We sought to determine whether the prehospital electrocardiogram (ECG) improves the
diagnosis of an acute coronary syndrome.
The ECG is the most widely used screening test for evaluating patients with chest
pain.
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.
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).
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.