The Association between Prehospital Time Intervals and ST-Elevation Myocardial Infarction System Performance

Steven Vandeventer, EMT-P2; Steven R. Ward, BA, NREMT-P2; Jonathan Studnek, PhD1,2; Lee Garvey, MD1; Tom Blackwell, MD1; Steven Vandeventer, EMT-P2; Steven R. Ward, BA, NREMT-P2; 1. Carolinas Medical Center, Department of Emergency Medicine, Charlotte, North Carolina, USA 2. Mecklenburg EMS Agency (a joint agency of Mecklenburg County, Carolinas Health Care System and Presbyterian Health Care System), Charlotte, North Carolina, USA

Introduction Current guidelines recommend that the interval from first medical contact to PCI be ≤ 90 minutes among individuals experiencing a ST elevation myocardial infarction (STEMI). There is little guidance regarding how EMS should optimize their time prior to hospital arrival.

Objectives Describe system time intervals from first medical contact to reperfusion by percutaneous coronary intervention (PCI), among STEMI patients. Assess associations between time intervals and achieving PCI in ≤ 90 minutes.

Objectives Derive theoretical benchmarks for system time intervals. Estimate probability of achieving PCI in ≤ 90 minutes based on proposed timing benchmarks.

Methods Retrospective analysis of prehospital patients presenting with an acute STEMI as diagnosed by prehospital ECG Used data from May 2007 - March 2009 Data for this registry were provided through a co-operative agreement with the three hospitals that perform PCI in the county

Methods All STEMI receiving centers were accredited by the Society of Chest Pain Centers EMS agency all ALS system with uniform triage, treatment, and transport protocols county wide All timing devices at PCI centers and EMS system were referenced to an atomic clock

Methods Emergency physicians notified by EMS providers of potential STEMI patients PCI center activated by emergency physician through central paging system ECG images were not transmitted

Methods Outcome – STEMI system performance First medical contact to reperfusion First medical contact defined as 911 call receipt Reperfusion time defined as first device deployment Analyzed as a dichotomous variable Defined as acceptable in patients with first medical contact to reperfusion ≤ 90 minutes

Methods Time Intervals Response Time ECG Time On scene Time Notification Time Table Time

Methods Data analysis plan Initial descriptive statistics t-tests for initial assessment of initial associations Independent variables assessed for linearity Selection of plausible benchmark times Logistic regression modeling

Results 181 patients included in analysis 165 (91.2%) had all time intervals available 110 (66.7%) patients received PCI ≤90 minutes after 911 call receipt Median time to PCI was 82.9 min 90% of patients received PCI in 118.0 minutes

Results Studnek et al. Circulation. 2010;122:1464-1469

Results Time Intervals Response Time ECG Time On scene Time ≤ 11 min ECG Time ≤ 8 min On scene Time ≤ 15 min Notification Time ≤ 10 min Table Time ≤ 30 min

Results Studnek et al. Circulation. 2010;122:1464-1469

Discussion In order to provide the best possible care to STEMI patients, process improvements must occur in both the prehospital and in-hospital setting Describing prehospital system time intervals and deriving theoretical benchmarks for these intervals is one method which may assist in the evaluation of process improvement for pre-hospital STEMI care

Discussion Not all benchmark may be feasible for implementation Focus on individual components with an overall design for implementation Current benchmarks are limited in overall scope Plausible starting point for EMS process improvement

Limitations Generalizability Unrecognized confounding Single EMS agency with integrated STEMI care system Uncommon definition for first medical contact Unrecognized confounding Age, gender, co-morbidities etc. Patient characteristics may further refine the constructed model

Limitations Misclassification Continuous variables transformed to dichotomous Likely misclassification of exposure not related to outcome (non-differential)

Conclusions Five theoretical benchmarks were derived from system time intervals Model created that estimates the probability of PCI Model may be most useful for identifying areas of system improvement