The effect of hypothermia and rewarming on cardiac electrophysiology and mechanical function

Hypothermia is defined as a core body temperature of 35°C or less and can be induced (i.e. therapeutic) or accidental. It is well established that hypothermia leads to a positive inotropic response which causes an increase in the magnitude of cardiac contraction, however rewarming from hypothermia is associated with a negative inotropic response, and the underlying mechanisms of this remain unclear. Accidental hypothermia is further complicated by risk of ventricular arrhythmias and cardiac arrest. This contributes to high mortality rates among these patients. Although hypothermia is used extensively as a therapeutic intervention and survival is possible after extreme exposure, treatment of arrhythmias during rewarming is still challenging. In order to develop targeted anti-arrhythmic strategies in this very specific situation, we first need to understand the basis for pro-arrhythmia during cooling and rewarming. This study aimed to examine the effect of hypothermia and rewarming on aspects of cardiac inotropy and excitability. An in vitro model of hypothermia and rewarming using isolated rat ventricular cardiomyocytes showed that following 3 hours of hypothermia there was a significant reduction in shortening upon rewarming. This was not accompanied by a change in intracellular Ca2+, suggesting a rewarming induced decrease in myofilament sensitivity to Ca2+. In separate experiments, animals underwent an in vivo hypothermia/rewarming procedure and displayed evidence of rewarming induced contractile dysfunction. Epicardial action potential (AP) measurements on these hearts showed a shortened AP duration (APD) when compared to normothermic control animals, which suggests that a sustained electrophysiological effect that could manifest as a shortened QT interval. In contrast to this, a period of transient hypothermia had alternative detrimental effects on the cardiac APD when compared to prolonged hypothermia, an effect that could predispose to the induction of long QT related arrhythmias and ventricular tachycardia. Separate experiments assessed the effect of moderate (31˚C) and severe (17˚C) hypothermia on cardiac excitability in Langendorff perfused rabbit hearts. Moderate hypothermia prolonged PR and QT intervals whilst in severe hypothermia all ECG parameters were prolonged. Ventricular activation times were unaffected at 31°C whilst action potential duration (APD90) was significantly prolonged. At 17°C there were significant and proportionally similar delays in both activation and repolarisation. Ventricular fibrillation (VF) threshold was significantly reduced at 31°C (pro-arrhythmic), but at 17°C VF threshold was >2x baseline (37°C) (anti-arrhythmic). At 31°C, transverse conduction (CVt) was relatively insensitive to cooling versus longitudinal conduction (CVl) but at 17°C both CVt and CVl were proportionately reduced to a similar extent. The gap junction uncoupler heptanol had a larger relative effect on CVt than CVl, and at 31°C was able to restore the CVt/CVl ratio, returning VF threshold to baseline values. This suggests that moderate hypothermia creates repolarisation abnormalities and is pro-arrhythmic. These divergent effects appear to be linked to a lower temperature sensitivity of gap junctions, a conclusion supported by the anti-arrhythmic effect of heptanol at 31°C

The positive role of Internet use for young people with additional support needs:Identity and connectedness

This article documents findings, from one of the first studies in this field of research, considering young people with Additional Support Needs’ use of the internet and how this might contribute to the development of identity and social connectedness. Six focus groups, including 36 young people with Additional Support Needs (aged 13–18) were completed. Transcribed group discussions were analysed using Framework Analysis. Two themes were developed: ‘Identity and Connectedness’ and ‘Issues related to Risk’. The theme ‘Identity and Connectedness’ is detailed in the current article and encompassed three sub-themes (implicit belonging, explicit belonging and competence). The use of the internet by adolescents in the current study appears to allow the young people to engage in activities which support the development of identity, competence and a sense of connectedness and belonging within a social network, essential to healthy development and psychological well-being and areas that may present a challenge for this population in offline environments. Findings also indicate a need to consider how best to support this group, in relation to understanding the role of supervision, the range of cognitive ability within this population and additional social pressures, which may impact on safe and effective internet use and this populations’ ability to take full advantage of what the internet has to offer

Intensity-dependence of exercise and active recovery in high-intensity interval training

Background: High-intensity interval training (HIIT) with interspersing active recovery is an effective mode of exercise training in cohorts ranging from athletes to patients. Here, we assessed the intensity-dependence of the intervals and active recovery bouts for permitting a sustainable HIIT protocol. Methods: 14 males completed 4x4-minute HIIT protocols where intensities of intervals ranged 80-100% of maximal oxygen uptake (VO2max) and active recovery ranged 60-100% of lactate (La-) threshold (LT). Blood La- measurements indicated fatigue, while tolerable duration of intervals indicated sustainability. Results: HIIT at 100% of VO2max allowed 44±10% [30-70%] completion, i.e. fatigue occurred after 7minutes:6seconds of the intended 16 minutes of high intensity, whereas HIIT at 95-80% of VO2max was 100% sustainable (p<0.01). Measured intensity did not differ from intended intensity across the protocols (p>0.05). Blood La- concentration [La-] increased to 9.3±1.4mM during HIIT at 100% of VO2max, whereas at 80-95% of VO2max stabilised at 2-6mM in an intensity-dependent manner (p<0.01 vs 100% of VO2max and p<0.05 vs baseline). Active recovery at 60-70% of LT during HIIT associated with steady-state blood [La-] peaking at 6-7mM, whereas at 80-100% of LT, blood [La-] accumulated to 10-13mM (p<0.05). After HIIT, active recovery at 80-90% of LT cleared blood [La-] 90% faster than at 60-70% of LT (p<0.05). Conclusions: To permit highest exercise stress during 4x4-minute HIIT, exercise intensity should be set to 95% of VO2max, whereas active recovery should be set to 60-70% of LT during HIIT and 80-90% of LT after HIIT to most efficiently prevent excess La- and aid recovery

Pre-transplant CDKN2A expression in kidney biopsies predicts renal function and is a future component of donor scoring criteria

CDKN2A is a proven and validated biomarker of ageing which acts as an off switch for cell proliferation. We have demonstrated previously that CDKN2A is the most robust and the strongest pre-transplant predictor of post- transplant serum creatinine when compared to “Gold Standard” clinical factors, such as cold ischaemic time and donor chronological age. This report shows that CDKN2A is better than telomere length, the most celebrated biomarker of ageing, as a predictor of post-transplant renal function. It also shows that CDKN2A is as strong a determinant of post-transplant organ function when compared to extended criteria (ECD) kidneys. A multivariate analysis model was able to predict up to 27.1% of eGFR at one year post-transplant (p = 0.008). Significantly, CDKN2A was also able to strongly predict delayed graft function. A pre-transplant donor risk classification system based on CDKN2A and ECD criteria is shown to be feasible and commendable for implementation in the near future

Runx1 deficiency protects against adverse cardiac remodeling following myocardial infarction

Background: Myocardial infarction (MI) is a leading cause of heart failure and death worldwide. Preservation of contractile function and protection against adverse changes in ventricular architecture (cardiac remodeling) are key factors to limiting progression of this condition to heart failure. Consequently, new therapeutic targets are urgently required to achieve this aim. Expression of the Runx1 transcription factor is increased in adult cardiomyocytes after MI; however, the functional role of Runx1 in the heart is unknown. Methods: To address this question, we have generated a novel tamoxifen-inducible cardiomyocyte-specific Runx1-deficient mouse. Mice were subjected to MI by means of coronary artery ligation. Cardiac remodeling and contractile function were assessed extensively at the whole-heart, cardiomyocyte, and molecular levels. Results: Runx1-deficient mice were protected against adverse cardiac remodeling after MI, maintaining ventricular wall thickness and contractile function. Furthermore, these mice lacked eccentric hypertrophy, and their cardiomyocytes exhibited markedly improved calcium handling. At the mechanistic level, these effects were achieved through increased phosphorylation of phospholamban by protein kinase A and relief of sarco/endoplasmic reticulum Ca2+-ATPase inhibition. Enhanced sarco/endoplasmic reticulum Ca2+-ATPase activity in Runx1-deficient mice increased sarcoplasmic reticulum calcium content and sarcoplasmic reticulum–mediated calcium release, preserving cardiomyocyte contraction after MI. Conclusions: Our data identified Runx1 as a novel therapeutic target with translational potential to counteract the effects of adverse cardiac remodeling, thereby improving survival and quality of life among patients with MI

Moderate but not severe hypothermia causes pro-arrhythmic changes in cardiac electrophysiology

Aims: Treatment of arrhythmias evoked by hypothermia/rewarming remains challenging, and the underlying mechanisms are unclear. This in vitro experimental study assessed cardiac electrophysiology in isolated rabbit hearts at temperatures occurring in therapeutic and accidental hypothermia. Methods and results: Detailed ECG, surface electrogram, and panoramic optical mapping were performed in isolated rabbit hearts cooled to moderate (31°C) and severe (17°C) hypothermia. Ventricular activation was unchanged at 31°C while action potential duration (APD) was significantly prolonged (176.9 ± 4.2 ms vs. 241.0 ± 2.9 ms, P < 0.05), as was ventricular repolarization. At 17°C, there were proportionally similar delays in both activation and repolarization. These changes were reflected in the QRS and QT intervals of ECG recordings. Ventricular fibrillation threshold was significantly reduced at 31°C (16.3 ± 3.1 vs. 35 ± 3.5 mA, P < 0.05) but increased at 17°C (64.2 ± 9.9, P < 0.05). At 31°C, transverse conduction was relatively unchanged by cooling compared to longitudinal conduction, but at 17°C both transverse and longitudinal conduction were proportionately reduced to a similar extent. The gap junction uncoupler heptanol had a larger relative effect on transverse than longitudinal conduction and was able to restore the transverse/longitudinal conduction ratio, returning ventricular fibrillation threshold to baseline values (16.3 ± 3.1 vs. 36.3 ± 4.3 mA, P < 0.05) at 31°C. Rewarming to 37°C restored the majority of the electrophysiological parameters. Conclusions: Moderate hypothermia does not significantly change ventricular conduction time but prolongs repolarization and is pro-arrhythmic. Further cooling to severe hypothermia causes parallel changes in ventricular activation and repolarization, changes which are anti-arrhythmic. Therefore, relative changes in QRS and QT intervals (QR/QTc) emerge as an ECG-biomarker of pro-arrhythmic activity. Risk for ventricular fibrillation appears to be linked to the relatively low temperature sensitivity of ventricular transmural conduction, a conclusion supported by the anti-arrhythmic effect of heptanol at 31°C

Statin use and risk of hepatocellular carcinoma in a U.S. population

Statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) are medications widely prescribed to reduce cholesterol levels. Observational studies in high-risk populations, mostly in Asia, have suggested that statins are associated with a reduced risk of hepatocellular carcinoma (HCC). The current study sought to evaluate the association of statin use and HCC in a U.S.-based, low-risk, general population

Blinded, multi-centre evaluation of drug-induced changes in contractility using human induced pluripotent stem cell-derived cardiomyocytes

Animal models are 78% accurate in determining whether drugs will alter contractility of the human heart. To evaluate the suitability of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) for predictive safety pharmacology, we quantified changes in contractility, voltage, and/or Ca2+ handling in 2D monolayers or 3D engineered heart tissues (EHTs). Protocols were unified via a drug training set, allowing subsequent blinded multicenter evaluation of drugs with known positive, negative, or neutral inotropic effects. Accuracy ranged from 44% to 85% across the platform-cell configurations, indicating the need to refine test conditions. This was achieved by adopting approaches to reduce signal-to-noise ratio, reduce spontaneous beat rate to ≤ 1 Hz or enable chronic testing, improving accuracy to 85% for monolayers and 93% for EHTs. Contraction amplitude was a good predictor of negative inotropes across all the platform-cell configurations and of positive inotropes in the 3D EHTs. Although contraction- and relaxation-time provided confirmatory readouts forpositive inotropes in 3D EHTs, these parameters typically served as the primary source of predictivity in 2D. The reliance of these “secondary” parameters to inotropy in the 2D systems was not automatically intuitive and may be a quirk of hiPSC-CMs, hence require adaptations in interpreting the data from this model system. Of the platform-cell configurations, responses in EHTs aligned most closely to the free therapeutic plasma concentration. This study adds to the notion that hiPSC-CMs could add value to drug safety evaluation

Additive Anti-Tumor Effects of Lovastatin and Everolimus In Vitro through Simultaneous Inhibition of Signaling Pathways

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are creditedThis work was supported by a research grant from the Ludwig-Maximilians University of Munich (Förderprogramm für Forschung und Lehre [FöFoLe], grant number 865/829)