What does the 'S' code indicate in the NBG classification?

The 'S' code in the NBG classification stands for single chamber pacing, which can either be A (atrial) or V (ventricular). This classification system helps to categorize pacing modalities based on the number of chambers being paced and the components involved. In the case of the 'S' code, it denotes that the pacemaker is designed to pace only one chamber, either the atrium or the ventricle, but not both simultaneously. This is important in understanding how pacemakers are utilized in clinical settings and their operational mechanics, as it affects patient management and the approach to pacing therapies.

In contrast, other options focus on more specific definitions, such as atrial pacing only, left ventricular pacing, or single electrode usage, each of which does not encompass the broader category indicated by the 'S' code, which includes either atrial or ventricular pacing as a single chamber approach.