Abnormal calcium flux

During each normal heartbeat, the wave of electrical activity means that calcium enters myocytes through L-type voltage-operated ion channels. This results in the controlled release of calcium from the sarcoplasmic reticulum that, in turn, activates contraction of the cardiac muscle.30 In atrial fibrillation (AF), calcium can leak from the sarcoplasmic reticulum, which influences conduction velocity and the atrial refractory period.6 

In addition, atrial myocytes compensate for the increased inward calcium current caused by frequent depolarisation by downregulating L-type calcium channels. This, however, reduces the duration of action potentials and the atrial refractory periods. So, this compensatory mechanism paradoxically promotes AF.31 Calcium channel blockers can be used to control heart rate in some AF patients.5

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