Removal of overdrive suppression can permit these cells to display slow spontaneous action potentials that can drive ventricular rate. Which option best describes these potentials?

• A. Rapid depolarizations
• B. Slow spontaneous action potentials
• C. Prolonged refractoriness
• D. Hyperpolarization

Answer: (B)

Removing overdrive suppression lets latent ventricular pacemaker cells regain automaticity. These cells, such as Purkinje fibers under certain conditions, emit slow diastolic depolarizations (phase 4) that gradually reach threshold and trigger action potentials. Because their intrinsic rate is slow, they can drive the ventricular rhythm if the dominant faster pacemaker (like the SA node) is not pacing effectively. This is exactly what “slow spontaneous action potentials” describes. Rapid depolarizations, prolonged refractoriness, or hyperpolarization don’t capture this automatic, diastolic-depolarization process that underlies ectopic ventricular pacing.