What is the hallmark ECG finding in acute pericarditis?

The hallmark ECG finding in acute pericarditis is diffuse ST segment elevation. This finding is characterized by ST segment elevations that are not confined to specific leads as seen in myocardial infarction but instead are widespread across multiple leads. This diffuse elevation typically presents in the precordial leads (V1-V6) as well as in the limb leads.

The elevation often resembles the "smiling" configuration on the ECG, where the ST segments rise and are convex upwards. Unlike myocardial infarction, which shows localized changes corresponding to the area of infarction, acute pericarditis usually presents stages of ST elevation along with PR segment depression. The ability to identify these diffuse ST elevations is crucial in distinguishing acute pericarditis from other cardiac conditions.

In summary, recognizing diffuse ST segment elevation as a key feature allows clinicians to diagnose acute pericarditis effectively.