Unnecessary Shocks Research Articles

Abstract 14731: T-wave Oversensing Secondary to an Inappropriate ICD Shock Resulting in Subsequent Unnecessary Shocks

Introduction: Inappropriate ICD shocks commonly result from persistent atrial arrhythmias or oversensing. We report a scenario where an ICD shock for a rapid, sustained atrial tachycardia (AT) resulted in T-wave oversensing (TWO), triggering further inappropriate shocks. Presentation: A 69-year-old woman with secondary prevention dual chamber ICD underwent pulmonary vein isolation for symptomatic paroxysmal atrial fibrillation (AF). The patient remained free of AT/AF off antiarrhythmics for 3 months after the procedure when she was admitted with four consecutive ICD shocks. Electrolytes were within normal limits. Device interrogation showed that the first shock was triggered by a rapid, sustained AT (cycle length: 270 msec) detected in the VF zone (single zone device; 280 msec cut-off) and failed ATP. Following the first shock, an irregular AT ensued, with cycle length ranging from 280-370 msec, but now with high amplitude T-waves in the RV channel, resulting in TWO and three subsequent inappropriate shocks (Figure). She received IV metoprolol and digoxin with subsequent resolution of AT and TWO. Beta-blocker dosing was increased and she has remained free of AT/AF at 6 month follow-up. Conclusions: ICD shocks can trigger marked repolarization changes in near-field intracardiac RV electrograms resulting in TWO and subsequent appropriate shocks. Further studies are warranted to understand the mechanism underlying this phenomenon and potential risk for these events.

Assessing the Cost and Resource Use Impact of Implantable Cardiac Defibrillator Shocks in the UK CareLink Population.

High voltage devices (implantable cardiac defibrillators (ICDs) and cardiac resynchronization therapy defibrillators referred to jointly as ICDs) reduce rates of sudden cardiac death in patients with cardiovascular disease. However, shocks from ICDs may be associated with healthcare resource use (HCRU) and costs. The aim of this study was to estimate the costs associated with both appropriate and inappropriate shocks from ICDs. Patients with appropriate and inappropriate shocks from ICDs were identified via CareLink data from Liverpool Heart and Chest Hospital between March 2017 and March 2019. The devices were SmartShock activated, with anti-tachycardia pacing. Costs were estimated according to the dominant episode of healthcare, from an NHS payer perspective. There were 2445 patients on the CareLink system with ICDs. Over the two-year period, HCRU data from 143 shock episodes among 112 patients were reported. The total cost for all shocks was £252,552 with mean costs of £1608 and £2795 for appropriate and inappropriate shocks respectively. There was substantial variation in HCRU between shock episodes. While there was a low rate of inappropriate shocks from ICDs, there were still substantial HCRU and costs incurred. In this study, the specific HCRU was not costed independently, meaning the costs reported are likely to be a conservative estimate. Whilst every attempt to reduce shocks should be made, appropriate shocks cannot be avoided. Strategies to reduce the incidence of inappropriate and unnecessary shocks should be implemented to reduce overall health care costs associated with ICDs.

Deactivation of implantable defibrillators at the end of life - A register-based study of ICD-deactivation at home and the impact of palliative care

BackgroundThe Implantable Cardioverter-Defibrillator (ICD) is a well-established life-saving therapy for heart failure patients, but due to the risk for unnecessary shocks, deactivation of ICD:s is recommended at the end of life.We aimed to identify i) how many people with HF and an ICD who died in Sweden in 2018 received Specialized Palliative Care (SPC), ii) of those dying outside of hospital, the proportion with deactivated ICDs prior to death for the group as a whole and by SPC access. Methods and resultsWe analyzed data from i) the Swedish ICD and Pacemaker Registry to find all who died with an ICD in Sweden in 2018, ii) the Swedish Register of Palliative Care and, iii) the Swedish Causes of Death Certificate Register to find those who died outside of hospital. Clinical records were obtained to assess if ICDs were deactivated before death. Descriptive statistics, t-tests and chi-squared tests were applied.46/406 (11%) of those who died with an ICD in Sweden in 2018 had SPC access, of whom 50% also had cancer. 86/164 (52%) ICDs were deactivated prior to death in people dying outside of hospital; higher in those accessing SPC (36/46, (78%) SPC access versus 151/360, (42%) no SPC access; p < 0.05). ConclusionsHalf of those with HF and an ICD dying outside of hospital had ICD deactivation prior to death. Those accessing SPC were more likely to have their ICD deactivated but few received SPC, without a comorbid cancer diagnosis.

Simulation and Compensation of Axial Geometric Errors for Cycloidal Gears Based on Form Grinding

To increase quality, reduce cycloidal gear noise, and avoid unnecessary vibration and shock, a compensation of axial geometric errors method is proposed based on the cycloidal gear form grinding. In the process of machining cycloidal gears, the relative position relationship between the grinding wheel and workpiece is affected by geometric errors of the motion axes, which has serious effects on the surface accuracy of the cycloidal gears. Combined with cycloidal gear form grinding kinematic principles, a geometric error model for each axis of a four-axis computer numerical control form grinding machine is established. By changing the compensation value of the geometrical errors on six degrees of freedom, the error of the cycloid gear tooth surface machined is obtained. Based on a sensitivity analysis of geometrical errors of each axis, the corrections are determined through an optimization process that targets the minimization of the tooth flank errors. The geometric errors of each axis of the cycloid gear grinding machine are compensated, and then, the cycloid gears produced by the machine are processed. Through the processing experiment, the error data of the actual processing before and after the compensation are compared, which indicates that the machining accuracy of the cycloid gear grinding machine is obviously improved. It has an important guiding significance in improving the precision and performance of large CNC form gear grinding machines.

The resuscitation status of implantable cardioverter-defibrillator patients according to electronic health records: are we ignoring the device?

Abstract Introduction/Background The Care Quality Commission (CQC) has recently raised concerns around resuscitation decisions in the UK. In our hospital an early resuscitation decision is made on admission, often by junior doctors, and documented in electronic notes. Concerns have been raised about the veracity of these discussions in patients with implantable cardioverter-defibrillators (ICD's). We investigated resuscitation status as documented on the electronic record for our ICD population. Methods The ICD database was interrogated in 2020 for patients under current follow-up. Baseline demographics, hospital admissions over the past 5 years and ICD indications were documented from the electronic hospital records. All patients with an electronic do-not-resuscitate (DNR) flag on the electronic system were recorded, as were any documented resuscitation discussions and ICD deactivations between 2015 and 2020. Any patient deaths were recorded and correlated with resuscitation status and ICD status at the time of death. Results Six-hundred and thirty-six patients with ICD's (transvenous, subcutaneous and CRT defibrillators) were identified under follow-up for the study period. The mean age of the population was 68 years old. 251 had an ischaemic cardiomyopathy, 209 had dilated cardiomyopathy, 50 prior ventricular fibrillation or tachycardia, 40 hypertrophic cardiomyopathy, 26 ARVC and the rest a channelopathy, congenital heart disease, sarcoidosis or valvular heart disease. Thirty-seven of the 636 patients were flagged on the electronic record as being not for resuscitation (5.9%). They had a mean age of 79 and 54% had an ischaemic cardiomyopathy. Of these, only 15 (39%) had their ICD deactivated and only 12 of those at the time of the resuscitation decision (32%). 15 of the 37 (39%) patients made DNR have subsequently died. Six of these (40%) had an active ICD at the time of death. In the 257 patients who had had a hospital admission in the study period, 34 were made not for resuscitation during the admission (13%) of whom 11 had their ICD deactivated at the time of discussion (32%). Patients with a DNR flag and an “active” ICD were contacted about deactivation of their ICD and offered discussion with a cardiologist or specialist nurse about ICD deactivation. Of these 9/27 (33%) stated that they wanted resuscitation and the alert was removed and the ICD kept on, although 3 subsequently had the device deactivated. Conclusions In this study the majority of patients with ICD's who were made not for resuscitation on admission to hospital did not have their ICD therapies switched off, therefore putting them at risk of unnecessary ICD shocks. In addition, one third these patients subsequently chose to be for resuscitation after discussion. These complex decisions would be improved with the early involvement of cardiologists and specialist nurses. Funding Acknowledgement Type of funding sources: None.

Psychological assessment of depression and anxiety in patients with implantable cardioverter-defibrillator: DEFibrillator-related distress and depression survey in Chiba 2

Abstract Background Despite the established treatment for life-threatening arrhythmias, the implantable cardioverter-defibrillator (ICD) therapy has emerged as a major determinant of psychological distress. Previous studies have showed several approaches to assess the ICD-specific psychological distress, however, the risk factors affecting psychological functioning are relatively variable across studies, and are not well studied in Japanese population. Therefore, we prospectively investigate the risk factors affecting the psychological functioning and assess the impact of ICD therapy in Japanese patients with ICD. Methods We prospectively enrolled consecutive 136 patients in the present study. At the time of ICD implantation and 1 year later, all patients completed the Florida Shock Anxiety Scale (FSAS), which is a tool designed to provide a quantitative measure of ICD shock-related anxiety. In addition, patients were also examined by psychiatrists using two assessment scales, Montgomery-Åsberg Depression Rating Scale (MADRS) and Hospital Anxiety and Depression Scale (HADS). Results The FSAS score was significantly correlated with the MADRS and HADS scores (Figure). During 1-year follow-up, 11 patients (8.1%) received ICD therapy. Younger age was significantly associated with the FSAS and MADRS scores at registration, but ICD therapy was the only independent factor associated with the increased risk of the FSAS score at 1 year later (p-value = 0.012). Conclusions ICD therapy has a strong impact on psychological distress in time course of ICD implantation. To reduce unnecessary shock therapy and optimal intervention by healthcare professionals may lead to the improvement of ICD-related psychological functioning. Funding Acknowledgement Type of funding sources: None. Figure 1. Correlation between MADRS and HADS scoreFigure 2. FSAS, MADRS and HADS scores

Implantable Cardiac Defibrillator Deactivation During End-of-Life Care in the COVID-19 Pandemic.

People with implantable cardiac defibrillators (ICDs) who are nearing the end of life are at risk for arrhythmias, which activate the ICD and may cause unnecessary shocks and suffering. Because ICDs have enabled more patients to live longer, they often succumb to noncardiac diseases and may be cared for by primary care physicians. Despite published recommendations 10 years ago regarding the management of ICDs during the end of life, over half of patients with ICDs who are dying still have not been offered the choice of deactivation. The Coronavirus disease 2019 (COVID-19) pandemic has complicated this issue and the need to discuss it because of practices that separate patients from loved ones and that modify the usual interactions of patients with doctors and nurses. We offer the following recommendations: (1) the management of ICDs at the end-of-life needs to be understood by all physicians who care for patients with ICDs; (2) discussions about deactivating the ICD should occur while patients have decision-making capacity and are clinically stable, beginning at the time of ICD implantation, then periodically at follow-up appointments, and certainly when a change in the patient's clinical status warrants a reconsideration of the goals of care; and (3) clinicians should compensate for the impediments to communication with patients and families associated with the COVID-19 pandemic, which includes patient isolation and restrictive visitor policies, by using devices that permit visual communication to reexamine goals of care, including defibrillator deactivation, in patients with ICDs who are expected to die.

Insights on arrhythmia termination and type 2 breaks after ICD therapy delivery.

Introduction of anti-tachycardia pacing (ATP) therapy and longer detection intervals delivery have allowed to safely reduce unnecessary shocks, improving survival and quality of life in implantable cardioverter defibrillator (ICD) patients. However, there are still outstanding issues, especially regarding the mode of arrhythmias termination after ATP or shock delivery. Regardless of ICD therapy efficacy, the arrhythmia interruption does not always occur abruptly, indeed both nonsustained tachy- or bradyarrhythmias have been described after ICD therapy delivery, being the former classified as type 2 interruption. Several physiopathological mechanisms have been suggested to be responsible for this phenomenon. Our aim is to review current data on postshock and post-ATP arrhythmias and to give insights on their possible mechanisms.

ICD-VAD Compatibility, Could You End up with a Deaf ICD after VAD Implantation?

Most heart failure patients undergoing ventricular assist device (VAD) implantation are managed with guideline-based therapy including the implantation of defibrillation capable device (ICD). Prior to surgery, programming allowing therapy with lower threshold could be lifesaving. After surgery, the defibrillator should be reprogrammed to protect the patient against painful, unnecessary shocks, as the circulation will be supported even in ventricular fibrillation. Difficulties in interrogation of ICD in patients with both HeartMate-II and HeartMate3 devices have been previously reported, related to the VAD-produced electromagnetic interference. Most cases result in a problem of communication between the ICD and the corresponding interrogating console. An electronic search was performed to identify all articles and abstracts published on the topic until July 2019. To the list, we added one case from our clinical experience as well as manufacturer described cases of incompatibility. We identified 473 publications. Fourteen publications were ultimately included. Those publications described 22 patients with device interrogation issues post VAD implantation. To regain control of the device complete replacement of the ICD/CRT/PM was performed in 10 patients, and in one the implantation side was changed. In 11 cases a shielding technique was successfully utilized. From the data, we can extract the names of 14 devices with a documented communication problem. There were no reported cases of adverse interaction between HeartWare and ICDs. Given the reported VAD-associated EMI interaction with ICD interrogation due to interruption of the handshake-signal to initiate ICD interrogation, it is likely all the variants of one specific ICD (1 lead, 2 lead, CRT) will also suffer from the same problem. More ex-vivo research is needed to better understand the phenomenon, and clinicians and patients with the listed ICDs need to be aware of the potential loss of ICD control with HM2 or HM3.

Real Time Non-Invasive Hemodynamic Assessment of Ventricular Tachycardia

Hemodynamically unstable ventricular tachycardia (VT) is a critical cardiac arrhythmia associated with hemodynamic compromise that requires immediate cardioversion to prevent sudden cardiac death. Since unnecessary cardioverter defibrillators shocks damage the heart and increase the risk of mortality, the discrimination between unstable (i.e. requiring cardioversion) and stable (i.e. not requiring cardioversion) VT is of paramount importance. The aim of this study was to propose and assess non-invasive identification of hemodynamically unstable VT using photoplethysmography (PPG). Seventy-five (n = 75) episodes of VT were recorded in 14 patients undergoing invasive electrophysiological studies for VT catheter ablation. Invasive continuous arterial blood pressure (ABP), PPG and electrocardiogram (ECG) were simultaneously recorded. VTs were classified as unstable if during the first 10 seconds from onset, the mean ABP ( $\overline {P_{VT}}\mathrm { ) was $\overline {P_{VT}}\mathrm { mmHg or if $\text{P}_{\mathrm {VT}}$ dropped more than 30% with respect to a 10 seconds baseline (i.e. ratio $\text{R}_{\mathrm {ABP}} ). Five PPG morphological features were derived and compared to the heart rate from the ECG. PPG markers detected hemodynamically unstable VT with accuracy as high as 86% and were more accurate than the heart rate. The mean absolute slope was the best PPG parameter for classification of $\overline {P_{VT}}\mathrm { mmHg (AUC = 0.85, Sensitivity = 72%, Specificity = 86%) and $\text{R}_{\mathrm {ABP}} (AUC = 0.90, Sensitivity = 83%, Specificity = 89%) and it was automatically selected in the best two-variables logistic regression, for which AUC = 0.94. In conclusion, PPG analysis can accurately identify haemodynamically unstable VTs and has potential to enable optimization of VT therapy and reduce unnecessary and harmful cardioversion shocks.

Deactivation of implantable defibrillators at end of life — Can we do better?

IntroductionDying patients with implantable defibrillators (ICD) have a risk of receiving unnecessary shocks before death. The aim of this study was to investigate if deactivation of shock therapy at end-of-life has increased since publication of new guidelines in 2010 on ICD management. Method and resultsThis is a study of two groups of ICD patients who died in hospitals before and after publication of new guidelines. Group 1 consists of 89 patients who died between 2003 and 2010. Group 2 consists of 252 patients, the total number of ICD patients in Sweden who died in hospital during 2014. Data was obtained from the Swedish ICD and Pacemaker Registry, Swedish Tax Agency and patient medical notes. Two-thirds died in wards other than Cardiology. Fifty-four percent in group 1 had a Do-Not-Resuscitate-order (DNR) compared to 73% in group 2. Shock deactivation was present in 52% in group 1 and 67% in group 2. The difference in shock deactivation between group 1 and 2 was only significant (p = 0.014) for DNR-patients treated in Cardiology. A significant difference (p = 0.036) was found in deactivation within group 2 between DNR-patients in Cardiology vs. DNR-patients in Non-Cardiology wards. ConclusionTwo-thirds of ICD patients die in wards other than Cardiology. Since publication of guidelines on ICD management there is a general increase in shock deactivation for DNR-patients, but only significant for patients in Cardiology. This implicate that actions have to be taken for patients treated in Non-Cardiology wards to bridge the gap between guidelines recommendations and clinical practice.

Novel CPR system that predicts return of spontaneous circulation from amplitude spectral area before electric shock in ventricular fibrillation

AimAmplitude spectral area (AMSA), an index for analysing ventricular fibrillation (VF) waveforms, is thought to predict the return of spontaneous circulation (ROSC) after electric shocks, but its validity is unconfirmed. We developed an equation to predict ROSC, where the change in AMSA (ΔAMSA) is added to AMSA measured immediately before the first shock (AMSA1). We examine the validity of this equation by comparing it with the conventional AMSA1-only equation. MethodWe retrospectively investigated 285 VF patients given prehospital electric shocks by emergency medical services. ΔAMSA was calculated by subtracting AMSA1 from last AMSA immediately before the last prehospital electric shock. Multivariate logistic regression analysis was performed using post-shock ROSC as a dependent variable. ResultsAnalysis data were subjected to receiver operating characteristic curve analysis, goodness-of-fit testing using a likelihood ratio test, and the bootstrap method. AMSA1 (odds ratio (OR) 1.151, 95% confidence interval (CI) 1.086–1.220) and ΔAMSA (OR 1.289, 95% CI 1.156–1.438) were independent factors influencing ROSC induction by electric shock. Area under the curve (AUC) for predicting ROSC was 0.851 for AMSA1-only and 0.891 for AMSA1+ΔAMSA. Compared with the AMSA1-only equation, the AMSA1+ΔAMSA equation had significantly better goodness-of-fit (likelihood ratio test P<0.001) and showed good fit in the bootstrap method. ConclusionsPost-shock ROSC was accurately predicted by adding ΔAMSA to AMSA1. AMSA-based ROSC prediction enables application of electric shock to only those patients with high probability of ROSC, instead of interrupting chest compressions and delivering unnecessary shocks to patients with low probability of ROSC.

Optimal Implantable Cardioverter Defibrillator Programming.

Optimal programming of implantable cardioverter defibrillators (ICDs) is essential to appropriately treat ventricular tachyarrhythmias and to avoid unnecessary and inappropriate shocks. There have been a series of large clinical trials evaluating tailored programming of ICDs. We reviewed the clinical trials evaluating ICD therapies and detection, and the consensus statement on ICD programming. In doing so, we found that prolonged ICD detection times, higher rate cutoffs, and antitachycardia pacing (ATP) programming decreases inappropriate and painful therapies in a primary prevention population. The use of supraventricular tachyarrhythmia discriminators can also decrease inappropriate shocks. Tailored ICD programming using the knowledge gained from recent ICD trials can decrease inappropriate and unnecessary ICD therapies and decrease mortality.

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.

Different impact of long-detection interval and anti-tachycardia pacing in reducing unnecessary shocks: data from the ADVANCE III trial.

AimsA long-detection interval (LDI) (30/40 intervals) has been proved to be superior to a standard-detection interval (SDI) (18/24 intervals) in terms of reducing unnecessary implantable cardioverter defibrillator (ICD) therapies. To better evaluate the different impact of LDI and anti-tachycardia pacing (ATP) on reducing painful shocks, we assessed all treated episodes in the ADVANCE III trial.Methods and resultsA total of 452 fast (200 ms < cycle length ≤ 320 ms) arrhythmic episodes were recorded: 284 in 138 patients in the SDI arm and 168 in 82 patients in the LDI arm (106/452 inappropriate detections). A total of 346 fast ventricular tachycardias (FVT) were detected in 169 patients: 208 in 105 patients with SDI and 138 in 64 patients with LDI. Setting LDI determined a significant reduction in appropriate but unnecessary therapies [208 in SDI vs. 138 in LDI; incidence rate ratio (IRR): 0.61 (95% CI 0.45–0.83), P = 0.002]. Anti-tachycardia pacing determined another 52% reduction in unnecessary shocks [208 in SDI with hypothetical shock-only programming vs. 66 in LDI with ATP; IRR: 0.37 (95% CI 0.25–0.53, P < 0.001)]. The efficacy of ATP in terminating FVT was 63% in SDI and 52% in LDI (P = 0.022). No difference in the safety profile (acceleration/degeneration and death/cardiovascular hospitalizations) was observed between the two groups.ConclusionThe combination of LDI and ATP during charging is extremely effective and significantly reduces appropriate but unnecessary therapies. The use of LDI alone yielded a 39% reduction in appropriate but unnecessary therapies; ATP on top of LDI determined another 52% reduction in unnecessary shocks. The strategy of associating ATP and LDI could be considered in the majority of ICD recipients.

The utility of shock coil and left ventricular tip–right ventricular coil impedance as a predictor of pneumothorax in cardiac resynchronization therapy implantation

A high defibrillation threshold (DFT) infrequently occurs during device implantation. The major cause of high DFT is pneumothorax. However, there are few data about shock coil and left ventricular tip–right ventricular coil (LV tip–RV coil) impedance as a marker of a high DFT caused by pneumothorax. A 65-year-old man, diagnosed with dilated cardiomyopathy, was referred for cardiac resynchronization therapy (CRT) defibrillator implantation with single shock coil lead. The shock coil impedance was high and LV tip–RV coil impedance was normal just before DFT test. Then, high DFT was detected. Afterwards, pneumothorax was found. After the treatment of the pneumothorax, the shock coil impedance decreased. However, the LV tip–RV coil impedance did not change. This discrepancy can be a useful predictor of the high DFT caused by pneumothorax. With these markers, we can predict high DFT and consequently can treat pneumothorax earlier without the unnecessary shock delivery.<Learning objective: Cardiac resynchronization therapy (CRT) implantation is widely performed. Pneumothorax is one of the complications of CRT implantation. High defibrillation threshold (DFT) is known as a predictor of the pneumothorax. However, the predictor of this complication has not fully been evaluated. The high shock coil impedance combined with normal left ventricular tip–right ventricular coil impedance can be a useful predictor of the high DFT caused by pneumothorax.>

Low inappropriate shock rates in patients with single- and dual/triple-chamber implantable cardioverter-defibrillators using a novel suite of detection algorithms: PainFree SST trial primary results.

The benefits of implantable cardioverter-defibrillators (ICDs) have been well demonstrated in many clinical trials, and ICD shocks for ventricular tachyarrhythmias save lives. However, inappropriate and unnecessary shock delivery remains a significant clinical issue with considerable consequences for patients and the healthcare system. The purpose of the PainFree SmartShock Technology (SST) study was to investigate new-generation ICDs to reduce inappropriate and unnecessary shocks through novel discrimination algorithms with modern programming strategies. This prospective, multicenter clinical trial enrolled 2790 patients with approved indication for ICD implantation (79% male, mean age 65 years; 69% primary prevention indication, 27% single-chamber ICD, 33% replacement or upgrade). Patients were followed for a minimum of 12 months, and mean follow-up was 22 months. The primary end-point of the study was the percentage of patients remaining free of inappropriate shocks at 1 year postimplant, analyzed separately for dual/triple-chamber ICDs (N = 2019) and single-chamber ICDs (N = 751). The inappropriate shock rate at 1 year was 1.5% for patients with dual/triple-chamber ICDs and 2.5% for patients with single-chamber devices. Two years postimplant, the inappropriate shock rate was 2.8% for patients with dual-/triple chamber ICDs and 3.7% for those with single-chamber ICDs. The most common cause of an inappropriate shock in both groups was atrial fibrillation or flutter. In a large patient cohort receiving ICDs for primary or secondary prevention, the adoption of novel enhanced detection algorithms in conjunction with routine implementation of modern programming strategies led to a very low inappropriate shock rate.

Troubleshooting implanted cardioverter defibrillator sensing problems I.

Multicenter studies1–3 demonstrate that unnecessary implanted cardioverter defibrillator (ICD) shocks can be reduced by evidence-based programming of detection rate and duration, antitachycardia pacing, and algorithms that discriminate supraventricular tachycardia (SVT) from ventricular tachycardia (VT). Reducing unnecessary shocks from oversensing has attracted less attention. Excluding patients with recalled leads, ventricular oversensing accounts for 100 000 patients; and, without an alert for oversensing, 50% of lead fractures present with ≥5 shocks.7,8 Thus, oversensing commonly produces severe symptoms, which may cause post-traumatic stress disorder.9 Furthermore, recognition of transient, asymptomatic oversensing may prevent major complications.7,8,10 Other sensing problems also provide challenges for ICDs. These include undersensing of VF, atrial undersensing, and oversensing in relation to SVT–VT discrimination, and unique issues related to sensing subcutaneous electrograms. In ICDs, sensing is usually defined as it is in pacemakers, the process for determining the timing of individual cardiac depolarizations. Correspondingly, detection is the process by which an ICD algorithm classifies a sequence of sensed signals to determine the cardiac rhythm. Thus, sensing typically precedes detection. However, algorithms that identify oversensing may be applied after detection, and subcutaneous ICDs may integrate traditionally distinct features of sensing and detection. This review focuses on ICD sensing problems. ### Electrogram Sources Analysis of sensing begins with ICD electrograms and corresponding annotated event markers (commonly referred to by the trademarked term Marker Channel, Medtronic Inc). ICDs store 2 to 4 channels of electrograms and telemeter them to the programmer. The 2 primary ICD electrograms are the shock or high-voltage electrogram displayed on …

Electrical storm: definition, prevalence, causes and prognostic implications

Electrical storm (ES) represents a state of cardiac electrical instability which manifests by multiple episodes of ventricular tachyarrhythmia (VT) within a short time. In patients with an implantable cardioverter-defibrillator (ICD), ES is best defined as ≥ 3 appropriate VT detections in 24 h, treated by antitachycardia pacing or shock. The number of shocks and inappropriate detections are irrelevant for the definition. Within a period of 3 years ES occurred in approximately 25 % of ICD patients with secondary prophylaxis indications of sudden cardiac death. Although the definition includes minor arrhythmic events, ES frequently consists of up to 50 VTs. Potential triggers found in 20-65 % of patients include new/deteriorated heart failure, diarrhea/hypokalemia, changes in antiarrhythmic medication, association with other illnesses, and psychological stress. In most patients ES consists of monomorphic VT indicating the presence of reentry while ventricular fibrillation indicating acute ischemia is rare. ES seems to have a low immediate mortality (1 %) but frequently (50-80 %) leads to hospitalization. Long-term prognostic implications of ES are unclear. The key intervention in ES is a reduction of the elevated sympathetic tone by beta blockers and also frequently sedation. Amiodarone i.v. is highly efficient in ES while class I antiarrhythmic drugs are usually unsuccessful. Substrate mapping and VT ablation may be useful in treatment and prevention of ES. Prevention of ES requires ICD programming systematically avoiding unnecessary shocks by long VT detection and numerous attempts of antitachycardia pacing before shock therapy which can fuel the sympathetic tone and prolong ES.

Does change in device detected frequency of non-sustained or diverted episodes serve as a marker for inappropriate shock therapy? Analyses from the INTRINSIC RV and ALTITUDE-REDUCES Trials

Implantable cardioverter-defibrillators (ICDs) treat ventricular tachycardia or fibrillation but may also deliver unnecessary shocks. We sought to determine if the frequency of ICD-detected non-sustained or diverted (NSD) episodes increases before appropriate or inappropriate ICD shocks. We evaluated NSD episodes in the INTRINSIC RV Trial and their relationship to ICD shocks (appropriate and inappropriate). Time from NSD to shock was analysed. Results were validated by utilizing 1495 adjudicated ICD and cardiac resynchronization therapy-defibrillator shocks following NSD episodes collected through the LATITUDE remote monitoring system as part of the ALTITUDE-REDUCES Study. In INTRINSIC RV, 185 participants received 373 shocks; 148 had at least 1 NSD episode. Non-sustained or diverted frequency increased 24 h before the first shock for those receiving an inappropriate (P < 0.01) but not an appropriate shock (P = 0.17). Patients with NSD episodes within 24 h of a shock were significantly more likely to receive inappropriate therapy [odds ratio (OR) = 3.12, P < 0.01]. At the receiver operator curve determined optimal cutoff, an NSD episode within 14 min before shock strongly predicted inappropriate therapy (sensitivity 48%, specificity 91%; OR = 8.8, and P < 0.001). The 14 min cut-off evaluated on an independent dataset of 1495 shock episodes preceded by an NSD in the ALTITUDE-REDUCES Study confirmed these results (sensitivity = 47%, specificity = 85%, OR = 5.0, and P < 0.001). Device-detected NSD episodes increase before inappropriate but not appropriate shocks. Novel alerts or automated algorithms based on NSD episodes may reduce inappropriate shocks.