Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Defibrillators”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 577 records · Page 32Linked to original sources
PubMed1996

[New aspects of defibrillator therapy].

The implantable cardioverter defibrillator is currently a therapy of first choice in patients with malignant therapy refractory ventricular arrhythmias. The occurrence of malignant ventricular tachycardia cannot be suppressed by the defibrillator but is treated using antitachycardia pacing, cardioversion or defibrillation. During recent years, electrodes, defibrillation shockforms and device size were continuously optimized. The development of transvenous lead systems resulted in significant reduction of perioperative mortality and morbidity. With the availability of biphasic shockforms and single-lead unipolar devices marked reduction of defibrillation thresholds were achieved and transvenous lead systems without subcutaneous could be implanted. Improvements in device technology lead to smaller devices which can be implanted subpectorally even using local anaesthesia. But there is still enormous potential to develop an ideal antiarrhythmic device. One of the most significant problems of the defibrillator therapy represents the delivery of inappropriate shocks due to supraventricular tachyarrhythmias and sinustachycardia. To solve this problem different approaches are currently developed. Extension in memory allows to store several data logs and intracardiac electrograms for individual adapted adjustment of the therapy. Intracardiac electrogram width measurement for discrimination between ventricular and supraventricular arrhythmias is currently evaluated. Dual-chamber arrhythmia discrimination algorithms of an integrated dual-chamber pacemaker and defibrillator are clinically studied. Hemodynamic sensors for determining the severity of the arrhythmia are currently under experimental evaluation. The combination of latissimus dorsi dynamic cardiomyoplasty and ICD therapy may improve survival in patients with severely depressed left ventricular function and malignant ventricular arrhythmias. Several randomized prospective trials are currently in progress potentially expanding the use of the ICD in patients at risk for sudden cardiac death. The high costs of defibrillator therapy is still a limitation for its use, but higher production figures and advancing technology could reduce the system prize.

Anti-Arrhythmia Agents↗
PubMedDate not supplied

Vector magnitude using orthogonal ECG leads during ventricular fibrillation is associated with defibrillation outcome.

Random fluctuations of ventricular fibrillation (VF) affect defibrillation; in addition, the heart is more susceptible to defibrillation at a higher absolute VF voltage (AVFV). Shocks delivered at higher AVFV waveforms from a single lead of the electrocardiogram (ECG) are more effective than conventional shocks. The authors investigated a new sensing method using multiple leads for better representation of the depolarization state of the heart. In this non-thoracotomy defibrillation study, a vector waveform derived from three orthogonal surface leads X, Y, and Z was analyzed in real time using two distinct defibrillation lead configurations, P1: RV-coil electrode (-) <--> (SVC-coil electrode + SCP) (+); and P2: RV-coil electrode (+) <--> (SVC-coil electrode + SCP) (-), where (-) represents cathode and (+) anode for the first phase of biphasic shock (RV = right ventricle, SVC = superior vena cava, SCP = subcutaneous patch). A PC-based closed-loop waveform-processing system, the peak-shock method (PSM), was developed to analyze the vector waveforms and trigger a biphasic shock at an AVFV peak. In using this defibrillation technique, an empirical threshold was applied to a weight function consisting of short-term and long-term moving averages of the vector VF waveform. A total of 340 shock trials in nine canine studies resulted in a significantly higher defibrillation success rate for the PSM compared with the conventional random-shock method (RSM), which involved shocking after a fixed VF time (54% for the PSM versus 42% for the RSM, p < 0.03). This further confirms that a susceptible period for defibrillation occurs during VF. The hardware/software design satisfied the requirements for processing the VF vector waveform in real time, and with the help of signal-processing techniques the high VF voltage could be detected at it occurred in real time. In addition, the P2 defibrillation lead configuration was significantly better than the P1 (p < 0.006).

Algorithms↗
PubMed1998

Importance of preimplantation procedures in candidates for an implantable atrial defibrillator.

INTRODUCTION: Due to the limited efficacy of antiarrhythmic drugs for the treatment of atrial fibrillation, several nonpharmacologic therapeutic options have been developed. One of these options is an implantable atrial defibrillator for patients with severe symptoms and infrequent drug-refractory episodes of atrial fibrillation. The purposes of this study were: (1) to evaluate how many patients with atrial fibrillation are possible candidates for an implantable atrial defibrillator; and (2) to report the results and findings of preimplantation testing in a single center. METHODS AND RESULTS: From our atrial fibrillation outpatient clinic, we evaluated the number of possible candidates for an atrial defibrillator using the following criteria: (1) recurrent persistent atrial fibrillation; (2) long-lasting but infrequent episodes; (3) refractory to antiarrhythmic drugs; (4) capability of maintaining normal sinus rhythm; and (5) no factors increasing proarrhythmic risk. In those patients eligible for an atrial defibrillator, a separate preimplantation test was performed to evaluate atrial defibrillation limits and patient acceptance. Thirty-one of 196 patients were possible candidates for an atrial defibrillator. Fourteen of these 31 patients agreed to participate in the METRIX clinical study phase I on atrial defibrillators. Six of these patients met implantation criteria; two patients refused permanent implantation because of intolerable pain. Implantation was performed in four patients; however, one patient could not be cardioverted intraoperatively despite a successful preimplantation test. CONCLUSION: About 16% of selected patients with atrial fibrillation are possible candidates for an atrial defibrillator. However, successful preimplantation testing does not exclude implantation failure.

Aged↗
PubMed1993

Effects of defibrillation shock energy and timing on 3-D computer model of heart.

We present computer simulations of electrical defibrillation in a three-dimensional model of the ventricles of the heart. In this model, called HEARTSIM, the ventricles are represented by 1473 cubic elements with 3 mm sides. The action potential is described by five discrete states; absolutely refractory, three relatively refractory, and repolarized. Activation is propagated to an element's six orthogonal neighbors with the conduction velocity dependent on the refractory state of the neighbor. Delivery of several extra-stimuli with decrementing coupling intervals results in ventricular fibrillation. Following the onset of ventricular fibrillation, we simulate defibrillation using various electrode configurations, shock energies, and timings. The current density distributions in the heart model resulting from the defibrillation shocks are determined from finite element analysis of the electric fields produced by the delivery of high energy shocks. The simulations suggest that successful defibrillation shocks produce a short period of low activation followed by a complete cessation of activation for a duration of 387 +/- 162 ms. In contrast, unsuccessful shocks produce a significantly shorter period of low activation (70 +/- 12 ms) after which ventricular fibrillation resumes. HEARTSIM mimics the experimentally reported, highly variable response to near-threshold shocks--the energy for successful defibrillation varies widely (20.8 +/- 20.7 J). In addition, the success rate vs. energy curve has a sigmoidal shape that is consistent with experiments. We demonstrate that this variability in the energy requirement results from dynamic variability in the number of elements made refractory by the shock and the relative distribution of the activation pattern at the time of the shock. Further, we show that it may be possible to lower the defibrillation energy requirements by delivery of two successive low energy pulses. The most efficient timing for the second pulse corresponds to the repolarization of the elements that were excited by the first pulse. Thus, when the interval between the two pulses was 85 +/- 18 ms, the defibrillation threshold energy (DFE) is reduced by 30.7 +/- 10% with pulses of 10 ms duration, and 62.6 +/- 7.9% with pulses of 5 ms duration. Our simulations also show that there is a delicate balance of energy between the two pulses that must be reached in order to achieve energy reduction with double pulse defibrillation. In conclusion, HEARTSIM serves as a tool for studying the underlying mechanisms of the effects of DF shocks on ventricular arrhythmias, and assists in evaluation of improved strategies for shock delivery.

Action Potentials↗
PubMed1985

Improved internal defibrillation with twin pulse sequential energy delivery to different lead orientations in pigs.

Internal cardiac defibrillation with an intravascular catheter was compared with a new method for internal cardiac defibrillation using 2 pulses delivered in sequence directly to the myocardium. For the sequential pulses, the first pulse was passed through an intravascular catheter (Medtronic 6880), between the anode in the superior vena cava-atrial junction region and the cathode in the apex of the right ventricle. The second pulse was delivered between the catheter tip in the right ventricular apex as cathode and an oval plaque electrode (Medtronic TX-7) secured on the epicardium of the left ventricular free wall as anode. Defibrillation pulses were of truncated, trapezoidal waveform (65% tilt), separated by 1, 10 and 100 ms. Using the catheter alone, 36 normal pig hearts could be defibrillated by 44 J. However, 22 pig hearts (60%) could not be defibrillated with energies below 35 J. Defibrillation threshold was improved with sequential twin pulses, the improvement being dependent on pulse separation (42, 34 and 19 J, at 100-, 10- and 1-ms separation, respectively; F = 14.6, df = 2.29, p less than 0.01). In conclusion, sequential twin pulse defibrillation provides a considerable reduction in energy necessary for defibrillation in comparison to single pulses using the catheter alone. In this study, the optimal separation was 1 ms.

Animals↗
PubMed1995

Organizing and implementing a hospital-wide first-responder automated external defibrillation program: strengthening the in-hospital chain of survival.

First-responder automated external defibrillation (AED) in the hospital is consistent with the American Heart Association's (AHA) early defibrillation standard or care. With trained personnel and automated external defibrillators immediately available, early defibrillation should have a greater impact on survival than early cardiopulmonary resuscitation (CPR). Therefore, in our hospitals we modified basic life support to include automated external defibrillation (BLS-AED) for all personnel who are expected to respond to a cardiac arrest, with rapid defibrillation taking priority over CPR. We describe how we organized and implemented this hospital-wide first-responder BLS-AED program. Planning the process includes gaining support from key leaders who are responsible for resuscitation practice, and identifying the target audience of the training program. Hospital unit needs for AED or conventional defibrillation and equipment must be identified, the training program developed, and existing policies and procedures modified. Several barriers to implementation may exist. Education about the efficacy and safety of AED and experience once the BLS-AED program is in place can overcome attitudes and bias. Concerns about the cost of equipment and training must be addressed. Program evaluation may include patient issues such as measuring the time to the first defibrillation and patient outcome; as well as training and retention issues.

Adult↗
PubMed1989

Effects of flecainide on defibrillation thresholds in the anesthetized dog.

The effects of flecainide on defibrillation thresholds in 21 open chest, anesthetized dogs were studied. Defibrillation was accomplished using nontruncated exponential pulses delivered through two epicardial patches. Multiple shocks of varying energy were administered after 10 s of ventricular fibrillation in random order. The percent success was plotted against the energy delivered for each dog. A sigmoidal curve was fit to the data and the energy associated with 50% success (E50) calculated. Flecainide (n = 16) or saline solution (n = 5) was then infused and E50 again determined. Flecainide infusion produced mean (+/- standard error of the mean) plasma levels of 610 +/- 111 ng/ml. Defibrillation thresholds were obtainable in 10 of 16 dogs that received flecainide infusion. Flecainide infusion increased E50 by 75% (from 6.5 +/- 1.9 to 11.4 +/- 2.6 J) (P less than 0.05). Infusion of saline solution did not significantly affect defibrillation energy. Of 16 dogs that received flecainide infusion, 12 had one or more complications: 6 had ventricular fibrillation resistant to defibrillation, 6 developed severe hypotension after successful defibrillation and 5 had spontaneous ventricular fibrillation after successful defibrillation. These effects were not seen in any control dogs. Flecainide infusion significantly increases defibrillation threshold and has important adverse arrhythmic and hemodynamic effects in this experimental preparation.

Animals↗
PubMed1996

Transthoracic defibrillation: importance of avoiding electrode placement directly on the female breast.

OBJECTIVES: This study sought to determine the effect on transthoracic impedance of placement of defibrillation electrodes on the female breast versus adjacent to or under the breast. BACKGROUND: Transthoracic impedance is a major determinant of transthoracic current flow in defibrillation. For a given energy setting, a high transthoracic impedance reduces current flow and may adversely affect the ability of electric shocks to accomplish defibrillation. We hypothesized that the increased interelectrode tissue associated with placement of the apex defibrillation electrode on the female breast would result in increased transthoracic impedance compared with electrode placement lateral to or under the breast. METHOD: Transthoracic impedance was measured noninvasively by passing a 5-V, 31.25-kHz square wave current through the chest and comparing the low level current flow to known references. We measured transthoracic impedance associated with three different apex defibrillation electrode positions--on the breast, under the breast and lateral to the breast--in 25 women (brassiere size 34A to 48C, 25 to 75 years old, body weight 128 to 328 lb [58 to 148 kg] and 2 men. The measurements were taken with a modified defibrillator that accurately predicts transthoracic impedance without delivering an actual shock. The measurement sequence was random. RESULTS: The average measured transthoracic impedance with placement of the apex defibrillation electrode on the breast was 95 +/- 25 ohms (mean +/- SD), under the breast 84 +/- 17* ohms and lateral to the breast 83 +/- 20* ohms (asterisk indicates p < 0.01 vs. on the breast by analysis of variance). The study cohort was also classified into two groups: large breasted (brassiere size > or = 40) and small breasted (brassiere size < or = 39). The measured transthoracic impedances for the large-breasted group were 112 +/- 20 ohms for on the breast, 94 +/- 13* ohms for under the breast and 98 +/- 19* ohms for lateral to the breast. For the small breasted group, the similar transthoracic impedance measurements were 81 +/- 21, 77 +/- 16 and 71 +/- 13* ohms, respectively. CONCLUSIONS: In women, placement of the apex defibrillation electrode on the breast results in higher transthoracic impedance, which will reduce current flow. We recommend placing the apex electrode lateral to or underneath the breast.

Adult↗
PubMed2004

Is optimal paddle force applied during paediatric external defibrillation?

INTRODUCTION: Optimal paddle force minimises transthoracic impedance; a factor associated with increased defibrillation success. Optimal force for the defibrillation of children < or =10 kg using paediatric paddles has previously been shown to be 2.9 kgf, and for children >10 kg using adult paddles is 5.1 kgf. We compared defibrillation paddle force applied during simulated paediatric defibrillation with these optimal values. METHODS: 72 medical and nursing staff who would be expected to perform paediatric defibrillation were recruited from a University teaching hospital. Participants, blinded to the nature of the study, were asked to simulate defibrillation of an infant manikin (9 months of age) and a child manikin (6 years of age) using paediatric or adult paddles, respectively, according to guidelines. Paddle force (kgf) was measured at the time of simulated shock and compared with known optimal values. RESULTS: Median paddle force applied to the infant manikin was 2.8 kgf (max 9.6, min 0.6), with only 47% operators attaining optimal force. Median paddle force applied to the child manikin was 3.8 kgf (max 10.2, min 1.0), with only 24% of operators attaining optimal force. CONCLUSION: Defibrillation paddle force applied during paediatric defibrillation often falls below optimal values.

Body Weight↗
PubMed2005

A probabilistic neural network as the predictive classifier of out-of-hospital defibrillation outcomes.

INTRODUCTION: Although modern defibrillators are nearly always successful in terminating ventricular fibrillation (VF), multiple defibrillation attempts are usually required to achieve return of spontaneous circulation (ROSC). This is potentially deleterious as cardiopulmonary resuscitation (CPR) must be discontinued during each defibrillation attempt which causes deterioration in the heart muscle and reduces the chance of ROSC from later defibrillation attempts. In this work defibrillation outcomes are predicted prior to electrical shocks using a neural network model to analyse VF time series in an attempt to avoid defibrillation attempts that do not result in ROSC. METHODS: The 198 pre-shock VF ECG episodes from 83 cardiac arrest patients with defibrillation conversions to different outcomes were selected from the Oslo ambulance service database. A probabilistic neural network model was designed for training and testing with a cross validation method being used for the better generalisation performance. RESULTS: We achieved an accuracy of 75% in overall prediction with a sensitivity of 84% and a specificity of 65% using VF ECG time series of an order of 1 s in length. CONCLUSION: Pre-shock VF ECG time series can be classified according to the defibrillation conversion to a return of spontaneous circulation (ROSC) or No-ROSC.

Area Under Curve↗
PubMed2006

Effects of compression depth and pre-shock pauses predict defibrillation failure during cardiac arrest.

BACKGROUND: Cardiopulmonary resuscitation (CPR) and electrical defibrillation are the primary treatment options for ventricular fibrillation (VF). While recent studies have shown that providing CPR prior to defibrillation may improve outcomes, the effects of CPR quality remain unclear. Specifically, the clinical effects of compression depth and pauses in chest compression prior to defibrillation (pre-shock pauses) are unknown. METHODS: A prospective, multi-center, observational study of adult in-hospital and out-of-hospital cardiac resuscitations was conducted between March 2002 and December 2005. An investigational monitor/defibrillator equipped to measure compression characteristics during CPR was used. RESULTS: Data were analyzed from 60 consecutive resuscitations in which a first shock was administered for VF. The primary outcome was first shock success defined as removal of VF for at least 5s following defibrillation. A logistic regression analysis demonstrated that successful defibrillation was associated with shorter pre-shock pauses (adjusted odds ratio 1.86 for every 5s decrease; 95% confidence interval 1.10-3.15) and higher mean compression depth during the 30s of CPR preceding the pre-shock pause (adjusted odds ratio 1.99 for every 5mm increase; 95% confidence interval 1.08-3.66). CONCLUSIONS: The quality of CPR prior to defibrillation directly affects clinical outcomes. Specifically, longer pre-shock pauses and shallow chest compressions are associated with defibrillation failure. Strategies to correct these deficiencies should be developed and consideration should be made to replacing current-generation automated external defibrillators that require long pre-shock pauses for rhythm analysis.

Aged↗
PubMed1997

Low-energy endocardial defibrillation using dual, triple, and quadruple electrode systems.

The feasibility of achieving both universal application of nonthoracotomy leads and low (< or = 15 J) defibrillation energy requirements by optimizing lead system configuration for use with low-output (<30 J) biphasic shock pulse generators was examined. Sixteen patients (mean age 62 +/- 8 years and mean left ventricular ejection fraction of 38 +/- 15%) were included in the study. All patients had either experienced syncope with induced ventricular tachycardia (n = 4) or had documented sustained ventricular tachycardia (n = 7) or ventricular fibrillation (n = 5). Defibrillation threshold testing was performed in 2 stages on different days in these patients. In the first stage, 2 defibrillation catheter electrodes were positioned in the right ventricle and superior vena cava with an axillary cutaneous patch. Fifteen-joule, 10- and 5-J biphasic shocks were delivered across 3 different electrode configurations-right ventricle to superior vena cava, right ventricle to axillary patch, right ventricle to a combination of superior vena cava and axillary patch. In the second stage, an 80-ml can electrode was added subcutaneously in a pectoral location to the previous leads. Configurations compared were the right ventricle to pectoral can, and right ventricle to an "array"-combining superior vena cava, can, and axillary patch leads. The defibrillation threshold was determined using a step-down method. In stage 1, mean defibrillation threshold for the right ventricle to axillary patch (12.7 +/- 5.9 J) and right ventricle to superior vena cava plus axillary patch (9.8 +/- 5.2 J) configurations was lower than the right ventricle to superior vena cava configuration (14.2 +/- 6.4 J, p <0.05). In stage 2, the defibrillation was higher for the right ventricle to pectoral can (9.2 +/- 5.1 J) configuration compared with the right ventricle to the array (5.6 +/- 3.6 J, p < or =0.05). The right ventricle to array had the lowest defibrillation threshold, whereas the right ventricle to pectoral can was the best dual electrode system. Low-energy endocardial defibrillation (< or =10 J) was feasible in 72% of tested patients with > 1 electrode configuration at 10 J, whereas only 53% of successful patients could be reverted at >1 electrode configuration at 5 J (p <0.05). Reduction in maximum pulse generator output to < or =25 J using these electrode configurations with bidirectional shocks is feasible and maintains an adequate safety margin.

Aged↗
PubMed1995

Clinical efficacy and safety of atrial defibrillation using biphasic shocks and current nonthoracotomy endocardial lead configurations.

We undertook a prospective randomized clinical trial evaluating efficacy and safety of internal atrial defibrillation in patients with drug-refractory atrial fibrillation (AF). Consecutive patients with paroxysmal or chronic AF were randomly tested with 3 internal atrial defibrillation lead configurations and biphasic shocks. Patients with implanted cardiac pacemakers were tested with the right atrium (RA) and left pulmonary artery or coronary sinus (CS) configuration. Shocks were initially delivered without anesthesia to assess patient tolerance. The need for backup ventricular defibrillation and pacing support was evaluated. Eighteen patients with (n = 15) or without (n = 3) structural heart disease, mean left ventricular ejection fraction 36 +/- 14%, and mean left atrial diameter 4.5 +/- 0.6 cm were studied. The mean defibrillation threshold in the best randomized lead configuration was 9.9 +/- 7.7 J. Mean defibrillation threshold for the right ventricle (RV) and superior vena cava configuration was 13.3 +/- 5 J, which was significantly lower than the RA and axilla configuration (20.1 +/- 7.4 J, p < 0.04) but not the RV to RA configuration (16.5 +/- 11 J, p > 0.2). The mean defibrillation threshold using the RA-left pulmonary artery/CS configuration was 8.9 +/- 9 J (p > 0.2 vs RV-superior vena cava). There was a bimodal distribution of defibrillation thresholds. Low atrial defibrillation thresholds correlated with absence of heart disease, higher ejection fraction, and smaller left ventricular end-diastolic diameter. Shocks were hemodynamically well tolerated, but 2 of 18 patients (11%) had nonsustained ventricular tachycardia after shock delivery. Six of 18 patients (33%) had postshock bradyarrhythmias. Fourteen of 16 patients perceived shocks > or = 3 J as intolerable.(ABSTRACT TRUNCATED AT 250 WORDS) [corrected]

Adult↗
PubMed2003

The effect of spatial scale of resistive inhomogeneity on defibrillation of cardiac tissue.

Defibrillation of cardiac tissue can be viewed in the context of dynamical systems theory as the attempt to move a dynamical system from the basin of attraction of one attractor (fibrillation) to another (the uniform rest state) by applying a stimulus whose form is physically constrained. Here we give an introduction to the physical mechanism of cardiac defibrillation from this dynamical perspective and examine the role of resistive inhomogeneity on defibrillation efficacy. Using numerical simulations with rotating waves on a one-dimensional periodic ring, we study the role of the spatial scale of resistive inhomogeneity on defibrillation. For a rotating wave on a periodic ring there are three stable attractors, namely the uniform rest state, a wave traveling clockwise and a wave traveling counterclockwise. As a result, the application of a stimulus has the potential for three different outcomes, namely elimination of the wave, phase resetting of the wave, and reversal of the wave. The results presented here show that with resistive inhomogeneities of large spatial scale, all three of these transitions are possible with large amplitude shocks, so that the probability of defibrillation is bounded well below one, independent of stimulus amplitude. On the other hand, resistive inhomogeneities of small spatial scale produce a defibrillation threshold that is qualitatively consistent with that found experimentally, namely the probability of defibrillation success is an increasing function that approaches one for large enough stimulus amplitude. Extending these results to higher dimensions, we describe conditions for successful defibrillation of functional reentry with large scale spatial inhomogeneity, but find that elimination of anatomical reentry is quite difficult. With small spatial scale inhomogeneity, there are no similar restrictions.

Atrial Fibrillation↗
PubMed1993

Maintenance of defibrillators in a state of readiness.

Since 1984, the US Food and Drug Administration (FDA) has utilized the Medical Device Reporting system as a mechanism for reporting adverse incidents associated with the use of medical devices, including external defibrillators. The frequency and content of these reports prompted an FDA-conducted five-state study of defibrillator-user training and maintenance practices for both devices and batteries. The study also included inspection and testing of defibrillators and batteries to assess their state of maintenance. A detailed review of the reports and of the five-state data confirmed that in the majority of cases, adverse incidents were related to improper defibrillator operation and maintenance, prompting the FDA Center for Devices and Radiological Health to launch an educational effort directed toward those who operate and maintain defibrillators. Proper maintenance of batteries (both nickel-cadmium and sealed lead-acid) was a major component of the educational thrust, because battery failure was identified as a recurrent and preventable problem. In an effort to correct the diverse types of incidents being reported, checklists were developed by the FDA for both manual and automated defibrillators. The checklists are designed to cover the spectrum of reported problems related to both device and user. The advent of more stringent FDA adverse incident-reporting regulations, coupled with increased use of defibrillators in diverse settings with varying usage frequencies, would seem to give a major impetus to the regular use of these checklists wherever defibrillators are employed.

Electric Countershock↗
PubMed1995

Measuring the call-receipt-to-defibrillation interval: evaluation of prehospital methods.

STUDY OBJECTIVE: Successful resuscitation of cardiac arrest depends partly on the time of first defibrillation. An accurate, practical method of measuring this time has not been devised. We attempted to determine the interval from receipt of a call by emergency medical services personnel to first defibrillation (total defibrillation interval) with synchronized clocks between computer-aided dispatch operations and an event-recording defibrillator. DESIGN: A 7-month prospective study measuring the total defibrillation interval. An automated code summary was to be submitted for each participant. SETTING: An urban, all-advanced life support, public utility model system. PARTICIPANTS: All primary ventricular fibrillation patients seen during the study period. RESULTS: Ninety-two patients met study criteria. Data are presented as median (interquartile range). The total defibrillation interval was 9.8 minutes (7.9 to 11.8 minutes). The call-receipt-to-vehicle-at-scene interval was 5.98 minutes (4.4 to 7.3 minutes). The vehicle-at-scene-to-defibrillation interval was 3.6 minutes (2.5 to 4.6 minutes). CONCLUSION: The use of synchronized clocks in automated event-recording systems may provide a method of accurately measuring the time elapsed before defibrillation.

Electric Countershock↗
PubMed2001

How often should defibrillation pads be changed?: the effect of evaporative drying.

OBJECTIVE: In order to minimise transthoracic impedance (TTI) during defibrillation, water-based pads are used to improve conductivity between metal defibrillation paddles and skin. Subjectively, these pads appear to dry very quickly; an effect that may lead to an increase in TTI due to poorer conduction between paddles and skin. This study was carried out to assess the effect of evaporative drying of defibrillation pads on TTI. MATERIALS AND METHODS: TTI was measured at 5-10 min intervals in 20 adult male volunteers across 3M defibrillation pads (2346N) placed in the anterior-apical position. Measurements of TTI were made at 30 kHz using a Bodystat MultiScan 5000 monitor at end-expiration. A third pad was placed on the left precordium and its mass recorded each time a TTI measurement was made. RESULTS: The median age of subjects was 22 years (range 21-52 years) and their median body mass index was 23.1 kg m(-2) (range 18.4-42.8 kg m(-2)). Median room temperature was 23.0 degrees C (range 19.0-24.0 degrees C) and the median humidity was 31.0% (range 28.0-48.0%). 3M defibrillation pads had an initial mean mass of 25.14 g (S.D. +/- 0.41 g). Changes in defibrillation pad mass due to evaporative loss occurred immediately and rapidly, with all measurements being significantly lower than the baseline value. Mean baseline TTI was 63.6 ohms (S.D. +/- 13.7 ohms). After 30 min a statistically significant (P = 0.012) rise of 1.4 ohms (2.2%), was observed corresponding to a 12.6% decrease in pad mass, after which TTI continued to increase in a linear fashion. CONCLUSION: In the absence of a defibrillation current. 3M defibrillation pads can safely be left on the chest wall for at least 25 min in a typical hospital environment before evaporative drying results in a significant increase in transthoracic impedance.

Adult↗
PubMed2002

Defibrillation by general practitioners.

OBJECTIVE: To investigate the mode of cardiac arrest in patients with acute myocardial infarction attended by general practitioners, and the effectiveness of early defibrillation. DESIGN: Retrospective observational study. SETTING: British general practice. PARTICIPANTS: General practitioners equipped with defibrillators by the British Heart Foundation. MAIN OUTCOME MEASURES: Cardiac rhythm when first monitored, response to defibrillation assessed by survival to reach hospital alive and survival to hospital discharge. INTERVENTIONS: Defibrillation and standard cardiopulmonary resuscitation in patients with cardiac arrest complicating acute myocardial infarction attended by British general practitioners. RESULTS: When a doctor equipped with a defibrillator witnessed an arrest or was able to initiate resuscitation within 4 min of the patient collapsing, 90% of patients were found to have developed a rhythm likely to respond to a defibrillatory shock. Defibrillation under these circumstances was very successful with more than 70% of patients subsequently admitted to hospital alive and approximately 60% surviving to be discharged alive. When the doctor commenced resuscitation later, fewer patients were found to have rhythms likely to be responsive to a DC shock. A greater proportion was in asystole and resuscitation was less frequently successful under these circumstances. When the arrest occurred in the doctor's surgery, 85% of patients were admitted to hospital alive and three quarters survived to hospital discharge. CONCLUSIONS: All those who provide the initial care for this vulnerable group of patients should be equipped with defibrillators. The more widespread deployment of defibrillators in the community may be a successful strategy for reducing unnecessary deaths from coronary heart disease.

Aged↗