• Re-entry and Supraventricular Tachycardia
• WPW Syndrome
• Atrioventricular Reentry Tachycardia (AVRT)
• Orthodromic, Antidromic, Retrograde, Anterograde?
• Orthodromic AVRT
• Antidromic AVRT
• Mechanism of Orthodromic AVRT
• Differential Diagnosis of AVRT
• ECG and Orthodromic AVRT
• Permanent Junctional Reentrant Tachycardia
• ECG and Antidromic AVRT

Re-entry and Supraventricular Tachycardia

• In supraventricular tachycardia (SVT), impulses originate in the atria or in the AV junction
• Re-entry is one of the mechanisms of tachycardia
• where the impulse circles in a loop, most commonly around an anatomical obstacle (scar tissue)

• Sinoatrial nodal re-entry tachycardia
• Re-entry is in the SA node
• or re-entry passes through the SA node
• Intra-atrial re-entry tachycardia
• Re-entry is somewhere in the atria
• most commonly around a scar (after a myocardial infarction)
• or re-entry occurs without an obstacle
• AV nodal re-entry tachycardia
• Re-entry is in the AV node
• AV re-entry tachycardia
• It is macro re-entry, the impulse circles between:
• the atria and ventricles via the AV node and an accessory pathway
• We know of 3 accessory pathways:
• Kent bundle (WPW syndrome)
• James bundle (LGL syndrome)
• Mahaim bundle (Mahaim syndrome)
• Atrial flutter
• It is macro re-entry, the impulse circles
• throughout most commonly the right atrium

Atrioventricular Reentry Tachycardia (AVRT)

• The impulse circulates through a macro reentry between the atria and ventricles
• There must be an accessory pathway (Kent bundle) present in the heart
• The circulating impulse is triggered by a ventricular or atrial extrasystole
• The impulse circulates through the reentry at a rate of 170-250/min
• It is paroxysmal (Suddenly starts and suddenly ends)
  
  
• Based on the direction of circulation of the impulse, there are 2 types of AVRT:
• Orthodromic AVRT (constitutes 95% of AVRT)
• Antidromic AVRT (constitutes 5% of AVRT)

Orthodromic AVRT

Orthodromic AVRT

• Comprises 95% of all AVRTs
• The impulse spreads through the macro reentry circuit orthodromically:
• Through the AV node it goes anterogradely
• Through the accessory pathway it goes retrogradely
  
  
• On the ECG, narrow QRS complexes (<0.12s) are observed
• Because the ventricles are activated through the AV node, and via the conduction system
• as in sinus rhythm

Mechanism of Orthodromic AVRT

Orthodromic AVRT

• 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) and travels to the ventricles through the AV node
• Ventricular extrasystole (VES)
• Occurs earlier than the expected P wave (sinus rhythm)
• The impulse from VES spreads retrogradely through the accessory pathway
• Not through the AV node, because the AV node is in the refractory period
• Retrograde P wave (P´)
• The atria are activated by the accessory pathway, so the P wave is negative
• During the course of orthodromic AVRT
• The ventricles are activated anterogradely through the AV junction
• The atria are activated retrogradely through the accessory pathway

ECG and Orthodromic AVRT

• Begins with a ventricular or atrial extrasystole
• Frequency: 150-250/min.
• Narrow QRS complexes (<0.12s)
• They can be widened (>0.12s) if aberrant conduction is present
• Inverted P waves behind QRS complexes
• P waves are often hidden in the T wave
• RP interval < PR interval
• RP interval > 90ms
• QRS alternans (the amplitude of QRS complexes changes)

Permanent Junctional Reentrant Tachycardia

• Permanent Junctional Reentrant Tachycardia (PJRT)
• It is very rare
• It is orthodromic AVRT with decremental conduction through the accessory pathway

Orthodromic AVRT

• Non-decremental (Not slowed)
• Conduction through the accessory pathway

PJRT

• Decremental (Slowed)
• Conduction through the accessory pathway

PJRT

• RP > PR interval

Wide-Complex Tachycardia

• Frequency: 180/min.
• QRS complexes are wide (>120ms)
• P waves are not distinguishable (likely just after the T wave)
• Patient has Antidromic AVRT
• Because a previous ECG showed WPW syndrome with sinus rhythm

WPW Syndrome

• On the ECG, there is WPW syndrome
• Shortened PQ interval
• Delta wave

Orthodromic AVRT

• Frequency: 180/min.
• Heart rate is regular
• P waves are not visible
• QRS complexes are narrow (<120ms), indicating supraventricular tachycardia, which could be:
• AVNRT
• Orthodromic AVRT
• The patient received adenosine, which interrupted the reentry circuit

WPW Syndrome (Type A)

• After adenosine, the rhythm reverted to sinus rhythm
• The patient has WPW Syndrome (Type A)
• Shortened PQ interval
• Delta wave
• The accessory pathway is in the left atrium
• The patient has WPW Syndrome
• On a previous ECG, Orthodromic AVRT was observed

Antidromic AVRT

• 37-year-old patient
• Frequency: 180/min.
• Heart rate is regular
• P waves cannot be differentiated
• QRS complexes are wide (>120ms), indicating a wide-complex tachycardia, which could be:
• Ventricular tachycardia
• Supraventricular tachycardia with aberrant conduction
• Antidromic AVRT
• The patient was circulatory unstable and underwent electrical cardioversion
• After electrical cardioversion, the rhythm reverted to sinus rhythm; see the following ECG

WPW Syndrome (Type B)

• After electrical cardioversion, the rhythm reverted to sinus rhythm
• This is WPW Syndrome (Type B)
• Shortened PQ interval
• QRS is borderline wide at 120ms
• Delta waves
• The accessory pathway is in the right atrium
• The patient has WPW Syndrome
• On the previous ECG, Antidromic AVRT was observed

Antidromic AVRT and Atrial Fibrillation

• Heart rate is irregular
• Average frequency is 200/min. (sometimes up to 300/min.)
• QRS complexes are wide (>0.12s)
• Could be atrial fibrillation with left bundle branch block
• However, the AV node cannot conduct impulses at a frequency of 300/min.
• The ECG shows Antidromic AVRT with atrial fibrillation
• Impulses are conducted to the ventricles
• Through the accessory pathway and intermittently through the AV junction
• A narrow QRS may occur, with captured and merged ventricular contraction