Usefulness of the 12-lead standard electrocardiogram in assessing myocardial infarct size.

The value of the electrocardiogram in assessing infarct size was studied using serial estimates of serum creatine phosphokinase (CPK) in serum and serial 12-lead electrocardiograms in patients admitted to a coronary care unit with acute myocardial infarction. Sum of the ST segment deviations from the isoelectric line (sigma ST12) and sum of the conventional scores of Q waves amplitude (sigma Q12) were obtained from each electrocardiogram, and then the time-course of these parameters was considered. The correlation between maximum sigma Q12 and CPK-peak in anterior infarcts, was highly significant (r = 0.733; P less than 0.001). Maximum sigma ST12, measured upon admission or immediately thereafter in patients hospitalized within 4 hours from the onset of chest pain, was found to correlate significantly with CPK-peak (r = 0.675, P less than 0.001 for the whole group; r = 0.758, P less than 0.01 for patients with inferior infarcts). Time-course of sigma ST12 and CPK showed 4 different patterns. Among them, type 1 ("rapid necrosis") showed the most significant correlations (maximum sigma ST12 within 4 hours from symptoms versus CPK-peak: r = 0.909, P less than 0.001; maximum sigma Q12 versus CPK-peak in anterior infarcts: r = 0.782, P less than 0,05; and maximum sigma ST12 within 4 hours from the onset of pain versus sigma Q12 in patients with anterior infarcts: r = 0.863, P less than 0,05). There was no correlation between sigma ST12 at any other time and CPK-peak: this observation is in accordance with the presence of a rapid decrease in the mean sigma ST12 after the first 3-4 hours from the beginning of symptoms. This study shows that the analysis of ST segment deviations and of Q waves development in the standard electrocardiogram provides useful information on the size of acute myocardial infarction as reflected by the peak value of serum CPK.