What is the appropriate workup for atrioventricular nodal reentrant tachycardia (AVNRT)?

Workup for AVNRT

The workup for AVNRT centers on obtaining a 12-lead ECG during tachycardia to confirm the diagnosis, followed by electrophysiology study (EPS) when definitive diagnosis or catheter ablation is planned. 1

Initial Clinical Assessment

History and Symptoms

• Document the pattern of palpitations—AVNRT characteristically starts and stops abruptly 2
• Ask specifically about neck pulsations, which are highly characteristic of AVNRT due to simultaneous atrial and ventricular contraction 3
• Assess for associated symptoms including chest discomfort, dyspnea, lightheadedness, dizziness, and anxiety 2, 3
• Syncope is rare in AVNRT but may occur with rapid rates or prolonged episodes causing decreased cardiac output 3
• Identify potential triggers such as exertion, coffee, tea, or alcohol 4

Physical Examination During Episode

• Assess hemodynamic stability first—look for hypotension, signs of myocardial ischemia (chest pain, diaphoresis), or acute heart failure (pulmonary edema, severe dyspnea) 1
• Check for regular rapid pulse (typically 150-250 bpm) 4
• Examine for jugular venous pulsations—prominent "frog sign" or cannon A waves suggest AVNRT 3

Electrocardiographic Workup

12-Lead ECG During Tachycardia (Essential)

• Narrow QRS complex (<120 ms) is typical for AVNRT 1
• Look for pseudo-r' waves in lead V1 or pseudo-S waves in inferior leads (II, III, aVF)—these represent retrograde P waves buried in or immediately after the QRS complex and are highly suggestive of AVNRT 5
• Absent visible P waves during tachycardia strongly suggests AVNRT, as the P wave is typically hidden within the QRS 6
• If discrete P waves are visible, measure the RP interval—in typical (slow-fast) AVNRT, the RP is very short (<70 ms) with P waves immediately after the QRS 5, 3
• In atypical (fast-slow) AVNRT, the P wave occurs late within or after the T wave with a long RP interval 3

12-Lead ECG During Sinus Rhythm

• Check for pre-excitation (delta waves) to rule out Wolff-Parkinson-White syndrome, which would indicate AVRT rather than AVNRT 1
• Absence of delta waves supports AVNRT over AVRT involving an accessory pathway 4

Differentiating AVNRT from AVRT

• The presence of pseudo-r' in V1 or pseudo-S in inferior leads favors AVNRT over AVRT 5
• RP interval <70 ms strongly suggests AVNRT 5
• ST-segment depression ≥2 mm may be present but is not specific 5

Electrophysiology Study (When Indicated)

Indications for EPS

• Definitive diagnosis when surface ECG findings are equivocal 4, 6
• Pre-ablation mapping when catheter ablation is planned 4, 6
• Differentiation from other SVTs (AVRT, atrial tachycardia) when clinical uncertainty exists 7, 6

EPS Findings Diagnostic of AVNRT

• Dual AV nodal physiology—demonstration of two distinct AV nodal pathways with different conduction velocities and refractory periods (fast pathway conducts faster but has longer refractoriness; slow pathway conducts slower with shorter refractoriness) 4, 6
• Reproducible induction and termination of tachycardia with programmed atrial or ventricular stimulation 6
• In typical AVNRT, the reentrant circuit uses the slow pathway antegradely and fast pathway retrogradely 3, 6
• Atrial activation sequence during tachycardia shows earliest activation in the His bundle region or coronary sinus ostium, with near-simultaneous activation of the atria 8
• VA interval <70 ms during tachycardia (measured from ventricular to atrial electrogram) 7

Advanced EPS Techniques for Localization

• Atrial resetting maneuvers can identify whether the right inferior extension (RIE) or left inferior extension (LIE) is the anterograde slow pathway—this occurs in 72% and 20% of cases, respectively 9
• Programmed ventricular extrastimuli (V2) during tachycardia: an SA-VA difference >70 ms confirms AVNRT and differentiates it from AVRT with septal or right-sided accessory pathways 7
• High-resolution 3D electroanatomic mapping during sinus rhythm can identify the most delayed atrial potential near the His bundle, which represents the slow pathway exit 10
• For atypical AVNRT, catheter placement on the tricuspid annulus is critical, as conventional His and CS catheter mapping misses 36% of RIE involvement 11

Common Pitfalls to Avoid

• Do not assume wide QRS tachycardia is AVNRT—this may represent ventricular tachycardia or SVT with aberrancy and requires different management 1
• Do not overlook pre-excitation on baseline ECG, as this indicates WPW syndrome and AVRT, not AVNRT; AV-nodal blockers are contraindicated in pre-excited atrial fibrillation 1
• Do not rely solely on His bundle and coronary sinus catheters during EPS for atypical AVNRT—this approach misses RIE involvement in over one-third of cases; place a catheter on the tricuspid annulus 11
• Do not confuse atypical AVNRT with atrial tachycardia—EPS with programmed stimulation and mapping is essential for accurate differentiation 11

When to Proceed to Catheter Ablation

• Offer catheter ablation as first-line definitive therapy for patients with documented AVNRT, especially those with recurrent symptomatic episodes, high-risk occupations (pilots, drivers), or preference to avoid lifelong medication 1
• Ablation provides a cure without chronic medication and has a high success rate (>95%) with low complication rates 1, 6
• Even in young children and infants presenting with AVNRT, cryoablation can be safely performed with 100% success and no recurrence 12