Arrhythmia Diagnosis During an Ajmaline Test

Figure 1 (A-C)
Figure 1: Arrhythmia Diagnosis During an Ajmaline Test
A 42-year-old male with a negative family history for sudden cardiac death was referred to our hospital after an episode of sudden syncope, not preceded by any prodrome. A complete clinical work-up excluded the presence of any cardiovascular disease. The decision to perform an ajmaline challenge was taken to unmask eventually a Brugada type I ECG pattern. The administration of the cited class I antiarrhythmic drug was stopped after the occurrence of a wide QRS arrhythmia, which spontaneously broke after 45 seconds. Figure 1A shows the transition from sinus rhythm to a right bundle branch block tachycardia with a heart rate of 140 bpm, with a wide QRS complex (220 msec) and a right axis deviation (as depicted in Figure 1B). Figure 1C displays spontaneous restoration of sinus rhythm.

What is the diagnosis of the tachycardia?

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