The advent of thrombolytic therapy for patients with suspected acute myocardial infarction has highlighted the importance of the initial electrocardiogram (ECG) in decision making. Thus we analysed the initial ECGs of 94 consecutive cases with suspected myocardial infarction who were seen within six hours after the onset of chest pain by a mobile coronary care unit. The study included 91 patients (three patients admitted twice) (61 male), aged 27–83 years (mean 60.5). Median time from onset of chest pain to arrival of the mobile coronary care unit was 75 minutes (range 15–345), and mean mobile coronary care unit response time was 12.3±7 (SD) minutes (range 5–45). The majority of cases (65 of 94, 69.1 per cent) were seen within two hours of the onset of symptoms. A final diagnosis of myocardial infarction was made in 48 of 94 (51.1 per cent) cases; 38 had unstable angina and eight other diagnoses. Of the 48 with myocardial infarction the initial ECG showed ST segment elevation in 37, ST depression and/or T wave inversion in six, Q waves only in three and left bundle branch block in two. No patient with an initially normal ECG had a myocardial infarction. Thrombolytic therapy was given out of hospital to 33 of 38 patients with ST segment elevation. In seven patients with ST elevation (median delay time to intensive care 60 minutes), rapid resolution of ST segment elevation occurred following thrombolytic therapy and there was no significant elevation of cardiac enzymes, suggesting that the infarct had been aborted. Eleven of the 48 (23 per cent) patients with infarction did not have ST segment elevation on the initial ECG, and only five received thrombolytic therapy given later, after transfer to hospital.Out-of-hospital administration of thrombolytic therapy has the potential to maximize myocardial salvage and even abort infarction, but it must be recognized that the initial ECG recorded early after the onset of symptoms may not display ST segment ele
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