AVNRT (atrioventricular nodal re-entrant tachycardia) is the most common form of paroxysmal supraventricular tachycardia (SVT) in adults. It occurs when electrical impulses travel in a rapid, self-sustaining circuit within or around the atrioventricular (AV) node, causing the heart to beat suddenly at a fast rate, typically between 140 and 220 beats per minute. Most people with AVNRT have a structurally normal heart.
AVNRT arises because of dual pathways within the AV node: a fast pathway that conducts quickly but has a longer refractory period, and a slow pathway that conducts more slowly but recovers more quickly. Under normal circumstances, impulses travel down the fast pathway. However, if a premature electrical impulse arrives while the fast pathway is still refractory (recovering), it travels down the slow pathway instead, and by the time it reaches the lower AV node, the fast pathway has recovered, allowing the impulse to loop back upwards. This circular movement sustains the tachycardia. It is distinct from AVRT (atrioventricular re-entrant tachycardia), which involves a separate accessory pathway outside the AV node such as in Wolff-Parkinson-White syndrome.
Episodes of AVNRT typically start and stop suddenly (paroxysmal) and cause symptoms including a rapid pounding heartbeat, dizziness, breathlessness and, in some cases, chest discomfort. Fainting is uncommon but can occur if the rate is very fast. An episode can often be terminated by Valsalva manoeuvres (bearing down) or carotid sinus massage, which increase vagal tone and slow AV nodal conduction. If these fail, intravenous adenosine, which briefly blocks the AV node, is highly effective at terminating AVNRT.
For long-term management, catheter ablation targeting the slow pathway is the definitive treatment, with a success rate above 95 percent and a very low risk of complications. It is recommended for patients with frequent or symptomatic episodes. Preventive medication (beta-blockers, calcium channel blockers, or flecainide) is an alternative for those who prefer not to undergo ablation. AVNRT itself does not cause sudden cardiac arrest in people with structurally normal hearts, but the symptoms can mimic those of more serious arrhythmias and appropriate investigation is always warranted.
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