Electrogram Width Parameter Analysis in Implantable Cardioverter Defibrillators: Influence of Body Position and Electrode Configuration

Abstract

The "EGM width criterion" is a discrimination algorithm that was available in the last generation ICDs. It improved ventricular tachycardia detection by withholding inappropriate therapy deliveries in the presence of narrow QRS tachycardias. The accuracy of the algorithm depends on the optimal settings of the intracardiac EGM source, the "slew thresholds," and the "width threshold." The possible dependence of these parameters on body position may affect the detection efficacy. Whether these effects can be minimized by a proper choice of the electrode configuration used for signal analysis is still to be investigated. This study aimed to evaluate the stability of the slew threshold and width threshold obtained in the supine and orthostatic positions detected by the tip-to-ventricular coil and can-to-ventricular coil electrode configurations. Their time dependence was also evaluated at the 6-month follow-up. Fifty-eight patients who were recipients of an ICD (model Medtronic 7223cx and 7227cx) were included in the study. Changing from supine to orthostatic position caused a marked variation of slew and width thresholds (21.0 +/- 13.9 V/s and 10.1 +/- 9.6 ms, respectively) in 36% of patients with tip-to-ventricular coil and in 44% of patients with can-to-defibrillating coil (the mean slew threshold variation was in this case 17.6 +/- 15.8 V/s, while the mean width threshold variation was 18.8 +/- 21.0 ms). Width threshold variation was statistically significant (P < 0.02) with the latter electrode configuration. Slew thresholds settings changed between the 1- and 6-month follow-ups in the 75% of patients with can-to-defibrillating coil configuration and in 50% with tip-to-defibrillating coil. These time related variations were significantly larger with the tip-to-defibrillating coil configuration (P < 0.01). In conclusion, EGM width parameters may change between supine and orthostatic position and over time with tip-to-defibrillating coil configuration and can-to-defibrillating coil configuration. The former configuration was less sensitive to body position changes, but more sensitive to time related variations. These findings may be useful for optimal programming of the EGM width criterion, but if parameter programming based on these results can improve the discrimination specificity still needs to be investigated.

Electrogram Configuration and Detection of Supraventricular Tachycardias by a Morphology Discrimination Algorithm in Single Chamber ICDs

“…EGM width had some limitations, as for example discrimination of SVT from VT in patients with bundle branch block. Furthermore, this early algorithm needed careful and experienced monitoring and device programming to provide a sufficient performance 8,10,19,20 . During spontaneous episodes, the Wavelet algorithm has been shown to be superior to EGM width for tachyarrhythmia discrimination 21 .…”

“…Furthermore, this early algorithm needed careful and experienced monitoring and device programming to provide a sufficient performance. 8,10,19,20 During spontaneous episodes, the Wavelet algorithm has been shown to be superior to EGM width for tachyarrhythmia discrimination. 21 The specificity we found for SVT detection using the Wavelet algorithm with the RV-Can source during exercise testing is similar to that reported for "morphology discrimination," 22 another discrimination algorithm.…”

Wavelet‐Based Tachycardia Discrimination in ICDs: Impact of Posture and Electrogram Configuration

“…Tachycardia discriminators based on the morphologic characteristics of the EGM have the theoretical advantage of differentiating VTs from abrupt‐onset, regular SVTs, such as atrial tachycardia, atrial flutter, AV nodal reentrant tachycardia, and orthodromic reentrant tachycardia. EGM width criterion (Medtronic Inc., Minneapolis, MN, USA), Morphology Discriminator feature (St. Jude Medical Inc., St. Paul, MN, USA), and the Vector Timing and Correlation Algorithm (Guidant Inc., St. Paul, MN, USA) were introduced earlier, which improved overall tachycardia discrimination 8–10 . More recently, a newer morphology‐based algorithm (wavelet feature, Medtronic Inc.) has been introduced, which compares the morphology of tachycardia EGMs based on wavelet decomposition of EGM signals, with an EGM template recorded during spontaneous, baseline rhythm 7,11 .…”

“…EGM width criterion (Medtronic Inc., Minneapolis, MN, USA), Morphology Discriminator feature (St. Jude Medical Inc., St. Paul, MN, USA), and the Vector Timing and Correlation Algorithm (Guidant Inc., St. Paul, MN, USA) were introduced earlier, which improved overall tachycardia discrimination. [8][9][10] More recently, a newer morphologybased algorithm (wavelet feature, Medtronic Inc.) has been introduced, which compares the morphology of tachycardia EGMs based on wavelet decomposition of EGM signals, with an EGM template recorded during spontaneous, baseline rhythm. 7,11 An automatic template collection feature continuously checks the quality of the template and updates the template when changes in the intrinsic EGM are identified.…”

Scaling Characteristics of Heart Rate Time Series Before the Onset of Ventricular Tachycardia

“…18,29 However, inappropriate defibrillator discharge or antitachycardiac pacing remain an important clinical problem in ICD therapy as they cause unnecessary pain and sometimes proarrhythmic effects. 7,34 Third generation ICDs are capable of storing the beat-to-beat intervals (BBIs) before VT. Therefore, an assessment of the autonomous nervous system (ANS) by means of heart rate variability (HRV) analysis has become available, opening a completely new perspective on the understanding of arrhythmogenesis on one hand and on the capability to intervene on the other hand.…”