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    • br Potential countermeasures for arrhythmias

    2019-04-29


    Potential countermeasures for arrhythmias during long-duration spaceflight A remote medical system will help to detect fatal arrhythmias in astronauts during the early stages. JAXA is in the process of developing a Remote Medical System [66]. This system consists of an electric stethoscope, pulse oximeter, Holter-ECG, sleep monitor and USB camera. It will allow flight surgeons to see the astronauts\' ECGs or Holter-ECGs and listen to their heartbeat from Earth. The flight surgeons can then not only identify the arrhythmias, but also give instructions about the medications [66]. A conventional stethoscope is not very effective at checking for subtle cardiac murmurs in the ISS, because of the high ambient noise levels [58]. The new system could help to detect any recent cardiac murmurs in space. Another cause of arrhythmias can be excessive radiation, which causes coronary arteriosclerosis. Coronary arteriosclerosis can be one of the main causes of fatal arrhythmias and SCD during long spaceflights. Avoiding excessive radiation is one possible countermeasure. Another possible countermeasure to the effects of radiation on the neuropeptide receptors would be a diet rich in antioxidants, such as vitamins E, C, A, and β-carotene. In fact, Scott Smith and colleagues at JSC have shown that blood concentrations of some antioxidants, such as vitamin E, are decreased during long-duration spaceflight [67], while several in vitro studies have indicated that several vitamins and supplements, such as vitamin E and co-enzyme Q10, may be effective countermeasures against oxidative stress caused by space radiation [68,69]. However, taking fresh fruits and vegetables on long-duration missions would be nearly impossible. Furthermore, it appears that vitamins and other supplements lose their stability during extended periods of spaceflight [70]. Another countermeasure for reducing the occurrence of SCD and AF is a healthy intake of omega-3 fatty acids. In a systematic review and meta-analysis of data pooled from 19 large prospective cohort studies and randomized trials, it was shown that omega-3 fatty acids reduce ischemic heart death and SCD [71]. Some observational studies have found an association between fish oil consumption and a reduced risk of AF [72]. These studies prove that a healthy diet including omega 3 fatty acids will not only reduce the risk of SCD, but also decrease the risk of ischemic heart deaths [71].
    Conclusion
    Conflict of interest
    Introduction The implantable cardioverter-defibrillator (ICD) has dramatically reduced the risk of sudden death in patients with malignant ventricular tachyarrhythmias [1,2]. However, 10–30% of patients who have undergone ICD implantation experience “electrical storms,” in which ventricular tachyarrhythmias occur ≥2 times within a 24-h period [3]. Patients with severe electrical storm are known to have a worse prognosis [4]. Some studies have demonstrated that ICD shocks increase the dispersion of ventricular repolarization [5,6]. The spatial dispersion of ventricular repolarization plays a role in the initiation and maintenance of malignant ventricular tachyarrhythmias, including electrical storms. The QT dispersion and recovery time dispersion are assumed to reflect the spatial heterogeneity [7,8]. Few therapeutic options are currently available for controlling electrical storms. Nifekalant hydrochloride (NIF) is a class III antiarrhythmic drug that causes dose-dependent prolongation of the action potential duration in both atrial and ventricular muscle, mainly by reducing the rapid component of the delayed rectifier K+ current (Ikr) [9,10]. Several clinical studies have demonstrated the effectiveness of intravenous NIF for recurrent ventricular tachyarrhythmias that are resistant to other antiarrhythmic drugs and ICD shock [11], especially electrical storms [12]. However, little is known about the electropharmacological basis of the efficacy of NIF in treating these arrhythmias. Moreover, the effect of NIF on the spatial dispersion of repolarization (SDR) has not been reported yet in any clinical study.
    Methods
    Results
    Discussion The major finding of the present study is that administration of NIF significantly suppressed the deterioration of SDR just after ICD shock. To the best of our knowledge, this is the first study to show that NIF significantly reduces the SDR after ICD shock in patients receiving oral amiodarone and β-blocker agents. A recent study reported that the SDR after ICD shock played an important role in the initiation and maintenance of ventricular tachyarrhythmias [5–7]. We therefore speculate that the reduction in SDR may be one of the mechanisms by which NIF suppresses the recurrence of ventricular tachyarrhythmias just after ICD shock in the presence of oral amiodarone and β-blocker administration.
    Conclusion
    Disclosure
    Conflicts of interest