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PubMed1994

Early defibrillation by police: initial experience with measurement of critical time intervals and patient outcome.

STUDY OBJECTIVE: To assess the feasibility of consistent acquisition of precise and clinically important time intervals in a city police department defibrillation study. DESIGN: On a daily basis, clocks at 911 dispatch were synchronized with those at ambulance dispatch, and all clocks on all defibrillators were synchronized to this time. Times were obtained from recordings at dispatch centers and from defibrillator memory modules. SETTING: City with a population of 70,745 and an area of 30 square miles. PARTICIPANTS: All patients in ventricular fibrillation (VF) treated by police officers using semiautomated defibrillators. INTERVENTIONS: On receipt of a call at 911 dispatch, the nearest squad car was dispatched. If police arrived before the ambulance and a cardiac arrest was confirmed, the closest squad car with a defibrillator was dispatched. Police delivered up to three shocks before ambulance arrival. RESULTS: Of 44 patients in VF, 14 were initially treated by police. Seven of 14 regained a spontaneous circulation with police shocks and seven required additional advanced life support care for restoration of pulses. Ten of the 14 were discharged home. The 911 call-to-shock time interval was 4.9 +/- 1.3 minutes for the seven who regained a spontaneous circulation with police shocks and 6.1 +/- 0.7 minutes for the seven without restoration of pulses by police (P = .035, one-sided, two-sample t-test). CONCLUSION: Acquisition of precise times for determination of time intervals is feasible with a concerted effort to synchronize all clocks from which times are derived. Even small differences in call-to-shock time intervals appear to be critical determinants of restoration of a spontaneous circulation.

Aged↗
PubMed1999

Predicting the relative efficacy of shock waveforms for transthoracic defibrillation in dogs.

STUDY OBJECTIVE: Previous work has shown that a passive membrane model using a parallel resistor-capacitor circuit is capable of predicting optimal waveforms for transvenous defibrillation. This study tested the ability of that model to predict optimal waveforms for transthoracic defibrillation. METHODS: This study was divided into 3 parts, each of which determined transthoracic defibrillation thresholds (DFTs) in 6 dogs for several different waveform shapes and durations. For each part, strength-duration relationships were determined from both experimental and model data and then compared with test model predictions. Part 1 DFTs were determined at various durations for 3 different monophasic waveforms-the ascending ramp, descending ramp, and square waveform. Part 2 DFTs were determined for 3 biphasic waveforms. Phase 1 was a 30-ms ascending ramp, and phase 2 was an ascending ramp, a descending ramp, or a square waveform. Part 3 DFTs were determined for 3 biphasic waveforms with very short second-phase durations. Phase 1 was a 30-ms ascending ramp, and phase 2 was a descending ramp. RESULTS: For part 1, the model was able to predict the relative defibrillation efficacy of the 3 monophasic waveforms ( P < .05). For parts 2 and 3, the model was able to predict the biphasic waveforms with the lowest DFTs. These predictions were based on the criterion that the model response at the end of the second phase should return to or slightly pass the model response value at the beginning of the first phase. CONCLUSION: The resistor-capacitor model successfully predicted the relative defibrillation efficacy of several different waveforms delivered transthoracically.

Analysis of Variance↗
PubMed1999

Effect of application of force to self-adhesive defibrillator pads on transthoracic electrical impedance and countershock success.

STUDY OBJECTIVE: To examine the effect of the application of force to self-adhesive defibrillator pads on transthoracic electrical impedance and countershock success. METHODS: A prospective, randomized, controlled pilot study was carried out in an experimental animal laboratory, involving 32 mixed-breed swine weighing 36.5 to 55.7 kg each. Ventricular fibrillation (VF) was induced, and the animals were randomly allocated to 1 of 4 groups, with 8 animals per group. Animals in groups I and II remained in VF for 30 seconds; those in groups III and IV remained in VF for 5 minutes. At the end of the VF period, up to 3 countershocks were given. In groups I and III, countershocks were delivered through the self-adhesive defibrillator pads alone; in groups II and IV, they were delivered through the defibrillator pads with 25 lb of applied force. Any animal without return of spontaneous circulation after 3 countershocks was given epinephrine after 1 minute of CPR, followed by 1 additional minute of CPR and 1 additional countershock if required. RESULTS: The main measurements included baseline and countershock transthoracic impedance, cumulative countershock success rate, and 30-minute survival rate. Application of 25 lb of force to the defibrillator pads significantly decreased transthoracic impedance, compared with baseline values (group II, 15. 1% decrease; group IV, 16.1% decrease). The first-shock success rate was higher when force was applied during the countershock (87.5% versus 50% for groups II and I, respectively; 62.5% and 37.5% for groups IV and III, respectively). In the animals who experienced 5 minutes of VF, there were greater rates of success after the second, third, and fourth countershocks when force was applied (group IV) than when no force was applied (group III). Groups I and II (VF for 30 seconds) demonstrated 100% survival at 30 minutes. Group IV had a higher 30-minute survival rate (3/8 animals) than did group III (1/8). However, the rates of countershock success and 30-minute survival were not statistically different among the groups. CONCLUSION: Application of force to self-adhesive defibrillator pads decreases transthoracic impedance during countershock. This effect may contribute to improving the countershock success rate.

Animals↗
PubMed2001

Does electrode polarity alter the energy requirements for transthoracic biphasic waveform defibrillation? Experimental studies.

BACKGROUND: Electrode polarity may alter the success of biphasic shocks from implantable systems. Whether the electrode polarity influences the success of transthoracic biphasic defibrillation is unknown. We determined the effect of electrode polarity on biphasic transthoracic defibrillation in a porcine model. METHOD: In ten anesthetized adult pigs, 16-28 kg, electrode pads were placed in two different orientations on the chest wall; apex-right parasternal and sternal-vertebral column. Ventricular fibrillation (VF) was electrically induced and allowed to persist for 30 s. Truncated exponential biphasic shocks (5/3 ms) were delivered at 20, 30, 50, 70 and 100 J. Four shocks at each energy level were delivered to construct energy vs. % success curves for VF termination. Electrode polarity for the first pulse was varied so that the first pulse cathode was either the apex (for apex-parasternal) or sternum (for sternum-vertebral column), or the reverse. The second pulse polarity was always the opposite of the first. RESULTS: VF termination success rose from 0 to 86% as energy increased from 20 to 100 J. Varying the electrode polarity did not alter success rates at any energy level with either electrode pad placement. CONCLUSION: In this porcine model of transthoracic defibrillation, varying the biphasic shock electrode polarity did not alter transthoracic defibrillation success. Positional labeling of transthoracic biphasic defibrillation electrode pads may be unnecessary.

Animals↗
PubMed2003

The acquisition and maintenance of defibrillation skills by lay first responders.

OBJECTIVE: Non-traditional and lay first responders increasingly are being trained in the skill of defibrillation. With simplification of new devices, there is a need to determine optimal first responder selection and training and maintenance of this important skill. These issues are of prime importance for the St John Ambulance Australia Operations Branch which already has a substantial first response defibrillation programme. DESIGN: We trained 12 trainers (3 h and 30 min), who subsequently instructed 41 further first responders (2 h and 30 min), a total group with a broad range of pre-existing experience and skill level, in the use of an automated external defibrillator (AED). Acquisition and maintenance of the AED skill was determined by four criteria at three monthly intervals. RESULTS: St John first responders with higher qualification levels were more likely to acquire the skill of defibrillation successfully (r=0.37, P<0.05). However, once acquired, the skill was easily maintained by virtually all (98%) members. A positive correlation was noted between the overall score achieved at the 6-month re-assessment and the number of times members had taken an AED 'on duty' (r=0.31, P<0.05). CONCLUSION: For St John first responders proficient in cardiopulmonary resuscitation (CPR), the skill of defibrillation with an AED is readily acquired and maintained. While less experienced members may be less likely to acquire the skill initially, once acquired the skill is equally maintained by all, provided ongoing 'on duty' exposure is available.

Australia↗
PubMed2003

Results of the introduction of an automated external defibrillation programme for non-medical personnel in Galicia.

OBJECTIVES: To describe the plan and development of a programme for the introduction of automated external defibrillation for non medical personnel and to report the results of the first 10 months of activity in a community which is predominently rural, such as Galicia. METHODS: The plan for introduction of the project included aspects of logistics, training and control. We studied cardiac arrests, that were treated in basic life support ambulances (BLS-A) equipped with automated external defibrillators (AEDs), from 1st March to 31st December 2001. RESULTS: Our community benefits from pioneering legislation in Spain. During the 10 months of study, 28 AEDs were in service, mostly in urban areas. In all cases, a thorough control of the quality of the service in which AEDs was used was carried out. 12% of the patients, who were victims of sudden cardiac death (SCD) and were found in ventricular fibrillation (VF), survived and were discharged from hospital. However, the percentage of patients found in VF is only around 26%. This is due to long assistance intervals (from the call to the arrival on site), and an important delay from the moment when circulatory collapse takes place until the emergency service 061 is called, more than 5 min in half the cases. CONCLUSIONS: The programme followed for the introduction of AEDs in Galicia was adapted to the socio-demographic characteristics of the population. The prehospital emergency assistance model was developed, executed and controlled by the Public Emergency Health Foundation of Galicia 061 (PEHF-061). The overall results of our first 10 months experience with the automated external defibrillation programme were as to be expected. In general, they are comparable to other published reports; however, ways of shortening the times from the point of collapse to defibrillation must be found, mainly by training the population and through the extension of automated external defibrillation provision to other first responders.

Adult↗
PubMed2003

What is the optimal paddle force during paediatric external defibrillation?

INTRODUCTION: Transthoracic impedance (TTI) is a major determinant of transmyocardial current flow, and therefore, the success of defibrillation. European Resuscitation Council (ERC) paediatric guidelines recommend that 'firm' paddle force should be applied to the paddles during defibrillation. No study has yet established the optimal paddle force required to minimise TTI in children of different ages. METHODS: Eighty patients aged 10 weeks to 17 yrs undergoing general anaesthesia for routine surgery were studied. Using defibrillation paddles placed in an anterior-apical position, TTI (Omega) was measured for increasing values of force from 0.5 kgf (baseline) to 6.5 kgf. The optimal force, the force to achieve 95% of the overall reduction in TTI, was then determined. According to current guidelines, paediatric paddles (surface area 16 cm2) were used for infants (< or =10 kg) and adult paddles (82 cm2) for older children. Optimal force was then calculated for infants < or =10 kg, children >10 kg and < or =8 yrs and children 9-17 yrs age. RESULTS: Increasing paddle force from 0.5 kgf progressively decreased TTI. Optimal force using paediatric paddles was 2.9 kgf in infants. Optimal force using adult paddles was 5.1 kgf in children >10 kg but < or = 8 yrs and 5.3 kgf in children aged 9-17 yrs. CONCLUSIONS: Force is an important determinant of TTI and therefore, outcome of defibrillation. It is recommended that a minimum of 3 kgf be applied to paddles when defibrillating infants with paediatric paddles, and a minimum of 5 kgf be applied to all older children when adult paddles are used.

Adolescent↗
PubMed2003

Immediate defibrillation versus interventions first in a swine model of prolonged ventricular fibrillation.

OBJECTIVES: we compared time-dependent rescue shock success when delivered immediately, to defibrillation preceded by 3 min of CPR, with and without high dose epinephrine (HDE) in a swine model of prolonged ventricular fibrillation (VF). Our hypotheses were that pretreatment with CPR and HDE would produce higher rates of successful first-shock defibrillation and would prevent decay of the VF waveform, as measured by the scaling exponent (ScE), when compared to immediate defibrillation. We also sought to determine the predictive value of the ScE in determining post-shock outcomes. METHODS: we anesthetized and instrumented 60 domestic swine (19.6-26.4 kg). VF was induced electrically and was untreated for 8, 11 or 14 min. ECG was recorded digitally at a rate of 1000 samples/s with 5-s epochs used to calculate the ScE. We assigned randomly swine to seven groups (number denotes timing of first rescue shock). Three groups had rescue shocks as the first intervention (RSF) after 8 min of VF (RSF-8), 11 min of VF (RSF-11), or 14 min of VF (RSF-14): two groups had CPR for 3 min (then rescue shock) beginning at 8 min (CPR-11) or 11 min of VF (CPR-14); and two groups got CPR for 3 min with 0.1 mg/kg epinephrine (adrenaline) (then rescue shock) beginning at 8 min of VF (HDE-11) or 11 min of VF (HDE-14). Fixed-dose 70 J BDW rescue shocks were used for all shocks. Defibrillation outcome was classified immediately and 30 s post-shock as successful (either restoration of spontaneous circulation [ROSC] or restoration of organized electrical activity [ROEA]), or failed (remained in VF, or asystole). Data were analyzed with RMANOVA, multiple logistic regression, Fisher's exact tests, and ROC curves. RESULTS: successful first-shock defibrillation occurred in 3/8 (38%) RSF-8; 1/9 (11%) RSF-11; 2/9 (22%) CPR-11; 7/9 (77%) HDE-11; 0/9 (0%) RSF-14; 0/7 (0%) CPR-14; and 1/8 (13%) HDE-14, (p=0.059 IRS-8 vs. HDE-11). First-shock ROSC occurred in 5/9 (56%) HDE-11 animals, 1/8 (13%) HDE-14 and zero in all other groups (p=0.03). Mean ScE values at 11 min VF for the RSF-11 (1.46) was higher than both CPR-11 (1.26), and HDE-11 (1.27); and RSF-14 (1.60) was higher than CPR-14 (1.47) and HDE-14 (1.46); group by time p=0.002. ROC areas under the curves using the ScE as a predictor of shock outcome were 0.84 for immediate success, 0.85 for sustained success, and 0.81 for ROSC. CONCLUSIONS: HDE-11 showed a tendency for producing a higher rate of first-shock success and ROSC. Interventions prior to rescue shock prevented deterioration of the VF waveform and improved rescue shock outcomes. The ScE accurately predicted 81-85% of post-rescue shock outcomes.

Animals↗
PubMed1997

Automated external versus blind manual defibrillation by untrained lay rescuers.

INTRODUCTION: sudden cardiac death is an important cause of mortality in the United States today. A major determinant of survival from sudden cardiac death is rapid defibrillation. Communities with high rates of bystander cardiopulmonary resuscitation (CPR) and early defibrillation enjoy the highest survival rates from out-of-hospital cardiac arrest. First responders and emergency medical technicians (EMTs) have been trained to use external defibrillators (AEDs). The period of instruction for successful use of the AED remains to be determined. It was the purpose of this study to compare AED versus blind manual defibrillation (BMD) by untrained lay rescuers using a simple instruction sheet and following a 20-min training period. METHODS: 50 employed volunteers were confronted with a stimulated cardiac arrest and asked to attempt defibrillation using either AED or BMD by following a written instruction sheet. Success was defined as delivery of three countershocks during the simulated resuscitation. Time to first and third shocks were recorded. RESULTS: 24 of 25 volunteers (96%) were successful in operating the AED compared to none in the BMD group. Time to delivery of first shock averaged 119.5 +/- 45.0 s and time to third shock averaged 158.7 +/- 46.3 s. A 95% confidence interval for time to first shock for untrained lay rescuers was 100.5-138.4 s. CONCLUSIONS: untrained lay rescuers demonstrated a very high success rate using the AED during simulated cardiac arrest. Success with BMD by untrained rescuers is poor. This study suggests that prehospital personnel can be successfully trained in the use of AED in a substantially shorter period of time than in current practice. Strategic placement of AEDs like fire hoses and pool-side life preservers could result in improved survival from sudden cardiac death.

Ambulatory Care↗
PubMed1976

Blind defibrillation outside the hospital.

Blind defibrillation, defibrillation of an unconscious, pulseless adult without electrocardiographic verification of arrhythmia, allows early definitive treatment of cardiac arrest victims. Basic EMT-As have the ability to perform blind defibrillation in a prehospital setting, and place an esophageal obturator airway. When basic EMT-As are performing blind defibrillation, there should be a standard operating procedure involving diagnosis, defibrillation, CPR and re-evaluation.

Allied Health Personnel↗
PubMed1987

Nonthoracotomy internal defibrillation in dogs: threshold reduction using a subcutaneous chest wall electrode with a transvenous catheter electrode.

The efficacy of truncated exponential waveform shocks using a cardioverter-defibrillator catheter with and without a 13.9 cm2 subcutaneous thoracic patch electrode was examined in 10 pentobarbital-anesthetized dogs. The cardioverter-defibrillator catheter was positioned through the external jugular vein with the distal 4 cm2 shocking electrode located in the right ventricular apex and the 8 cm2 proximal electrode located in the superior vena cava. Four electrode configurations were tested: 1) distal electrode (cathode) to proximal electrode and chest wall patch (common anodes), 2) distal electrode (cathode) to chest wall patch (anode), 3) distal electrode (cathode) to proximal electrode (anode), and 4) chest wall patch (cathode) to proximal electrode (anode). The lowest randomized energy resulting in termination of alternating current-induced ventricular fibrillation on four trials at that energy was 20.2, 21.3, 27.4 and greater than 40 J, respectively, for configurations 1 through 4. The energy requirements for configurations 1, 2 and 3 were significantly lower than for configuration 4 (p less than 0.001). Additionally, configurations incorporating the distal electrode and the patch electrode (configurations 1 and 2) were significantly better than the catheter alone (configuration 3; p less than 0.05). There was no significant difference between configurations 1 and 2. In conclusion, the addition of a subcutaneous chest wall electrode to the cardioverter-defibrillator catheter significantly lowered energy requirements for defibrillation, suggesting that a nonthoracotomy approach for the automatic implantable cardioverter-defibrillator is feasible.

Animals↗
PubMedDate not supplied

Rapid on-site defibrillation versus community program.

INTRODUCTION: For patients who suffer out-of-hospital cardiac arrest, the time from collapse to initial defibrillation is the single most important factor that affects survival to hospital discharge. The purpose of this study was to compare the survival rates of cardiac arrest victims within an institution that has a rapid defibrillation program with those of its own urban community, tiered EMS system. METHODS: A logistic regression analysis of a retrospective data series (n = 23) and comparative analysis to a second retrospective data series (n = 724) were gathered for the study period September 1994 to September 1999. The first data series included all persons at Casino Windsor who suffered a cardiac arrest. Data collected included: age, gender, death/survival (neurologically intact discharge), presenting rhythm (ventricular fibrillation (VF), ventricular tachycardia (VT), or other), time of collapse, time to arrival of security personnel, time to initiation of cardiopulmonary resuscitation (CPR) prior to defibrillation (when applicable), time to arrival of staff nurse, time to initial defibrillation, and time to return of spontaneous circulation (if any). Significantly, all arrests within this series were witnessed by the surveillance camera systems, allowing time of collapse to be accurately determined rather than estimated. These data were compared to those of similar events, times, and intervals for all patients in the greater Windsor area who suffered cardiac arrest. This second series was based upon the Ontario Prehospital Advanced Life Support (OPALS) Study database, as coordinated by the Clinical Epidemiology Unit of the Ottawa Hospital, University of Ottawa. RESULTS: The Casino Windsor had 23 cases of cardiac arrests. Of the cases, 13 (56.5%) were male and 10 (43.5%) were female. All cases (100%) were witnessed. The average of the ages was 61.1 years, of the time to initial defibrillation was 7.7 minutes, and of the time for EMS to reach the patient was 13.3 minutes. The presenting rhythm was VF/VT in 91% of the case. Fifteen patients were discharged alive from hospital for a 65% survival rate. The Greater Windsor Study area included 668 cases of out-of-hospital cardiac arrest: Of these, 410 (61.4%) were male and 258 (38.6%) were female, 365 (54.6%) were witnessed, and 303 (45.4%) were not witnessed. The initial rhythm was VF/VT was in 34.3%. Thirty-seven (5.5%) were discharged alive from the hospital. CONCLUSION: This study provides further evidence that PAD Programs may enhance cardiac arrest survival rates and should be considered for any venue with large numbers of adults as well as areas with difficult medical access.

Aged↗
PubMed2002

Mexiletine related chronic defibrillation threshold elevation: case report and review of the literature.

Many antiarrhythmic drugs may produce a rise in defibrillation threshold. Mexiletine is a frequently used antiarrhythmic drug in patients with an implantable cardioverter defibrillator, usually thought of as producing no or minimal effects on the defibrillation threshold. The current case report presents a patient with an endocardial implantable cardioverter defibrillator being treated with mexiletine, which precluded the ability to defibrillate the patient.

Adult↗
PubMedDate not supplied

The impact of including passive benefits in cost-effectiveness analysis: the case of automated external defibrillators on commercial aircraft.

OBJECTIVE: Traditional cost-utility analysis assumes that all benefits from health-related interventions are captured by the quality-adjusted life-years (QALYs) gained by the few individuals whose outcome is improved by the intervention. However, it is possible that many individuals who do not directly benefit from an intervention receive utility, and therefore QALYs, because of the passive benefit (aka sense of security) provided by the existence of the intervention. The objective of this study was to evaluate the impact that varying quantities of passive benefit have on the cost-effectiveness of airline defibrillator programs. METHODS: A decision analytic model with Markov processes was constructed to evaluate the cost-effectiveness of defibrillator deployment on domestic commercial passenger aircraft over 1 year. Airline passengers were assigned small incremental utility gains (.001-.01) during an estimated 3-hour flight to evaluate the impact of passive benefit on overall cost-effectiveness. RESULTS: In the base case analysis with no allowance for passive benefit, the cost-effectiveness of airline automated external defibrillator deployment was US dollars 34000 per QALY gained. If 1% of all passengers received utility gain of.01, the cost-effectiveness declined to US dollars 30000. Cost-effectiveness was enhanced when the quantity of passive benefit was raised or the percentage of individuals receiving passive benefit increased. CONCLUSIONS: Automated external defibrillator deployment on passenger aircraft is likely to be cost-effective. If a small percentage of airline passengers receive incremental utility gains from passive benefit of automated external defibrillator availability, the impact on overall cost-effectiveness may be substantial. Further research should attempt to clarify the magnitude and percentage of patients who receive passive benefit.

Aircraft↗
PubMed2002

Atrial signal analysis and defibrillation threshold assessment in chronic persistent and reinduced atrial fibrillation.

INTRODUCTION: Induced versus spontaneous atrial fibrillation (AF) is of interest for assessing atrial defibrillation threshold reproducibility. METHODS AND RESULTS: Twenty-one patients with chronic AF underwent internal cardioversion with assessment of atrial defibrillation threshold at baseline and at reinduced AF. High right atrial (HRA) and coronary sinus (CS) bipolar recordings were analyzed to measure the mean local atrial period, its coefficient of variation, the 5th (P5) and 95th (P95) percentiles of atrial intervals, and the percentage of points lying at the baseline (number of occurrences), and to quantify AF organization. Atrial defibrillation threshold was comparable in baseline and reinduced AF in terms of leading-edge voltage and delivered energy. Baseline and reinduced AF were comparable with regard to overall signal parameters (both in HRA and CS) and the presence of an organized arrhythmia pattern. As for individual variables, P5 increased while P95 and coefficient of variation decreased in reinduced AF compared with spontaneous AF (statistical significance was achieved for all these parameters in HRA, but only for coefficient of variation and P95 in CS). CONCLUSION: Sustained AF reinduced after cardioversion of chronic AF is comparable with baseline AF in terms of atrial defibrillation threshold, atrial cycle length, and pattern of organization. Therefore, a clinical model based on reinduction of sustained AF after cardioversion is suitable for studying the effects of a series of interventions on atrial defibrillation threshold. However, because this model does not yield a form of AF with comparable indices of local refractoriness (e.g., P5), it is not recommended when analyzing local electrophysiologic properties.

Adult↗
PubMed2004

Improvement of defibrillation efficacy with preshock synchronized pacing.

INTRODUCTION: We previously demonstrated that wavefront synchronization by spatiotemporal excitable gap pacing (Sync P) is effective at facilitating spontaneous termination of ventricular fibrillation (VF). Therefore, we hypothesized that a spatiotemporally controlled defibrillation (STCD) strategy using defibrillation shocks preceded by Sync P can improve defibrillation efficacy. METHOD AND RESULTS: We explored the STCD effects in 13 isolated rabbit hearts. During VF, a low-voltage gradient (LVG) area was synchronized by Sync P for 0.92 second. For Sync P, optical action potentials (OAPs) adjacent to four pacing electrodes (10 mm apart) were monitored. When one of the electrodes was in the excitable gap, a 5-mA current was administered from all electrodes. A shock was delivered 23 ms after the excitable gap when the LVG area was unexcitable. The effects of STCD was compared to random shocks (C) by evaluating the defibrillation threshold 50% (DFT(50); n = 35 for each) and preshock coupling intervals (n = 208 for STCD, n = 172 for C). Results were as follows. (1) Sync P caused wavefront synchronization as indicated by a decreased number of phase singularity points (P < 0.0001) and reduced spatial dispersion of VF cycle length (P < 0.01). (2) STCD decreased DFT(50) by 10.3% (P < 0.05). (3) The successful shocks showed shorter preshock coupling intervals (CI; P < 0.05) and a higher proportion of unexcitable shock at the LVG area (P < 0.001) than failed shocks. STCD showed shorter CIs (P < 0.05) and a higher unexcitable shock rate at LVG area (P < 0.05) than C. CONCLUSION: STCD improves defibrillation efficacy by synchronizing VF activations and increasing probability of shock delivery to the unexcitable LVG area.

Animals↗
PubMed2005

Defibrillation depends on conductivity fluctuations and the degree of disorganization in reentry patterns.

UNLABELLED: Defibrillation depends on conductivity and disorganization. INTRODUCTION: Cardiac fibrillation is the deterioration of the heart's normally well-organized activity into one or more meandering spiral waves, which subsequently break up into many meandering wave fronts. Delivery of an electric shock (defibrillation) is the only effective way of restoring the normal rhythm. This study focuses on examining whether higher degrees of disorganization requires higher shock strengths to defibrillate and whether microscopic conductivity fluctuations favor shock success. METHODS AND RESULTS: We developed a three-dimensional computer bidomain model of a block of cardiac tissue with straight fibers immersed in a conductive bath. The membrane behavior was described by the Courtemanche human atrial action potential model incorporating electroporation and an acetylcholine- (ACh) dependent potassium current. Intracellular conductivities were varied stochastically around nominal values with variations of up to 50%. A single rotor reentry was initiated and, by adjusting the spatial ACh variation, the level of organization could be controlled. The single rotor could be stabilized or spiral wave breakup could be provoked leading to fibrillatory-like activity. For each level of organization, multiple shock timings and strengths were applied to compute the probability of shock success as a function of shock strength. CONCLUSIONS: Our results suggest that the level of the small-scale conductivity fluctuations is a very important factor in defibrillation. A higher variation significantly lowers the required shock strength. Further, we demonstrated that success also heavily depends on the level of organization of the fibrillatory episode. In general, higher levels of disorganization require higher shock strengths to defibrillate.

Acetylcholine↗
PubMedDate not supplied

Automatic adjustment of biphasic pulse duration in transthoracic defibrillation.

Many studies have proven that biphasic defibrillation pulses are more efficient than the damped sinusoid monopolar waveform. Transthoracic resistance was shown to change during the two phases. On the other hand, it was proven that transthoracic resistance plays an important role in the defibrillation process, yielding the current for selected energy or voltage. Pre-shock measurement of the resistance may lead to improved selection. Stabilized current defibrillators are of low stored-to-delivered energy ratio. Therefore, automatic dynamic adjustment of some defibrillator parameters with respect to transthoracic resistance changes seems rational. An approach is known for modifying the pulse duration, in order to deliver a selected energy. A method is proposed here and an experimental defibrillator is developed for dynamic pulse duration adjustment with the purpose of obtaining a desired optimal time-course of the cardiac cell transmembrane potential.

Animals↗