Termination mechanism:

• After establishing the reentry circuit, sudden blockade of retrograde conduction in the fast pathway, hence no excitation of the atria (absent P wave at the end of the QRS complex); termination of the reentry circuit
  
• Renewed sinus rhythm

ECG characteristics:

• Regular tachycardia with narrow ventricular complex; retrograde P wave at the end of the QRS (“rSr configuration in V1”)

Differential diagnosis:

• Orthodromic WPW reentry tachycardia
  
• AV nodal reentry tachycardia (fast–slow type)
  
• Atrial flutter (2:1; 1:1 conduction)
  
• Atrial ectopic tachycardia
  
• Sinus tachycardia/reentry

Differential diagnosis:

• Orthodromic WPW reentry tachycardia
  
• AV nodal reentry tachycardia (fast–slow type)
  
• Atrial flutter (2:1; 1:1 conduction)
  
• Atrial ectopic tachycardia
  
• Sinus tachycardia/reentry

Differential diagnosis:

• Ventricular tachycardia
  
• Antidromic Mahaim tachycardia
  
• Supraventricular tachycardia with left bundle branch block
  
• Antidromic WPW tachycardia

Mechanism:

• Rare form of AV nodal reentry tachycardia in which the antegrade conduction (from atrium to ventricle) occurs via the “fast pathway” and the retrograde excitation of the atria via the “slow pathway”

ECG characteristics:

• Regular tachycardia with narrow ventricular complex; retrograde (negative) P wave in front of QRS (interval “PR” < “RP”)

Etiology:

• Existence of two different approaches to the AV node with different electrophysiological properties (“slow” and “fast” pathway region)

Treatment:

• Ablation of the slow pathway (risk of complete block)
  
• Antiarrhythmics (class Ic, III, IV)
  
• In acute cases: 12–18 mg adenosine i.v.

Induction mechanism:

• With SVES antegrade blockade of the Kent fiber, impulse conduction via the AV node, excitation of the ventricles, retrograde impulse conduction via Kent, and commencement of reentry

ECG characteristics:

• Tachycardia with narrow ventricular complex
  
• Retrograde P wave in front of QRS (interval “PR” > “RP”)