The<unk>  is the part between the P wave and the Q. The<unk>  is sometimes called<unk>  (P - atrial T)<unk>  or PR or PQ or PTp (P - T wave of P wave)<unk> .ABILDSKOV JA. The atrial complex of the electrocardiogram. Am Heart J 1959 Jun; 57(6) 930-41. pmid:13649561. PubMed HubMed .
It can be depressed in pericarditis or atrial myocardial infarction.
Below is an image of EKG depicting overt<unk>  depression in a patient with pericarditis.
PTa segment
QRS complex
T wave
N-terminus
ST interval
P wave
V wave
Atrioventricular nodal branch