G. Sartori

Analysis of implantable cardioverter defibrillator signals for non conventional cardiac electrical activity characterization

Implantable cardioverter defibrillators (ICDs) can store intracardiac electrograms (EGMs) in sinus rhythm (SR), at the onset of spontaneous ventricular tachyarrhythmias (VT) or during their course. This allows the investigation of unknown features of the heart electrical activity associated with different cardiac rhythms. In this study we propose a non conventional cardiac electrical activity characterization (CEAC) that extracts quantitative information about the power spectrum wideness and variability of the beat-by-beat morphology. We analyze 293 EGMs from 40 patients who underwent implantation of St Jude Medical–Ventritex ICDs that allow the storage of EGMs with two different modes of recording: bipolar (BIP) and unipolar or far-field (FF). The EGMs are studied with this CEAC by (1) exploring differences between the CEAC measured from FF and BIP EGMs during similar cardiac rhythms, and (2) investigating the mode of recording that allows a better separation between SR and VT rhythms. Results show that, with similar cardiac rhythm, the CEACs from FF or BIP recordings are different (for SR rhythm: sensitivity 81.5%, specificity 93.6%; for VT rhythm: sensitivity and specificity 100%); thus FF and BIP EGMs analyze different aspects of cardiac activity.The CEAC applied to FF EGMs distinguishes better EGMs obtained during SR from VT rhythms (VT vs SR with sensitivity 92.7% and specificity 79.7%) than when it is applied to BIP signals (VT vs SR with sensitivity 60% and specificity 73.3%).

On cardiac activity characterization from Implantable Cardioverter Defibrillator electrogram analysis: is far-field better?

The new generation of Implantable Cardioverter Defibrillators (ICDs) allows storage of intracardiac electrograms (EGMs) recorded immediately before the onset of malignant ventricular tachyarrhythmias (VTs) and during their course. Although all devices base most of diagnostic parameters on the bipolar EGMs, some of them allow two types of EGM recordings: bipolar (potential is obtained between two electrodes at the tip of the electrocatheter) and far-field (potential is recorded between the tip of the electrocatheter and the active can device). The main objective of this work is to study which differences can be observed from the analysis of bipolar or far-field EGMs when deterministic chaos methods are being applied to bipolar or far-field EGM recordings. For this analysis we considered 20 EGMs obtained from 6 patients with ICDs. Some of the EGMs contain VT episodes, other are collected in basal heart conditions. Within the limited set of EGM considered in this work, results indicate that far field recordings, monitoring the whole heart activity, allow better characterization of heart substrate, and they are more indicated when deterministic chaos analysis would be applied.

Low complexity methods for intracardiac atrial electrogram compression

This paper studies methods for intracardiac atrial electrograms compression suitable with implementation on implantable devices. Algorithms are based an piecewise linear approximation, beat detection, and their combination. Bipolar intracardiac electrograms were obtained during electrophysiological studies and divided into 3 rhythm groups. The authors analyzed 2196 seconds of sinus rhythm (SR), 786 sec. of atrial fibrillation (AF) and 1793 sec. of atrial flutter (AFL). Performance over the whole data base reach average compressed data rate (CDR) ranging between 500 and 850 (bits/second), and the percent of root mean square difference (PRD) varies from 2 to 12% depending on the choice of methods and accepted errors. Preliminary results show that time consumption can be reduced to enable real time compression with implanted devices.

Differences in mode of onset of ventricular tachyarrhythmias in dilated cardiomyopathies and coronary artery diseases

This explorative study focuses on differences between the onset of spontaneous ventricular tachyarrhythmias (VT) of patients with implantable cardioverter defibrillator (ICD) and affected by coronary artery disease (CAD) or dilated cardiomyopathy (DCM). From 57 patients (40 CAD and 17 DCM), 35 (24 CAD and 11 DCM) we retrieved a total of 154 spontaneous VTs (72 CAD and 82 DCM). Three modes of VT onset are observed: (i) premature ventricular contraction (PVC); (ii) PVC preceded by a short-long-short cycle; (Hi) PVC preceded by a paced beat immediately after PVC pause. The analysis indicates that (i) average number of spontaneous VTs is much higher in DCM than CAD (7.5 vs. 3 VTs per patients in patient with VTs); (ii) modes of onset are more variable in DCM (1 patient experienced all 3 modes, 5 experienced 2 modes,) than CAD (only 2 patients experienced 2 modes) patients

Remarks on non conventional cardiac electrical activity characterization from implantable cardioverter defibrillator signals

Implantable cardioverter defibrillators (ICDs) can store intracardiac electrograms (EGMs) with 2 modes of recording: bipolar (BIP) or far-field (FF). Aims of this study are: (i) to propose a non conventional cardiac electrical activity characterization (CEAC); (ii) to investigate the mode of recording that better allows retrieving information from measured EGMs with CEAC. We consider 293 EGMs during sinus rhythm (SR) or ventricular tachyarrhythmia (VT) from 40 patients implanted with ICDs. 196 were FF EGMs and 97 BIP EGMs. CEAC analysis of SR rhythms (FF vs. BIP) shows sensitivity 81.5% and specificity 93.6%; with VT rhythms both were 100 %. CEAC analysis of FF signals (SR vs. VT rhythms) give sensitivity 92.7 and specificity 79.7; with BIP EGMs they are 60% and 73.3%, respectively. We conclude that: (i) CEAC analysis requires to analyze FF or BIP signals separately; (ii) CEAC better discriminates SR from VT when far-field EGMs are used

Mode of onset of spontaneous ventricular tachyarrhythmias from implantable cardioverter defibrillator electrograms

This work investigates the correlation between the cardiac electrical activity underlying spontaneous ventricular tachyarrhythmias and their modes of onset. We analyzed 81 episodes of spontaneous ventricular tachycardia (VT) and ventricular fibrillation (VF) lasting at least 5 seconds from 17 patients. The cardiologist classified VT/VF malignancy by considering fast VT as more malignant. We study 3 modes of onset: (i) premature ventricular contraction (PVC group); (ii) PVC preceded by a short-long-short cycle (SLS group); (iii) PVC preceded by a paced beat after a previous PVC compensatory pause (PM group). In 4 patients more than one mode of VT/VF onset is present, in the other 13 patients VT/VF always started with the same mode. Cardiac electrical activity is characterized by power spectral density and correlation dimension analyses; statistical analysis is carried on using one way ANOVA in order to test significant differences among the mean values of PVC, SLS and PM populations. Preliminary results shows significant differences at 5% level in two of the considered quantitative parameters. Although initial significant differences have been obtained, the limited number of ICDs and the small variability of the intra-subject characterization suggest that further research is needed to conclude that dynamics underlying VT/VF and the VT/VF mode of onset are strictly related.

Methods for intracardiac electrogram compression suitable with implantable devices

Studies methods for intracardiac electrogram compression that are suitable for implementation in implantable devices. The algorithms are based on piecewise linear approximation (PLA) methods and beat detection (the peak method). Intracardiac electrograms were obtained, from the right atrium and ventricle, during electrophysiological studies. The total atrial set consists of 5060 s of bipolar recordings and 680 s of unipolar electrograms; the ventricular data set contains 1210 s of bipolar and 480 s of unipolar signals. The peak method clearly performs better than the others to compress bipolar signals, while PLA methods are needed in order to have reliably compressed unipolar data. Performances over the whole bipolar database (including atrial and ventricular sets) reached an average compression ratio (CR) of 7.6, while first-order piecewise linear approximation on unipolar electrograms reached CR=6.6. These preliminary results show that time consumption can be reduced suitably with real-time compression for implantable devices. The ability to compress and store intracardiac electrograms in implantable devices allows detailed verification of appropriate intervention of the device and it might open up new perspectives in the study of the mechanisms involved in the onset of malignant tachyarrhythmias.

A new method for fibrillation detection from endocardial electrograms

A new approach is presented for automatic efficient detection of atrial fibrillation not based on heart rate, but on morphologic analysis of the electrogram. Endocardiac signals have been collected from 9 patients (4 of them affected by chronic atrial fibrillation and 5 affected by other disturbances of the rhythm) during human cardiac electrophysiologic (EP) studies using a Manta Mennen Poligraph and cut into short intervals of different duration (from 0.5 to 20 seconds). 1018 seconds of sinus rhythm (SR) and 726 seconds of atrial fibrillation (AF) have been analyzed. Then the authors divided all segments in two separate groups: the training group to define appropriate discrimination threshold and the test group to quantify results. Results for the 4-seconds decision time show 94 and 96 values of 94 The method is straightforward and compatible with implantable devices (easy implementation and real time).