The Hidden Reveals the Hidden

ECG CHALLENGEA 59-year-old man with no history of cardiovascular disease was admitted to the emergency department with sudden onset of rapid palpitations and dizziness 2 hours before admission.ECG (Figure 1) revealed a rapid irregular wide QRS complex tachycardia with right bundle-branch block morphology and alternating QRS width.Because the patient was hemodynamically unstable, immediate direct current cardioversion was performed, restoring normal sinus rhythm (Figure 2).After that, physical examination was unremarkable and transthoracic echocardiogram ruled out overt structural heart disease.Ionic disturbances were ruled out as well.The patient denied history of syncope or palpitations and was not on any medication.He was referred for electrophysiologic study.The tachycardia shown in Figure 3 was reproducibly induced.What is the most likely diagnosis for the patient?What mechanism would explain the exclusive changes in ventricular repolarization during tachycardia?What is the appropriate management of the patient?Please turn the page to read the diagnosis.