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ACLS Pearls: Simplified Approach for Analysis of Narrow Tachycardia

The tachycardia algorithm in ACLS asks the basic questions:

Signs and symptoms due to tachycardia:

Narrow complex tachycardia: Usually more than 150 bpm.

Narrow complex QRS:

1. Look at the 12-lead ECG and ask:

Irregular + no P = Atrial fibrillation (may be junctional tachycardia)

Irregular + P: Multifocal atrial tachycardia (3 different P morphologies)

Regular: most everything else

2. Where is the P wave located with respect to the R?

*Compare QRS complex with resting; retrograde P manifesting as pseudo s in II, III,

aVR, or r’ in V1 may be a subtle finding.

P closely follows R: typical AVNRT (“slow-fast”), junctional tachycardia

R follows P closely: sinus tachycardia, atypical (“fast-slow”)

No P: Usually AVNRT (P hidden in QRS complex)

P halfway: any of the above. Consider atrial flutter.

AV dissociation with intermittent retrograde P. Junctional tachycardia.

3. Shape of the P wave?

Sawtooth shape: atrial flutter

P same as resting: Sinus Tachycardia; rarely, atypical flutter

P wave morphology different from sinus: ectopic atrial rhythm or retrograde P seen

in junctional tachycardia.

4. Delta wave or shortened PR interval:

Suggests WPW or pre-excitation.

5. Rate?

150: consider atrial flutter with 2:1 block.

Above 250? Consider bypass tract.

6. Response to adenosine? *Avoid in COPD/asthma/WPW with atrial

fibrillation (usually wide complex QRS) because adenosine block of the AV

nodal pathway can speed up the rate.

-Underlying atrial rhythm as ventricular rate slows?

-Any retrograde P at the end of the tachycardia?

-AVRT and AVNRT terminate frequently with retrograde P. MAT splits 40%

of the time. Ectopic atrial tachycardia can split.

-Sinus tachycardia resulting from sinus nodal reentry can be terminated by


7. Junctional tachycardia is rare. AVNRT is more common than junctional tachycardia.


Usual junctional tachycardia rate 70-120. Usually VA 1:1 conduction.

-Diff DX: cardiac ischemia, dig toxicity, post cardiac surgery, metabolic, COPD

Automatic junctional tachycardia (rare, rare, rare): rate 110-250, with frequent AV

dissociation. Benign in adults, but dangerous in peds.


AVNRT: atrio-ventricular nodal re-entry tachycardia

AVRT: Atrial ventricular re-entrant tachycardia (bypass tract)

WPW: Wolff Parkinson White

MAT: Multi-focal atrial tachycardia