| Hundreds of thousands of patients are treated every year for a wide variety of cardiac diseases and abnormalities with implantable cardiac devices such as pacemakers, implantable cardioverter defibrillators (ICDs), and cardiac resynchronization therapy devices (CRTs). Although these devices vary in their treatments and treatment options, they have fundamental components in common: all have the capability to pace the heart with a low-voltage output to elicit a cardiac contraction and all have some electrical sensing capability via implanted intracardiac leads. The electrical activity sensed from these intracardiac leads is primarily local phenomenon; e.g. the signal sensed from the right ventricular lead is primarily of right ventricular origin. This is quite useful for ascertaining pacemaker timing cycles, but does not adequately represent the electrocardiogram (ECG), the "gold standard" global view of cardiac activity that clinicians are accustomed to viewing in a clinical situation.;Meanwhile in a different branch of cardiology, specifically risk stratification and the identification of unexplained syncope, there have been advances in insertable loop recorders (ILRs): small devices that are implanted subcutaneously that have two electrodes to view a "semi-global" view of cardiac activity which is more similar to the ECG (a Subcutaneous Small Vector ECG, or SQSVECG), morphologically, than the intracardiac electrogram. These ILRs are custom devices that are not subject to the traditional implant location and geometry of pacemakers, ICDs or CRTs.;The topic of this thesis, thus, is one of convergence: given the current geometry and implant location of pacemakers, ICDs and CRTs, it explores whether SQSVECG technology can be incorporated into these devices in a manner that is useful to a clinical cardiologist. That is, a signal that shows both atrial and ventricular cardiac information in a reliable manner without additional burden on the implanting or following physician. This dissertation examines the use of multiple simultaneous SQSVECG signals from multiple electrodes and orthogonal orientations (unneeded in current ILRs where the implant location and electrode spacing can be optimized) in the pectoral region, enhanced by the timings established from the intracardiac electrograms (unavailable to existing ILRs), to form one clinically useful signal, as validated by the gold standard ECG. The dissertation focuses on creating one, singular, SQSVECG signal from multiple constituent components available to the device in real-time, representing the atrial contribution and ventricular contribution to the signal, without artificially distorting the signal. The motivation behind this is multifold: simplicity for the clinician, acceptable storage requirements, and minimal telemetry bandwidth requirements for the implantable device.;Throughout the course of this dissertation an algorithm for disassembling these constituent (atrial and ventricular) components from the various SQSVECG vectors, selecting among them, and reassembling them into one SQSVECG signal is developed. The algorithm is first developed through the use of data from humans with multiple SQSVECG vectors recorded sequentially, then validated to be implementable in real-time in animals with multiple vectors recorded simultaneously. The animal data was collected through the use of a novel prototype device capable of simultaneous multi-vector SQSVECG sensing as well as dual chamber intracardiac sensing and pacing developed specifically for this research. |
