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    • br Materials and methods br Results br Discussion The presen

    2019-05-29


    Materials and methods
    Results
    Discussion The present study has demonstrated that the Wavelet discrimination algorithm is affected by myopotential interference, as evidenced by the large number of patients (55%) showing positive morphology change (defined as the percent-match score of the Wavelet less than 70%) during the isometric chest press by pressing the palms together. In fact, inappropriate tachycardia detections induced by myopotential interference occurred in two patients (5%) during a mean follow-up AZD 8055 of 49 months. Further, amplitude of the Can-RV coil EGM less than 5mV and male sex were candidate predictors of positive morphology change. A previous study reported that the use of the morphology discrimination algorithm alone was effective in terms of differentiation of SVT from VT [27]. Later studies demonstrated that the advanced morphology-based algorithms reduced inappropriate therapy without decrease in the sensitivity of VT [18,28]. More recently, it was reported that the tachycardia discrimination using Wavelet was excellent [29,30]. The START study reported that the specificity rate for rejection of 50 atrial arrhythmias was 92% in single-chamber ICDs equipped with the Wavelet algorithm [29]. However, the atrial arrhythmias were induced in the electrophysiological laboratory by programmed stimulation or burst pacing in the supine position [29]. Further, PainFree SST (SmartShock™ technology algorithms) trial, a large patient cohort study receiving ICDs, has underscored the usefulness of novel discrimination algorithms (including the Wavelet) with modern programming strategies in terms of reducing inappropriate shocks of less than 3% at 1 year [30]. In this trial, the most frequent cause of an inappropriate shock was atrial fibrillation, followed by oversensing due to EGM noise. Thus, it is important to note that EGM noise is a critical cause of inappropriate shocks even in the use of modern ICD devices. Previous studies reported that inappropriate detections caused by myopotential interference were observed in Section 2.3 − 5% of patients using the Wavelet algorithm [18,21,22]. This is similar to the present study showing that the rate of inappropriate detections was 5% (2 of 40 patients). In fact, one patient received an inappropriate shock due to the Wavelet misclassification produced by myopotential interference (Fig. 5). Therefore, we should consider the possibility of myopotential noise interfering with the Wavelet algorithm that could result in the misclassification of tachycardia episodes in a small number of patients. However, no study has identified factors associated with myopotential interference in the Wavelet algorithm to date. To our knowledge, the present study is the first to demonstrate that (a) Can-RV coil EGM amplitude less than 5mV and (b) male sex would be independent predictors of positive morphology change caused by myopotential interference (Fig. 3). The fusion of myopotential noise to the Can-RV coil EGM could affect the morphology of the true ventricular electrogram. When the amplitude of the Can-RV coil EGM is smaller, the relative influence of the myopotential noise would be larger, thereby leading to lower percent-match scores in the Wavelet algorithm. As the nominal Can-RV coil EGM of the Wavelet algorithm derives from far-field potentials, it might be influenced by muscular mass and strength. Thus, patients with morphology change appear to have high physical activity level with muscularity. We should recognize that such patients might be more susceptible to myopotential interference when the amplitude of the Can-RV coil EGM is less than 5mV. Changing the EGM source of the wavelet algorithm may be one of the methods to resolve myopotential interference. We did not use the near-field EGM on the Wavelet algorithm because it reduced the sensitivity for VT detection [20,21]. Among the far-field EGM configurations, either Can-SVC coil or RV coil-SVC coil configurations can be selected. However, the morphology of the Can-SVC coil EGM is likely to be influenced by an increase in heart rate and changes in posture [23,24], whereas that of the RV coil-SVC coil EGM is stable during postural change [24]. At present, no comparative data between RV coil-SVC coil EGM and Can-RV coil EGM are available. Whether or not a more sophisticated algorithm [31] could reduce inappropriate detections due to myopotential interference requires further investigations.