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Background: Implantable cardioverter defibrillators (ICDs) offer effective therapy for the prevention of sudden cardiac death (SCD) due to ventricular arrhythmias. However, inappropriate shocks have detrimental effects on survival and quality of life. The addition of hemodynamic monitoring may be useful in discriminating clinically important ventricular arrhythmias. Objective: In this study, we assess the ability of laser Doppler flowmetry to assess the hemodynamic effect of paced atrial and ventricular arrhythmias using mean arterial blood pressure as the reference. Methods: In this acute human study in patients undergoing an elective electrophysiological study, laser Doppler flowmetry, arterial blood pressure, and surface ECG were acquired during high‐rate atrial and ventricular pacing to simulate supraventricular and ventricular tachycardias. Results: Arterial blood pressure and laser Doppler flow signals correlated well during atrial and ventricular pacing (rho = 0.694, p <.001). The hemodynamic impairment detected by both methods was greater during ventricular pacing than atrial pacing (–1.0% vs. 19.0%, p <.001). Laser Doppler flowmetry performed better than rate alone to identify hemodynamic impairments. Conclusion: In this acute study, laser Doppler flowmetry tissue perfusion served as a good surrogate measure for arterial pressure, which could be incorporated into future ICDs. [ABSTRACT FROM AUTHOR]

Background: Appropriate implantable cardioverter‐defibrillator (ICD) shocks are associated with an increased risk of mortality and heart failure (HF) events. The first appropriate shock may occur late after implantation. However, whether the timing of the first appropriate shock influences prognosis is unknown. This study aimed to evaluate the clinical significance of the timing of the first appropriate shock in patients with ICD. Methods: This retrospective and observational study enrolled 565 consecutive ICD patients. Patients who received an appropriate shock were divided into the early group (first appropriate shock <1 year after ICD implantation) and late group (first appropriate shock ≥1 year after ICD implantation). All‐cause mortality was compared between the two groups. Results: Over a median follow‐up of 5.6 years, 112 (19.8%) patients received an appropriate shock, including 32 patients (28.6%) in the early group and 80 patients (71.4%) in the late group. Comparisons of baseline characteristics at ICD implantation revealed that the late group was more likely to receive cardiac resynchronization therapy (66.3% vs. 31.3%, p < 0.001), ICD for primary prevention (60.0% vs. 31.3%, p = 0.001), and angiotensin‐converting enzyme inhibitor or angiotensin‐receptor blocker treatment (88.8% vs. 71.9%, p = 0.028). Survival after shock was significantly worse in the late group than in the early group (p = 0.027). In multivariable Cox proportional hazards analysis, the late group had an increased risk of all‐cause mortality compared with the early group (HR: 2.22; 95% CI 1.01–4.53; p = 0.029). In both groups, the most common cause of death was HF. Conclusions: Late occurrence of the first appropriate ICD shock was associated with a worse prognosis compared with early occurrence of the first appropriate shock. Cardiac death was the most common cause of death in patients who experienced late occurrence of the first appropriate ICD shock, resulting from HF in most cases. [ABSTRACT FROM AUTHOR]

The article presents a case study of a 30-year-old Caucasian female with with past medical history of multifocal ectopic Purkinje related premature contractions syndrome. Topics include presence of scar on cardiac magnetic resonance imaging and family history of sudden cardiac death (SCD) receiving a subcutaneous implantable cardioverter-defibrillator (S-ICD); and S-ICD constituting a novel approach for prevention of SCD resulting from ventricular arrhythmias in selected patients.

Background: Patients with post‐infarct cardiomyopathy and ventricular arrhythmias (VT) necessitating implantable cardioverter defibrillators (ICD) are at risk of recurrent shocks with increased morbidity. Methods: A comprehensive search of electronic databases for all randomized clinical trials that evaluated the role of catheter ablation as a preventive strategy at the time of secondary prevention ICD implantation was performed. We calculated hazard ratios (HR) and 95% confidence intervals (CI) using random‐effects model. Results: Four trials were identified with a total of 505 patients (average age 66.4 ± 9.0 years; 87.7% were male). Preventive ablation was associated with a significant reduction in appropriate device therapies (shocks and/or anti‐tachycardia therapy) (HR = 0.62; 95% CI = 0.46‐0.82; P <.01), sustained VT (HR = 0.74; 95% CI = 0.55‐0.99; P =.04) compared to control. There were no differences in inappropriate device shocks (HR = 0.80; 95% CI = 0.38‐1.71), all‐cause death (HR = 0.93; 95% CI = 0.53‐1.64), cardiac death (HR = 0.63; 95% CI = 0.29‐1.36), arrhythmic death (HR = 0.26; 95% CI = 0.05‐1.31), or cardiac hospitalization (HR = 0.79; 95% CI = 0.57‐1.11) between strategies. Preventive ablation was associated with improved SF‐36 physical component (mean difference = 2.81; 95% CI‐0.53‐5.10; P =.02), but not the mental component (mean difference = 1.30; 95% CI = ‐2.06‐4.66). Conclusion: Among patients with post‐infarct cardiomyopathy and VT, preventive catheter ablation at the time of ICD implantation is associated with a significant reduction of appropriate ICD therapy and sustained VT, and improvement in the physical component of quality‐of‐life, but no reduction in mortality. [ABSTRACT FROM AUTHOR]

Background: Antitachycardia pacing (ATP), which may avoid unnecessary implantable cardioverter‐defibrillator (ICD) shocks, does not always terminate ventricular arrhythmias (VAs). Mean entropy calculated using cardiac magnetic resonance texture analysis (CMR‐TA) has been shown to predict appropriate ICD therapy. We examined whether scar heterogeneity, quantified by mean entropy, is associated with ATP failure and explore potential mechanisms using computer modeling. Methods: A subanalysis of 114 patients undergoing CMR‐TA where the primary endpoint was delivery of appropriate ICD therapy (ATP or shock therapy) was performed. Patients receiving appropriate ICD therapy (n = 33) were dichotomized into "successful ATP" versus "shock therapy" groups. In silico computer modeling was used to explore underlying mechanisms. Results: A total of 16 of 33 (48.5%) patients had successful ATP to terminate VA, and 17 of 33 (51.5%) patients required shock therapy. Mean entropy was significantly higher in the shock versus successful ATP group (6.1 ± 0.5 vs 5.5 ± 0.7, P =.037). Analysis of patients receiving ATP (n = 22) showed significantly higher mean entropy in the six of 22 patients that failed ATP (followed by rescue ICD shock) compared to 16 of 22 that had successful ATP (6.3 ± 0.7 vs 5.5 ± 0.7, P =.048). Computer modeling suggested inability of the paced wavefront in ATP to successfully propagate from the electrode site through patchy fibrosis as a possible mechanism of failed ATP. Conclusions: Our findings suggest lower scar heterogeneity (mean entropy) is associated with successful ATP, whereas higher scar heterogeneity is associated with more aggressive VAs unresponsive to ATP requiring shock therapy that may be due to inability of the paced wavefront to propagate through scar and terminate the VA circuit. [ABSTRACT FROM AUTHOR]

Background: Programmed long AV delays and intrinsic long first degree AV block may increase risk for competitive atrial pacing (CAP) in devices without CAP avoidance algorithms. Methods: Patients identified with CAP‐induced mode switch episodes were followed clinically from September 2013 to August 2019. Attempts to avoid CAP included shortening of postventricular atrial refractory period (PVARP) or postventricular atrial blanking period (PVAB), or change to AAI or DDI modes. After observing associations with sensor‐driven pacing, rate response was inactivated in a subset. Results: Among 23 patients identified with CAP (22 St Jude Medical [Abbott]; one Boston Scientific Corporation devices), atrial fibrillation (AF) was induced in 12 (52%), lasting 10 seconds to 28 hours and 32 minutes. In one patient with an ICD CAP‐induced AF with rapid ventricular rates that triggered a shock, inducing ventricular fibrillation, syncope, and another shock. Changing AV delays and shortening of PVARP failed to resolve CAP. After noting that all had CAP during sensor‐driven pacing, rate response was inactivated in seven, resolving further device‐induced AF in the three of seven that had prior CAP‐induced AF. In two patients with intact AV conduction, AAI(R) pacing resolved further documentation of CAP. Conclusions: CAP predominantly occurs during sensor‐driven atrial pacing that competes with intrinsic atrial events falling in PVARP. Inactivation of the activity sensor or change to atrial‐based pacing modes (AAI/R) appears to effectively prevent induction of device‐induced atrial proarrhythmia. Ultimately, a corrective algorithm is needed to avoid CAP‐induced proarrhythmia. [ABSTRACT FROM AUTHOR]

Background: Atrial fibrillation (AF) is frequently present in patients with heart failure (HF) and an implantable cardioverter‐defibrillator (ICD). This study aims to identify clinical factors associated with a baseline history of AF in ICD recipients, and compares subsequent clinical outcomes in those with and without a baseline history of AF. Methods: We studied 566 consecutive first‐time ICD recipients at an academic center between 2011 and 2018. Logistic regression multivariable analyses were used to identify clinical factors associated with a baseline history of AF at the time of ICD implant. Cox‐proportional hazard regression models were constructed for multivariate analysis to examine associations between a baseline history of AF with subsequent clinical outcomes, including ICD therapies, HF readmission, and all‐cause mortality. Results: Of all patients, 201 (36%) had a baseline history of AF at the time of ICD implant. In multivariate analyses, clinical factors associated with a baseline history of AF included hypertension, valvular heart disease, body weight, PR interval, and serum creatinine level. After multivariate adjustment for potential confounders, a baseline history of AF was associated with an increased risk of anti‐tachycardia pacing (HR = 1.84, 95% CI = 1.19‐2.85, P =.006), appropriate ICD shocks (HR = 1.80, 95% CI = 1.05‐3.09, P =.032), and inappropriate ICD shocks (HR = 3.72, 95% CI = 1.7‐7.77, P =.0001), but not other adverse outcomes. Conclusion: Among first‐time ICD recipients, specific clinical characteristics were associated with a baseline history of AF at the time of ICD implant. After adjustment for potential confounders, a baseline history of AF was associated with a higher risk of all ICD therapies in follow‐up. [ABSTRACT FROM AUTHOR]

Background: Advancement of digital technology now allows patients to have access to data from their cardiac implantable electronic devices (CIEDs). However, patients' understanding regarding CIED data and perceived personal usability remain unclear. The present study is a prospective survey to examine patients' understanding of their CIEDs and their perception of what is important. Methods: We screened 400 patients between July and December 2018 who presented to our outpatient clinic for a CIED interrogation. Patients received a one‐page questionnaire asking baseline demographics, their perception about their own knowledge about their device, and multiple‐choice questions in seven basic categories: type of CIED, original indication, functionality, manufacturer, number of active leads, estimated battery life, and number of shocks received. We compared these answers to their interrogation reports to assess accuracy. We also asked participants what they would like to be aware of regarding their CIED. Results: From this cohort, 344 of 400 (86%) (62.9 ± 12.8 years and 64 % males) agreed to take the survey and were included in the analysis. At baseline, 63.2% agreed or strongly agreed that they were knowledgeable about their devices. The overwhelming majority of patients demonstrated CIED knowledge deficits in at least one content area (n = 294, 86%), or more than two content areas (n = 176, 51%). Patients agreed or strongly agreed that they had a desire to have information regarding each of the following: battery life (84%), activity level (79%), heart rate trend (75%), and ventricular arrhythmias (74%). Conclusion: There is a large discrepancy in patients' level of knowledge regarding their CIEDs and their wish to know more details. Future technologies should satisfy providers' goals to educate their patients with basic information and fulfill patients' desire to obtain more data from their CIEDs. [ABSTRACT FROM AUTHOR]

Background: Implantable cardioverter‐defibrillator (ICD) recipients who receive appropriate device therapies have limited survival, and survival benefit in chronic kidney disease (CKD) has been questioned. We examined the association between CKD and survival after cardiac resynchronization therapy (CRT)‐defibrillator tachyarrhythmia therapies. Methods: We compared overall survival after appropriate shocks or anti‐tachycardia pacing in 439 CRT‐defibrillator recipients with left ventricular ejection fraction (LVEF) ≤35%, non‐right bundle‐branch block QRS pattern, and QRS duration >130 ms according to glomerular filtration rate (GFR) at implant, including 31 patients with GFR ≤30, 164 patients with GFR 31‐60, and 244 patients with GFR >60. At least one shock occurred in 302 patients (24 with GFR ≤30, 102 with GFR 31‐60, and 176 with GFR >60). Serial echocardiograms were also compared. Results: Patients were followed 64 months (interquartile range [IQR]: 29‐94) after implant, including 32 months (IQR: 12‐61) after first therapy. Time to first therapy or shock was similar across GFR groups. However, survival after first therapy declined directly with declining GFR (P <.001), with median postshock survival of 90 days for GFR ≤30 (95% confidence of interval [CI]: 0‐233), 612 days (95% CI: 365‐859) for GFR 31‐60, and 1672 days (95% CI: 1396‐1948) for GFR >60. Declining GFR category, ischemic heart disease, diabetes, and increasing age were independently associated with increased postshock mortality. Echocardiographic response was similar across GFR groups and was not associated with post‐therapy survival. Conclusions: Survival after appropriate tachyarrhythmia therapies, particularly shocks, is attenuated in patients with GFR ≤30. This raises concern over potential lack of survival benefit conferred by CRT‐defibrillators versus CRT‐pacemakers in this population. [ABSTRACT FROM AUTHOR]

Background: Due to high failure rates, Medtronic withdrew the Sprint Fidelis lead (SFL) from the market. Passive fixation lead models exhibited better survival than active models, but most studies have limited follow‐up. Aim of this study was to give insights into passive lead survival with a follow‐up of 10 years. Methods: In two large Swiss centers, patients with passive SFLs were identified and data from routine implantable cardioverter defibrillator (ICD) follow‐ups were collected. Patients were censored at time of death, last device interrogation (if lost to follow‐up), time of lead revision (in non‐SFL‐related problems), or at database closure (31th December 2017). We defined lead failure as any of the following: lead fracture with inappropriate discharge; sudden increase in low‐voltage impedance to >1500 or high‐voltage impedance to >100 Ω; >300 nonphysiological short VV‐intervals. Results: We identified 145 patients. Age at implant was 60 ± 12 years with a median follow‐up of 10.2 (interquartile range [IQR]: 5.0‐11.2) years. Thirty‐five percent of patients died after 5.4 ± 2.7 years. A total of 19 leads (13%) failed after 6.7 ± 3.2 years (range: 1.2‐12.0). Overt malfunction with shocks existed in four patients (3%). Cumulative lead survival was 93.1% at 6, 88.2% at 8, 83.8% at 10, and 77.6% at 11 years, respectively, with 35% of implanted leads under monitoring at 10 years. Lead survival fits best a Weibull distribution with accelerating failure rates (k = 1.95, 95% CI 1.32‐2.87, P < 0.001). Conclusions: During very long‐term follow‐up, failure rate of the passive SFL shows an increase resulting in an impaired lead survival of 84% at 10 years. [ABSTRACT FROM AUTHOR]

Background: Subcutaneous implantable cardioverter‐defibrillator (S‐ICD) is gaining in popularity for primary and secondary prevention of sudden cardiac death. The objective was to evaluate the safety and clinical effectiveness of the S‐ICD for prevention of sudden cardiac death compared to transvenous cardioverter‐defibrillator (TV‐ICD). Methods: A systematic review with meta‐analyses was performed. The electronic databases MEDLINE, EMBASE, SCI, and Cochrane Central Register of Controlled Trials were consulted in March 2018 with no restrictions on publication date. Predefined criteria were used to determine inclusion of studies and to assess their methodologic quality. Results: Ten longitudinal‐observational studies with comparison group presenting moderate methodologic flaws were included (N = 7820). The combination of results indicates that health‐related quality of life is not significantly different between S‐ICD and TV‐ICD groups (Physical health: MD = 2.90; 95% CI = −3.88, 9.68/Mental health: MD = 0.13; 95% CI = −2.11, 2.37). Mortality occurred in 4.4% of S‐ICD patients and 5.9% of TV‐ICD patients died (OR = 0.79; 95% CI = 0.50, 1.24). The incidence of infections (OR = 1.79; 95% CI = 0.93, 3.43) and inappropriate shocks (OR = 1.28, 95% CI = 0.91, 1.78) is not significantly different between both groups. The S‐ICD reduces complications related to electrodes/leads (OR = 0.13, 95% CI = 0.05, 0.29) and has lower electrodes/leads movement compared with TV‐ICD (OR = 0.26; 95% CI 0.10, 0.67). In contrast, pneumothorax is more likely in TV‐ICD than S‐ICD (OR = 0.17; 95% CI = 0.03, 0.97). Conclusions: S‐ICD reduces electrodes/leads movement, electrodes/leads related complications, and pneumothorax. Our study did not demonstrate a statistically significant difference in mortality, health‐related quality of life, and infection rate between S‐ICD and TV‐ICD. [ABSTRACT FROM AUTHOR]

Introduction: The longevity of a cardiac implantable electronic device (CIED) depends on how quickly the powers consumed by the device's functions exhaust its usable battery energy. A mathematical model for CIED power consumptions was developed and validated against longevity data from manufacturers. Methods: The programmable parameters for the Resonate X4 cardiac resynchronization therapy defibrillators (CRT‐Ds) on the Boston Scientific (St. Paul, MN, USA) online longevity calculator were designated as independent terms in the sum for the total power consumption. The reciprocal of longevity was plotted against variations in these terms. Linear and nonlinear regression analyses were used to fit the plots. The power consumed by pacing was theoretically derived and used as the calibrating tool for estimating the powers consumed by other functions and the usable battery energy. The same methodology was applied to the longevity data of other manufacturers' CRT‐Ds. Results: Single chamber 100% pacing at 60 beats/min, 2.5 V, 0.4 ms, 500 Ω consumes ≈ 144 J/year. Shock therapy is 45–85% energy efficient. Multichamber pacing modes and maintaining readiness to pace a chamber consume power even if no pacing is delivered. Switching voltage regulation is theoretically more energy efficient than linear voltage regulation for powering pacing. Conclusions: The powers consumed by therapy functions are dictated by the patient's clinical needs, but healthcare professionals can extend device longevity by switching off dormant functions and simplifying the pacing mode. Choosing a device model with large usable battery energy, low background power, and energy efficient pacing and shock therapy for implantation will increase the probability of a long service lifespan. [ABSTRACT FROM AUTHOR]

Coronary disease is a common condition in patients affected by heart failure with severely reduced ejection fraction (HFrEF). This condition represents an indication for implantable cardioverter defibrillator (ICD) in order to reduce the risk of sudden death related to arrhythmias. Nevertheless, inappropriate shocks are associated with worse quality of life, hospitalization, and death. We present the case of an inappropriate shock related to percutaneous coronary intervention during the insertion and advancement of the guidewire into the left anterior descending artery (LAD) in a patient with an ICD. Physicians' awareness about the clinical implication of noise arising during a coronary procedure is very important in patients with an ICD or pacemaker, to avoid inappropriate shock or pacing inhibition and to raise the possibility of lead implantation in or helix protrusion into the coronary lumen. [ABSTRACT FROM AUTHOR]

Abstract: Background: Patient‐reported outcomes of implantable cardioverter defibrillator (ICD), such as those with shock anxiety, have emerged as important endpoints that are related to quality of life (QOL), but they have not been well studied in a sample of the Japanese population. Therefore, we prospectively examined changes in shock anxiety in a large sample of Japanese patients with an ICD. Methods: We recruited 214 consecutive patients with an ICD who visited the outpatient clinic. At registration and 12 months later, all patients completed the Florida Shock Anxiety Scale (FSAS) questionnaire to allow us to examine changes in shock anxiety over the course of the first year after registration. Results: During the 12‐month follow‐up period, 10.5% of the patients received ICD shock therapy. Female sex, secondary prevention, and experience of ICD shock therapy were associated with high FSAS scores at registration. The FSAS scores in both patients with appropriate and inappropriate shock were significantly higher at the 12‐month follow‐up interval than at registration, and there was no significant difference in the extent of changes in FSAS scores (Δ = 5.2 ± 5.1 and Δ = 6.3 ± 9.9, respectively, P = 0.62). Conclusions: Female sex, secondary prevention, and experience of ICD shock therapy are important risk factors affecting shock anxiety in Japanese patients. Attention should be paid to the after‐effects of ICD shock in these patients, regardless of the shock type, with particular attention to women and patients who require secondary prevention. [ABSTRACT FROM AUTHOR]

The article discusses a case study of 45-year-old man who was presented with a coronary artery disease. Figures are presented depicting results of the patient's implantable cardioverter defibrillator (ICD) shock from device parameters. Also tackled is the stored electrogram from device interrogation.

Background: Shock anxiety has been documented irrespective of shock exposure in implantable cardioverter defibrillator (ICD) recipients. The presence of tachyarrhythmia may lead to an anticipation of receiving a shock and thereby give rise to shock anxiety. The aims were to assess: (1) the level of shock anxiety in a sample of ICD recipients, (2) the relationship between such anxiety and shock exposure, and (3) the relationship between recent tachyarrhythmia and shock anxiety. Methods: ICD recipients (n = 167) completed the Florida Shock Anxiety Scale measure of shock anxiety. The recipients were divided into three groups: (1) Recipients with no documented tachyarrhythmia over the previous 12 months (n = 56), (2) recipients with documented tachyarrhythmia over the previous twelve months (n = 54), and (3) recipients with any history of shocks (n = 57). Results: Of the recipients, 44% experienced some form of shock anxiety, whereas 15% reported general shock anxiety. Analyses of covariance revealed that recipients with recent tachyarrhythmia (F = 7.675 df = 9/100, P = 0.007) as well as recipients with a shock history (F = 9.976, df = 9/103, P = 0.002) reported higher levels of shock anxiety than recipients with no recent tachyarrhythmia. Conclusion: This study indicates that although a substantial proportion of the ICD recipients experienced some form of shock anxiety, only a relatively small proportion reported general shock anxiety. ICD recipients with recent tachyarrhythmia, in addition to recipients with shock history, appear to be at greater risk for development of shock anxiety. This implies that these recipients may profit from clinical-based strategies and interventions targeting shock anxiety (PACE 2012; 35:1369-1376) [ABSTRACT FROM AUTHOR]

The article discusses research investigating the patient-centered outcomes of an implantable cardioverter defibrillator (ICD) shock. The authors cite a literature review within the issue examining the effects of ICD shock, which suggests that ICD shock has less of an impact on an individual's quality of life (QOL) than previously hypothesized. An in-depth review of the clinical experiences of ICD patient management is presented.

The article presents a case of an 11-year-old boy with two episodes of syncope. The baseline electrocardiogram (ECG) showed sinus rhythm with frequent premature ventricular contractions (PVCs). The ECG showed the bigeminal PVC couplet which resulted in the false detection of ventricular fibrillation (VF) and an inappropriate shock. The EGC was sent to St. Jude Medical Inc. for further clarification.

The upper limit of vulnerability (ULV) is the weakest shock strength at or above which ventricular fibrillation (VF) is not induced when the shock is delivered during the vulnerable period. The ULV, a measurement made in regular rhythm, provides an estimate of the minimum shock strength required for reliable defibrillation that is as accurate or more accurate than the defibrillation threshold (DFT). The ULV hypothesis of defibrillation postulates a mechanistic relationship between the ULV—measured during regular rhythm—and the minimum shock strength that defibrillates reliably. Vulnerability testing can be applied at implantable cardioverter defibrillator (ICD) implant to confirm a clinically adequate defibrillation safety margin without inducing VF in 75%–95% of ICD recipients. Alternatively, the ULV provides an accurate patient-specific safety margin with a single fibrillation–defibrillation episode. Programming first ICD shocks based on patient-specific measurements of ULV rather than programming routinely to maximum output shortens charge time and may reduce the probability of syncope as ICDs age and charge times increase. Because the ULV is more reproducible than the DFT, it provides greater statistical power for clinical research with fewer episodes of VF. Limited evidence suggests that vulnerability testing is safer than conventional defibrillation testing. [ABSTRACT FROM AUTHOR]

UJHELYI, M., et al.: Nitrous Oxide Sedation Reduces Discomfort Caused by Atrial Defibrillation Shocks. An implantable cardioverter defibrillator with atrial therapies (ICD-ATs) is an effective therapy to manage atrial tacharrhythmias. Acceptance of this therapy is limited by atrial shock related anxiety and discomfort. Inhaled nitrous oxide (N2O) is a potent sedative-analgesic-anxiolytic agent that may mitigate shock discomfort and anxiety and improve patient ICD-AT acceptance. ICD-AT patients with more than one ambulatory atrial shock within 12 months were enrolled and grouped by ICD-AT shock method; awake (n = 9) or asleep (n = 4) when ambulatory ICD-AT shock is delivered. A baseline questionnaire assessed the most recent ambulatory ICD-AT shock (3 ± 3 months). A 65% N2O/35% O2 mixture was inhaled for 4 minutes followed by an ICD-AT test shock (18 ± 8 J). The test shock mimicked the awake shock method. The test shock experience during N2O was evaluated via questionnaire immediately following and 24 hours after the shock. Shock related anxiety, intensity, pain, and discomfort were assessed using a ten-point rank scale. Baseline test shock scores were similar between the shock method groups. In the awake shock method group, N2O greatly reduced preshock anxiety by 48% (6.4 ± 2.4 to 3.3 ± 2.0, or), and shock related intensity (5.9 ± 3.1 to 3.3 ± 2.5), pain (5.0 ± 2.6 to 2.0 ± 2.1), and discomfort (5.6 ± 2.4 to 1.3 ± 1.4) from baseline values by 45%, 60%, and 78% (P < 0.05), respectively. The asleep shock method group reported no changes in shock related anxiety, intensity, pain, or discomfort. Atrial shock concern, assessed via a five-point rank scale (5 = extreme concern) was improved by N2O but only in the awake group (3.1 ± 1.0 baseline to 1.6 ± 0.5 N2O, P = 0.008). There were no adverse events with N2O and patients fully recovered within 5 minutes after N2O. In conclusion, 65% N2O greatly reduced shock related pain and discomfort, and significantly reduced atrial shock concern but only in the awake shock method group. The benefits of N2O therapy may expand the use and acceptability of ICD-AT therapy into a larger atrial fibrillation cohort. (PACE 2004; 27:485–491) [ABSTRACT FROM AUTHOR]

In patients with CDs. rapid VT's are usually treated with shocks. It is unknown, if anti tachycardia pacing (ATP) delivered once for rapid VT during capacitor charging can avoid painful shocks without increasing the risk of syncope. In patients in whom rapid monomorphic VT (cycle length 300-220 ms) could be reproducibly Induced during predischarge ICD testing, the success of cardioversion (defibrillation threshold plus 10 J) and a single ATP attempt (burst with 8 or 16 stimuli) was compared using a randomized crossover study design. Consciousness of the patients was checked by the signal from a button constantly pushed bv the patient. In 20 patients (ejection fraction 0.50 ± 0.19) rapid VTs (253 ± 26 ms) were reproducibly induced. A single burst successfully terminated 11 (55%) of 20 rapid VTs, 6 episodes could not be terminated with a single burst pacing and 3 VTs accelerated. Rapid VTs not terminated by ATP were significantly faster than those that could be terminated (246 vs 258 ms, P = 0.026). Cardioversion (19 ± 3 J) terminated the VTs in all cases. No patient suffered syncope during rapid VTs. A single ATP may terminate rapid VT with cycle lengths < 300 ms in 55% of patients without increasing the risk of syncope. Therefore, in rapid VTs one attempt of ATP may be suitable as an additional therapy option during ICD capacitor charging to avoid painful shocks without compromise of safety. Thus, future ICDs should implement the option of ATP during charging of capacitors. [ABSTRACT FROM AUTHOR]

The defibrillation threshold is markedly reduced very early following the initiation of ventricular fibrillation. The purpose of this study was to determine if the same finding holds true for atrial defibrillation. Sustained, reproducible AF was induced with programmed atrial pacing using acetyl-β-methylcholine chloride (40-640 µL/min] in six adult sheep (heart weight 245-300 g]. Seven timing intervals (125 ms, 200 ms, 1 s, 3 s, 10 s, 30 s, and 5 min after AF induction) and two lead configurations; (1) RA as cathode and CS as anode; and (2) RA as cathode and RV apex as anode were tested. Single capacitor biphasic waveforms (3/1 ms) were delivered and atrial defibrillation thresholds (ADFTs) were determined in random order. No significant differences in leading edge voltage and total energy were detected for the RA-CS configuration for the seven timing intervals. For the RA-RV configuration, a significant difference was detected comparing the voltage for 125 ms to the 5-minute timing interval. For all times except 125 ms, the RA-RV threshold was significantly higher than the RA-CS level. In contrast to ventricular defibrillation, the ADFT does not change significantly within the first 5 minutes after the initiation of AF for the RA-CS configuration. However, if the shock is given very early (125 ms after AF induction) with the RA-RV configuration, the ADFT is lowered almost to the RA-CS level. [ABSTRACT FROM AUTHOR]

At present the only method for measuring the high voltage system lead impedance in patients with an ICD is to deliver a low energy test shock. This is painful, requires sedation, and carries a risk of ventricular fibrillation induction. We sought to assess the shock lead and electrode function by calculating IMP using low voltage pacing pulses, and compared it to the treasured impedance of a shock through the same lead. This was performed in both an intact and a modified lead system in order to mimic common clinical scenarios that alter lead system IMP (e.g., lead fracture). In an anesthesized canine model (n = 12) a standard (S) transvenous defibrillation lead (TDL), a modified (M) TDL (two-thirds of coil covered with heat-shrunk tubing), an active can (AC), and a M epicardial patch (EP) (two of four coils were disconnected) were used. Three configurations (C) were tested: C1: S/TDL→ AC, C2: M/TDL→ AC, and C3: M/TDL→ MEP. A measured IMP was obtained by an ICD using a 5-J shock as control. IMP was calculated using a 5-J shock, pacing pulses of 10-, 5-. 2-, and 1- V amplitude, as well as from a square wave drive train of low amplitude/high frequency signals (1 and 0.2 V, at 10 kHz) in all Cs. Ohm's law (V = IR) was utilized for measuring calculated IMP. As the surface area of the high voltage lead system decreased, the mean measured IMP (control) increased from C 1 to 3 (63 ± 10, 95 ± 4, and 127 ± 20 Ω, respectively). The correlation of calculated IMP from all Cs to measured impedance (control) remained high throughout the IMP range (range of correlation coefficient (r): 0.921-0.981). Calculated IMP using delivery of pacing pulses is highly correlated to IMP measured during shock delivery. This correlation remains high over a clinically significant range of high voltage lead system IMP changes. This study suggests that pacing pulses can be used to predict the IMP changes in the high voltage lead... [ABSTRACT FROM AUTHOR]

The time to first ICD shock has been extensively studied in patients with coronary artery disease (CAD). However, there are no published data on ICD shocks in patients with Chagas cardiomyopathy (ChC). The occurrence of the first appropriate ICD shock during the first 6 months follow-up in 20 patients with ChC (group 1) and 35 CAD patients (group 2) was analyzed retrospectively. All patients had received a third-generation pectoral ICD for ventricular tachycardia or fibrillation (VT/VF). Indications for ICD implantation were refractoriness to drug therapy or noninducibility of VT/at EPS in cardiac arrest survivors. Results: The mean age, left ventricular ejection fraction (LVEF), in groups I and II were 57.4 ± 7 years versus 64 ± 9 (P < 0.01), 30.9% ± 10% versus 32.9% ± 10% NS), and 10 men versus 31 women (P < 0.005), respectively. Six months after ICD implantation, 85% (17/20) group I patients received appropriate ICD shocks versus 51 % (18/35) in group 2, a statistically significant difference (P < 0.02, RR: 1.65, OR: 5.35). Conclusions: The incidence of appropriate ICD within the first 6 months postimplantation was significantly higher in ChC patients than in CAD patients. ChC patients were younger and more often women than CAD patients. [ABSTRACT FROM AUTHOR]

To determine the incidence of complications of third-generation implantable cardioverter defibrillator (ICD) therapy, 144 patients were prospectively studied who underwent first implant of third-generation devices (i.e., ICD systems with biphasic shocks, ECC storage capability, and nonthoracotomy lead systems). During 21 ± 15 months of follow-up, 41 (28%) patients had one or more complications. No patient died perioperatively (30 days) and no ICD infection was observed during follow-up. Complications included bleeding or pocket hematoma (hemoglobin drop > 2 g/dL) in 5 (3%) patients, prolonged reversible ischemic neurological deficit in 1 (1 %) patient, postoperative deep venous thrombosis of leg in 1 (1 %) patient, pneumothorax in 2 (1 %) patients, difficulty to defibrillate ventricular fibrillation intraoperatively in 2 (1 %) patients, generator malfunction in 1 (1 %) patient, arthritis of the shoulder in 3 (2%) patients, and allergic reaction to prophylactic antibiotics in 2 (1 %) patients. A total of seven lead related complications were observed in six (4%) patients including endocardial lead migration in four (3%) patients. Twenty-three (16%) patients received inappropriate shocks for supraventricular tachyarrhythmias (n = 13), non-sustained ventricular tachycardia (VT) (n = 7), or myopotential oversensing (n = 3). We conclude that serious complications such as perioperative death or ICD infection are rare in patients with third-generation ICDs. Lead-related problems and inappropriate shocks during follow-up are the most frequent complications of third-generation ICD therapy. Recognition of these complications should promote advances in ICD technology and management strategies to avoid their recurrence. [ABSTRACT FROM AUTHOR]

Thee purpose of the present study was to determine the clinical significance of consecutive automatic shocks delivered by implantable cardioverter defibrillators (ICDs). Sixty-four patients who received ICDs at our institution between January 1990 July 1997 were included in this study. There were 53 men and 11 women with a mean age of 50 ± 14 During a follow-up period ranging between 0.2 and 73 months (mean 23 ± 21 months), 17 patients received consecutive shocks (group A), 29 patients received single shocks (group B), and 18 patients received no ICD therapy (group C). Clinical characteristics, episodes of ICD therapy, and prognosis compared among the three groups. There were no significant differences among the three groups with regard to clinical characteristics, time to first ICD therapy, number of antitachycardia pacing episodes, frequency of inappropriate discharges. The mortality rate was higher in group A than in groups B and (P = 0.0021). The sensitivity of consecutive shocks in predicting death was 70%, the specificity was and the predictive accuracy was 81% in patients with left ventricular ejection fractions < 35%. In summary, consecutive shocks are a clinically important event in patients with ICDs. Specifically, patients receive consecutive shocks and have a depressed left ventricular function should be considered particularly high risk. [ABSTRACT FROM AUTHOR]

Shock impedance is an important determinant of defibrillation efficacy. Lead configuration, shock polarity, and delivered energy can affect shock impedance, but these variables have not been studied in active can lead systems. The present study was a prospective evaluation of 25 patients undergoing initial transvenous defibrillator implantation. In all patients, a dual coil lead and pectoral emulator were placed and three lead configurations were tested in random order: Lead (distal to proximal coil), unipolar (distal coil to can), and triad (distal coil to can + proximal coil). Shock energies of 0.1- to 15-J shock were evaluated. Impedance increased a mean of 21% as delivered energy was decreased (P < 0.001), an effect independent of lead configuration. At all delivered energies, impedances in the unipolar configuration were about 40% higher than triad, while the lead configuration was about 20% higher than triad (ps < 0.001). Polarity did not affect impedance. These results indicate that transvenous lead configurations and delivered energy, but not polarity, significantly influence shock impedance. The magnitude of the increase of impedance at low energies is independent of the shocking pathway. This effect has important implications for low energy shocks used to terminate atrial fibrillation or ventricular tachycardia. [ABSTRACT FROM AUTHOR]

During testing of a CPI model 1715 ICD, an apparent sensing abnormality was noted following shock delivery for VF. Close inspection of the recording prior to the defibrillation attempt revealed that the surface leads spontaneously lost 848 ms of data while the event marker was unaffected. Computer simulations revealed that an inadequate buffer size for the amplified (surface ECG) data was the likely source of data loss. It is important to recognize that a discordance between surface leads and event marker may represent an abnormality in the data acquisition system and simulate on ICD or lead malfunction. [ABSTRACT FROM AUTHOR]

Pectorally implanted ICDs that defibrillate with the RV electrode and the ICD housing have gained clinical acceptance. However, it is still debatable whether adding an SVC electrode connected to the housing will further reduce the threshold of defibrillation (DFT). This study utilized eight pigs. DFTs were measured with a 50 V step-down protocol starting at 650 V (20 J). Shock strength for 50% success (E50) was estimated with the average of three reversals. In addition to a dummy device. Lead I (Pacesetter Models 1558 and 1538) or Lead II (Endotak 72) were used. Leads I are active fixation, true bipolar sensing with 5-cm shocking coils. Lead II has an integrated bipolar sensing with a 4.7-cm RV and 6.9-cm SVC shocking coils. A 95 i±F defibrillation system was used to deliver a 44% tilt tuned biphasic 1,6/2.5 ms waveform, and to measure lead impedance. The RV electrode was the anode during phase I. With Lead IRV → CAN the DFT was 531 ± 75 V (13.6 ± 3.8 J) and the E50 was 496 ± 89 (12 ± 4.3 J). These were not significantly (NS) different than the DFT for RV → CAN and SVC which was 518 ± 84 V (13 ± 4.2 f) or the E50 which was 476 ± 184V(11 ± 3.9 J). Similar results were obtained with Lead II. Despite a decrease in lead impedance there was no apparent benefit from the addition of the SVC electrode. Lead I provided equivalent DFT performance to Lead II. [ABSTRACT FROM AUTHOR]

The heart has been shown to be more susceptible to defibrillation at a higher absolute ventricular fibrillation voltage (AVFV) measured on the surface ECG. This study evaluated in a closed-chest canine model (n = 7) the clinical applicability of using a real-time VF waveform analysis system using an electrogram defined between the generator can and an RV endocardial electrode. Under fluoroscopic guidance, superior vena cava and R V spring coil catheter electrodes were inserted through the external jugular vein. A subcutaneous patch was placed on the left chest. A two-parameter tracking algorithm was used to dynamically identify the high A VFV area, and a biphasic shock was triggered synchronously at the next pea&. The performance of this new peak shock method (PSM) was compared to the conventional method of shocking at a fixed time in 175 paired trials. Five shocks per voltage and five voltages per animal were randomized between the two methods to permit the generation of sigmoidal dose response curves for the estimation of 50% (E50), 75% (E75), and 100% (E100) success energies. Induction of VF and discharge voltage were kept constant while energy delivered, impedance (R), and A VFV at the point of shock were measured. Energy (8.63 ± 0.40 vs 8.64 ± 0.40 J), R (48.60 ± 0.30 vs 48.59 ± 0.30 Ω), and current (7.50 ± 0.18 vs 7.51 ± 0.16 A) were not significantly different between trials for either the conventional or the PSM. The time from the onset of VF until the defibrillation shock was 7.98 ± 1.44 seconds. Higher overall successes (46.3% vs 33.1%; P < 0.01) and lower E50, E75, and E100 were observed for the PSM. Finally, the significantly higher AVFV (9.12 ± 0.32 vs 4.73 ± 0.34 mV; P < 0.0001) with the peak method suggests that the high VF voltage could be detected as it occurred in real-time. The improved defibrillation success supports the use of this method for nonthoracotomy defibrillation. [ABSTRACT FROM AUTHOR]

The article presents a list of subjects included in the April 1995 issue of the journal "Pacing and Clinical Electrophysiology." Some of them are: A Model Study of Reentrant Activity in 2D Cardiac Tissue; Early Aftercontractions Precede Early Afterdepolarizations Induced by Isoproterenol in Canine Ventricular Myocytes; Spatial Changes in Transmembrane Potential During a Shock; Defibrillation in a Caprine Model of Chronic Atrial Fibrillation; The Relationship Between Atrial Fibrillation Wavefronts and Accessory Pathway Conduction.

The article focus on the definition of the defibrillation threshold (DFT), methods for its determination, the usefulness of various clinical testing techniques and factors that influence the DFT. Current experience and experimental evidence suggest that successful defibrillation of the heart is determined by a number of variables that include the shock waveform, the electrode size and geometry and the cardiac mass encompassed in the defibrillation field. The ability of the shock to defibrillate depends on the alteration of the transmembrane potential of the cardiac cells. An electrical gradient is created by defibrillation, which varies directly with resistance and the current density.

The article presents information on the toxic effects shock energies from implantable defibrillators. Newer implantable defibrillators offer a much wide choice of shock energies, ranging approximately from 0.1 to 40 J. Most considerations about choosing the shock strength for these newer devices have dealt with the therapeutic rather than the toxic effects of the shock. Strong shocks have numerous detrimental effects. These detrimental effects include mechanical dysfunction, ST-T changes, bradycardia, atrioventricular block, conduction block, tachyarrhythmias, fibrillation, necrosis and death.

A 31-year-old man who received an automatic cardioverter defibrillator subsequently underwent exercise testing. During exercise, a sinus tachycardia resulted above his device detect rate prompting two shocks, the second of which produced an unstable polymorphous ventricular tachycardia. In this article, we review the literature on automatic cardioverter defibrillator-induced ventricular tach-yarrhythmias as well as the management of exercise testing in patients with these devices. [ABSTRACT FROM AUTHOR]

This case report describes a patient with an automatic N2D who suffered a defibrillation shock without warning symptoms. An electrical interference can be observed in the stored EGM of the episode. The patient explained that the moment he felt the shock he was touching a washing machine. After correct grounding of this machine the patient did not suffer more inappropriate shocks. [ABSTRACT FROM AUTHOR]

The article presents a case study of a 60-year-old man with ischemic cardiomyopathy who was admitted to the hospital's cardiac care unit with cardiogenic shock. During the patient's stay in the cardiac unit, he experienced multiple paced wide-complex tachycardia accompanied by hemodynamic deterioration. The article discusses the tachycardia and the mechanism of change in its cycle length.