Signal Transmission in the Auditory System

Contains table of contents for Section 3, an introduction and reports on five research projects.National Institutes of Health Grant R01-DC-00194National Institutes of Health Grant P01-DC-00119Charles S. Draper Laboratory Contract DL-H-496015National Institutes of Health Grant R01 DC00238National Institutes of Health Grant R01-DC02258National Institutes of Health Grant T32-DC00038National Institutes of Health Grant RO1 DC00235National Institutes of Health Grant P01-DC00361National Institutes of Health Contract N01-DC-6-210

Pressure-Frequency Sensing Subxiphoid Access System for Use in Percutaneous Cardiac Electrophysiology: Prototype Design and Pilot Study Results

We have designed, built, and tested an early prototype of a novel subxiphoid access system intended to facilitate epicardial electrophysiology, but with possible applications elsewhere in the body. The present version of the system consists of a commercially available insertion needle, a miniature pressure sensor and interconnect tubing, read-out electronics to monitor the pressures measured during the access procedure, and a host computer with user-interface software. The nominal resolution of the system is <0.1 mmHg, and it has deviations from linearity of <1%. During a pilot series of human clinical studies with this system, as well as in an auxiliary study done with an independent method, we observed that the pericardial space contained pressure-frequency components related to both the heart rate and respiratory rate, while the thorax contained components related only to the respiratory rate, a previously unobserved finding that could facilitate access to the pericardial space. We present and discuss the design principles, details of construction, and performance characteristics of this system

Epicardial left atrial appendage clip occlusion also provides the electrical isolation of the left atrial appendage

OBJECTIVES: The exclusion of the left atrial appendage (LAA) has been used to reduce the risk of stroke associated with atrial fibrillation (AF). While LAA exclusion has been associated with a reduced risk of stroke, the effect on the electrical activity of the LAA (a potential source of AF) remains unknown. As such, we sought to demonstrate whether surgical epicardial clip occlusion leads to the electrical isolation of the LAA. METHODS: From December 2010 until August 2011, 10 patients with paroxysmal AF underwent off-pump coronary artery bypass surgery with bilateral pulmonary vein isolation and an LAA clip occlusion with a new epicardial clip. Before and after the clip was placed, pacing manoeuvres were performed to assess the electrical exit and entry blocks from the LAA. RESULTS: All clips were applied successfully. The mean procedure time for the clip application was 4 ± 1 min. No complications occurred related to clip application. Prior to the pericardial closure, 18 ± 3 min after the clip placement, the LAA stimulation and pacing manoeuvres demonstrated complete electrical isolation of the LAA in all cases. CONCLUSIONS: Epicardial LAA clip occlusion leads to the acute electrical isolation of the LAA and may not only provide stroke prevention but also reduce the recurrence of AF

Scar voltage threshold determination using ex vivo magnetic resonance imaging integration in a porcine infarct model: Influence of interelectrode distances and three-dimensional spatial effects of scar.

BackgroundStudies analyzing optimal voltage thresholds for scar detection with electroanatomic mapping frequently lack a gold standard for comparison.ObjectiveThe purpose of this study was to use a porcine infarct model with ex vivo magnetic resonance imaging (MRI) integration to characterize the relationship between interelectrode spacing and bipolar voltage thresholds and examine the influence of 3-dimensional scar on unipolar voltages.MethodsThirty-two combined endocardial-epicardial electroanatomic maps were created in 8 postinfarct porcine subjects (bipolar 2-mm, 5-mm, and 8-mm interelectrode spacing and unipolar) for comparison with ex vivo MRI. Two thresholds were compared: (1) 95% normal distribution and (2) best fit to MRI. Direct electrogram analysis was performed in regions across from MRI-defined scar and adjacent to scar border zone.ResultsA linear increase in optimal thresholds was observed with wider bipole spacing. The 95% thresholds for scar were lower than MRI-matched thresholds with moderate sensitivity for nontransmural scar (54% endo, 63% epi). Unipolar endocardial scar area exceeded MRI-defined scar, resulting in mismatched false scar in 5 of 8 (63%). Endocardial and epicardial unipolar voltages were lower than normal in regions adjacent and across from scar.ConclusionVariations in interelectrode spacing necessitate tailored bipolar voltage thresholds to optimize scar detection. Statistical 95% thresholds appear to be conservative and not fully sensitive for the detection of scar defined by high-resolution ex vivo MRI. In the presence of endocardial scar, unipolar mapping to quantitatively characterize epicardial scar may be overly sensitive due to 3-dimensional spatial averaging