A 21-year-old woman presented to the emergency department with sustained palpitations for approximately 1 h. She had had these palpitations previously, but they always stopped spontaneously. On presentation, she had no chest pain and no dyspnoea. She had not consumed any alcohol, coffee or other substances. Her ECG showed a narrow QRS complex tachycardia with a frequency around 170 bpm (Fig. 1a). Following adenosine administration, the tachycardia terminated with the ECG showing a sinus rhythm of 70 bpm (Fig. 1b). What is your differential diagnosis and can you explain the mechanism?

Fig. 1
figure 1

a Narrow complex tachycardia of approximately 170 bpm upon presentation; b ECG after administration of adenosine showing sinus rhythm of 70 bpm

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Answer

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