Utility of the prehospital electrocardiogram in diagnosing acute coronary syndromes: the Myocardial Infarction Triage and Intervention (MITI) Project.
OBJECTIVE
We sought to determine whether the prehospital electrocardiogram (ECG) improves the diagnosis of an acute coronary syndrome.


BACKGROUND
The ECG is the most widely used screening test for evaluating patients with chest pain.


METHODS
Prehospital and in-hospital ECGs were obtained in 3,027 consecutive patients with symptoms of suspected acute myocardial infarction, 362 of whom were randomized to prehospital versus hospital thrombolysis and 2,665 of whom did not participate in the randomized trial. Prehospital and hospital records were abstracted for clinical characteristics and diagnostic outcome.


RESULTS
ST segment and T and Q wave abnormalities suggestive of myocardial ischemia or infarction were more common on both the prehospital and hospital ECGs of patients with as compared with those without acute coronary syndromes (p < or = 0.00001). Those with prehospital thrombolysis were more likely to show resolution of ST segment elevation by the time of hospital admission (14% vs. 5% in patients treated in the hospital, p = 0.004). In patients not considered for prehospital thrombolysis, both persistent and transient ST segment and T or Q wave abnormalities discriminated those with from those without acute coronary ischemia or infarction. Compared with ST segment elevation on a single ECG, added consideration of dynamic changes in ST segment elevation between serial ECGs improved the sensitivity for an acute coronary syndrome from 34% to 46% and reduced specificity from 96% to 93% (both p < 0.00004). Overall, compared with abnormalities observed on a single ECG, consideration of serial evolution in ST segment, T or Q wave or left bundle branch block (LBBB) abnormalities between the prehospital and initial hospital ECG improved the diagnostic sensitivity for an acute coronary syndrome from 80% to 87%, with a fall in specificity from 60% to 50% (both p < 0.000006).


CONCLUSIONS
ECG abnormalities are an early manifestation of acute coronary syndromes and can be identified by the prehospital ECG. Compared with a single ECG, the additional effect of evolving ST segment, T or Q waves or LBBB between serially obtained prehospital and hospital ECGs enhanced the diagnosis of acute coronary syndromes, but with a fall in specificity.
Department of Medicine, University of Washington, Seattle 98195-6422, USA.
P J
PJ
Kudenchuk
C
C
Maynard
L A
LA
Cobb
M
M
Wirkus
J S
JS
Martin
J W
JW
Kennedy
W D
WD
Weaver
D002037:Bundle-Branch Block / Q000175:diagnosis / Q000188:drug therapy; D004562:Electrocardiography / Q000187:drug effects; D004632:Emergency Medical Services; D006801:Humans; D009203:Myocardial Infarction / Q000175:diagnosis* / Q000188:drug therapy; D017202:Myocardial Ischemia / Q000175:diagnosis / Q000188:drug therapy; D012680:Sensitivity and Specificity; D015912:Thrombolytic Therapy; D010959:Tissue Plasminogen Activator / Q000627:therapeutic use*; D016896:Treatment Outcome; D014218:Triage
D010959:Tissue Plasminogen Activator