If an ectopic atrial focus fires faster than the sinoatrial node, the SA node temporarily stops firing. The property of cardiac pacemakers responsible for this phenomenon is called:

• A Accommodation
• B Decremental conduction
• C Post-repolarisation refractoriness
• D Overdrive suppression ✓

Explanation

Overdrive suppression occurs because frequent activation drives more sodium into pacemaker cells than the Na+-K+ ATPase can extrude, hyperpolarising them and suppressing their intrinsic phase 4 depolarisation. When the faster focus stops, the SA node resumes after a brief pause. Decremental conduction, option B, describes amplitude decay of impulses in the AV node and does not explain pacemaker hierarchy.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.