Calcium channel blockers act to decrease the current of Ca into SA nodal pacemaker cells.  This reduces the SA node depolarization (I4) rate and causes a delayed onset of the AV node AP due to a slow exit from the SA node. 

Decreases in SA node:

  • I4 depolarization

Decreases in AV node:

  • I0 rate of rise
  • AP amp
  • AP velocity
  • Heart rate (=longer R-R)

EKG effects: Longer PR & RR.  QRS occurs later.

Clinical: Ca blockers are given to treat hypertension and circuitous reentries (tachyarrhymthias).