Rapid regular palpitations for two hours

The case

52-year-old man. Rapid regular palpitations for two hours

No significant past medical history. Takes no regular medication. Presented to the emergency department with a two-hour history of sudden-onset palpitations. He is haemodynamically stable. The initial twelve-lead ECG showed a regular narrow-complex tachycardia at 150 per minute. The registrar administered intravenous adenosine 6 mg as a rapid bolus. A twelve-lead ECG was recorded during the injection.

Stage 1 of 1

A 52-year-old man presents with a two-hour history of regular palpitations at 150 per minute. He is haemodynamically stable. The registrar suspects an SVT and gives intravenous adenosine 6 mg. A twelve-lead ECG is recorded during the injection.

During the pause produced by adenosine, a sawtooth pattern becomes visible in the baseline. What underlying rhythm does this reveal?

• AAtrial flutter with 2:1 conduction Correct answer Your answer
• BSinus tachycardia at 150 per minute Your answer
• CAtrioventricular nodal re-entrant tachycardia Your answer
• DAtrial fibrillation with a rapid ventricular response Your answer

Why did the tachycardia resume after adenosine rather than terminating?

• AThe re-entrant circuit does not use the AV node Correct answer Your answer
• BThe dose was too low to reach therapeutic levels Your answer
• CThe injection was given too slowly for the drug to act Your answer
• DThe patient has accessory pathway conduction Your answer

Adenosine has unmasked atrial flutter. Which drug class is first-line for rate control in this patient?

• AClass IC antiarrhythmic such as flecainide Your answer
• BAtropine Your answer
• CAmiodarone Your answer
• DBeta-blocker Correct answer Your answer

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