Electrocardiographic phasing of acute myocardial infarction.

The use of reperfusion therapy has been demonstrated to reduce the mortality rate from acute myocardial infarction (AMI), and a relationship has been established with the historical time from the onset of symptoms.’ The only additional, readily available clinical information that might assist in the early decision about reperfusion is the standard 12 -lead electrocardiogram (ECG). This study was undertaken to evaluate electrocardiographic recordings taken early after patient presentation with regard to changes that might indicate the stage of evolution of the infarct process. Utilizing paired ECGs from 154 patients with AM1 from the Myocardial Infarction, Triage and Intervention project2 at the University of Washington, Seattle, where thrombolysis was not given in the interval between tracings, a phasing system was designed.3,4 Phasing of the “acuteness” of the infarction process was based on ST elevation measured at the J point, the presence or absence of tall T waves (2 1 .O mV in precordial leads or 2 0.5 mV in the limb leads), T wave morphology, and the presence of abnormal Q waves, according to the initial version of the form in the Appendix. Each electrocardiographic lead with the exception of aVR was assigned a phase according to Table 1. The earliest phase of the prehospital electrocardiogram (ECGl) in any of the 11 leads was phase IA or 1 B in 15 1 patients, was unchanged in the hospital electrocardiogram (ECG2) in 67% of patients, moved to a later phase in 3 I%, and moved to an earlier