Atrioventricular node reentrant tachycardia (AVNRT) is an arrhythmia that is regular, fast (180-250 bpm) and originating from the AV node. The P wave is often hidden within the QRS complex. There may be a little second R wave (R') but the QRS can still be narrow. AVNRT can be treated with valsalva, carotid sinus massage, adenosine, verapamil, diltiazem or electrical cardioversion.
The two main forms of AVNRT are slow-fast (common, 90%) and fast-slow (uncommon, 6%). In slow-fast AVNRT, the impulse first travels to the ventricles via the slow pathway and returns to the atria via the fast pathway. There can be a retrograde P at the end of the QRS. In fast-slow AVNRT, the opposite occurs and the P can be far behind the QRS. It is also possible to have slow-slow AVNRT (4%).