Diagnostic dilemma with a narrow QRS regular rhythm at normal rates in a patient with corrected transposition of great arteries

A 35 year old male, known case of corrected transposition of great arteries presented with exertional dyspnea and recurrent pre-syncope. 12 lead electrocardiogram revealed a regular rhythm at 75 beats per minute, P waves occurring on the upstroke of T waves and apparent 1:1 P-QRS relationship. The possibilities to be considered – complete AV block with junctional escape, junctional rhythm with 1:1 retrograde conduction, junctional rhythm with isorhythmic AV dissociation and prolonged PR interval have been discussed.