Factors associated with false-positive emergency medical services triage for percutaneous coronary intervention.

backgroundIn 2005, Orange County California Emergency Medical Services (EMS) initiated a field 12-lead program to minimize time to emergency percutaneous coronary intervention (PCI) for field-identified acute myocardial infarction (MI). As the program matured, "false-positive" (defined as no PCI or coronary artery occlusion upon PCI) field MI activations have been identified as a problem for the program.

objectivesTo identify potentially correctable factors associated with false-positive EMS triage to PCI centers.

methodsThis was a retrospective, outcome study of EMS 12-lead cases from February 2006 to June 2007. The study system exclusively used cardiac monitor internal interpretation algorithms indicating an acute myocardial infarction as the basis for triage. Indicators and variables were defined prior to the study. Data, including outcome, was from the Orange County EMS database, which included copies of 12-lead ECGs used for field triage. Negative odds ratios (OR) of less than 1.0 for positive PCI were the statistical measure of interest.

resultsFive hundred forty-eight patients were triaged from the field for PCI. We excluded 19 cases from the study because of death prior to PCI, refusal of PCI, and co-morbid illness (sepsis, altered consciousness) that precluded PCI. Three hundred ninety-three (74.3%) patients had PCI with significant coronary lesions found. False-positive field triages were associated with underlying cardiac rhythm of sinus tachycardia [OR = 0.38 (95% CI 0.23, 0.62)]; atrial fibrillation [OR = 0.43 (95% CI = 0.20, 0.94)]; an ECG lead not recorded [OR = 0.39 (95% CI = 0.20, 0.76)]; poor ECG baseline [OR = 0.59 (95% CI = 0.25, 1.37)]; One of three brands of monitors used in the field [OR = 0.35 (95% CI = 0.21, 0.59)]; and female gender [OR = 0.50 (95% CI = 0.34, 0.75)]. Age was not associated with false-positive triage as determined by ordinal regression (p=1.00).

conclusionFor the urban-suburban EMS field 12-lead program studied, age was not associated with false-positive triage. It was unexpected that female gender was associated with false-positive triage. False-positive triage from the field was associated with poor ECG acquisition, underlying rhythms of atrial fibrillation and sinus tachycardia, and one brand of 12-lead monitor.