337 - Stability of AsymptomaticDiaphragmatic Stimulation Thresholds after 1 Year: Results of the Epiphrenic IIPilot

Abstract

Introduction: Asymptomatic Diaphragmatic Stimulation (ADS) is a heart failure therapy concept under investigation. Within a range of voltages, electrical stimulation of the diaphragm synchronized to the cardiac cycle alters cardiovascular hemodynamics including venous return and preload by modulating diaphragmatic movement and intrathoracic pressure. The Epiphrenic II pilot utilized a cross-over design to investigate the chronic effects of continuous ADS on cardiac function, including changes to the minimum pacing output required to asymptomatically capture the diaphragm. Hypothesis: Within one year diaphragmatic pacing voltage and pulse width would not change significantly. Methods: In the Epiphrenic II pilot, post CABG patients received CRT devices branched to provide ADS via an epicardial electrode surgically fixated to the left diaphragm. ADS stimulation outputs were determined by using a clinical assessment of the minimum output required to evoke a palpable subcostal yet asymptomatic diaphragmatic response. Therapy was synchronized to left ventricular activation for each cardiac cycle. Upon completion of the formal study protocol at 9 weeks post-implant, patients were provided the option to continue with ADS and CRT, and were invited for a routine follow-up examination at one year post implant. Results: All 24 patients receiving ADS at baseline were alive at their 1 year follow-up, but five refused the follow-up examination and one had relocated. Eighteen patients agreed to perform a one year follow-up, of which one had diaphragmatic pacing off due to non-ADS related device issues, resulting in 17 paired data sets. Diaphragmatic pacing voltage and pulse width at 1 year were compared to those at 9 weeks post-implant. Capture thresholds were not significantly different between 9 weeks and 1 year (2.8 ± 0.8 vs 2.9 ± 0.9 V, paired t-test, P = .8), nor was pulse width significantly different (0.5 ± 0.3 vs 0.6 ± 0.3 msec, paired t-test, P = .1). Conclusions: This limited patient set suggests that asymptomatic diaphragmatic threshold values are stable during constant electrical stimulation, providing credence to the hypothesis the diaphragm can be continuously paced for over one year with no changes to stimulation output, which is a minimum requisite for ADS to reliably augment cardiac function chronically.