What are atrioventricular nodal re‑entrant tachycardia (AVNRT) and atrioventricular re‑entrant tachycardia (AVRT), and how are they diagnosed and managed?

What is AVNRT or AVRT?

AVNRT (atrioventricular nodal reentrant tachycardia) and AVRT (atrioventricular reentrant tachycardia) are the two most common types of paroxysmal supraventricular tachycardia, distinguished by their reentrant circuits: AVNRT uses dual pathways within the AV node itself, while AVRT requires an accessory pathway connecting atrium to ventricle outside the normal conduction system. 1

Anatomic and Mechanistic Differences

AVNRT Circuit

• The reentrant circuit is confined to the AV node and a small amount of perinodal atrial tissue, involving two functionally distinct pathways termed "fast" and "slow" pathways 2, 3
• In typical AVNRT (90% of cases), anterograde conduction occurs down the slow pathway and retrograde conduction up the fast pathway 4, 3
• The fast pathway conducts faster but has a longer refractory period than the slow pathway 2

AVRT Circuit

• The electrical pathway requires an accessory pathway (an extranodal connection between atrial and ventricular myocardium across the AV groove), the atrium, AV node, and ventricle 4
• In orthodromic AVRT (the most common form), the reentrant impulse uses the accessory pathway in the retrograde direction from ventricle to atrium, and the AV node in the anterograde direction 4
• This accessory pathway is anatomically separate from the AV node, fundamentally distinguishing it from AVNRT 4

ECG Diagnosis

AVNRT ECG Features

• Atrial activation occurs nearly simultaneously with ventricular activation, causing P waves to be buried within or at the end of the QRS complex 1, 4
• Pseudo-S waves appear as narrow negative deflections in inferior leads (II, III, aVF) 1, 4
• Pseudo-R' waves appear as slightly positive deflections at the end of the QRS complex in lead V1 1, 4
• The RP interval is typically <90 ms, classified as "short RP" tachycardia 1

AVRT ECG Features

• Retrograde P waves are usually clearly visible in the early part of the ST-T segment, separate from the QRS complex 1, 4
• The P wave morphology reflects the location of the accessory pathway (e.g., deeply inverted P waves in inferior leads when the pathway is posteroseptal) 4
• The RP interval is short but longer than AVNRT, with P waves visible between QRS complexes 1

Clinical Presentation

Demographics

• AVNRT is more common in middle-aged or older patients with female predominance (>60% women), with mean symptom onset at 32±18 years 1, 4
• AVRT is more prevalent in adolescents and younger adults, with mean symptom onset at 23±14 years 1, 4, 5

Symptoms

• AVNRT-specific: "Neck pounding" or "shirt-flapping" sensations are highly specific, caused by cannon A-waves when the right atrium contracts against a closed tricuspid valve 1, 6, 4
• AVNRT-specific: Polyuria is particularly common due to elevated atrial natriuretic peptide from increased right atrial pressures 1, 6
• Both: Palpitations, lightheadedness, chest discomfort, dyspnea, and anxiety 6, 7
• Both: True syncope is infrequent (4-15% of cases) but more common in elderly patients with AVNRT despite slower heart rates 6, 7

Heart Rate

• AVNRT typically presents with rates of 180-200 bpm but ranges from 110 bpm to >250 bpm 1
• Both arrhythmias have abrupt onset and termination, a hallmark feature 1, 6

Acute Management

First-Line Interventions (Both AVNRT and AVRT)

• Vagal maneuvers are recommended as initial therapy (Class I, Level B-R) 1, 4
• Adenosine is recommended for acute termination (Class I, Level B-R) because both respond by blocking AV nodal conduction 1, 4, 2

Second-Line Pharmacologic Options

• Intravenous beta blockers, diltiazem, or verapamil are reasonable for hemodynamically stable patients (Class IIa, Level B-R) 1

Critical Pitfall in AVRT

• Never administer verapamil or diltiazem during pre-excited atrial fibrillation in AVRT with Wolff-Parkinson-White syndrome, as this may cause hemodynamic collapse or ventricular fibrillation 4, 8

Cardioversion

• Synchronized cardioversion is recommended for hemodynamically unstable patients when adenosine and vagal maneuvers fail (Class I, Level B-NR) 1

Ongoing Management

AVNRT

• Catheter ablation of the slow pathway is recommended as definitive therapy (Class I, Level B-NR), with high success rates and low complication risk 1, 2, 3
• Oral verapamil, diltiazem, or beta blockers are recommended for patients who are not candidates for or prefer not to undergo catheter ablation (Class I, Level B-R) 1
• Flecainide or propafenone is reasonable in patients without structural heart disease when first-line agents are ineffective (Class IIa, Level B-R) 1

AVRT

• Catheter ablation of the accessory pathway itself is the definitive treatment, with success rates of 95-100% 4
• Medical management follows similar principles to AVNRT for patients declining ablation 1

Diagnostic Pitfalls

• Misattribution to panic or anxiety disorders occurs in 54% of patients, with women more likely to be mislabeled than men 1, 6
• Atypical AVNRT variants can produce long RP intervals that mimic atrial tachycardia, requiring careful ECG analysis 4
• Brief or asymptomatic episodes may go undetected; 64% of patients with accessory pathways present with symptoms, but 20% develop symptoms later 6