Atrioventricular Nodal Reentrant Tachycardia (AVNRT): A Simple Explanation
AVNRT is a common heart rhythm problem where electrical signals travel in a circular pattern within the AV node of the heart, causing a rapid heartbeat that typically ranges between 140-250 beats per minute.
What is AVNRT?
AVNRT is the most common form of paroxysmal supraventricular tachycardia (PSVT). It occurs due to the presence of two functionally distinct electrical pathways within and around the AV node:
- Fast pathway: Conducts electrical signals quickly but has a longer recovery time
- Slow pathway: Conducts electrical signals more slowly but has a shorter recovery time
In AVNRT, these pathways form a circuit where electrical signals continuously loop around, causing the heart to beat rapidly.
How AVNRT Works
In typical AVNRT (90% of cases):
- Electrical signal travels down the slow pathway (anterograde direction)
- Returns up the fast pathway (retrograde direction)
- Creates a "slow-fast" circuit 1
In atypical AVNRT (less common):
- Signal travels down the fast pathway and up the slow pathway ("fast-slow")
- Or between two slow pathways ("slow-slow") 1
Common Symptoms
- Sudden onset palpitations (often described as "heart racing")
- Neck pulsations (many patients report feeling pulsations in their neck)
- Dizziness or lightheadedness
- Anxiety
- Chest discomfort
- Shortness of breath
- Rarely, syncope (fainting) 1, 2
Key Characteristics
- Paroxysmal nature: Episodes start and stop suddenly
- Regular rhythm: Consistent heart rate during episodes
- Not usually associated with structural heart disease 1
- More common in females 1
- Can occur at any age, but typically first appears in adulthood (mean age of onset around 32 years in adults, 11 years in children) 1
ECG Features
During an AVNRT episode, the ECG typically shows:
- Narrow QRS complexes (unless there's pre-existing bundle branch block)
- Absent or hidden P waves - in typical AVNRT, P waves are often buried within the QRS complex or appear immediately after it (creating a "pseudo-r'" pattern in lead V1)
- Short RP interval in typical AVNRT (P wave close to preceding QRS) 1, 3
Treatment Options
Acute termination:
- Vagal maneuvers (bearing down, ice water to face)
- Adenosine (first-line medication)
- Calcium channel blockers (verapamil, diltiazem) 4
Long-term management:
Important Distinctions
AVNRT differs from other types of SVT, particularly atrioventricular reentrant tachycardia (AVRT), which involves an accessory pathway outside the AV node connecting the atrium and ventricle.
Understanding AVNRT is important because it's the most common form of regular narrow-complex tachycardia, and while rarely life-threatening, it can significantly impact quality of life.