Medtronic Implantable Cardioverter Defibrillators Research Articles

T-Wave Oversensing with Contemporary Implantable Cardioverter-Defibrillators.

Implantable cardioverter-defibrillators (ICDs) need to reliably detect ventricular tachycardia (VT) and ventricular fibrillation (VF) while avoiding T-wave oversensing (TWOS), which is associated with a risk of inappropriate therapies. The incidence of TWOS with endovascular ICDs appears to differ between manufacturers. We aimed to evaluate the incidence and clinical consequences of TWOS with contemporary Medtronic and Boston Scientific ICDs. Consecutive patients implanted with a recent Medtronic or Boston Scientific ICD and remotely monitored at three French centers were included. All transmitted EGMs labelled as VF, VT, non-sustained VT (NSVT), or ventricular oversensing (Medtronic) were screened for TWOS. Among 7589 transmitted episodes from 674 patients with a Boston Scientific ICD, we did not identify a single case of TWOS. Among 16,790 transmitted episodes from 1733 patients with a Medtronic ICD, we identified 60 patients (3.4%) with at least one episode of TWOS. In 46 patients, TWOS was intermittent (NSVT episodes). In the remaining 14 patients, TWOS resulted in 60 sustained episodes (completed counters). No inappropriate therapies were delivered in 12 of these patients because no therapies were programmed (in monitor zones, 11 episodes) or because therapies were inhibited by the morphology discriminator (Wavelet, 19 episodes) or by the anti-TWOS algorithm (26 episodes). Two patients received inappropriate therapies due to TWOS (0.1% of patients with Medtronic ICDs). On review of 24,379 transmitted episodes from 2407 patients with endovascular ICDs, we found no case of TWOS with Boston Scientific devices, whereas TWOS was not uncommon with Medtronic devices. However, the risk of inappropriate therapy with Medtronic ICDs was very low (0.1%) due to the often intermittent nature of this phenomenon, the morphology discriminator, and the anti-TWOS algorithm.

Clinical performance of implantable cardioverter-defibrillator lead monitoring diagnostics.

Implantable cardioverter-defibrillator (ICD) lead monitoring diagnostic alerts facilitate the diagnosis of structural lead failure. The purpose of this study was to prospectively study the performance of Medtronic ICD lead monitoring alerts. A prespecified ancillary substudy, World-Wide Randomized Antibiotic Envelope Infection Prevention Trial, was conducted in patients with an ICD with all available alerts enabled. The investigators reported possible lead system events (LSEs), with or without an alert. An independent committee reviewed all data and classified events as lead failure, other LSE, or nonlead system events (NLEs). In 4942 patients who were followed for 19.4 ± 8.7 months, there were 124 alerts (65 LSEs, 59 NLEs) and 19 LSEs without an alert. Lead monitoring alerts had 100% sensitivity for the 48 adjudicated lead failures (95% confidence interval 92.6%-100%) and for 10 events adjudicated as either lead failure or connection issue. The positive predictive value of alerts forlead failure was 38.7% (48 of 124). For 34 pace-sense lead failures,an alert that incorporated oversensing was more sensitivethan thepacing impedance threshold alert (33 patients [97.1%] vs 9 patients[26.5%]; P < .0001). However, the sensitivity was only 13.6% for lead dislodgments or perforations. Inappropriate shocksoccurred in 2 patients with pace-sense lead failure (5.9%). No patient had unnecessary lead replacement for any of the NLEs. In this first real-world prospective study, lead monitoring alerts had 100% sensitivity for identifying lead failures. Although their positive predictive value was modest, no false-positive alerts resulted in an unnecessary lead replacement. For the diagnosis of pace-sense lead failure, an alert for oversensing was more sensitive than a pacing impedance threshold alert. ClinicalTrials.gov identifier: NCT02277990.

Predictores e impacto de la adopción de programación basada en la evidencia en la incidencia de terapias del desfibrilador automático implantable

Introduction and objectivesThe ADVANCE III trial showed that a delayed-detection strategy reduces implantable cardioverter-defibrillator (ICD) therapies. Here, we describe the adherence to and predictors of ADVANCE adoption and compare ICD therapy rates between patients with and without ADVANCE programming. MethodsThis observational retrospective study analyzed patients implanted with Medtronic ICDs included from 2005 to 2016 in a Spanish national multicenter registry (UMBRELLA database; ClinicalTrials.gov, NCT01561144). Changes in ADVANCE programming adoption were described in relation to a) publication of the ADVANCE trial, b) implementation of an “ADVANCE awareness” campaign, and c) publication of an expert consensus statement. Multivariate logistic regression identified predictors of adoption. Therapy incidence rates were compared between groups by estimating the adjusted incidence rate ratio (aIRR) using negative binomial regression. ResultsA total of 3528 patients were included. An ADVANCE strategy was used in 20% overall and in 44% at the end of the study. ADVANCE III adoption increased after trial publication, with less growth after an “ADVANCE awareness” campaign and after expert consensus statement publication. Predictors of ADVANCE adoption were as follows: ICD device with a nominal number of intervals to detect 30/40 (aOR, 4.4; 95%CI, 3.5-5.4), implantation by an electrophysiologist (aOR, 1.7; 95%CI, 1.4-2.2), and secondary prevention (aOR, 3.2; 95%CI, 2.6-3.9). Dual-chamber ICDs (aOR, 0.6; 95%CI, 0.5-0.8) and cardiac resynchronization-defibrillators (aOR, 0.5; 95%CI, 0.4-0.7) were associated with lower adoption. ADVANCE programming was associated with reduced total therapy burden (aIRR, 0.77; 95%CI, 0.69-0.86) and fewer inappropriate shocks (aIRR, 0.66; 95%CI, 0.52-0.85). ConclusionsADVANCE adoption remains modest and can be improved through evidence-driven selection of nominal ICD settings. ADVANCE programming is associated with reduced therapy rates in real-world ICD recipients.

Do ICD diagnostics predict failure of ventricular tachycardia response to antitachycardia pacing and need for shock?

Among heart failure patients with implantable cardioverter defibrillators (ICDs), monomorphic ventricular tachycardia (MMVT) failing antitachycardia pacing (ATP) and terminated by shock renders higher mortality as compared to MMVT terminated by ATP only. It is unknown if the higher mortality in ATP failure reflects decompensated heart failure. It was the purpose of the present study to determine if ICD heart failure diagnostics can predict the failure of ATP and the need to shock to terminate MMVT. This was a single-center retrospective review of 103 consecutive patients with Medtronic ICDs who had MMVT and received ICD therapy. Heart failure diagnostics preceding each MMVT event were reviewed including atrial fibrillation burden, patient activity, night heart rate, heart rate variability, Optivol® fluid index, and MMVT heart rate. A total of 452 MMVT events were analyzed, of which 23% required shock. Compared to MMVT that responded to ATP, MMVT that failed ATP and required shock had significantly faster heart rates and higher atrial fibrillation burden. Patient activity, night heart rate, heart rate variability, and OptiVol® fluid index were similar between ATP responsive MMVT events and those that failed ATP. In a multivariate analysis adjusting for baseline characteristics, higher atrial fibrillation burden and lower patient activity were associated with ATP failure and shock termination. Device diagnostics associated with decompensated heart failure identified MMVT events that failed ATP and necessitated shock.

Predictors of adoption and impact of evidence-based programming on the incidence of implantable cardioverter-defibrillator therapies

Introduction and objectivesThe ADVANCE III trial showed that a delayed-detection strategy reduces implantable cardioverter-defibrillator (ICD) therapies. Here, we describe the adherence to and predictors of ADVANCE adoption and compare ICD therapy rates between patients with and without ADVANCE programming. MethodsThis observational retrospective study analyzed patients implanted with Medtronic ICDs included from 2005 to 2016 in a Spanish national multicenter registry (UMBRELLA database; ClinicalTrials.gov, NCT01561144). Changes in ADVANCE programming adoption were described in relation to a) publication of the ADVANCE trial, b) implementation of an “ADVANCE awareness” campaign, and c) publication of an expert consensus statement. Multivariate logistic regression identified predictors of adoption. Therapy incidence rates were compared between groups by estimating the adjusted incidence rate ratio (aIRR) using negative binomial regression. ResultsA total of 3528 patients were included. An ADVANCE strategy was used in 20% overall and in 44% at the end of the study. ADVANCE III adoption increased after trial publication, with less growth after an “ADVANCE awareness” campaign and after expert consensus statement publication. Predictors of ADVANCE adoption were as follows: ICD device with a nominal number of intervals to detect 30/40 (aOR, 4.4; 95%CI, 3.5-5.4), implantation by an electrophysiologist (aOR, 1.7; 95%CI, 1.4-2.2), and secondary prevention (aOR, 3.2; 95%CI, 2.6-3.9). Dual-chamber ICDs (aOR, 0.6; 95%CI, 0.5-0.8) and cardiac resynchronization-defibrillators (aOR, 0.5; 95%CI, 0.4-0.7) were associated with lower adoption. ADVANCE programming was associated with reduced total therapy burden (aIRR, 0.77; 95%CI, 0.69-0.86) and fewer inappropriate shocks (aIRR, 0.66; 95%CI, 0.52-0.85). ConclusionsADVANCE adoption remains modest and can be improved through evidence-driven selection of nominal ICD settings. ADVANCE programming is associated with reduced therapy rates in real-world ICD recipients.

What is ventricular fibrillation undersensing?

Ventricular fibrillation (VF), uninterrupted, is fatal within minutes. Implantable cardioverter defibrillators (ICDs) sense ventricular electrograms (EGMs) during VF and detect the VF rhythm (a sequence of VF sensed events) to deliver a shock to terminate VF and save lives. VF sensing and detection in Medtronic ICDs has been reported to be highly sensitive. However, Castellano et al. reported that Medtronic ICDs have the potential for high levels of undersensing in VF, sufficient to underdetect VF and withhold life-saving therapy. This manuscript reviews the process of EGM sensing and VF detection in ICDs and compares the process of sensing in Medtronic ICDs with the process described in this recent publication.

T-wave oversensing is more dependent on ICD sensitivity algorithm than lead sensing configuration

Modern implantable cardioverter defibrillators (ICD) employ dynamic sensing algorithms in order to protect against fine ventricular fibrillation without oversensing intrinsic activity. We present a patient with a Medtronic ICD who had inhibition of pacing and not inappropriate shocks due to T wave oversensing (TWOS) in both true bipolar (TB) and integrated bipolar (IB) sensing configurations. Rather than alternatives such as lead revision or programming to an unacceptably insensitive value, this was solved by exchanging for a Boston Scientific ICD. Although the literature suggests lead sensing configuration impacts TWOS, this case demonstrates ICD sensitivity algorithm may be a key determinant.

Concurrent Validity of Daily Activity Data From Medtronic ICD/CRT Devices and the Actigraph GT3X Triaxial Accelerometer: A Pilot Study

Purpose: The purpose of this pilot study was to examine the concurrent validity of daily activity data from Medtronic implantable cardioverter defibrillator (ICD) and cardiac resynchronization therapy (CRT) devices and the Actigraph GT3X triaxial accelerometer in patients with heart failure (HF). Methods: Analysis of the first 16 subjects with HF completing 3-month follow-up in a randomized trial with a secondary purpose to examine concurrent validity of Medtronic ICD/CRT device-based daily activity and the following Actigraph GT3X parameters: hours of activity per day, activity counts, and steps per day. Daily activity data were measured at baseline and 3-month follow-up and analyzed using Pearson correlation coefficients to measure intraindividual correlations and Bland–Altman plots to examine agreement between devices. Results: Moderate-to-strong, statistically significant correlations were found between the Medtronic ICD/CRT and Actigraph GT3X devices for all parameters measured. The Bland–Altman plots revealed approximately 0.80 hours less activity per day measured by the Medtronic ICD/CRT compared with the Actigraph GT3X. Strong agreement for the 7-day average and moderate-to-strong agreement for all daily observations for hours of activity per day was found between both devices. Similarly, there was moderate-to-strong agreement for change in hours of activity and steps per day between baseline and 3-month follow-up. Conclusions: The Medtronic ICD/CRT devices seem to be a sufficiently accurate, responsive measure of daily activity in patients with HF when compared with the Actigraph GT3X.

Exercise- and Psychosocial-Based Interventions to Improve Daily Activity in Heart Failure: A Pilot Study

In individuals with heart failure (HF), low daily activity is associated with a poorer prognosis. The purpose of this pilot study was to investigate the effects of two home-based interventions on the primary HF-related outcome of daily activity and secondary outcomes of exercise tolerance, HF-related health status, and lower extremity functional strength in 16 patients with HF and implanted Medtronic implantable cardioverter defibrillator and cardiac resynchronization devices using a single-blind, randomized controlled pilot trial. Interventions were either daily activity feedback and encouragement or health coaching and home-based exercise. There were no significant differences in primary or secondary outcomes either between or within groups. Three subjects in each treatment group improved in two or more secondary outcomes, and only one improved in daily activity. Although the present pilot study incorporated both exercise and psychosocial components in the intervention, there was no effect on daily activity, perhaps because readiness for behavioral change was not accounted for either in group stratification/allocation or inclusion criteria.

Investigation of the Utility of the Audible Alert in Recent Generation Medtronic Implantable Cardioverter Defibrillators.

Medtronic implantable cardioverter defibrillators (ICDs; Medtronic Inc., Mounds View, MN, USA) are equipped with Patient Alert™, a feature in which the ICD generator emits a series of audible tones to notify patients of possible system malfunction. A prior study of this issue revealed that only 50% of patients with older Medtronic devices were able to hear alerts. More recently, Medtronic has incorporated modifications to the alert. Therefore, we studied how frequently alert tones emitted by the current generation of Medtronic ICDs are audible by patients. A series of patients were evaluated in an outpatient ICD clinic. Alert tones were demonstrated using a device programmer in a quiet room and in the presence of low-level background noise. Patients reported whether they heard the tones, and they completed questionnaires regarding the tones. The total sample size was 100 patients, 81 male, who ranged from 29 years to 94 years of age (mean age 72.1 ± 11.8). Among the study subjects, 46% were older than 75 years, 41% were between 55 years and 75 years, and 13% were younger than 55 years. In the absence of background noise, 94% of patients were able to hear both alerts, 1% heard only one alert, and 5% heard neither. In the presence of background noise, 88% of patients heard both the alerts, 7% heard only one alert, and 5% heard neither alerts. Our results demonstrate that alert tones in recent generation Medtronic ICDs have improved audibility, compared to prior published data, among a large outpatient ICD population.

Sensing and detection in Medtronic implantable cardioverter defibrillators.

Ensuring sensing and detection of ventricular tachycardia (VT) and ventricular fibrillation (VF) was a prerequisite for the clinical trials that established the survival benefit of implantable cardioverter defibrillators (ICDs). However, for decades, a high incidence of unnecessary shocks limited patients' and physicians' acceptance of ICD therapy. Oversensing, misclassification of supraventricular tachycardia (SVT) as VT, and self-terminating VT accounted for the vast majority of unnecessary shocks. Medtronic ICDs utilize sensitive baseline settings with minimal blanking periods to ensure accurate sensing of VF, VT, and SVT electrograms. Programmable algorithms reject oversensing caused by far-field Rwaves, Twaves, and non-physiologic signals caused by lead failure. A robust hierarchy of SVT-VT discriminators minimize misclassification of SVT as VT. These features, combined with evidence-based programming, have reduced the 1‑year inappropriate shock rate to 1.5 % for dual-/triple-chamber ICDs and to 2.5 % for single-chamber ICDs.

Performance of Lead Integrity Alert to Assist in the Clinical Diagnosis of Implantable Cardioverter Defibrillator Lead Failures

Background— The Lead Integrity Alert (LIA) was developed for Medtronic implantable cardioverter defibrillators to reduce inappropriate shocks for rapid oversensing caused by conductor fractures and reported for Medtronic Fidelis conductor fractures. The goal of this study was to compare the performance of LIA with conventional impedance monitoring for identifying lead system events (LSEs) and lead failures (LFs) in lead families that differ from Fidelis. Methods and Results— We analyzed data from 12 793 LIA enabled implantable cardioverter-defibrillator and lead combinations including 6123 St. Jude Riata or Durata, 5114 Boston Scientific Endotak, and 1556 Fidelis combinations followed in the CareLink remote monitoring network for LSEs and LFs. Each alert was adjudicated based on implantable cardioverter-defibrillator stored electrograms/diagnostics and clinical data as an LSE or non–lead system event by 2 physicians after reviewing the electrograms and clinical data. During 13 562 patient-years of LIA follow-up, there were 179 adjudicated alerts, of which 84 were LSEs (including 65 LFs) and 95 were non–lead system events. LIA identified &gt;66% more LSE and &gt;67% more LF compared with conventional impedance monitoring and did not differ by lead family for LSE ( P =0.573) or LF ( P =0.332). Isolated spikes on electrogram were associated more often with LF in St. Jude leads (71%) compared with Endotak (9%; P &lt;0.001) and Fidelis leads (11%; P &lt;0.001). The non–lead system event detection rate was different among lead families ( P &lt;0.001) ranging from 1 in every 78.5 years (Endotak), 228.9 years (St. Jude leads), and 627.6 years (Fidelis). Conclusions— LIA markedly increased the detection rate of LSE compared with conventional impedance monitoring.

ICD Lead Parameters, Performance, and Adverse Events following Continuous‐Flow LVAD Implantation

Ventricular arrhythmias (VAs) in the months following continuous-flow left ventricular assist devices (LVADs) implantation are common and associated with increased morbidity and mortality. We sought to evaluate for changes in implantable cardioverter defibrillator (ICD) performance following LVAD implantation. We retrospectively reviewed the ICD interrogation reports and medical records of patients who received a continuous-flow LVAD at the University of Chicago Medical Center between January 2008 and December 2010. Patients who did not have an ICD prior to LVAD implantation were excluded. Forty-four patients were included. Median right ventricular lead sensing amplitude decreased from 10.0 (interquartile range 7.6-13.6) mV prior to LVAD to 7.9 (5.9-9.3) mV after LVAD implantation (P < 0.01). Significant reductions in sensing threshold were associated with smaller lead diameters, smaller pace/sense electrode surface areas, and Medtronic ICD leads (Medtronic Inc., Minneapolis, MN, USA). Lead impedance and capture threshold did not change significantly. ICD-related adverse events occurred in 30% of patients and led to ICD modification in 18% of patients. Implantation of a continuous-flow LVAD is associated with changes in the performance of preexisting ICDs. ICD-related adverse events were encountered following LVAD implantation in this cohort, and at times resulted in invasive and noninvasive ICD system modification. Reductions in ICD sensing threshold after LVAD implantation may adversely affect ICD function. Formal ICD interrogation in addition to the regular follow-up testing is warranted post-LVAD.

Telediagnosis of heart failure with continuous intrathoracic impedance monitoring by Medtronic CareLink Network: Importance of the elevation pattern of OptiVol Fluid Index

BackgroundThe Medtronic implantable cardioverter defibrillator (ICD) and cardiac resynchronization therapy with defibrillator (CRT-D) device is equipped with the OptiVol fluid status monitoring system, which continuously measures intrathoracic impedance and provides an early warning of thoracic fluid retention, which is indicative of decompensated heart failure (HF). The accuracy of the telediagnosis of HF with this system still remains to be elucidated. MethodsWe studied 82 chronic HF patients implanted with a Medtronic ICD/CRT-D (mean age 66±12 years, 62 men, ICD in 44 and CRT-D in 38, left ventricular ejection fraction 37±14%). During follow-up, we analyzed OptiVol alerts, which were sent by monthly scheduled transmission and by unscheduled CareAlerts transmission for threshold-crossing events. The elevation patterns of OptiVol Fluid Index (OVFI), including the duration of threshold crossing, time interval from threshold crossing to peak OVFI, and peak OVFI, were compared between true decompensated HF and false-positive events. ResultsDuring a mean period of 861±239 days, 612 OptiVol alerts were transmitted from 70 of the 82 patients (85.4%). These 612 alerts were derived from 298 episodes that potentially represented decompensated HF (2.1 alerts per episode). Of these 298 possible HF events, 119 (40%) were judged as true decompensated HF based on clinical findings, while the other 179 events (60%) were false positives, including unexpected OVFI elevation (n=83), paroxysmal atrial fibrillation (n=37), excessive exercise (n=18), non-sustained ventricular tachycardia (n=10), and other causes. The analysis of the OVFI elevation pattern revealed that both the duration of threshold crossing and the peak OVFI value were significantly related to decompensated HF. The cutoff value for the duration of threshold crossing of OVFI for the diagnosis of HF was 21 days, showing 87% sensitivity and 85% specificity. The cutoff value of OVFI peak was 136.0Ω, showing 90% sensitivity and 92% specificity. ConclusionsNot every OptiVol alert is indicative of decompensated HF. A threshold-crossing OVFI for >21 days and an OVFI peak>136Ω are both strongly indicative of decompensated HF, and may be useful in the telediagnosis of HF.

Real‐World Data on the Lifespan of Implantable Cardioverter‐Defibrillators Depending on Manufacturers and the Amount of Ventricular Pacing

Implantable cardioverter-defibrillator (ICD) longevity is crucial for both patients and public health systems because it determines the number of surgical ICD replacements, which can generally be considered an additional risk factor for complications, and the cost-effectiveness of ICD therapy. Our objective was to obtain insight into the "real-world" longevities of implantable cardioverter-defibrillators, which quite often differ from those stated in the manufacturers' declarations. On the basis of a prospective database, we analyzed all ICD implantations performed in our hospital from June 1988 to June 2009. We studied 980 patients (follow-up 58 ± 51 months) with 1,502 ICDs and all respective data until August 2010. We compared the percentage of still operating ICDs at different points in time in relation to manufacturers, types of device (single chamber 623, dual chamber 588, cardiac resynchronization therapy ICDs [CRT-D] 291), and amount of right ventricular pacing (VP). We found distinct differences between the mean lifespans of ICDs of different manufacturers (Biotronik 4.3 years, Sorin 4.5 years, Guidant/Boston Scientific 4.7 years, St. Jude Medical 5 years, Medtronic 5.8 years). CRT-D devices (hazard ratio [HR] 1.778, P = 0.0005) were associated with an elevated annual relative risk for device replacement while a decrease in the proportion of VP (HR 0.934 for each 10% decrease in VP, P < 0.0001) and Medtronic ICDs were associated with a reduced risk of device replacement (HR 0.544, P < 0.0001). CRT-Ds and an elevated percentage of VP are associated with a significantly elevated risk for device replacement, while Medtronic ICDs showed the longest lifespans.

Prospective comparison of discrimination algorithms to prevent inappropriate ICD therapy: Primary results of the Rhythm ID Going Head to Head Trial

Inappropriate therapy for supraventricular arrhythmias remains a significant source of morbidity in implantable cardioverter-defibrillator (ICD) recipients. The Rhythm ID Goes Head to Head Trial (RIGHT) was designed to compare rhythm discrimination and inappropriate therapies among patients with ICDs from 2 manufacturers. Patients with standard ICD indications were randomized to receive a Guidant VITALITY 2 with Rhythm ID or selective Medtronic pulse generators using the Enhanced PR Logic or Wavelet discrimination algorithms. A single- or dual-chamber device was implanted based on clinical indications and programmed in 2 detection zones with detection enhancements enabled for rates between 150 and 200 bpm. Algorithm performance was compared between randomization groups, stratified by single or dual chamber, for the primary end point of first inappropriate therapy (shock or antitachycardia pacing) for supraventricular arrhythmias. There were 1962 patients enrolled and followed for 18.3 ± 9.2 months, with no difference in all-cause mortality between groups. There were 3973 treated episodes where electrograms were available and adjudicated. The primary end point of inappropriate therapy occurred in 246 of 985 VITALITY 2 patients vs 187 of 977 specific Medtronic ICD patients (hazard ratio = 1.34; confidence interval = 1.11-1.62; P = .003). Differences in inappropriate therapy were confined to single-chamber ICDs. Inappropriate shocks were more frequent in VITALITY 2 ICDs (hazard ratio = 1.63; confidence interval = 1.29-2.06; P < .001), with most therapies and performance differences occurring at slower rhythms (rates < 175 bpm). Rhythm discrimination performed better in the specific Medtronic than in VITALITY 2 ICDs evaluated, particularly for single-chamber devices. Inappropriate therapies, and differences in performance, may be reduced with the use of rate cutoff above 175 bpm.

Charge Circuit Timeout

Since the advent of the implantable cardioverter-defibrillator (ICD) for primary prevention of sudden cardiac death, much attention has been given to the possibility of ICD or lead hardware failures resulting in inappropriate ICD function. Less attention has been given to the potential for software programming errors resulting in inappropriate device behavior. We report a case of a software programming error that led to a premature “end of service” alert that triggered a “lock-up” of the device antitachycardia therapies. Typically, the capacitor charge time for the Medtronic Secura ICD in anticipation of a full energy shock is about 7.7 to 9.2 seconds, depending on how close the device is to the elective replacement time and other factors.1 A charge circuit timeout indicates that at least 1 charging period exceeded 30 seconds. When 3 consecutive charging periods each exceed 30 seconds, the ICD charge circuit becomes inactive, and all automatic therapy functions and manual system tests become disabled except for emergency VVI pacing, all for the purpose of conserving battery voltage for pacemaker dependent patients when the generator reaches end of service.1 An alert is displayed to indicate that the time allotted to reach the programmed output energy (30 seconds) has been exceeded. A charge circuit timeout usually occurs when the battery voltage is depleted below the “elective replacement indicator.” In this specific instance, the charge circuit timeout occurred because of a glitch in the software. Three events occurred almost simultaneously, exposing the software programming error.2 These events occurred during an episode of tachycardia in the brief time span between the end of charging the capacitors and redetection/confirmation before delivery of a shock. The 3 events are:

Defibrillation testing during implantable cardioverter-defibrillator implantation in Italian current practice: The Assessment of Long-term Induction clinical ValuE (ALIVE) project

Clinical practice with regard to defibrillation threshold (DFT) testing during implantable cardioverter-defibrillator (ICD) implantation varies considerably, even among experienced implanting centers. International guidelines do not as yet mandate DFT testing. The objective of this project is to assess current clinical decision making regarding DFT testing during ICD implantation. The ALIVE project collected data on DFT testing from a multicenter network of Italian clinicians sharing a common system for the collection, management, analysis, and reporting of clinical and diagnostic data from patients with Medtronic (Minneapolis, MN) implantable devices. Data on 2,082 consecutive patients implanted with a Medtronic ICD in 111 Italian centers, over the period 2007 to 2010, were analyzed. Defibrillation threshold testing was performed in 33% of cases (678/2,082). The main reasons for performing the test were physician's clinical practice ("I always perform DFT") (80%) and secondary prevention implantation (12%). The main reasons for not performing DFT testing were centers' practice (44%), primary prevention (31%), and device replacement (15%). In 22 patients, ventricular fibrillation induction was not achieved; 656 patients completed DFT testing: 633 patients (96%) performed a single test, 19 patients (3%) performed a second induction test, and 4 patients (0.6%) underwent an additional induction test. The preliminary results of the ALIVE project show that a great number of implant procedures are performed without DFT testing in the common practice of the participating centers. We also measured an inhomogeneous, center-dependent DFT testing behavior, which suggests the importance of defining a common guideline for ICD implant testing. Follow-up data on our patients will provide more information on the clinical value of the test.

Predictors of All‐Cause 1‐Year Mortality in Implantable Cardioverter Defibrillator Patients with Chronic Chagas’ Cardiomyopathy

Implantable cardioverter defibrillators (ICDs) have been used in the treatment of either sustained ventricular tachycardia or ventricular fibrillation in patients with Chagas' cardiomyopathy. This study aimed at determining mortality rate and risk factors of all-cause 1-year mortality in primary and secondary ICD patients with Chagas' cardiomyopathy. One hundred and forty-eight Chagas' patients with ICDs were included from the Medtronic ICD Registry Latin America. All patients were followed for 1 year. At implant, mean age was 60.1 ± 9.4 years and 72.9% were male. Mean left ventricular ejection fraction (LVEF) was 40.1 ± 11%. Mean follow-up was 12 ± 7 months. During the follow-up, 15 patients died (10.2%). Patients who died were older (64 ±10.8 years vs 59 ± 9.1; P = 0.04), had more atrial fibrillation (13.3% vs 3.8%; P = 0.02), had lower LVEF (33.4%± 9.8 vs 40.9%± 11.3; P = 0.01), and worse functional class (III/IV 40% vs 21.8%; P = 0.03). The multivariate analysis showed that two independent predictors of all-cause 1-year mortality remained statistically significant: age more than 65 (hazard ratio [HR] = 2.85, 95% confidence interval [CI] 1.77-3.92; P = 0.03) and LVEF less than 30% (HR = 2.68, 95% CI 1.57-3.79; P = 0.04). This analysis showed that patients older than 65 years of age and with LVEF less than 30% were independent predictors of all-cause 1-year mortality in patients with chronic Chagas' cardiomyopathy.

Ventricular oversensing due to manufacturer-related differences in implantable cardioverter-defibrillator signal processing and sensing lead properties

Ventricular oversensing remains a significant problem in modern implantable cardioverter-defibrillator (ICD) systems. The role of manufacturer-related differences in device-based signal processing on the one hand and sensing lead properties on the other is largely unknown. This retrospective study aimed to evaluate and compare the incidence and mechanisms of ventricular oversensing in single- or dual-chamber ICD systems from Biotronik (BTK), Guidant (GDT), and Medtronic (MDT). In 245 consecutive patients, device function, stored episodes, and lead parameters were evaluated at implant and during 243 ± 18 days of follow-up. Oversensing occurred in 3.3% of the patients [four T-wave oversensing (TWO), three R-wave double-sensing, and one diaphragmatic myopotentials]. The incidence of ventricular oversensing was generally low if an ICD device and an ICD lead were from one identical manufacturer (BTK: 2/68, GDT: 1/80, and MDT: 1/69; P = 0.67). In the subgroup of ICDs connected to leads from other manufacturers, however, ventricular oversensing was observed in none of 19 GDT and MDT ICDs but in 4 of 9 BTK devices (44.4%, P = 0.012). These four cases of oversensing (three R-wave double-sensing and one TWO) all occurred in BTK ICDs connected to integrated bipolar ICD leads from other manufacturers. Significant manufacturer-related differences exist in the incidence of ventricular oversensing in single- and dual-chamber ICD systems. Biotronik devices connected to integrated bipolar ICD leads from other manufacturers have an increased risk for R-wave double-sensing.