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AV Nodal Re-entry Tachycardia (AVNRT)

AV nodal reentry tachycardia, Paroxysmal supraventricular tachycardia, Paroxysmal atrial tachycardia

AV Nodal Re-entry Tachycardia (AVNRT)

• In the AV node, there are 2 pathways where the impulse starts to circulate (micro re-entry)
• with a frequency of: 120-250/min.
• Heart rhythm is thus regulated by the AV node (overdrive suppression)
• It is not Junctional Tachycardia
• which has increased automaticity in the AV node (not re-entry)
• It is the most common cause of palpitations (heart pounding)
• Especially in young healthy women
• It is paroxysmal (sudden onset and termination)
• It constitutes 60% of all paroxysmal SVTs
• Most common triggering factors:
• Alcohol, stress, fatigue, coffee, energy drinks
  
  
• It is often incorrectly labeled as
• Paroxysmal Supraventricular (SVT) Tachycardia
• Paroxysmal Atrial Tachycardia

How Does AVNRT Occur?

• AVNRT occurs after a atrial extrasystole (very rarely after a ventricular extrasystole)
• The impulse from the extrasystole must reach the AV node at a time when the AV node is not in the refractory period

atria (P)
Sinus Rhythm: Anterograde impulse of the slow pathway is blocked by the retrograde impulse from the fast pathway. The impulse activates the ventricles only through the fast pathway.

AES
Impulse from Atrial Extrasystole (PES) travels anterograde through the slow pathway, as the fast pathway is still in the refractory period (from the previous sinus beat). The fast pathway has a longer refractory period.

P´
AVNRT: The impulse circulates in re-entry within the AV node. Anterograde through the slow pathway (creating a QRS complex), retrograde through the fast pathway (creating a retrograde P wave).

AV Nodal Re-entry Tachycardia

• Laddergram illustrates the spread of the impulse through the conduction system
• A - Atria, AV - AV junction, V - Ventricles
• P wave (P)
• Originates from the SA node (Sinus Rhythm)
• Atrial Extrasystole (P*)
• Occurs earlier than the expected P wave (Sinus Rhythm)
• PP* interval is shorter than the previous PP interval
• P*Q interval is prolonged because the ventricles (R) are activated by the atrial extrasystole through the slow pathway
• AVNRT
• Anterograde activation of the ventricles (R) through the slow pathway
• and then retrograde activation of the atria (P´) through the fast pathway
• Retrograde P waves are negative because the atrial vector is directed from the AV node towards the SA node

ECG and AVNRT

• Heart Rate: 120-250/min.
• 90% of all AVNRT cases are Typical (Slow-Fast) AVNRT, which shows:
• Pseudo S wave (II, III, aVF)
• Pseudo R wave (V1)
• Atypical and Rare AVNRT do not show pseudo waves
  
  
• AVNRT is paroxysmal
• It starts suddenly (after an extrasystole) and ends suddenly
• Narrow QRS complexes (< 0.12s)
• QRS complexes may be widened (> 0.12s) with aberrant conduction
• Heart Rate is regular
• QRS alternans (changing amplitude of QRS complexes) may be present

Typical (Slow-Fast) AVNRT

• Most common AVNRT, accounts for 90% of all AVNRT cases
• The impulse circulates:
• Anterogradely through the Slow pathway to the ventricles
• Retrogradely through the Fast pathway to the atria
• Retrograde P' wave
• Appears just after the QRS
• Forms pseudo waves (r,s)
• Atria are activated through the Fast pathway (just after the ventricles)
• Sometimes it is hidden in the QRS and not visible
  • When the ventricles and atria are activated "simultaneously"
    
    
    
• ECG and Typical (Slow-Fast) AVNRT
• Pseudo S wave (II, III, aVF)
• Pseudo R wave (V1, V2)

Typical (Slow-Fast) AVNRT

• The image shows an ECG from a single patient
• Upper V1 lead
• Sinus rhythm, Frequency 90/min.
• There is no pseudo R wave (circle) at the end of the QRS
• Lower V1 lead
• The patient experienced sudden palpitations (heartbeats)
• It is supraventricular tachycardia, with a frequency of 240/min.
• Between the QRS complexes are T waves, not P waves
• A pseudo R wave (circle) appeared at the end of the QRS
• In the inferior leads (II, III, aVF) there is certainly a pseudo S wave
• It is Typical Fast-Slow AVNRT

Atypical (Fast-Slow) AVNRT

• Accounts for 8% of all AVNRT cases
• The impulse circulates:
• Anterogradely through the Fast (rapid) pathway to the ventricles
• Retrogradely through the Slow (slow) pathway to the atria
• Retrograde P' wave:
• Occurs after the QRS complex (it is further behind the QRS compared to typical AVNRT)
  
  
• ECG and Atypical (Fast-Slow) AVNRT
• Retrograde P' wave after QRS (II, III, aVF)
• P wave after QRS (V1, V2, aVR)
• Represents a typical retrograde P wave (not adjacent to QRS as seen in typical AVNRT)

Rare (Slow-Slow) AVNRT

• Accounts for 2% of all AVNRT cases
• Impulse circulates:
• Anterogradely through the Slow (slow) pathway to the ventricles
• Retrogradely through the Slow (slow) pathway to the atria
  
  
• ECG and Rare (Slow-Slow) AVNRT
• Retrograde P wave is located almost in the middle between RR intervals
• Definitive diagnosis is made through electrophysiological examination

Typical AVNRT (Slow-Fast)

• RP < PR
• RP < 90ms

Atypical AVNRT (Fast-Slow)

• RP > PR

Rare AVNRT (Slow-Slow)

• RP < PR
• RP > 90ms

Sinus Rhythm

• This ECG is from the previous patient
• On this ECG, there is a sinus rhythm with a frequency of 100/min.
• No pseudo waves (r, s) are present
• The re-entry circuit in the AV node was interrupted (after carotid sinus massage)

Typical (Slow-Fast) AVNRT

• Continuous ECG recording from lead II
• Upper ECG
• Typical (Slow-Fast) AVNRT
• RP interval < 90ms
• Pseudo s wave (at the end of QRS)
• Middle ECG
• The patient received intravenous 6mg Adenosine
• Adenosine slows conduction through the AV node (interrupts re-entry)
• Ventricular extrasystoles occurred, followed by sinus rhythm
• Lower ECG
• Sinus rhythm
• Pseudo s wave at the end of QRS has disappeared
• There is a P wave before each QRS

Typical (Slow-Fast) AVNRT

• Frequency: 135/min.
• Narrow QRS complexes (< 120ms)
• Retrograde P waves after the QRS complex
• (not "stuck" to the end of the QRS complex)
• Negative in the inferior leads (II, III, aVF)
• Positive in the leads (aVR, V1-V3)
• This is a Typical (Slow-Fast) AVNRT
• RP interval < 90ms (even if P waves are further after the QRS complex)

Typical (Slow-Fast) AVNRT and Sinus Rhythm

• Typical (Slow-Fast) AVNRT
• Frequency: 136/min.
• Pseudo r wave (V1)
• RP interval < 90ms
• It is not functional incomplete right bundle branch block
• Because there is no deep S wave in V6
• Sinus Rhythm
• Frequency: 107/min.
• Pseudo r wave (disappeared)