A Reliable Downscaling of ECG Signals for the Detection of T wave Heterogeneity Features

In cardiovascular disease the definition and the detection of the ECG parameters related to repolarization dynamics in post MI patients is still a crucial unmet need. In addition, the use of a 3D sensor in the implantable medical devices would be a crucial mean in the assessment or prediction of Heart Failure status, but the inclusion of such feature is limited by hardware and firmware constraints. The aim of this thesis is the definition of a reliable surrogate of the 500 Hz ECG signal to reach the aforementioned objective. To evaluate the worsening of reliability due to sampling frequency reduction on delineation performance, the signals have been consecutively down sampled by a factor 2, 4, 8 thus obtaining the ECG signals sampled at 250, 125 and 62.5 Hz, respectively. The final goal is the feasibility assessment of the detection of the fiducial points in order to translate those parameters into meaningful clinical parameter for Heart Failure prediction, such as T waves intervals heterogeneity and variability of areas under T waves. An experimental setting for data collection on healthy volunteers has been set up at the Bakken Research Center in Maastricht. A 16 – channel ambulatory system, provided by TMSI, has recorded the standard 12 – Leads ECG, two 3D accelerometers and a respiration sensor. The collection platform has been set up by the TMSI property software Polybench, the data analysis of such signals has been performed with Matlab. The main results of this study show that the 125 Hz sampling rate has demonstrated to be a good candidate for a reliable detection of fiducial points. T wave intervals proved to be consistently stable, even at 62.5 Hz. Further studies would be needed to provide a better comparison between sampling at 250 Hz and 125 Hz for areas under the T waves.

Fabrication of 2D and 3D microelectrode arrays for amperometric dopamine sensing: towards a metal free approach to bioelectronics

Dopamine is a neurotransmitter which has a role in several psychiatric and neurological disorders. In-vivo detection of its concentration at the microscopic scale would benefit the study of these conditions and help in the development of therapies. The ideal sensor would be biocompatible, able to probe concentrations in microscopic volumes and sensitive to the small physiological concentrations of this molecule (10 nM - 1 μM). The ease of oxidation of dopamine makes it possible to detect it by electrochemical methods. An additional requirement in this kind of experiments when run in water, though, is to have a large potential window inside which no redox reactions with water take place. A promising class of materials which are being explored is the one of pyrolyzed photoresists. Photoresists can be lithographically patterned with micrometric resolution and after pyrolysis leave a glassy carbon material which is conductive, biocompatible and has a large electrochemical water window. In this work I developed a fabrication procedure for microelectrode arrays with three dimensional electrodes, making the whole device using just a negative photoresist called SU8. Making 3D electrodes could be a way to enhance the sensitivity of the electrodes without occupying a bigger footprint on the device. I characterized the electrical, morphological, and electrochemical properties of these electrodes, in particular their sensitivity to dopamine. I also fabricated and tested a two dimensional device for comparison. The three dimensional devices fabricated showed inferior properties to their two dimensional counter parts. I found a possible explanation and suggested some ways in which the fabrication could be improved.