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Condition

AVNRT

Reentrant tachycardia within the AV nodal region using two functionally distinct inputs — a slow pathway with short refractoriness and a fast pathway with long refractoriness. The most common regular SVT in adults, especially women.

ECG features

  • ▸Regular narrow-complex tachycardia, typically 150–220 bpm
  • ▸Pseudo-r' in V1 representing a retrograde P buried in the terminal QRS (typical AVNRT)
  • ▸Pseudo-S in inferior leads (II, III, aVF) from the same retrograde P
  • ▸RP interval < 70 ms and RP < PR in typical (slow-fast) AVNRT
  • ▸Long RP with negative P in inferior leads in atypical (fast-slow) AVNRT
  • ▸Initiation typically by a PAC with sudden PR prolongation (jump onto slow pathway)
  • ▸Termination on a QRS (retrograde P) rather than a non-conducted P

Differential

  • ▸Orthodromic AVRT — RP usually >70 ms, P clearly separated from QRS
  • ▸Atrial tachycardia — RP > PR, warm-up onset, P morphology distinct from sinus
  • ▸Sinus tachycardia with first-degree AV block at fast rates
  • ▸Junctional tachycardia — overlaps mechanistically, ablation strategy differs
  • ▸Atrial flutter with 2:1 conduction (look for flutter waves in V1 and inferior leads)

Mechanism

AVNRT lives in the AV junction, not the AV node itself in any clean anatomic sense. Two regions with different conduction properties form the substrate.

  • Slow pathway: posterior input near the CS os, short refractory period, slow conduction. Travels along the tricuspid annulus.
  • Fast pathway: anterior/superior input near the apex of Koch’s triangle, fast conduction, long refractory period.
  • A PAC blocks in the fast pathway (still refractory), conducts antegrade down the slow pathway, and by the time it reaches the lower common pathway the fast pathway has recovered — retrograde conduction up the fast pathway completes the loop. The classic “PR jump” on initiation is the giveaway.

Typical vs atypical

  • Typical (slow-fast): antegrade slow, retrograde fast. Short RP. Retrograde P buried in or just after the QRS.
  • Atypical (fast-slow): antegrade fast, retrograde slow. Long RP, mimics AT. Deeply negative inferior Ps.
  • Slow-slow: rare variant using two slow inputs. Intermediate RP.

ECG features

Lead V1 and the inferior leads do most of the diagnostic work.

  • Pseudo-r’ in V1 — a terminal positive deflection in QRS that wasn’t there in sinus rhythm.
  • Pseudo-S in II/III/aVF — a notch on the downslope of the QRS, the same retrograde P viewed from below.
  • Compare to a baseline sinus ECG whenever possible; the “pseudo” findings are only visible by comparison.
  • RP < 70 ms strongly favors AVNRT over AVRT.
  • Onset captured on monitor: a sudden long PR followed by tachycardia is the slow pathway jump.

Maneuvers and adenosine

  • Vagal maneuvers (Valsalva, modified Valsalva with leg lift, carotid sinus massage) terminate ~25–50%.
  • Adenosine 6 mg IV push followed by saline flush, escalate to 12 mg. Termination is diagnostic and therapeutic.
  • Watch the monitor during adenosine: termination on a P wave (block in slow pathway) is classic for AVNRT. Termination on a QRS without a following P also fits.
  • If tachycardia persists despite AV block — think AT or flutter.

EP study findings

  • Dual AV nodal physiology: AH jump of ≥50 ms with a 10 ms decrement of A1A2.
  • Echo beats during programmed stimulation.
  • Earliest atrial activation during tachycardia at the His or just posterior to it (typical), or at the CS os (atypical).
  • VA interval ≤70 ms on His electrogram in typical.
  • Para-Hisian pacing distinguishes from septal AP — nodal pattern in AVNRT.
  • Entrainment from RV: V-A-V response (rules out AT), corrected post-pacing interval and SA-VA interval support AVNRT over AVRT.

Ablation

  • Target: slow pathway, anterior approach into Koch’s triangle. Map between the CS os and the tricuspid annulus along the septal TV.
  • Anatomic landmarks: CS os posteriorly, His anterosuperiorly, TV annulus laterally. The compact AV node sits at the apex — stay away.
  • Energy: RF 30–50 W titrated. Cryoablation in young patients or anatomy close to His for reversibility.
  • Endpoints: elimination of slow pathway conduction or a single residual echo beat with no sustained tachycardia on isoproterenol with and without atropine.
  • Junctional beats during RF mean you’re on the slow pathway — monitor VA conduction during every junctional. Loss of VA or fast junctional without retrograde P means stop immediately.

Practical lab notes

  • Most cases are quick — diagnostic study plus ablation in 60–90 minutes.
  • Femoral access only; no transseptal needed.
  • Most patients walk out the same day.
  • Recurrence is uncommon (<5%) but typically presents within the first 3 months.

Watch

Short videos to help illustrate this topic. Embedded from the original channels — content belongs to them.

Video pending Add a youtube video ID to display: Dual AV nodal physiology and the slow pathway jump
Dual AV nodal physiology and the slow pathway jump · EP educational channel · Animation of the reentry circuit and how a PAC initiates AVNRT.

Last reviewed by Dr. Colombowala on May 22, 2026.

Not medical advice. This page is educational. Your situation may differ — discuss it with Dr. Colombowala or your treating physician before making decisions.