Christine Henry

Preliminary clinical experience with the first dual chamber pacemaker defibrillator.

The lack of specificity of VT detection is a significant shortcoming of current ICDs. In a French multicenter study, 18 patients underwent implantation of the Defender 9001 (ELA Medical), an ICD utilizing dual chamber pacing and arrhythmia detection. Over a mean follow‐up period of 7.1 ± 4.5 months, 176 tachycardia episodes recorded in the device memory were analyzed, and physician diagnosis was compared with that by the device. All 122 VT/VF episodes were correctly diagnosed, as were 51 of 53 supraventricular tachyarrhythmias. Two episodes of AF with rapid regular ventricular rates were treated as VT, and a third episode, treated as VT, could not be diagnosed with certainty. A dual chamber pacemaker defibrillator offers improved diagnostic specificity without loss of sensitivity, in addition to the hemodynamic benefit of dual chamber pacing. (PACE 1997;20

Arrhythmia Discrimination in Implantable Cardioverter Defibrillators Using Support Vector Machines Applied to a New Representation of Electrograms

Arrhythmia classification remains a major challenge for appropriate therapy delivery in implantable cardioverter defibrillators (ICDs). The purpose of this paper is to present a new algorithm for arrhythmia discrimination based on a statistical classification by support vector machines of a novel 2-D representation of electrograms (EGMs) named spatial projection of tachycardia (SPOT) EGMs. SPOT-based discrimination algorithm provided sensitivity and specificity of 98.8% and 91.3%, respectively, on a test database. A simplified version of the algorithm is also presented, which can be directly implemented in the ICD.

Obesity-Associated Alterations in Glucose Metabolism Are Reversed by Chronic Bilateral Stimulation of the Abdominal Vagus Nerve.

Acute vagal stimulation modifies glucose and insulin metabolism, but the effect of chronic bilateral vagal stimulation is not known. Our aim was to quantify the changes in whole-body and organ-specific insulin sensitivities 12 weeks after permanent, bilateral, vagal stimulation performed at the abdominal level in adult mini-pigs. In 15 adult mini-pigs, stimulating electrodes were placed around the dorsal and ventral vagi using laparoscopy and connected to a dual-channel stimulator placed subcutaneously. Animals were divided into three groups based on stimulation and body weight (i.e., lean nonstimulated, obese nonstimulated, and obese stimulated). Twelve weeks after surgery, glucose uptake and insulin sensitivity were measured using positron emission tomography during an isoglycemic clamp. Mean whole-body insulin sensitivity was lower by 34% (P < 0.01) and the hepatic glucose uptake rate was lower by 33% (P < 0.01) in obese-nonstimulated mini-pigs but was no different in obese-stimulated compared with lean mini-pigs. An improvement in skeletal glucose uptake rate was also observed in obese-stimulated compared with obese-nonstimulated groups (P < 0.01). Vagal stimulation was associated with increased glucose metabolism in the cingulate and prefrontal brain areas. We conclude that chronic vagal stimulation improves insulin sensitivity substantially in diet-induced obesity by both peripheral and central mechanisms.

Vagus nerve stimulation: State of the art of stimulation and recording strategies to address autonomic function neuromodulation

OBJECTIVEnNeural signals along the vagus nerve (VN) drive many somatic and autonomic functions. The clinical interest of VN stimulation (VNS) is thus potentially huge and has already been demonstrated in epilepsy. However, side effects are often elicited, in addition to the targeted neuromodulation.nnnAPPROACHnThis review examines the state of the art of VNS applied to two emerging modulations of autonomic function: heart failure and obesity, especially morbid obesity.nnnMAIN RESULTSnWe report that VNS may benefit from improved stimulation delivery using very advanced technologies. However, most of the results from fundamental animal studies still need to be demonstrated in humans.

Model-Based Design and Experimental Validation of Control Modules for Neuromodulation Devices

Goal: The goal of this paper is to propose a model-based control design framework, adapted to the development of control modules for medical devices. A particular example is presented in which instantaneous heart rate is regulated in real-time, by modulating, in an adaptive manner, the current delivered to the vagus nerve by a neuromodulator. Methods: The proposed framework couples a control module, based on a classical PI controller, a mathematical model of the medical device, and a physiological model representing the cardiovascular responses to vagus nerve stimulation (VNS). In order to analyze and evaluate the behavior of the device, different control parameters are tested on a “virtual population,” generated with the model, according to the Latin Hypercube sampling method. In particular, sensitivity analyses are applied for the identification of a domain of interest in the space of the control parameters. The obtained control parameter domain has been validated in an experimental evaluation on six sheep. Results: A range of control parameters leading to accurate results was successfully estimated by the proposed model-based design method. Experimental evaluation of the control parameters inside such a domain led to the best compromise between accuracy and time response of the VNS control. Conclusion: The feasibility and usefulness of the proposed model-based design method were shown, leading to a functional, real-time closed-loop control of the VNS for the regulation of heart rate.

Selective ENG recordings using a multi-contact cuff electrode

This paper describes the design, microfabrication, characterization and experimental validation of a 6-contact cuff electrode embedded in a parylene-based flexible support. This type of electrode is well suited for both peripheral nerve recording and stimulation and offers improved spatial selectivity as compared to conventional ring electrodes. Both measured and modeled impedance spectra are detailed. An experimental validation is performed on an earthworm with both multi-contact cuff (MCC) electrode recording and ring stimulation electrodes. Single fiber action potentials, elicited by the electrical stimulation, are well discriminated on the 6 contacts. Spontaneous activity is also recorded with burst of spikes.

New sectorized implantable microelectrode fabrication, packaging and ageing for neural sensing and stimulation

This paper describes the fabrication and the packaging of a flexible parylene-based multi-contact electrode embedded in a silicone-based cuff. This type of electrode is well suited for peripheral nerve recording and offers improved spatial selectivity. We conducted mechanical and electrical tests for assessing the reliability by using an accelerated lifetime protocol. Test structures made with platinum sandwiched with parylene C were designed. The accelerated lifetime soaking tests in phosphate buffered saline (PBS) solution at 67°C showed a longer life time (approximatively 4.5 years) with a dehydration bake introduction in the process flow and a parylene thickness increase. A specific test bench was developed for the mechanical cycling and for evaluating the mechanical robustness of the thin film devices.