Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

Definition

AVNRT is the most common SVT. It involves a reentrant circuit utilizing two functionally distinct pathways within or near the AV node: a slow pathway (inferoposterior to the compact AV node) and a fast pathway (near the apex of Koch's triangle). Typical AVNRT uses the slow pathway anterograde and the fast pathway retrograde ("slow-fast"). Atypical AVNRT uses the fast pathway anterograde and slow pathway retrograde ("fast-slow"), or two slow pathways ("slow-slow"). sources/svt-aha-2015 (rating: very high)

Key Concepts

Epidemiology and Clinical Features

• Most common SVT; >60% of cases in women; most prevalent in middle-aged/older patients sources/svt-aha-2015
• Ventricular rate typically 180–200 bpm; range 110 to >250 bpm; occasionally <100 bpm
• Onset often spontaneous or provoked by exertion, coffee, tea, or alcohol
• Usually well tolerated; syncope rare
• Cannon a-waves and polyuria: Atrial contraction against closed tricuspid valve generates cannon a-waves → "neck pounding" or "shirt flapping"; elevated RA pressure releases ANP → polyuria (more pronounced than in AVRT)
• Hemodynamic drop in BP greatest in first 10–30 seconds (partial recovery at 30–60 s); typical AVNRT causes marked initial systemic BP fall and stable hypotension due to simultaneous atrial/ventricular contraction

ECG Features

• Typical AVNRT (slow-fast): Short RP tachycardia; atrial activation nearly simultaneous with QRS → P wave at end of QRS complex → pseudo-S wave in inferior leads (II, III, aVF) and pseudo-R' in V1; 1:1 AV relationship (2:1 AV block has been described but is rare)
• Atypical AVNRT (fast-slow): Long RP tachycardia; retrograde P wave visible in early part of TP segment, deeply negative in inferior leads; morphologically similar to PJRT and low septal AT
• Differential: typical AVNRT (short RP) vs orthodromic AVRT (short RP, P visible in ST segment after QRS) sources/svt-aha-2015

Pathophysiology

• Substrate: dual AV nodal physiology — anatomically or functionally distinct fast and slow pathways
• In typical AVNRT: premature atrial impulse blocks in fast pathway (shorter ERP) → conducts anterograde down slow pathway → retrograde up fast pathway when fast pathway recovers → "echo beat" / AVNRT initiation
• Atrial activation nearly simultaneous with ventricular activation in typical AVNRT → minimal RP interval on surface ECG

Acute Treatment (Class-Based)

• Class I/B-R: Vagal maneuvers (Valsalva; carotid sinus massage) — first-line; 27.7% overall success when switching techniques sources/svt-aha-2015
• Class I/B-R: Adenosine — terminates AVNRT in ~95% of patients; also diagnostic if flutter/AT present
• Class I/B-NR: Synchronized DC cardioversion if hemodynamically unstable and pharmacotherapy fails/not feasible
• Class I/B-NR: Synchronized DC cardioversion if hemodynamically stable and pharmacotherapy fails
• Class IIa/B-R: IV diltiazem, verapamil, or beta blockers (hemodynamically stable patients only; NOT in VT or pre-excited AF)
• Class IIb/C-LD: Oral beta blockers/diltiazem/verapamil may be reasonable for acute termination (limited data; combination diltiazem + propranolol studied)
• Class IIb/C-LD: IV amiodarone when other therapies ineffective or contraindicated

Ongoing Management (Class-Based)

• Class I/B-NR: Catheter ablation of slow pathway — first-line; success >95%; <1% risk of complete AV block; cryoablation alternative (lower AV block risk but higher recurrence rate) sources/svt-aha-2015
• Class I/B-R: Oral verapamil or diltiazem — for patients not pursuing ablation
• Class I/B-R: Oral beta blockers — for patients not pursuing ablation; similar efficacy to verapamil/diltiazem in one small RCT
• Class IIa/B-R: Flecainide or propafenone (no structural/ischemic heart disease) — 86–93% 12-month freedom from recurrence; "pill-in-the-pocket" flecainide for infrequent AVNRT studied but evidence limited
• Class IIa/B-NR: Observation without treatment — reasonable for minimally symptomatic patients; ~50% improved or became asymptomatic over 15-year follow-up without therapy
• Class IIb/B-R: Sotalol or dofetilide (can be used in structural heart disease; monitor QT in-hospital)
• Class IIb/B-R: Digoxin or amiodarone — third-line; limited efficacy evidence; significant toxicity concerns

ESC 2019 Updates on AVNRT

Onset pattern: Bimodal — early in life OR fourth/fifth decade; ~50% with minimal symptoms become asymptomatic within 1–3 years without treatment sources/svt-esc-2019 (rating: very high)

AVNRT → AF relationship: AVNRT may trigger AF; AF usually resolves after catheter ablation of AVNRT sources/svt-esc-2019

ECG additional criteria (ESC 2019): Pseudo-R in aVR has higher sensitivity and specificity than pseudo-R in V1 for typical AVNRT; QRS notch in lead aVL also reliable criterion; RP difference between V1 and III >20 ms → AVNRT (rather than AVRT with posteroseptal AP) sources/svt-esc-2019

Acute treatment — added detail: Single dose oral diltiazem 120 mg + propranolol 80 mg may convert up to 94% of patients; risk of hypotension, transient AV block, or syncope — use with caution especially in elderly sources/svt-esc-2019

Catheter ablation (ESC 2019 RCT evidence): RCT comparing catheter ablation as first-line vs antiarrhythmic drugs demonstrated significant benefit in arrhythmia-related hospitalizations; ablation success 97%; recurrence 1.3–4%; AV block <1% in modern series targeting inferior nodal extension and avoiding mid-septum and roof of coronary sinus sources/svt-esc-2019

Pre-existing first-degree AV block is a risk factor for late AV block — avoid extensive slow-pathway ablation in this setting sources/svt-esc-2019

Cryoablation (ESC 2019): Lower AV block risk; significantly higher recurrence rate than RF; preferred in children due to favourable safety profile sources/svt-esc-2019

Ablation Outcomes

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

Contradictions / Open Questions

• Minimally symptomatic AVNRT: ablation is potentially curative but ~50% improve spontaneously — observation is a reasonable alternative; patient preference and frequency/severity of episodes should drive the decision sources/svt-aha-2015
• Cryoablation vs RF: tradeoff between AV block risk and recurrence risk not fully resolved; lesion size and procedural endpoint affect recurrence
• "Fast-slow" and "slow-slow" AVNRT variants: ECG appearance similar to PJRT and low septal AT; EP study required to distinguish

Connections

• Related to concepts/SVT-Management — AVNRT is the most common SVT addressed in the guideline
• Related to concepts/AVRT-Accessory-Pathway — main differential diagnosis for regular narrow-QRS tachycardia
• Related to concepts/Wide-Complex-Tachycardia — rarely AVNRT can present with wide QRS if aberrant conduction
• Related to concepts/Antiarrhythmic-Drugs — detailed drug dosing for AVNRT management

Sources

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