Recognized electrocardiographic abnormalities associated with pericardial disease include ventricular repolarization phenomena and simultaneous electrical alternans of the P wave and QRS complex. Atrial ST segment changes (S-Ta segment) have also been described in pericardial disease but not recently emphasized. Five patients had S-Ta segment changes (two with uremic pericarditis, two with hemorrhagic pericarditis caused by ruptured aneurysms, and one with idiopathic pericarditis). Four patients had S-Ta segment change resolution concomitant with clinical improvement; the remaining patient died prior to pericarditis resolution. The electrocardiographic findings in each case demonstrated elevation of S-Ta segments in aVR and depressions in other leads in addition to ventricular repolarization abnormalities. Atrial injury currents occur in pericarditis in the absence of other known causes of atrial injury. The incidence of this electrocardiographic finding in pericarditis is unknown but is apparently common.
Charles MA, Bensinger TA, Glasser SP. Atrial Injury Current in Pericarditis. Arch Intern Med. 1973;131(5):657-662. doi:10.1001/archinte.1973.00320110041005