Electrophysiologic study (EPS) in advanced conduction disease showing intra-Hisian block

The tracing, obtained during an electophysiologic study, records three surface electrocardiogram (ECG) leads (1, 2, and V1) and the bundle of His electrogram (HBE). The first two sinus beats (SB) are conducted normally from the atrium to the ventricle, but the HBE manifests a split bundle of His electrograms (H and H'). The proximal component (H) is present following a nonconducted P wave (P*), but the distal bundle of His (H') is not activated. The level of atrioventricular block is sharply defined as being intra-Hisian, indicating advanced conduction system disease.