Atrial tachycardia is usually a narrow complex tachyarrhythmia accounting for 10% of supraventricular tachycardias.
The mechanism of atrial tachycardia is usually re-entrant but may be due to enhanced automaticity of the atrial myocardium.
The atrial rate is between 150 and 250 bpm. At higher rates there may be variable AV block.
Diagnostic criteria (1)
Atrial rate is usually between 150-250/minute but may also be as low as 110/minute.
Every P wave is NOT followed by a QRS complex.
Block is generally 2:1 or 3:1. Wenkebach type block may also be observed. Complete AV block is seen very infrequently.
Since the impulse originates from an ectopic focus, P wave shape may be different than that of the sinus P wave. P wave shape depends on the site of atrial focus.
Since the impulse originates in the atrium, QRS complexes are expected to be narrow (<120ms).
Isoelectric baseline is observed between P waves.
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Reference:
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