Background The pre-hospital 12-lead electrocardiogram (PHECG) is recommended in patients presenting to emergency medical services (EMS) with suspected acute coronary syndrome (ACS). Prior research found PHECG was associated with improved 30-day survival, but a third of ACS patients under EMS care did not have PHECG. Such patients tended to be female, older and/or with comorbidities. This previous study was undertaken when thrombolytic treatment was the main treatment for ST segment elevation myocardial infarction (STEMI); practice has since shifted to a predominant interventional strategy – primary percutaneous coronary intervention (pPCI). Moreover, the previous study relied solely on data collected by the Myocardial Ischaemia National Audit Project (MINAP), which does not include information on symptoms, EMS personnel gender, and other factors that may influence decision-making. The PHECG2 study addresses the following research questions: a) Is there a difference in 30-day mortality and reperfusion between those who do and do not receive PHECG? b) Has the proportion of eligible patients who receive PHECG changed since the introduction of pPCI networks? c) Are patients that receive PHECG different from those that do not in social and demographic factors, and in pre-hospital clinical presentation? d) What factors do EMS clinicians report as influencing their decision to perform PHECG?

Methods Explanatory sequential Quan-Qual mixed methods study comprising 4 Work Packages (WPs): WP1 a population based, linked data analysis of MINAP from 2010–2017 (n=510,000); WP2 retrospective chart review of EMS records from 3 EMS; WP3 focus groups with personnel from 3 EMS. WP4 will synthesise findings from WP1-3.

Conclusions Gaining an understanding into the clinical and non-clinical factors influencing EMS clinicians’ decisions to record PHECG will enable us to develop (and later test through a randomised trial) an intervention to improve PHECG uptake and patient outcomes following an ACS event.