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Background
AVNRT is the most common type of paroxysmal supraventricular tachycardia (PSVT), characterized by a reentrant circuit located within or adjacent to the atrioventricular (AV) node. It causes a sudden onset and termination of a regular, narrow complex tachycardia typically with rates between 140–250 bpm. Episodes often begin with a premature atrial beat that exploits dual AV nodal physiology.
II) Classification/Types
By Circuit Pathway:
- Typical (slow-fast) AVNRT – Most common; antegrade conduction via slow pathway and retrograde via fast pathway
- Atypical (fast-slow or slow-slow) – Less common; altered conduction directions within nodal pathways
By Duration:
- Paroxysmal: Sudden onset and spontaneous resolution
- Persistent: Sustained, may require intervention to terminate
Pathophysiology
AVNRT arises due to dual AV nodal pathways: a slow pathway with a short refractory period and a fast pathway with a longer refractory period. A premature atrial contraction finds the fast pathway refractory and conducts down the slow pathway. By the time it reaches the distal node, the fast pathway has recovered, allowing retrograde conduction, which re-excites the atria and perpetuates the circuit.
Epidemiology
- Accounts for ~60% of all PSVTs
- Predominantly affects females
- Commonly presents in adolescents and young to middle-aged adults
- Often occurs in structurally normal hearts
- Can be induced during exercise, emotional stress, or alcohol/caffeine use
Etiology
I) Causes
- Dual AV nodal pathway physiology (congenital)
- Triggered by premature atrial beats
- Increased sympathetic tone (exercise, stress)
- Dehydration or fever
- Stimulant use (caffeine, nicotine, alcohol)
II) Risk Factors
- Female sex
- Age 15–50 years
- History of palpitations or prior SVT
- High catecholamine states
- Structural or congenital AV nodal abnormalities (rare)
Clinical Presentation
I) History (Symptoms)
- Sudden-onset palpitations, often described as “pounding”
- Lightheadedness or presyncope
- Dyspnea or chest tightness
- Anxiety during episode
- Fatigue post-episode
- Rarely syncope
- Asymptomatic between episodes
II) Physical Exam (Signs)
- Regular narrow complex tachycardia (140–250 bpm)
- Rapid pulse with abrupt onset/offset
- Cannon A waves in neck (if AV dissociation occurs)
- Stable blood pressure in most cases
- Normal cardiac exam findings between episodes
Differential Diagnosis (DDx)
- AV Reentrant Tachycardia (AVRT, e.g., WPW)
- Sinus tachycardia
- Atrial flutter with 2:1 conduction
- Atrial tachycardia
- Junctional tachycardia
- Ventricular tachycardia (if wide QRS)
- Anxiety-induced palpitations
Diagnostic Tests
Initial Work-Up
- ECG (during episode): Regular, narrow QRS tachycardia; P waves may be absent or retrograde (buried in or after QRS)
- ECG (baseline): Often normal; may show dual AV nodal physiology if captured during EPS
- Vagal maneuvers: May terminate AVNRT
- Adenosine test: Transient AV block may terminate AVNRT and confirm diagnosis
- Holter/Event Monitor: Useful in paroxysmal or infrequent cases
- Echocardiography: To rule out structural heart disease
- Electrophysiology Study (EPS): Definitive diagnostic tool and used for curative ablation
Treatment
I) Initial Approach
Hemodynamically unstable:
- Immediate synchronized cardioversion
Hemodynamically stable:
- Vagal maneuvers (Valsalva, carotid massage)
- IV adenosine if vagal maneuvers fail
II) Medications
Drug Class | Examples | Notes |
Adenosine | IV bolus | First-line; rapidly terminates AVNRT by transient AV block |
Beta-blockers | Metoprolol, Esmolol | Prevent recurrence; caution in asthma |
Calcium channel blockers | Verapamil, Diltiazem | Alternative to beta-blockers; avoid in hypotension |
Antiarrhythmics | Flecainide, Propafenone | For recurrent AVNRT in patients not candidates for ablation |
Radiofrequency ablation | Catheter ablation | Curative with >95% success; indicated in symptomatic or drug-refractory cases |
Consults/Referrals
- Cardiology: For diagnosis and medication initiation
- Electrophysiology: For definitive diagnosis and ablation
- Emergency Medicine: For acute symptomatic tachycardia
- Primary Care: Long-term rhythm surveillance and risk management
Patient Education, Screening, Vaccines, Education
- Recognize signs of an episode
- Perform vagal maneuvers when trained
- Avoid stimulants (caffeine, nicotine, alcohol)
- Adhere to medications
- Understand curative potential of ablation
Screening/Prevention
- ECG monitoring in recurrent cases
- EPS in frequent or poorly tolerated episodes
- Avoid trigger exposure in susceptible individuals
Vaccinations
- Routine age-appropriate vaccinations
- No specific vaccines required for arrhythmia
Follow-Up
Short-Term
- Evaluate response to acute management (vagal or adenosine)
- Outpatient Holter or event monitor
- Reassess for structural or functional abnormalities
Long-Term
- Monitor frequency and severity of episodes
- Consider ablation for recurrent or drug-refractory AVNRT
- Periodic rhythm surveillance if symptoms recur
- Educate on medication adherence and trigger avoidance
Prognosis
- Excellent prognosis with catheter ablation (>95% cure rate)
- Most patients lead normal lives with minimal interruption
- Low risk of sudden death or major complications
- Long-term medications often not required after ablation
- Recurrence is rare but possible in a small percentage of cases
