa00.8 vs 22xa0±xa05xa0h, Pxa0<xa00.0001). Our results demonstrate that following defined myocardial injury, the rise and fall in the serum of cMyC is more rapid than that of cTnT. We speculate that these characteristics could enable earlier diagnosis of myocardial infarction and reinfarction in suspected non-STEMI, a population not included in this early translational study.