Frequency of non-ST-segment elevation injury patterns on prehospital electrocardiograms

Introduction. Prehospital electrocardiograms (ECGs) have been recommended to facilitate early diagnosis of ST-segment elevation myocardial infarction (STEMI). However, prehospital ECGs can also be used to triage patients with nonST-segment elevation acute coronary syndromes, who comprise a majority of patients with ischemic events presenting by ambulance to overcrowded emergency departments. Objective. We assessed the frequency of nonST-segment elevation injury patterns on prehospital ECGs in patients with a chief complaint of chest pain evaluated by the emergency medical services (EMS) system. Methods. We analyzed prehospital ECGs of patients with the chief complaint of chest pain during a nine-month period. The ECGs were divided into three categories: injury pattern; no injury pattern; and technically uninterpretable. Injury pattern criteria were as follows: 1) regional ST depression ≥1.0 mm; 2) regional T-wave inversion (TWI) ≥3 mm; 3) left bundle branch block (LBBB); and 4) regional ST-segment elevation ≥1.0 mm. Descriptive statistics with 95 confidence intervals (CIs) are presented. Results. Prehospital ECGs were obtained for 322 of 340 chest pain patients: 72 were men; the average age was 60 years (range 1896 years). Seventy-seven ECGs (24, 95 CI 19.328.9) met the criteria for injury pattern, 230 (71) did not show injury, and 15 (5) were uninterpretable. Of the 77 ECGs that exhibited an injury pattern, 39 (51) showed ST depression, seven (9) TWI, seven (9) LBBB, and 24 (31) ST-segment elevation. Thus, nonST-segment elevation injury patterns (ST depression/TWI/LBBB) accounted for 53 (17, 95 CI 12.620.9) of the total 322 prehospital ECGs. Conclusion. Our findings demonstrate a relatively high frequency (17) of nonST-segment elevation injury patterns on prehospital ECGs of patients who summon EMS because of chest pain. These results suggest the potential of prehospital ECGs to facilitate early triage in these high-risk chest pain patients who present to overcrowded emergency departments.