| Ventricular fibrillation (VF) is the leading cause of sudden cardiac death, killing 300,000 people annually in the United States. Atrial fibrillation (AF), while not immediately life threatening, is a significant health problem, as well. Currently, a large electrical shock is the most effective treatment for these arrhythmias. This dissertation sought to investigate possible alternative electrical therapies for halting fibrillation through construction of an intelligent, multichannel stimulator (IMS). The IMS was developed for use in research of these and other cardiac electrophysiological therapies. The system consists of 16 channels of sense/stimulation electronics controlled by a digital signal processor (DSP) data acquisition card and a host computer.; Pace-termination of atrial fibrillation would be clinically useful because pain normally associated with atrial defibrillation shocks would be eliminated. While this has yet to be accomplished, local capture of cardiac tissue during fibrillation has been demonstrated in both the atria and the ventricles using non-adaptive, fixed-rate pacing. The IMS was used to implement adaptive pacing algorithms to investigate pacing during VF in pig right ventricles. At least 4 cm2 of capture was achieved in 71% of the pacing episodes; however, the adaptive algorithms were not significantly better than a control non-adaptive algorithm. The occurrence of capture was predictable through electrophysiological feedback. Once capture occurred, the pacing interval could be decreased by a mean of 7.6 msec before capture was lost; however, the area of capture progressively decreased. The pattern of capture was found to be similar within and across animals, probably as a result of functional and structural characteristics of the myocardium.; Additionally, the IMS was used to investigate the possibility of creating uniform electric fields with a set of evenly spaced ring electrodes that spanned the length of the heart in order to achieve low-energy defibrillation. While some low-energy defibrillation shocks were successful, the majority of shocks were not better than standard transvenous catheter defibrillation; none was better than in other low-energy defibrillation studies. The pacing study and the ring defibrillation study both demonstrated the IMS to be a useful cardiac electrophysiological research tool. |
