br Material and methods br Results Thirty

Material and methods
Results Thirty-one patients were enrolled consecutively, in this randomized study, between January 2010 and March 2012. The mean age was 65.5±13.7 years. The proportion of patients with primary prevention indication was 25.8% and ischemic cardiomyopathy was 29.0%. All reported patient characteristics are shown in Table 1. Among the consecutive patients, 5 patients were excluded from this study for the following conditions: 2 patients were excluded for old age, 1 patient, for deteriorated general condition due to cancer, and the last 2 patients, for low cardiac function.
Discussion While ICD shock therapy has prevented sudden cardiac death, shock therapy may induce myocardial damage and influence cardiac hemodynamics or life expectancy [1–3,14–17]. It has been suggested that myocardial damage resulting from shock therapy contributes to poor prognosis, whereas the use of ATP minimizes damage and does not affect prognosis. It is therefore important to terminate ventricular arrhythmias with the first ICD shock and minimize the number of inappropriate and unnecessary ICD shocks. The safety of defibrillation with prolonged detection duration has been a following website of concern owing to the possibility of defibrillation threshold (DFT) elevation and creation of unstable VF waves over time. Windecker et al. noted that VF episodes lasting 10s or more may have adverse effects on DFTs and negatively affect the effectiveness of ICD therapy [11]. Increasing VF NID prolongs the detection duration and may also cause unstable VF waves, resulting in additional undersensed VTAs. This study demonstrated that NID 30/40 increased the time from VF induction to detection by 2.84s; however, the defibrillation success rate was 100% by the first ICD shock, and the numbers of undersensed peaks were similar between both NID groups. Further, in patients with cardiac dysfunction, smaller VF waves may lead to more undersensed peaks that could cause prolongation of the time from VF induction to termination. The present study showed no differences in the number of undersensed peaks between patients with cardiac dysfunction and normal cardiac function, even in the NID 30/40 group. These results suggest that VF NID could be increased to 30/40 in a safe manner, with no effects on the sensitivity to VTA or the defibrillation success rate. Along with the discrimination algorithms, inappropriate and unnecessary shocks could be avoided by ATP or ICD programming. According to the PainFREE and PainFREE Rx II clinical trials, the ATP success rate in the FVT detection zone (188–250bpm) was approximately 70% [4,6]. While ATP therapy may terminate FVT and avoid unnecessary shocks, it cannot revert VF, which requires ICD shock therapy. The Primary Prevention Parameters Evaluation (PREPARE) trial reported that in primary prevention patients, increased NID (30/40) and ATP attempts for FVTs decreased the incidence of ICD complications (including appropriate, inappropriate, and unnecessary ICD shocks) without posing safety concerns and improved the life expectancy of ICD recipients [7]. The RELEVANT study showed that prolonged detection duration (NID 30/40) led to a dramatic reduction of ICD interventions without jeopardizing ICD therapy capabilities or increasing morbidity in primary prevention patients [8]. The MADIT-RIT trial also reported that ICD programming for high-rate therapy or delayed therapy in primary prevention patients reduced the occurrence of inappropriate therapy [9]. Furthermore, the ADVANCE III study demonstrated that prolonged detection duration, NID 30/40, could reduce ICD therapy rate including ATP and shocks in both primary and secondary prevention patients safely [10]. Although this study is not exactly comparable to the ADVANCE III study, as ATP therapy was programmed in the ADVANCE III study, the results of the present study are in line with those of the ADVANCE III study. Among the studies described above, the programming of VF detection interval is different. It still remains unclear how the detection interval should be programmed; therefore, further evaluation of the appropriate detection interval and detection duration is required. In the present study, we aimed to determine whether increased VF NID (from 18/24 to 24/32 or 30/40) reduced the number of inappropriate shocks. In the retrospective analysis of inappropriate shocks, the majority of VF episodes occurred in the pre-programmed R–R interval, while AF and oversensing episodes were more likely to deviate from the VF detection zone. This suggests that increased VF NID is effective in preventing inappropriate shocks due to AF and oversensing. In this study, all 5 inappropriate shock episodes due to AF were avoidable when modeling NID 24/32 and 30/40. For instance, in the 5 episodes with NID 30/40, the maximum number of abnormal beats counted was 20–27, suggesting the necessity of a longer monitoring time sufficient to count approximately 30 beats. Since AF is considered the most common cause of inappropriate shock [1,18], increasing VF NID would be effective in avoiding these shocks. Furthermore, the shock reduction rate was 42.9% or 57.1% in the lead fracture cases with NID 24/32 or 30/40, respectively. Early detection is an important measure against lead fractures. The Lead Integrity Alert, which allows such early warnings and prolongs the detection duration to NID 30/40, has been shown to avoid inappropriate shocks [19–21]. According to the CONNECT trial [22], the time from event onset to clinical decision in response to alerts for AT/AF burden, ventricular rate during AT/AF, and lead impedance out of range could be significantly reduced with a remote monitoring system. In the future, remote monitoring systems will make it possible to more effectively avoid inappropriate shock delivery in addition to the prolonged VF NID approach.