Equivalence of the standard monophasic waveform shocks delivered by automated external defibrillators?

Biphasic versus monophasic defibrillation in out-of-hospital cardiac arrest: a systematic review and meta-analysis

OBJECTIVE

Biphasic defibrillation is more effective than monophasic one in controlled in-hospital conditions. The present review evaluated the performance of both waveforms in the defibrillation of patients of out-of-hospital cardiac arrest (OHCA) with initial ventricular fibrillation (Vf) rhythm under the context of current recommendations for cardiopulmonary resuscitation.

METHODS

From inception to June 2012, Medline, Embase, and the Cochrane Central Register of Controlled Trials were searched systemically for randomized controlled trials (RCTs) and observational cohort studies that compared the effects of biphasic and monophasic shocks on Vf termination, return of spontaneous circulation (ROSC), and survival to hospital discharge in OHCA patients with initial Vf rhythm. No restrictions were applied regarding language, population, or publication year.

RESULTS

Four RCTs including 572 patients were identified from 131 potentially relevant references for meta-analysis. The synthesis of these RCTs yielded fixed-effect pooled risk ratios (RRs) for biphasic and monophasic waveforms on Vf termination survival to hospital discharge (RR, 1.14; 95% CI, [0.84-1.54]).

CONCLUSION

Biphasic waveforms did not seem superior to monophasic ones with respect to Vf termination, ROSC, or survival to hospital discharge in OHCA patients with initial Vf rhythm under the context of current guidelines. However, most trials were conducted in accordance with previous guidelines for cardiopulmonary resuscitation. Therefore, further trials are needed to clarify this issue.

Ventricular fibrillation and defibrillation

Cardiac arrest in children is not often due to a disturbance in rhythm that is amenable to electrical defibrillation, contrary to the situation in adults. When a shockable rhythm is present, defibrillation using an external electric shock applied at an early stage after pre-oxygenation and chest compressions is of proven efficacy. Success at conversion of ventricular fibrillation is dependent on the delay before delivering the shock and defibrillation efficiency, which is itself a function of thoracic impedance, energy dose and waveform.

Transthoracic impedance does not affect defibrillation, resuscitation or survival in patients with out-of-hospital cardiac arrest treated with a non-escalating biphasic waveform defibrillator

OBJECTIVE

This is a study of the influence of transthoracic impedance (TTI) on defibrillation, resuscitation and survival in patients with out-of-hospital cardiac arrest (OHCA), treated with a non-escalating impedance-compensating 150 J biphasic waveform defibrillator.

METHODS

Cardiac arrest data from two EMS systems were analyzed retrospectively. All witnessed arrests from patients who presented with a shockable rhythm and were treated initially by BLS personnel were included (n = 102). For each defibrillation and resuscitation outcome variable, we tested differences in mean TTI for successful versus unsuccessful outcome. The effect of call-to-shock time on overall outcome was also examined.

RESULTS

Initial shocks defibrillated 90% [83-95%] (95% confidence interval) of patients. Cumulative success with two shocks was 98% [93-100%] and with three shocks was 99% [95-100%]. TTI averaged 90 +/- 23 Omega. First-shock success, cumulative success through two shocks and cumulative success through the first-shock series were unrelated to TTI, as were BLS ROSC, pre-hospital ROSC, hospital admission and discharge. In contrast and consistent with previous findings, call-to-shock time was highly predictive of survival.

CONCLUSIONS

High impedance patients were defibrillated by the biphasic waveform used in this study at high rates with a fixed energy of 150 J and without energy escalation. Rapid defibrillation rather than differences in patient impedance accounts for resuscitation success.

Body weight does not affect defibrillation, resuscitation, or survival in patients with out-of-hospital cardiac arrest treated with a nonescalating biphasic waveform defibrillator

BACKGROUND

This is a study of the influence of body weight on defibrillation, resuscitation, and survival in patients with out-of-hospital cardiac arrest treated with a nonescalating impedance-compensating 150-J biphasic waveform defibrillator.

METHODS

Cardiac arrest data from Rochester, MN, emergency medical services over a 6-yr period was retrospectively analyzed. Patient weight data were available for 62 of the 68 patients who were treated initially by basic life support personnel and who presented with a shockable rhythm. For each defibrillation and resuscitation outcome variable, we tested for differences in body weight for successful vs. unsuccessful outcome.

RESULTS

Initial shocks defibrillated 92% (83% to 97%) of patients. Cumulative success with two shocks was 98% (confidence interval, 92% to 100%) and with three shocks was 100% (confidence interval, 95% to 100%). The mean shock impedance was 90 +/- 21 ohms. The average body weight was 84 +/- 17 kg (minimum, 53 kg; maximum, 135 kg) and was normally distributed. Based on the body mass index for 46 patients, approximately 41% were classified as overweight (body mass index, > or = 25), 24% obese (body mass index, > or = 30), and 4% extremely obese (body mass index, > or = 40). The remaining 31% were classified as normal or underweight. First-shock success, cumulative success through two shocks, and cumulative success through the first-shock series were unrelated to body weight, as were basic life support restoration of spontaneous circulation, prehospital restoration of spontaneous circulation, hospital admission, and discharge.

CONCLUSIONS

Overweight patients were defibrillated by the biphasic waveform used in this study at high rates, with a fixed energy of 150 J, and without energy escalation.

Waveforms for defibrillation and cardioversion: recent experimental and clinical studies

PURPOSE OF REVIEW

The advent of biphasic waveforms for external defibrillation has generated extensive experimental and clinical investigation. At the same time, it has led to the development and clinical use of biphasic waveforms of several different designs. Finally, other types of waveforms, primarily triphasic, have entered experimental evaluation.

RECENT FINDINGS

There is virtually universal agreement that biphasic waveforms, regardless of design, have greater efficacy in defibrillation of ventricular fibrillation and in cardioversion of atrial fibrillation when compared with monophasic waveforms. It remains unresolved, however, whether any specific biphasic waveform has greater clinical superiority than others. Likewise, it remains to be demonstrated whether any biphasic waveform is less injurious to myocardial function than another and whether injury, if it is incurred, is secondary to peak delivered current or to delivered energy. Biphasic truncated exponential waveforms are used by most manufacturers, whereas a rectilinear biphasic waveform and a pulsed waveform also are being used clinically.

SUMMARY

Biphasic waveforms have supplanted monophasic waveforms for defibrillation and cardioversion. They include biphasic truncated exponential, rectilinear, and pulsed biphasic versions. At this time, there is no certain evidence of clinical superiority of one waveform over another in terms of either efficacy or myocardial injury.

Defibrillation waveform and post-shock rhythm in out-of-hospital ventricular fibrillation cardiac arrest

BACKGROUND

The importance of the defibrillation waveform on the evolving post-shock cardiac rhythm is uncertain. The primary objective of this study was to evaluate cardiac rhythms following the first defibrillation shock, comparing biphasic truncated exponential (BTE), monophasic damped sinusoidal (MDS), and monophasic truncated exponential (MTE) waveforms in patients experiencing out-of-hospital ventricular fibrillation cardiac arrest (OHCA).

METHODS

We reviewed the automated external defibrillator (AED) and emergency medical services (EMS) records of 366 patients who suffered OHCA and were treated with defibrillation shocks by first-tier emergency responders between 1 January 1999 and 31 August 2002 in King County, Washington. The post first shock rhythms were determined at 5, 10, 20, 30, and 60 s and compared according to defibrillation waveform.

RESULTS

The MDS and BTE waveforms were associated with significantly higher frequency of defibrillation than the MTE waveform, though only the BTE association persisted to 30 and 60 s. No difference in defibrillation rates was detected between MDS and BTE waveforms. By 60 s, an organized rhythm was present in a greater proportion for BTE (40.0%) compared with MDS (25.4%, P=0.01) or MTE (26.5%, P=0.07).

CONCLUSION

In this retrospective cohort investigation, MDS and BTE waveforms had higher first shock defibrillation rates than the MTE waveform, while patients treated with the BTE waveform were more likely to develop an organized rhythm within 60 s of the initial shock. The results of this investigation, however, do not provide evidence that these surrogate advantages are important for improving survival. Additional investigation is needed to improve the understanding of the role of waveform and its potential interaction with other clinical factors in order to optimize survival in OHCA.

A prospective, randomised and blinded comparison of first shock success of monophasic and biphasic waveforms in out-of-hospital cardiac arrest

BACKGROUND

Evidence suggests that biphasic waveforms are more effective than monophasic waveforms for defibrillation in out-of-hospital cardiac arrest (OHCA), yet their performance has only been compared in un-blinded studies.

METHODS AND RESULTS

We compared the success of biphasic truncated exponential (BTE) and monophasic damped sine (MDS) shocks for defibrillation in OHCA in a prospective, randomised, double blind clinical trial. First responders were equipped with MDS and BTE automated external defibrillators (AEDs) in a random fashion. Patients in ventricular fibrillation (VF) received BTE or MDS first shocks of 200 J. The ECG was recorded for subsequent analysis continuously. The success of the first shock as a primary endpoint was removal of VF and required a return of an organized rhythm for at least two QRS complexes, with an interval of <5 s, within 1 min after the first shock. The secondary endpoint was termination of VF at 5 s. VF was the initial recorded rhythm in 120 patients in OHCA, 51 patients received BTE and 69 received MDS shocks. The success rate of 200 J first shocks was significantly higher for BTE than for MDS shocks, 35/51 (69%) and 31/69 (45%), P=0.01. In a logistic regression model the odds ratio of success for a BTE shock was 4.01 (95% CI 1.01-10.0), adjusted for baseline cardiopulmonary resuscitation, VF-amplitude and time between collapse and first shock. No difference was found with respect to the secondary endpoint, termination of VF at 5 s (RR 1.07 95% CI: 0.99-1.11) and with respect to survival to hospital discharge (RR 0.73 95% CI: 0.31-1.70).

CONCLUSION

BTE-waveform AEDs provide significantly higher rates of successful defibrillation with return of an organized rhythm in OHCA than MDS waveform AEDs.

Comparison of six clinically used external defibrillators in swine

BACKGROUND

External defibrillation has long been practiced with two types of monophasic waveforms, and now four biphasic waveforms are also widely available. Although waveforms and clinical dosing protocols differ among defibrillators, no studies have adequately compared performance of the monophasic or the biphasic waveforms. This is the first study to compare defibrillation efficacy among biphasic external defibrillators, and does so as part of a study comparing all commonly available waveforms using their respective manufacturer-provided and clinically used doses.

METHODS AND RESULTS

Efficacy of six waveforms was tested in 852 short-duration ventricular fibrillation episodes in 14 swine. Protocol 1: 200-J monophasic damped sine (MDS) and monophasic truncated exponential (MTE) shocks were compared to 150-J biphasic shocks in six swine at the low-impedance of these animals. Protocol 2: Four commercially available biphasic defibrillators were compared using their respective manufacturer-recommended dose protocols in eight swine at low and simulated high-impedance. At low-impedance, all biphasic shocks achieved near-perfect success, while efficacy was significantly lower for MDS (67%) and MTE (30%) shocks. In protocol 2, first-shock success rates of the four biphasic defibrillators were uniformly high (97, 100, 100, and 94%) for low-impedance shocks, and decreased for high-impedance shocks (62, 92, 82, and 64%). There were statistically significant differences in efficacy among devices.

CONCLUSIONS

Commonly used MDS and MTE waveforms provide markedly dissimilar efficacies. Despite impedance-compensation schemes in biphasic defibrillators, impedance has an impact on their efficacy. At high-impedance, modest efficacy differences exist among clinically available biphasic defibrillators, reflecting differences in both waveforms and manufacturer-provided doses.

Refibrillation, resuscitation and survival in out-of-hospital sudden cardiac arrest victims treated with biphasic automated external defibrillators

PRIMARY OBJECTIVE

Defibrillation is essential for victims of sudden cardiac arrest (SCA) with ventricular fibrillation (VF), yet it does not terminate the underlying causes of VF. Prior to more definitive interventions, these same causes may result in recurrence of VF following defibrillation (refibrillation). The incidence and course of refibrillation, and its relation to patient outcomes, has not been previously described in the context of treatment of out-of-hospital SCA with biphasic waveform automated external defibrillators (AEDs).

MATERIALS AND METHODS

ECGs were recovered from all shocks delivered with biphasic AEDs by Basic Life Support (BLS) first responders, primarily police, in witnessed cardiac arrests occurring from December 1996 to December 2001 in the Rochester, MN public service area. Only events prior to administration of cardio-active medications were considered. Frequency and time to occurrence of refibrillation were compared in patients in relation to the progress of their resuscitation and survival.

RESULTS AND CONCLUSIONS

One hundred and sixteen of 128 shocks delivered under BLS care to 49 patients with witnessed cardiac arrests presenting with VF terminated VF. Most patients (61%) refibrillated while under BLS care, many (35%) more than once. Occurrence of and time to refibrillation were unrelated to achievement of return of spontaneous circulation (ROSC) under BLS care (BLS ROSC), to survival to hospital discharge and to neurologically intact survival.