Narrow Complex Tachycardia
February 15th, 2021
Overview
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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