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

2. 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

3. 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.

4. 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.

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

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

7. 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

8. 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

9. 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

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

11. 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

12. 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 minutes

13. Results
Studnek et al. Circulation. 2010;122:

14. 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

15. Results
Studnek et al. Circulation. 2010;122:

16. 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

17. 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

18. 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

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

20. 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