An irritable focus in the atria may fire at a rate greater than the inherent rate of the SA node. This causes an atrial tachycardia, which has all the characteristics of a PAC, including its P wave morphology, PR interval, and QRS complex. However, in atrial tachycardia, the entire rhythm strip is involved, not merely a single beat (see Figure 4.4). 

Atrial tachycardia is a regular rhythm with a rate of 150–250 bpm. As with PACs, atrial P waves are present.

Related Video – ECG Rhythm Review – Atrial Tachycardia

Figure 4.4. Atrial Tachycardia

An abnormal P wave morphology with a positive deflection in lead V1 and a negative deflection in lead II.

Characteristics of Atrial Tachycardia

1. Regular rhythm 
2. Rate: 150–250 bpm
3. Atrial P wave differs from a sinus P wave 
4. P wave may be visible or may be buried within a T wave
5. Normal PR interval:  120–200 milliseconds
6. Normal QRS complex: < 120 milliseconds