Reperfusion is a pre-requisite to salvaging viable myocardium, following an acute myocardial infarction. Reperfusion of ischaemic myocardium, however, is not without risk, as the act of reperfusion itself can paradoxically result in myocyte death: a phenomenon termed lethal reperfusion-induced injury. Therapeutic strategies that target and attenuate reperfusion-induced cell death may provide novel pharmacological agents, which can be used as an adjunct to current reperfusion therapy, to limit myocardial infarction. Recent evidence has implicated apoptotic cell death during the phase of reperfusion as an important contributor to lethal reperfusion-induced injury. Targeting anti-apoptotic mechanisms of cellular protection at the time of reperfusion may therefore offer a potential approach to attenuating reperfusion-induced cell death. In this regard, ischaemia-reperfusion has been shown to activate the anti-apoptotic pro-survival kinase signalling cascades, phosphatidylinositol-3-OH kinase (PI3K)-Akt and p42/p44 extra-cellular signal-regulated kinases (Erk 1/2), both of which have been implicated in cellular survival. Activating these pro-survival kinase cascades at the time of reperfusion has been demonstrated to confer protection against reperfusion-induced injury. We and others have shown that insulin, insulin-like growth factor-1 (IGF-1), transforming growth factor-beta1 (TGF-beta1), cardiotrophin-1 (CT-1), urocortin, atorvastatin and bradykinin protect the heart, by activating the PI3K-Akt and/or Erk 1/2 kinase cascades, when given at the commencement of reperfusion, following a lethal ischaemic insult. Pharmacological manipulation and up-regulation of these pro-survival kinase cascades, which we refer to as the Reperfusion Injury Salvage Kinase (RISK) pathway, as an adjunct to reperfusion may therefore protect the myocardium from lethal reperfusion-induced cell death and provide a novel strategy to salvaging viable myocardium and limiting infarct size.

We report that, the survival kinase cascades PI3K-Akt and MEK1/2-Erk1/2, which are recruited at the time of reperfusion in response to ischemic preconditioning, exhibit 'cross-talk' such that inhibiting one cascade activates the other and vice versa. Furthermore, at the time of reperfusion, these kinase cascades mediate IPC-induced protection, by acting in concert via p70S6K.

Coronary heart disease (CHD) is the leading cause of morbidity and mortality worldwide. For a large number of patients with CHD, coronary artery bypass graft (CABG) surgery remains the preferred strategy for coronary revascularization. Over the last 10 years, the number of high-risk patients undergoing CABG surgery has increased significantly, resulting in worse clinical outcomes in this patient group. This appears to be related to the ageing population, increased co-morbidities (such as diabetes, obesity, hypertension, stroke), concomitant valve disease, and advances in percutaneous coronary intervention which have resulted in patients with more complex coronary artery disease undergoing surgery. These high-risk patients are more susceptible to peri-operative myocardial injury and infarction (PMI), a major cause of which is acute global ischaemia/reperfusion injury arising from inadequate myocardial protection during CABG surgery. Therefore, novel therapeutic strategies are required to protect the heart in this high-risk patient group. In this article, we review the aetiology of PMI during CABG surgery, its diagnosis and clinical significance, and the endogenous and pharmacological therapeutic strategies available for preventing it. By improving cardioprotection during CABG surgery, we may be able to reduce PMI, preserve left ventricular systolic function, and reduce morbidity and mortality in these high-risk patients with CHD.

No abstract

This paper presents a new algorithm to automatically segment the myofibrils, mitochondria and nuclei within single adult cardiac cells that are part of a large serial-block-face scanning electron microscopy (SBF-SEM) dataset. The algorithm only requires a set of manually drawn contours that roughly demarcate the cell boundary at routine slice intervals (every 50 th , for example). The algorithm correctly classified pixels within the single cell with 97% accuracy when compared to manual segmentations. One entire cell and the partial volumes of two cells were segmented. Analysis of segmentations within these cells showed that myofibrils and mitochondria occupied 47.5% and 51.6% on average respectively, while the nuclei occupy 0.7% of the cell for which the entire volume was captured in the SBF-SEM dataset. Mitochondria clustering increased at the periphery of the nucleus region and branching points of the cardiac cell. The segmentations also showed high area fraction of mitochondria (up to 70% of the 2D image slice) in the subsarcolemmal region, whilst it was closer to 50% in the intermyofibrillar space. We finally demonstrate that our segmentations can be turned into 3D finite element meshes for cardiac cell computational physiology studies. We offer our large dataset and MATLAB implementation of the algorithm for research use at www.github.com/CellSMB/sbfsem-cardiac-cell-segmenter/. We anticipate that this timely tool will be of use to cardiac computational and experimental physiologists alike who study cardiac ultrastructure and its role in heart function.

No abstract

No abstract

IMPORTANCEThere are few data on remote postdischarge treatment of patients with acute myocardial infarction.OBJECTIVE To compare the safety and efficacy of allied health care practitioner-led remote intensive management (RIM) with cardiologist-led standard care (SC). DESIGN, SETTING, AND PARTICIPANTSThis intention-to-treat feasibility trial randomized patients with acute myocardial infarction undergoing early revascularization and with N-terminal-pro-B-type natriuretic peptide concentration more than 300 pg/mL to RIM or SC across 3 hospitals in Singapore from July 8, 2015, to March 29, 2019. RIM participants underwent 6 months of remote consultations that included β-blocker and angiotensinconverting enzyme inhibitor/angiotensin receptor blocker (ACE-I/ARB) dose adjustment by a centralized nurse practitioner team while SC participants were treated face-to-face by their cardiologists. MAIN OUTCOMES AND MEASURESThe primary safety end point was a composite of hypotension, bradycardia, hyperkalemia, or acute kidney injury requiring hospitalization. To assess the efficacy of RIM in dose adjustment of β-blockers and ACE-I/ARBs compared with SC, dose intensity scores were derived by converting comparable doses of different β-blockers and ACE-I/ARBs to a scale from 0 to 5. The primary efficacy end point was the 6-month indexed left ventricular end-systolic volume (LVESV) adjusted for baseline LVESV.RESULTS Of 301 participants, 149 (49.5%) were randomized to RIM and 152 (50.5%) to SC. RIM and SC participants had similar mean (SD) age (55.3 [8.5] vs 54.7 [9.1] years), median (interquartile range) N-terminal-pro-B-type natriuretic peptide concentration (807 [524-1360] vs 819 [485-1320] pg/mL), mean (SD) baseline left ventricular ejection fraction (57.4% [11.1%] vs 58.1% [10.3%]), and mean (SD) indexed LVESV (32.4 [14.1] vs 30.6 [11.7] mL/m 2 ); 15 patients [5.9%] had a left ventricular ejection fraction <40%. The primary safety end point occurred in 0 RIM vs 2 SC participants (1.4%) (P = .50). The mean β-blocker and ACE-I/ARB dose intensity score at 6 months was 3.03 vs 2.91 (adjusted mean difference, 0.12 [95% CI, −0.02 to 0.26; P = .10]) and 2.96 vs 2.77 (adjusted mean difference, 0.19 [95% CI, −0.02 to 0.40; P = .07]), respectively. The 6-month indexed LVESV was 28.9 vs 29.7 mL/m 2 (adjusted mean difference, −0.80 mL/m 2 [95% CI, −3.20 to 1.60; P = .51]).CONCLUSIONS AND RELEVANCE Among low-risk patients with revascularization after myocardial infarction, RIM by allied health care professionals was feasible and safe. There were no differences in achieved medication doses or indices of left ventricular remodeling. Further studies of RIM in higher-risk cohorts are warranted.