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PubMed1995

Threshold reduction with biphasic defibrillator waveforms. Role of charge balance.

Mechanism underlying improved defibrillation efficacy of biphasic waveforms at low shock intensities remain poorly understood. Recent studies suggest that biphasic waveforms produce a longer mean postshock response throughout the ventricle. This prolongs the cellular refractory period, blocks fibrillation wave fronts, and causes fibrillation to cease. Previous studies showed that hyperpolarizing monophasic waveforms, delivered during the refractory period, can shorten action potential duration (APD90), which would be deleterious for defibrillation. This study tested the hypothesis that a balanced-charge biphasic waveform produces a longer mean total mean APD than a comparable monophasic waveform by preventing this shortening in hyperpolarized regions as well as by prolonging APD in depolarized regions. To test this hypothesis, the authors examined transmembrane potential changes produced by hyperpolarizing and depolarizing monophasic and balanced-charge symmetrical biphasic waveforms using a computer model of the ventricular action potential. Shock intensities within the low-intensity "window," where biphasic waveforms defibrillate with higher efficacy than monophasic waveforms (1.5-3 times diastolic threshold), were used. Results show that biphasic S2 produced a significantly longer response both under hyperpolarizing and depolarizing conditions. The hyperpolarizing/depolarizing biphasic S2 produced a prolonged response with a well-defined plateau. Following the depolarizing/hyperpolarizing S2, APD90 did not shorten as with the hyperpolarizing monophasic S2. Rather, repolarization continued near the original S1 times course, but with slight prolongation of S1 APD90. These results suggest that biphasic waveforms enhance the prolonged refractory periods required for defibrillation throughout the heart, including regions exposed to both anodal and cathodal stimulation.

Action Potentials↗
PubMed1988

Assessment of a device for trans-telephonic control of defibrillation.

The safety and efficacy of a device allowing the trans-telephonic control of defibrillation have been assessed in 32 attempted defibrillations performed in 29 patients. The initial rhythm was atrial fibrillation in 27; ventricular tachycardia in 4; and ventricular flutter in 1. Satisfactory voice and ECG transmission were established in all cases. The mean time taken by the patient unit to dial and activate the base station was 20.3 seconds. The mean defibrillator charge time was 5.5 seconds to 50 joules and 9.3 seconds to 360 joules. A total of 84 synchronised and 5 unsynchronised shocks were delivered satisfactorily. Lay persons were trained to use the patient unit, and were able to operate the device at home. This device has the potential for rapid defibrillation of patients who develop ventricular fibrillation outside hospital.

Adult↗
PubMed1990

Transtelephonic defibrillation.

STUDY OBJECTIVES: This study was undertaken to assess the safety and reliability of a device for transtelephonic defibrillation. DESIGN: The transtelephonic system consists of a patient unit and a base station. The patient unit contains a monitor-defibrillator, electrode pads, microphone, microprocessor, and DC defibrillator. The base station comprises a control panel, computer, and ECG display. SETTING: Fifteen patients who were treated in our emergency department for cardiac arrest were placed on patient units that activated our base station in a remote location within the ED. TYPE OF PARTICIPANTS: Thirteen patients were treated for ventricular fibrillation, and two patients were treated for ventricular tachycardia. INTERVENTIONS: Thirty-one shocks were delivered transtelephonically. MEASUREMENTS AND MAIN RESULTS: In all cases, voice and ECG transmission were established without difficulty. CONCLUSIONS: We conclude that this system represents a safe and reliable method for the treatment of ventricular fibrillation, and we advocate additional use to study the prehospital applications of transtelephonic defibrillation.

Aged↗
PubMed1989

EMT-defibrillation: the Wisconsin experience.

The survival rate for patients with prehospital cardiac arrest has improved in some communities with early defibrillation by emergency medical technician-defibrillators (EMT-Ds). In rural areas, previous studies on survival with defibrillation by EMT-Ds have been variable. We conducted an EMT-D study to determine effectiveness in various prehospital settings. Sixty-four ambulance services from communities ranging in size from rural areas to city suburbs participated in our prospective study. EMTs were trained in rhythm recognition and the use of a manual defibrillator during a standardized 20-hour course. Over 18 months, data were collected locally for central analysis. Five hundred sixty-six patients with primary cardiac arrest were included in our study: 36 (6.4%) survived. Retrospective review revealed survival before EMT-D implementation to be 3.6% (P less than .02). Three hundred four patients (54%) had an initial rhythm of ventricular fibrillation, with 33 (11%) surviving. The survival rate for EMT-D-witnessed arrest with an initial rhythm of ventricular fibrillation was 42%. Patients with asystole were countershocked in our study; however, there were no survivors from this group. The neurologic status of survivors at time of hospital discharge was normal in 72%. The average response time, defined as time of emergency medical services activation to the time of EMT-D arrival, was 7.3 +/- 5.8 and 3.7 +/- 2.0 minutes for nonsurvivors and survivors, respectively (P less than .002). There were no survivors when the response time was more than eight minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

From concept to standard-of-care? Review of the clinical experience with automated external defibrillators.

There is now both national and international acceptance of the "principle of early defibrillation," which contends that whoever arrives first at the scene of a cardiac arrest should have a defibrillator. The almost revolutionary technological event that permits widespread implementation of this principle has been the development of automated external defibrillators (AEDs). The simplicity, accuracy, and safety of these devices markedly expands the range of people who can deliver early defibrillation, which includes minimally trained emergency personnel, lay and community responders, and family members of high-risk patients. Even though AEDs now approach the status of "standard of care," the AED, as an example of a new technology, has not followed the classic technology paradigm: conceptualization, experimentation, dissemination, and standard of care. Instead, like many other technical innovations in emergency medicine, the development of AEDs proceeded simultaneously on many fronts, and implementation often occurred before confirmation of important subissues. AEDs may experience the life cycle of many new ideas: initial enthusiasm and widespread adoption, followed by disillusionment and rejection, and finally a mature, proper perspective. Careful implementation and continued evaluation may help emergency personnel avoid periods of disillusionment with AEDs and move steadily and uneventfully to a proper perspective.

Electric Countershock↗
PubMed1989

Development of a decision algorithm for a semiautomatic defibrillator.

A decision algorithm was developed for a semiautomatic defibrillator. The function of the algorithm is to evaluate the ECG of a patient and determine whether a defibrillation shock should be delivered. The development process included establishment of defibrillation criteria, creation of ECG databases, algorithm design, development of test protocols, and clinical testing. The result was an algorithm with sensitivity and specificity sufficiently accurate to allow a defibrillation shock to be delivered safely outside the hospital.

Algorithms↗
PubMed1995

Effect of out-of-hospital defibrillation by basic life support providers on cardiac arrest mortality: a metaanalysis.

STUDY OBJECTIVE: Although some studies demonstrate otherwise, we hypothesized that metaanalysis would demonstrate a reduction in the relative risk of mortality when basic life support (BLS) providers can defibrillate out-of-hospital cardiac arrest patients. DESIGN: Metaanalysis of studies meeting the following criteria: single-tier or two-tier emergency medical service (EMS) system, survival to hospital discharge for patients in ventricular fibrillation, and manual and/or automatic external defibrillators. The alpha error rate was .05. RESULTS: Seven trials qualified for metaanalysis. Across all trials, the risk of mortality for BLS care with defibrillation versus that without was .915 (P = .0003). Separate subset analyses of single-tier and two-tier EMS systems demonstrated similar results. CONCLUSION: BLS defibrillation can reduce the relative risk of death for out-of-hospital cardiac arrest victims in ventricular fibrillation. Weaknesses in individual study designs and regional clustering limit the strength of this metaanalysis and conclusion.

Electric Countershock↗
PubMed1996

Relationship of timeliness of paramedic advanced life support interventions to outcome in out-of-hospital cardiac arrest treated by first responders with defibrillators.

STUDY OBJECTIVE: We sought to determine whether the interval between the arrival of first responder/defibrillators and paramedic advanced life support (ALS) interventions is associated with outcome. METHODS: We carried out a prospective observational study of adults in out-of-hospital cardiac arrest treated by both first responders and paramedics in an urban emergency medical services system between July 15, 1992, and May 27, 1993 (N = 544). RESULTS: The gap between first-responder and medic arrival was short (3.2 minutes); medics arrived before first-responder shock in 22% of ventricular fibrillation (VF) cases. Just 10% of patients has a pulse when medics arrived, but the presence of pulse on medic arrival was a powerful predictor of hospital discharge (odds ratio [OR], 20.5; sensitivity, 39%; specificity, 98%; positive predictive value, 55%; negative predictive value, 97%) or a Cerebral Performance Category score on discharge of 1 or 2 (OR, 2.9). No response or individual ALS treatment interval was related to outcome, including the interval from first-responder to medic arrival. ALS interventions by medics were associated with poorer outcomes; even the need for nothing more than additional defibrillation by medics decreased the survival rate of VF patients threefold. By contrast, bystander CPR improved survival more than fourfold and early defibrillation of VF by first responders more than ninefold. Ninety-one percent of all patients discharged from the hospital who received only minimal ALS other than intubation had good neurologic outcome and longer survival after discharge. Half the total survivors of VF arrest (and 59% of all arrest survivors) were resuscitated by medics with aggressive ALS measures, but 80% had very poor neurologic outcomes and 50% died within a year of hospital discharge. Even the need for only additional defibrillation by medics worsened neurologic outcome by a factor of 2.8. CONCLUSION: Faster response by medics, or any individual ALS intervention other than first-responder defibrillation, demonstrated no benefit in this urban population with short intervals between responder arrivals. Aggressive ALS increased the number of survivors but also decreased their neurologic quality. The benefit of rapid ALS backup to first responder/defibrillators needs further study in other systems. System performance cannot be judged without knowledge of neurologic outcome.

Adult↗
PubMed1998

Effects of transthoracic impedance and peak current flow on defibrillation success in a prehospital setting.

STUDY OBJECTIVE: To assess whether transthoracic impedance and peak current are determinants of defibrillation success in patients with out-of-hospital ventricular fibrillation (VF). METHODS: A retrospective cohort study was carried out in a suburban Canadian EMS system. Participants were patients who experienced out-of-hospital cardiac arrest in the regional municipality of Ottawa-Carleton, had VF rhythm at presentation, and received countershocks from the Laerdal Heartstart 2000 automated external defibrillator. RESULTS: A total of 310 patients met the inclusion criteria. Collectively they received 717 countershocks. The first shocks were successful in converting VF rhythm 25.5% of the time. The most important determinant of shock success was the interval from when the call was received until delivery of the first shock (P<.01). Length of time at scene, current, impedance, and patient age were not significant determinants of success of first shock. The time interval until first shock was also a determinant of survival (P<.01). EMS response time, whether the arrest was witnessed, initial impedance, and current were not determinants of survival. CONCLUSION: OHCA shock success and survival are associated with EMS system factors such as the interval from when the call was received until delivery of the first shock. The importance of impedance and peak current remain theoretic for out-of-hospital defibrillation success and did not influence defibrillation success in this study.

Age Factors↗
PubMed2002

Predicting the success of defibrillation by electrocardiographic analysis.

BACKGROUND: We investigated an electrocardiographic signal analysis technique for predicting whether an electrical shock would reverse ventricular fibrillation (VF) in an effort to minimize the damaging effects of repetitive shocks during CPR. METHODS AND RESULTS: An established model of CPR was utilized. VF was electrically induced in anesthetized 40 kg domestic pigs. Defibrillation was attempted after either 4 or 7 min of untreated VF. Failing to reverse VF, a 1 min interval of precordial compression and mechanical ventilation preceded each subsequent defibrillation attempt. The amplitude frequency spectrum of digitally filtered VF wavelets was computed with Fourier analysis during uninterrupted precordial compression from conventional right infraclavicular and left apical electrodes. Of a total of 34 electrical defibrillation attempts, 24 animals were restored to spontaneous circulation (ROSC). An amplitude spectrum analysis (AMSA) value of 21 mV Hz had a negative predictive value of 0.96 and a positive predictive value of 0.78. CONCLUSIONS: AMSA predicted when an electrical shock failed to restore spontaneous circulation during CPR with a high negative predictive value. This method potentially fulfills the need for minimizing ineffective defibrillation attempts and their attendant adverse effects on the myocardium.

Analysis of Variance↗
PubMed2002

Transthoracic biphasic waveform defibrillation at very high and very low energies: a comparison with monophasic waveforms in an animal model of ventricular fibrillation.

The purpose of this study was to compare truncated exponential biphasic waveform versus truncated exponential monophasic waveform shocks for transthoracic defibrillation over a wide range of energies. Biphasic waveforms are more effective than monophasic shocks for defibrillation at energies of 150-200 Joules (J) but there are few data available comparing efficacy and safety of biphasic versus monophasic defibrillation at energies of <150 J or >200 J. Thirteen adult swine (weighing 18-26 kg, mean 20 kg) were deeply anesthetized and intubated. After 15 s of electrically-induced ventricular fibrillation (VF), each pig received truncated exponential monophasic shocks (10 ms) and truncated exponential biphasic shocks (5/5 ms) in random order. Energy doses ranged from 70 to 360 J. Success was defined as termination of VF at 5 s post-shock. For both biphasic and monophasic waveforms success rate rose as energy was increased. Biphasic waveform shocks (5/5 ms) were superior to 10 ms monophasic waveform shocks at the very low energy levels (at 70 J, biphasic: 80+/-9%, monophasic; 32+/-11% and at 100 J, biphasic; 96+/-3% and monophasic 39+/-11%, both P < 0.01). No significant differences in shock success were seen between biphasic and monophasic waveform shocks at 200 J or higher energy levels. Shock success of > 75% was achieved with 200 J (10 J/kg) for both waveforms. Pulseless electrical activity (PEA) or ventricular asystole occurred in 4 animals receiving monophasic shocks and 1 animal receiving biphasic shocks. Biphasic waveform shocks (5/5 ms) for transthoracic defibrillation were superior to monophasic shocks (10 ms) at low energy levels. Percent success increased with increasing energies. PEA occurred infrequently with either waveform.

Animals↗
PubMed2002

Automated external defibrillation in cardiac surgery.

Revision open heart surgery may be impeded by a dense network of pericardial adhesions rendering cardiac mobilization laborious or incomplete, and internal defibrillation impossible. External defibrillation, the current alternative to internal defibrillation, may result in myocardial stunning secondary to the delivery of escalating, monophasic, high-energy shocks. Automated external defibrillation, by delivering consecutive, non-escalating, impedance-compensated, low-energy, biphasic electric shocks to the myocardium, may provide a more effective and safer option whilst reducing the risk of myocardial stunning.

Adult↗
PubMed2003

The critical importance of minimal delay between chest compressions and subsequent defibrillation: a haemodynamic explanation.

Outcome after prehospital defibrillation remains dire. The aim of the present study was to elucidate the pathophysiology of cardiac arrest and to suggest ways to improve outcome. Ventricular fibrillation (VF) was induced in air-ventilated pigs, after which ventilation was withdrawn. After 6.5 min of VF, ventilation with 100% oxygen was initiated. In six pigs (group I), defibrillation was the only treatment carried out. In another six pigs (group II), mechanical chest compression-decompression CPR (mCPR) was carried out for 3.5 min followed by a 40-s hands-off period before defibrillation. If unsuccessful, mCPR was resumed for a further 30 s before a second or a third, 40-s delayed, shock was given. In a final six pigs (group III) mCPR was applied for 3.5 min after which up to three shocks (if needed) were given during on-going mCPR. Return of spontaneous circulation (ROSC) occurred in none of the pigs in group I (0%), in 1 of six pigs in group II (17%) and in five of six pigs in group III (83%). During the first 3 min of VF arterial blood was transported to the venous circulation, with the consequence that the left ventricle emptied and the right ventricle became greatly distended. It took 2 min of mCPR to establish an adequate coronary perfusion pressure, which was lost when the mCPR was interrupted. During 30 s of mCPR coronary perfusion pressure was negative, but a carotid flow of about 25% of basal value was obtained. In this pig model, VF caused venous congestion, an empty left heart, and a greatly distended right heart within 3 min. Adequate heart massage before and during defibrillation greatly improved the likelihood of return of spontaneous circulation (ROSC).

Animals↗
PubMed1998

Theoretical calculation of maximum attainable benefit of public access defibrillation in Belgium. Belgian Cardio Pulmonary Cerebral Resuscitation Study Group.

OBJECTIVE: Assuming that a lay person performing cardiopulmonary resuscitation (CPR) will also use an automatic external defibrillator (AED) wherever available, we tried to estimate the maximal attainable benefit of public access defibrillation in some centres in Belgium. METHODS: We analysed retrospectively the data from the Belgian Cardio Pulmonary Cerebral Resuscitation Registry collected between 1991 and June 1996. The majority of these emergency medical service (EMS) systems are two-tiered with an early defibrillation program for the first tier and a physician-staffed second tier. RESULTS: The data show that, in 5543 registered cases, there were 1001 (18%) adults with non-traumatic ventricular fibrillation/ventricular tachycardia (VF/VT) as the first monitored rhythm. In this subgroup there were 419 (42%) cases who had lay CPR. The duration of lay CPR before the first defibrillation either by the first or the second tier is known in 357 cases. This duration was more than 5 min and 10 min, in 80% and 53% of the cases, respectively. The median (Q1, Q3) lay CPR duration was 11 (7, 15) min. Survival to hospital discharge in this subgroup was achieved in 80/357 (22%) patients. Using Weaver's linear model for survival after witnessed VF/VT, an estimated increase of more than 30% in survival rate was calculated. CONCLUSION: It is concluded that in our EMS system, laymen reach a substantial number of VF/VT victims many minutes before the arrival of the professional EMS teams. Therefore, a substantial increase in the number of survivors could be expected if lay responders were prepared to use an AED.

Aged↗
PubMed1998

Transthoracic defibrillation: does electrode adhesive pad position alter transthoracic impedance?

Successful termination of ventricular fibrillation by transthoracic shocks is dependent on achieving adequate current flow, which in turn is governed by transthoracic impedance (TTI). The American Heart Association (AHA) Advanced Cardiac Life Support textbook recommends three electrode positions for defibrillation: (1) anterior-apex, (2) apex-posterior and (3) anterior-posterior. However, there are few data available comparing TTI of these positions. To study this, we applied large (78 cm2) self-adhesive monitor-defibrillator pads to 20 subjects (ten male, ten female, ages 21-79) and measured TTI using a validated test-pulse technique which does not require actual shocks. We performed two studies. In Study 1 (all 20 subjects) the electrode pads were applied in the three positions recommended by the AHA, with the posterior electrode placed in the right infrascapular location. All TTI measurements were made at end-expiration and body surface area (BSA) was recorded. The results (TTI, omega, mean +/- S.D.) for the respective positions were the following: anterior-apex, 82.0+/-24.7; apex-posterior, 71.2+/-23.5; anterior-posterior, 77.0+/-24.7 (P NS). In Study 2 (six subjects) we compared the effect of right vs. left infrascapular posterior electrode placement (TTI, omega): apex-right infrascapular (RIS), 76.8+/-18.4; apex-left infrascapular (LIS), 72.1+/-18.7; anterior-RIS, 72.5+/-19.4; anterior-LIS, 71.6+/-18.6 (P NS). Correlation of TTI (anterior-apex placement) with BSA: TTI = 15.9 (BSA) + 46.7, r = 0.60, P < 0.01; the correlations of TTI and BSA were similar in the other two electrode positions. Thus, the three AHA-recommended electrode positions for transthoracic defibrillation have equivalent and acceptable TTIs; current flow should be similar using any of these positions. Furthermore, the posterior electrode may be placed in either the right or the left infrascapular position without affecting TTI. TTI is related to BSA in any of the three recommended positions; patients with high BSA and TTI may require higher energy selection to achieve defibrillation.

Adult↗
PubMed1992

Long-term multicenter experience with a second-generation implantable pacemaker-defibrillator in patients with malignant ventricular tachyarrhythmias. The Guardian Multicenter Investigators Group.

A second-generation implantable pacemaker-cardioverter-defibrillator was evaluated in 200 patients with sustained ventricular tachycardia, ventricular fibrillation or prior cardiac arrest. The device permits demand ventricular pacing for bradyarrhythmias and for long QT interval or tachycardia suppression, uses programmable (3 to 30 J) energy shocks for conversion of ventricular tachycardia and ventricular fibrillation and is used with conventional pacing and defibrillation leads. Ventricular tachycardia/fibrillation recognition is based on the ventricular electrogram rate and requires reconfirmation before shock delivery. Two hundred patients (mean age 62 years, mean left ventricular ejection fraction 36%) were enrolled and followed up for 0 to 23 months (mean 12). Epicardial lead system implantation was performed with use of an anterolateral thoracotomy (38%), median sternotomy (26%) and subxiphoid (20%) or subcostal (16%) approach. Perioperative mortality rate was 5.5% (all nonarrhythmic deaths). Implant defibrillation threshold ranged from 3 to 30 J (mean 15), with initial programmed shock energy ranging from 3 to 30 J (mean 22). Ventricular tachycardia/fibrillation sensing threshold ranged from 0.7 to 1.8 mV (median 1) and the tachycardia detection interval from 288 to 416 ms (median 320). Reprogramming of implant variables was necessary for reliable electrographic sensing (54 patients), programmed shock therapy (61 patients) and tachycardia detection rate (63 patients). Device activation for potential shock delivery occurred in 111 patients (55.5%) with actual shock delivery after ventricular tachycardia/fibrillation reconfirmation in 66 patients (33%). During follow-up study, there was a 1% arrhythmia mortality rate, 6.5% cardiac mortality rate and 10.5% total mortality rate. This study demonstrates that the programmable implantable pacemaker-cardioverter-defibrillator is effective in preventing arrhythmic death, yet reduces patient exposure to repeated shock therapy. Reprogramming is usually necessary during follow-up for optimal function.

Adolescent↗
PubMed1983

Evaluation of a new defibrillation pathway--the tongue-epigastric route. I. Experimental studies in dogs.

The purpose of this study was to determine the efficacy of a tongue-epigastric defibrillation route in anesthetized dogs. Ventricular fibrillation was induced by rectangular pulses passed down a transvenous catheter into the right ventricle. Three groups of dogs were studied. Group I (15 dogs) received shocks from a 12 cm2 tongue electrode, a 50 cm2 circular, gelled self-adhesive electrode pad placed on the epigastrium and standard transthoracic defibrillator paddle electrodes. Shocks were given at energy levels of 50 to 460 joules (delivered energy, 50 ohm resistance). The success of the tongue-epigastric shocks in achieving defibrillation, and the resistance and current flow were determined at each energy level and compared with the same energy shocks from the standard transthoracic electrodes. In Group II (five dogs), comparisons were made between the 12 cm2 tongue electrode used in the first group of dogs and a larger tongue electrode of 40 cm2. In Group III (five dogs), intracardiac current flow (potential gradient) with tongue-epigastric and standard transthoracic electrodes was studied. In Group I, defibrillation success with the tongue-epigastric electrodes ranged from no success at 50 to 100 joules to 83% success at 460 joules. With standard transthoracic electrodes, success rates ranged from 65% at 50 joules to 100% at 300 joules. At all energies tested, the resistance was significantly higher and current significantly lower using tongue-epigastric compared with transthoracic electrodes. The higher tongue-epigastric resistance is probably related to the longer interelectrode distance; the correlation between interelectrode distance (x, in centimeters) and resistance (y, in ohms) in these dogs was y = 2.2x + 29.6, r = 0.78.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdomen↗
PubMed1984

Evaluation of a new defibrillation pathway: tongue-epigastric/tongue-apex route. II. Impedance characteristics in human subjects.

An automated device for defibrillation using a vertical shock pathway (tongue-epigastric or tongue-apex) has been developed. The energy requirements for defibrillation using vertical pathways are uncertain and will be determined largely by the impedance of the pathway. The purpose of this study was to determine the impedance characteristics of vertical defibrillation pathways in human subjects. Twenty patients undergoing elective cardioversion of atrial fibrillation or atrial flutter, or both, were studied. Patients received shocks from electrodes placed in tongue-epigastric or tongue-cardiac apex positions. The tongue electrode was a 12 cm2 metal plate fixed to a standard plastic oropharyngeal airway. The epigastric or cardiac apex electrode was a 40 cm2 self-adhesive pad. The electrodes were connected to a standard damped-sinusoidal waveform defibrillator. It was found that the two vertical shock pathways had substantially higher impedance than the standard transthoracic pathway: tongue-epigastric pathway 130 +/- 11 omega (SD), tongue-apex pathway 115 +/- 12 omega, transthoracic pathway 68 +/- 11 omega (p less than 0.05). The higher impedance is probably due to the longer interelectrode distances of vertical pathways: tongue-epigastric 33 +/- 3 cm, tongue-apex 28 +/- 3 cm, transthoracic 23 +/- 3 cm (p less than 0.05). Vertical pathway shocks were successful in the cardioversion of 15 of 20 patients. Four of the five patients in whom vertical shocks were unsuccessful subsequently underwent successful cardioversion by transthoracic shocks; the transthoracic shocks achieved a higher current because of lower impedance of the transthoracic route.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdomen↗