What is AVNRT?
AVNRT (atrioventricular nodal reentrant tachycardia) is the most common form of paroxysmal supraventricular tachycardia, caused by a reentrant circuit within or near the AV node utilizing dual AV nodal pathways with different conduction properties. 1
Mechanism and Substrate
The anatomic substrate of AVNRT is dual AV nodal physiology involving two pathways with distinct electrophysiological properties 2:
- Fast pathway: Conducts rapidly but has a longer refractory period
- Slow pathway: Conducts more slowly but has a shorter refractory period
Typical (Common) AVNRT (~90% of cases)
The reentrant circuit uses the slow pathway in the anterograde direction (atrium to ventricle) and the fast pathway retrogradely (ventricle to atrium), resulting in nearly simultaneous atrial and ventricular activation 3, 4.
Atypical (Uncommon) AVNRT (~10% of cases)
The circuit direction is reversed—the fast pathway conducts anterogradely and the slow pathway retrogradely, producing delayed atrial activation 3.
Clinical Presentation
AVNRT typically occurs in young adults without structural heart disease, with >60% of cases in women 1. The arrhythmia is often well tolerated and rarely life-threatening 2.
Characteristic Symptoms
- Sudden onset palpitations (hallmark feature)
- Neck pulsations (highly characteristic due to simultaneous atrial and ventricular contraction)
- Shortness of breath
- Dizziness or lightheadedness
- Chest discomfort
- Syncope (rare manifestation) 2, 4
Triggers
AVNRT may occur spontaneously or be provoked by:
- Exertion
- Coffee or tea
- Alcohol 2
Electrocardiographic Features
Heart Rate
Typically 180-200 bpm, but ranges from 110 bpm to >250 bpm (rarely <100 bpm) 1.
Typical AVNRT (Short RP Pattern)
- P waves obscured by QRS complex or present at its terminal portion
- Pseudo r' pattern in lead V1 (small terminal positive deflection)
- Pseudo S waves in inferior leads (II, III, aVF)
- P wave closer to the prior QRS than the subsequent QRS 2, 5
Atypical AVNRT (Long RP Pattern)
- Retrograde P wave (negative in inferior leads) occurs late
- P wave within or after the T wave
- P wave closer to the subsequent QRS complex 2
Electrophysiological Characteristics
The reentrant circuit is limited to the AV node and a small amount of perinodal atrial tissue 6. The arrhythmia can be reproducibly initiated and terminated by cardiac pacing during electrophysiological study 6.
Clinical Significance
While generally benign, AVNRT can cause:
- Heart failure exacerbation in patients with poor left ventricular function
- Angina or myocardial infarction in patients with coronary artery disease
- Syncope with rapid ventricular rates due to decreased cardiac output and cerebral hypoperfusion 4
The recurrent symptomatic nature often leads to repeated emergency department visits and reduced quality of life, warranting definitive therapy 5.