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PubMed1994

Oversensing during ventricular pacing in patients with a third-generation implantable cardioverter-defibrillator.

OBJECTIVES: The purpose of this study was to identify the causes of oversensing during ventricular pacing in patients with a third-generation implantable cardioverter-defibrillator. BACKGROUND: Third-generation implantable cardioverter-defibrillators have the capability for bradycardia pacing as well as antitachycardia pacing and defibrillation. With the Ventritex Cadence Tiered Therapy Defibrillator System, the pulse generator sensitivity is increased during bradycardia pacing to prevent undersensing of an arrhythmia with small amplitude signals. METHODS: Records from 85 consecutive patients who underwent implantation of a Cadence device for treatment of ventricular tachyarrhythmias were reviewed. RESULTS: Four patients required continuous pacing for bradyarrhythmias. In three of these patients, ventricular pacing was accomplished using the bradycardia pacing feature of the Cadence device. All three experienced spurious device discharges or had aborted shocks for oversensing. Analysis of real-time and stored electrograms revealed intermittent high frequency, large amplitude noise in two patients and oversensing of maximally gained R and T waves in the remaining patient. No evidence of lead fracture was found in any patient. The problem was solved by implantation of a separate permanent pacemaker in two patients and was partially solved by reprogramming of the device in the remaining patient. CONCLUSIONS: Although the Cadence implantable cardioverter-defibrillator has the capability for ventricular pacing in patients with bradyarrhythmias, certain features of its automatic gain control circuit limit its utility in this instance. Oversensing occurs commonly, leading to device discharges or aborted shocks. Implantation of a separate permanent pacemaker may be required in patients who have a Cadence device for tachyarrhythmia control and who also need pacing for bradycardia.

Aged↗
PubMed1993

Hemodynamic changes due to intraoperative testing of the automatic implantable cardioverter defibrillator: implications for anesthesia management.

During the insertion of an automatic implantable cardioverter defibrillator, repeated induction of ventricular tachycardia or ventricular fibrillation and subsequent defibrillation is performed to determine the defibrillation threshold. In this study, the influence of these testing episodes on myocardial function was investigated in 13 patients under general anesthesia. Preoperative ejection fraction (EF) was 41 (14 to 84) % (median and range). Testing was performed 3 (2-5) times. During these testing episodes the patients received a total of 4 (2-8) countershocks. Patients with a preoperative EF < 30% (N = 5) showed a significant reduction of cardiac index (CI) from 2.2 (1.5-3.3) L/min/m2 before testing to 1.5 (1.3-2.3) L/min/m2 after the last testing episode, and of left ventricular stroke work index (LVSWI) from 32 (14-53) g.m/m2 before testing to 22 (7-43) after the last testing episode. These changes were not related to the total fibrillation time or the cumulative defibrillation energy. Patients with a preoperative EF > 30% (N = 8) showed no significant changes of CI (2.15 [1.8-3.0] L/min/m2 v 2.15 [1.7-3.0] L/min/m2) or LVSWI (35 [28-48] g.m/m2 v 33.5 [27-52] g.m/m2). Comparison of the two patient groups revealed similar hemodynamic baseline values, but significant differences in LVSWI after the last testing episode. Defibrillation testing may produce a further reduction in myocardial performance in patients with preexisting poor cardiac function.

Adolescent↗
PubMed2006

Withdrawing implantable defibrillator shock therapy in terminally ill patients.

PURPOSE: The purpose of this study is to review a multidisciplinary strategy used to identify patients with terminal illnesses and initiate withdrawal of implantable cardioverter defibrillator (ICD) shock therapy as part of a comprehensive comfort care approach. With indications for ICDs increasing, more patients are receiving devices. Once protected from an arrhythmic death, these patients may develop other terminal diseases such as cancer or congestive heart failure. It is appropriate to withdraw defibrillator shock therapy when such patients desire only comfort care. METHODS: The charts of ICD patients who had died were reviewed. Two groups emerged: Group 1 (20) included patients whose defibrillator was turned off through the comprehensive comfort care approach. Group 2 (43) included patients whose clinical course was so rapid that the defibrillator was not turned off. Pacing therapy was not withdrawn in either group. RESULTS: Defibrillator discharges, cause of death, and time from ICD discharge to death were compared. Group 2 patients died more acutely than Group 1. Group 1 experienced fewer shocks prior to death when compared to Group 2. Comparing pacemaker dependent and non-dependent patients, there was no difference in the time between therapy discontinuation and death. CONCLUSION: This is the largest study to date to review the characteristics of patients with ICDs and terminal illness. Only one-third of terminally ill patients with ICDs were able to have shock therapy withdrawn as part of a comfort care strategy. These patients experienced fewer shocks in the final days of their illness.

Aged↗
PubMed2005

Automated external defibrillators: to what extent does the algorithm delay CPR?

STUDY OBJECTIVE: Maximizing cardiopulmonary resuscitation (CPR) during resuscitation may improve survival. Resuscitation protocols stack up to 3 shocks to achieve defibrillation, followed by an immediate postdefibrillation pulse check. The purpose of this study is to evaluate outcomes of rhythm reanalyses immediately after shock, stacked shocks, and initial postshock pulse checks in relation to achieving a pulse and initiating CPR. METHODS: We conducted an observational study of patients with ventricular fibrillation treated by first-tier emergency medical services (EMS). We collected data from EMS, dispatch, and hospital records. Additionally, we analyzed automatic external defibrillator recordings to determine the proportion of cardiac arrest victims who were defibrillated and achieved a pulse according to shock number (single versus stacked shock), proportion of victims with a pulse during the initial postdefibrillation pulse check, and interval from initial shock to CPR. RESULTS: The study included 481 cardiac arrest subjects. Automatic external defibrillators terminated ventricular fibrillation with the initial shock in 83.6% (n=402) of cases. A second shock terminated ventricular fibrillation in an additional 7.5% (n=36) of cases, and a third shock terminated ventricular fibrillation in 4.8% (n=23) of cases. The initial sequence of 3 shocks failed to terminate ventricular fibrillation in 4.1% (n=20) of cases. In total, automatic external defibrillators performed 560 rhythm reanalyses during the initial shock sequence and delivered 122 "stacked" shocks. Termination of ventricular fibrillation was not synonymous with return of a pulse. The initial shock produced a pulse that was eventually detected in 21.8% (105/481) of cases. Stacked shocks produced a pulse in 10.7% (13/122) of cases. For the 24.5 % (n=118) of cases in which a pulse returned, the pulse was detected during the initial postshock pulse check only 12 times, or 2.5% of all cases. The median interval from initial shock until CPR was 29 (23,41) seconds. CONCLUSION: Rhythm reanalyses, stacked shocks, and postshock pulse checks had low yield for achieving or detecting return of a pulse. CPR was not initiated until 29 seconds after the initial shock.

Aged↗
PubMed2005

Safety and efficacy of radiofrequency energy catheter ablation of atrial fibrillation in patients with pacemakers and implantable cardiac defibrillators.

BACKGROUND: Catheter ablation has significantly transformed the clinical management of atrial fibrillation (AF). The safety and efficacy of this procedure are not well understood in patients with pacemakers and defibrillators. OBJECTIVES: The purpose of this study was to study the impact of radiofrequency catheter ablation of AF in patients with pacemakers and implantable cardiac defibrillators. METHODS: We studied 86 patients with pacemakers and defibrillators (group I) and a similar number of age- and gender-matched controls (group II) who underwent AF ablation between 1999 and 2004. Clinical and procedural variables were compared between the two groups. In group I, various generator and lead parameters were compared before and after the procedure. Resurgence of clinical AF after 2 months was considered recurrence. RESULTS: Both groups were similar with regard to age, gender, body mass index, and type of AF. Group I had a higher incidence of diabetes (17% vs 6%, P = .03), coronary artery disease (25% vs 13%, P = .05), less prolonged AF (31 +/- 21 vs 45 +/- 30 months, P <.001), lower left ventricular ejection fraction (49 +/- 13% vs 52 +/- 9%, P = .03), and left ventricular end-diastolic dimensions (4.97 +/- 0.81 vs 4.72 +/- 0.67, P = .03). No changes in the sensing and pacing thresholds, impedance of atrial and ventricular leads, or defibrillator coil impedance after AF ablation were observed in group I. Atrial lead dislodgment was seen in two patients. Transient abnormal but "expected" pulse generator behavior was seen in 25% of patients without permanent malfunction. Stroke (1% vs 1%, P = 1.000), pulmonary vein stenosis (2% vs 1%, P = .77), and AF recurrence rates at 12 months were similar between groups I and II, respectively (19% vs 21%, P = .73). CONCLUSION: AF ablation is safe and efficacious in patients with pacemakers and defibrillators.

Atrial Fibrillation↗
PubMed2006

Stepped defibrillation waveform is substantially more efficient than the 50/50% tilt biphasic.

BACKGROUND: Even with biphasic waveforms, patients with high defibrillation thresholds (DFTs) still are seen; thus, improved defibrillation waveforms may be of clinical utility. The stepped waveform has three parts: the first portion is positive with two capacitors in parallel, the second is positive with the capacitors in series, and the last portion is negative, also with the capacitors in series. OBJECTIVES: The purpose of this study was to assess the clinical utility of improved defibrillation waveforms. METHODS: We measured the delivered energy DFT in 20 patients in a dual-site study using the stepped waveform and a 50/50% tilt biphasic truncated exponential as the control. All shocks were delivered using an arbitrary waveform defibrillator, which was programmed to mimic two 220-microF capacitors (110 microF in series and 440 microF in parallel). RESULTS: The peak voltage at DFT was reduced in 19 of the 20 patients. The median peak voltage was reduced by 32.0%, from 472 V to 321 V (P <.001). The median energy DFT was reduced by 33%, from 11.7 J to 7.8 J (P = .008). The mean voltage and energy were reduced by 25.3% and 20.2%, respectively. On average, the stepped waveform was able to defibrillate as well as the 50/50% tilt biphasic, with 33% more energy. The benefit was more pronounced in patients with either a lower ejection fraction or a superior vena cava coil. The benefit of the stepped waveform had an inverse quadratic correlation with the resistance (r(2) = 0.47), suggesting that the capacitance values chosen for the stepped waveform were close to optimal for a 35-Omega resistance. CONCLUSION: The stepped waveform reduced the DFT compared to the 50/50% tilt waveform in this preliminary study.

Arrhythmias, Cardiac↗
PubMed2005

Better outcome after pediatric defibrillation dosage than adult dosage in a swine model of pediatric ventricular fibrillation.

OBJECTIVES: This study was designed to compare outcome after adult defibrillation dosing versus pediatric dosing in a piglet model of prolonged prehospital ventricular fibrillation (VF). BACKGROUND: Weight-based 2 to 4 J/kg monophasic defibrillation dosing is recommended for children in VF, but impractical for automated external defibrillator (AED) use. Present AEDs can only provide adult shock doses or newly developed attenuated adult doses intended for children. A single escalating energy sequence (50/75/86 J) of attenuated adult-dose biphasic shocks (pediatric dosing) is at least as effective as escalating monophasic weight-based dosing for prolonged VF in piglets, but this approach has not been compared to standard adult biphasic dosing. METHODS: Following 7 min of untreated VF, piglets weighing 13 to 26 kg (19 +/- 1 kg) received either biphasic 50/75/86 J (pediatric dose) or biphasic 200/300/360 J (adult dose) therapies during simulated prehospital life support. RESULTS: Return of spontaneous circulation was attained in 15 of 16 pediatric-dose piglets and 14 of 16 adult-dose piglets. Four hours postresuscitation, pediatric dosing resulted in fewer elevations of cardiac troponin T (0 of 12 piglets vs. 6 of 11 piglets, p = 0.005) and less depression of left ventricular ejection fraction (p < 0.05). Most importantly, more piglets survived to 24 h with good neurologic scores after pediatric shocks than adult shocks (13 of 16 piglets vs. 4 of 16 piglets, p = 0.004). CONCLUSIONS: In this model, pediatric shocks resulted in superior outcome compared with adult shocks. These data suggest that adult defibrillation dosing may be harmful to pediatric patients with VF and support the use of attenuating electrodes with adult biphasic AEDs to defibrillate children.

Age Factors↗
PubMed2004

Differing operational outcomes with six commercially available automated external defibrillators.

INTRODUCTION: In general automated external defibrillators (AED) are handled easily, but some untrained lay rescuers may have major problems with the use of such products. This may result in delayed shock delivery and delay in basic life support (BLS) after use of the AED. To study the effect of voice prompts and design solutions we tested the time from the first shock to the initiation of BLS for six defibrillators available in Austria. METHODS: Volunteers, who had no AED training, were evaluated to see when they delivered the first shock and how often BLS was started after the voice prompts were given by the defibrillators. RESULTS: Time to first shock delivered ranged from 78 (95% CI: 68-89) to 128 (95% CI: 110-146)s. The defibrillator-type had a significant influence on the time to first shock delivered (P < 0.0001). The proportion of volunteers who started BLS after defibrillation ranged from 93 to 33% and differed significantly between the AEDs used (P < 0.03). CONCLUSIONS: We demonstrated that there are significant differences between AEDs, concerning important operational outcomes like time to first shock and the start of BLS. Further research and development is urgently required to optimise user-friendliness and operational outcomes.

Cardiopulmonary Resuscitation↗
PubMed2004

Preliminary in-hospital experience with a fully automatic external cardioverter-defibrillator.

BACKGROUND: Ventricular fibrillation (VF) and ventricular tachycardia (VT) are frequently present as initial rhythms during in-hospital cardiac arrest. Although ample evidence exists to support the need for rapid defibrillation, the response to in-hospital cardiac arrest remains without major advances in recent years. The delay between the arrhythmic event and intervention is still a challenge for clinical practice. OBJECTIVE: To analyze the performance and safety of in-hospital use of a programmable, fully automatic external cardioverter-defibrillator (AECD). METHODS: We conducted a prospective study at the Emergency Department of a university hospital. A total of 55 patients considered to be at risk of sustained VT/VF were included. Patients underwent monitoring of their cardiac rhythm by the AECD. Upon detection of a ventricular tachyarrhythmia, the AECD was programmed to automatically deliver shock therapy. RESULTS: We recorded 19 episodes of VT/VF in 3 patients. The median time between the beginning of the arrhythmia and the first defibrillation was 33.4 s (21-65 s). One episode of spontaneous reversion of VT was documented 20 s after its origin and shock therapy was aborted. The defibrillation success was 94.4% (17/18) for the first shock and 100% (1/1) for the second shock. No case of inappropriate shock discharge was registered during the study period. CONCLUSION: The AECD has the feasibility to combine long-term monitoring with automatic defibrillation safely and effectively. It presents the possibility of providing rapid identification of, and response to, in-hospital ventricular tachyarrhythmias.

Defibrillators↗
PubMed2005

Post-shock chest compression delays with automated external defibrillator use.

PRIMARY OBJECTIVE: In a swine model of out-of-hospital ventricular fibrillation (VF) cardiac arrest, we established that automated external defibrillator (AED) defibrillation could worsen outcome from prolonged VF compared with manual defibrillation. Worse outcomes were due to substantial interruptions and delays in chest compressions for AED rhythm analyses and shock advice. In particular, the mean interval from first AED shock to first post-shock compressions was 46+/-6s. We hypothesized that the delay from shock to provision of chest compressions is similar in the out-of-hospital setting. MATERIALS AND METHODS: We conducted a retrospective observational review of AED-treated adult VF cardiac arrest victims over a 26-month period to determine the interval from the first AED defibrillation attempt to the initial provision of post-shock chest compressions for out-of-hospital VF cardiac arrests. A two-tiered, single emergency medical service (EMS) system with AED-equipped first responders serves our area of 400 km2 with a population of 487,000 people. The defibrillators record a detailed sequence of events during the resuscitation effort that includes the electrocardiogram with real clock times and a recording of surrounding audible actions. RESULTS: A median of 38 s (IQR 15, 61 s) elapsed between the first shock and the initiation of chest compressions. Approximately half of the delay was due to mechanical/electronic factors and the remainder due to human factors. Of 64 adults in VF, 45 (70%) died before hospital admission, 19 (30%) survived to admission and 10 (16%) survived to hospital discharge. CONCLUSION: Substantial delays in the provision of post-shock chest compressions are typical in this EMS system with AED-equipped first responders.

Adult↗
PubMed2005

Pediatric defibrillation doses often fail to terminate prolonged out-of-hospital ventricular fibrillation in children.

BACKGROUND: The recommended dose for pediatric defibrillation is 2 J/kg, based on animal studies of brief duration ventricular fibrillation (VF) and a single pediatric study of short duration in-hospital VF. In a piglet model of out-of-hospital (prolonged) cardiac arrest, this recommended dose was usually ineffective at terminating VF. We, therefore, hypothesized that pediatric dose defibrillation may be less effective for prolonged out-of-hospital pediatric VF. METHODS: We evaluated retrospectively all cardiac arrests in children less than 13 years old in Tucson from November 1998 to April 2003, with special attention to all children in ventricular fibrillation. We determined the rate of ventricular fibrillation termination after pediatric dose shocks in this cohort, and compared this rate with a published historical pediatric in-hospital defibrillation control group. A pediatric dose shock was defined as 2 J/kg (+/-10 J). All shocks in both groups were provided as monophasic damped sinusoidal waveforms. RESULTS: Thirteen of 151 (9%) children with out-of-hospital cardiac arrest had documented VF. Eleven children received a total of 14 pediatric dose shocks. The median minimum untreated dispatch-to-shock time in unwitnessed arrest or collapse-to-shock in witnessed arrest for those 11 children was 11 min (interquartile range 25-75%; 9-15.5 min). Seven of the 14 pediatric dose shocks terminated the VF (six to asystole, one to pulseless electrical activity). Nine children (68%) died in the emergency department and four (31%) in the pediatric intensive care unit; none survived to hospital discharge. Failure to terminate VF after a pediatric dose shock in this study group with prolonged out-of-hospital ventricular fibrillation was substantially more common than the previously reported in-hospital data (7/14 versus 5/57; OR 10.4; 95% CI 2.6-42; P=0.001). CONCLUSIONS: Termination of VF after a pediatric defibrillation dose is substantially worse for prolonged pediatric out-of-hospital VF cardiac arrest compared with in-hospital (short duration) ventricular fibrillation. The optimal pediatric defibrillation dose for prolonged VF is not known.

Adolescent↗
PubMed2001

Fractal correlation properties of heart rate dynamics and adverse events in patients with implantable cardioverter-defibrillators.

The aim of this study was to determine the prognostic significance of nonlinear and standard heart rate (HR) variability parameters in predicting future adverse events (AEs) in patients with implantable cardioverter-defibrillators. In postinfarction studies, nonlinear measures of HR variability obtained from long-term electrocardiographic recordings have been suggested to be better predictors of adverse outcomes than conventional HR variability measures. Fifty-five high-risk patients with reduced left ventricular function and an implantable cardioverter-defibrillator had a 10-minute, high-resolution electrocardiographic recording after which they were followed for 25 months on average. Implantable cardioverter-defibrillator shock or death was determined as the end point. The SD of all normal-to-normal RR intervals, the square root of the mean squared differences of successive normal-to-normal RR intervals, and the proportion of interval differences of successive normal-to-normal RR intervals >50 ms, low-frequency and high-frequency powers of the power spectrum and their ratio were calculated as conventional measures of HR variability. The short-term scaling exponent (alpha(1)) and approximate entropy were determined as nonlinear measures of HR variability. AEs occurred in 23 patients (42%). Patients with AEs had significantly lower alpha(1) than event-free patients: 0.81 +/- 0.29 (mean +/- SD) versus 1.01 +/- 0.30 (p = 0.02). None of the other HR variability parameters differed significantly between patients with and without AEs. In the Cox proportional-hazards model including age, gender, ejection fraction, occurrence of ventricular tachyarrhythmia before defibrillator implantation, beta-blocker usage, and alpha(1), only alpha(1) was an independent predictor of AEs: hazard ratio 1.20 (95% confidence interval 1.03 to 1.39) for every 0.10 decrease in alpha(1) (p = 0.020). In conclusion, alpha(1) obtained from a 10-minute electrocardiographic recording yields important prognostic information about the risk of AEs in patients with implantable cardioverter-defibrillators.

Aged↗
PubMed1997

Predischarge arrhythmia induction testing of implantable defibrillators may be unnecessary in selected cases.

Complete postoperative evaluation of implantable cardioverter-defibrillators (ICDs) before discharge, including arrhythmia induction, has been the standard since their introduction. Whereas the original ICDs provided little telemetered information and used separate pace-sense and defibrillation leads, modern, third-generation devices provide pace-sense function information in addition to other data and are used in conjunction with integrated transvenous endocardial leads that combine pace-sense and defibrillation function. Changes in lead position, which can potentially result in either an inability to detect fibrillation or to terminate it, should be mirrored by changes in resting pace-sense function. Thus, for newer ICDs implanted with integrated endocardial lead systems, it is possible that in at least some cases predischarge arrhythmia inductions can be avoided. Two hundred patients receiving third-generation ICDs in conjunction with integrated transvenous leads were evaluated before discharge. Defibrillation detection or termination problems were seen in 8. Declines in resting R-wave amplitude and pacing impedance were significantly associated with such complications (-7 +/- 5 vs -0.3 +/- 2.3 mV [p <0.0001] and -158 +/- 138 vs -93 +/- 76 omega [p <0.05], for those with vs without complications, respectively), as were gross right ventricular lead migrations on chest x-ray. No patient with a defibrillation complication had an R-wave change of <3 mV. However, 13% of patients without complications had R-wave changes of >3 mV. It is concluded that a pace-sense evaluation of ICDs may be a satisfactory screen to determine those who need to go on to complete testing with arrhythmia induction in selected cases.

Aged↗
PubMed1996

The additional hospital costs generated in the management of complications of pacemaker and defibrillator implantations.

The rapid approach of capitated reimbursement mandates that providers examine their practice patterns associated with all surgical procedures. Documentation of (1) the complications associated with these procedures and (2) the additional hospital costs associated with the management of these complications is critical for comprehensive fiscal accountability. This study analyzed (1) the feasibility of obtaining accurate hospital cost data specific for complications and (2) the outcome in terms of fully loaded hospital costs generated in the management of the most common surgical complications associated with pacemaker and nonthoracotomy implantable defibrillator therapies. Between July 1989 and September 1994, a total of 1031 pacemaker and 105 implantable defibrillator procedures were performed by a cardiac surgeon in a tertiary-level teaching hospital setting. The additional fully loaded hospital costs were determined by (1) correlating clinical data from the complete medical record with complete hospital charge data for the admission(s) related to the complication, (2) carving out complication-related charges based on the clinical data, (3) converting complication-related charges to fully loaded costs based on conversion factors in effect at the time of service, and (4) correlating cost with hospital net reimbursement and payor source. The feasibility study determined that accurate and reliable cost data specific to complications can be obtained, although the process was cumbersome and difficult. The outcomes study determined that mean fully loaded complication costs were $4345 +/- $1540 for pacemaker lead revision and $4879 +/- $3167 for implantable defibrillator lead dislodgement, $24,459 +/- $14,585 for pacemaker infection, and $13,736 +/- $12,505 for defibrillator generator system malfunction. The one infected defibrillator cost $57,213 to treat. Costs exceeded reimbursement for almost all Medicare patients with complications in this study, suggesting that similar shortfalls would occur under a capitation scheme. This information is critical to a complete understanding of the financial impact of interventional procedures in a capitated reimbursement environment.

Adult↗
PubMed1998

Clinical experience with downsized lower energy output implantable cardioverter defibrillators. Ventak Mini II Clinical Investigators.

BACKGROUND AND STUDY OBJECTIVE: Technical improvements in cardioverter defibrillators technology has resulted in decrease in can size coupled with improved electrodes technology. A decrease in maximum energy output allows further decrease in device size. The aim of this study was to evaluate the feasibility of a single lead transvenous implant employing a downsized cardioverter-defibrillator (volume 59 cm3), with a related decrease in maximum energy output (29-31 joules as stored energy and 25-27 joules as delivered energy). METHODS AND RESULTS: Fifty-five patients with ventricular tachyarrhythmias were enrolled in 17 European institutions for implantation. At implantation step-down defibrillation threshold (DFT) was determined and the device was implanted only if a safety margin > or =10 joules was maintained between DFT and maximum programmable output. Implantation was performed in 54 of the 55 referred patients (98%) in a single electrode-device configuration. Step-down DFT testing was performed in 44 patients (43 finally implanted) and DFT was 7.77+/-4.41 joules (range 3-20). In 20 of the tested patients (45%) DFT was < or =5 joules, in 26 patients (59%) was < or =8 joules and in 34 patients (77%) it was < or =10 joules. No differences were found in DFT comparing patients with left ventricular ejection fraction < or = or >40% or patients treated or not with antiarrhythmic drugs or beta-blockers. Mean implant duration was 85+/-34 min. CONCLUSIONS: Employing a downsized cardioverter defibrillator, successful transvenous implantation can be achieved in 98% of the patients, with maintenance of adequate defibrillation safety margins despite a reduction in stored energy to 29 joules.

Adult↗
PubMed2003

Biphasic and monophasic shocks for transthoracic defibrillation: a meta analysis of randomised controlled trials.

INTRODUCTION: Biphasic waveforms are routinely used for implantable defibrillators. These waveforms have been less readily adopted for external defibrillation. This study was performed in order to evaluate the efficacy and harms of biphasic waveforms over monophasic waveforms for the transthoracic defibrillation of patients in ventricular fibrillation (VF) or haemodynamically unstable ventricular tachycardia. METHODS: Studies included randomised controlled trials comparing monophasic and biphasic external defibrillation for participants with VF or hemodynamically unstable ventricular tachycardia. Seven trials (1129 patients) were included in the analysis. All trials were conducted during electrophysiology procedures or implantable cardioverter/defibrillator testing. RESULTS: Compared with 200 J monophasic shocks, 200 J biphasic shocks reduced the risk of post-first shock asystole or persistent VF by 81% (relative risk (RR) 0.19; 95% confidence intervals (CI) 0.06-0.60) for the first shock. Reducing the energy of the biphasic waveform to 115-130 J resulted in similar effectiveness compared with the monophasic waveform at 200 J (RR 1.07, CI 0.66-1.74). Low energy biphasic shocks produce less myocardial injury than higher energy monophasic shocks as determined by ST segment deflection after shock. CONCLUSIONS: Biphasic waveforms defibrillate with similar efficacy at lower energies than standard 200 J monophasic waveforms, and greater efficacy than monophasic shocks of the same energy. Available data suggests that lower delivered energy and voltage result in less post-shock myocardial injury.

Defibrillators, Implantable↗
PubMed1997

High incidence of appropriate implantable cardioverter-defibrillator therapy in patients with syncope of unknown etiology and inducible ventricular arrhythmias.

OBJECTIVES: This study evaluates the hypothesis that in patients with syncope of unknown origin, inducible ventricular arrhythmias are specific arrhythmias and therefore should be appropriately treated. BACKGROUND: Although syncope is a common clinical entity, the evaluation and treatment of patients with syncope without a clear etiology are not well defined. Many patients with syncope of undetermined origin undergo invasive electrophysiologic evaluation. Abnormalities of the sinus node, prolongation of conduction times or inducible arrhythmias found at these evaluations are usually assumed to be the cause of syncope and are therefore treated. However, whether tachyarrhythmias are truly the cause of syncope, and whether treatment of these tachyarrhythmias can prevent recurrent syncope and arrhythmic death, is unknown. METHODS: This study included 50 consecutive patients with syncope of undetermined origin, ventricular tachyarrhythmias at electrophysiologic evaluation and treatment with an implantable cardioverter-defibrillator. RESULTS: Ventricular stimulation led to sustained monomorphic ventricular tachycardia in 36 patients, nonsustained ventricular tachycardia in 5 and ventricular fibrillation in 9. Over a 23 +/- 15-month (mean +/- SD) follow-up period, 18 patients received appropriate implantable cardioverter-defibrillator shock. Actuarial probability of appropriate therapy was 22% at 1 year and 50% at 3 years. Recurrent syncope was seen in five patients, three of whom had appropriate defibrillatory detections at the time of syncope. Four patients died (sudden death in one, congestive heart failure in two). CONCLUSIONS: In patients with syncope of undetermined origin and inducible ventricular tachyarrhythmias, appropriate implantable cardioverter-defibrillator therapy is common at follow-up. Sudden cardiac death is uncommon. This low incidence of sudden cardiac death and high incidence of appropriate defibrillator therapy support the current practice of using implantable cardioverter-defibrillators in patients with syncope of unknown origin and inducible ventricular arrhythmias.

Adult↗
PubMed2003

Prospective randomized comparison of 65%/65% versus 42%/42% tilt biphasic waveform on defibrillation thresholds in humans.

BACKGROUND: The waveform tilt of biphasic shocks yielding the lowest defibrillation threshold (DFT) is not well defined. Some evidence indicates that tilts less than 65% may improve DFTs. METHODS: In 57 patients undergoing ICD implantation, DFTs were determined with truncated exponential biphasic waveform tilts at 65%/65% and at 42%/42%. An external defibrillator with custom software was used for testing. The effective capacitance of the defibrillator was 132-microF for both waveforms. DFTs were determined using a binary search method starting with 12 Joules (J). Patients were randomly assigned to initial testing with either one of the two tilts. Thirty patients (Group 1) were tested with a two electrode (active can to RV coil, or SVC coil to RV coil) and 27 patients (Group 2) were tested with a three electrode system (subcutaneous patch or active can + SVC coil to RV coil). RESULTS: Groups 1 and 2 did not differ in age, ejection fraction or antiarrhythmic medications. Group 1 delivered energy DFTs were 10.1 +/- 5.5 J with the 65%/65% tilt and 10.1 +/- 5.9 J for the 42%/42% tilt (p = 0.92). In group 2 the average DFT for the 65%/65% tilt was 8.4 +/- 5.7 J and for the 42%/42% tilt was 8.1 +/- 5.3 J (p = 0.70). There were no significant differences in DFTs for either group. The system impedance for Group 1 was 64 +/- 12 ohms and for Group 2 was 39 +/- 6 ohms (p < 0.0001). CONCLUSIONS: We found no differences in DFTs between 65%/65% tilt and 42%/42% tilt using either 2- or 3-electrode defibrillation systems. Further research is needed to optimize waveforms in order to minimize DFTs, which will result in smaller ICDs and/or greater safety margins for defibrillation.

Aged↗