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Test Findings

Narrow Complex Tachycardia

April 24th, 2019


Narrow complex tachycardia refers to an ECG rhythm with ventricular rate >100bpm and a QRS complex duration of <120ms. This implies that the rhythm is supraventricular in origin.
  • Causes of Narrow Complex Tachycardia

  • Regular

  • Sinus tachycardia
  • Focal atrial tachycardia
  • Atrial flutter
  • AV nodal reentrant tachycardia
  • AV reentrant tachycardia
  • Irregular

  • Multifocal atrial tachycardia
  • Atrial fibrillation
  • Atrial flutter with variable block
  • Pearls

  • Focal tachycardia presents with abnormal P wave morphology.
  • Multifocal atrial tachycardia manifests with at least three different P wave morphologies.
  • Atrial flutter typically produces a sawtooth wave between QRS complexes, classically at an atrial rate of 300bpm and a ventricular rate of 150bpm.
  • Atrial fibrillation is an irregular narrow complex tachycardia without P waves, and a baseline fibrillatory wave may be seen.
  • AV nodal reentrant tachycardia is often difficult to diagnose as the p wave is hidden within the QRS complex.
  • Orthodromic AV reentrant tachycardia results in P waves occuring after the QRS interval.
Adenosine is a useful diagnostic tool for narrow complex tachycardia as it suppresses AV nodal conduction and can reveal the underlying rhythm. Adenosine must be given in a monitored setting by experienced clinicians.
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