Remote, Wireless, Ambulatory Monitoring of Implantable Pacemakers, Cardioverter Defibrillators, and Cardiac Resynchronization Therapy Systems: Analysis of a Worldwide Database

Study Objective: To describe the daily routine application of a new telemonitoring system in a large population of cardiac device recipients.
Methods: Data transmitted daily and automatically by a remote, wireless Home Monitoring™ system (HM) were analyzed. The average time gained in the detection of events using HM versus standard practice and the impact of HM on physician workload were examined. The mean interval between device interrogations was used to compare the rates of follow-up visits versus that recommended in guidelines.
Results: 3,004,763 transmissions were made by 11,624 recipients of pacemakers (n = 4,631), defibrillators (ICD; n = 6,548), and combined ICD + cardiac resynchronization therapy (CRT-D) systems (n = 445) worldwide. The duration of monitoring/patient ranged from 1 to 49 months, representing 10,057 years. The vast majority (86%) of events were disease-related. The mean interval between last follow-up and occurrence of events notified by HM was 26 days, representing a putative temporal gain of 154 and 64 days in patients usually followed at 6- and 3-month intervals, respectively. The mean numbers of events per patient per month reported to the caregivers for the overall population was 0.6. On average, 47.6% of the patients were event-free. The mean interval between follow-up visits in patients with pacemakers, single-chamber ICDs, dual chamber ICDs, and CRT-D systems were 5.9 ± 2.1, 3.6 ± 3.3, 3.3 ± 3.5, and 1.9 ± 2.9 months, respectively.
Conclusions: This broad clinical application of a new monitoring system strongly supports its capability to improve the care of cardiac device recipients, enhance their safety, and optimize the allocation of health resources.     

远程心电监测仪在心律失常射频消融术及心脏起搏器/ICD植入术后早期随访中的应用

目的:探讨远程心电监测仪在心律失常射频消融术及心脏起搏器/ICD植入术后早期随访中的应用价值.方法:回顾性分析2010年10月~2011年9月我科收治的70例心律失常行射频消融术或永久人工心脏起搏器/ICD植入术的患者及心力衰竭行CRT/CRTD植入术的患者术后进行一月的远程心电监测资料.结果:远程电话传输9000次,图形清晰,均接收成功.射频消融术41例中室上性心动过速18例未见复发;阵发性房颤4例未见复发,持续性房颤2例有1例阵发性房颤发作;频发室早14例中有3例复发,室性心动过速3例未见复发.29例永久起搏器/ICD/CRT/CRTD植入术患者,未见起搏器起搏功能异常,起搏器感知不良1例,未见ICD误治疗,未见起搏器介导的心律失常发生.结论:远程心电监测仪能及时发现心律失常及起搏器异常工作情况,可作为射频消融术及心脏起搏器/ICD/CRT/CRTD植入术后早期随访的常规检查.     

Transtelephonic Monitoring and Transmission of Stored Arrhythmia Detection and Therapy Data From an Implantable Cardioverter Defibrillator

A new transtelephonic monitoring device designed for use with implantable Cardioverter defibrillators (ICDs) was evaluated. It is capable of interrogating ICDs and transmitting the following data via telephone: programmed parameters (e.g., ventricular tachycardia [VT] and ventricular fibrillation [VF] detection, therapies), number of VT and VF episodes, identification of successful therapies, the 20 cycle lengths preceding the last episode detected, the 10 cycle lengths after the last delivered therapy, battery voltage, and real-time transmission of the patient's rhythm. Eighteen patients (mean age 64 ± 17years; 15 males) were implanted with an ICD and epicardial lead system. The patients who did not live near the primary hospital were provided with this transmitter and instructed to transmit monthly and whenever presyncope, syncope, or a shock were experienced. Five hundred ten episodes of spontaneous arrhythmia (495 VT, 15 VF) were detected in 14 of 18 patients in a 24-month period and the success of each therapy (antitachycardia pacing, cardioversion 0.4-34 J, defibrillation 34 J) was analyzed. The number of therapies delivered and their success (%) in terminating the arrhythmia were: 380 ramp/86%, 116 burst/84%, 119 cardioversion/57%, and 15 defibrillations/ 100%. Sixty-three (42%) of the 152 transmissions indicated an arrhythmia. Twenty-five (16%) of the 152 were transmitted because of symptoms. Sixteen (9.7%) of 165 VT episodes could not be terminated by the full set of programmed VT therapies. Analysis of the pre- and post-episode intervals along with the patient's transmitted rhythm indicated that sinus tachycardia or atrial fibrillation were likely responsible for these episodes. The transmitted data included the real-time ECG, which provided acute rhythm status plus stored data from the ICDs memory identifying the chronic arrhythmias detected, the therapies delivered, and the number and type of successful and ineffective therapies. This information provided the clinical data to the primary physician in order to determine the effectiveness of the programmed detection and therapy parameters and in some cases recommend to the home physician modifications to the device parameters or medication adjustments for enhanced arrhythmia control. We conclude that telephone transmission of stored ICD data is feasible and useful for patient management. It may obviate the need for patients experiencing symptoms to return to a site capable of device interrogation.     

Remotely monitored death of a patient with implanted ICD

Remote monitoring is useful for management of implantable cardioverter defibrillator (ICD) patients regarding detection of arrhythmias and probable device or lead failure. We report the case of a patient who died suddenly while being on remote monitoring. The ICD was not retrieved postmortem. Even though clinical circumstances were suspicious of an arrhythmic death, this was excluded due to a distinctive manufacturer feature of the system.     

Prevention of Inappropriate Shocks in ICD Recipients: A Review of 10,000 Tachycardia Episodes

Background: The efficacy of dual-chamber ICD arrhythmia classification algorithms is crucial to prevent inappropriate shocks. We report our experience from a meta-analysis of five prospective clinical studies with inclusion phases ranging between 1997 and 2003.
Methods: Dual-chamber ICD using standard dual-chamber arrhythmia classification algorithms were implanted in 802 patients (mean age = 64 ± 11 years, 88% men) in 74 medical centers. The ICD indication was secondary prevention in 95% of patients. Supraventricular tachyarrhythmias (SVT) were previously documented in 26% of patients. All spontaneous tachyarrhythmic events documented by the device memories were analyzed by a adjudicating committee. The episodes lasting >12 seconds and/or treated by the ICD were analyzed.
Results: Over a mean follow-up of 302 ± 113 days, 9,690 events were reported. Mean heart rate at the time of events was 131 ± 45 bpm (100–430). Events were classified as oversensing in 1.4%, sinus tachycardia (ST) in 66%, SVT in 13%, slow (<150 bpm) ventricular tachycardia (VT) in 8.7%, and VT or ventricular fibrillation (VF) in 10.3%. The sensitivity of slow VT detection was 94%, and of VT/VF detection 99.3%. The specificity of sinus rhythm/ST/SVT recognition was 94%, positive predictive value 79.3%, and negative predictive value 99.2%. A total of 1,918 episodes were treated in 330 patients: 1,472 appropriately in 213, and 446 inappropriately in 117 (15% of the overall population) patients. Only 62 episodes were inappropriately treated by shocks in 40 patients, representing 5% of the overall population.
Conclusions: In this conventional ICD population, the overall specificity of standard dual-chamber arrhythmia detection settings reached 94%. This feature allows efficient detection of fast as well as slow VT events with a very low rate of inappropriate shocks.     

Patient and nurse-related implications of remote cardiac telemetry

The purposes of this study were (a) to determine the frequency of rhythm disturbance events among patients on remote cardiac telemetry, (b) to identify how many of these events were detected by the telemetry nurses, and (c) to explore the impact of managing telemetry on nurses' workload This prospective observational study took place in a nine-bed Coronary Respiratory Care Unit (CRCU) in a tertiary Canadian University Hospital. No lethal arrhythmias were detected during 420 hours of observation. There were a high number of remote telemetry warning arrhythmias, the vast majority of which were artifact (80.2%). A warning alarm occurred every 2.1 to 6.2 minutes. Nurses detected between 60% to 100% of valid warning alarms. Remote cardiac telemetry without a dedicated monitor-watcher places unnecessary demand on CRCU nurses' time because the vast majority of arrhythmia alarms are inconsequential. The addition of monitoring remote telemetry to the CRCU nurse's workload has the potential to negatively influence the care provided to CRCU patients.     

The Value of Electrophysiology Study and Prophylactic Implantation of Cardioverter Defibrillator in Patients with Hypertrophic Cardiomyopathy

Fifty-three consecutive patients with hypertrophic cardiomyopathy (HCM) and no history of sudden death underwent electrophysiology (EP) study. Sustained polymorphic ventricular tachycardia (VT) or ventricular fibrillation (VF) was induced in 19 patients (35%). Patients with prior syncope or near syncope had a higher incidence of VT/VF inducibility. An implantable cardioverter defibrillator (ICD) was placed in 14 of the 19 patients. Of the remaining 5 patients with inducible VT/VF, three refused ICD implantation, while two underwent septal myectomy and VT/VF was no longer inducible afier the operation. None of the patients received antiarrhythmic drugs. During a mean follow-up period of 47 ± 31 (2–117) months, no events occurred in the 34 patients with negative EP study. Three events occurred among the 19 patients with inducible VT/VF. One patient died suddenly, one developed wide complex tachycardia which required resuscitation, and one patient received an appropriate ICD shock. In conclusion, sustained polymorphic VT/VF was inducible in about one-third of patients with HCM. Noninducibility of VT/VF appeared to predict a favorable prognosis. Although the overall event rate was low in patients with inducible VT/VF, prophylactic ICD implantation in patients with multiple risk factors may be appropriate.     

Alert Tones Are Frequently Inaudible among Patients with Implantable Cardioverter-Defibrillators

Background: Current management guidelines for patients with Medtronic Sprint Fidelis ICD leads (Medtronic Inc., Minneapolis, MN, USA) include prominent use of Patient Alert™, a feature in which the ICD generator emits audible beeps at two programmable frequencies. Because hearing loss is highly prevalent beyond the sixth decade of life, the utility of this feature is unclear. Therefore, we conducted a survey of patients' ability to hear the Medtronic Patient Alert™.
Methods: During visits to an outpatient device clinic, patients with Medtronic ICDs were evaluated for their ability to hear ICD tones.
Results: The patient group consisted of 102 patients. Patients older than 70 years comprised 68% of the sample, with 16% between 60 and 70, and 17% younger than 60 years. Of the 102 patients, 59% (56% of males and 70% of females) were able to hear at least one tone. Ability to hear ICD tones decreased with advancing age. Among patients over 60 and 70 years, 52% and 43%, respectively (P < 0.001 vs. patients below 60 and 70 years), could hear at least one tone.
Conclusions: The Patient Alert™ feature is not useful among a large proportion of ICD patients. Patients with Sprint Fidelis leads should be evaluated for their ability to hear audible ICD tones. For patients who cannot hear the Patient Alert™ feature, a wireless remote monitoring and/or daily application of a magnet by a caregiver should be considered. Device manufacturers should include nonauditory alert technologies such as wireless remote monitoring and vibratory stimulation in future devices.     

Risk of interference from transcutaneous electrical nerve stimulation on the sensing function of implantable defibrillators

Background: The use of transcutaneous electrical nerve stimulation (TENS) for pain relief is increasing. At the same time the implantable cardioverter defibrillator (ICD) is a routine treatment for malignant tachyarrhythmias. Today patients often need devices for more than one condition, and consideration must be given to the interaction between them. We studied the risk of interference between TENS and the ICD function.
Methods and Results: Thirty patients who had received an ICD underwent a test protocol including TENS at the mammilla and hip levels, at two energy levels, and at the highest comfortable stimulation level. The effects of TENS on the electrocardiogram lead II, intracardiac electrograms, and the ICD marker channels were analyzed. Disturbance from TENS on the sensing function was seen at all stimulation attempts. Interference between the systems was observed in 16 patients. In eight patients (27%) the interpretation was VT/VF and in 14 patients (47%) as ventricular premature extra beats. Other kinds of interactions were seen in five patients (16%). Each patient could have more than one kind of interference.
Conclusions: Noise reversion and undersensing might prevent the ICD from delivering shock when it should and the interpretation as VT/VF could result in inappropriate shocks. Because of the potentially serious consequences of interference we do not recommend the use of TENS in patients with ICD.     

Failure of Third-Generation Implantable Cardioverter Defibrillators to Abort Shock Therapy for onsustained Ventricular Tachycardia Due to Shortcomings of the VF Confirmation Algorithm

Unnecessary shocks by ICDs for rhythms other than sustained VT or VF have been described as the most frequent adverse event in ICD patients. To avoid unnecessary shocks for self-terminating arrhythmias, the third-generation Jewel PCD defibrillators 7202, 7219, and 7220 Plus use a specially designed VF confirmation algorithm after charge end. The purpose of this study was to determine the ability of this VF confirmation algorithm to recognize nonsustained VT, and to analyze the reasons for failure of the PCD device to abort shock therapy for nonsustained VT despite use of this VF confirmation algorithm. Analysis of stored electrograms of electrical events triggering high voltage capacitor charging in the programmed VF zone of the device showed 36 spontaneous episodes of nonsustained VT (227 ± 21 beats/mm) during 18 ± 7 months follow-up in 15 patients who had a Jewel PCD implanted at our hospital. Intracardiac electrogram recordings and simultaneously retrieved marker channels demonstrated that the ICD shock was appropriately aborted according to the VF confirmation algorithm in 24 (67%) of 36 episodes of nonsustained VT. Twelve episodes (33%) of nonsustained VT, however, were followed by a spontaneous ICD shock in 6 (40%) of the 15 study patients. The only reason for all 12 shocks for nonsustained VT was the inability of the device to recognize the absence of VT after charge end due to shortcomings of the VF confirmation algorithm: 11 of the 12 shocks for nonsustained VT were triggered by the occurrence of paced beats during the VF confirmation period and 1 shock for nonsustained VT was triggered by the occurrence of 2 premature beats after charge end. Thus, better VF confirmation algorithms need to be incorporated in future PCD devices to avoid unnecessary shocks for nonsustained VT.     

Significance of Supraventricular Tachyarrhythmias in Patients with Implanted Pacing Cardioverter Defibrillators

Eighty-six patients were treated with an implantable cardioverter defibrillator (ICD) because of sustained ventricalar tachycardia (VT) or ventricular fibrillation (VF). In 27 patients an epicardial system was used, in 59 patients a transvenous system with a subcutaneous patch electrode was implanted. During a mean follow-up time of 17 ± 9 months, inappropriate activations of the ICD due to supraventricular tachycardia were documented by Holter monitoring in 14 patients (16%). In 8 patients paroxysmal atrial fibrillation (AF), in 2 patients chronic AF, in 1 patient atrial flutter, and in 3 patients sinus tachycardia triggered antitachycardia pacing functions (12 patients) or internal defibrillation (2 patients). In 3 patients (5%) VT was induced by inappropriate antitachycardia pacing. In an additional 18 patients (21%) inappropriate activation of antitachycardia functions due to atrial tachyarrhythmias were suspected based on telemetry readouts or the patient's history. Inappropriate activation of ICD therapy triggered by intermittent supraventricular tachyarrhythmias is common. Further improvements of detection algorithms for supraventricular tachycardia are required in future device generations.     

Ventricular Arrhythmia Inducibility Predicts Subsequent ICD Activation in Nonischemic Cardiomyopathy Patients: A DEFINITE Substudy

Objectives: We evaluated whether electrophysiologic (EP) inducibility predicts the subsequent occurrence of spontaneous ventricular tachycardia (VT) or ventricular fibrillation (VF) in the Defibrillators in Nonischemic Cardiomyopathy Treatment Evaluation (DEFINITE) trial.
Background: Inducibility of ventricular arrhythmias has been widely used as a risk marker to select implantable cardioverter defibrillator (ICD) candidates, but is believed not to be predictive in nonischemic cardiomyopathy patients.
Methods: In DEFINITE, patients randomized to the ICD arm, but not the conventional arm, underwent noninvasive EP testing via the ICD shortly after ICD implantation using up to three extrastimuli at three cycle lengths plus burst pacing. Inducibility was defined as monomorphic or polymorphic VT or VF lasting 15 seconds. Patients were followed for a median of 29 ± 14 months (interquartile range = 2–41). An independent committee, blinded to inducibility status, characterized the rhythm triggering ICD shocks.
Results: Inducibility, found in 29 of 204 patients (VT in 13, VF in 16), was associated with diabetes (41.4% vs 20.6%, P = 0.014) and a slightly higher ejection fraction (23.2 ± 5.9 vs 20.5 ± 5.7, P = 0.021). In follow-up, 34.5% of the inducible group (10 of 29) experienced ICD therapy for VT or VF or arrhythmic death versus 12.0% (21 of 175) noninducible patients (hazard ratio = 2.60, P = 0.014).
Conclusions: In DEFINITE patients, inducibility of either VT or VF was associated with an increased likelihood of subsequent ICD therapy for VT or VF, and should be one factor considered in risk stratifying nonischemic cardiomyopathy patients.     

Sudden Death Due to Atrial Fibrillation in Hypertrophic Cardiomyopathy:

FAVALE, S., et al .: Sudden Death Due to Atrial Fibrillation in Hypertrophic Cardiomyopathy: A Predictable Event in a Young Patient. This case refers to a 39-year-old woman with hypertrophic cardiomyopathy (HCM) and family history of sudden death (SD). In 1985, high rate atrial stimulation induced VF. In 1996 an ICD was implanted and she remained without arrhythmic events until November 2000 when the device reported one episode of atrial fibrillation degenerating into VF and terminated by the ICD. The VF induction mechanism recorded by the ICD was similar to that observed in 1985. The high incidence of atrial tachyarrhythmias in HCM renders cases like this at higher risk of SD. The predictive role of incremental atrial stimulation merits highlighting in future studies. (PACE 2003; 26[Pt. I]:637–639)     

Is Defibrillation Testing Safe?

Determination of defibrillation thresholds (DFTs) and implantable cardioverter defibrillalur (ICD) testing requires repeated inductions of ventricular fibrillation (VF) and defibrillation attempts using known energy outputs. Little is known about the individual and cumulative effects of repetitive brief episodes of VF and hypoperfusion on cerebral function. The potential clinical utility of quantitative electroencephalographic (QEEG) monitoring during intraoperative ICD testing, by using processed 19-channel EEG (0.5–35 Hz bandwidth), was examined in ten anesthetized patients, five males and five females (mean age 62 ± 10 years), who underwent ICD implantation and testing. Ischemic QEEG patterns were defined as those with a 3 standard deviation increase (P < 0.01) in absolute delta (1.5–3.5 Hz) power persisting for ≥ 2.5 minutes. The majority (80%) of the VF episodes (70) were accompanied by QEEG "slowing" (doubling of the pre-VF low frequency delta waves amplitude). All the patients (5/5) experiencing > 6 VF episodes showed a statistically significant increase in the low frequency amplitude. In contrast, this EEG abnormality was apparent in only one of five patients experiencing < 6 VF episodes. These results suggest a cumulative QEEG depression associated with ICD testing. QEEG may provide an objective means for establishing an individualized upper safe limit of DFT testing and the total number of induced VF episodes.     

Outcomes of Elderly Recipients of Implantable Cardioverter Defibrillators

Aims of the Study: To examine the patterns of use, complication rates, and survival in elderly recipients of implantable cardioverter defibrillators (ICD).
Methods and Results: We followed 500 consecutive patients included in the Marburg Defibrillator database for 48 ± 39 months. There were 40 patients (8%) ≥75 and 460 (92%) <75 years of age at the time of implant. The 5-year Kaplan-Meier estimate for appropriate treatment of VT or VF by ICD was 49% among patients <75- versus 57% among patients ≥75-years-old (P = 0.17). The 5-year sudden death rate was similarly low in both groups of patients (2% versus 3%). The 5-year overall mortality rate was significantly higher in patients ≥75 than in patients <75 years of age (55% versus 21%, P = 0.001), due to a higher mortality from heart failure (HF). All procedure-related, lead-related, and pulse generator-related complications were similar in both patient groups (23% versus 25%).
Conclusions: ICD therapy was equally effective in patients ≥75 and patients <75 years of age in the prevention of sudden cardiac death. While the complication rates were similar in both age groups, the long-term mortality was considerably higher in elderly patients, due to a higher mortality from HF. The current ICD therapy guidelines appear applicable to elderly patients who are otherwise medically stable and without advanced HF.     

Automatic determination of timing intervals for upper limit of vulnerability using ICD electrograms

Background: Implantable cardioverter defibrillator (ICD) implant testing based on the upper limit of vulnerability, or vulnerability testing, permits assessment of defibrillation safety margins without inducing ventricular fibrillation (VF) in most patients. Vulnerability testing requires that T-wave shocks be timed at the most vulnerable intervals of the cardiac cycle, defined as intervals at which the strongest shock induces VF. Our goal was to develop and test an automated method to select these timing intervals using ICD intracardiac electrograms (EGMs).
Methods: At ICD implant in 22 patients, we determined the range of the most vulnerable intervals by scanning the T wave with shocks. Simultaneously, EGMs were recorded for 351 pacing sequences used for measurement of timing intervals or T-wave shocks. EGMs were analyzed off-line using a novel automated method to identify a stable point near the maximum slope of the T wave in the far-field (shock) EGM. Fiducial timing points based both on the EGM and on the electrocardiogram (ECG) were used to predict the most vulnerable intervals. We compared the predicted most vulnerable to the measured most vulnerable intervals determined by T-shock scans.
Results: Automatically determined timing points from EGMs and operator-determined timing points from the surface ECG had comparable accuracy in identifying the measured most vulnerable intervals (91% EGM vs 86% ECG, P = NS).
Conclusions: An automated method based on ICD EGMs identifies the most vulnerable intervals with accuracy comparable to the operator-performed, clinical method based on the surface ECG. This EGM method can be implemented efficiently in an ICD to automate vulnerability testing.     

Inappropriate ICD therapy due to proarrhythmic ICD shocks and hyperpolarization

A 50-year-old man with an ischemic cardiomyopathy underwent ICD implantation for inducible ventricular fibrillation (VF). Sixteen months later he experienced inappropriate ICD therapy due to atrial fibrillation with a rapid ventricular response. The initial shock resulted in the initiation of VF (proarrhythmia) and the patient received an additional shock converting his rhythm to an idioventricular rhythm with a cycle length of 490 ms (122 beats/min). Due to lead hyperpolarization, the device oversensed ventricular events and the patient subsequently received additional shocks.     

Shock on T versus direct current voltage for induction of ventricular fibrillation: a randomized prospective comparison

VF is induced during ICD implantation to determine efficacy of therapy. Establishing the best clinical method of induction of VF would potentially be beneficial in reducing the number of induction attempts and reducing the frequency of inadvertent induction of VT. Commonly used methods to induce VF include shock in the T wave vulnerable period (T shock) and high frequency stimulation. This study compared the efficacy of T shock with a new induction method using a 9-V DC pulse. The study was a randomized, prospective, case crossover trial in patients receiving ICDs. VF was induced by T shock and DC in a randomized sequence during an ICD implant. VF was induced at least four times in each patient (two T shocks and two DC inductions) and with each induction; attempts were continued with modifications until successful. A paired evaluation between the T shock/DC induction was performed in 37 patients (28 men, age 64 +/- 12 years) with a left ventricular ejection fraction of 0.40 +/- 0.20. Arrhythmia indications were VT (n = 23), VF (n = 10), and VT/VF (n = 4). Drug therapy included amiodarone (n = 10), metoprolol (n = 6), digoxin (n = 1), and lidocaine (n = 1). The average T shock voltage was 207.0 +/- 16.1 V. The S1 cycle drive length was consistently 400 ms, and the mean S2 coupling interval was 317.8 +/- 19.6 ms. The length of time DC applied averaged 3.8 +/- 1.4 seconds. A total of 148 episodes of VF were included in the analysis. T shock induced VF with a cycle length of 213.5 +/- 35.1 ms, and DC induced VF with a cycle length of 214.6 +/- 34.5 ms (P = 0.86). Although VF was eventually induced for each randomization, the number of attempts required were dependent on the method of induction. The successful DC first attempt VF induction rate was 96%, with three patients requiring two attempts during one of the DC inductions. T shock had a 68% first attempt success rate with 21 patients requiring multiple T shocks to induce VF. All nine female patients had at least one unsuccessful first attempt T shock, which contributed to an overall unsuccessful first attempt induction rate significantly higher in women then men (36.1% vs 12.5%, P = 0.001). A constant DC voltage induction of VF may be more effective than T shock for induction of VF in a clinical setting because it reduces the number of attempts required to induce VF. By either method, VF appears to be more difficult to induce in women. DC induction has the advantage of simple programming of only duration of stimulation. These findings have implications particularly for ICD implantation with conscious sedation.     

Prevalence of Cancelled Shock Therapy and Relationship to Shock Delivery in Recipients of Implantable Cardioverter-Defibrillators Assessed by Remote Monitoring

Background: Cancelled shock therapy (CxTx) may presage shock delivery and shorten battery longevity of implantable cardioverter-defibrillators (ICDs). However, it is silent and has received little attention. Remote home monitoring (HM) with continuous surveillance and automatic daily data archiving allows investigation of CxTx.
Methods and Results: We retrospectively analyzed a database of 4,960 recipients of HM ICD, from 2002 to 2007. Over a mean follow-up of 445 ± 253 days, CxTx occurred in 1,392 (28%) patients, mostly as single episodes (n = 1,120). However, 142 patients (10% of patients with CxTx, 2.9% of the whole ICD population) had >10 CxTx. CxTx was followed by shock delivery in 432 patients, in 239 (55%) of whom CxTx occurred >10 days prior to shock delivery. In 113 patients (26%), CxTx occurred in the 72-hour period preceding the shock. A single CxTx preceded the shock in 74 of these 113 patients, and only eight patients had >3 CxTx.
Conclusion: CxTx was highly prevalent in unselected ICD recipients, though the intraindividual density of episodes was low. In 2.9% of the overall population, the number of CxTx was sufficient to shorten the battery longevity. A high number of CxTx usually did not predict the delivery of shocks.     

The Role of Implantable Cardioverter Defibrillators in Non VT/VF Sudden Deaths

Implantable cardioverter defibrillator (ICD) therapy has been an impressive success in preventing sudden cardiac death (SCD). Electrocardiographic documentation of SCD in ICD patients has been rare, but usually arrhythmias other than ventricular tachycardia/ventricular fibrillation (VT/VF; asystole and electromechanical dissociation [EMD]) have been implicated. This raises the question whether backup bradycardia pacing can prevent deaths due to asystole and EMD in such patients. We studied the outcome of 88 patients with permanent bradycardia pacemakers and compared them to 500 consecutive nonpacemaker patient controls, sustaining out-of-hospital cardiac arrest and undergoing resuscitation by paramedics. Mean age of the pacemaker patients was 73.5 ± 10.3 years and 64% males, compared to mean age of 68.2 ± 6.7 years and 67% males in the control group. Overall success of resuscitation and survival rates were similar. When the documented rhythm was VT/VF or asystole there were no differences in resuscitation or survival rates for the pacemaker or nonpacemaker patients. However, resuscitation rate was significantly higher in pacemaker patients than nonpacemaker patients with EMD: 47% versus 20% ( P < 0.03). For EMD, survival rate for the pacemaker patients was 13% compared to 5% in the nonpacemaker patients, but this difference was not statistically significant. Backup bradycardia pacing in future generation devices may improve the outcome of non VT/VF sudden cardiac death in at least some of the ICD recipients.