Atrial Repolarization

Atrial repolarization occurs with every atrial depolarization, though is usually hidden within the QRS complex. The atrial repolarization wave is in the opposite direction of the depolarization wave (upright P wave will cause an inverted repolarization wave) as the atria are depolarized and repolarized different than the ventricles. These repolarization waves are sometimes called the atrial T wave. Patients with inverted P waves will have an upright repolarization wave; this is commonly seen in arrhythmias that have a 'low atrium' P wave-usually an ectopic atrial rhythm or junctional rhythm with P wave before the QRS (junctional with retrograde P waves). Although the repolarization waves are commonly hidden within the QRS, these atrial T waves may move into the ST segment if the P wave is close to the QRS (usually atrial tachycardia and junctional rhythm). This may produce false ST elevation. Those with a 'high atrial' rhythm where the P wave may be partially upright may have false ST depression with the atrial T wave.

In patients with normal PR intervals, sometimes the atrial repolarization is noted. The beginning of the atrial repolarization wave may start before the QRS complex, causing mild PR depression towards the end of the PR interval. This atrial repolarization wave can extend beyond the QRS segment to the ST segment, causing mild ST depression at the beginning of that interval as well. Although we commonly compare the ST segment to the TP segment in evaluating the ST segment for ischemia, it should also be compared to the PR segment in case the atrial repolarization wave is visible to not mistakenly label these EKG's as having ischemia. The depressed PR and ST segments notably form a smile face type morphology as noted below. However, an isoelectric ST segment in a patient with PR depression due to atrial repolarization actually represents ST elevation as the ST segment should be depressed with the atrial repolarization. Atrial repolarization, when not from an ectopic atrial rhythm, is most commonly seen when a patient is tachycardic due to increased sympathomimetic lengthening of the atrial repolarization wave.

This can be differentiated from the PR depression of pericarditis as pericarditis tends to have a sharp decline to a more horizontal PR segment.

Examples:

Further Reading:

http://hqmeded-ecg.blogspot.com/search/label/atrial%20repolarization%20wave