The ST segment axis as a differential diagnostic feature between acute pericarditis and acute inferior myocardial infarction.

The ST segment electrical axis in the frontal plane was calculated in 20 patients with an acute inferior myocardial infarction (AIMI) and another 20 patients with the acute phase of pericarditis (AP). The ST segment axis of patients with AIMI ranged from 100 degrees-120 degrees (mean 114 degrees). The ST segment axis of patients with AP ranged from 30 degrees-60 degrees (mean 45 degrees). Thus, the ST segment axis can be used for the differential diagnosis in the early acute phase, especially when there are no other important distinguishing factors between these two conditions.