Atrioventricular Nodal Reentrant Tachycardia

Atrioventricular nodal reentrant tachycardia (AVNRT) is caused by a reentrant loop within the atrioventricular node. With AVNRT, the atrioventricular node has two pathways, fast and slow, which allows for a reentrant loop. The differential for a regular, narrow complex tachycardia includes sinus tachycardia, atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reentrant tachycardia (AVRT), atrial flutter, and atrial tachycardia. P waves can aid the diagnosis but are often absent. At faster rates, sinus tachycardia can be obscured when P waves are buried within the T waves. P waves in a sawtooth pattern favors atrial flutter (2:1 conduction usually has a ventricular response rate around 150 bpm). While most cases of AVNRT do not have visible P waves, up to one third of AVNRT cases will show retrograde P’ waves immediately following the QRS complex, giving the appearance of a “pseudo-S wave” in the inferior limb leads, or a “pseudo-R wave” in V1. Rarely, atypical “fast-slow” AVNRT can produce retrograde P’ waves that precede the QRS complex.



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