Early versus Later Rhythm Analysis in Patients with Out-of-Hospital Cardiac Arrest: A Quantitative Critique

Submitted by Lacy Kusy, MSN, APRN-C

Tags: cardiac cardiac arrest literature review Quantitative Critique study

Early versus Later Rhythm Analysis in Patients with Out-of-Hospital Cardiac Arrest: A Quantitative Critique

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The critique of the study Early versus Later Rhythm Analysis in Patients with Out-of-Hospital Cardiac Arrest evaluates strengths and weaknesses in relation to the generalizability of the study. The significance of the study is assessed, as well as the literature review, purpose, hypothesis, findings, and limitations. The study provided information regarding protocols on performing CPR on out-of-hospital patients. Although the findings were not clinically or statistically significant, the study did offer useful knowledge that both methods of rhythm analysis with CPR provide similar outcomes. This study failed to provide additional knowledge on the topic. Ultimately, further research should be completed on the best treatments for out-of-hospital cardiac arrests.  

Early versus Later Rhythm Analysis in Patients with Out-of-Hospital Cardiac Arrest: A Quantitative Critique

The quantitative study titled Early versus Later Rhythm Analysis in Patients with Out-of-Hospital Cardiac Arrest discusses two methods of performing cardio-pulmonary resuscitation (CPR) on patients experiencing cardiac arrest outside of the hospital. A total of 27 doctors participated in the research of the study. The study was conducted to determine if the two approaches of CPR measured would provide different outcomes of patients with out-of-hospital cardiac arrests. A critique was completed assessing strengths, weaknesses, and the applicability of the study to the evidence based practice of nursing. Nurses receive many patients status post cardiac arrest in the field and would benefit from a well conducted study comparing two approaches of CPR.

Background and Significance

In the United States and Canada, an estimated 330,000 deaths occur each year from out-of-hospital cardiac arrests. The rate of survival to hospital discharge of patients with out-of-hospital cardiac arrests treated by emergency medical services (EMS) ranges from three percent to 16.3%. Different methods of the initiation of CPR have been recommended including the initiation of CPR before analysis of cardiac rhythm and the early analysis of cardiac rhythm as quickly as possible and defibrillating as necessary. The 2010 American Heart Association guidelines state that inconsistent data exists to support or refute either of these two methods (Stiell et al., 2011). The clinical significance of this study to the evidence based practice of nursing revolves around understanding what the most clinically significant method is for CPR that yields the greatest chance of survival and discharge from hospital.

Ethical Aspects

The protocol for the study was approved by the institutional review board and research ethics board at each site participating in the study. The patients participating in the study were not required to provide informed consent as the study was conducted during an emergency situation. Under the regulations of the Food and Drug Administration and Canadian Tri-Council agreement, this study was exempt from providing informed consent due to its emergency nature. EMS assisting in the research completed additional training prior to the study as reminders on how to properly treat those during a cardiac arrest. The study was supported by the National Heart, Lung, and Blood Institute and authors of the study are affiliated with such institutes as Johns Hopkins Medical Institutions and the Division of Emergency Medicine (Stiell et al., 2011). Ethical considerations were appropriately conducted during this study and research authors are qualified to conduct the study. Participants in the study have no additional risks in participation as the study is conducted during emergency situations.

Purpose Statement

The purpose of the study was to compare two approaches of CPR, a brief period of CPR with prompt initiation of rhythm analysis versus a longer period of CPR before the first analysis of cardiac rhythm (Stiell et al., 2011). The purpose of the study compared these two methods of CPR and described them as an early analysis versus the late analysis.

Literature Review

The purpose of the literature review is to analyze research sources to determine what is known and not known about a certain topic (Groves, Burns, & Gray, 2013). The literature review completed prior to this study discovered that the preferred initial approach to CPR in out-of-hospital cardiac arrests remains uncertain. In comparing five research studies, the researchers discovered that three studies supported guidelines for early CPR before analysis of cardiac rhythm; however, two different studies did not support these findings (Stiell et al., 2011). Therefore, the literature review discerned that more knowledge was needed to better prepare guidelines for out-of-hospital cardiac arrests.

Conceptual Framework and Diagram

Hypothesis and Research Design

The hypothesis presented in this study was that “patients with an out-of-hospital cardiac arrest might benefit from the administration of CPR by EMS personnel for approximately three minute before the first analysis of cardiac rhythm (Stiell et al., 2011, p. 793). The hypothesis addresses the appropriate population of those experiencing an out-of-hospital cardiac arrest and assists the researchers in identifying the variables involved in the study, such as early versus late rhythm analysis.

The design of the study is defined as a quasi-experimental cluster-randomized trial. A cluster sample involves a population not readily accessible, therefore a list of sites that could be used in the study is created, and a randomized sample is drawn from the list. A quasi-experimental design has limited control over random selection and random assignment (Groves, Burns, & Gray, 2013). The included cluster sites for this study were 10 Resuscitation Outcomes Consortium sites in the United States and Canada (Stiell et al., 2011). Limited control in the study yields to the possibility of type one errors, in which the hypothesis is rejected when it is actually true. The design, however, does allow the researchers to analyze data from a variety of location sites to test the hypothesis.

Population, Sample, and Setting

The researchers seek to generalize the data from the study to the target population, which includes all adults experiencing an out-of-hospital cardiac arrest. The accessible population for the study comes from the natural setting of 10 Resuscitation Outcomes Consortium sites in the US and Canada, including Dallas, Toronto, and San Diego. Each site was divided into subunits according to geographic boundaries and designated at random to a CPR strategy: early versus late rhythm analysis. The sample population included those appropriate for the study and excluded adults experiencing cardiac arrest in relation to drowning, strangulation, or electrocution. Therefore, of the 13,460 patients screened, 9,933 were included in the randomization for data analysis. The sample is a probability sample as each adult in the sample population had an equal chance of being selected. The cluster method chosen allowed researchers to randomly select patients from each site who experienced an out-of-hospital cardiac arrest. The enrollment of 13,239 adults to be evaluated allowed for a 99.6% power, a 95% confidence interval, and a P of 0.59 (Stiell et al., 2011). The study, however, needed 14,154 participants to have a 90% power to detect a 25% difference between the outcomes of the trial. No effect size was mentioned in this study and data was collected from only 9,933 patients; therefore, the sample size is not sufficient. This insufficient sample size is a weakness in the study and could lead to a type two error.

Data Collection Instruments and Procedures

The early analysis group was assigned to receive 30 to 60 seconds of CPR before rhythm analysis, whereas the late analysis group received three minutes of CPR before rhythm analysis. The subgroups consisted of 5,290 in the early and 4,643 in the late. The assigned intervention for each adult was assigned by the first responder to the scene. Start and stop times of CPR was recorded by a responder. Every six months, EMS providers received training on adhering to the protocol to ensure appropriate data. The primary outcome expected was survival to hospital discharge with functional status. Functional status was measured by the Rankin scale, which is a validated scale used for measuring performance of daily activities on patients who have had a stroke. A score of three or below identifies adequate functional status (Stiell et al., 2011). Continuous training strengthens the method of data collection; however, one major weakness in data collection was the method of determining which group the patient would belong to. The risk exists that an equal number of participants would not be in each group (early or late) due to which EMS responder arrived at the scene first. Nevertheless, due to the emergency nature of the study, the researchers would have acted unethically had they assigned certain responders arrive at specified locations and perform either early or late rhythm analysis.

Data/Statistical Analysis and Findings

A pre-specified and post hoc subgroup analysis was completed. The hoc subgroup analysis is used to determine differences in studies with two or more groups (Groves, Burns, & Gray, 2013). Further analysis was completed using an exploratory analysis, which revealed that no significant difference existed among the two groups. The range of difference from the early verses late group with survival of functional status was -1.1 to 0.7 (Stiell et al., 2011). The data is nominal, non-parametric, and descriptive in nature as it represents the survival rate of patients experiencing cardiac arrest out of the hospital. The primary categories of grouping are survival to functional status and no survival post out-of-hospital cardiac arrest.

Of the 9,933 patients included in the study, 5,290 were in the early analysis of cardiac rhythm group, and 4,643 were in the late analysis. Of the two groups, 310 (5.9%) of the patients in the early analysis group, and 273 (5.9%) of the patients in the late analysis group met the criteria for the primary outcome of a score of three of lower on the Rankin scale (Stiell et al., 2011). The hypothesis was neither accepted nor rejected as no clear significance was discovered among the two methods. Because this study did not provide any new useful information to the body of healthcare knowledge, the results are not clinically significant.


Due to the complex emergency of out-of-hospital cardiac arrests, precise control over time to first analysis of cardiac rhythm is difficult to achieve. One limitation was that the duration of CPR prior to analysis of cardiac rhythm was not within the assigned target in 36% of the patients. Also, the study does not address witnessed cardiac arrests by EMS or immediate recognition of cardiac rhythm prior to any CPR (Stiell et al., 2011). Of the limitations in the study, the one with the most impact is that of 36% of patients were not within the assigned target for duration of CPR prior to rhythm analysis. However, 68% of patients in the early analysis group received rhythm analysis within zero to 60 seconds and 60% of the late analysis group received analysis in the target range of 150 to 210 seconds (Stiell et al., 2011). The lack of precise control can lead to a type one error. Despite this limitation, the study represents an appropriate degree of accuracy that would be practiced typically during an out-of-hospital cardiac arrest situation, and a majority of the sample population was within the target time analysis.

Study Conclusions, Implications, and Recommendations

The study achieved its purpose of comparing early versus late cardiac rhythm analysis, but concluded that no significant difference existed between the two groups in relation to survival with functional status. No advantage was discovered by initiating CPR for three minutes prior to rhythm analysis. The outcomes of the data suggest that brief CPR may be appropriate in patients who have received CPR by a bystander prior to EMS arrival; however, there is no clear advantage to brief versus longer CPR prior to analysis of rhythm. The study recommends that each EMS system assess each situation and decide on the strategy most appropriate for the patient (Stiell et al., 2011). The importance of these study conclusions, implications, and recommendations allows future researches to utilize the knowledge gained by this study to further investigate the most beneficial protocol for CPR with functional survival.

Critical Reflection and Conclusion

Although the findings for the study provided no clinical significance between the two methods of CPR, the study did provide useful information that more knowledge is needed to adequately assess how to treat out-of-hospital cardiac arrests. Further research with a sufficient sample size needs to be done to discover evidence based knowledge on how to attain functional status for these patients at hospital discharge. The insufficient sample size and lack of precise control can lead to a type one and two error. The lack of significant findings; however, could also be associated with the inadequate sample size. Due to the increasing number of patients who have out-of-hospital cardiac arrests, more clinical research is necessary to provide a body of knowledge that can improve patient outcomes.


  1. Grove, S.K., Burns, N., & Gray, J.R. (2013). The practice of nursing research: Appraisal, synthesis, and generation of evidence. (7th ed.). St. Louis, MO: Elsevier Saunders.
  2. Stiell, I., Nichol, G., Leroux, B., Rea, T., Ornato, J., Powell, J., et al. (2011). Early versus later rhythm analysis in patients with out-of-hospital cardiac arrest. The New England Journal of Medicine, 365(9), 787-797.