A Review on Recent Patents in Digital Processing for Cardiac Electric Signals (II): Advanced Systems and Applications

Digital signal processing algorithms for cardiac recordings have been paid much attention in recently disclosed patents. In this second part of our review of the state-of-art patents, systems for sudden cardiac death prediction, as well as for apnea analysis, are summarized. Advanced digital signal processing algorithms for cardiac electric signals are specifically reviewed, including independent component decompositions, and nonlinear methods (chaos, fractals, and entropies). Finally, systems aiming to solve the inverse problem in electrocardiography are presented. Concluding remarks on these systems and on the whole review are discussed. In the companion paper (1), a compilation of recent patents on digital processing algorithms for cardiac signals analysis has been presented. This review included systems for basic feature extraction of the electric signals recorded from electrodes in the skin (called electrocardiogram, ECG), or from electrode systems in catheters placed inside the heart (called electrograms, EGM). Systems for analyzing cardiac arrhythmias in different applications have also been assembled therein. In this paper, we include relevant higher-level systems that use digital processing algorithms in advanced applications related with electrocardiology and with cardiac electrophysiology environments. Specifically, the problem of accurate sudden cardiac death (SCD) prediction (2,3) has been targeted by a large number of disclosed systems. Also, apnea analysis (4) has been addressed in the recently disclosed patents. Special attention is paid here to advanced signal processing algorithms, such as blind source separation techniques or nonlinear analysis procedures including chaos, fractals and entropy principled algorithms, which have been disclosed as a part of advanced application systems. Finally, the inverse problem in electrocardiography (5), consisting of creating an anatomically detailed image of the electrical underlying cardiac activity from a diversity of electric signals, continues to be a field in which disclosed advanced systems aim to give to the clinician the best view of the cardiac electric activity. The structure of this second part of the review is as follows. Section 2 deals with patents devoted to SCD risk stratification and prediction. Section 3 briefly deals with