Narrow QRS Tachycardia


  • Required Reading: Introduction to Arrhythmia Diagnosis 
  • Narrow QRS is ≤ 120ms
  • Narrow QRS = Simultaneous activation of both ventricles
  • A narrow QRS tachycardia activates both ventricles simultaneously.
    • Atrial tachycardias generally have a narrow QRS because their ventricular activation occurs via the AV node and the ventricular conduction system (His-Purkinje system), which leads to simultaneous activation of both ventricles.
    • NOTE: Atrial tachycardias can have a wide QRS, often in the presence of a RBBB, LBBB, or pre-excitation.
  • NOTE: The term “SVT – Supraventricular Tachycardia” refers to narrow-QRS REGULAR tachycardia.  Even though atrial fibrillation is “supraventricular”, it is not classically called SVT. 

The Approach

  1. Describe the ECG & Frame the Problem
    • Step 1: Narrow vs. Wide (≥120ms?)
    • Step 2: Regular vs. Irregular (use calipers)
  2. Present a differential diagnosis (see Tables)
  3. Narrow the differential diagnosis (understanding the mechanisms of arrhythmia)
DDx of an IRREGULAR narrow QRS Tachycardia:
  • Atrial Fibrillation
  • Atrial Flutter with a variable AV block
  • Multifocal Atrial Tachycardia (very rare)

NOTE: List not exhaustive, other mechanisms exist

Differential Diagnosis of a REGULAR Narrow QRS Tachycardia
  1. Sinus Tachycardia (ST)
  2. Focal Atrial Tachycardia
  3. Atrial Flutter (AFL)
  4. AV-Nodal Re-entrant Tachycardia (AVNRT)
  5. Atrioventricular Re-entrant Tachycardia (AVRT)
  6. Less Common:
    • Junctional Tachycardia (JT) 
    • Ventricular Tachycardia – Often with high-septal origin, which accesses the HIS-Purkinje system.
Narrow QRS Tachycardia Approach

Narrow QRS Regular Tachycardia

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