A regular wide QRS tachycardia with right bundle branch block morphology and left QRS axis deviation.

A 76-year-old male called an emergency medical service after his smartwatch detected rapid heart rate. ECG obtained on ambulance recorded a regular, wide QRS tachycardia (150 bpm) having a morphology of right bundle branch block and left QRS axis. Two main diagnoses were discussed: a) any type of supraventricular tachycardia associated with ventricular aberration; b) ventricular tachycardia originating close to the posterior fascicle of the left ventricle. The final diagnosis was made after performing carotid sinus massage.