Overview
AV reentrant tachycardias occur when an atrial impulse is conducted through an accessory pathway - either retrogradely following AV conduction (orthodromic) or anterogradely (antidromic).
Pathogenesis
Mechanism
- AVRT requires the presence of a distinct accessory pathway, most commonly in the setting of Wolff-Parkinson-White syndrome.
In orthodromic AVRT, a premature atrial impulse is conducted by the AV node and then is propagated retrogradely up the abnormal accessory pathway, commencing a re-rentry circuit.
In antidromic AVRT, an atrial impulse is conducted by the abnormal accessory pathway and is then propagated retrogradely back through the AV node, commencing a re-entry circuit.
Diagnosis
ECG Findings
- Orthodromic AVRT (90%) - regular narrow complex tachycardia with no P waves (hidden in QRS) or P waves after QRS complex. No delta wave will be seen.
- Antidromic AVRT (10%) - regular broad complex tachycardia (easily mistaken for VT)
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