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A wearable cardioverter defibrillator (WCD) is indicated in appropriate patients to reduce the risk for sudden cardiac death. Challenges for patients wearing a WCD have been frequent false shock alarms primarily due to electrocardiogram noise and wear discomfort. The objective of this study was to test a contemporary WCD designed for reduced false shock alarms and improved comfort.One hundred and thirty patients with left ventricular ejection fraction ≤40% and an active implantable cardioverter defibrillator (ICD) were fitted with the ASSURE WCD (Kestra Medical Technologies) and followed for 30 days. WCD detection was enabled and shock alarm markers recorded, but shocks and shock alarms were disabled. All WCD episodes and ICD ventricular tachycardia/ventricular fibrillation (VT/VF) episodes were adjudicated. The primary endpoint was the false-positive shock alarm rate with a performance goal of 1 every 3.4 days (0.29 per patient-day).Of 163 WCD episodes, 4 were VT/VF and 159 non-VT/VF (121 rhythms with noise, 32 uncertain with noise, 6 atrial flutter without noise). Only three false-positive shock alarm markers were recorded; one false-positive shock alarm every 1333 patient-days (0.00075 per patient-day, 95% confidence interval: 0.00015-0.00361; p .001). No ICD recorded VT/VF episodes meeting WCD detection criteria (≥170 bpm for ≥20 s) were missed by the WCD during 3501 patient-days of use. Median wear was 31.0 days (interquartile range [IQR] 2.0) and median daily use 23.0 h (IQR 1.7). Adverse events were mostly mild: skin irritation (19.4%) and musculoskeletal discomfort (8.5%).The ASSURE WCD demonstrated a low false-positive shock alarm rate, low patient-reported discomfort, and no serious adverse events.

Background: Infection following cardiovascular implantable electronic device (CIED) replacement is a serious complication, and rates of infection have increased. Analysis of procedural and clinical data from device replacement procedures collected by the REPLACE Registry may provide insights into infection prevention strategies and outcomes. Methods: We prospectively evaluated procedural complications in patients undergoing CIED replacement over 6 months from 72 U.S. sites. Major and minor infections were predefined and adjudicated by an independent blinded clinical events committee. Data regarding infection prevention strategies and infectious outcomes were analyzed for their potential relationships. Results: A total of 1,744 patients were included in REPLACE. All patients received preoperative intravenous antibiotics and 68.7% received postoperative systemic antibiotic therapy. CIED infection developed in 22 patients (1.3%), of which 14 cases were major (0.8%, 95% confidence interval [CI] 0.4%–1.3%) and eight were minor (0.5%, 95% CI 0.2%–0.9%). Patients with infections were more likely to have had postoperative hematomas (five of 22 [22.7%] vs 17 of 1,722 [0.98%], P = 0.002). Participating sites experiencing infection rates >5% were more likely to use povidone-iodine for topical antisepsis, had lower implantation volume, and had patients with higher Charlson Comorbidity Index (2.79 vs 2.32, 95% CI for difference 0.08–0.86, P = 0.019). Conclusions: In this multicenter prospective study with 6 months of follow-up, infections associated with CIED replacements were surprisingly infrequent, possibly due to the use of preoperative antibiotics. Patients with infections were more likely to have had a postoperative hematoma, and sites with higher infection rates had sicker patients and lower overall procedural volume. (PACE 2012; 35:81–87)

Introduction: The Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) demonstrated that implantable cardioverter defibrillator (ICD) therapy reduced overall mortality in patients with class II or III heart failure and left ventricular ejection fraction (LVEF) ≤ 35%, while amiodarone had no effect on survival. There are limited data regarding the influence of gender on outcome of patients receiving ICDs for primary prevention. Methods: We examined gender differences in response to treatment and outcome in this cohort. Results: Women comprised 23% of the SCD-HeFT cohort, with similar percentages in the amiodarone, ICD, and placebo groups. Compared with men, women were more likely to be non-Caucasian, to have class III heart failure, and nonischemic heart disease. After adjustment for baseline differences, overall mortality risk was lower in women than in men. The gender difference in overall mortality was seen in the placebo group, while no gender difference in overall mortality was seen in the ICD group. There was a significantly lower absolute risk of death in the placebo arm women, compared with the placebo arm men (annual mortality rate approximately 4% vs. 6%). Conclusions: The impact of ICD therapy appears to differ between men and women in this trial, with a smaller ICD benefit among women. However, the test for an interaction between gender and therapy was not significant. The lower overall mortality risk in women in the placebo group and the smaller number of women enrolled may help to explain why treatment differences in women were much smaller and difficult to detect.

Because cardiac device infections may include fastidious pathogens, extended incubation of blood cultures is suggested. A patient with an infection of a right ventricular lead implantable cardioverter defibrillator (ICD) system is described. The device was implanted 6 months earlier. The pathogen was identified as Haemophilus parainfluenzae, which was cultured within 72 hours and was presumably from a respiratory tract infection. Extended incubation was not necessary to culture this fastidious pathogen. Two large retrospective studies suggest that prolonged incubation for fastidious organisms is generally not necessary because of advances in culture media and automated blood culture systems.

Biphasic Waveform Defibrillation. Introduction: New automatic external defibrillators (AEDs), which are smaller, lighter, easier to use, and less costly make the goal of widespread AED deployment and early defibrillation for out-of-hospital cardiac arrest feasible. The objective of this study was to observe the performance of a low-energy impedance-compensating biphasic waveform in the out-of-hospital setting on 100 consecutive victims of sudden cardiac arrest. Methods and Results: AEDs incorporating a 150-J impedance-compensating biphasic waveform were used by 12 EMS systems. Data were obtained from the AED PC card reporting system. Defibrillation was defined as conversion to an organized rhythm or to asystole. Endpoints included: defibrillation efficacy for ventricular fibrillation (VE); restoration of an organized rhythm at the time of patient transfer to an advanced life support (ALS) team or to the emergency department (ED); and time from AED power-on to first defibrillation. The AED correctly identified 44 of 100 patients presenting in VE as requiring a shock (100% sensitivity) and 56 of 100 patients not in VF as not requiring a shock (100% specificity). The time from 911 call to first shock delivery averaged 8.1 ± 3.0 minutes. A single 150-J biphasic shock defibrillated the initial VE episode in 39 of 44 (89%) patients. The average time from power-on to first defibrillation was 25 ± 17 seconds. At patient transfer to ALS or ED care, an organized rhythm was present in 34 of 44 (77%) patients presenting with VF. Asystole was present in 7 (16%) and VE in 3 (7%). Conclusions: Low-energy impedance-compensating biphasic waveforms terminate long-duration VE at high rates in out-of-hospital cardiac arrest. Use of this waveform allows AED device characteristics consistent with widespread AED deployment and early defibrillation.

The purpose of this report is to review the gross and histological cardiac anatomical findings in patients with chronically indwelling coronary sinus leads at the time of autopsy or cardiac transplantation. Transvenous cardioverter defibrillators offer effective protection against sudden death. The use of a coronary sinus electrode has been shown in some patients to decrease the defibrillation threshold. The anatomical consequences of chronically indwelling coronary sinus cardioversion/defibrillation electrodes in patients having transvenous implantable cardioverter defibrillators is unknown. The hearts of seven patients with chronically indwelling coronary sinus electrodes were evaluated following autopsy (n = 2) or cardiac transplantation (n = 5). The coronary sinus electrode in each case was a 6.5 French silicone lead with a 5-cm long defibrillation coil (Medtronic CS lead model 6933) that was positioned as distally as possible within the coronary sinus at the time of implantable cardioverter defibrillator surgery. The seven hearts examined were derived from patients whose age ranged between 49 and 69 (mean 56 +/- 7 years). Six had coronary artery disease and one had idiopathic dilated cardiomyopathy. The time from implant to death or cardiac transplantation was 8 +/- 6 months, range 1-18 months. In all seven patients, there was no evidence of any significant damage from the presence of the coronary sinus lead. The only finding in each case was the scattered presence of a thin white fibrous sheath over the lead that intermittently adhered to the coronary sinus endothelium and, in the two patients transplanted 1-3 months after implantable cardioverter defibrillator insertion, a mild inflammation reaction adjacent to the leads in the coronary sinus endothelium. There was no evidence of coronary sinus occlusion, adjacent coronary artery injury, coronary sinus perforation, coronary sinus burn, or myocardial injury adjacent to the lead. Cause of death was due to end-stage congestive heart failure and thrombotic stroke, respectively, in the two patients examined at autopsy. Coronary sinus defibrillation leads can be used safely without harmful anatomical effect.

Serial DFT Measures in Man. Introduction; The defibrillation threshold (DFT) may change throughout the first year following implantation of a cardioverter defibrillator, but it remains uncertain if changes are a consequence of changes in clinical condition or are related to fundamental alterations at the electrode-tissue interface. The purpose of this study was to evaluate the extent and time course of DFT changes over the first year following implantable cardioverter defibrillator (ICD) surgery when extraneous clinical and device variables potentially affecting the DFT were excluded. Methods and Results.: We prospectively enrolled 61 patients undergoing epicardial or non-thoracotomy/transvenous ICD therapy into a series of follow-up studies where the DFT was measured at implant and at 1, 6,12, and 52 weeks following implantation in a uniform manner. Stored energy DFT was measured and recorded for all patients. Patient exclusion criteria were: (1) inability to complete all five measures of the DFT; (2) institution of Class I or Class III antiarrhythmic drugs at any time during the study; (3) lead system changes (relocation or new leads) or programming changes in pulse width or current pathway; or (4) development of a significant change in their clinical status, such as decompensated congestive heart failure or acute ischemia. Only 20 of the 61 patients satisfied the criteria required to complete the study. Two of the excluded patients developed high DFTs, which required reprogramming of the current pathway. Eight patients had an epicardial lead system, and 12 had a nonthoracotomy lead system. The rise in DFT over the first 12 weeks was significant for the eight epicardial lead system patients (P = 0.05) and for the 12 nonthoracotomy lead system patients (P = 0.004). The peak rise in DFT occurred at 1 week for the patients with an epicardial lead system (3.4 ± 1.8 J to 7.9 ± 3.8 J) and at 12 weeks for the patients with a transvenous lead system (10.3 ± 5.3 J to 16.1 ± 7.4 J). Conclusions: This study confirms a transient significant rise in the DFT in the first 12 weeks following ICD surgery that partially returns to the implant value over the remainder of the year. Because specific clinical and technical variables were excluded from this study, the observations made in this patient population suggest that the rise in DFT may be a consequence of changes at the electrode-tissue interface.

Atrial Fibrillation After Ventricular Defibrillation. Introduction: The induction of atrial fibrillation (AF) following implantable defibrillator therapy of ventricular fibrillation carries multiple risks. The frequency of shock-induced AF may be more problematic in patients with transvenous defibrillators because current is often delivered through atrial tissue. Thus, the purpose of this study was to determine the incidence of AF following transvenous ventricular defibrillation. Methods and Results: Atrial electrograms were recorded before and after energy delivery in patients undergoing intraoperative testing of transvenous defibrillation lead systems. A total of 114 tracings were examined from 21 patients following ventricular defibrillation. Transvenous deflbrillation shock strength ranged between 200–800 volts (2–40 joules). Bipolar atrial electrograms were obtained from atrial electrodes with 1-cm interelectrode spacing located on one of the defibrillation catheters. The timing of the ventricular defibrillation shock was expressed as a percentage of the preceding sinus PP interval. Three of the 114 transvenous shocks (2.6%) generated AF. Each episode of AF occurred in a different patient. The shocks responsible for AF occurred at 21%, 43%, and 84% of the preceding sinus PP interval. No relation was found between AF induction and the timing of pulse delivery, pulse strength, or pulse number. Conclusion: We conclude that transvenous ventricular defibrillation infrequently causes AF and that timing shock delivery to the atrial cycle is likely to be of marginal or no benefit in the prevention of shock-induced AF. (J Cardiovasc Electrophysiol, Vol. 3, pp. 411–417, October 1992)

Effect of Defibrillation on Pacing Thresholds. Introduction: Significant increases in ventricular pacing threshold have been observed following monophasic waveform ventricular defibrillation shocks. High-output pacing is recommended to ensure consistent capture, particularly in pacemaker-dependent patients who are likely to be defibrillated. Whether biphasic waveform defibrillation compounds this problem is not known. The purpose of this prospective study was to examine serial changes in ventricular pacing thresholds following single, multiple, low- and high-energy biphasic defibrillation sbocks from an implanted defibrillator. Methods and Results: Bipolar pacing thresholds before and after defibrillation, and the adequacy of pacing capture at three times preshock threshold in the immediate aftermath of ventricular defibrillation, were prospectively evaluated in 67 consecutively tested recipients of a biphasic implanted cardioverter defibrillator. Overall, serial pacing thresholds following successful defibrillation were completely unchanged after 141 of 177 (80%) ventricular fibrillation inductions. In no case did the threshold pulse width increment > 0.06 msec from its baseline value after shock, nor did pacing at a pulse width of three times preshock threshold from dedicated bipolar pacing electrodes fail to result in successful ventricular capture. Changes in threshold were not related to when measured from the time of shock, defibrillation energy, number of shocks, electrode system, chronicity of leads, shock orientation, or to clinical factors. Conclusions: No clinically important changes in pacing threshold were observed after biphasic waveform defibrillation. Bradycardia pacing at conventional pacemaker outputs of three times baseline pulse width threshold from bipolar electrodes dedicated exclusively to pacing or sensing (but not defibrillation) consistently allowed for an adequate safety margin following defibrillation.