Electrophysiologic studies in sick sinus syndrome following surgery for d-transposition of the great arteries.

His bundle electrograms and atrial pacing are reported in a 10 1/2-year-old boy and a 12-year-old girl, both of whom underwent Mustard repair for complete d-transposition of the great arteries. Each patient had progressive evidence of sick sinus syndrome culminating in syncope. Improvement occurred after insertion of a demand pacemaker.