Conventional Implantable Cardioverter-defibrillators Research Articles

Subcutaneous Implantable Cardioverter Defibrillator

Implantable cardioverter-defibrillators (ICDs) represent a very effective therapy for primary and secondary prevention of sudden cardiac death (SCD). However, implantation of endocardial leads using a transvenous approach is associated with significant procedural and long term complications. An entirely subcutaneous ICD (S-ICD) has been developed, potentially eliminating many of the complications associated with traditional transvenous ICDs. This novel approach has been demonstrated to be a reliable and effective system for detection and termination of ventricular arrhythmias. The available therapeutic interventions are a result of the unique characteristics of a high energy subcutaneous delivery system, and therefore require appropriate patient selection to optimize therapeutic benefit and minimize the limitations of the first generation S-ICD. By maintaining the effectiveness of conventional ICDs while limiting the associated complications, the S-ICD provides an alternative therapy for clinicians treating many patients at risk for SCD. This review will examine the development of the subcutaneous ICD, its advantages, limitations, and potential clinical role in the treatment of ventricular tachyarrhythmias and prevention of SCD. Despite advances in cardiovascular care, SCD remains a significant public health issue.1 A variety of nonpharmacologic therapies for primary and secondary prevention of SCD exist, including ICDs by endovascular lead implantation or placement of epicardial defibrillation patches. Nonimplantable strategies for SCD protection in high risk patients have also been attempted, including a wearable defibrillator vest,2,3 as well as automated external defibrillator use at home in selected cohorts.4 The subcutaneous ICD provides an alternative device for treatment of SCD.5 The development of an entirely subcutaneous ICD was motivated initially by special circumstances where a traditional endovascular system was not practical. It was first applied in the pediatric population, where congenital anatomic variation often precludes safe endocardial lead placement; the technique was extended to other patient populations in whom venous …

A novel approach to eliminate intraventricular lead placement in patients with congenital heart disease

We describe two patients with congenital heart disease who were referred for implantable cardioverter-defibrillator (ICD) placement. Both patients possessed factors causing the conventional transvenous approach to be undesirable. We therefore devised a technique which circumvented both intravascular ICD lead placement, as well as placement of leads across the tricuspid valve. For both patients, a bipolar pace-sense lead was successfully placed in a branch of the coronary sinus. A shocking coil was then tunneled from the posterolateral margin of the device pocket, being positioned posterior and inferior to the cardiac silhouette. Defibrillation testing was carried out with goal of a 10-J safety margin. We were able to successfully achieve ICD implantation in both patients with complex congenital heart disease without requirement for surgical thoracotomy or a lead across the AV valve. R waves in excess of 5 mV were obtained and acceptable defibrillation characteristics were achieved. Both patients are doing well after mid-term follow-up. A new implant approach is presented, which involves minimal intravascular hardware and eliminates passage across the atrioventricular valve for patients with congenital heart disease in whom conventional ICD implant techniques may be undesirable or not possible. This procedure is technically straightforward with proper technique and knowledge of the patient specific anatomy.

Subcutaneous Implantable Cardioverter Defibrillator in a Patient with Pectus Excavatum

Sudden cardiac arrest in young healthy adults has concerned the medical and social communities due to its fatal effect. Implantable cardioverter defibrillator (ICD) has been demonstrated to be an effective measure for prevention of sudden death in patients at risk of ventricular arrhythmia. Subcutaneous ICD has been developed to overcome some problems associated with transvenous leads in the conventional ICD. In this case report, we describe the use of completely subcutaneous ICD for a young patient with pectus excavatum following presentation with out-of-hospital VF arrest with no complication in device or lead positioning.

Rationale and design of the PRAETORIAN trial: A Prospective, RAndomizEd comparison of subcuTaneOus and tRansvenous ImplANtable cardioverter-defibrillator therapy

Implantable cardioverter-defibrillators (ICDs) are widely used to prevent fatal outcomes associated with life-threatening arrhythmic episodes in a variety of cardiac diseases. These ICDs rely on transvenous leads for cardiac sensing and defibrillation. A new entirely subcutaneous ICD overcomes problems associated with transvenous leads. However, the role of the subcutaneous ICD as an adjunctive or primary therapy in patients at risk for sudden cardiac death is unclear. The PRAETORIAN trial is an investigator-initiated, randomized, controlled, multicenter, prospective 2-arm trial that outlines the advantages and disadvantages of the subcutaneous ICD. Patients with a class I or IIa indication for ICD therapy without an indication for bradypacing or tachypacing are included. A total of 700 patients are randomized to either the subcutaneous or transvenous ICD (1:1). The study is powered to claim noninferiority of the subcutaneous ICD with respect to the composite primary endpoint of inappropriate shocks and ICD-related complications. After noninferiority is established, statistical analysis is done for potential superiority. Secondary endpoint comparisons of shock efficacy and patient mortality are also made. The PRAETORIAN trial is a randomized trial that aims to gain scientific evidence for the use of the subcutaneous ICD compared with the transvenous ICD in a population of patients with conventional ICD with respect to major ICD-related adverse events. This trial is registered at ClinicalTrials.gov with trial ID NCT01296022.

BAYESIAN META-ANALYSIS ON MEDICAL DEVICES: APPLICATION TO IMPLANTABLE CARDIOVERTER DEFIBRILLATORS

Objectives: The aim of this study is to describe and illustrate a method to obtain early estimates of the effectiveness of a new version of a medical device.Methods: In the absence of empirical data, expert opinion may be elicited on the expected difference between the conventional and modified devices. Bayesian Mixed Treatment Comparison (MTC) meta-analysis can then be used to combine this expert opinion with existing trial data on earlier versions of the device. We illustrate this approach for a new four-pole implantable cardioverter defibrillator (ICD) compared with conventional ICDs, Class III anti-arrhythmic drugs, and conventional drug therapy for the prevention of sudden cardiac death in high risk patients. Existing RCTs were identified from a published systematic review, and we elicited opinion on the difference between four-pole and conventional ICDs from experts recruited at a cardiology conference.Results: Twelve randomized controlled trials were identified. Seven experts provided valid probability distributions for the new ICDs compared with current devices. The MTC model resulted in estimated relative risks of mortality of 0.74 (0.60–0.89) (predictive relative risk [RR] = 0.77 [0.41–1.26]) and 0.83 (0.70–0.97) (predictive RR = 0.84 [0.55–1.22]) with the new ICD therapy compared to Class III anti-arrhythmic drug therapy and conventional drug therapy, respectively. These results showed negligible differences from the preliminary results for the existing ICDs.Conclusions: The proposed method incorporating expert opinion to adjust for a modification made to an existing device may play a useful role in assisting decision makers to make early informed judgments on the effectiveness of frequently modified healthcare technologies.

Impact of continuous intracardiac ST-segment monitoring on mid-term outcomes of ICD-implanted patients with coronary artery disease. Early results of a prospective comparison with conventional ICD outcomes

BackgroundAlthough myocardial ischaemia monitored by some implantable cardioverter-defibrillators (ICDs) might improve patient care, the clinical usefulness of this technology has not yet been validated.ObjectiveTo investigate the potential impact of ICD-based...

Abstract 17073: Avoiding Shocks by Programming a High Number of Antitachycardia Pacing Attempts for Fast Ventricular Tachycardia: A Prospective Study

Purpose: Antitachycardia pacing (ATP) is a painless therapy reducing defibrillation shocks in implantable cardioverter-defibrillator (ICD) recipients. One or 2 ATP attempts are usually programmed to terminate fast ventricular tachycardia (FVT) episodes and avoid shocks without delaying successful treatment in case of ATP failure. Programming more ATP attempts could probably reduce the occurrence of shocks. Objective: We sought to analyze the long-term efficacy and safety of programming a high number of ATP attempts for FVT. Methods: All patients receiving a first ICD in our center for coronary artery disease (CAD) and dilated cardiomyopathy in primary and secondary prevention indications between 2000 and 2009 were prospectively included in the study. ICDs were programmed to deliver 10 ATP attempts for FVT cycle lengths (CL) of 250 to 300 ms (200 to 240 bpm) before high energy shock delivery (5 bursts, then 5 ramps; 8 to 10 extrastimuli at 81 to 88% of the FVT CL; minimal pacing CL 180 ms). Results: We prospectively included 770 patients (men 84%; CAD 75.5%; age 63.2 ± 11 years; secondary indication 54.3%; left ventricular ejection fraction 30.3±9%), followed for 40.6 ± 25.6 months. Among them, 137 patients (17.8%) had a total of 1839 episodes of FVT (mean frequency 209 ± 9.2 bpm). ATP terminated 1713 episodes of FVT (unadjusted efficacy, 93.1%; GEE adjusted 81.7%) and acceleration occurred in 5.8% of episodes. A large majority of episodes were successfully treated (98.3%) by 1 or 2 ATP sequences. Conversely, the patient-based analysis showed that 17 (12.4%), 8 (5.8%) and 5 patients (2.1%) had one episode or more treated by at least 3, 4 or 5 ATP attempts, respectively. These patients would have been shocked with a conventional ICD programming. The benefit of this strategy was reduced for 6 to 10 attempts and only 10 patients were shocks for ATP failure (20 episodes, 1.1%). Despite the high number of attempts programmed, FVT episodes were mainly asymptomatic and found during device interrogation: syncope and pre-syncope occurred in 0.2% and 0.4% of episodes, respectively. Conclusions: Programming a high number of ATP attempts (at least 4 or 5 ATP sequences) in the FVT zone is both safe and useful. It could prevent painful shocks for FVT in a high proportion of ICD recipients.

Ventricular tachycardia or ventricular fibrillation occurs less often in patients with left bundle branch block and combined resynchronization and defibrillators than in patients with narrow QRS and conventional defibrillators

Mortality in chronic heart failure (CHF) patients with left bundle branch block (LBBB) is high. Cardiac resynchronization therapy (CRT) reduces symptoms and mortality in CHF patients with LBBB. Whether CRT promotes or prevents ventricular tachycardia (VT)/ventricular fibrillation (VF) remains controversial, however. Therefore, we aimed to analyse arrhythmia-related CRT effects and characterized the VT/VF incidence in CRT-defibrillator patients and matched controls with conventional implantable cardioverter-defibrillators (ICDs) for primary prevention of sudden cardiac death. We enrolled 134 patients [110 men, left ventricular ejection fraction (LVEF) 24 ± 8%, 71 coronary artery disease, CRT-ICD 67, conventional ICD matched controls 67, follow-up 31 ± 17 months] and monitored overall survival and the time to a first VT/VF episode. Controls did not have LBBB. They were otherwise matched for age, LVEF, and follow-up duration. Gender and underlying disease did not differ between the groups. Kaplan-Meier analysis revealed more favourable arrhythmia-free survival in CRT-ICD vs. conventional ICD patients [hazard ratio (HR) 2.26, confidence interval (CI) 1.09-4.67, log rank P = 0.023]. The difference persisted in the multivariate Cox regression analysis (HR 3.25, CI 1.18-8.93, P= 0.022). Overall survival was similar in both groups (HR 1.45, CI 0.55-3.82, P = 0.45). Chronic heart failure patients with LBBB treated with CRT-ICD, experience less and delayed VT/VF episodes compared with matched controls without LBBB receiving conventional ICD. In the long-term, CRT appears to exert antiarrhythmic effects and to attenuate the particularly high arrhythmia-related risk of CHF patients with LBBB. The incremental benefit of adding the ICD option to CRT pacing in LBBB patients appears questionable.

Clinical experience with a novel subcutaneous implantable defibrillator system in a single center

BackgroundImplantable cardioverter-defibrillators (ICDs) reduce mortality in both primary and secondary prevention, but are associated with substantial short- and long-term morbidity. A totally subcutaneous ICD (S-ICD) system has been developed. We report the initial clinical experience of the first 31 patients implanted at our hospital.MethodsAll patients had an ICD indication according to the ACC/AHA/ESC guidelines. The first 11 patients were part of the reported CE trial. The implantation was performed without fluoroscopy. The device was implanted subcutaneously in the anterior axillary line, with a parasternal lead tunneled from the xiphoid to the manubrial–sternal junction. Ventricular fibrillation (VF) was induced to assess detection accuracy and defibrillation efficacy using 65 J shocks.ResultsPost-implant, 52 sustained episodes of VF were induced. Sensitivity was 100% and induced conversion efficacy was 100% (with standard polarity in 29 patients). Mean time to therapy was 13.9 ± 2.5 s (range 11–21.6 s). Late procedure-related complications were observed in 2 of the first 11 implantations (lead migration). During follow-up, spontaneous ventricular arrhythmias occurred in four patients, with accurate detection of all episodes. Inappropriate therapy was observed in five patients. Recurrences were prevented with reprogramming.ConclusionsThe S-ICD system can be implanted without the use of fluoroscopy by using anatomical landmarks only. Episodes of VF were accurately detected using subcutaneous signals, and all induced and clinical episodes were successfully converted. The S-ICD system is a viable alternative to conventional ICD systems for selected patients.

Novel intravascular defibrillator: Defibrillation thresholds of intravascular cardioverter-defibrillator compared to conventional implantable cardioverter-defibrillator in a canine model

An intravascular, percutaneously placed implantable defibrillator (InnerPulse percutaneous intravascular cardioverter-defibrillator [PICD]) with a right ventricular (RV) single-coil lead and titanium electrodes in the superior vena cava (SVC) and the inferior vena cava (IVC) has been developed. The purpose of this study was to compare defibrillation thresholds (DFTs) of the PICD to those of a conventional implantable cardioverter-defibrillator (ICD) in canines. Eight Bluetick hounds were randomized to initial placement of either a PICD or a conventional ICD. For PICD DFTs, a single-coil RV defibrillator lead was placed in the RV apex, and the device was positioned in the venous vasculature with electrodes in the SVC and IVC. With the conventional ICD, an RV lead was placed in the RV apex and an SVC coil was appropriately positioned. The ICD active can (AC) was implanted in a subcutaneous pocket formed in the left anterior chest wall and connected to the lead system. DFT was determined by a three-reversal, step up-down method to estimate the 80% success level. Two configurations were tested for the conventional ICD (#1: RV to SVC+AC; #2: RV to AC). A single configuration (RV to SVC+IVC) was evaluated for the PICD. Mean PICD DFT was 14.8 ± 1.53 (SE) J. Conventional #1 configuration demonstrated mean DFT of 20.2 ± 2.45 J and #2 of 27.5 ± 1.95 J. The PICD had a significantly lower DFT than the better conventional ICD configuration (#1; mean difference 5.4 ± 2.1 J, P <.05, paired t-test, N = 8). The new intravascular defibrillator had a significantly lower DFT than the conventional ICD in this canine model.

Tracing the European course of cardiac resynchronization therapy from 2006 to 2008

Cardiac resynchronization therapy (CRT) is a highly efficient treatment modality for patients with severe congestive heart failure and intraventricular dyssynchrony. However, the high individual cost and technical complexity of the implantation may limit its widespread utilization. The European Heart Rhythm Association (EHRA) launched a project to assess treatment of arrhythmias in all European Society of Cardiology member countries in order to have a platform for a progressive harmonization of arrhythmia treatment. As a result, two EHRA White Books have been published in 2008 and 2009 based on governmental, insurance, and professional society data. Our aim was to analyse the local differences in the utilization of CRT, based on these surveys. A total of 41 countries provided enough data to analyse years 2006-2008. Significant differences were found in the overall number of implantations and the growth rate between 2006 and 2008. Other contributing factors include local reimbursement of CRT, the existence of national guidelines, and a high number of conventional implantable cardioverter-defibrillator implantations, while GDP or healthcare spending has less effect. Focusing on improving these factors may increase the availability of CRT in countries where it is currently underutilized.

Implementation of device therapy (cardiac resynchronization therapy and implantable cardioverter defibrillator) for patients with heart failure in Europe: changes from 2004 to 2008

Heart failure (HF) patients increasingly receive device therapy, either an implantable cardioverter defibrillator (ICD) or a biventricular pacemaker, also called cardiac resynchronization therapy (CRT), or a CRT device with an ICD (CRT-D). However, epidemiological data on the use of device therapy in Europe are limited. Data on implantation rates for conventional pacemakers, ICD, CRT, and CRT-D in 15 Western European countries were obtained from the Eucomed Registry for the 5-year period 2004-2008. Implantation of conventional pacemakers increased by 9% in Europe over the 5 years (reaching 907/million in 2008) and there were significant differences between countries. Implantable cardioverter defibrillator implantations increased by 75% from 80/million in 2004 to 140/million in 2008, and differences between countries were larger than those for conventional pacemakers. Implantation rates for CRT-P alone increased slightly from 2004 to 2006, but remained at 25/million thereafter in Europe overall. The total number of CRT implants (CRT-P and -D) markedly increased from 46/million in 2004 to 99/million in 2008 (115%), but this was mainly due to more CRT-D implants, i.e. an increase in the proportion of CRT-D (from 55% in 2004 to 75% in 2008). Implantation rates for ICD, CRT, and CRT-D remained markedly different throughout the study period between countries. Implantation rates of devices for HF, in particular ICD and CRT-D, have increased significantly between 2004 and 2008 in Europe, but there remain major differences between countries.

A Comparison of Chronaxies for Ventricular Fibrillation Induction, Defibrillation, and Cardiac Stimulation: Unexpected Findings and Their Implications

A low-energy (<or= 4 J) cardioversion shock (LEC) either terminates reentrant ventricular tachycardia (VT) or accelerates it to ventricular fibrillation (VF). Optimization of the duration and amplitude of LEC shocks could improve the success rate of VT termination without VF induction. In order to learn how LEC shocks may be optimized, we used an animal model to compare the strength-duration curve for VF induction and the strength-duration curve for cardiac stimulation via the shock coil. Conventional implantable cardioverter-defibrillator (ICD) leads were implanted in 12 narcotized pigs from 20 kg to 25 kg in weight. Stimulation, VF induction, and defibrillation pulses were delivered by custom-designed stimulators at preset pulse durations and amplitudes. The corresponding hyperbolic strength-duration curves were constructed using the least-squares fit method and averaged for all the animals. The mean chronaxie for stimulation via the shock coil of 0.23 ms was significantly shorter than both defibrillation (4.8 ms) and VF induction (3.1 ms) chronaxie values. At a shock duration of 0.3 ms or less, the mean VF-induction threshold amplitude exceeded 300 V. It may be reasonable to study whether LEC pulses from 0.25 ms to 0.30 ms in duration and up to 250 V in amplitude would increase therapeutic yield in VT termination without VF induction in humans. Contrary to the current belief, the discrepancy between defibrillation and stimulation chronaxie is not caused by different electrode size. We postulate that the time constant of the fast sodium channel reactivation may be the underlying reason.

Implantable Cardioverter-Defibrillator Lead Performance

Implantable cardioverter-defibrillators (ICDs) have revolutionized the treatment of patients at risk for sudden cardiac death. In the nearly 3 decades since the first human ICD implant,1 millions of devices have been implanted worldwide and innumerable lives have been saved. Successful resuscitation of a potentially lethal ventricular arrhythmia by an ICD system depends on successful arrhythmia detection and timely delivery of therapy. Both the ICD generator and the ICD lead are critical components of this system. The lead, in particular, is literally a lifeline whose purpose is to convey critical information about the heart’s rhythm to the ICD generator and, in turn, to deliver life-sustaining therapy when needed. Failure of an ICD lead may result in significant clinical events, including failure to pace, failure to defibrillate, inappropriate shocks, and even death. Article p 2727 ICD leads, like many medical technologies, have undergone a remarkable transformation. Epicardial leads, which necessitated a thoracotomy for lead placement, have given way to transvenous leads, which are easier to implant, less costly, and associated with decreased morbidity and mortality.2 Important advances in transvenous lead technology, such as the development of steroid elution, smaller diameter leads, novel insulations, and multipolar leads, have translated into meaningful clinical benefits for patients. Although modern ICD leads consist primarily of electrodes, conductors, insulation, and a fixation mechanism to attach the lead to the myocardium, lead design and performance vary from model to model. Indeed, monitoring of performance is critical not only to identify products with increased failure rates but also to provide physicians and patients with realistic expectations of device performance. In the current issue of Circulation , Eckstein et al add to our understanding of ICD lead performance.3 The investigators conducted a retrospective analysis of 1317 consecutive patients who received ICD systems (including 38 different ICD lead …

Socio-economic analysis of cardiac resynchronization therapy

The field of electrical device therapy has benefited from two basically independent lines of investigation demonstrating mortal benefit from either cardiac resynchronization therapy (CRT) or implantable cardioverter-defibrillator (ICD) therapy in patients with heart failure. Current clinical evidence data is insufficient to conclude that CRT-defibrillation (CRTD) offers an advantage over CRT-pacing (CRTP) alone. The cost of adding a defibrillator to the CRTP device is substantial and will act as a barrier to wide scale penetration. Annualized sudden death rates are very low in certain primary prevention populations. Consequently, the potential for overtreatment is very large and the negative costs of ICD therapy are distributed equally among those patients who will have a life saving benefit and those who were "destined" never to require the therapy. The perception that these costs are acceptable if lives are saved is commonly cited as justification for expensive therapy on a population scale, but there is an important and practical difference between costs per unit life saved and costs among patients who really never needed the device. Until the a priori predictors of volumetric response to CRT are better understood, the use of CRTD in class IV patients should be discouraged since ICD therapy is unlikely to extend life in volumetric non-responders. Similarly, the use of CRTD in patients who are "destined" for significant volumetric response is probably unwise since their risk of sudden death is minimized due to favorable substrate modification. Clinical trials comparing conventional ICDs, CRTP and CRTD are necessary to rationalize use of expensive hardware resources among different patient populations. Additionally, the importance of patient preference regarding end of life care should receive greater emphasis. While CRTP may be considered palliative in terminal heart failure, the decision to offer CRTD must include a discussion with the patient regarding mode of death and the potential for the defibrillator to replace a sudden and peaceful death with a prolonged death from progressive pump failure.

The Managed Ventricular Pacing™ Versus VVI 40 Pacing (MVP) Trial: Clinical Background, Rationale, Design, and Implementation

Implantable cardioverter defibrillators (ICDs) reduce mortality among appropriately selected patients who have had or are at risk for life-threatening ventricular arrhythmia. Right ventricular apical (RVA) pacing has been implicated in worsening heart failure and death. The optimal pacemaker mode for bradycardia support while minimizing unnecessary and potentially harmful RVA pacing has not been determined. The Managed Ventricular pacing vs. VVI 40 Pacing Trial (MVP) is a prospective, multicenter, randomized, single-blind, parallel, controlled clinical trial designed to establish whether atrial-based dual-chamber managed ventricular pacing mode (MVP) is equivalent or superior to back-up only ventricular pacing (VVI 40) among patients with standard indications for ICD therapy and no indication for bradycardia pacing. The MVP Trial is designed with 80% power to detect a 10% reduction in the primary endpoint of new or worsening heart failure or all-cause mortality in the MVP-treated group. Approximately 1,000 patients at 80 centers in the United States, Canada, Western Europe, and Israel will be randomized to MVP or VVI 40 pacing after successful implantation of a dual-chamber ICD. Heart failure therapies will be optimized in accordance with evidence-based guidelines. Prespecified secondary endpoints will include ventricular arrhythmias, atrial fibrillation, new indication for bradycardia pacing, health-related quality of life, and cost effectiveness. Enrollment began in October 2004 and concluded in April 2006. The study will be terminated upon recommendation of the Data Monitoring Committee or when the last patient enrolled and surviving has reached a minimum 2 years of follow-up. The MVP Trial will meet the clinical need for carefully designed prospective studies to define the benefits of atrial-based dual-chamber minimal ventricular pacing versus single-chamber ventricular pacing in conventional ICD patients.

Impact of Upgrade to Cardiac Resynchronization Therapy on Ventricular Arrhythmia Frequency in Patients With Implantable Cardioverter-Defibrillators

This study compared cardiac resynchronization therapy's (CRT) impact on ventricular tachyarrhythmia susceptibility in patients who, due to worsening heart failure (HF) symptoms, underwent a replacement of a conventional implantable cardioverter-defibrillator (ICD) with a CRT-ICD. Cardiac resynchronization therapy is an effective addition to conventional treatment of HF in many patients with left ventricular systolic dysfunction. However, whether CRT-induced improvements in HF status also reduce susceptibility to life-threatening arrhythmias is less certain. Clinical and ICD electrogram data were evaluated in 18 consecutive ICD patients who underwent an upgrade to CRT-ICD. Pharmacologic HF therapy was not altered during follow-up. The definition of ventricular tachycardia (VT) and ventricular fibrillation (VF) for each patient was as determined by device programming. Statistical comparisons used paired t tests. Findings were recorded during two time periods: 47 +/- 21 months (range 24 to 70 months) before and 14 +/- 2 months (range 9 to 18 months) after CRT upgrade. At time of upgrade, patient age was 69 +/- 11 years and ejection fraction was 21 +/- 8%. Before CRT the frequency of VT, VF, and appropriate ICD shocks was 0.31 +/- 1.23, 0.047 +/- 0.083, and 0.048 +/- 0.085 episodes/month/patient, respectively. After CRT-ICD, VT and VF arrhythmia burdens and frequency of shocks were respectively 0.13 +/- 0.56, 0.001 +/- 0.004, and 0.003 +/- 0.016 episodes/month/patient (p = 0.59, 0.03, and 0.05 vs. pre-CRT). Arrhythmia frequency and number of appropriate ICD treatments were reduced after upgrade to CRT-ICD for HF treatment. Thus, apart from hemodynamic benefits, CRT may also ameliorate ventricular tachyarrhythmia susceptibility in HF patients.

Novel approach for low-voltage termination of anatomically defined reentry

Implantable cardioverter defibrillator (ICD) therapy for termination of cardiac arrhythmias is not optimal. High energy electrical shocks can cause side effects including electroporation, tissue damage, pain and traumatic patient experience. Reducing the shock energy would result in a profound improvement of the therapy. Eighty percent of patients receiving ICD therapy have a history of coronary artery disease and thus have the substrate for anatomically defined reentrant tachyarrhythmia. An applied electric field induces virtual electrode polarization at anatomical heterogeneities, which may also serve as the core of anatomical reentry. We have shown theoretically that interaction of the electric field with the core of reentry could potentially result in a 100-fold reduction of defibrillation energy. Methods and Results: We used a superfused isolated rabbit right ventricular preparation as a model of the endocardial border zone (n 14). Survival of only 50-200 m of the endocardial layer was verified by anti-Connexin43 immunostaining. Stable reentry was induced by burst pacing. Monophasic shocks (10 ms, 0.2-3.6 V/cm) were applied parallel to the endocardium from mesh electrodes located in the bath. Optical imaging revealed that the stable reentrant circuits were pinned to the endocardial trabeculae and were maintained with a cycle length of 155.78 38.58 ms. A total of 192 reentries were initiated and terminated by appropriately timed virtual electrode-induced excitation of either the anatomical obstacle serving as the core of reentry or a heterogeneity near the core. E50 (field at which 50% of reentries were terminated) was 1.4 V/cm, which corresponds to 3.4 times the average field excitation threshold. Conclusions: These results indicate that low-voltage termination of reentry is achievable and may be a promising new alternative to conventional ICD therapy.

Initial experience with a home monitoring system in implantable cardioverter defibrillator recipients

The Biotronik Home Monitoring (HM) system was developed to improve the management of patients (pts) with implantable pacemakers and defibrillators. This single center observational study aimed to evaluate feasibility and potential clinical utility of HM in implantable cardioverter defibrillator (ICD) recipients. Device related clinical events including unscheduled visits and hospitalisations were analysed in 22 consecutive pts (mean age 65±9,7 y., M/F 20/2) implanted with defibrillators equipped with a HM feature which completed 6 month follow-up. Results No major technical difficulties regarding data transmission were encountered. A total of 3453 HM reports including 87 event reports were received. Out of 87 event reports, 83 were prompted by arrhythmic events, one was related to lead complication, and one report disclosed premature battery depletion. In response to the ER received, phone consultation (9 pts), ICD reprogramming (10 pts), modification of antiarrhythmic medication (3 pts) or ICD replacement (1 pt) were performed. In pts with unscheduled visits or hospitalisations (n=9), significantly more event reports were transmitted than in pts with uncomplicated followup (6,8±6.1 vs. 2±1.3, p=0,01). HM users found the system “easy to handle” (92%) and perceived HM as providing “increased safety” (84%). and “improving patient care” (100%) Conclusions Apart from demonstrating the technical feasibility of HM, this pilot study highlights the potential of this technology to improve the management and enhance the safety of pts with ICDs. However, randomized studies in a larger population are required to prove the superiority of HM-based patient management over conventional ICD follow-up.

Verification of implantable cardioverter defibrillator (ICD) interventions by nonlinear analysis of heart rate variability ? preliminary results

Conventional ICD algorithms yield approximately 10-30% of spurious interventions. Our aim was to check whether nonlinear dynamics methods might be useful in the verification of ICD interventions. We extracted 190 consecutive RR files (approximately 2000-9000 RR intervals long) from the ICDs of 70 patients (36 with coronary artery disease, 8 with hypertrophic cardiomyopathy, 19 with dilated cardiomyopathy and 7 with other diseases). The 3D phase space trajectories in delay coordinates, window pattern entropy, and algorithmic complexity of the RR intervals were examined within a 50 beat sliding window. Data were not filtered for arrhythmia and artefacts. Of the 83 recordings with appropriate interventions 79 were correctly recognised in a blind test. Two interventions were not identified in patients with fast atrial fibrillation and two in cases of complex and frequent forms of arrhythmia. There were nine spurious interventions. In all except one case (atrial fibrillation with a fast ventricular response) the analysis by nonlinear methods showed that the intervention was not necessary. All of the 98 control recordings were correctly identified in the blind test. The results show that nonlinear dynamics methods may be used to supplement the existing ICD detection algorithms to enhance the detection success rate.