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  • Our investigation suggests that cardiac

    2019-05-08

    Our investigation suggests that cardiac pacing improves not only CSA but also OSA. The mechanism by which SDB is improved is unclear. CSA might be improved by reduction of periodic variations in heart rate, which are increased by R406 and may result in part from changes in autonomic tone. OSA might be improved by a reduction of subclinical edema of the upper airway tract dependent on bradycardia. Recently, Yumino et al. described the concept of “Fluid Shift” [10]. Their findings suggested nocturnal rostral fluid shift as a unifying concept contributing to the pathogenesis of both OSA and CSA in patients with heart failure. Our patients׳ mean heart rate during the sleep period was significantly increased from baseline (by 30%). Therefore, their cardiac output was increased during the sleep period. Increasing cardiac output decreases “Fluid Shift.” Thus, long-term cardiac pacing improved not only CSA but also OSA. These effects were not observed in the short-term (1 week) pacing period in our study. Yunino et al. also reported that the variations in the degree of fluid retention and overnight rostral fluid shift were related to changes in the predominant type of sleep apnea. One week of cardiac pacing might be a period too short to radically improve the degree of fluid retention and overnight rostral fluid shift.
    Study limitations
    Conclusions
    Conflict of interest
    Introduction High-voltage (HV) short circuit is a critical failure of an ICD lead. In general, an HV short circuit occurs because of interaction between HV conductors, such as the device can and either the superior vena cava (SVC) or the right ventricular (RV) conductors, or in the venous system between conductors and coils. If a high voltage conductor or device comes in contact with a pace–sense conductor, a shock would normally be delivered, though some pace–sense failures—e.g., a rising pacing threshold, or decreasing R-wave sensing—could be implicated in failure to shock, because high currents could drain into a pace–sense conductor. An HV short circuit is defined as shock-system failure combined with failure to shock. Gummert et al. [1] found evidence of an HV short circuit related to the sensing lead in the device pocket. In theory, an HV short circuit is very unlikely to be created between the sensing lead alone and the device can. Recently, Goldstein et al. reported a case of an ICD short circuit [2]. They did not find any evidence of HV short circuit in the device pocket. Therefore, Suppressor (intragenic) suspected that the HV short circuit had occurred in relation to the RV coil. The shorting was contact between the RV ring conductor and the RV coil inside the lead at the level of the RV coil. Unfortunately, they did not extract the problem lead. In both of the above cases, inappropriate shocks were detected before the HV short circuit was identified. This was considered to be the evidence of pace–sense conductor failure. Both case reports suggested the possibility of the pace–sense conductor being related to an HV short circuit.
    Material and methods
    Results The results are shown in Tables 2 and 3, and prove that the RV ring was not related to an HV short circuit in an ICD system in either Experiment A or Experiment B. All shocks were delivered without problems.
    Discussion This raises the question of why the pace–sense lead created an HV short circuit in the case reported by Gummert et al. [1]. Epstein et al. reported a similar case [3]. In both cases, an integrated bipolar dual coil lead was used. In an integrated bipolar lead configuration, the RV conductor is bifurcated in the yoke of the lead. One conductor is a pace–sense conductor, which is assigned as a sensing anode, and the other conductor is a defibrillation connector, which is assigned as a shock cathode. The RV coil conductor plays two roles: one as pace–sense anode and the other as shocking cathode (Figs. 2 and 3). In Epstein׳s case [3], the HV short circuit was created in the yoke because of dislodgement of the yoke splice crimp tube. The SCV conductor was abraded by the crimp, thus creating a short circuit with the RV coil conductor in the yoke. In Gummert׳s case [1], the lead was modern, with IS1 and DF1 connectors. The pace–sense conductor from the yoke was running in the lead to the IS1 connector. The sensing anode conductor was also bifurcated from the RV coil conductor in the yoke. The pace–sense lead from the yoke was abraded by the edge of the ICD can and the HV short circuit was created within the device pocket. Hence, the sensing conductor in the pace–sense lead was the RV coil conductor.