Contemporary Implantable Cardioverter Defibrillator Research Articles

Implantable Cardioverter Defibrillator Tachycardia Therapies: Past, Present and Future Directions.

Implantable cardioverter defibrillators (ICDs) have a long history and have progressed significantly since the 1980s. They have become an essential part of the prevention of sudden cardiac death, with a proven survival benefit in selected patient groups. However, with more recent trials and with the introduction of contemporary heart failure therapy, there is a renewed interest and new questions regarding the role of a primary prevention ICD, especially in patients with heart failure of non-ischaemic aetiology. This review looks at the history and evolution of ICDs, appraises the traditional evidence for ICDs and looks at issues relating to patient selection, risk stratification, competing risk, future directions and a proposed contemporary ICD decision framework.

“Real-world” analysis of battery longevity of implantable cardioverter-defibrillators: an in-depth analysis of a prospective defibrillator database

BackgroundThere is a lack of evidence regarding contemporary implantable cardioverter-defibrillator (ICD) battery longevity. Our aim was to assess battery longevity in ICDs in a real-world setting.MethodsRetrospective cross-sectional single center study of a prospectively collected database of consecutive patients who underwent ICD implantation from January 2010 to December 2015. Clinical data and battery longevity of all manufacturers were collected.ResultsA total of 351 patients (84.6% males, mean age of 61 ± 12 years) were included in the study (292 VVI; 6 VDD; 53 DDD). All manufacturers (Abbott, Biotronik, Boston, Medtronic and Microport) were equally represented in the study (p = 0.110). Median battery longevity was 10.8 years (11 years for VVI and 8.5 for DDD). After a follow-up time of 5 years, 98% of VVI and DDD were still in service (vs. industry-projected longevity of 98%). During this time, 89 patients (25.4%) underwent device replacement − 69 patients (77.5%) due to battery depletion, 6 patients due to infection, 3 patients due to dysfunction and 13 patients due to upgrade to CRT-D. Patients with Medtronic or Biotronik ICDs had a greater probability of being replaced earlier due to battery depletion (Biotronik HR 6.87, 95% CI 2.54–18.58, p < 0.001; Medtronic HR 6.08, 95% CI 2.45–15.06 p < 0.001).ConclusionsVVI and DDD ICD battery longevity matched industry-projected longevity after 5 years of follow-up. Medtronic and Biotronik ICDs appeared to have an earlier battery depletion. Further randomized studies are required to ensure optimal care.

Long-term outcomes among a cohort of 4296 implantable cardioverter-defibrillator patients: insights from the UMBRELLA study

Abstract Background Large observational real-world studies describing modern implantable cardioverter-defibrillator (ICD) populations with long-term follow-up are lacking. Purpose To assess the incidence of arrhythmias in a cohort of contemporary patients undergoing ICD implant from 2005 and 2017 and to analyze the arrhythmic risk and mortality according to their clinical profiles. Methods UMBRELLA (NTC01561144) is a prospective, multicentre, nationwide study of ICD patients followed by remote monitoring. All device information was automatically stored through the remote monitoring system and a blinded review of all the stored arrhythmic episodes was performed. The study outcomes were first appropriate ICD therapy and all-cause death. Results The study population consisted of 4296 patients (61.9±12.9 years, ischaemic cardiomyopathy (ICM): n=2150, dilated cardiomyopathy (DCM): n=1166, valvular heart disease (VHD): n=119, hypertrophic cardiomyopathy (HCM): n=294, arrhythmogenic right ventricular cardiomyopathy (ARVC): n=71, Brugada syndrome (BS): n=143, long QT syndrome (LQTS): n=43, and adult congenital heart disease (ACHD): n=60)). Primary prevention (PP) was the main indication (n=2758). During a mean follow-up of 46.6±27.3 months, 16,067 episodes of sustained ventricular arrhythmia (SVA) occurred in 1344 patients. Appropriate ICD therapy was delivered to 85.7% (n=13,767) episodes of SVA in 1173 patients (27.3% of population). A higher risk of first appropriate ICD therapy was observed in VHD (HR: 1.94, 95% CI: 1.43–2.62), ARVC (HR: 1.84, 95% CI: 1.28–2.66), ICM (HR: 1.51, 95% CI: 1.29–1.78), and DCM (HR: 1.28, 95% CI: 1.07–1.53) whereas patients with HCM (HR: 0.72, 95% CI: 0.54–0.96) and BS (HR: 0.25, 95% CI: 0.14–0.45) were at significantly lower risk (Figure 1A). In multivariate analysis (Table 1), age, gender, atrial fibrillation (AF), secondary prevention, LVEF ≤35%, and QRS width emerged as clinical predictors of appropriate ICD therapy, whereas CRT-D correlated with lower risk. An independently higher risk was found in DCM, VHD, and ARVC, and a lower risk in BS patients. At follow-up, 590 deaths (13.4% of population) were reported. Patients with ICM (HR 3.90, 95% CI: 2.58–5.90), DCM (HR 3.33, CI 95%: 2.18–5.10), and VHD (HR 3.97, CI 95%: 2.25–6.99) had worse prognoses and it was significantly better in BS patients (HR 0.11, 95% CI: 0.01–0.67, p=0.017) (Figure 1B). In multivariate analysis, age, gender, AF, renal failure, diabetes and reduced LVEF, emerged as independent predictors of all-cause death (Table 1). Conclusions Irrespective of the aetiology, contemporary ICD patients with an arrhythmic substrate derived from left ventricular systolic dysfunction had a similar risk of ICD life-saving interventions and death. Funding Acknowledgement Type of funding sources: None. Table 1Figure 1

Contemporary ICD Use in Patients with Heart Failure.

Despite constant breakthroughs in heart failure (HF) therapy, the population of HF patients resume to grow and is linked to increased mortality and morbidity. Ventricular arrhythmias (VA) are one of the leading causes of mortality in HF subjects. Implantable cardioverter-defibrillators (ICDs) are currently the gold standard in treatment, preventing arrhythmic sudden cardiac death (SCD) episodes. However, the death rates related to HF remain elevated, as not all HF subjects benefit equally. Cardiac resynchronization therapy (CRT) has emerged as a novel approach for HF patients. These devices have been thoroughly investigated in major randomized controlled studies but continue to be underutilized in various countries. This review discusses the use of ICD in HF populations on top of treatments.

Long-Term Outcomes Among a Nationwide Cohort of Patients Using an Implantable Cardioverter-Defibrillator: UMBRELLA Study Final Results.

BackgroundLarge‐scale studies describing modern populations using an implantable cardioverter‐defibrillator (ICD) are lacking. We aimed to analyze the incidence of arrhythmia, device interventions, and mortality in a broad spectrum of real‐world ICD patients with different heart disorders.Methods and ResultsThe UMBRELLA study is a prospective, multicenter, nationwide study of contemporary patients using an ICD followed up by remote monitoring, with a blinded review of arrhythmic episodes. From November 2005 to November 2017, 4296 patients were followed up. After 46.6±27.3 months, 16 067 episodes of sustained ventricular arrhythmia occurred in 1344 patients (31.3%). Appropriate ICD therapy occurred in 27.3% of study population. Patients with ischemic cardiomyopathy (hazard ratio [HR], 1.51; 95% CI, 1.29–1.78), dilated cardiomyopathy (HR, 1.28; 95% CI, 1.07–1.53), and valvular heart disease (HR, 1.94; 95% CI, 1.43–2.62) exhibited a higher risk of appropriate ICD therapies, whereas patients with hypertrophic cardiomyopathy (HR, 0.72; 95% CI, 0.54–0.96) and Brugada syndrome (HR, 0.25; 95% CI, 0.14–0.45) showed a lower risk. All‐cause death was 13.4% at follow‐up. Ischemic cardiomyopathy (HR, 3.09; 95% CI, 2.58–5.90), dilated cardiomyopathy (HR, 3.33; 95% CI, 2.18–5.10), and valvular heart disease (HR, 3.97; 95% CI, 2.25–6.99) had the worst prognoses. Delayed high‐rate detection was enabled in 39.7% of patients, and single‐zone programming occurred in 52.6% of primary prevention patients. Both parameters correlated with lower risk of first appropriate ICD therapy, with no excess risk of mortality. The rate of inappropriate shocks at follow‐up was low (6%) and did not differ among type of ICD but was lower in SmartShock‐capable devices.ConclusionsIrrespective of the cause, contemporary ICD patients with heart failure–related disorders had a similar risk of ICD life‐saving interventions and death. Current ICD programming recommendations still need to be implemented.RegistrationURL: https://www.clinicaltrials.gov; Unique identifier: NTC01561144.

Transient ICD malfunctions during oncologic radiotherapy: a multi-centre, randomized, in-vitro study

Abstract Background Direct exposure of implantable cardioverter-defibrillators (ICDs) during radiotherapy is still considered potentially harmful, or even unsafe, by manufacturers and current recommendations. The effects of photon beams on ICDs are unpredictable, depending on multiple factors, and malfunctions may present during exposure. Purpose To evaluate transient ICD malfunctions by direct exposure to doses up to 10 Gy during low-energy RT, forty-three contemporary wireless-enabled ICDs, with at least 4 months to elective replacement indicator (ERI) were evaluated in a real-time in-vitro session in three different centres. Methods All ICDs had baseline interrogation. Single chamber devices were programmed to the VVI/40 mode and dual or triple chamber devices were programmed to the DDD/40 mode. Rate response function and antitachycardia therapies were disabled, with the ventricular tachycardia (VT)/ventricular fibrillation (VF) detection windows still active. A centring computed tomography was performed to build the corresponding treatment plan and the ICDs were blinded randomized to receive either 2-, 5- or 10-Gy exposure by a low photon-energy linear accelerator (6MV) in a homemade water phantom (600 MU/min). The effective dose received by the ICDs was randomly assessed by an in-vivo dosimetry. During radiotherapy, the ICDs were observed in a real-time session using manufacturer specific programmer, and device function (pacing, sensing, programmed parameters, arrhythmia detections) was recorder by the video camera in the bunker throughout the entire photon exposure. All ICDs had an interrogation session immediately after exposure. Results During radiotherapy course, almost all ICDs (93%) recorded major or minor transient electromagnetic interferences. On detail, sixteen ICDs (37.2%) reported atrial and/or ventricular oversensing, with base-rate-pacing inhibition and VT/VF detection. Twenty-four ICDs (55.8%) recorded non clinically relevant noise, and no detections were observed. Only three ICDs (7%) reported neither transient malfunction nor minor noise, withstanding direct radiation exposure. At immediate post-exposure interrogation, the ICDs that recorded major real-time malfunctions had VT/VF detections stored in the device memory. In none of the ICDs spontaneous changes in parameter settings were reported. Malfunctions occurred regardless of either 2-, 5- or 10-Gy photon beam exposure. Conclusions Transient electromagnetic interferences were observed in most of the contemporary ICDs during radiotherapy course, regardless of photon dose. To avoid potentially life-threatening ICD malfunctions such as pacing inhibition or inappropriate shock delivery, magnet application on the pocket site or ICD reprogramming to the asynchronous mode are still suggested in ICD patients ongoing even low energy radiotherapy exposure. Funding Acknowledgement Type of funding source: None

910Noise-related malfunctions in modern ICDs during oncologic radiotherapy: a multicentre, real-time, in-vitro observation

Abstract Funding Acknowledgements None Background Direct photon exposure of implantable cardioverter-defibrillators (ICDs) during radiotherapy is still considered not recommended, or even unsafe, by manufacturers and guidelines. The effects of photon beams on ICDs are unpredictable, depending on multiple factors, and electromagnetic interferences (EMIs) may present during exposure. Purpose To evaluate transient ICD malfunctions by direct exposure to doses up to 10 Gy during low-energy radiotherapy, 36 contemporary wireless-enabled ICDs, with at least 4 months to elective replacement indicator (E.R.I.) were evaluated in a realtime in-vitro session. Methods All ICDs had baseline interrogation. Single chamber devices were programmed in the VVI/40 mode and dual or triple chamber devices were programmed in the DDD/40 mode. Rate response function and antitachycardia therapies were disabled, with the ventricular tachycardia (VT)/ventricular fibrillation (VF) detection windows still working. A centering computed tomography was performed to build the corresponding treatment plan and the ICDs were blinded randomized to receive either 2, 5 or 10 Gy exposure by a low photon-energy linear accelerator (6MV) in a homemade water phantom (600 MU/min). The effective dose received by the ICDs was randomly assessed by an in-vivo dosimetry. During radiotherapy course, the devices were observed in a real-time session using manufacturer specific programmer, and ICD function (pacing, sensing, programmed parameters, detection) was recorder by the video camera in the bunker throughout the entire photon exposure. All ICDs had an interrogation session immediately after exposure. Results During radiotherapy course, almost all ICDs (90.9%) recorded major or minor transient EMIs. On detail, 16 ICDs (44.4%) reported EMI-related atrial and/or ventricular oversensing, with base-rate-pacing inhibition and VT/VF detection. 16 ICDs (44.4%) recorded not clinically relevant minor EMIs, and no detections were observed. Only 4 ICDs (11.2%) reported neither transient malfunction nor minor EMIs, withstanding direct radiation exposure. At immediate post-exposure interrogation, the ICDs that recorded major real-time malfunctions had VT/VF detections stored in the device memory. In none of the ICDs spontaneous changes in parameter settings were reported. EMI-related malfunctions occurred regardless of either 2, 5 or 10 Gy photon beam exposure. Conclusions Transient EMIs were observed in most of the contemporary ICDs. To avoid potentially life-threatening ICD malfunctions such as pacing inhibition or inappropriate shock delivery, magnet application on the pocket site or reprogramming in the asynchronous mode are still suggested in ICD patients ongoing even low energy radiotherapy exposure.

Electrical Storm in Patients with Inappropriate Implantable Cardioverter-Defibrillator Therapy: Current Trends in Clinical Practice between Guidelines and Technology Progress

The term “Electrical Storm” (ES) indicates cardiac electrical instability manifested by several episodes of ventricular tachyarrhythmias within a short time. In the contemporary implantable cardioverter-defibrillator (ICD) era, ES is defined as recurrent (three or more separate episodes) of ICD discharges over 24 hours. Some ESs are due to inappropriate repetitive shock and are potentially lethal for the patient. The most common causes of inappropriate ICD shock include supraventricular tachycardia with high ventricular response and oversening of peaked T waves or R wave, myopotentials or electrical noise. Appropriate diagnosis and treatment are critical in the Emergency Department. To approach these patients systematically, it is important to understand, that there are four causes of shock. Modern ICD incorporate sophisticated tachycardia detection algorithms within their programming designed to minimize devices’ detection mistakes and ICD-related information can also be checked using remote home monitoring systems. However, these opportunities are often not utilized to their full benefit. Thus, careful attention should be paid to the programming of the device. Fine tuning of the detection and differentiation algorithms is critical, and best done by a practitioner who understands the subtle differences among the different manufacturers. The racommendations for those problems should be revised.

SVT discrimination algorithms significantly reduce the rate of inappropriate therapy in the setting of modern-day delayed high-rate detection programming.

Contemporary implantable cardioverter-defibrillator (ICD) programming involving delayed high-rate detection and use of supraventricular tachycardia (SVT) discriminators has significantly reduced the rate of inappropriate shocks. The extent to which SVT algorithms alone reduce inappropriate therapies is poorly understood. PainFree SST enrolled 2770 patients with a single- or dual-chamber ICD or cardiac resynchronization defibrillator. Patients were followed for 22 ± 9 months with SVT discriminators on in 96% of patients. Sustained ventricular tachyarrhythmias and SVT episodes were adjudicated by an independent physician committee. For this analysis, all episodes were subjected to postprocessing computer simulation with SVT discriminators off with and without delayed high-rate detection criteria (ventricular fibrillation zone only, 30/40 at 320 ms). There were 3282 adjudicated SVT episodes of which 115 resulted in an ICD shock and 113 received only ATP (2-year inappropriate shock and therapy rates of 3.1% and 4.1%). Therapy was appropriately withheld for the remaining 3054 SVT episodes. With both SVT discriminators and delayed high-rate detection simulated off, the 2-year inappropriate therapy rate would have been 22.9% (hazard ratio [HR] = 6.24; 95% confidence interval [CI]: 5.20-7.49). With SVT discriminators simulated off and delayed high-rate detection simulated on in all patients, the 2-year rate would have been 6.4% (HR = 1.63; CI: 1.44-1.85). The use of SVT discriminators has a significant role in reducing the rate of inappropriate ICD therapy even in the setting of delayed high-rate detection settings. Deactivating SVT discriminators would have resulted in an overall increase in the inappropriate ICD therapy rate by 63% and 524% with and without delayed high-rate detection programming, respectively.

2410Oncologic radiotherapy-induced implantable cardioverter-defibrillator malfunctions: a real-time, in-vitro evaluation

Abstract Background Direct exposure of implantable cardioverter-defibrillators (ICDs) during radiotherapy is still considered not recommended, or even unsafe, by manufacturers and guidelines. The effects of photon beams on ICDs are unpredictable, depending on multiple factors, and malfunctions may occur during exposure. Purpose To evaluate transient ICD malfunctions by direct exposure to doses up to 10 Gy during low-energy radiotherapy, 33 contemporary wireless-enabled ICDs, with at least 4 months to elective replacement indicator (E.R.I.) were evaluated in a realtime in-vitro session. Methods All ICDs had baseline interrogation. Single chamber ICDs were programmed in the VVI/40 mode and dual or triple chamber ICDs were programmed in the DDD/40 mode. Rate response function and antitachycardia therapies were disabled, with the ventricular tachycardia (VT)/ventricular fibrillation (VF) detection windows still active. A centering computed tomography was performed to build the corresponding treatment plan and the ICDs were blinded randomized to receive either 2, 5 or 10 Gy exposure by a low photon-energy linear accelerator (6MV) in a homemade water phantom (600 MU/min). The effective dose received by the ICDs was assessed by an in-vivo dosimetry. During radiotherapy, the devices were observed in a real-time session using manufacturer specific programmer, and ICD function (pacing, sensing, programmed parameters, detection) was recorder by the video camera in the bunker throughout the entire photon exposure. All ICDs had an interrogation session immediately after exposure. Results During radiotherapy course, almost all ICDs (90.9%) recorded major or minor transient electromagnetic interferences. On detail, 13 ICDs (39.4%) reported atrial and/or ventricular oversensing, with base-rate-pacing inhibition and VT/VF detection. 16 ICDs (48.5%) recorded non clinically relevant noise, and no detections were observed. Only 4 ICDs (12.1%) reported neither transient malfunction nor minor noise, withstanding direct radiation exposure. At immediate post-exposure interrogation, the ICDs that recorded major real-time malfunctions had VT/VF detections stored in the device memory. In none of the ICDs spontaneous changes in parameter settings were reported. Malfunctions occurred regardless of either 2, 5 or 10 Gy photon beam exposure. Conclusions Transient electromagnetic interferences were observed in most of the contemporary ICDs during radiotherapy course, regardeless of photon dose. To avoid potentially life-threatening ICD malfunctions such as pacing inhibition or inappropriate shock delivery, magnet application on the pocket site or reprogramming devices in the asynchronous mode are still suggested in ICD patients ongoing even low energy radiotherapy exposure. Acknowledgement/Funding None

Trends of Cardiovascular Implantable Electronic Device Infection in 3 Decades: APopulation-Based Study.

This study assessed trends in the incidence of cardiovascular implantable electronic device (CIED) infection in the last 3 decades using a population-based records linkage study. Infection remains an important issue associated with increased implantation rate and dwell time ofCIEDs. We identified a cohort of all adults with CIEDs who resided in Olmsted County, Minnesota, from 1988 to 2015, using the medical linkage system of the Rochester Epidemiology Project. Standardized criteria were used to identify all CIED infection cases. The cumulative rate of CIED infection was estimated using the Kaplan-Meier method, and the trends of CIED infection incidence were calculated with person-years of follow-up after device implantation. The cumulative probabilities of overall CIED infection were 6.2% (95% confidence interval [CI]: 4.0% to 8.4%) at 15 years and 11.7% (95%CI: 6.8% to 17.3%) at 25 years of follow-up. The incidence of CIED infection every 7years from 1988 to 2015 was 1.3, 5.7, 4.1, and 4.7 per 1,000-person years, respectively. The 15-year cumulative probabilities of CIED infection after the initial, second, and third procedures were 2.6% (95%CI: 1.4% to 3.8%), 2.7% (95%CI: 1.2% to 4.2%), and 24.1% (95%CI: 3.8% to 44.4%), respectively. Generator changes (hazard ratio [HR]: 3.91; 95%CI: 1.47 to 10.37; p=0.006) and upgrades (HR: 3.08; 95%CI: 1.24 to 7.62; p=0.02) were significantly associated with infection. The incidence of CIED infection had a trend of increasing in the past 2 decades. Contemporary implantable cardioverter-defibrillator and cardiac resynchronization therapies and repeated manipulation of device pockets introduced a greater risk of CIED infection.

The Subcutaneous Implantable Cardioverter-Defibrillator: New Insights and Expanding Populations

Implantable cardioverter defibrillators (ICDs) have become a mainstay of treatment in patients at risk for sudden cardiac death. The majority of contemporary ICDs are implanted transvenously; however, this approach carries acute procedural and long-term risks. The subcutaneous ICD (S-ICD) was developed, in part, to circumvent some of these adverse events or as an alternative option in patients unable to undergo transvenous implantation. Early promising trials evaluating the S-ICD were small and focused on niche populations. More recently, larger trials included broader populations with worse heart failure and co-morbidities that may be more representative of typical ICD recipients. These studies have consistently demonstrated positive results. This review describes the S-ICD system, implantation, and the safety and efficacy of the device.

Low risk of electromagnetic interference between smartphones and contemporary implantable cardioverter defibrillators.

Manufacturers of implantable cardioverter defibrillators (ICDs) recommend that cell phones be maintained at a distance of ∼15 cm from the implanted device in order to avoid risk of dysfunction due to electromagnetic interference (EMI). Data relating to this issue are outdated and do not reflect modern technology. Our aim was to evaluate whether EMI is still an issue with contemporary ICDs and smartphones. Consecutive patients implanted with a wireless-enabled ICD were tested for potential interference with two models of recent 4G smartphones in conditions intended to maximize risk of EMI. A magnet effect (due to the phone speakers) was tested by placing the smartphones in the standby mode directly over the ICD generator. The presence of EMI artefacts on the real-time electrograms was evaluated by placing the smartphones in the standby, dialling, and operating modes directly over the generator casing and over the parasternal region in the vicinity of the ventricular lead. A total of 63 patients equipped with 29 different models of single, dual, or biventricular ICDs from five major manufacturers were included. None of the patients showed any evidence of interference with the smartphones during any of the 882 tests. The risk of EMI between modern smartphones and contemporary ICDs is low. This is probably due to the filters incorporated in the ICDs and low emission by the phones, as well as the small size of the magnets in the smartphones tested. NCT02330900 (http://www.clinicaltrials.gov).

Electrical storm in patients with implantable cardioverter-defibrillator in the era of catheter ablation: Implications for better rhythm control

The modern era of cardiology has changed the population of implantable cardioverter-defibrillator (ICD) recipients. Identifying predictors of electrical storm (ES) in contemporary ICD patients could improve risk stratification, therapeutic strategies, and mortality. The purpose of this study was to address these points in a real-world setting. In 330 consecutive patients (65 ± 11 years, 81% male, left ventricular ejection fraction 29% ± 9%) with ICD implanted because of ischemic (n, 204) or nonischemic dilated cardiomyopathy (n, 126), we analyzed the prevalence, predictors, and outcome of ES (≥3 separate VT/VF episodes within 24 hours) therapy. During a median of 21 months (range 17-36 months), 23 patients (7%) had ES. Secondary prevention (61% vs 24%, P <.01), single-chamber devices (57% vs 38%, P = .02), and prior appropriate (96% vs 24%, P < .001) and inappropriate (30% vs 9%, P = .004) therapies were more prevalent in these patients. In ES patients, first appropriate therapy occurred more often in the first year after implantation than in the rest of the cohort (85% vs 45%, P = .008), and mortality was significantly higher (22% vs 2%, P < .001). Multivariate Cox regression analysis showed that secondary prevention (hazard ratio [HR] 2.83, 95% confidence interval [CI] 1.21-6.61, P = .016) and prior appropriate (HR 88.99, 95% CI 11.73-675, P < .001) and inappropriate (HR 2.83, 95% CI 1.14-7.0, P = .04) therapies were independent predictors of ES. ES is not uncommon in ICD recipients. A secondary prevention indication and the occurrence of both appropriate and inappropriate ICD therapies increase the risk for ES. Prompt initiation of aggressive treatment, especially catheter ablation, should be considered for these patients.

Troubleshooting implantable cardioverter-defibrillator sensing problems II.

Accurate atrial sensing during tachycardia is essential for reliable determination of atrial rate, which is a critical component of interval-based dual-chamber supraventricular tachycardia (SVT)–VT discrimination algorithms.1 Thus, atrial sensing in dual-chamber implantable cardioverter-defibrillators (ICDs) must be reliable at fast ventricular rates, a technically challenging requirement. Determining the atrial rate during rapidly conducted atrial flutter (AF) requires accurate sensing of low-amplitude signals (Figure I in the Data Supplement). The required high atrial sensitivity increases the risk of atrial oversensing, especially of far-field R waves. Pacemakers rely on a long postventricular atrial blanking period (PVAB) to prevent oversensing of far-field R waves, but ICDs cannot: for a fixed PVAB, the blanked fraction of the cardiac cycle increases with the ventricular rate. For example, a 100-ms PVAB blanks 10% of the cycle at a bradycardia pacing cycle length of 1000 ms, but 33% during rapidly conducted AF with ventricular cycle length of 300 ms. PVABs longer than ≈80 ms produce clinically significant, functional atrial undersensing in rapidly conducted AF,2 and any PVAB may cause undersensing of alternate atrial electrograms in AF with 2:1 atrioventricular conduction. The inherent trade-off between atrial oversensing and undersensing is problematic. Both cause errors in dual-chamber SVT–VT discrimination algorithms.2–6 In contemporary ICDs, ventricular electrogram morphology algorithms mitigate this problem but do not eliminate it. ### Determinants of Far-Field R Waves #### General Considerations In the absence of atrial lead dislodgement, the amplitude of far-field R wave depends on 4 variables. The first is the amplitude of the ventricular electrogram in ventricular myocardium. Thus, there is a correlation between far-field R–wave oversensing and left ventricular hypertrophy.7 The second is interelectrode spacing.8 Closely spaced electrodes (1.1 mm) minimize far-field R waves in comparison with conventional 10-mm spacing, but they also reduce the amplitude of atrial electrograms during short-term follow-up9,10 and …

Radiation tolerance of contemporary implantable cardioverter-defibrillators

Implantable cardioverter-defibrillators (ICDs) are complex instruments using integrated circuit technology. Previous studies suggested risk to the device when exposed to a radiation environment. Little data is available on contemporary ICD systems. The purpose of the present study was to assess the ability of contemporary ICD designs to resist the damaging effects of direct exposure to therapeutic doses of radiation. Four contemporary ICDs and four legacy ICDs devices were exposed to escalating doses of photon irradiation (XRT) from a 6-MV linear accelerator. Escalating doses were administered over 8days to a maximum cumulative dose of 131.11Gy or catastrophic failure. Each legacy device had catastrophic failure following the 6th XRT session, characterized by failure to deliver shock therapy. All four contemporary devices remained fully functional following the 8th and final XRT session (P = 0.03). The cumulative, survived radiation dose was significantly different between the contemporary and legacy groups (131.11 vs. 41.11Gy, P = 0.01). Changes seen in the legacy devices were sudden and not anticipated by trends in prior sessions. The results of this study suggest that contemporary ICD designs may be more robust than earlier designs in a radiation environment.

Longitudinal Follow-Up of Implantable Cardioverter Defibrillator Leads

Although implantable cardioverter defibrillator (ICD) leads are prone to failure and Food and Drug Administration recall, comprehensive longitudinal studies investigating contemporary ICD lead survival rate in the United States are lacking. All patients receiving Medtronic, Boston Scientific, or St. Jude Medical transvenous ICD leads at the hospitals of the University of Pittsburgh Medical Center from 2000 to 2012 were included. Leads were classified as (1) functional lead, patient deceased; (2) functional lead, replaced; (3) failed lead, replaced; or (4) functional lead, active. Kaplan-Meier survival curves were constructed for all lead models separately and in aggregate. We followed 5,288 patients (1,020 Quattro, 623 Fidelis, 627 Riata, 828 Durata, and 2,190 Reliance) over 3.7 ± 3.3 years. Functional leads that were replaced included 30 Quattro (3%), 99 Fidelis (16%), 24 Riata (4%), 24 Durata (3%), and 62 Reliance (3%). Leads replaced because of failure included 11 Quattro (1%), 47 Fidelis (8%), 38 Riata (6%), 18 Durata (2%), and 26 Reliance (1%; p <0.001 for Food and Drug Administration recalled vs nonrecalled leads). Overall survival rate of all leads was 89.3% at 5 years. Survival curves of Riata and Fidelis diverged from nonrecalled leads at approximately 2 years. In conclusion, the overall survival rate of ICD leads is nearly 90% at 5 years. Survival curves of recalled leads diverge from nonrecalled leads after 2 years of implantation. These data have important implications on postmarket release monitoring of ICD leads and physicians' choice of leads.

Dynamic Analysis of Cardiac Rhythms for Discriminating Atrial Fibrillation From Lethal Ventricular Arrhythmias

Implantable cardioverter-defibrillators (ICDs), the first line of therapy for preventing sudden cardiac death in high-risk patients, deliver appropriate shocks for termination of ventricular tachycardia (VT)/ventricular fibrillation. A common shortcoming of ICDs is imperfect rhythm discrimination, resulting in the delivery of inappropriate shocks for atrial fibrillation (AF). An underexplored area for rhythm discrimination is the difference in dynamic properties between AF and VT/ventricular fibrillation. We hypothesized that the higher entropy of rapid cardiac rhythms preceding ICD shocks distinguishes AF from VT/ventricular fibrillation. In a multicenter, prospective, observational study of patients with primary prevention ICDs, 119 patients received shocks from ICDs with stored, retrievable intracardiac electrograms. Blinded adjudication revealed shocks were delivered for VT/ventricular fibrillation (62%), AF (23%), and supraventricular tachycardia (15%). Entropy estimation of only 9 ventricular intervals before ICD shocks accurately distinguished AF (receiver operating characteristic curve area, 0.98; 95% confidence intervals, 0.93-1.0) and outperformed contemporary ICD rhythm discrimination algorithms. This new strategy for AF discrimination based on entropy estimation expands on simpler concepts of variability, performs well at fast heart rates, and has potential for broad clinical application.

Who benefits from implantable cardioverter defibrillator therapy, and who pays the price?

Who benefits from implantable cardioverter defibrillator therapy, and who pays the price?

Counting Down Before Blasting Off

Since the first generation of implantable cardioverter-defibrillators (ICDs), technologic advances have markedly enhanced their efficacy and safety and improved the accuracy of arrhythmia detection algorithms. Despite these developments, inappropriate therapies for sinus or supraventricular tachyarrhythmias or lead noise remain a major limitation of contemporary ICDs, with a substantial proportion of patients receiving inappropriate shocks. Psychosocial issues appear to reflect the level of distress related to ICD shocks, with fear of shocks associated with increased anxiety, avoidance behaviors, and perceived functional limitations. 1 Sears Jr., S.E. Conti J.B. Understanding implantable cardioverter defibrillator shocks and storms: medical and psychosocial considerations for research and clinical care. Clin Cardiol. 2003; 26: 107-111 Crossref PubMed Scopus (131) Google Scholar , 2 Irvine J. Dorian P. Baker B. et al. Quality of life in the Canadian Implantable Defibrillator Study (CIDS). Am Heart J. 2002; 144: 282-289 PubMed Google Scholar , 3 Kuhl E.A. Dixit N.K. Walker R.L. Conti J.B. Sears S.F. Measurement of patient fears about implantable cardioverter defibrillator shock: an initial evaluation of the Florida Shock Anxiety Scale. Pacing Clin Electrophysiol. 2006; 29: 614-618 Crossref PubMed Scopus (83) Google Scholar Although all ICD recipients are potentially at risk, reported rates of inappropriate shocks are particularly high in the young, growing, and complex population with congenital heart disease. 4 Khairy P. Harris L. Landzberg M.J. et al. Implantable cardioverter-defibrillators in tetralogy of Fallot. Circulation. 2008; 117: 363-370 Crossref PubMed Scopus (352) Google Scholar , 5 Berul C.I. Van Hare G.F. Kertesz N.J. et al. Results of a multicenter retrospective implantable cardioverter-defibrillator registry of pediatric and congenital heart disease patients. J Am Coll Cardiol. 2008; 51: 1685-1691 Abstract Full Text Full Text PDF PubMed Scopus (290) Google Scholar , 6 Khairy P. Harris L. Landzberg M.J. et al. Sudden death and defibrillators in transposition of the great arteries with intra-atrial baffles: a multicenter study. Circ Arrhythm Electrophysiol. 2008; 1: 250-257 Crossref PubMed Scopus (182) Google Scholar , 7 Khairy P. Defibrillators and cardiac resynchronisation therapy in congenital heart disease. Exp Rev Med Devices. 2008; 5: 267-271 Crossref PubMed Scopus (11) Google Scholar On the basis of the global literature and ICD interrogation in multicenter cohorts with congenital heart disease, it appeared reasonable to speculate that many inappropriate or unnecessary shocks may potentially be averted by tailored programming. This prompted our succinct “Hands On” article offering 10 programming tips in congenital heart disease. 8 Khairy P. Mansour F. Implantable cardioverter-defibrillators in congenital heart disease: 10 programming tips. Heart Rhythm. 2011; 8: 480-483 Abstract Full Text Full Text PDF PubMed Scopus (21) Google Scholar A more detailed general review of ICD programming beyond nominal settings was subsequently proposed. 9 Mansour F. Khairy P. Programming ICDs in the modern era beyond out-of-the box settings. Pacing Clin Electrophysiol. 2011; 34: 506-520 Crossref PubMed Scopus (26) Google Scholar To the Editor—Programming tips and practical programmingHeart RhythmVol. 8Issue 6PreviewI would like to offer two comments on Khairy and Mansour's well-written article on programming of implantable cardioverter-defibrillators (ICDs) in the March 2011 issue of Heart Rhythm.1 Full-Text PDF