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AV Nodal Re-entry Tachycardia

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  • More common in women than men

Clinical Presentation

  • Sudden onset of rapid, regular palpitations
  • Associated symptoms:
    • Presyncope or syncope due to a transient fall in blood pressure
    • Chest pain (esp. if underlying coronary artery disease)
    • Dyspnoea
    • Anxiety
    • Polyuria from elevated atrial pressure causing release of atrial natriuretic peptide

Pathophysiology

The following is the pathophysiology for the ‘slow-fast’ varient of AVNRT

  • Requires two specific pathways within the AV node:
    • Slow conducting pathway (alpha) with a short refractory period
    • Fast conducting pathway (beta) with a long refractory period
  1. PAC arrives while fast pathway is refractory and goes down the slow pathway
  2. When the effective refractory period in the alpha pathway ends, the impulse travels retrogradely up the fast pathway
  3. Impulse continually cycles around the two pathways

ECG Features

  • Regular tachycardia ~140-280 bpm
  • Narrow QRS complexes (<120ms) unless there is a co-existing bundle branch block, accessory pathway, or rate related aberrant conduction
  • P waves if visible exhibit retrograde conduction with P-wave inversion in leads II, III, aVF; they may be buried within or visible after the QRS complex (very rarely before) causing a pseudo R’ or S wave

  • Narrow complex tachycardia at 150 bpm with no visible P waves
  • Pseudo R’ waves in V1-2

ST Depression in AVNRT

Widespread ST depression is a common ECG finding in AVNRT and does not necessarily indicate myocardial ischaemia, provided the changes resolve once the rhythm is sinus After resolution of the AVNRT:

  • Here there is residual ST depression in inferior and lateral leads (V4-6) ⇒ patient had rate-related myocardial ischaemia

Differentiating orthodromic AVRT and AVNRT

  • Typically AVNRT has retrograde P waves that occur early (typically buried in the QRS or pseudo R’ waves at the terminal portion of the QRS)
  • In AVRT, retrograde P waves occur later, with a longer RP interval (typically >70 ms)
  • Management however is the same between the two conditions and may reveal the underlying accessory pathway in AVRT once reverted
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Management

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