AVNRTAVRT

AVNRT and AVRT are two common forms of supraventricular tachycardia (SVT) that arise from reentrant circuits involving the atrioventricular (AV) region. The combined term AVNRTAVRT is not a standard distinct diagnosis; rather, it describes SVTs that use either the AV node (AVNRT) or an accessory pathway (AVRT) to form a reentrant tachycardia.

AVNRT mechanisms involve reentry within the AV node, typically using dual nodal pathways (a slow and a fast pathway). The common slow-fast AVNRT creates a rapid, regular rhythm with remarkably short or hidden atrial activity, and P waves may be unseen or after the QRS complex.

AVRT requires an accessory pathway connecting atrium and ventricle outside the AV node. In orthodromic AVRT, antegrade conduction goes through the AV node and retrograde conduction occurs via the accessory pathway, producing a narrow QRS. In antidromic AVRT, the antegrade limb is the accessory pathway and the QRS is wide. AVRT is often associated with WPW syndrome when a delta wave is present on a resting ECG.

Clinical presentation typically includes sudden onset palpitations, rapid heart rate, and sometimes dizziness or chest discomfort. AVNRT is the most common SVT in adults; AVRT is commonly linked to the presence of an accessory pathway.

Diagnosis relies on ECG during tachycardia, which in AVNRT usually shows a regular narrow-complex tachycardia with subtle or absent P waves, while AVRT may show preexcitation on a baseline ECG if WPW is present. An electrophysiology study can confirm the circuit.

Management includes acute termination with vagal maneuvers and adenosine; other agents such as beta-blockers or nondihydropyridine calcium channel blockers can be used when appropriate. Definitive therapy is often catheter ablation: slow-pathway modification for AVNRT and accessory-pathway ablation for AVRT, offering high success and potential cure.