Acute human defibrillation performance of a subcutaneous implantable cardioverter-defibrillator with an additional coil electrode.

BACKGROUND: The subcutaneous implantable cardioverter-defibrillator (S-ICD) delivers 80 J shocks from an 8 cm left-parasternal coil to a 59 cm3 left lateral pulse generator (PG). A system that defibrillates with lower energy could significantly reduce PG size. Computer modeling and animal studies suggested that a second shock coil either parallel to the left-parasternal coil or transverse from the xiphoid to the PG pocket would significantly reduce the defibrillation threshold. OBJECTIVE: The purpose of this study was to acutely assess the defibrillation efficacy of parallel and transverse configurations in patients receiving an S-ICD. METHODS: Testing was performed in patients receiving a conventional S-ICD system. Success at 65 J was required before investigational testing. A second electrode was temporarily inserted from the xiphoid incision connected to the PG with an investigational Y-adapter. Phase 1 (n = 11) tested the parallel configuration. Phase 2 (n = 21) tested both parallel and transverse configurations in random order. RESULTS: This study enrolled 35 patients (28 males (80%); mean age 51 ± 17 years; left ventricular ejection fraction 40% ± 15%; body mass index 26 ± 4 kg/m2; prior myocardial infarction 46%; congestive heart failure 49%; cardiomyopathy 63%). Compared to the conventional S-ICD system, mean shock impedance decreased for both parallel (69 ± 15 Ω vs 86 ± 20 Ω; n = 33; P < .001) and transverse (56 ± 14 Ω vs 81 ± 21 Ω; n = 20; P < .001) configurations. Shock success rates at 20, 30, and 40 J were 55%, 79%, 97%, and 25%, 70%, 90% for parallel and transverse configurations, respectively. Defibrillation threshold testing was well tolerated with no serious adverse events. CONCLUSION: Adding a second shock coil, particularly in the parallel configuration, significantly reduced the impedance and had a high likelihood of defibrillation success at energies ≤40 J. This may enable the development of a smaller S-ICD.

Effect of Channel Envelope Synchrony on Interaural Time Difference Sensitivity in Bilateral Cochlear Implant Listeners.

OBJECTIVES: For a periodic acoustic input signal, the channel envelopes coded by current bilateral cochlear implant sound processors can be asynchronous. The effect of this asynchrony on sensitivity to interaural time differences (ITDs) was assessed. DESIGN: ITD sensitivity was measured in six bilateral cochlear implant listeners for single- and three-electrode stimuli. The three-electrode stimuli contained envelope modulations, either synchronous or asynchronous across electrodes, with delays of 1.25 up to 5.00 ms. Each individual electrode carried the same ITD. Either neighboring electrodes were chosen or a separation of four electrodes to investigate the effect of electrode distance. RESULTS: With synchronous envelopes, no difference in ITD sensitivity was found among single-electrode, adjacent three-electrode, and spaced three-electrode stimuli. A decrease in ITD sensitivity was found with increasing across-channel envelope asynchrony, which was consistent with the use of the across-electrode aggregate stimulation pattern rather than individual information channels for ITDs. No consistent effect of electrode separation was found. CONCLUSIONS: While the binaural system was resilient to small delays between envelopes, larger delays significantly deceased ITD sensitivity, both for adjacent and further spaced electrodes.

Modulation enhancement in the electrical signal improves perception of interaural time differences with bimodal stimulation.

Interaural timing cues are important for sound source localization and for binaural unmasking of speech that is spatially separated from interfering sounds. Users of a cochlear implant (CI) with residual hearing in the non-implanted ear (bimodal listeners) can only make very limited use of interaural timing cues with their clinical devices. Previous studies showed that bimodal listeners can be sensitive to interaural time differences (ITDs) for simple single- and three-channel stimuli. The modulation enhancement strategy (MEnS) was developed to improve the ITD perception of bimodal listeners. It enhances temporal modulations on all stimulated electrodes, synchronously with modulations in the acoustic signal presented to the non-implanted ear, based on measurement of the amplitude peaks occurring at the rate of the fundamental frequency in voiced phonemes. In the first experiment, ITD detection thresholds were measured using the method of constant stimuli for five bimodal listeners for an artificial vowel, processed with either the advanced combination encoder (ACE) strategy or with MEnS. With MEnS, detection thresholds were significantly lower, and for four subjects well within the physically relevant range. In the second experiment, the extent of lateralization was measured in three subjects with both strategies, and ITD sensitivity was determined using an adaptive procedure. All subjects could lateralize sounds based on ITD and sensitivity was significantly better with MEnS than with ACE. The current results indicate that ITD cues can be provided to bimodal listeners with modified sound processing.

The effect of interaural differences in envelope shape on the perceived location of sounds (L).

Users of bilateral cochlear implants and a cochlear implant combined with a contralateral hearing aid are sensitive to interaural time differences (ITDs). The way cochlear implant speech processors work and differences between modalities may result in interaural differences in shape of the temporal envelope presented to the binaural system. The effect of interaural differences in envelope shape on ITD sensitivity was investigated with normal-hearing listeners using a 4 kHz pure tone modulated with a periodic envelope with a trapezoid shape in each cycle. In one ear the onset segment of the trapezoid was transformed by a power function. No effect on the just noticeable difference in ITD was found with an interaural difference in envelope shape, but the ITD for a centered percept was significantly different across envelope shape conditions.

Enhancement of interaural level differences improves sound localization in bimodal hearing.

Users of a cochlear implant together with a contralateral hearing aid-so-called bimodal listeners-have difficulties with localizing sound sources. This is mainly due to the distortion of interaural time and level difference cues (ITD and ILD), and limited ITD sensitivity. An algorithm is presented that enhances ILD cues. Horizontal plane sound-source localization performance of six bimodal listeners was evaluated in (1) a real sound field with their clinical devices, (2) in a virtual sound field, under direct computer control, and (3) in a virtual sound field with ILD enhancement. The results in the real sound field did not differ significantly from the results in the virtual field, and ILD enhancement improved localization performance by 4°-10° absolute error, relative to a mean absolute error of 28° in the condition without ILD enhancement.

Bimodal listeners are not sensitive to interaural time differences in unmodulated low-frequency stimuli (L).

Sensitivity to interaural time differences (ITDs) with unmodulated low-frequency stimuli was assessed in bimodal listeners who had previously shown to be good performers in ITD experiments. Two types of stimuli were used: (1) an acoustic sinusoid combined with an electric transposed signal and (2) an acoustic sinusoid combined with an electric clicktrain. No or very low sensitivity to ITD was found for these stimuli, even though subjects were highly trained on the task and were intensively tested in multiple test sessions. In previous studies with users of a cochlear implant (CI) and a contralateral hearing aid (HA) (bimodal listeners), sensitivity was shown to ITD with modulated stimuli with frequency content between 600 and 3600 Hz. The outcomes of the current study imply that in speech processing design for users of a CI in combination with a HA on the contralateral side, the emphasis should be more on providing salient envelope ITD cues than on preserving fine-timing ITD cues present in acoustic signals.

Sensitivity of bimodal listeners to interaural time differences with modulated single- and multiple-channel stimuli.

In a previous study, it was shown that users of a cochlear implant and a contralateral hearing aid are sensitive to interaural time differences (ITDs). In the current study, we investigated (1) the influence on ITD sensitivity of bilaterally varying the place of excitation in the cochlea and of modulation frequency, and (2) the sensitivity to ITD with a 3-channel stimulus generated using continuous-interleaved-sampling (CIS)-like processing. The stimuli were (1) a high-frequency carrier (acoustic sinusoid and single-electrode electric pulse train), modulated with a half-wave-rectified low-frequency sinusoid (a so-called transposed stimulus), and (2) a 3-channel stimulus, generated by sending an acoustic click train through processing similar to the CIS strategy. Four bimodal listeners were sensitive to ITD for both stimulus types. For the first stimulus type, there was no significant influence on ITD sensitivity of the acoustic carrier frequency. Performance decreased with increasing modulation frequency with a limit of sensitivity at around 150-200 Hz. Sensitivity was similar for the single- and 3-channel stimulus. The results indicate the possibility of ITD perception with adapted clinical processors, which can lead to improved sound source localization and binaural unmasking.

Neurodevelopmental disorders in males related to the gene causing Rett syndrome in females (MECP2).

Mutations in the MECP2 (methyl-CpG-binding protein 2) gene are known to cause Rett syndrome, a well-known and clinically defined neurodevelopmental disorder. Rett syndrome occurs almost exclusively in females and for a long time was thought to be an X-linked dominant condition lethal in hemizygous males. Since the discovery of the MECP2 gene as the cause of Rett syndrome in 1999, MECP2 mutations have, however, also been reported in males. These males phenotypically have classical Rett syndrome when the mutation arises as somatic mosaicism or when they have an extra X chromosome. In all other cases, males with MECP2 mutations show diverse phenotypes different from classical Rett syndrome. The spectrum ranges from severe congenital encephalopathy, mental retardation with various neurological symptoms, occasionally in association with psychiatric illness, to mild mental retardation only. We present a 21-year-old male with severe mental retardation, spastic tetraplegia, dystonia, apraxia and neurogenic scoliosis. A history of early hypotonia evolving into severe spasticity, slowing of head growth, breathing irregularities and good visual interactive behaviour were highly suggestive of Rett syndrome. He has a de novo missense mutation in exon 3 of the MECP2 gene (P225L). The clinical spectrum and molecular findings in males with MECP2 mutations are reviewed.