We evaluated the intracardiac conduction intervals using His bundle recordings in 40 patients with ventricular inversion and I-transposition of the great arteries. Twenty-nine subjects had 1:1 atrioventricular (AV) conduction. In 15 of those with normal PR intervals and QRS durations, the conduction intervals were not different from those of subjects with normal hearts. In the 14 patients with first-degree AV block, the block was located between the sinus node and AV node in four, between the low right atrium and bundle of His in seven, and below the common bundle of His in four.
In 11 subjects with complete AV block, the site of block was above the site of the His potential in four, below in two and within the His bundle in one. In four patients we could not record a His potential and thus could not localize the site of block. Complete block below the His recording site was associated with syncope in one patient and sudden death in another. His bundle recording is a safe technique for studying the conduction system in children with ventricular inversion and I-transposition of the great arterie.