MYOCARDIAL-INFARCTION WITH AN INITIALLY NORMAL ELECTROCARDIOGRAM - ANGIOGRAPHIC FINDINGS

To analyze the paradox of acute myocardial infarction (AMI) with an in itially normal electrocardiogram (ECG), we reviewed the records of 732 patients discharged with a final diagnosis of AMI over a 2-year perio d. 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 identifie d: 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 c reatine kinase (CK), timing of the first ECG change, life-threatening complications, and location of the infarct-related coronary lesion wer e recorded. Infarct-related coronary lesions were also classified into those in a major coronary trunk versus those in secondary branches. T he incidence of AMI with a normal ECG was 3.7%. There was no differenc e in the frequency of coronary artery involvement in the groups studie d: left anterior descending (33%), right coronary artery (38%), and ci rcumflex (28%). All ECG changes developed within the first 48 h of hos pitalization; 17 +/- 15 in Group 1, and 24 +/- 12 h in Group 2. All si x 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). Pat ients who developed ST elevation or Q waves (Group 1) always had a maj or artery trunk involved (p < 0.05 when compared with Group 2 plus Gro up 3). Patients in Group 3 had less myocardial damage and fewer compli cations 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 usu ally occurs within the first 48 h of hospitalization. Patients whose E CGs remain normal appear to have culprit lesions in coronary branches, smaller infarctions, and fewer in-hospital complications.