Failure to detect life-threatening arrhythmias in ICDs using single-chamber detection criteria.

Background: There are anecdotal reports of sudden death despite a functional implantable cardioverter defibrillator (ICD). We sought to describe scenarios leading to fatal or near-fatal outcome due to inappropriately inhibited ICD therapy in devices programmed with single-chamber detection criteria.

Methods: Programmed settings, episode lists, and intracardiac electrograms from 24 patients with a life-threatening event (n = 12) or fatal outcome (n = 12) related to failed ventricular arrhythmia detection were used to clarify the underlying scenario.

Biventricular Paced QRS Area Predicts Acute Hemodynamic CRT Response Better Than QRS Duration or QRS Amplitudes.

Introduction: Vectorcardiographic (VCG) QRS area of left bundle branch block (LBBB) predicts acute hemodynamic response in cardiac resynchronization therapy (CRT) patients. We hypothesized that changes in QRS area occurring with biventricular pacing (BV) might predict acute hemodynamic CRT response (AHR).

Methods And Results: VCGs of 624 BV paced electrocardiograms (25 LBBB patients with 35 different pacing configurations) were calculated according to Frank's orthogonal lead system.

Alternans of the Ventricular Electrogram in Patients with an Implanted Cardioverter-Defibrillator.

Background: The occurrence and significance of alternans of the ventricular electrogram (VEGM) in patients with an implanted cardioverter-defibrillator (ICD) has been rarely reported.

Objectives And Methods: This report describes our observations of VEGM alternans documented in nine patients with an ICD (seven new cases and two previously published cases for comparison).

Results: We found seven new cases of near-field VEGM alternans and added two of our previously reported examples.

Atrioventricular block precipitated by isoproterenol.

An isoproterenol infusion was administered during an electrophysiologic study (EPS) in a patient with a history of near syncope, left bundle branch block, and no documented atrioventricular (AV) block. Isoproterenol precipitated classic 2:1 Infra-Hisian AV block most probably proximal to the site of recording a His-Purkinje potential consistent with right bundle branch activity. Paroxysmal AV block also occurred during isoproterenol washout at a different site located distal to the presumed right bundle branch potential.

A review of the confirmation algorithm and related timing cycles of St. Jude ICDs.

The confirmation algorithm of implantable cardioverter-defibrillators (ICDs) functioning in the uncommitted mode verifies the presence of a continuing tachyarrhythmia during or following charging of the capacitor. Confirmation is usually applied in relation to the first shock. The details of the normal reconfirmation process of St.

Automatic mode switching of a dual chamber implantable cardioverter-defibrillator induced by a ventricular escape rhythm.

This report describes a form of group beating induced by a St Jude dual chamber ICD which interpreted a ventricular escape rhythm (with retrograde conduction) as premature ventricular complexes (PVC). These pacemaker-defined PVCs activated the atrial pace-PVC algorithm in 2 steps. 1.

Undersensing by an ICD due to alternans of the ventricular electrogram.

Alternans of the ventricular electrogram (VEGM) during ventricular tachycardia (VT) is a rare cause of ventricular undersensing by an implantable cardioverter-defibrillator (ICD). This report describes a patient with a St. Jude ICD who exhibited sustained monomorphic VT associated with surface QRS alternans, alternating cycle lengths, alternans of the VEGM causing intermittent undersensing of the smaller component, and intermittent 2:1 counting of ventricular intervals during 1:1 sensing in response to the ICD detection algorithm.

Dissimilar ventricular rhythms: implications for ICD therapy.

Sensing of left ventricular (LV) activity in some devices used for cardiac resynchronization therapy (CRT) was designed primarily to prevent the delivery of an LV stimulus into the LV vulnerable period. Such a sensing function of the LV channel is not universally available in contemporary CRT devices. Recordings of LV electrograms may provide special diagnostic data unavailable solely from the standard right ventricular electrogram and corresponding marker channel.

Functional atrial undersensing associated with switching to a tracking mode of pacing.

We have previously demonstrated that contemporary St. Jude devices (pacemakers and implantable cardioverter-defibrillators [ICDs]; St. Jude Medical, Sylmar, CA, USA) are designed to generate an extended postventricular atrial refractory period (PVARP) of 475 ms at the termination of conventional automatic mode switching (AMS) in response to atrial tachyarrhythmias .

Rise in ICD shock impedance: lead fracture or death?

Background: Remote monitoring allows for interrogation and extensive data retrieval of implantable cardioverter-defibrillators (ICDs). Data on ICD parameters at the time of death and afterwards are limited. The purpose of this retrospective study was to examine the changes in lead impedances of ICDs at the time of death and afterwards.