Clinical introduction An 84-year-old woman presented with palpitations. Her past medical history included tissue aortic valve replacement and coronary artery bypass, left ventricular impairment and bronchiectasis. An ECG is shown in Figure 1A. She was diagnosed with supraventricular tachycardia.

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Figure 1

(A) ECG prior to cardioversion. (B) ECG postcardioversion.

Adenosine 12 mg intravenously failed to restore sinus rhythm, even though she experienced the usual side effects of flushing and bronchoconstriction. She was then electrically cardioverted: ECG postcardioversion is shown in Figure 1B.

Question Which is the most likely diagnosis?

A Atrial flutter

B Atrioventricular nodal re-entrant tachycardia

C Bundle branch re-entrant ventricular tachycardia (VT)

D Fasicular VT

E Right ventricular outflow tract (RVOT) VT