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type=\u0022text\/css\u0022 rel=\u0022stylesheet\u0022 href=\u0022\/\/d282kpwvnogo5m.cloudfront.net\/sites\/default\/files\/cdn\/css\/http\/css_Xg7z6oCTVgud_Q0huYz9x9iiD5H_2YPSJ5z2ZViSWdY.css\u0022 media=\u0022all\u0022 \/\u003E\n\u003Clink rel=\u0027stylesheet\u0027 type=\u0027text\/css\u0027 href=\u0027\/sites\/all\/modules\/contrib\/panels\/plugins\/layouts\/onecol\/onecol.css\u0027 \/\u003E\u003C\/head\u003E\u003Cbody\u003E\u003Cdiv class=\u0022panels-ajax-tab-panel panels-ajax-tab-panel-sageoa-tab-art\u0022\u003E\u003Cdiv class=\u0022panel-display panel-1col clearfix\u0022 \u003E\n  \u003Cdiv class=\u0022panel-panel panel-col\u0022\u003E\n    \u003Cdiv\u003E\u003Cdiv class=\u0022panel-pane pane-highwire-markup\u0022 \u003E\n  \n      \n  \n  \u003Cdiv class=\u0022pane-content\u0022\u003E\n    \u003Cdiv class=\u0022highwire-markup\u0022\u003E\u003Cdiv xmlns=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022 id=\u0022content-block-markup\u0022 xmlns:xhtml=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022\u003E\u003Cdiv class=\u0022article fulltext-view \u0022\u003E\u003Cspan class=\u0022highwire-journal-article-marker-start\u0022\u003E\u003C\/span\u003E\u003Cdiv class=\u0022section abstract\u0022 id=\u0022abstract-1\u0022\u003E\u003Ch2\u003ESummary\u003C\/h2\u003E\u003Cp id=\u0022p-1\u0022\u003EIn the Micra Transcatheter Pacing Study, a novel leadless pacemaker system delivered using a transcatheter system, was tested for strength duration and battery longevity. Despite its size, the electrical performance of the device was comparable with current ventricular demand pacemakers and utilization of 0.24 vs 0.4 milliseconds pulse width increased the projected battery longevity by 0.83 years.\u003C\/p\u003E\u003C\/div\u003E\u003Cul class=\u0022kwd-group\u0022\u003E\u003Cli class=\u0022kwd\u0022\u003Eleadless transcatheter pacemaker\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003Ebattery longevity\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003Etranscatheter pacing system\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003EMicra TPS\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003ENCT02004873\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003Eatrial fibrillation\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003Ecardiology \u0026amp; cardiovascular medicine clinical trials\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003Einterventional techniques \u0026amp; devices\u003C\/li\u003E\u003C\/ul\u003E\u003Cdiv class=\u0022section\u0022 id=\u0022sec-1\u0022\u003E\u003Cp id=\u0022p-2\u0022\u003EResults of the Micra Transcatheter Pacing Study [Ritter P et al. \u003Cem\u003EEur Heart J\u003C\/em\u003E. 2015], which examined the pacing threshold curve at 3 months following delivery and the projected longevity of a new leadless pacing system delivered using a transcatheter delivery system (TPS), found pacing thresholds were low at the time of implantation and stable at 3 months. Use of a 0.24 vs 0.4 milliseconds pulse width increased the projected battery longevity by 0.83 years noted Clemens Steinwender, MD, Linz University Hospital, Linz, Austria.\u003C\/p\u003E\u003Cp id=\u0022p-3\u0022\u003EThe Micra TPS system is a new miniature leadless pacemaker that is interventionally delivered via the femoral vein using a transcatheter delivery system. Because of its small size, the pacing threshold and battery life are of particular interest. Chronaxie is the minimum time (pulse width) required for excitation of a structure (eg, a muscle or nerve) by a voltage of 2 times the rheobase voltage. The rheobase voltage is the threshold at an infinite pulse width. Chronaxie is considered the pulse width that minimizes the use of pacing energy. The Micra TPS device has a nominal pacing pulse width of 0.24 milliseconds, which is close to the chronaxie.\u003C\/p\u003E\u003Cp id=\u0022p-4\u0022\u003EIn the Micra Clinical Study, the threshold, impedance, pacing percentage, and heart rate were analyzed in the first 60 patients to reach the 3-month follow-up visit. Pacing threshold measurements were conducted at 0.24, 0.4, and 1.0 milliseconds with a voltage resolution of 0.125 V at implant and 3 months. The Lapicque equation [V\u2005=\u2005rheobase\u2005\u00d7\u2005(1\u2005+\u2005chronaxie\u2005\/\u2005pulse width)] was used to determine chronaxie, rheobase, and the strength duration curve given the 2 measurements at 0.24 and 1.0 milliseconds.\u003C\/p\u003E\u003Cp id=\u0022p-5\u0022\u003EIndividual patient battery longevity was projected using programmed pacing amplitude, pulse width, impedance, pacing percentage, and heart rate at the 3-month visit assuming a 5-month shelf life prior to implant.\u003C\/p\u003E\u003Cp id=\u0022p-6\u0022\u003EThe most common indication for pacing was atrial fibrillation with pauses. At 3 months, the mean impedance was 651 \u03a9, mean pacing percentage was 49%, mean heart rate was 72 bpm, and 59 of 60 patients were programmed to a pulse width of 0.24 milliseconds. Impedance decreased and R-waves increased over time.\u003C\/p\u003E\u003Cp id=\u0022p-7\u0022\u003EMean thresholds at implant were 0.57 at 0.24 milliseconds, 0.46 at 0.4 milliseconds, and 0.37 at 1.0 milliseconds. Mean thresholds at 3 months were 0.51 at 0.24 milliseconds, 0.43 at 0.4 milliseconds, and 0.34 at 1.0 milliseconds. There were 4 and 2 patients with thresholds at 0.24 milliseconds \u0026gt;\u20051.0 V at implant and 3 months, respectively.\u003C\/p\u003E\u003Cp id=\u0022p-8\u0022\u003EThe strength duration curve and projected longevity calculated from 55 patients at 3 months are shown in \u003Ca id=\u0022xref-fig-1-1\u0022 class=\u0022xref-fig\u0022 href=\u0022#F1\u0022\u003EFigure 1\u003C\/a\u003E. The mean rheobase was 0.28 V and the chronaxie was 0.23 milliseconds. Battery life was projected at greater than 10 years.\u003C\/p\u003E\u003Cdiv id=\u0022F1\u0022 class=\u0022fig pos-float  odd\u0022\u003E\u003Cdiv class=\u0022highwire-figure\u0022\u003E\u003Cdiv class=\u0022fig-inline-img-wrapper\u0022\u003E\u003Cdiv class=\u0022fig-inline-img\u0022\u003E\u003Ca href=\u0022http:\/\/d282kpwvnogo5m.cloudfront.net\/content\/spmdc\/15\/22\/10\/F1.large.jpg?width=800\u0026amp;height=600\u0026amp;carousel=1\u0022 title=\u0022Strength Duration Curve and Projected Device LongevityReproduced with permission from C Steinwender, MD.\u0022 class=\u0022fragment-images colorbox-load\u0022 rel=\u0022gallery-fragment-images-1089869927\u0022 data-figure-caption=\u0022Strength Duration Curve and Projected Device LongevityReproduced with permission from C Steinwender, MD.\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003E\u003Cimg class=\u0022fragment-image\u0022 alt=\u0022Figure 1.\u0022 src=\u0022http:\/\/d282kpwvnogo5m.cloudfront.net\/content\/spmdc\/15\/22\/10\/F1.medium.gif\u0022\/\u003E\u003C\/a\u003E\u003C\/div\u003E\u003C\/div\u003E\u003Cul class=\u0022highwire-figure-links inline\u0022\u003E\u003Cli class=\u00220 first\u0022\u003E\u003Ca href=\u0022http:\/\/d282kpwvnogo5m.cloudfront.net\/content\/spmdc\/15\/22\/10\/F1.large.jpg?download=true\u0022 class=\u0022highwire-figure-link highwire-figure-link-download\u0022 title=\u0022Download Figure 1.\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003EDownload figure\u003C\/a\u003E\u003C\/li\u003E\u003Cli class=\u00221\u0022\u003E\u003Ca href=\u0022http:\/\/d282kpwvnogo5m.cloudfront.net\/content\/spmdc\/15\/22\/10\/F1.large.jpg\u0022 class=\u0022highwire-figure-link highwire-figure-link-newtab\u0022 target=\u0022_blank\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003EOpen in new tab\u003C\/a\u003E\u003C\/li\u003E\u003Cli class=\u00222 last\u0022\u003E\u003Ca href=\u0022\/highwire\/powerpoint\/16738\u0022 class=\u0022highwire-figure-link highwire-figure-link-ppt\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003EDownload powerpoint\u003C\/a\u003E\u003C\/li\u003E\u003C\/ul\u003E\u003C\/div\u003E\u003Cdiv class=\u0022fig-caption\u0022 xmlns:xhtml=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022\u003E\u003Cspan class=\u0022fig-label\u0022\u003EFigure 1.\u003C\/span\u003E \u003Cp id=\u0022p-9\u0022 class=\u0022first-child\u0022\u003EStrength Duration Curve and Projected Device Longevity\u003C\/p\u003E\u003Cp id=\u0022p-10\u0022\u003EReproduced with permission from C Steinwender, MD.\u003C\/p\u003E\u003Cdiv class=\u0022sb-div caption-clear\u0022\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/div\u003E\u003Cp id=\u0022p-11\u0022\u003EThe findings of this study were limited by the number of patients and relatively short follow-up. In addition, longevity projections assume that pacing threshold, impedance, pacing rate, and pacing percentage do not change after 3 months. However, the estimated longevity of the device is comparable with current ventricular demand pacemakers. The miniature size of this device does not appear to detract from its electrical performance.\u003C\/p\u003E\u003C\/div\u003E\u003Cul class=\u0022copyright-statement\u0022\u003E\u003Cli class=\u0022fn\u0022 id=\u0022copyright-statement-1\u0022\u003E\u00a9 2015 SAGE Publications\u003C\/li\u003E\u003C\/ul\u003E\u003Cspan class=\u0022highwire-journal-article-marker-end\u0022\u003E\u003C\/span\u003E\u003C\/div\u003E\u003Cspan id=\u0022related-urls\u0022\u003E\u003C\/span\u003E\u003C\/div\u003E\u003Ca href=\u0022http:\/\/mdc.sagepub.com\/content\/15\/22\/10.abstract\u0022 class=\u0022hw-link hw-link-article-abstract\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003EView Summary\u003C\/a\u003E\u003C\/div\u003E  \u003C\/div\u003E\n\n  \n  \u003C\/div\u003E\n\u003C\/div\u003E\n  \u003C\/div\u003E\n\u003C\/div\u003E\n\u003C\/div\u003E\u003Cscript type=\u0022text\/javascript\u0022 src=\u0022http:\/\/mdc.sagepub.com\/sites\/all\/modules\/highwire\/highwire\/plugins\/highwire_markup_process\/js\/highwire_figures.js?nzl3n2\u0022\u003E\u003C\/script\u003E\n\u003Cscript type=\u0022text\/javascript\u0022 src=\u0022http:\/\/mdc.sagepub.com\/sites\/all\/modules\/highwire\/highwire\/plugins\/highwire_markup_process\/js\/highwire_openurl.js?nzl3n2\u0022\u003E\u003C\/script\u003E\n\u003C\/body\u003E\u003C\/html\u003E"}