| Description |
The specialized conduction system provides an electrically efficient pathway for the synchronous contraction of the heart. The His bundle (HB) is the most accessible structure of the conduction system that is paced for therapeutic applications. However, there are inherent limitations in localizing the HB using the standard single screw electrode. Therefore, a real-time stimulation and recording system was developed which is interfaced with a matrix of electrodes. The system visualizes and records the raw electrograms as well as their spatial derivatives. Spatial derivatives use adjacent electrodes' information to highlight the electrical activity underneath each electrode which significantly improves HB sensing. The system's stimulation module may be used to pace through any matrix electrode of choice. Using a flat electrode array matrix in rabbit hearts, the system detected HB activations and rates during both sinus rhythm as well as during ventricular fibrillation (VF). Subsequently, the system was used to characterize the effect of selective HB pacing during early VF in rabbit hearts. Critically timed pacing of the myocardium leads to the capture of tissue around the electrode. Therefore, in VF induced in rabbit hearts, the HB and the nearby working myocardium were paced at rates faster than the intrinsic ventricular or HB rates. The effect of different pacing rates and locations was studied from the endocardial electrical activity recorded using a basket array inserted in the left ventricle. As opposed to the HB's endocardially superficial location in rabbit hearts, the HB is situated underneath a layer of the myocardium in large animal and human hearts. If a iv multielectrode array technique were to be used for HB sensing and pacing, a multielectrode array is required which can access the sub-myocardial HB. The Utah Electrode Array (UEA) has a multitude of 1.5 mm long, closely spaced needle-like electrodes protruding from a plaque. Biphasic pulses of 1 ms duration per phase were driven at up to 8 mA through the electrodes. The integrity of electrode tips was assessed using electrochemical and high-resolution imaging techniques. The applicability of the UEA to sense and pace the HB was also demonstrated in explanted goat hearts. Thus, two aspects of the cardiac HB were investigated in this dissertation. Firstly, tools for better discrimination of the HB were developed and characterized. Secondly, the effect of selective HB pacing during early VF was also characterized. |
