Antitachycardia pacing success in implantable cardioverter-defibrillators by patient, device, and programming characteristics.

Background: Antitachycardia pacing (ATP) is an established implantable cardioverter-defibrillator (ICD) therapy that terminates ventricular tachycardias (VTs) without painful ICD shocks. However, factors influencing ATP success are not well understood.

Objective: The purpose of this study was to examine ATP success rates by patient, device, and programming characteristics.

The development of the extravascular defibrillator with substernal lead placement: A new Frontier for device-based treatment of sudden cardiac arrest.

Introduction: The extravascular implantable cardioverter-defibrillato (EV ICD) system with substernal lead placement is a novel nontransvenous alternative to current commercially available ICD systems. The EV ICD provides defibrillation and pacing therapies without the potential long-term complications of endovascular lead placement but requires a new procedure for implantation with a safety profile under evaluation.

Methods: This paper summarizes the development of the EV ICD, including the preclinical and clinical evaluations that have contributed to the system and procedural refinements to date.

First-in-Human Chronic Implant Experience of the Substernal Extravascular Implantable Cardioverter-Defibrillator.

Objectives: The aim of this study was to evaluate the safety and performance of an extravascular (EV) implantable cardioverter-defibrillator (ICD).

Background: Limitations of existing transvenous and subcutaneous ICD systems include lead reliability and morbidity issues associated with ICD lead implantation in the vasculature or lack of pacing therapies (e.g.

Direct comparison of a novel antitachycardia pacing algorithm against present methods using virtual patient modeling.

Background: Antitachycardia pacing (ATP) success rates as low as 50% for fast ventricular tachycardias (VTs) have been reported providing an opportunity for improved ATP to decrease shocks.

Objective: The purpose of this study was to determine how a new automated antitachycardia pacing (AATP) therapy would perform compared with traditional burst ATP using computer modeling to conduct a virtual study.

Methods: Virtual patient scenarios were constructed from magnetic resonance imaging and electrophysiological (EP) data.

Therapy From a Novel Substernal Lead: The ASD2 Study.

Objectives: The ASD2 (Acute Extravascular Defibrillation, Pacing, and Electrogram) study evaluated the ability to adequately sense, pace, and defibrillate patients with a novel implantable cardioverter-defibrillator (ICD) lead implanted in the substernal space.

Background: Subcutaneous ICDs are an alternative to a transvenous defibrillator system when transvenous implantation is not possible or desired. An alternative extravascular system placing a lead under the sternum has the potential to reduce defibrillation energy and the ability to deliver pacing therapies.

Initial Clinical Experience With a New Automated Antitachycardia Pacing Algorithm: Feasibility and Safety in an Ambulatory Patient Cohort.

Background: Antitachycardia pacing (ATP) in implantable cardioverter-defibrillators (ICD) decreases patient shock burden but has recognized limitations. A new automated ATP (AATP) based on electrophysiological first principles was designed. The study objective was to assess the feasibility and safety of AATP in ambulatory ICD patients.

Effect of ICD Therapies on Mortality in the OMNI Trial.

Background: Analyses from primary prevention trials on implantable cardioverter defibrillator (ICD) therapy have shown an association between shocks and increased mortality. Recent data suggest a similar association with antitachycardia pacing (ATP).

Objective: The OMNI study is an observational study of pacemaker and ICD use.

A multicenter study of shock pathways for subcutaneous implantable defibrillators.

Introduction: A purely subcutaneous implantable cardioverter defibrillator (ICD) requires higher energy but may be an effective alternative to transvenous ICDs to deliver lifesaving therapies.

Objective: To identify combinations of anteroposterior subcutaneous shock pathways and waveforms with defibrillation efficacy comparable to transvenous ICDs.

Methods: Defibrillation testing was performed in 141 patients temporarily implanted with an active can emulator and subcutaneous coil electrodes.

Differences in effects of electrical therapy type for ventricular arrhythmias on mortality in implantable cardioverter-defibrillator patients.

Background: Implantable cardioverter-defibrillator (ICD) shocks have been associated with an increased risk of death. It is unknown whether this is due to the ventricular arrhythmia (VA) or shocks and whether antitachycardia pacing (ATP) termination can reduce this risk.

Objective: The purpose of this study was to determine whether mortality in ICD patients is influenced by the type of therapy (shocks of ATP) delivered.

Acute defibrillation performance of a novel, non-transvenous shock pathway in adult ICD indicated patients.

Objectives: The purpose of this study was to evaluate the efficacy of a totally subcutaneous, anteroposterior defibrillation shock pathway using a long time-constant shock waveform that emulates a proposed device having approximately twice the capacitance and thus twice the available energy of traditional transvenous devices.

Background: A non-transvenous defibrillation system potentially offers advantages over a transvenous system including simplification of the implant procedure and reduction of the impact of device complications by eliminating the need to place a lead within the heart. Previous non-transvenous defibrillation efficacy studies have been reported using anterolateral and anterior-anterior shock vectors.

Optimizing implantable cardioverter-defibrillator treatment of rapid ventricular tachycardia: antitachycardia pacing therapy during charging.

Background: Previous studies in implantable cardioverter-defibrillator (ICD) patients demonstrated the efficacy and safety of antitachycardia pacing (ATP) for rapid ventricular tachycardias (VT). To prevent shock delay in case of ATP failure, a new feature (ATP during charging) was developed to deliver ATP for rapid VT while charging for shock.

Objective: The purpose of this study was to determine the efficacy and safety of this new feature.

The dilemma of ICD implant testing.

Ventricular fibrillation (VF) has been induced at implantable cardioverter defibrillator (ICD) implant to ensure reliable sensing, detection, and defibrillation. Despite its risks, the value was self-evident for early ICDs: failure of defibrillation was common, recipients had a high risk of ventricular tachycardia (VT) or VF, and the only therapy for rapid VT or VF was a shock. Today, failure of defibrillation is rare, the risk of VT/VF is lower in some recipients, antitachycardia pacing is applied for fast VT, and vulnerability testing permits assessment of defibrillation efficacy without inducing VF in most patients.

Direct measurements of membrane time constant during defibrillation strength shocks.

Background: Defibrillation shocks impose significant energy demand on implantable cardioverter-defibrillators (ICDs). Several modeling studies have been devoted to optimizing shock parameters, and a large number of these studies treat the heart as a simplified lumped network. The time constant of membrane polarization (tau(m)) is a key variable for such modeling efforts.

QRS duration does not predict occurrence of ventricular tachyarrhythmias in patients with implanted cardioverter-defibrillators.

Objectives: The aim of this study was to determine whether QRS duration (QRSd) correlates with occurrence of ventricular arrhythmia in patients with coronary disease (CAD) receiving implantable cardioverter-defibrillators (ICDs).

Background: A QRSd measured on a standard electrocardiograph (ECG) correlates with total mortality risk in CAD patients at high risk for sudden death; however, the relationship between QRSd and risk of ventricular tachyarrhythmias (ventricular tachycardia/ventricular fibrillation [VT/VF]) is unclear.

Methods: PainFREE Rx II was a randomized trial, comparing efficacy of antitachycardia pacing versus shock therapy for VT/VF in patients receiving ICDs.

Appropriate and inappropriate ventricular therapies, quality of life, and mortality among primary and secondary prevention implantable cardioverter defibrillator patients: results from the Pacing Fast VT REduces Shock ThErapies (PainFREE Rx II) trial.

Background: Implantable cardioverter defibrillators (ICDs) reduce mortality in primary and secondary prevention. Quality of life, mortality, appropriate therapies for specific ventricular rhythms, and inappropriate therapies for supraventricular tachycardia (SVT) were compared among 582 patients (primary prevention=248; secondary prevention=334) in PainFREE Rx II, a 634-patient prospective, randomized study of antitachycardia pacing or shocks for fast ventricular tachycardia (FVT).

Methods And Results: ICDs were programmed identically with 3 zones (ventricular tachycardia [VT] <188 bpm; FVT=188 to 250 bpm; ventricular fibrillation [VF] >250 bpm) but randomized to antitachycardia pacing or shock as initial therapy for FVT.

Improved defibrillation efficacy with an ascending ramp waveform in humans.

Objectives: The purpose of this study was to compare an ascending ramp waveform (RAMP) with a standard, clinically available biphasic truncated exponential waveform (BTE) for defibrillation in humans.

Background: In animal studies, RAMP had a lower defibrillation threshold (DFT) than BTE.

Methods: We studied 63 patients at implantable cardioverter-defibrillator placement using a dual-coil lead and left pectoral active can.

Prospective randomized multicenter trial of empirical antitachycardia pacing versus shocks for spontaneous rapid ventricular tachycardia in patients with implantable cardioverter-defibrillators: Pacing Fast Ventricular Tachycardia Reduces Shock Therapies (PainFREE Rx II) trial results.

Background: Successful antitachycardia pacing (ATP) terminates ventricular tachycardia (VT) up to 250 bpm without the need for painful shocks in implantable cardioverter-defibrillator (ICD) patients. Fast VT (FVT) >200 bpm is often treated by shock because of safety concerns, however. This prospective, randomized, multicenter trial compares the safety and utility of empirical ATP with shocks for FVT in a broad ICD population.

Incidence and characteristics of type-2 breaks in response to antitachycardia pacing therapy in implantable cardioverter defibrillator patients.

Introduction: Antitachycardia pacing (ATP) effectively treats monomorphic ventricular tachycardia (VT). The VT may cease immediately upon ATP completion (type-1 break), or it may persist or change to another tachyarrhythmia for one or more beats before termination (type-2 break). We investigated the prevalence and characteristics of type-2 breaks in ICD patients.

Prospective randomized comparison of 65%/65% versus 42%/42% tilt biphasic waveform on defibrillation thresholds in humans.

Background: The waveform tilt of biphasic shocks yielding the lowest defibrillation threshold (DFT) is not well defined. Some evidence indicates that tilts less than 65% may improve DFTs.

Methods: In 57 patients undergoing ICD implantation, DFTs were determined with truncated exponential biphasic waveform tilts at 65%/65% and at 42%/42%.