Atrial pacing, and His bundle electrograms were recorded in a 62-year-old man with sinus bradycardia and a complex junctional arrhythmia. The arrhythmia was shown to be due to His bundle extrasystoles. The recognition of main-stem extrasystoles, based on analysis of surface electrocardiogram may not be possible, and His bundle electrocardiographic studies are necessary for the precise diagnosis of His bundle extrasystoles.
Abedin Z, Sapru RP. His Bundle Ectopic BeatsHis Bundle Electrocardiographic Study. JAMA. 1974;227(5):549–551. doi:10.1001/jama.1974.03230180047012