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PubMed2002

Lack of benefit of an active pectoral pulse generator on atrial defibrillation thresholds.

INTRODUCTION: Atrial defibrillation can be achieved with standard implantable cardioverter defibrillator leads, which has led to the development of combined atrial and ventricular devices. For ventricular defibrillation, use of an active pectoral electrode (active can) in the shocking pathway markedly reduces defibrillation thresholds (DFTs). However, the effect of an active pectoral can on atrial defibrillation is unknown. METHODS AND RESULTS: This study was a prospective, randomized, paired comparison of two shock configurations on atrial DFTs in 33 patients. The lead system evaluated was a dual-coil transvenous defibrillation lead with a left pectoral pulse generator emulator. Shocks were delivered either between the right ventricular coil and proximal atrial coil (lead) or between the right ventricular coil and an active can in common with the atrial coil (active can). Delivered energy at DFT was 4.2 +/- 4.1 J in the lead configuration and 5.0 +/- 3.7 J in the active can configuration (P = NS). Peak current was 32% higher with an active can (P < 0.01), whereas shock impedance was 18% lower (P < 0.001). Moreover, a low threshold (< or = 3 J) was observed in 61% of subjects in the lead configuration but in only 36% in the active can configuration (P < 0.05). There were no clinical predictors of the atrial DFT. CONCLUSION: These results indicate that low atrial DFTs can be achieved using a transvenous ventricular defibrillation lead. Because no benefit was observed with the use of an active pectoral electrode for atrial defibrillation, programmable shock vectors may be useful for dual-chamber implantable cardioverter defibrillators.

Atrial Fibrillation↗
PubMed1996

Implantable cardioverter-defibrillator advances.

Significant advances in the basic science of implantable cardioverter-defibrillator therapy have led to improvements in defibrillation waveforms and in capacitor technology. Nonthoracotomy devices with biphasic waveforms can be implanted with a near 100% success rate. Although fewer patients with implantable cardioverter-defibrillators are being treated with concomitant antiarrhythmic drug therapy, sotalol appears to decrease the defibrillation threshold. Controversy still exists over the optimal design for defibrillator sensing leads. Tachyarrhythmia detection enhancement increase specificity for sensing ventricular tachycardia but may risk undersensing. A variety of subsets of patients receiving implantable cardioverter-defibrillators have been identified; patients presenting with ventricular fibrillation appear to have the most unfavorable prognosis. Controversy exists as to the true impact of implantable cardioverter-defibrillator therapy on subsequent survival. Randomized clinical trials such as AVID (Antiarrhythmics Versus Implantable Defibrillators) are designed to determine the true benefits of implantable cardioverter-defibrillators and may lead to expanded indications.

Anti-Arrhythmia Agents↗
PubMed2004

Effect of digital cellular phones on tachyarrhythmia analysis of automated external defibrillators.

OBJECTIVES: Emergency services personnel, family members, laypersons or patients often carry and use mobile phones on sites of emergencies. As there are reported effects on implanted pacemakers and cardioverter defibrillators, the influence of digital cellular phones on automated external defibrillators was studied. METHODS: Twelve automated external defibrillator models were bench tested for their correct decision to or not to advise a shock, while being exposed to electromagnetic interference from a handheld cellular phone with 2 W or a portable cellular phone with 8 W transmitting power. The phones were programmed by a special subscriber identity module card to maximum output power with a carrier frequency of 906.2 MHz. The tests were conducted with a burst frequency of 217 Hz in speech mode and 2-8 Hz in discontinuous transmitting exchange mode. The sensitivity and specificity of electrocardiogram analysis systems were tested, with shockable and non-shockable rhythms provided by an electrocardiogram simulator and on two human subjects with normal sinus rhythm. RESULTS: A total of 8640 tests were recorded, each automated external defibrillator was tested a total of 720 times. The automated external defibrillators demonstrated a sensitivity of 100% and a specificity of 100%, representing a positive likelihood ratio of 8641 and a negative likelihood ratio of 0.000. In this setting all automated external defibrillators analysed correctly even under worst-case testing conditions, and performed excellently without any single failure. In some devices, voice prompts were distorted beyond comprehension, as the coil of the automated external defibrillator speaker received the pulsed signals. CONCLUSION: Shock advisory systems of automated external defibrillators are not susceptible to electromagnetic interference of 900 MHz cellular phones. Voice prompts, however, could be distorted by the operation of nearby digital mobile phones. During automated external defibrillator training this issue needs to be addressed.

Cell Phone↗
PubMed2007

Cost-effectiveness of automated external defibrillators in public places: con.

PURPOSE OF REVIEW: To discuss the clinical effectiveness, public health impact and cost-effectiveness of public access defibrillation. RECENT FINDINGS: High rates of survival from prehospital ventricular fibrillation have been documented in patients treated by first responders using automated external defibrillators. The recent Public Access Defibrillation trial demonstrated a doubling of cardiac arrest survival in community units where volunteers trained in cardiopulmonary resuscitation were additionally equipped with automated external defibrillators. The cost-effectiveness analysis of the Public Access Defibrillation trial has not yet been published, and previous analyses have lacked full data on cost, outcome, or both. Data from many sources indicate that automated external defibrillator placement at sites with an expected rate of one cardiac arrest per defibrillator per 5 years, as recommended by the American Heart Association, addresses only around 1-2% of prehospital arrests, and will have a minimal impact on population survival. SUMMARY: While highly targeted provision of automated external defibrillators in areas of greatest risk, such as casinos and airports, may be cost-effective, it will have little impact at a population level. Provision of more widespread public access defibrillation to sites with lower incidence of cardiac arrest is unlikely to be cost-effective, and may represent poorer value for money than alternative healthcare interventions in coronary artery disease.

Cost-Benefit Analysis↗
PubMed1996

Thoracoscopic approach to implantable cardioverter defibrillator patch electrode implantation.

Even if transvenous lead system for automatic implantable cardioverter defibrillators (ICDs) has been one of the main surgical advances in the recent past, its major limitation is the high defibrillation thresholds in some cases. Thus, an additional patch may be required and implanted either in a subcutaneous position or in an epicardial position. We describe another possibility: the implantation of extrapericardial patch under video-thoracoscopic control. This new technique allows a deep implantation of the whole material without thoracotomy. Seven patients were included in our preliminary experience. During defibrillation threshold evaluation, two patients required 34 J with the single transvenous lead system, and five patients were not defibrillated with the single lead system; therefore, they required a 300-J external rescue shock. We decided to implant an additional patch in those seven patients with high defibrillation thresholds. This patch was inserted into the pleural cavity through a left subcostal incision. Under video thoracoscopy, it was positioned and stitched onto the pericardium. The defibrillation generator was then implanted through the left subcostal incision in a subdiaphragmatic space. As a result, preoperative defibrillation thresholds were significantly reduced (14.29 +/- 3.45 J, mean +/- SD) and remained stable during follow-up controls (eighth day and second month). Long-term follow-up (14 +/- 4.5 months) was uneventful, with an excellent tolerance for the patients. In conclusion, extrapericardial implantation of defibrillation patches under video thoracoscopy is an easy technique that allows low defibrillation thresholds.

Adult↗
PubMed1997

Biphasic waveforms for ventricular defibrillation: optimization of total pulse and second phase durations.

Waveform parameters may affect the efficacy of ventricular defibrillation. Certain biphasic pulse waveforms are more effective for ventricular defibrillation than monophasic waveforms, but the optimal biphasic waveform parameters have not been identified. The purpose of this study was to investigate the effects of total pulse duration and the duration of the second (negative) phase on voltage and energy defibrillation requirements using biphasic waveforms. Defibrillation efficacy was evaluated in an isolated rabbit heart model using the Langendorff technique. The biphasic waveform was a truncated exponential with the initial voltage of the second phase equal to 50% of the final voltage of the first phase. An up/down protocol was used to determine the 50% probability-of-success levels (E50) for delivered energy and initial voltage. First, using pulse waveforms with equal positive and negative phase durations, test waveforms with total durations of 4 ms (2 ms positive + 2 ms negative), 6 ms (3 + 3 ms), and 16 ms (8 + 8 ms) were compared to the control waveform of 8 ms (4 + 4 ms) in 30 experiments. Defibrillation voltage requirements with 4 ms (174 +/- 56 V) were higher (P = 0.001) compared to 8 ms (127 +/- 49 V). Defibrillation voltage requirements for the 6-ms and 16-ms waveforms were similar to the 8-ms control waveform. Delivered energies tended to be higher with the 4-ms waveform. A second series of 40 experiments were performed to compare monophasic (4 + 0 ms) and three asymmetric biphasic waveforms (4 + 2 ms, 4 + 8 ms, and 4 + 16 ms) to the symmetric control waveform (4 + 4 ms). The monophasic (2.15 +/- 1.21 J) and the 4 + 16 ms waveform (1.86 +/- 1.09 J) required higher energies (P < or = 0.05) than the control waveform (1.24 +/- 0.41 J and 0.87 +/- 0.7 J, respectively). The monophasic waveform also resulted in greater voltage requirements (223 +/- 64 V) compared to the control waveform (160 +/- 26 V) (P = 0.02). Energy and voltage requirements were similar for the 4 + 2 ms and 4 + 8 ms waveforms compared to the control. Defibrillation requirements with biphasic waveforms were affected by total and second phase duration. For waveforms with equal phase durations, total durations between 6-16 ms resulted in the lowest values for defibrillation. For waveforms with variable second (negative) phase durations, durations ranging from 50%-200% of the first phase did not affect defibrillation efficacy.

Animals↗
PubMed1997

Atrial fibrillation/flutter induced by implantable ventricular defibrillator shocks: difference between epicardial and endocardial energy delivery.

INTRODUCTION: We evaluated the incidence and energy dependence of atrial fibrillation/flutter (AF) induced by implantable ventricular defibrillator shocks in 63 patients tested in the operating room or electrophysiology laboratory. METHODS AND RESULTS: Defibrillator shocks were epicardial monophasic in 32 patients, and through an Endotak lead endocardial monophasic in 19 and biphasic in 12 patients. The epicardial and endocardial patient groups had similar clinical characteristics. A total of 517 defibrillator shocks were given. The epicardial group received 336 total defibrillator shocks and 10 +/- 6 shocks (mean +/- SD) per patient compared with the endocardial group, which received 181 total shocks and 6 +/- 4 defibrillator shocks per patient (P = 0.004). In the epicardial group, AF occurred in 13 (41%) patients and in 17 (5%) of the 336 shocks. No AF was induced with endocardial defibrillator shocks. The epicardial mean energy was 16 +/- 9 J, lower than the endocardial mean energy of 20 +/- 9 J (P < 0.004). In the epicardial monophasic group, energy correlated with AF induction. Each patient received 7 +/- 6 defibrillator shocks < 15 J and 4 +/- 2 shocks > or = 15 J, yet AF occurred in only 2.3% versus 9.6% (P < 0.05) of defibrillator shocks < 15 J and > or = 15 J, respectively. Of note, AF was not induced with energy < 4 J or > 31 J. CONCLUSIONS: In the epicardial configuration, AF induction is energy dependent, with an apparent lower and upper limit of vulnerability. AF induction by defibrillator shocks delivered through an Endotak lead is very rare, possibly related to an apparent upper limit of vulnerability of less energy, avoidance of thoracotomy, or different energy field distribution.

Adult↗
PubMed1999

A four-shock Bayesian up-down estimator of the 80% effective defibrillation dose.

INTRODUCTION: New defibrillation techniques are often compared to standard approaches using the defibrillation threshold. However, inference from thresholding data necessitates extrapolation from reactions to relatively ineffective shocks, an error prone procedure requiring large sample sizes for hypothesis testing and large safety margins for defibrillator implantation. In contrast, this article presents a clinically validated statistical model of a minimum error, four-shock defibrillation testing protocol for estimating the 80% effective defibrillation strength for a given patient (ED80). METHODS AND RESULTS: A Bayesian statistical model was constructed assuming that the defibrillation dose-response curve is sigmoidal, and the ED80 is between 150 and 750 V. The model was used to design a minimum predicted error testing protocol and estimates. To prospectively validate the testing protocol and estimates, 170 patients received voltage-programmed biphasic testing. Four fibrillation episodes were induced and terminated in each patient according to the Bayesian up-down protocol. In addition, a validation attempt was made at the estimated ED80 rounded up to the nearest 50 V. In order to estimate the safety margin, in 136 patients, a defibrillation attempt was made at the rounded ED80 + 100 V. Of the 170 attempts at the rounded ED80, 143 (84%) attempts terminated fibrillation. Of the 136 attempts at the rounded ED80 + 100 V, 133 (98%) were effective. CONCLUSIONS: The four-shock Bayesian up-down protocol is the first clinical protocol to accurately predict an ED80 voltage. A 100 V increment above the ED80 provides an adequate safety margin. This simple and accurate method for estimating a highly effective defibrillation dose may be a valuable tool for population-based clinical hypothesis testing, as well as defibrillator implantation.

Adult↗
PubMed1995

Position of epicardial patch electrodes for implantable defibrillation significantly affects shock strength requirements.

OBJECTIVE: To assess the impact of epicardial patch electrode position on internal defibrillation efficacy. METHODS: Two mesh patch electrodes (13 cm2) were positioned on the epicardium of acute, isoflurane-anesthetized pigs (n = 7, 40-47 kg). Defibrillation efficacy was determined for three different patch positions: P1 = anterior-basal right ventricle (RV) and lateral-apical left ventricle (LV); P2 = lateral RV and lateral LV; and P3 = anterior-basal septal region and posterior-apical septal region. To quantify defibrillation efficacy, single capacitor discharge, fixed-tilt (68%) biphasic waveforms were delivered to the heart 10 seconds after initiation of ventricular fibrillation. Initial shock intensities were selected using an up/down protocol. Conversion data were used to construct sigmoidal curves relating probability of defibrillation to energy delivered, peak voltage, and peak current in each animal. RESULTS: Mean peak voltage and current at 50% defibrillation probability were 40% higher for P2 than they were for either P1 or P3 (p < 0.05). Similarly, mean energy delivered was 75% higher for P2. In this pig model, position of epicardial patch electrodes affects defibrillation efficacy. CONCLUSION: Apical-to-basal shock vectors (P1 and P3) yielded significantly lower defibrillation shock strength requirements than did a lateral-wall-to-lateral-wall vector (P2), which was perpendicular to the intraventricular septum. These data may help explain the disparity in defibrillation thresholds observed in the human population of patients undergoing implantable cardioverter defibrillator testing with epicardial patch electrodes.

Animals↗
PubMed1993

Implications for present and future applications of the implantable cardioverter-defibrillator resulting from the use of a simple model of cost efficacy.

OBJECTIVE: To develop a model to assess the cost-efficacy of the implantable cardioverter defibrillator to prevent sudden death. The model must be sufficiently flexible to allow the use of cost and survival figures derived from different sources. SETTING: The study was conducted in a teaching hospital department of cardiology with experience of 40 implantable cardioverter defibrillator implants and a large database of over 500 survivors of myocardial infarction. PROCEDURE: The basic costs of screening tests, stay in hospital, and purchase of implantable cardioverter defibrillators were derived from St George's Hospital during 1991. To assess the cost-efficacy of various strategies for the use of implantable cardioverter defibrillators, survival data taken from published studies or from our own database. Implications of the national cost of the various strategies were calculated by estimating the number of patients a year requiring implantation of a defibrillator if the strategy was adopted. RESULTS: Use of implantable cardioverter defibrillators in survivors of cardiac arrest costs between 22,400 pounds and 57,000 pounds for each year of life saved. Most of the strategies proposed by the current generation of implantable cardioverter defibrillator trials have cost efficacies in the same range, and adoption of any one of these strategies in the United Kingdom could cost between 2 million pounds and 100 million pounds a year. Future technical and medical developments mean that cost-efficacy may be improved by up to 80%. Due to the limitations of screening tests currently available restriction on the use of implantable cardioverter defibrillators to those groups where it seems highly cost-effective will result in a small impact on overall mortality from sudden cardiac death. CONCLUSION: Present and possible future applications of the implantable cardioverter defibrillator seem expensive when compared with currently accepted treatments. Technical and medical developments are, however, likely to result in a dramatic improvement in cost efficacy over the next few years.

Clinical Trials as Topic↗
PubMed1993

Implantable transvenous cardioverter-defibrillators.

BACKGROUND: Implantable transvenous cardioverter-defibrillators offer a significant opportunity to decrease procedural morbidity and medical costs in the care of patients with life-threatening ventricular arrhythmias who otherwise would have required a sternotomy or thoracotomy for device insertion. The purpose of this study was to examine prospectively the safety, efficacy, and limitations associated with the use of a transvenously implanted, tiered-therapy cardioverter-defibrillator with antitachycardia pacing function in a consecutive population of 84 ventricular fibrillation (VF) and sustained ventricular tachycardia (VT) survivors. METHODS AND RESULTS: The index arrhythmia promoting transvenous cardioverter-defibrillator implantation was VF in 41 patients, VT in 27, and both VF and VT in 16. In each patient, transvenous defibrillation via a coronary sinus, a right ventricular, a superior vena caval, and/or a subcutaneous chest patch lead system was attempted. The pulsing methods used include two-electrode single-pathway pulsing or three-electrode dual-pathway simultaneous or sequential pulsing. A transvenous cardioverter-defibrillator was inserted if the defibrillation threshold (DFT) was < or = 20 J. Successful implantation of a transvenous cardioverter-defibrillator was possible in 80 of 84 (95%) patients. The mean implant DFT was 10.9 +/- 4.8 J. After cardioverter-defibrillator implantation, all patients were extubated in the operating room and sent to a standard telemetry ward for monitoring. No patient suffered a postoperative pulmonary complication or perioperative flurry of cardiac arrhythmias. Postoperative complications included lead dislodgments in eight, transient long thoracic nerve injury in one, asymptomatic left subclavian vein occlusion in two, asymptomatic small pericardial effusion in one, subcutaneous patch pocket hematomas in four, pulse generator pocket infection in one, and lead fracture in one. As experience was gained with the procedure, it was routine to discharge patients 3 days after surgery. The mean hospital stay was 6.0 +/- 2.4 days. Upon discharge, all patients returned to their prehospital activities including those with complications except for the patient with a pocket infection, who required intravenous antibiotic therapy. Patient survival using an intention-to-treat analysis was 98% over an 11 +/- 7-month follow-up period. During this time period, 31 of the 80 patients (39%) with transvenous lead systems were successfully treated by their device for sustained VT or VF. Antitachycardia pacing was used in 424 episodes of monomorphic VT and was successful in 371 (88%). All episodes of VF were aborted by the device. Antiarrhythmic drugs were used after device implantation in only eight of 80 patients (10%). CONCLUSIONS: Transvenous cardioverter-defibrillator implantation is practical in most candidates. Implant DFTs are usually low, surgical morbidity and postoperative complications are modest, therapy of VT and VF is efficient, and survival is excellent.

Algorithms↗
PubMed1993

Low-energy endocardial defibrillation using an axillary or a pectoral thoracic electrode location.

BACKGROUND: A significant proportion of patients receiving endocardial defibrillation lead systems must accept either high defibrillation thresholds (DFTs) with lower safety margins or lead implantation by thoracotomy. We examined the feasibility of achieving universal application of endocardial leads and lower defibrillation energy requirements by optimizing the lead system location in conjunction with biphasic shocks. METHODS AND RESULTS: Two defibrillation catheter electrodes were positioned in the right ventricle and superior vena cava. Thoracic patch electrodes were placed at three sites (apical, pectoral, and axillary). Fifteen-joule, 10-J, and 5-J bidirectional simultaneous biphasic shocks were delivered across three different triple electrode configurations (right ventricle, superior vena cava, and patch) after inducing ventricular fibrillation (VF), and DFT was determined. All patients in whom VF was reproducibly inducible (14 patients) could be reproducibly defibrillated at 15 J at one or more patch electrode locations. Fifteen-joule shocks were effective at three thoracic electrode locations in 12 patients and at two electrode locations in 6 patients. The lowest mean single-shock DFT was 8.1 +/- 3.8 J. In 4 patients, ventricular flutter was reproducibly induced and reverted at 15 J in all patients. Mean DFT for the axillary location was 8.3 +/- 3.5 J and was significantly lower than apical (12.8 +/- 5.6 J, P = .008) and pectoral (11.6 +/- 4.1 J, P < .04) patch locations. The probability of success was significantly higher at 10 J with axillary location (78% of patients, P < .03 compared with both other sites) and at 15 J (P < .05 compared with the apical location). Low-energy endocardial defibrillation (< or = 10 J) was feasible in 10 of 14 tested patients at more than 1 thoracic electrode location at 10 J, whereas only 1 of 7 successful patients could be reverted at more than 1 electrode location at 5 J (P < .02). CONCLUSIONS: The use of axillary or pectoral patch lead location can allow endocardial defibrillation with biphasic shocks at energies < or = 15 J in this lead configuration. Virtually universal application of endocardial defibrillation lead systems can be predicted from these data. Reduction in maximum pulse generator output to < or = 25 J using these two thoracic electrode locations with bidirectional shocks can be feasible and maintain an adequate safety margin and permit thoracic pulse generator implantation. Lowering endocardial defibrillation energy < 10 J requires increasing specificity of thoracic electrode location.

Aged↗
PubMed1997

Defibrillation efficacy of commercially available biphasic impulses in humans. Importance of negative-phase peak voltage.

BACKGROUND: Recent studies have shown that specifically shaped biphasic waveforms can lower energy requirements for ventricular defibrillation. We prospectively compared the defibrillation efficacy of three different biphasic wave shapes incorporated in three commercially available implantable defibrillators. The results led to the development of a second protocol in which the importance of negative-phase peak voltage and duration was investigated. METHODS AND RESULTS: Defibrillation threshold (DFT) testing using different biphasic waveforms was performed randomly on 42 patients undergoing implantation of a cardioverter-defibrillator for ventricular arrhythmias. In 23 patients (group 1), 3 waveforms were tested: a CPI waveform with 60% positive-phase (P1) tilt and 50% negative-phase (P2) tilt, a Medtronic waveform with 65% fixed tilt in both P1 and P2, and a Ventritex waveform with 60% P1 tilt and a P2 leading edge voltage equal to half of the P1 trailing edge voltage. In 19 patients (group 2), 3 biphasic waveforms with equal P1 tilt at 65% but shorter P2 duration or smaller P2 peak voltage were tested. The Endotak C 60 series lead system (CPI) was used in 11 patients in group 1 and 10 patients in group 2. A Transvene lead system (Medtronics) was used in the remaining patients. Stored energy required for defibrillation was significantly lower with the CPI waveform compared with the Ventritex waveform. In group 2, energy requirements were significantly increased for the waveform with a smaller P2 peak voltage, whereas a short P2 duration did not influence defibrillation success. CONCLUSIONS: Our results suggest that specifically shaped biphasic waveforms delivered from commercially available devices can affect energy requirements for defibrillation. More importantly, the amplitude of the P2 peak voltage may be a more critical determinant than the P2 duration for defibrillation success of biphasic waveforms in humans.

Aged↗
PubMedDate not supplied

Does device-based testing save time during automatic implantable cardioverter-defibrillator implantation?

BACKGROUND: Defibrillation testing can be done either via an external cardiac defibrillator or directly via the implanted defibrillator during implantation (device-based testing). The advantage of one testing methodology over the other has not been adequately studied. METHODS AND RESULTS: Seventy-four patients (72% men) were randomized into two groups depending on the defibrillation testing methodology used--external cardiac defibrillation and device-based testing groups. R-wave, pacing threshold, pacing impedance, defibrillation threshold, defibrillation pathway impedance and total procedure time were not significantly different between the two groups. CONCLUSIONS: Device-based testing did not significantly reduce the procedure time. Lead and defibrillation parameters were similar in both the groups; lead repositioning and replacement were required in three patients in the external cardiac defibrillation group.

Aged↗
PubMed1996

Direct comparison of monophasic, biphasic and sequential pulse defibrillation over a single current pathway.

BACKGROUND: Defibrillation waveform and its spatial and temporal distribution are important determinants of its efficacy. Previous comparisons of monophasic, biphasic and sequential waveforms have used one current pathway for monophasic and biphasic defibrillation and two pathways for sequential defibrillation thus confounding a direct comparison of the waveforms. DESIGN: This study compared monophasic, biphasic and sequential pulse defibrillation over a single current pathway using a nonthoracotomy and a thoracotomy lead system in a dog model. MAIN RESULTS: Eight mongrel dogs (mean weight 21.6+/-2.9 kg) first underwent nonthoracotomy defibrillation testing followed by a median sternotomy and implantation of two 13.9 cm2 epicardial patch electrodes posterior = cathode). Nonthoracotomy electrode configuration consisted of a right ventricular catheter (cathode) and a chest wall subcutaneous patch (anode). After 10 s of alternating current induced ventricular fibrillation, defibrillation was attempted with a test shock. Monophasic, biphasic and sequential shocks of 10 ms total duration were compared. Biphasic and sequential shocks consisted of two 5 ms components separated by 0.25 ms switch time constant. Four trials of five leading edge voltages were performed for each waveform and stepwise logistic regression analysis was used to determine 80% probability of successful defibrillation (E80). For epicardial defibrillation, E80s were monophasic 11.3+/-1.5 J; biphasic 7.9+/-1.2 J; and sequential 12.1+/-1.4 J. For nonthoracotomy defibrillation, E80s were monophasic 17.7+/-3.4 J; biphasic 13.8+/-3.3 J; and sequential 18.2+/-3.5 J. The mean E80 for biphasic pulses was significantly lower than monophasic or sequential pulses for either lead system. CONCLUSIONS: Biphasic pulses are superior to monophasic or sequential pulses delivered over a single current pathway.

Animals↗
PubMed2001

Improving survival from sudden cardiac arrest: the role of the automated external defibrillator.

CONTEXT: Sudden cardiac death is a major public health problem in the United States, and improving survival after out-of-hospital cardiac arrest has been the subject of intense study. Early defibrillation has been shown to be critical to improving survival. Use of automated external defibrillators (AEDs) has become an important component of emergency medical systems, and recent advances in AED technology have allowed expansion of AED use to nontraditional first responders and the lay public. OBJECTIVES: To examine advancements in AED technology, review the impact of AEDs on time to defibrillation and survival, and explore the future role of AEDs in the effort to improve survival following sudden cardiac arrest. DATA SOURCES: MEDLINE was searched for articles from 1966 through December 2000 (Medical Subject Headings: electric countershock, heart arrest, resuscitation, emergency medical services; keywords: automatic external defibrillator, automated external defibrillator, public access defibrillation). Reference lists of relevant articles, news releases, and product information from manufacturers were also reviewed. STUDY SELECTION: Initial MEDLINE search produced 4816 articles, from which 101 articles were selected for referencing based on having been published in a peer-reviewed journal and on relevance to the subject of the manuscript as determined by all 5 authors. DATA EXTRACTION: All studies were critically reviewed for relevance, accuracy, and quality of data and study design by all authors. DATA SYNTHESIS: Recent advances in AED technology and design have resulted in marked simplification of AED operation, improvements in accuracy and effectiveness, and reductions in cost. Use of AEDs by first responders and laypersons has reduced time to defibrillation and improved survival from sudden cardiac arrest in several communities. Initial studies of the cost-effectiveness of AED use in comparison with other commonly used treatments are favorable. CONCLUSION: The AED represents an efficient method of delivering defibrillation to persons experiencing out-of-hospital cardiac arrest and its use by both traditional and nontraditional first responders appears to be safe and effective. The rapidly expanding role of AEDs in traditional emergency medical systems is supported by the literature, and initial studies of public access to defibrillation offer hope that further improvements in survival after sudden cardiac death can be achieved.

Cost-Benefit Analysis↗
PubMed2003

Delaying defibrillation to give basic cardiopulmonary resuscitation to patients with out-of-hospital ventricular fibrillation: a randomized trial.

CONTEXT: Defibrillation as soon as possible is standard treatment for patients with ventricular fibrillation. A nonrandomized study indicates that after a few minutes of ventricular fibrillation, delaying defibrillation to give cardiopulmonary resuscitation (CPR) first might improve the outcome. OBJECTIVE: To determine the effects of CPR before defibrillation on outcome in patients with ventricular fibrillation and with response times either up to or longer than 5 minutes. DESIGN, SETTING, AND PATIENTS: Randomized trial of 200 patients with out-of-hospital ventricular fibrillation in Oslo, Norway, between June 1998 and May 2001. Patients received either standard care with immediate defibrillation (n = 96) or CPR first with 3 minutes of basic CPR by ambulance personnel prior to defibrillation (n = 104). If initial defibrillation was unsuccessful, the standard group received 1 minute of CPR before additional defibrillation attempts compared with 3 minutes in the CPR first group. MAIN OUTCOME MEASURE: Primary end point was survival to hospital discharge. Secondary end points were hospital admission with return of spontaneous circulation (ROSC), 1-year survival, and neurological outcome. A prespecified analysis examined subgroups with response times either up to or longer than 5 minutes. RESULTS: In the standard group, 14 (15%) of 96 patients survived to hospital discharge vs 23 (22%) of 104 in the CPR first group (P =.17). There were no differences in ROSC rates between the standard group (56% [58/104]) and the CPR first group (46% [44/96]; P =.16); or in 1-year survival (20% [21/104] and 15% [14/96], respectively; P =.30). In subgroup analysis for patients with ambulance response times of either up to 5 minutes or shorter, there were no differences in any outcome variables between the CPR first group (n = 40) and the standard group (n = 41). For patients with response intervals of longer than 5 minutes, more patients achieved ROSC in the CPR first group (58% [37/64]) compared with the standard group (38% [21/55]; odds ratio [OR], 2.22; 95% confidence interval [CI], 1.06-4.63; P =.04); survival to hospital discharge (22% [14/64] vs 4% [2/55]; OR, 7.42; 95% CI, 1.61-34.3; P =.006); and 1-year survival (20% [13/64] vs 4% [2/55]; OR, 6.76; 95% CI, 1.42-31.4; P =.01). Thirty-three (89%) of 37 patients who survived to hospital discharge had no or minor reductions in neurological status with no difference between the groups. CONCLUSIONS: Compared with standard care for ventricular fibrillation, CPR first prior to defibrillation offered no advantage in improving outcomes for this entire study population or for patients with ambulance response times shorter than 5 minutes. However, the patients with ventricular fibrillation and ambulance response intervals longer than 5 minutes had better outcomes with CPR first before defibrillation was attempted. These results require confirmation in additional randomized trials.

Adult↗
PubMed1998

Ventricular fibrillation-induced intracellular Ca2+ overload causes failed electrical defibrillation and post-shock reinitiation of fibrillation.

Despite high efficacy, electrical defibrillation shocks can fail or ventricular fibrillation (VF) is reinitiated after the application of the initial shock. The goal of this study was to determine whether [Ca2+]i overload, induced by VF itself, can cause failed electrical defibrillation and post-shock reinitiation of VF. For this purpose, we simultaneously measured [Ca2+]i transients (assessed by indo-1 fluorescence) and defibrillation energies (assessed by a modified implantable cardioverter defibrillator) in intact perfused rat hearts during pacing-induced sustained VF (10 min) in the absence of ischemia. We found that increasing [Ca2+]i during VF (by increasing [Ca2+]o from 3 to 6 mM) increased the defibrillation threshold (DFT) from 1.9 +/- 0.6 to 3.5 +/- 0.5 J/g (P<0.05) and also increased the total defibrillation energy (TDE) required for stabilization of sinus rhythm from 15.6 +/- 7.7 to 48.6 +/- 7.42 J/g (P<0.05). In addition, both DFT and TDE correlated linearly with [Ca2+]i (r=0.69 and 0.83, P<0.05). Furthermore, shortening the duration of VF from 10 to 1.5 min tended to limit [Ca2+]i overload and decreased TDE. Finally, all successful defibrillation shocks led to a sudden reduction of VF-induced [Ca2+]i overload (-115 +/- 3%). In contrast, failed shocks did not alter [Ca2+]i. Incomplete reduction of [Ca2+]i overload after initially successful shocks were often followed by synchronized spontaneous [Ca2+]i oscillations and subsequent reinitiation of VF. In conclusion, the present study showed for the first time that VF-induced [Ca2+]i overload can cause failed electrical defibrillation and post-shock reinitiation of VF. Because VF inevitably causes [Ca2+]i overload, this finding might be a crucial mechanism of failed defibrillation and spontaneous reinitiation of VF.

Animals↗