Atrioventricular Reentrant Tachycardia (AVRT) and Accessory Pathways

Definition

An accessory pathway (AP) is an extranodal AV pathway connecting atrial and ventricular myocardium across the AV groove, bypassing the normal AV node–His Purkinje system. Manifest pathways conduct anterogradely, causing ventricular pre-excitation (delta wave, short PR) on the ECG. Concealed pathways conduct only retrogradely and are not visible on resting ECG. AVRT is a reentrant tachycardia requiring the AP, atrium, AV node (or second AP), and ventricle as obligate circuit components. WPW syndrome = pre-excitation pattern + documented SVT or consistent symptoms. sources/svt-aha-2015 (rating: very high)

Key Concepts

Accessory Pathway Types

• Manifest AP (WPW pattern): Anterograde conduction → delta wave on ECG; prevalence 0.1–0.3% in general population
• Concealed AP: Retrograde conduction only; no pre-excitation on resting ECG; AVRT indistinguishable from AVNRT on ECG without EP study
• Orthodromic AVRT (oAVRT): Anterograde via AV node, retrograde via AP → narrow complex (90–95% of AVRT); may be wide if bundle branch block coexists
• Antidromic AVRT: Anterograde via AP, retrograde via AV node (or second AP) → maximally pre-excited wide complex; ~5% of AVRT in manifest AP patients
• PJRT (Permanent form of junctional reciprocating tachycardia): Rare; nearly incessant orthodromic AVRT via slowly conducting (decremental) concealed posteroseptal AP; deeply inverted P waves in inferior leads; long RP; tachycardia-induced cardiomyopathy common
• Atriofascicular (Mahaim) pathway: Decremental anterograde conduction; LBBB morphology tachycardia; retrograde via AV node/His Purkinje; no retrograde conduction
• Nodofascicular/nodoventricular pathways: Rare; AV node–fascicle or AV node–ventricle connections
• Pre-excitation risk is highest in first 2 decades of life; SCD 10-year risk 0.15–0.24% sources/svt-aha-2015

ECG Features

• Manifest pre-excitation (sinus rhythm): Short PR (<120 ms), delta wave (slurred QRS upstroke), QRS widening
• Orthodromic AVRT: Regular narrow-complex tachycardia; P wave visible in early ST segment after QRS (short RP); retrograde P wave in tachycardia vs absent or terminal P in AVNRT
• Antidromic AVRT: Regular wide-complex tachycardia; maximally pre-excited QRS (fully delta wave pattern)
• Pre-excited AF: Irregular wide-complex tachycardia with variable QRS morphology (fusion between AV nodal and AP conduction); DANGER — rates can exceed 300 bpm → VF
• PJRT: Long RP tachycardia; deeply negative P waves in II, III, aVF; nearly incessant; may mimic atypical AVNRT or low septal AT

Risk Stratification of Accessory Pathways

• Low-risk markers (noninvasive):
  • Abrupt loss of pre-excitation on exercise testing (Class I/B-NR): ~90% PPV for pathway incapable of sustaining rapid conduction
  • Intermittent loss of pre-excitation on ECG/ambulatory monitor (Class I/C-LD): similarly predicts low-risk pathway
• EP study (Class IIa/B-NR): Reasonable for risk stratification in asymptomatic pre-excitation
• High-risk EP findings: Shortest pre-excited R-R interval ≤250 ms during induced AF; AVRT precipitating pre-excited AF; multiple APs; AP effective refractory period <240 ms; inducible sustained AVRT
• EP study complication rate 0.09–1% in one series of 2,169 patients sources/svt-aha-2015

Acute Treatment — Orthodromic AVRT

• Class I/B-R: Vagal maneuvers — first-line
• Class I/B-R: Adenosine — terminates oAVRT in 90–95%; caution: may precipitate AF which then conducts rapidly over manifest AP → cardioversion must be available
• Class I/B-NR: Synchronized cardioversion if hemodynamically unstable and vagal/adenosine fail
• Class I/B-NR: Synchronized cardioversion if hemodynamically stable and pharmacotherapy fails
• Class IIa/B-R: IV diltiazem, verapamil (B-R) or beta blockers (C-LD) — for hemodynamically stable patients WITHOUT pre-excitation on resting ECG (concealed AP)
• Class IIb/B-R: IV diltiazem/verapamil/beta blockers may be considered for oAVRT WITH pre-excitation on resting ECG if other therapies have failed (AVRT may convert to pre-excited AF; must have cardioversion immediately available) sources/svt-aha-2015

Acute Treatment — Pre-Excited AF (Critical Safety)

• Class I/B-NR: Synchronized DC cardioversion — hemodynamically unstable pre-excited AF
• Class I/C-LD: IV ibutilide or IV procainamide — hemodynamically stable pre-excited AF; both slow conduction over AP and may terminate AF
• CLASS III/HARM: IV digoxin, IV amiodarone, IV or oral beta-blockers, diltiazem, verapamil
  • Mechanism of harm: (1) block/slow AV nodal conduction → remove competitive concealed retrograde conduction into AP → enhanced AP conduction; (2) drug-induced hypotension → catecholamine release → enhanced AP conduction; (3) digoxin directly shortens AP refractoriness
  • Consequence: ventricular rate may accelerate to >300 bpm → VF → SCD sources/svt-aha-2015

Ongoing Management

• Class I/B-NR: Catheter ablation of AP — first-line definitive therapy for AVRT and/or pre-excited AF; ~93–95% acute success; 3% major complications; also effective for PJRT (~90% success) and Mahaim fibers (70–100%)
• Class I/C-LD: Oral beta blockers/diltiazem/verapamil for concealed AP (no pre-excitation on resting ECG); effective in ~50% of patients
• Class IIa/B-R: Oral flecainide or propafenone (no structural/ischemic heart disease) — 85–90% symptom reduction; 30% complete absence of tachycardia; directly slows/blocks AP conduction
• Class IIb/B-R: Oral dofetilide or sotalol (can be used in structural heart disease; in-hospital initiation required)
• Class IIb/C-LD: Oral amiodarone — small observational data; reserved for failed other drugs; not for long-term due to toxicity
• Class IIb/C-LD: Oral beta blockers/diltiazem/verapamil may be reasonable for oAVRT with manifest AP (pre-excitation on resting ECG) — WITH CAUTION; patient must understand that AVRT may convert to pre-excited AF while on these agents
• Class IIb/C-LD: Oral digoxin for AVRT in concealed AP (very limited evidence; not suitable for manifest AP)
• CLASS III/HARM: Oral digoxin in patients with AVRT or AF and pre-excitation on resting ECG sources/svt-aha-2015

Asymptomatic Pre-Excitation Management

• Class I/B-NR (or C-LD): Noninvasive risk stratification (exercise testing/ambulatory monitoring) to identify low-risk pathways
• Class IIa/B-NR: EP study for risk stratification
• Class IIa/B-NR: Catheter ablation if EP study identifies high-risk pathway (RCT: 7% events with ablation vs 77% without over 8 years)
• Class IIa/B-NR: Ablation reasonable if pre-excitation precludes specific employment (pilots, professional athletes)
• Class IIa/B-NR: Observation without treatment — also reasonable; most adults with asymptomatic pre-excitation have benign course; SCD risk low but exists (mainly in first 2 decades)

Ablation Outcomes

• Acute success: ~93%
• Recurrence: ~8%
• Major complications: 2.8% overall; 0.3% permanent pacemaker; 0.1% death; 0.4% tamponade
• Left-sided pathways: higher success rates; right-sided (especially anteroseptal/para-Hisian): higher risk of AV block → cryoablation preferred
• In children with Ebstein anomaly: acute success 75–89%; combined catheter + surgical approach 94% vs catheter alone 76% sources/svt-aha-2015

ESC 2019 Key Updates — AVRT/Accessory Pathways

Acute antidromic AVRT (new ESC 2019 recommendation): In antidromic AVRT, drugs acting on AP should be preferred because AP is both the anterograde and potentially retrograde limb; AV nodal blocking agents ineffective if both limbs use APs; ibutilide/procainamide/flecainide/propafenone or DC cardioversion: IIa/B; amiodarone refractory cases: IIb/B sources/svt-esc-2019 (rating: very high)

IV amiodarone in pre-excited AF — ESC 2019 strengthened evidence (Class III/B): ESC 2019 explicitly states "IV amiodarone may not be as safe as previously thought — enhanced pathway conduction and ventricular fibrillation have been reported." Procainamide appears safer in pre-excited AF. This aligns with and strengthens the AHA 2015 Class III/Harm recommendation. sources/svt-esc-2019

Asymptomatic pre-excitation — ESC 2019 upgrades:

• EPS with isoprenaline for high-risk occupations (pilots, professional drivers) and competitive athletes: now Class I/B (upgraded from IIa/B in AHA 2015)
• Catheter ablation for high-risk EP features (SPERRI ≤250 ms, AP ERP ≤250 ms, multiple APs, inducible AVRT): Class I/B in both guidelines — consistent
• Intermittent pre-excitation now recognized as imperfect risk marker (ESC 2019): >1/5 patients with intermittent pre-excitation have AP ERP <250 ms; ESC no longer endorses it as a reliable low-risk criterion
• LV dysfunction from electrical dyssynchrony in asymptomatic pre-excitation → ablation IIa/C sources/svt-esc-2019

Ablation outcomes (ESC 2019 Table 11):

Cardiac tamponade 0.13–1.1%; AV block 0.17–2.7% (septal APs). Cryoenergy: lower AV block risk but significantly higher recurrence for septal APs. sources/svt-esc-2019

Contradictions / Open Questions

• Asymptomatic pre-excitation: ESC 2019 takes more aggressive stance (I/B EPS for athletes/high-risk occupations; ablation I/B for high-risk EP findings) than AHA 2015 (IIa); however, ESC notes that even EPS does not confer absolute certainty — 25% of young WPW patients with cardiac arrest did not have high-risk EPS features or inducible AVRT sources/svt-esc-2019
• Intermittent pre-excitation: ESC 2019 explicitly downgraded it as a reliable low-risk marker (>20% have ERP <250 ms); AHA 2015 lists it as a Class I/C-LD low-risk criterion — this is a significant guideline contradiction sources/svt-aha-2015 sources/svt-esc-2019
• AV nodal blockers in manifest AP: both guidelines agree these are risky in pre-excited AF (Class III/Harm); AHA 2015 allows IIb use in oAVRT with manifest AP if other therapies fail; ESC 2019 limits CCBs/BBs to "if no signs of pre-excitation on resting ECG" (IIa) — stricter criterion sources/svt-aha-2015 sources/svt-esc-2019
• Cryoablation vs RF for septal APs: both guidelines note lower AV block risk with cryo but higher recurrence; practice varies by centre

Connections

• Related to concepts/SVT-Management — AVRT management framework
• Related to concepts/AVNRT — main differential for regular narrow-QRS SVT
• Related to concepts/Wide-Complex-Tachycardia — antidromic AVRT/pre-excited AF as causes of WCT
• Related to entities/Atrial-Fibrillation — pre-excited AF: unique and dangerous scenario
• Related to concepts/Antiarrhythmic-Drugs — flecainide/propafenone direct AP blocking; digoxin/CCB dangerous in WPW

Sources

• sources/svt-aha-2015
• sources/svt-esc-2019