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Narrow Complex Tachycardia



  • 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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