Lesson 4: Narrow Complex Tachycardia 1

Summary of Learning Points

• Narrow Complex Tachycardias can be classified as regular vs irregular and as having short RP vs long RP interval.

  • RP interval represents time between ventricular and atrial depolarization.

• The regular NCTs are regular because their underlying etiology is typically a well-defined circuit.

• Often it is difficult to determine the etiology of a NCT with 12-lead ECG alone, especially if rate > 150. Other helpful pieces of information include:

  • Telemetry: See how the rhythm began – Was there a preceding PAC with long PR? Was there a PVC? This can point you in the right direction.

  • Formal EP study: Often necessary for identifying the exact etiology and can be therapeutic (ablation) as well.

• Short RP NCTs:

  • AVNRT

    • Circuit is WITHIN the AV node

    • Often begins with PAC

  • AVRT

    • Circuit includes an ACCESSORY PATHWAY and the AV node

    • Often begins with PAC or PVC

    • Orthodromic = circuit conduction progresses down AV node

    • Antidromic = circuit conduction progresses up AV node

      • Typically has WIDE QRS

  • Acute management is the same for both:

    • Hemodynamically stable: Vagal maneuvers, beta blockers, calcium channel blockers, adenosine 

    • Hemodynamically unstable: Synchronized cardioversion

• Long RP NCTs:

  • Sinus tachycardia

  • Atrial tachycardia

    • Ectopic focus or foci within the atrium resulting in p-waves with abnormal axis and morphology

    • Typically due to underlying medical disease (infection, pulmonary disease, etc.) and scarring/edema from prior ablations

Practice ECG

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