Extravascular Implantable Cardioverter-Defibrillator Sensing and Detection in a Large Global Population.

Background: The extravascular (EV) implantable cardioverter-defibrillator (ICD) includes features to address sensing and arrhythmia detection challenges presented by its substernal lead location.

Objectives: In this study, the authors sought to evaluate sensing and detection performance in 299 patients discharged with an EV-ICD in the global pivotal study.

Methods: We reviewed and adjudicated all induced ventricular fibrillation (VF) episodes and spontaneous device-stored episodes that satisfied rate and duration criteria in a programmed ventricular tachycardia (VT)/VF therapy zone.

Polarity-Dependent, Reduced or No-Output Shocks in Implantable Cardioverter-Defibrillators.

Recently, polarity-dependent shock failures were reported in implantable cardioverter-defibrillators caused by structural failure in the high-voltage feedthrough. Short circuits may occur when the right ventricular coil is cathodal for phase 1 of biphasic shocks (cathodal shock). This viewpoint proposes a mechanism for observed polarity dependence and considers whether the same mechanism may apply in other shock-induced, short circuits.

Time course of oversensing and impedance changes in developing implantable cardioverter-defibrillator lead fracture.

Background: Pace-sense conductors comprise a pacing coil to the tip electrode and cable to the ring-electrode. Implantable cardioverter-defibrillator (ICD) lead-monitoring diagnostics include pacing impedance (direct current resistance [DCR]) and measures of oversensing. How they change as fractures progress is unknown.

Clinical performance of implantable cardioverter-defibrillator lead monitoring diagnostics.

Background: Implantable cardioverter-defibrillator (ICD) lead monitoring diagnostic alerts facilitate the diagnosis of structural lead failure.

Objective: The purpose of this study was to prospectively study the performance of Medtronic ICD lead monitoring alerts.

Methods: A prespecified ancillary substudy, World-Wide Randomized Antibiotic Envelope Infection Prevention Trial, was conducted in patients with an ICD with all available alerts enabled.

Interpreting device diagnostics for lead failure.

Implantable cardioverter-defibrillators (ICDs) incorporate automated, lead-monitoring alerts (alerts) and other diagnostics to detect defibrillation lead failure (LF) and minimize its adverse clinical consequences. Partial conductor fractures cause oversensing, but pacing or high-voltage alerts for high impedance detect only complete conductor fracture. In both pacing and high-voltage insulation breaches, low-impedance alerts require complete breach with metal-to-metal contact.

Impedance in the Diagnosis of Lead Malfunction.

Impedance is the ratio of voltage to current in an electrical circuit. Cardiovascular implantable electronic devices measure impedance to assess the structural integrity electrical performance of leads, typically using subthreshold pulses. We review determinants of impedance, how it is measured, variation in clinically measured pacing and high-voltage impedance and impedance trends as a diagnostic for lead failure and lead-device connection problems.

Why low-voltage shock impedance measurements fail to reliably detect insulation breaches in transvenous defibrillation leads.

Background: Implantable cardioverter-defibrillators (ICDs) use low-voltage measures of shock impedance (LVSZ) to monitor integrity of leads.

Objective: To determine the separation distance between conductors required for LVSZ to detect insulation breaches that produce short circuits during shocks, causing failed defibrillation.

Methods: We simulated in-pocket insulation breaches between the ICD generator (CAN) and cables to the distal coil of 10 leads from 2 manufacturers.

Endpoints for Successful Slow Pathway Catheter Ablation in Typical and Atypical Atrioventricular Nodal Re-Entrant Tachycardia: A Contemporary, Multicenter Study.

Objectives: This study sought to investigate markers of success following slow pathway ablation for atrioventricular nodal re-entrant tachycardia (AVNRT).

Background: Published data are conflicting.

Methods: The authors studied 1,007 patients with typical AVNRT and 77 patients with atypical AVNRT.

Inappropriate disabling of an ICD noise-detection algorithm in pacemaker-dependent patients.

SecureSense is an implantable cardioverter defibrillator algorithm that differentiates lead-related oversensing from ventricular tachycardia/ventricular fibrillation by continuous comparison between the near-field (NF) and the far-field (FF) electrogram. If lead noise is identified, inappropriate therapy is withheld. Undersensing on the FF channel could result in inappropriate inhibition of life-saving therapy.

Monitoring for and Diagnosis of Lead Dysfunction.

The predominant structural mechanisms of transvenous lead dysfunction (LD) are conductor fracture and insulation breach. LD typically presents as an abnormality of electrical performance; the earliest sign usually is either oversensing or out-of-range pacing or shock impedance. Accurate diagnosis of LD requires discriminating patterns of oversensing and impedance trends that are characteristic of LD from similar patterns that occur in other conditions.

Early Diagnosis of Defibrillation Lead Dislodgement.

Objectives: This study sought to develop and evaluate an algorithm for early diagnosis of dislodged implantable cardioverter-defibrillator (ICD) leads.

Background: Dislodged defibrillation leads may sense atrial and ventricular electrograms (EGMs), triggering shocks in the vulnerable period that induce ventricular fibrillation (VF).

Methods: We developed a 2-step algorithm by using experimental lead dislodgements (LDs) at ICD implantation and a control dataset of newly implanted, in situ leads.