Myocardial infarction with an initially normal electrocardiogram--angiographic findings

To analyze the paradox of acute myocardial infarction (AMI) with an initially normal electrocardiogram (ECG), we reviewed the records of 732 patients discharged with a final diagnosis of AMI over a 2-year period. Twenty-one patient were identified whose initial ECG was normal and who underwent coronary arteriography during the index hospitalization. According to the ECG evolution, three distinct groups were identified: Group 1: those who subsequently developed ST elevation or Q waves (n = 7), Group 2: those who developed ST depression or T-wave inversion (n = 8), and Group 3: those whose ECG remained normal ( n = 6). Peak creatine kinase (CK), timing of the first ECG change, life-threatening complications, and location of the infarct-related coronary lesion were recorded. Infarct-related coronary lesions were also classified into those in a major coronary trunk versus those in secondary branches. The incidence of AMI with a normal ECG was 3.7%. There was no difference in the frequency of coronary artery involvement in the groups studied: left anterior descending (33%), right coronary artery (38%), and circumflex (28%). All ECG changes developed within the first 48 h of hospitalization; 17 +/- 15 in Group 1, and 24 +/- 12 h in Group 2. All six patients who had a persistently normal ECG (Group 3) had lesions in branch vessels (p < 0.05 when compared with Group 1 plus Group 2). Patients who developed ST elevation or Q waves (Group 1) always had a major artery trunk involved (p < 0.05 when compared with Group 2 plus Group 3). Patients in Group 3 had less myocardial damage and fewer complications compared with the other two groups. Myocardial infarction with an initial normal ECG is uncommon and may result from involvement of any of the three coronary arteries. Electrocardiographic evolution usually occurs within the first 48 h of hospitalization. Patients whose ECGs remain normal appear to have culprit lesions in coronary branches, smaller infarctions, and fewer in-hospital complications.