AV nodal re-entrant tachycardia (AVNRT)

Definition

AV nodal reentrant tachycardia (AVNRT) is a paroxysmal supraventricular tachycardia in which the reentrant circuit lies within the AV node and its inputs. Paroxysmal supraventricular tachycardias are sudden-onset, sudden-offset, rapid (120–250/min), regular tachycardias, usually with a narrow QRS complex, that are neither sinus tachycardia nor atrial fibrillation or flutter.

Classification

• Typical AVNRT (slow-fast): antegrade conduction via the slow pathway, retrograde via the fast pathway; about 90 % of cases
• Atypical AVNRT (fast-slow): reentry in the opposite direction, more often triggered by a ventricular premature beat; P wave in the second half of the RR interval (long RP tachycardia)

Occurrence & epidemiology

Paroxysmal supraventricular tachycardias have an incidence of about 35 per 100,000 and a prevalence of 2–3 per 1,000 people (US data). In adults AVNRT is the most common form at about 50–60 %; in children it is much less common. It usually occurs in people with otherwise healthy hearts, and symptoms typically begin in young adulthood or middle age.

Aetiopathogenesis

The AV node has several inputs: a fast pathway (superior/anterior extension) with a longer refractory period and a slow pathway (inferior/posterior extension) with a shorter refractory period. An early atrial premature beat is blocked in the still refractory fast pathway and conducted via the slow pathway; on the ECG the PR interval of this beat suddenly lengthens. If conduction is slow enough, the fast pathway can be activated retrogradely, and a reentrant circuit within the AV node develops.

Clinical features

Typical are paroxysmal, sudden-onset, sudden-offset, rapid, regular palpitations, often with dyspnea, chest discomfort or light-headedness. Attacks last seconds to hours, rarely longer than 12 hours. The heart rate is 120–240/min, most commonly 180–210/min; between attacks the examination is usually unremarkable.

Diagnosis

• ECG: rapid, regular narrow-complex tachycardia; wide QRS complexes only with coexisting bundle branch block
• Typical AVNRT: retrograde P waves usually in the terminal portion of the QRS complex, often seen as a pseudo-r′ in V1; about one third lie just after the QRS complex, very few immediately before it; the P wave is negative in II, III and aVF
• Atypical AVNRT: P wave in the second half of the RR interval (RP longer than PR)
• Previous ECGs are reviewed for pre-excitation (WPW) or pre-existing bundle branch block; the resting ECG is usually normal in AVNRT.
• Ambulatory ECG or event recorder for infrequent attacks; electrophysiological study demonstrates dual AV nodal conduction.

Keep learning in the app

Further reading (open access)

1. MSD Manual Professional: Reentrant (Paroxysmal) Supraventricular Tachycardias (PSVT)
2. StatPearls: Atrioventricular Nodal Reentry Tachycardia
3. MSD Manual Professional: Overview of Arrhythmias

Cross-references