Tachycardias with sinus node-like P wave

Based upon P wave morphology these tachycardias cannot be distinguished in 12 lead ECG:

1. Sinus Tachycardia (ST)

2. Inappropriate sinus tachycardia (IST)

3. Sinoatrial nodal reentrant tachycardia (SNRT)

4. Atrial tachycardia (AT), originating near the sinus node

But there are a couple of features that might assist in the differential.

• ST and IST usually range from 100-180 beats/min. AT, SNRT may be faster.
• In ST and IST there is almost always a 1:1 relationship between atrial and ventricular activity.
• If vagal manoeuvres or adenosine are administered, in ST and IST there is a gradual slowing of the atrial and ventricular rates. Whereas SNRT may terminate abruptly. AT may increase the atrial:ventricular rate ratio