Charles D. Swerdlow

Discrimination of Ventricular Tachycardia from Supraventricular Tachycardia by a Downloaded Wavelet-Transform Morphology Algorithm: A Paradigm for Development of Implantable Cardioverter Defibrillator Detection Algorithms

Morphology Download. Introduction: Present implantable cardioverter defibrillators (ICDs) have algorithms that discriminate supraventricular tachycardia (SVT) from ventricular tachycardia (VT). One type of algorithm is based on differences in morphology of ventricular electrograms during VT and SVT. Prior SVT‐VT discrimination algorithms have not undergone real‐time evaluation in ambulatory patients until they were incorporated permanently into ICDs. This approach may result in incomplete testing of electrogram morphology algorithms because they are influenced by posture, activity, and electrogram maturation. We downloaded software into implanted ICDs to study a novel algorithm that compares morphologies of baseline and tachycardia electrograms based on differences between corresponding coefficients of their wavelet transforms. This comparison is expressed as a match‐percent score.

Worldwide clinical experience with a new dual-chamber implantable cardioverter defibrillator system

New Dual‐Chamber ICD. Introduction: Management of atrial tachyarrhythmias represents a significant challenge in patients with implantable cardioverter defibrillators (ICDs). Drug therapy of these arrhythmias is limited by moderate efficacy, ventricular proarrhythmia, and drug‐device interactions. This study tested the safety and efficacy of a new dual‐chamber ICD to detect and treat atrial as well as ventricular tachyarrhythmias.

Supraventricular Tachycardia‐Ventricular Tachycardia Discrimination Algorithms in Implantable Cardioverter Defibrillators: State‐of‐the‐Art Review

SVT‐VT Discrimination Algorithms in ICDs. To reduce inappropriate therapy of supraventricular tachycardia (SVT), implantable cardioverter defibrillators (ICDs) include algorithms to discriminate ventricular tachycardia (VT) from SVT. Dual‐chamber algorithms analyze atrial and ventricular rates or AV relationship. They provide advantages over single‐chamber algorithms, but introduce new ways to detect SVT as VT inappropriately and to underdetect VT. Unlike pacemakers, dual‐chamber ICDs require accurate atrial sensing during high ventricular rates. A postventricular atrial blanking period prevents oversensing of far‐field R waves as atrial electrograms, but causes underdetection of atrial fibrillation during high ventricular rates. Tachycardias with 1:1 AV relationship and VT during atrial tachyarrhythmias present specific SVT‐VT discrimination problems. The first dual‐chamber algorithms performed comparably to single‐chamber algorithms. Present dual‐chamber algorithms correct some limitations of earlier versions.

Current Concepts of Ventricular Defibrillation

Mechanisms of Deflbhllation. The aim of this article is to review the current concepts of ventricular defibrillation. We studied the interaction between strong electrical stimulas and cardiac responses in both animal models and in humans. We found that a premature stimulus (S2) of appropriate strength results in figure‐eight reentry in vitro by inducing propagated graded responses. The same stimulation protocol induces figure‐eight reentry and ventricular fibrillation (VF) in vivo. When the S2 strength and the magnitude of graded responses increase beyond a critical level, the increase in refractoriness at the site of the stimulus becomes so long that the unidirectional block becomes bidirectional block, preventing the formation of reentry (upper limit of vulnerability [DLV]). In other studies, we found that the effects of an electrical stimulation on reentry is in part determined by the timing of the stimulus. A protective zone is present after the induction of VF and after an unsuccessful defibrillation shock during which an electrical stimulus can terminate reentry and protect the heart from VF. These results indicate that the effects of a defibrillation shock is dependent on both the strength and the timing of the shock. Timing is not important in areas where the shock field strength is < ULV because the shock terminates all reentry hut cannot reinitiate new ones. However, in areas where shock field strength is < ULV, the effects of the shock are determined by the timing of the shock relative to local VF activations. This ULV hypothesis of defibrillation explains the probablistic nature of ventricular defibrillation. It also indicates that, to achieve a high probability of successful defibrillation, a shock must result in a shock field strength of < ULV throughout the ventricles.

Optimal Combination of Discriminators for Differentiating Ventricular from Supraventricular Tachycardia by Dual‐Chamber Defibrillators

Introduction: Dual‐chamber implantable cardioverter defibrillators (ICDs) use discriminators to differentiate between supraventricular tachycardias (SVTs) and ventricular tachycardias (VT), the accuracy of which may depend on the type and method used. ICDs can combine rate branching of tachyarrhythmias according to their A:V relationship with two SVT‐VT discriminators in each rate branch, using ANY (either) or ALL (both) logic. Our goal was to determine the optimal discriminator combination.

THE ZONE OF VULNERABILITY TO T WAVE SHOCKS IN HUMANS

Vulnerability to VF in Humans. Introduction: Shocks during the vulnerable period of the cardiac cycle induce ventricular fibrillation (VF) if their strength is above the VF threshold (VFT) and less than the upper limit of vulnerability (ULV). However, the range of shock strengths that constitutes the vulnerable zone and the corresponding range of coupling intervals have not been defined in humans. The ULV has been proposed as a measure of defibrillation because it correlates with the defibrillation threshold (DFT), but the optimal coupling interval for identifying it is unknown.

Effect of programmed number of intervals to detect ventricular fibrillation on implantable cardioverter-defibrillator aborted and unnecessary shocks

Introduction: Detection of self‐terminating arrhythmias by implantable cardioverter‐defibrillators (ICDs) causes unnecessary battery depletion and unnecessary shocks. Our goal was to estimate the effect of the programmed number of intervals to detect (NID) ventricular fibrillation (VF) on ICD temporal episode rate, unnecessary shocks, and delay in detection of VF.

Determinants of first-shock success for atrial implantable cardioverter defibrillators

Atrial Defibrillation. Introduction: The aim of this study was to identify determinants of first‐shock success for defibrillation of spontaneous atrial fibrillation (AF) in ambulatory patients with an atrial implantable cardioverter defibrillator (ICD). The determinants of first‐shock success in ambulatory patients with atrial ICDs are unknown.

Effect of shock waveform on relationship between upper limit of vulnerability and defibrillation threshold

ULV‐DFT Waveform. Introduction: The upper limit of vulnerability (ULV) correlates with the defibrillation threshold (DFT). The ULV can he determined with a single episode of ventricular fibrillation and is more reproducible than the single‐point DFT. The critical‐point hypothesis of defibrillation predicts that the relation between the ULV and the DFT is independent of shock waveform. The principal goal of this study was to test this prediction.

Discrepancies between the upper limit of vulnerability and defibrillation threshold: prevalence and clinical predictors.

Introduction: Upper limit of vulnerability (ULV) has a strong correlation with defibrillation threshold (DFT) in patients with implantable cardioverter defibrillators (ICDs). Significant discrepancies between ULV and DFT are infrequent. The aim of this study was to characterize patients with such discrepancies.