MYOCARDIAL INFARCTION WITH AN INITIALLY NORMAL ELECTROCARDIOGRAM

Abstract

To analyze the paradox of acute myocardial infarction(AMI) with an initially normal electrocardiogram(ECG), we reviewed the records of 100 patients discharged with 21 final diagnosis of AM1 over a 1-year period. Twentyonepatient were identified whose initial ECG was normal andwho underwent coronary arteriography during the index hospitalization. According to the ECG evolution, three distinctgroups were identified: Group 1 : those who subsequently developedST elevation or Q waves (n = 7), Group 2: those whodeveloped ST depression or T-wave inversion (n = 8), andGroup 3:those whose ECG remained normal (n = 6). Trop-T positive, Peakcreatine kinase (CK), timing of the first ECG change, lifethreateningcomplications, and location of the infarct-relatedcoronary lesion were recorded. Infarct-related coronary lesionswere also classified into those in a major coronary trunkversus those in secondary branches. The incidence of AMI with a normal ECG was 3.7%. There was no difference in thefrequency of coronary artery involvement in the groups studied:left anterior descending (33%), right coronary artery(38%). and circumflex (28%). All ECG changes developedwithin the first 48 h of hospitalization; 17±15 h in Group 1, and24±12 h in Group 2. All six patients who had a persistentlynormal ECG (Group 3) had lesions in branch vessels (p <0.05 when compared with Group 1 plus Group 2). Patientswho developed ST elevation or Q waves (Group 1) alwayshad a major artery trunk involved (p <0.05 when comparedwith Group 2 plus Group 3). Patients in Group 3 had less myocardial damage and fewer complications compared with theother two groups. Myocardial infarction with an initial normalECG is uncommon and may result from involvement of any ofthe three coronary arteries. Electrocardiographic evolutionusually occurs within the first 48 h of hospitalization. Patientswhose ECGs remain normal appear to have culprit lesions incoronary branches, smaller infarctions, and fewer in-hospital complications.