;Criteria for left atrial voor left atrial enlargement. Either
:P wave with a broad (>0,04 sec or 1 small square) and deeply negative (>1 mm) terminal part in V1
:P wave duration >0,12 sec in laeds I and / or II
[[Image:left_atrial_enlargement.jpg|thumb| Left atrial enlargement]]
[[Image:LAE_2.png|thumb| Left atrial enlargement with ECG.]]
[[Image:ECG_LAtrD_v1.jpg|thumb| Left atrial enlargement as seen in lead V1.]]
Left atrial enlargement is often seen in mitral valve insufficiency, resulting in backflow of blood from the left ventricle to the left atrium and subsequent incresed local pressure.
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===Right atrial enlargement===
;Right atrial enlargement is defined as either:
:P >2,5 mm in II / III and / or aVF
:P >1,5 mm in V1.
[[Image:right_atrial_enlargement.jpg|thumb| Right atrial enlargement]]
[[Image:Rae.png|thumb| Right atrial enlargement]]
Right atrial enlargement can result from increased pressure in the pulmonary artery, e.g. after pulmonary embolisation. A positive part of the biphasic p-wave in lead V1 larger than the negative part indicates right atrial enlargement. The width of the p wave does not change.
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===Biatrial enlargement===
;Biatrial enlargement
:Biphasic p wave in V1 of more than 0.04 sec duration. The positive initial part is > 1.5mm and the negative terminal part > 1mm
In biatrial enlargement is the ECG whos signs of both left and right atrial enlargement. In V1 the p wave has large peaks first in positive and later in negative direction.
The p wave morphology can reveal right or left atrial stretch.
The P-wave morphology is best determined in leads II and V1 during sinus rhythm.
The normal P wave
Normal sinus rhythm with a positive p wave in leads I, II en AVF and a biphasic p wave in V1.
Characteristics of a normal p wave:Spodick
The maximal height of the P wave is 2.5 mm in leads II and / or III
The p wave is positive in II and AVF, and bifasic in V1
The p wave duration is usually shorter than 0.12 seconds
Elevation or depression of the PTa segment (the part between the p wave and the beginning of the QRS complex) can result from Atrial infarction or pericarditis.
If the p-wave is enlarged, the atria are enlarged.
