From the Guidelines

Pericarditis is typically characterized by widespread ST-segment elevation on EKG, which is a hallmark sign of the condition.

The EKG changes in pericarditis are highly variable and can evolve over time, but widespread ST-segment elevation is a common finding, reported in up to 60% of cases 1.
PR depression is also a characteristic EKG finding in pericarditis, particularly in the early stages of the disease 1.
The EKG changes in pericarditis can be difficult to distinguish from those seen in acute coronary syndromes, but the presence of ST-segment elevation without reciprocal ST depression can help to suggest pericarditis 1.

The diagnosis of pericarditis is typically based on a combination of clinical, EKG, and imaging findings, including pericardial effusion on echocardiography and biological signs of inflammation such as elevated C-reactive protein and erythrocyte sedimentation rate 1.
Cardiac magnetic resonance (CMR) imaging can also be useful in diagnosing pericarditis, particularly in cases where the diagnosis is uncertain or where there is suspicion of myocardial involvement 1.

From the Research

The EKG findings in pericarditis can be summarized as follows:

Widespread ST-segment elevation or PR depression are the most commonly used ECG criteria recommended by international guidelines for diagnosing acute pericarditis 2
ECG changes are often temporally dynamic, evolve rapidly during the course of disease, and may be influenced by a number of factors such as disease severity, time (stage) of presentation, degree of myocardial involvement, and the treatment initiated 2
ECG changes, mainly widespread ST-segment elevation, can be recorded in about one-quarter of patients with pericarditis, and were not associated with a worse prognosis 3
ECG changes may reflect concurrent myocarditis that should be ruled out 3

The types of EKG changes that can be observed in pericarditis include:

ST-segment elevation: This is the most common EKG finding in pericarditis, and can be widespread or focal 2, 3, 4
PR depression: This can be observed in conjunction with ST-segment elevation 2
T wave inversion: This can occur as the EKG changes evolve over time 5
Normalization of the EKG: This can occur as the disease resolves, and can take several days to several weeks 5

It's important to note that the EKG findings in pericarditis can be similar to those observed in other conditions, such as:

Myocardial infarction: This can be difficult to distinguish from pericarditis, especially if the EKG shows focal ST-segment elevation 6, 4
Myopericarditis: This is a condition that involves both the pericardium and the myocardium, and can have similar EKG findings to pericarditis 4, 5