The ECG finding of an atrial infarction is PR segment elevation in leads V5, V6 and lead I. There is reciprocal PR segment depression in leads V1 and V2.

Approximately 10% of patients with acute myocardial infarctions have atrial involvement. Atrial infarctions can result in atrial arrhythmias including atrial fibrillation which makes the ECG diagnosis more challenging. There is no major clinical significance to an atrial infarct since the atrial contraction contributes only a small amount to the overall cardiac output.

Reference:

Liu CK, et al. Circulation. 1961;23:331-338.