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Procedure

SVT Ablation

Catheter ablation of AVNRT, AVRT, or focal atrial tachycardia. Diagnostic EP study identifies the mechanism, ablation targets the critical substrate. High success, low complication rate.

Typical duration
1.5–2 h
Sedation
Moderate sedation

Equipment & setup

  • ▸Femoral venous access kit, dual or triple right groin access
  • ▸Quadripolar catheter to the right ventricular apex
  • ▸Quadripolar or fixed-curve catheter to the His position
  • ▸Decapolar catheter to the coronary sinus
  • ▸Ablation catheter — irrigated or non-irrigated 4 mm tip RF, or cryoablation catheter for septal AVNRT
  • ▸Programmed stimulator for induction and entrainment maneuvers
  • ▸Isoproterenol for facilitation
  • ▸3D mapping system for atrial tachycardia or unusual AVRT pathways
  • ▸Activated clotting time monitor and heparin (for left-sided cases)

Common pitfalls

  • ▸Inadequate induction — always have isoproterenol available and use a structured pacing protocol
  • ▸Misdiagnosing AVNRT vs AVRT vs AT without proper entrainment and PPI analysis
  • ▸AV block during slow pathway modification — junctional ectopy during ablation is expected, but loss of VA conduction is a warning sign
  • ▸Failure to retest after waiting period — late recovery of conduction can mimic procedural success
  • ▸Missed left-sided accessory pathway requiring retrograde aortic or transseptal access
  • ▸Concealed pathways in patients with intermittent pre-excitation — easy to miss without retrograde mapping

Indications

  • Symptomatic recurrent SVT of any mechanism in patients preferring definitive therapy over chronic drugs
  • Symptomatic Wolff-Parkinson-White
  • High-risk asymptomatic WPW — short pre-excited RR in AF, multiple pathways, athletes
  • Incessant atrial tachycardia causing tachycardia-induced cardiomyopathy
  • Drug intolerance or failure

Pre-procedure prep

  • Anticoagulation not required for right-sided ablations; therapeutic for left-sided cases or LA mapping
  • NPO after midnight
  • AV nodal blockers held for 24–48 hours pre-procedure to facilitate induction
  • Baseline 12-lead ECG including any documentation of pre-excitation
  • Sedation plan: moderate sedation is standard; deep sedation can suppress inducibility — coordinate with anesthesia

Setup & equipment

  • Three right femoral venous accesses: His, CS, ablation
  • Some operators use an additional RV catheter for ventricular pacing maneuvers
  • Heparin only for left-sided work
  • Programmed stimulator ready for atrial and ventricular pacing protocols

Technique

Baseline EP study

  • Sinus rhythm assessment: AH and HV intervals, presence of pre-excitation
  • Atrial pacing protocols: incremental and extrastimulus to assess AV node and pathway conduction
  • Ventricular pacing: VA conduction time, retrograde activation pattern (concentric vs eccentric)
  • Tachycardia induction: burst and extrastimulus pacing, plus isoproterenol if needed

Diagnostic maneuvers

  • AVNRT signature: dual AV node physiology (AH jump), septal earliest A on tachycardia, VA time <70 ms, V-A-V response after RV overdrive
  • Orthodromic AVRT signature: eccentric retrograde A (location depends on pathway), VA >70 ms, V-A-V response, para-Hisian pacing showing pathway behavior
  • AT signature: V-A-A-V response after RV overdrive, variable AV relationship possible, P morphology distinct from sinus
  • Concealed pathway: VA time during ventricular pacing constant with rate; AV node decremental

Ablation strategy

AVNRT — slow pathway modification

  • Target the slow pathway anatomically: posterior-inferior septal RA, between the tricuspid annulus and CS os
  • Look for slow pathway potential (small atrial deflection followed by larger ventricular)
  • RF at 25–40 W; cryoablation 4–6 mm tip catheter is an alternative with lower AV block risk
  • Watch for junctional rhythm during ablation — desired endpoint, but monitor VA conduction; loss of VA = stop immediately
  • Endpoint: non-inducibility on and off isoproterenol, with elimination of slow pathway or single residual echo beat acceptable

AVRT — accessory pathway ablation

  • Right-sided pathways: ablate from the RA at the tricuspid annulus, mapped by earliest delta wave (manifest) or earliest atrial activation (concealed)
  • Left-sided pathways: retrograde aortic approach to the mitral annulus, or transseptal approach
  • Mid-septal and parahisian pathways: high risk for AV block — consider cryoablation
  • Map carefully for shortest AV time on the annulus
  • RF at the target; success often within seconds of starting if mapping is correct

Focal AT

  • Activation mapping during tachycardia identifies the earliest atrial site
  • 3D mapping invaluable, especially for non-PV foci
  • Target the focus; success indicated by termination during energy delivery and non-inducibility

Confirming cure

  • Wait 20–30 minutes after ablation
  • Repeat induction protocols with and without isoproterenol
  • For AVNRT: residual slow pathway conduction without inducibility is acceptable
  • For AVRT: complete pathway block (no conduction antegrade or retrograde) is the goal
  • For AT: non-inducibility and absence of spontaneous foci

Complications

  • AV block requiring permanent pacing: <1% overall, higher for septal pathways and aggressive slow pathway ablation
  • Vascular complications: ~1%
  • Tamponade: rare, more likely with transseptal or aggressive ablation near the annulus
  • Stroke: rare, mainly with left-sided work
  • Recurrence: 3–5% for AVNRT, 5–10% for AVRT depending on location

Post-procedure care

  • Bed rest 2–3 hours, then ambulate
  • Same-day discharge for uncomplicated cases
  • Anticoagulation for 4 weeks after left-sided ablation; not needed for right-sided
  • Follow-up at 4–6 weeks; counsel patients that occasional palpitations during the first few weeks are common and don’t necessarily indicate failure
  • Antiarrhythmics typically discontinued at discharge

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: Slow pathway modification: anatomy and approach
Slow pathway modification: anatomy and approach · EP teaching channel · Koch's triangle, slow pathway location, junctional rhythm monitoring.

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.