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?
The correct answer is: D. Ventricular tachycardia originating from the left anterior fascicle
Figure 2 gives the explanation to the enigma. HRA p and d (proximal and distal High Right Atrium) and RV (Right Ventricle) channels show the electrograms originating in the right atrium and in the right ventricle, respectively. The number of ventricular electrograms (RV channel) is clearly superior to the number of atrial electrograms (red arrows on HRAd channel), indicating a dissociation in the activation of the atria and the ventricles, which makes ventricular tachycardia the most probable diagnosis.