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Velilla Moliner J, Salazar González JJ, Asso Abadía A, Giménez Valverde A, Marquina Lacueva MI, Placer Peralta LV
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Regular tachycardia with a narrow QRS complex is a common presenting complaint in
emergency departments. The differential diagnosis includes atrioventricular reentrant
tachycardia (intranodal or accessory pathway-mediated) and atrial tachycardia (atrial
flutter). These types of tachycardia are commonly treated using vagal manoenvures and
adenosine. We describe a patient with a history of paroxysmal atrial fibrillation receiving
regular treatment with flecainide who presented with a regular narrow QRS-complex
tachycardia (205 beats/min). After administration of adenosine the heart rate slowed
briefly, followed by regular wide QRS-complex tachycardia at the same rate as before
and apparently ventricular in origin. The patient was in class 1C atrial flutter with 1:1
atrioventricular conduction. Severe conduction disturbance due to flecainide treatment
was intermittently exacerbated by the adenosine-induced atrioventricular block.
