The His bundle potential on an intracardiac tracing is identified by which combination of events?

• A. Earliest His deflection and earliest ventricular activation
• B. Latest His deflection and latest atrial activation
• C. Latest His deflection and latest ventricular activation
• D. Earliest ventricular activation and earliest atrial activation

Answer: (A)

The His bundle potential is the discrete deflection that marks activation of the His-Purkinje system, and it lies between the atrial activation and the ventricular activation on an intracardiac trace. To identify it, you look for the earliest deflection that represents activation of the His bundle, and you should then see the ventricles activate soon after. This sequence—atrial activity, then the earliest His deflection, followed by the earliest ventricular activation—best identifies the His bundle potential. The other timings either skip the His signal or place the activation later than expected, which doesn’t correctly pinpoint the His bundle.