Abstract:

Deep hypothermic circulatory arrest is necessary for some types of cardiac and aortic surgery. Perfusion of the brain can be maintained using a heart-lung machine and unilateral antegrade cerebral perfusion (ACP). Cooling rates during extracorporeal circulation depend on local perfusion. A core temperature of 24-25 degrees C is aimed at to extend ischemic tolerance of tissues. Information on cerebral perfusion and temperature is important for the safety of patients but hardly accessible to measurement. A combined simulation model of haemodynamics and temperature is presented in this paper. The haemodynamics model employs the transmission line approach and integrates the Circle of Willis. This allows for parametrization of individual aberrations. Simulation results of cerebral perfusion are shown for two configurations of the Circle of Willis. The temperature model provides spatial information on temperature fields. It considers heat transfer in the various tissues retrieving data of local tissue perfusion from the haemodynamics model. The combined model is evaluated by retrospective simulation of two aortic operations.

Abstract:

Radiofrequency ablation (RFA) is a standard clinical procedure for treating many cardiac arrhythmias. In order to increase the success rate of this treatment, the evaluation of lesion development with the help of intracardiac electrogram (EGM) criteria has to be improved further. We are investigating in-vitro the electrophysiological characteristics of cardiac tissue by using fluorescence-optical and electrical techniques. In this project, it is intended to create ablation lesions under defined conditions in rat atria or ventricle and to determine the electrical activity in the myocardium surrounding these lesions less than 1 s after the ablation. Therefore, we developed a semi-automatic RFA procedure, which was integrated into an existing experimental setup. Firstly, a controllable protection circuit board was designed to galvanically isolate the sensitive amplifiers for measuring extracellular potentials during the ablation. Secondly, a real-time system was implemented to control and to autonomously monitor the RFA procedure. We verified each component as well as the different sequences of the RFA procedure. In conclusion, the expanded setup will be used in future in-vitro experiments to determine new EGM criteria to assess lesion formation during the RFA procedure.

Abstract:

Atrial fibrillation represents the most frequent cardiac arrhythmia in the western world. One of the medical treatments for atrial fibrillation is the radiofrequency ablation (RFA) therapy. Unfortunately, a recurrence rate of RFA of about 35-45% exists. In order to improve the efficiency of the therapy a precise knowledge about the electrophysiological properties of the ablation lesions is necessary. With the help of an experimental setup the electrical activity of cardiac tissue can be measured by using optical and electrical techniques. The goal of this project is to set an ablation lesion under defined conditions and measure the extracellular potentials around the acute ablation lesion less than 1s after the ablation, to determine electrophysiological changes around the acute lesion. In order to realise this goal an extension of the setup is necessary. First, a Protection Circuit board (PCB), which is connected to a preamplifier and main amplifier system, is imple- mented. The main function of the PCB is to ensure, that either the ablation lesion is set or the extracellular potentials are measured with the help of a multielectrode array on a cardiac tissue and forwarded via the PCB to the preamplifier.Second, a Control board (CB) with a μC and GUI for user inputs is integrated. One part of the CB regulates the connection of the ablation electrode with the HF generator for the ablation, another functions as external control for this generator. At last a μC is competent for the activation of the relays on both boards and checks the switching state of the relays on the PCB.The order of the activation of the relays, as well as specific waiting times are implemented in the μC following a sequence planning. The ablation and waiting times can be defined in a Matlab GUI by the user. Both boards are integrated in the experimental setup and are tested in a test phase with a saline solution instead of cardiac tissue.The switching times of the relays, as well as the communication between all components are successfully tested. Therefore, the boards are integrated effectively in the setup and their functionality is proven by performing the procedure of ablation and measurement with the same settings as during a process with cardiac tissue.