Avnrt: Symptoms, Types, Causes and Treatment

Atrioventricular nodal reentrant tachycardia (AVNRT) is one of the most common forms of supraventricular tachycardia. It affects people of all ages, from children to the elderly, and is often responsible for sudden, sometimes alarming episodes of rapid heartbeats. Understanding AVNRT—its symptoms, types, causes, and treatment options—can empower patients and families to navigate this condition with greater confidence.

Below, we’ll explore AVNRT step-by-step, using current research to provide the most accurate and practical information.

Symptoms of Avnrt

AVNRT often presents with a surprising, rapid heartbeat that feels like it starts and stops abruptly. For many, these episodes can trigger anxiety and confusion, especially if they're mistaken for panic attacks or other conditions. Recognizing the common symptoms is the first step to seeking appropriate care.

Symptom	Description	Frequency/Age Group	Source(s)
Palpitations	Sensation of rapid, pounding, or fluttering heart	All ages; most common	3 4 5
Chest pain	Discomfort or pain in the chest	Children & elderly	3 5
Syncope	Fainting or loss of consciousness	More frequent in females	2 3 5
Lightheadedness	Feeling faint or dizzy	All ages	2 3 4
Fatigue	Unusual tiredness after episodes	All ages	3
Polyuria	Increased urination following episodes	Adults	4
Anxiety	Feeling anxious during or after episodes	All ages; often misdiagnosed	4 5
Dyspnea	Shortness of breath	Adults	4

Table 1: Key Symptoms

Palpitations: The Core Symptom

Palpitations are the hallmark of AVNRT, often described as a sudden fluttering, pounding, or racing of the heart. These sensations usually begin and stop abruptly, sometimes lasting seconds to hours. The abrupt nature is what distinguishes AVNRT from other forms of arrhythmias, which may start or end more gradually 3 4.

Associated Symptoms

• Chest Pain & Fatigue: While palpitations dominate, some individuals—especially children and older adults—may experience chest discomfort or fatigue after an episode 3 5.
• Syncope (Fainting): In some cases, the rapid heart rate reduces blood flow to the brain, leading to lightheadedness or even syncope. This is more often reported in females and can lead to injury if a person falls 2 3.
• Polyuria: An increase in urination after episodes is sometimes seen, likely due to hormonal changes during tachycardia 4.
• Anxiety & Misdiagnosis: The sudden, intense symptoms can cause significant anxiety. In elderly patients, AVNRT is sometimes misdiagnosed as panic attacks, leading to years of inappropriate treatment 5.

Symptom Triggers and Patterns

• AVNRT episodes can be triggered by stress, caffeine, alcohol, or sometimes occur without any clear reason.
• The condition is characterized by an "on/off" phenomenon, making it unpredictable and sometimes distressing for patients 4.

Types of Avnrt

Not all AVNRT is the same. Variations exist based on the pathways involved in the heart's electrical circuit. Understanding these types helps tailor treatment and anticipate outcomes.

Type	Pathway Involvement	Prevalence	Source(s)
Slow-Fast	Antegrade slow, retrograde fast	~81% (common/typical)	6 10 9
Slow-Slow	Antegrade slow, retrograde slow	~14% (atypical)	6 17 18
Fast-Slow	Antegrade fast, retrograde slow	~5% (atypical)	6 8 18
Multiple Pathways	More than two slow/fast options	~5% (triple pathways)	7

Table 2: Main AVNRT Types

The Typical Type: Slow-Fast AVNRT

• Mechanism: Electrical impulses travel down the "slow" pathway and return via the "fast" pathway, creating a reentrant loop 6 9 10.
• Prevalence: This is by far the most common form, responsible for around 80% of cases.
• Features: Regular, narrow QRS tachycardia; abrupt onset/termination.

Atypical Types: Slow-Slow and Fast-Slow AVNRT

• Slow-Slow: Both conduction down and back up occur via slow pathways 6. Less common, but can be harder to diagnose due to subtle ECG differences. Slightly higher recurrence after ablation 18.
• Fast-Slow: The impulse travels down the fast pathway and up the slow pathway. Rare and may present with unusual ECG patterns 6 8 18.

Multiple Pathways and Variants

Some patients have more than two functional pathways (e.g., triple or quadruple), which can complicate both diagnosis and treatment 7. These cases may exhibit multiple types of AVNRT or more complex arrhythmias.

Special Variants

• Superior Slow Pathway: Rare forms involve a "superior" slow pathway with unique electrophysiological features, sometimes requiring ablation in less common sites 8.

Diagnostic Considerations

• Electrocardiogram (ECG): Most types show regular, narrow QRS tachycardia, but P wave patterns and intervals help distinguish subtypes 3 6 13.
• Electrophysiology Study (EPS): Direct study of conduction pathways is often required to definitively identify the AVNRT type and plan targeted therapy 6 7 8.

Causes of Avnrt

What leads to AVNRT? The answer lies in a mix of cardiac anatomy, genetics, and sometimes family history. While the basic mechanism involves a reentrant circuit in the AV node, underlying causes can differ from person to person.

Cause	Description	Evidence Level	Source(s)
Dual Pathways	Two (or more) conduction pathways in AV node	Universal in AVNRT	3 6 7 9
Genetic Factors	Variants in ion channel and conduction genes	Strong (familial & sporadic cases)	11 12 14
Age & Sex	More common in women, peaks <40 years	Epidemiological	11 2 5
Familial Clustering	Family history of AVNRT	Documented	12 14
Triggers	Stress, caffeine, alcohol, exercise	Observational	4 19

Table 3: Main Causes

The Reentrant Circuit: Dual Pathway Physiology

At the heart of AVNRT is the presence of two (or sometimes more) conduction pathways within or near the AV node:

• Fast Pathway: Rapid conduction, but longer refractory period.
• Slow Pathway: Slower conduction, but shorter refractory period. A premature electrical impulse can trigger a loop—down one pathway and up the other—leading to the rapid rhythm 3 6 7.

Genetic and Familial Factors

• Ion Channel Gene Variants: Recent sequencing studies reveal that a significant proportion of AVNRT patients carry variants in genes related to sodium and calcium handling in cardiac cells (e.g., SCN1A, RYR2, PRKAG2, HCN, and others) 11 12 14.
• Familial Aggregation: Whole-exome sequencing in families has identified shared variants, supporting a genetic predisposition 12 14.
• Calcium Signaling Pathway: Genes like RYR2, CASQ2, TRDN, and others, involved in calcium regulation, are implicated—suggesting that subtle changes in calcium handling may promote reentry circuits 14.

Demographics and Risk Factors

• Age: AVNRT is often diagnosed in younger adults (<40 years), but can occur at any age—even in people over 80, where it's sometimes mistaken for anxiety or panic attacks 5 11.
• Sex: Women are affected about twice as often as men, and are more likely to have severe symptoms or syncope 2 11.

Triggers

• Episodes may be brought on by:
  • Physical or emotional stress
  • Caffeine or stimulants
  • Alcohol
  • Exercise
  • Sometimes, episodes occur without any trigger 4 19

Treatment of Avnrt

Treatment for AVNRT focuses on terminating acute episodes and preventing recurrences. Options range from simple maneuvers to advanced catheter ablation, with high success rates and low complication risks.

Treatment	Description	Effectiveness/Notes	Source(s)
Vagal Maneuvers	Stimulate vagus nerve to slow heart rate	20–40% success acutely	4 19
Adenosine	Rapid IV medication to block AV node temporarily	>90% conversion rate; short-lived side effects	19
Calcium Channel Blockers	Verapamil/diltiazem to slow conduction	As effective as adenosine; fewer side effects	19
Beta-blockers	Slow heart rate, less effective acutely	Not first-line	19 16
Electrical Cardioversion	Shock to restore normal rhythm	For unstable patients	19
Catheter Ablation	Destroy slow pathway with energy (RF/cryo)	>95% cure rate, low recurrence	15 16 17 18
Cryoablation	Freezes tissue instead of burning	Effective; very low risk of AV block	18
Medical Therapy	Chronic drug therapy (beta-blockers, CCBs)	Less effective long-term; not well tolerated	2 16

Table 4: Treatment Approaches

Acute Management

• Vagal Maneuvers: Techniques like the Valsalva maneuver (bearing down) or carotid massage can terminate AVNRT in about 20–40% of cases. They work by stimulating the vagus nerve, which slows AV node conduction 4 19.
• Adenosine: A rapid intravenous push of adenosine temporarily blocks the AV node, often stopping AVNRT within seconds. Though safe, it can cause brief chest discomfort, flushing, or a sense of impending doom. Contraindicated in patients with certain asthma or heart block conditions 19.
• Calcium Channel Blockers: IV verapamil or diltiazem are equally effective for terminating AVNRT, with fewer minor side effects compared to adenosine. They are a good alternative when adenosine is not tolerated or fails 19.
• Electrical Cardioversion: For patients who are hemodynamically unstable (e.g., low blood pressure, chest pain, fainting), synchronized cardioversion is recommended 19.

Long-Term Management and Cure

• Catheter Ablation: The gold standard for recurrent or symptomatic AVNRT. A catheter delivers radiofrequency (RF) energy to the slow pathway, preventing reentry without affecting normal conduction. Success rates exceed 95%, with a very low risk of AV block (<1–2%) 15 16 17.
  • Cryoablation: Freezes instead of burns the tissue; similar efficacy, but with an even lower risk of damaging the AV node permanently. Especially useful in children or when the ablation site is close to the normal conduction system 18.
  • Atypical and Multiple Pathway AVNRT: Conventional slow pathway ablation is effective for both typical and atypical forms, as well as in patients with multiple pathways 17.

Medical Therapy

• Chronic Medication: Beta-blockers or calcium channel blockers can be used for symptom control, especially when ablation is not available or in mild cases. However, in randomized studies, long-term drug therapy is less effective and less well tolerated than ablation 2 16.
• Pediatric and Elderly Considerations: In children with mild symptoms, observation may be sufficient. Elderly patients benefit from ablation, which can resolve misdiagnosed "panic attacks" 2 5.

Recurrence and Follow-Up

• Recurrence Rates: After successful ablation, recurrence is rare (<5–11%), with most occurring within the first months to years. Atypical forms may recur slightly more often 1 17 18.
• Prognosis: AVNRT is rarely life-threatening. With treatment, most patients remain symptom-free and return to normal activities 2 3 5 17.

Conclusion

Atrioventricular nodal reentrant tachycardia (AVNRT) is a common, often distressing—but highly treatable—heart arrhythmia. Here are the key takeaways:

• Symptoms include sudden palpitations, lightheadedness, chest pain, fatigue, and sometimes syncope or anxiety. Symptoms can be misdiagnosed, especially in the elderly.
• Types include typical (slow-fast), and atypical (slow-slow, fast-slow), as well as rare multiple pathway variants. Diagnosis often requires electrophysiological studies.
• Causes are rooted in dual AV node pathways, with genetic predisposition (especially in familial cases) and certain demographic factors (more common in women and younger adults).
• Treatment focuses on acute termination (vagal maneuvers, adenosine, calcium channel blockers), with catheter ablation (RF or cryo) as the definitive, highly effective cure. Long-term prognosis is excellent.

In summary:

• AVNRT is common, recognizable, and almost always curable.
• Most patients can expect a return to full, normal activity after appropriate therapy.
• Catheter ablation should be considered the treatment of choice for most symptomatic patients.

If you or a loved one experiences sudden episodes of rapid heartbeat, consult a healthcare provider. Early diagnosis and modern treatment can make a world of difference.