Like other areas of medicine, there is often lag time, or an ‘evidence to practice gap,’ between when new cardiac arrest guidelines are published and when they are incorporated into routine clinical practice. For example, among 174 US-based emergency medical services (EMS) agencies, it took over a year on average (mean 416 d) to implement the 2005 AHA guideline changes. For some agencies in the study, the transition time was ≥2 y. In the in-hospital setting, Ross and colleagues demonstrated in an interrupted time series analysis that 2010 and 2015 pediatric guideline changes for the use of lidocaine and sodium bicarbonate were not temporally associated with a change in pediatric IHCA medication administration patterns. Multiple years after the incorporation of TTM into cardiac arrest guidelines, the Resuscitation Outcomes Consortium demonstrated a continued low rate of use of TTM after OHCA (median 27.5% across 186 hospitals) with a high degree of variability among sites. These findings highlight the need for improved strategies to bridge the gap between cardiac arrest research-informed guidelines and actual clinical practice.

Deviations in the quality of chest compressions and intra-arrest ventilation performed during cardiac arrest are also common. Abella and colleagues found low rates of adherence to guideline-recommended chest compression rates and depth during IHCA, reporting compression rates below the recommended rate in 28.1% of epochs of CPR, and inadequate depth in 37.4% of compressions. Similarly, a 2023 study of chest compressions delivered by firefighters during OHCA observed that only about one-third (33.58%) of the 134 analyzed patients received chest compressions within the recommended depth range (50– 60 mm). Additionally, ventilation rates frequently deviate from guidelines. Excessive intra-arrest ventilation has been demonstrated in multiple adult cardiac arrest studies. ^,, A pediatric study by Sutton and colleagues found that no observed cardiac arrest events had an intra-arrest ventilation rate of 10 breaths per min (which was the guideline-recommended rate at the time), with a median ventilation rate significantly exceeding recommendations (29.8 breaths/min). ^, Collectively, these studies emphasize substantial gaps in guideline adherence in the administration of both chest compressions and ventilations during CPR.

Best practices for OHCA care prior to EMS arrival are also difficult to achieve. Globally, only 35% to 45% of OHCA victims are estimated to receive lay responder CPR, with this low rate reflecting racial, ethnic, and gender disparities, among other drivers. ^,,, Black and Hispanic individuals have significantly lower rates of receiving lay responder CPR compared to White individuals, both at home (38.5% vs 47.4%) and in public settings (45.6% vs 60.0%). Public access automated external defibrillators (AEDs), which are critical for early defibrillation and improved survival outcomes, are vastly underutilized, with AED usage occurring in fewer than 3% of OHCA cases. ^, Frequently identified barriers to AED use include lack of public awareness about locations, inadequate AED maintenance, and insufficient training and engagement.

Significant deviations from guideline-based post-arrest care have been observed, characterized by notable variability in adherence to critical therapies, such as TTM, timely CAG, and neurodiagnostic testing. Within 1 regional EMS system, implementation rates among hospitals admitting OHCA patients ranged from 12% to 49% for CAG and 17% to 92% for TTM, with institutional characteristics, such as hospital size and academic affiliation, significantly influencing care variability. Additionally, despite guideline recommendations advocating for multimodal neuroprognostic testing at least 3 d after cardiac arrest, a national electronic health record-based study of 34,585 patients with non-traumatic OHCA in the United States found that only 9% of patients that did not survive to hospital discharge underwent at least 1 neuroprognostic test. This study highlights a widespread and critical deviation from recommended prognostic practices that could contribute to inappropriate early withdrawal of life-sustaining therapies. These findings demonstrate significant opportunities to improve adherence to recommended post-arrest prognostic and therapeutic interventions.

While implementing effective systems of care during complex sociotechnical interactions will always face obstacles, it is possible to improve patient outcomes through interventions that improve implementation. This is most evident in: (1) the observed differences in outcomes based on where an individual has their cardiac arrest and (2) strong examples of process changes resulting in improved outcomes.

In both the in-hospital and out-of-hospital settings, survival rates vary based on where a patient is treated. Among AHA GWTG-R registry hospitals submitting adult IHCA events, risk-standardized rates of survival to hospital discharge ranged from 11% to 35% (in events occurring from 2007– 2010) and risk-standard rates of return of spontaneous circulation ranged from 42.2% to 84.6% (in events occurring from 2014– 2017). ^, In a survey of national and regional OHCA registries, survival rates vary from 3.1% to 20.4%. Variation in outcomes across hospitals, EMS agencies, and geographic areas, even when accounting for risk-standardized survival as in the in-hospital setting, underscores the importance of optimizing resuscitation quality of care in order to save the most lives.

There are many effective examples of the impact of initiatives aimed at optimizing local implementation on process measures and patient outcomes. ^,,,,,

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  For instance, King County, Washington has enacted a multifaceted, comprehensive OHCA response system with iterative improvements over multiple decades. This effort has included defibrillation by emergency medical technicians, dispatcher-assisted CPR, public access defibrillation, and a CPR-defibrillation protocol that replaced delivery of 3 sequential shocks with administration of one shock followed by 2 min of CPR. They report notably high survival rates (16.3% for non-shockable rhythms and 39.9% for shockable rhythms). ^,

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  Hospitals with the highest risk-standardized survival rates are more likely to have dedicated resuscitation teams with diverse multidisciplinary team members, clear team roles and responsibilities, better communication and leadership during IHCA, and in-depth mock codes.

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  In a single center, 3 y study of pediatric IHCA, a 7-element quality bundle comprised of a CPR coach, cardiac arrest data evaluations, implementation of action-linked phrases, CPR choreography, ergonomic standardization, structured debriefing, and simulation resulted in a significant increase in the proportion of ‘excellent’ epochs of CPR (guideline-compliant rate, depth, and fraction) from 19.9% in the first year of the study to 44.3% in the final year of the study.

Collectively, these examples underscore the ability of effective systematic implementation to significantly improve resuscitation quality and patient outcomes.

IS is the “scientific study of methods to promote the systematic uptake of research findings and other evidence-based practices into routine practice, and hence, to improve the quality and effectiveness of health services and care.” ^,, One of the essential primary components of IS is an efficacious practice to be studied. Unlike study designs that seek to determine efficacy, the practice being studied using IS methodology should already be evidence-based. The focus of study is not on determining practice effectiveness but instead understanding the how and why of practice implementation. Put simply, rather than ask the question of what the best treatment for a condition is, IS asks the question of how to get the identified best treatment to all appropriate patients. Additionally, IS not only aims to most effectively implement a practice, but also to produce generalizable knowledge that can inform optimal implementation of the practice across different contexts; this crucial difference is one of the most important reasons that it should be used in addressing implementation challenges in cardiac arrest care.

In resuscitation science, as in many other areas of health care, not all recommended practices have a robust supporting evidence base of randomized controlled trials. In these cases, IS study is usually still possible. Expert consensus practices (e.g. those included in published cardiac arrest guidelines) are also appropriate choices for IS efforts. An insufficient evidence base for a practice of interest can also be addressed through hybrid effectiveness-implementation trials, which enable simultaneous study of both the effectiveness and implementation of an intervention. In fact, most clinical trials can incorporate some ISs components. Resuscitation scientists should carefully consider whether the results of their clinical trials could be strengthened by the addition of IS objectives.

To produce the descriptive and explanatory generalizable knowledge that is a cornerstone of IS research, in-depth contextual characterization is needed. IS studies are grounded in a foundation of theories, models, and frameworks that serve this purpose. Most often, IS researchers will describe and categorize their data based on determinant and/or evaluation frameworks. The most pervasive of the determinant frameworks, which identify and organize the factors that influence implementation, is the Consolidated Framework for Implementation Research (CFIR). It is comprised of 5 domains (the innovation, outer setting, inner setting, individuals, and the implementation process) and associated constructs. Fig. 1 is a modified representation of the CFIR for a hypothetical IS study aimed at decreasing interruptions during CPR in the in-hospital setting. The outcomes of interest studied in IS also differ from those of traditional clinical trials ( Box 3 ).

Adaptation of the five domains of the Consolidated Framework for Implementation Research to an in-hospital cardiac arrest initiative to minimize interruptions in chest compressions.

Adapted from Damschroder, L. J., Reardon, C. M., Widerquist, M. A. O., et al. (2022). The updated consolidated framework for implementation research based on user feedback. Implementation Science, 17, 75. https://doi.org/10.1186/s13012-022-01245-0. Image adapted by The Center for Implementation, © 2025. Version: V2025.01. https://thecenterforimplementation.com/toolbox/cfir .