Article, Emergency Medicine

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

a b s t r a c t

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 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.

(C) 2013

Introduction

Out-of-hospital cardiac arrest (OHCA) is a common and lethal problem that leads to an estimated 330000 deaths annually in the United States and Canada [1]. Approximately 60% are treated by emergency medical services (EMS) [2]. Published rates of OHCA survival to hospital discharge range from 0.3% [3] to 20.4% [4]. Many of these deaths are due to ventricular fibrillation (Vf), which can be treated effectively by prompt defibrillation [5].

The 2010 American Heart Association (AHA)/International Liaison Committee on Resuscitation guidelines suggest that biphasic waveforms are more effective for defibrillation than monophasic ones [6]. However, according to Randomized controlled trials , it remains inconclusive whether biphasic defibrillators result in higher rates of survival to hospital discharge than monophasic ones [6].

? Funding source: None.

?? Conflicts of interests: None.

* Corresponding author. Tel.: +886 2-23123456×65792; fax: +886 2 2322 3150.

E-mail address: [email protected] (W.-J. Chen).

Moreover, three RCTs [7-9] presented in the guidelines as evidence of the superiority of biphasic over monophasic defibrillation have some limitations: one [7] used both monophasic truncated exponential (MTE) and monophasic damped sine (MDS) waveforms in the monophasic group, in which MTE waveforms were inferior to MDS ones for defibrillation in some studies [10,11]; one [8] demonstrated the superiority of biphasic waveforms with respect to defibrillation outcomes within one minute rather than five seconds as defined by the guidelines [6]; and one [9] demonstrated the superiority of biphasic waveforms used in stacked shocks up to three times, which is not applied in current practice [6].

Most trials in favor of biphasic waveforms were performed in accordance with the 2000 AHA/ILCOR guidelines [12], which recommend stacked shocks up to three times for defibrillation. Considering the substantial changes in the 2010 AHA/ILCOR guide- lines and the concerns described above, the present review reeval- uates the performance of both waveforms–biphasic and monophasic

–in the defibrillation of OHCA patients under the context of current recommendations [6] as well as their effects on the return of spontaneous circulation (ROSC) and survival to hospital discharge.

0735-6757/$ – see front matter (C) 2013 http://dx.doi.org/10.1016/j.ajem.2013.07.033

Methods

Data sources and searches

We performed this meta-analysis in accordance with the PRISMA (Preferred Reporting Items for Systematic reviews and Meta- Analyses) guidelines [13] for RCTs and the MOOSE (Meta-analysis Of Observational Studies in Epidemiology) guidelines [14] for observational cohort studies. Two authors (CHW and CHH) indepen- dently searched Medline, Embase, and the CENTRAL (Cochrane Central Register of Controlled Trials) from inception to June 2012 according to a pre-specified protocol available online (http://www. crd.york.ac.uk/PROSPERO/; registration number: CRD42012002520). Search terms included “monophasic,” “biphasic,” “cardiac arrest,” and “cardiopulmonary resuscitation.” There were no restrictions on language, population, or publication year. The Medline search strategy is presented in an example in the appendix. We did not search abstracts from conferences, proceedings, or clinical trial registries. Instead, we manually reviewed the bibliographies of relevant studies, reviews, and meta-analyses to identify references we may have missed during our primary search. The authors of the included trials were contacted for missing information if necessary.

Study selection

Two authors (CHW and CHH) independently scanned the titles and abstracts of all retrieved manuscripts and selected the manu- scripts pertinent to this review. The following prespecified inclusion criteria were used (a) RCTs or observational cohort studies (no case series), (b) comparisons between biphasic and monophasic defibril-

lation in OHCA patients with initial rhythm of Vf, and (c) primary outcomes reported as Vf termination after first shock.

After retrieving full reports from potentially relevant trials, 2 reviewers (CHW and WTC) independently assessed each study’s eligibility on the basis of the inclusion criteria and settled differing opinions by consensus or consultation with a third investigator (WJC).

Data extraction and quality assessment

Four authors independently extracted data using a prespecified protocol (MST, SHL, CYW, and YCL). Each trial was reviewed independently by 2 of these 4 authors to ensure the correctness of the extracted data, which included (a) study design, (b) study population characteristics, (c) details of intervention and controls, (d) types of outcomes measured, and (e) covariates controlled in observational cohort studies. The appendix contains a detailed list of these variables. The Cochrane risk of bias tool was adopted to assess the risk of bias for each RCT. Each RCT was scored as “high risk,” “low risk,” or “unclear” with respect to random sequence generation, allocation concealment, blinding process, incomplete outcome data, and selective reporting [15]. Observational cohort studies were further evaluated using the Newcastle-Ottawa Scale, which is useful for rating the quality of observational studies in a standardized format on the basis of clearly defined patient selection, assessment of exposures and outcome, comparability of groups, and adequacy of follow-up to hospital discharge [16,17]. Observational cohort studies were excluded from

analysis if they did not satisfy any one of these quality indicators.

Discrepancies in assessment were resolved through discussions between the extraction authors or consultation with the supervising investigators (ZSY and CCF).

Fig. 1. Literature search flow diagram. CENTRAL, Cochrane Central Register of Controlled Trials.

Data synthesis and analysis

Data synthesis and analysis were performed using R 2.11.1

Table 2

Risks of Bias assessment for biphasic versus monophasic waveforms in randomized controlled trials included in the analysis of termination of ventricular fibrillation

software (R Foundation for Statistical Computing; Vienna, Austria) in the metafor package. A 2-sided P <= .05 was considered statistically significant. Dichotomous outcomes were collected to determine risk

Reference Random sequence generation

Allocation concealment

Blinding process

Incomplete outcome data

Selective reporting

ratios (RRs) with 95% confidence intervals (CIs) of the individual studies. Heterogeneity was tested according to the I2 statistic, in which I2 >=50% indicated a substantial level of heterogeneity, and the statistical test of heterogeneity, in which P <= .05 indicated heterogeneity. The random-effects summary estimates (according to the DerSimonian-Laird method) were reported if significant hetero- geneity was evident according to either test; otherwise, fixed-effect summary estimates (according to the Mantel-Haenszel method) were reported.

We used a Galbraith plot to identify potential sources of heterogeneity when significant statistical heterogeneity was detected [18]. Additionally, we performed meta-regression to test the significance of each pre-specified covariate when significant statistical heterogeneity was detected; these covariates included witnessed cardiac arrest, bystander cardiopulmonary resuscitation (CPR), first shock energy, and EMS dispatch-to-first-shock time. We created a funnel plot to evaluate publication bias.

Results

Search results and description

The systemic review identified four RCTs and 14 observational cohort studies after scanning titles and abstracts (Fig. 1). In the full- text review, none of the 14 observational cohort studies met the a priori inclusion criteria or quality measures. The reasons for exclusion included failure to comparably report outcome data for biphasic and monophasic groups (n = 8), reporting of duplicate cohorts (n = 1), evaluation of Implantable cardioverter-defibrillator (n = 1), not reporting the outcome of Vf termination (n = 2), review article (n = 1), and abstract only (n = 1). Thus, only 4 RCTs [7-9,19] including 572 patients were eligible for inclusion in the meta- analysis (Table 1).

As shown in Table 2, most trials did not clearly report the random sequence generation or allocation concealment. In all trials, random- ization was conducted at the level of EMS units rather than at the patient level. Schneider et al. randomized treatment by date [7]. Most data were managed by intention-to-treat (ITT) analysis. Kudenchuk et

Schneider [7] Unclear High Low Low Low van Alem [8] Unclear Unclear Low Low Low Morrison [9] Low Low Low Low Low Kudenchuk [19] Unclear Unclear Low Low Low

al [19] determined the outcome of first shock by ITT analysis and other outcomes by per-protocol analysis in cases of more than one shock, because of the presence of mixed biphasic and monophasic shocks.

Three trials [7,8,19] enrolled OHCA patients with an initial rhythm of Vf. Morrison et al [9]. enrolled patients who received at least one shock at any time during resuscitation, regardless of the initial presenting rhythm. In this review, only the data of OHCA patients with initial Vf were extracted.

All studies were performed before 2005. Two trials each were conducted in North America [9,19] and Europe [7,8], respectively. One trial [9] involved paramedics only, one [8] involved non-medical First responders only, and two [7,19] involved both emergency medical technicians and paramedics or physicians. Three trials [8,9,19] used the 2000 AHA/ILCOR guidelines [12], and one [7] adopted the 1998 European Resuscitation Council guidelines [20]. Two trials [7,8] investigated the effects of automated external defibrillators (AEDs), one [9] investigated manual defibrillators, and one [19] investigated a mixed use of AEDs and manual defibrillators. The rates of witnessed cardiac arrest ranged from 71% to 96%. The rates of bystander CPR ranged from 44% to 54%. The response time from EMS dispatch to first shock ranged from 7.5 to 10.7 minutes.

All trials used biphasic truncated exponential waveforms. Three trials [8,9,19] used MDS waveforms, while one [7] used both MDS and MTE waveforms in monophasic groups. The first shock energy in the biphasic and monophasic groups was 120-200 and 200 J, respectively. Stacked shocks up to three times were adopted to treat Vf in all trials according to previous guidelines [12]. In current review, we extracted the defibrillation results of first shock only rather than consecutive shocks in the context of current guidelines [6].

Clinical outcome data are provided in Table 3. The definition of Vf termination differed with respect to rhythms following shocks and the timing of outcome recording. Two trials [7,8] defined Vf termination as post-shock transition into Non-shockable rhythm, one [9] defined post-

Table 1

Characteristics of biphasic and monophasic waveforms in randomized controlled trials included in the analysis of termination of ventricular fibrillation

Author

Year

N

Region

Mean age

Male (%)

Analysisa

Witnessed cardiac arrest (%)

Bystander CPR (%)

EMS dispatch to first shockb (min)

Biphasic waveformsc

Monophasic waveformsc

Schneider [7]

2000

115

Belgium/Finland/ Germany

66

76

ITT

88

44

8.9

Waveforms: truncated exponential; Energy:

Waveforms: damped sine and truncated

van Alem [8]

2003

120

Netherlands

66

80

ITT

96

54

8

150/150/150 J

Waveforms: truncated

exponential; Energy: 200/200/360 J

Waveforms: damped

Morrison [9]

2005

165

Canada

67

73

PP

78

44

10.7

exponential; Energy: 200/200/360 J

Waveforms: truncated

sine; Energy: 200/200/360 J

Waveforms: damped

exponential; Energy:

120/150/200 J

sine; Energy:

200/300/360 J

Kudenchuk [19]

2006

168

US

64

77

ITT/PP

71

52

7.5

Waveforms: truncated exponential; Energy: 200/200/360 J

Waveforms: damped sine; Energy: 200/200/360 J

a PP, per-protocol.

b Average time; van Alem et al. report median time.

c All trials followed previous guidelines for CPR, which recommended stacked shocks up to three times for ventricular fibrillation. The energy levels used in consecutive three times of shocks are reported.

Table 3

Clinical outcomes of biphasic and monophasic waveforms in randomized controlled trials

Reference Termination of ventricular

fibrillation after first shocka

Return of organized rhythm after

first shocka

Return of spontaneous circulationa

Survival to hospital dischargea

Biphasic waveform(%)

Monophasic waveform(%)

Biphasic waveform(%)

Monophasic waveform(%)

Biphasic waveform(%)

Monophasic waveform(%)

Biphasic waveform(%)

Monophasic waveform(%)

Schneider [7]

44/48 (91.7)

44/67 (65.7)

Not reported

Not reported

39/48 (81.3)

35/67 (52.2)

16/48 (33.3)

18/67 (26.9)

van Alem [8]

50/51 (98.0)

63/69 (91.3)

Not reported

Not reported

31/51 (60.8)

45/69 (65.2)

7/51 (13.7)

13/69 (18.8)

Morrison [9]

Not reported

Not reported

19/83 (22.9)

10/82 (12.2)

40/86 (46.5)

39/83 (47.0)

8/85 (9.4)

6/82 (7.3)

Kudenchuk [19]

65/74 (87.8)

75/91(82.4)

24/74 (32.4)

24/91 (26.4)

60/68 (88.2)

67/80 (83.8)

28/68 (41.2)

27/80 (33.8)

a Outcomes are expressed as “events/patients.”

shock transition into organized rhythm, and one [19] reported the results of both definitions. One trial [8] reports the outcomes after shocks both at five seconds and one minute. The 2010 AHA/ILCOR guidelines [6] define successful defibrillation as the absence of Vf five seconds after shock delivery that is not influenced by other subsequent interventions such as chest compression and ventilation. Post-shock transition into asystole or organized rhythm was considered as successful defibrillation [21]. Therefore, we extracted the results recorded five seconds after first shock delivery, which were further categorized into Vf termination (ie, post-shock transition into non- shockable rhythm, including asystole and other organized rhythms) and the return of organized rhythm (ie, post-shock transition into organized rhythms).

Quantitative data synthesis

The summary estimates of Vf termination exhibited significant statistical heterogeneity among trials (RR, 1.14; 95% CI, [1.00, 1.30]; I2, 73.8%) (Fig. 2A). The Galbraith plot indicated that the trial by Schneider et al [7] might be a potential source of heterogeneity. After exclusion of the trial by Schneider et al., the I2 decreased significantly from 74% to 0% and the summary estimates of Vf termination did not indicate that biphasic waveforms were signifi- cantly superior to monophasic waveforms (RR, 1.07; 95% CI, [0.99,

1.16]; I2, 0%) (Fig. 2B). Furthermore, the summary estimates of the return of organized rhythm were not significant with respect to waveforms (RR, 1.44; 95% CI, [0.97, 2.13]; I2, 0%) (Fig. 3).

The pooled results regarding ROSC revealed significant statistical heterogeneity (RR, 1.11; 95% CI, [0.91, 1.36]; I2, 65.4%) (Fig. 4A). The

Galbraith plot also indicated the trial by Schneider et al [7]. as a potential source of heterogeneity. Excluding this trial significantly decreased I2 from 65% to 0%; moreover, the pooled results regarding ROSC did not indicate any benefit of biphasic waveforms (RR, 1.00; 95% CI, [0.88, 1.14]; I2, 0%) (Fig. 4B). The summary estimate of survival to hospital discharge also revealed non-significant results with respect to waveforms (RR, 1.14; 95% CI, [0.84, 1.54]; I2, 0%) (Fig. 5).

Regarding the summary estimate of Vf termination, meta-regression indicated that several pre-specified covariates differed significantly among trials, including time from EMS dispatch to first shock (P = .03), first shock energy (P = .01), and bystander CPR rate (P = .01).

The funnel plot indicated some publication bias, with the trial by Schneider et al [7]. being the possible outlier.

Discussion

A previous meta-analysis [22] indicated that biphasic waveforms were more effective in defibrillation than monophasic ones. However, the studies included in the meta-analysis [22] were conducted under

Fig. 2. A, Forest plot of the summary effect estimates of termination of ventricular fibrillation after first shock between biphasic and monophasic waveforms in patients experiencing out-of-hospital cardiac arrest. W (random), weights in random-effects DerSimonian-Laird model. B, Forest plot of the summary effect estimates of termination of ventricular fibrillation after first shock between biphasic and monophasic waveforms in patients experiencing out-of-hospital cardiac arrest after exclusion of the trial by Schneider et al [8]. W (fixed), weights in fixed-effect Mantel-Haenszel model.

Fig. 3. Forest plot of the summary effect estimates of return of organized rhythm after first shock between biphasic and monophasic waveforms in patients experiencing out-of- hospital cardiac arrest. W (fixed), weights in fixed-effect Mantel-Haenszel model.

highly controlled in-hospital conditions, such as electrophysiology laboratories. OHCA victims suffer from more complicated conditions in which Vf exists longer than that in in-hospital conditions. Therefore, we further examined whether the effect of biphasic waveforms on Vf termination in controlled in-hospital conditions can be extrapolated to more complicated out-of-hospital situations.

Biphasic waveforms did not seem to be superior to monophasic ones with respect to Vf termination, return of organized rhythm, ROSC, or survival to hospital discharge. These results seemed to be against the treatment recommendations of the 2010 AHA/ILCOR guidelines [6], which attribute the superiority of biphasic waveforms to the three RCTs [7-9]. Two of these 3 RCTs [8,9] did not demonstrate the superiority of biphasic waveforms when we examined the results of the first shock at five seconds only; furthermore, the other trial by Schneider et al [7], which involved the mixed use of MTE and MDS in the monophasic group, was a potential statistical outlier and source of heterogeneity in the current review.

Meta-regression revealed that the trial by Schneider et al [7] differed significantly from other trials [8,19] with a lower rate of

bystander CPR, longer time from EMS dispatch to first shock, and lower energy of first shock. These factors might decrease the successful defibrillation rate. Nonetheless, the successful defibrilla- tion rate in their biphasic group was approximately 92%, which is comparable to the results of the other two trials [8,19]. Meanwhile, the successful defibrillation rate in the monophasic group of their study was approximately 66%, which is much lower than the results of the other 2 trials [8,19]. Schneider et al used AEDs delivering either MTE or MDS waveforms in the monophasic group. Some studies suggest that MTE waveforms are less effective for defibril- lation than MDS waveforms [10,11]. In a report of the same cohort, Martens et al [11]. revealed that the MTE AEDs composed approximately 80% of all monophasic AEDs in the trial by Schneider et al [7]. Martens et al [11] also point out that biphasic waveforms exhibited significantly better defibrillation efficacy than MTE waveforms but not the MDS ones. Although Martens et al [11] indicated that MTE and MDS waveforms do not differ with respect to efficacy in a post-hoc analysis, the mixed use of these two types of monophasic waveforms might explain the relatively high efficacy

Fig. 4. A, Forest plot of the summary effect estimates of return of spontaneous circulation between biphasic and monophasic waveforms in patients experiencing out-of-hospital cardiac arrest. W (random), weights in random-effects DerSimonian-Laird model. B, Forest plot of the summary effect estimates of return of spontaneous circulation between biphasic and monophasic waveforms in patients experiencing out-of-hospital cardiac arrest after exclusion of the trial by Schneider et al [8]. W (fixed), weights in fixed-effect Mantel-Haenszel model.

Fig. 5. Forest plot of the summary effect estimates of survival to hospital discharge between biphasic and monophasic waveforms in patients experiencing out-of-hospital cardiac arrest. W (fixed), weights in fixed-effect Mantel-Haenszel model.

of biphasic waveforms reported by Schneider et al [7] (RR: 1.40) compared to the other two trials [8,9] (RR: both 1.07), thus resulting in significant statistical heterogeneity.

Weisfeldt et al propose a three-phase time-sensitive model, indicating a distinct optimal therapeutic approach in each phase of resuscitation [23]. This model emphasizes the primacy of defibrilla- tion if the collapse time is less than four minutes (ie, the electrical phase) and the primacy of chest compression when the collapse time is between four and ten minutes (ie, the circulatory phase). After approximately ten minutes of cardiac arrest (ie, the metabolic phase), the effectiveness of both defibrillation and chest compression decreases rapidly and survival rates appear poor. The observed time from EMS dispatch to first shock in the current review ranged from 7.5 to 10.7 minutes, suggesting that most of the shocks were performed in the circulatory or metabolic phase. The lack of effectiveness of defibrillation during prolonged Vf might explain why biphasic waveforms were not significantly superior to monophasic ones in current review [24,25]. Besides, when Vf was associated with acute myocardial ischemia, conditions frequently encountered in OHCA patients, the energy increases substantially regardless of waveform [26-28]. These two reasons might explain why the superiority of biphasic waveforms in terminating Vf of brief duration under controlled laboratories could not be extrapolated to OHCA patients.

There was no significant difference between biphasic and mono- phasic waveforms with respect to the rates of ROSC or survival to hospital discharge. Five key factors in the Chain of survival are proposed: rapid EMS access, early CPR, Early defibrillation, early advanced cardiac life support, and effective care after resuscitation [5]. Shock success represents only one of five factors. Thus, it might be difficult to observe significant improvements in ROSC or survival to hospital discharge by changing one covariate only.

All RCTs in the current review randomly distributed tested defibrillators to EMS units. Therefore, clusters of individuals rather than individuals were randomized to different waveforms. We cannot assume that the individuals resuscitated by the same EMS units were independent of one another. Without considering clustering, the calculations of the sample size and corresponding statistical analysis would be incorrect [29]. Besides, by ignoring the effect of clustering, analyses create a “unit of analysis error” and produce over-precise results and artificially small P values, resulting in false-positive conclusions favoring intervention [29]. Introducing intra-cluster Correlation coefficients and the mean size of clusters into statistical analysis could prevent these issues [29]. However, we could not correct the unit of analysis error in the current meta-analysis because of limited available information. Since most uncorrected results did not produce positive findings, the potential of overestimations and false-positive conclusions might be less concerning.

The 2010 AHA/ILCOR guidelines present several observational cohort studies [21,30-32] as evidence of the superiority of biphasic

waveforms because of better results regarding Vf defibrillation [21], return of organized rhythm [31], ROSC [32], and neurologic outcomes [30]. However, none of these trials provide adjusted effect estimates in their outcomes. Using unadjusted effect estimates is considered a failure to establish comparability between intervention and control groups with respect to each confounder and is not recommended for synthesis in meta-analysis [33].

Although the pooled result showed null effects of biphasic over monophasic waveforms the beneficial trend still could be observed in Vf termination or return of organized rhythm. Accordingly, lack of statistically significant result might be attributed to lack of statistical power, ie, type II error. To establish statistical significance for the observed average difference of Vf termination in trials by van Alem et al [8] and Kudenchuk et al [19] (90% vs 85%), with 80% power and a 2-sided alpha of 0.05, the sample size would demand enrollment of at least 784 patients in a single trial. Even though we used all available trial results, the number of included subjects in current meta-analysis was still far below that required with adequate statistical power. Observational studies might be performed more easily to examine the effects of different waveforms with a substantially large sample size. However, the results of observational studies showed both positive [30]and null [34] effects too. As previously discussed, most of these studies failed to establish comparability to avoid selection bias and could not be quantitatively synthesized to achieve conclusion.

In summary, the results of the current meta-analysis indicate that biphasic waveforms seem not to be superior to monophasic ones with respect to Vf termination, return of organized rhythm, ROSC, or survival to hospital discharge in OHCA patients with initial rhythm of Vf in the context of current guidelines. Since most trials were conducted according to previous guidelines for CPR, more trials are needed to conclusively answer this question.

Limitations

We did not search abstracts from conferences, proceedings, or clinical trial registries; therefore, our literature search may be incomplete. We tried to compensate for this shortcoming by manually checking the bibliographies of relevant studies, reviews, and meta-analyses.

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