Av Nodal Reentrant TachycardiaEdit
Av nodal reentrant tachycardia (AVNRT) is the most common form of supraventricular tachycardia (SVT). It originates from a reentry circuit that forms within or immediately around the Atrioventricular node due to the presence of dual pathways for conduction. In the typical form, slow conduction antegrade through a slow pathway and retrograde conduction through a fast pathway create a self-sustaining loop that produces rapid heart rates.
AVNRT can occur in otherwise healthy people, though it is more frequently encountered in adults and adolescents. Episodes are often recurrent and can be triggered by stimulants such as caffeine or alcohol, dehydration, stress, or sleep deprivation. Patients commonly report abrupt onset of palpitations, sometimes accompanied by dizziness or lightheadedness; syncope may occur in more pronounced cases. The tachycardia is usually regular and narrow-complex on surface electrocardiography recording, because the ventricular activation proceeds via the normal His-Purkinje system. P waves, when visible, may be buried in or immediately follow the QRS complex.
Pathophysiology
AVNRT relies on dual AV nodal physiology, with two closely spaced conduction pathways in or near the AV node—one slower and one faster. In the typical (slow-fast) variant, antegrade conduction travels down the slow pathway while retrograde conduction uses the fast pathway, establishing a reentry loop. This mechanism leads to sustained, organized atrioventricular activation and rapid ventricular rates. The atypical (fast-slow) variant exists but is less common and can produce a somewhat different ECG pattern and clinical behavior.
Key concepts include: - Dual-pathway physiology at the AV node, which permits reentrant circuits under appropriate conditions. - A reentrant loop that is often initiated by a premature atrial or ventricular beat, a change in autonomic tone, or a sudden shift in conduction properties. - The characteristic narrow QRS complex with a tachycardia rate in the range of roughly 140–220 beats per minute, depending on patient factors.
Clinical features
Most AVNRT episodes begin abruptly and terminate spontaneously, though patients may seek care when symptoms are bothersome or prolonged. Common symptoms include: - Palpitations or a sensation of a racing heart - Lightheadedness or dizziness - Shortness of breath or chest discomfort in some cases - Rarely, syncope
The episode duration is variable, from seconds to hours. In patients with frequent recurrences, AVNRT can cause significant impairment to daily activity and quality of life, though long-term prognosis for otherwise healthy individuals is excellent with appropriate management.
Diagnosis
Diagnosis is based on clinical presentation and ECG characteristics. During an episode, the ECG typically shows a regular, narrow-complex tachycardia. P waves may be: - Hidden within the QRS complex - Appearing immediately after the QRS complex if retrograde atrial activation is present
Between episodes, the patient’s baseline rhythm is usually normal. Diagnostic strategies include: - Intermittent monitoring or patient-activated recording to capture the tachycardia - Electrophysiology studies to map the conduction pathways and confirm dual AV nodal physiology
In distinguishing AVNRT from other SVTs, clinicians consider the nature of the QRS complexes, the relationship between atrial and ventricular activity, and the response to vagal maneuvers or pharmacologic testing (for example, adenosine can transiently interrupt AV nodal conduction and terminate AVNRT).
Management
Management aims to terminate an acute episode and reduce future recurrence. The approach depends on symptom burden, episode frequency, and patient risk factors.
- Acute termination: Vagal maneuvers (such as the Valsalva maneuver) can often terminate AVNRT by increasing vagal tone and altering AV nodal conduction. If vagal maneuvers fail, pharmacologic therapy with Adenosine is commonly used to transiently block AV nodal conduction and restore normal rhythm.
- Medications for prevention: For patients with recurrent episodes who do not undergo ablation, rate-control medications such as beta-blockers or non-dihydropyridine calcium channel blockers can reduce the frequency of episodes.
- Catheter ablation: The most definitive and durable treatment for AVNRT is catheter ablation of the slow pathway within or near the AV node. This procedure has high success rates (generally >90–95% in experienced centers) and a favorable long-term prognosis, with a relatively small risk of complications such as AV block. Information about the ablation targets and techniques is detailed in Radiofrequency ablation and Electrophysiology study.
Special considerations: - In pregnancy or in patients with certain comorbidities, treatment choices may be tailored to minimize fetal or systemic effects. - In patients with AVNRT, ablation is often preferred for those with frequent symptoms or reduced quality of life, given its high success and potential to eliminate episodes.
Prognosis
For most people with AVNRT, the prognosis is excellent. Episodes can be managed effectively with lifestyle adjustments, pharmacologic therapy, or definitive catheter ablation. Recurrence after ablation is uncommon but not impossible, and patients should have access to prompt evaluation if episodes recur.