Atypical electrocardiogram in acute pericarditis: characteristics and prevalence.

Stage One ST segment deviations are virtually diagnostic of acute pericarditis when typically distributed among limb and precordial ECG tracings. Atypical ECG responses include absence of ST deviations, which conceals the diagnosis, and restricted distribution of ST deviations, which suggests myocardial injury. Among 44 consecutive patients with acute pericarditis, 19 (43%) had atypical ECGs. Although all 19 had a pericardial rub, eight had no ST deviations in the limb leads and seven developed no ST changes, including three with no ECG abnormalities of any kind. Patients with typical ECGs by ST segment criteria were more likely to progress to T wave inversion. PR segment deviations occurred in 14 patients with typical, and 14 with atypical ECGs. In four of the latter, the PR segment shifts were the only ECG sign. Presence or absence of heart disease and etiology of pericarditis could not be statistically associated with particular electrocardiographic responses.