cardiolab logocardiolab

SVT (AVNRT)

caution
Lead II
25 mm/s10 mm/mV
Heart rate
72bpm
RR
833ms
QT
243ms

SVT (AVNRT)

A re-entrant tachycardia using dual pathways within the AV node (typical AVNRT). The most common form of paroxysmal SVT. The fast and slow AV nodal pathways form a circuit that sustains rapid, regular conduction at 150–220 bpm.

Recognition· 4
  • Regular narrow QRS tachycardia (150-220 bpm)
  • No visible P waves (buried in QRS)
  • Abrupt onset and offset
  • QRS looks identical to sinus rhythm
Mechanism

Re-entrant circuit in AV node using fast and slow pathways

Dual pathways within the AV node (fast and slow) form a circular pathway. An early beat enters the slow pathway (which has recovered), conducts down slowly, then returns up the fast pathway (which has now recovered). This creates a self-sustaining circuit firing at 150-220 bpm.

Findings· 4
  • Regular narrow-complex tachycardia at 150–220 bpm.
  • No visible P waves (retrograde P buried in QRS — may cause pseudo-R' in V1 or pseudo-S in inferior leads).
  • QRS morphology identical to sinus rhythm.
  • Abrupt onset and offset.
Clinical Impact
Palpitations and anxiety
↓
Lightheadedness or syncope (if very fast)
↓
Rarely causes hemodynamic instabilityRISK

Usually tolerated well — palpitations, lightheadedness

Management· 3
1

Primary Treatment

Vagal maneuvers (Valsalva, carotid massage).

2

If ineffective

IV adenosine 6mg rapid push, then 12mg if needed.

3

Recurrent episodes

catheter ablation (>95% cure rate).

Differential· 2
Sinus Tachycardia

Both regular narrow-complex. Sinus tachy has gradual onset, visible P waves, lower rate.

Atrial Flutter 2:1

Regular narrow-complex ~150 bpm. Adenosine reveals flutter waves without terminating rhythm.