Approximately 1% to 3% of all emergency department (ED) visits, as many as atrial fibrillation, and up to 6% of all hospital admissions are due to syncope 
. Though vasovagal reflex-mediated syncope and orthostatic hypotension are the two most common types with benign courses 
, a cardiac etiology of syncope is associated with significantly higher rates of morbidity and mortality 
Patients who present to the ED tend to be older and are more likely to have a cardiac etiology 
. Notably, experiencing syncope affects patients’ quality of life (QoL), and those with more frequent syncope report overall lower physical and mental health and impairment in activities of daily living 
. The QoL among patients with recurrent syncope appears equivalent to those with severe rheumatoid arthritis or chronic lower back pain 
. Recurrent syncope can also lead to long-term facility stay and a devastating loss of independence 
. In addition to the negative effects on QoL, syncope also has an economic impact. The U.S. Healthcare Utilization Project has estimated total annual hospital costs of greater than $4.1 billion in 2014 dollars with a mean cost of $9400 per admission 
. One 2017 article showed that, after adjusting for inflation, the median hospital charge for a single admission for syncope increased by 1.5 times from the preceding decade 
Due to concerns that patients presenting with syncope are at risk for an impending catastrophic event, overuse and inappropriate use of testing and hospital admission are common 
. Indisputably, among patients who present with syncope, clinicians must identify those at high risk of adverse outcomes. Nonetheless, the majority are at low risk. To assist clinicians in assessing patient risk, several syncope risk stratification calculators have been developed over the last 20 years; however, one study found that the concordance between different risk scores was only moderate and the application of both decision rules and clinical judgement may lead to some clinical benefit 
. A body of literature documents under-utilization of efficient tests, over-utilization of unnecessary tests, excess rates of admissions with limited diagnostic or therapeutic yield, over-expenditure associated with syncope management, and heightened risk to patients due to unnecessary tests and hospitalizations, including iatrogenic harms such as medication errors and in-hospital delirium 
. Given the frequency of syncope as a symptom, the cumulative cost and burden to the healthcare system and patients is substantial.
Aiming to provide guidance on optimizing the evaluation and management of syncope, a collaboration of the American College of Emergency Physicians, Society for Academic Emergency Medicine, American College of Cardiology (ACC), American Heart Association (AHA) and Heart Rhythm Society (HRS) issued a Guideline for the Evaluation and Management of Patients With Syncope in 2017 
. The 2017 Syncope Guideline represents an effort to standardize clinical practice and reduce unnecessary services. However, the mere existence of a guideline does not guarantee effective use. Evidence shows that the development of clinical guidelines alone is often not sufficient, even if recommendations in the guideline have been demonstrated to be effective on the structure, process and/or outcomes of patient care 
. Indeed, one recent study suggested that the current clinical guidelines have not significantly impacted resource utilization surrounding ED evaluation of syncope, and novel strategies are keenly needed to change ED practice patterns for such patients 
. Matching implementation strategies to barriers and facilitators for the use of the syncope guideline and tailoring strategies to local context hold significant promise for a successful implementation 
. However, evidence on effective implementation strategies for syncope care in the ED is scarce. Project MISSION, leveraging an engaged interdisciplinary team, aimed to facilitate the efficient and systematic implementation of high-value care to patients presenting to an ED with syncope.
2. Planning Implementation Success of Syncope Clinical Practice Guidelines in the Emergency Department Using CFIR Framework
2.1. Evaluation of Barriers Is a Necessity in Planning CPGs Implementation
Despite substantial efforts by medical researchers and professional societies 
, overuse and inappropriate use of testing and hospital admission are common in patients presenting with syncope. The most efficient solution to improve patient outcomes is most likely to adopt standardized criteria for evaluation and treatment administration based on the recommendations contained in guidelines. However, the uneven implementation of evidence-based CPGs is widely recognized as a continuing challenge to improving healthcare delivery and public health 
. Implementation science provides an empirical base for promoting adoption of CPGs and its research is dedicated to accelerating the pace of implementing evidence-based interventions in real-world healthcare settings. What determines the rate and extent of adoption is the interaction among characteristics of the CPG, the intended users, and a particular context of care setting. As part of the clinical guideline implementation planning process, a more detailed evaluation of underlying barriers and facilitators and how these determinants can be addressed by strategies is needed.
2.2. Local Context Tailored Implementation Strategy Is Essential
While tailoring to local context seems intuitive, most studies have not tailored implementation strategies to context. Healthcare delivery settings influence every step of how care is given, yet far more work is needed to effectively describe and link these structural and process characteristics to outcomes and to develop setting-changing interventions to improve care. Numerous conceptual frameworks (e.g., CFIR) have been developed to guide the identification and systematically assess potential determinants within local settings. Project MISSION was the first effort that specifically applied IS principles and methods to develop strategies and plan implementation processes to overcome multilevel barriers to deliver guideline-recommended, high-value care to patients presenting with syncope in the ED. It integrated behavioral interventions and healthcare process redesign, used stakeholder-engaged and local-context congruent approaches, and fostered a learning health system approach spanning an academic medical center and community hospitals. Development of MISSION ensured tailoring of implementation strategies in the local setting to accommodate variations and to sustain improved syncope care through tailored implementation. For example, patient educational videos can be edited by inserting a tailored intro and outro delivered by a recognizable, local clinician to enhance patient buy-in. In addition, the video can be presented in various ways based on each system’s infrastructure: via its system-wide patient education platform (either standalone or part of electronic health record-EHR), through a QR code to play on patients’ smartphones, or through an iPad in patient rooms. Another example, supported by an external implementation mentor, is that the local implementation team can use local detailed process maps to systematically identify process steps with opportunities, and test and refine strategies to increase guideline-recommended syncope care delivery through iterative test cycles.
Effective multifaceted implementation strategies targeting individuals, teams, and healthcare systems should be employed to plan successful implementation and promote adherence to CPGs. MISSION, developed by following implementation science principles, can optimize syncope care and translate CPGs into widespread clinical practice.