Studies in cardiac defribrillation

Cardiac disease resulting in cardiac arrest is one of the most common fatal diseases in the developed world. Defibrillation is the medical procedure used to correct the irregular cardiac rhythm (ventricular fibrillation (VF)) which is very often detected in patients suffering cardiac arrest. In the work reported in this thesis, two aspects of the defibrillation of patients in VF were examined. The first area of investigation concentrated on the use of multiple defibrillation electrodes to be used during closed chest (transthoracic) defibrillation. This study was carried out in a saline bath and centred on “focusing” electric fields from perimeter electrodes into a specified area in the bath. A number of perimeter electrode combinations were investigated during this work and an optional combination for the saline bath was identified. The second area of investigation involved the frequency analysis of body surface potential patterns (ECG) recorded from patients suffering VF who were defibrillated. A total of 26 traces were analysed and data paramaters (ie median frequency, total relative power and peak power frequency) were extracted for each trace. The data were sorted into categories based on whether the patient survived or died during VF. The values of the paramaters for patients who survived and patients who died had a large overlap. However, the mean values calculated for each parameter range may be a possible indicator of defibrillation success. It is concluded that the use of multiple defibrillation electrodes as opposed to the conventional two electrode technique may be a possible means of lowering the total energy required for transthoracic defibrillation. This may decrease the risk of patient damage from the treatment. The frequency analysis of body surface potential patterns may prove useful in the determining of the best time to deliver the defibrillation shock to improve defibrillation success rates.