Overview
AV nodal reentrant tachcardia (AVNRT) is the most common type of paroxysmal supraventricular tachycardia (pSVT), and occurs due to a reentrant loop within the AV node.
Pathogenesis
Mechanism
- The AV node normally contains two pathways - a slow pathway (short refractory period) and fast pathway (long refractory period) - that then combine to form a common pathway into the bundle of His. Normally, an atrial impulse is conducted down the two pathways with no recirculation of the impulse, as both pathways are within their refractory periods.
In AVNRT, an atrial impulse is conducted by one pathway and then hits the other pathway when it is outside its refractory period, propagating up the other pathway and creating a re-entry circuit.
In slow-fast AVNRT (90%), a premature atrial impulse travels down the slow pathway and is propagated up the fast pathway.
In fast-slow AVNRT (10%) an impulse travels retrogradely up the slow pathway.
Diagnosis
ECG Findings
- Heart rate 100-250bpm
- Regular rhythm
- Late P waves - may be hidden within the QRS complex, cause a pseudo S wave in inferior leads / pseudo R wave in right precordial leads (slow-fast AVNRT), or appear after the QRS complex (fast-slow AVNRT)
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