Atrial Tachycardia is a regular atrial rhythm originating from the atrium at 100 to 240 bpm. It is a long RP tachycardia but can also be short RP tachycardia when there is delayed AV conduction.
ECG Recognition:
- The heart rate may be as low as 100 to as high as 240 bpm and rhythm is regular.
- The contour of the P wave depends on the site of origin. The P wave is different during sinus rhythm but may look like the appearance during sinus rhythm if the origin is near the SA node. It may also be low amplitude or negative in II, III and aVF.
- The PRI may be normal or prolonged.
- The AV conduction ratio may be 1:1 at rates about 240 bpm.
- At rapid rates, there may be an AV block (atrial tachycardia with a block) because the impulse will encounter the AV node in the refractory period.
- The AV block can be 2:1 or the ratio may be higher.
- A Wenckebach block is common.
AT can be transient, recurrent, sustained, or incessant is sustained if it last longer than 30 seconds or paroxysmal if it is of short duration.
As mentioned earlier, AT is regular but focal AT can show variations (to as much as 15%). So, it can look irregular.
If there are more than 3 wave morphologies and the atrial rate is more than 100 bpm then it is called multifocal atrial tachycardia (MAT).
If there are more than 3 wave morphologies and the atrial rate is more than 100 bpm then it is called multifocal atrial tachycardia (MAT).
Sometimes it is difficult to tell atrial tachycardia from atrial flutter (AFL) based on surface ECG criteria. It is because AT from a scarred myocardium can be rapid and can mimic AFL. AFL can also mimic AT by showing distinct isoelectric baseline in diseased atria (atrial myopathy) or in presence of antiarrhythmic drugs.
It is easier to identify atrial tachycardia in monitored patients because you can catch the beginning, middle and end/termination of the arrhythmia. The heart rate histogram is also a valuable tool to determine if you are dealing with sinus tachycardia or atrial tachycardia. Sinus tachycardia will have a gradual increase and decrease in heart rate but it will be a sudden increase and decrease for atrial tachycardia.
Atrial tachycardia. There is sudden onset of tachycardia with an atrial rate of about 150 bpm. The P waves are marked with red arrows. It initially started with long RP-short PR but later can be noted to have short RP-long PR due to AV delay.
Atrial tachycardia. Three 10 seconds strips covering initiation (A), middle (B) and termination (C) of the tachycardia. If you look at strip B, it will look like sinus tachycardia. However, the sudden onset (A) and termination (B) argues against sinus tachycardia but confirms that the arrhythmia is atrial tachycardia. This shows that AT is easier to identify in cardiac telemetry.
Paroxysmal atrial
tachycardia.
There is sudden onset and termination of narrow QRS complex tachycardia with distinct P waves best seen in
V1
Atrial tachycardia. There is sudden onset of tachycardia with an atrial rate of about 150 bpm. The P waves are marked with red arrows. It initially started with long RP-short PR but later can be noted to have short RP-long PR due to AV delay.
Atrial tachycardia. Three 10 seconds strips covering initiation (A), middle (B) and termination (C) of the tachycardia. If you look at strip B, it will look like sinus tachycardia. However, the sudden onset (A) and termination (B) argues against sinus tachycardia but confirms that the arrhythmia is atrial tachycardia. This shows that AT is easier to identify in cardiac telemetry.
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