A therapeutic solution for potential victims of sudden cardiac death is the implantation of a device, the implantable cardioverter defibrillator (ICD), which automatically detects potentially lethal ventricular fibrillation (VF) and provides high energy defibrillation shock therapy. These devices, although lifesaving, still beg design modifications to ensure comfortable integration into patient's lives. In particular, minimization of the energy needed for therapy would increase device longevity (reducing surgical explant) and be more tolerable for the patient (reducing false shock and trepidation of false shock). To achieve this, VF must be accurately, confidently detected so the ICD can treat less serious rhythms, especially ventricular tachycardia (VT), with lower-energy therapies instead of shock.

This dissertation examined limitations of current technology in distinguishing VT and VF and addressed these limitations with an improved algorithmic design incorporating digital signal processing methods. A comparison of the detection algorithms of three commercial ICDs was performed via computer simulations. Multiple parameters were tested which demonstrated that present technology is unable to provide unique VF detection with a specificity of only 10-21% at nominal values. In order to create true design improvements to the device, a novel algorithm was developed which addressed VT versus VF detection while considering constraints specific to ICD. A special electrode configuration with two closely spaced paired unipolar electrograms was demonstrated to display concordance during coherent rhythms such as VT and normal rhythms, and disconcordance during VF. This research included definition of the electrode configuration, quantification of the concordance, and integration into an overall scheme, called paired signal concordance (PSC), which included rate to minimize computation.

PSC was successfully tested on passages of VT, VF, and confounding rhythms such as supraventricular tachycardias. VT detection specificity for PSC was 93% compared to commercial devices (15%-60%) and provided a potential battery savings of 20%. In conclusion, with paired signal concordance, the intelligent reduction of high-energy false shocks would extend device longevity and would reduce apprehension, aggravation, and painful episodes in future candidates for the life-saving device.