Q: It is a common practice to give calcium to counteract aarrhythmias. But in which condition, it may not be a good move or actually, it may be harmful to the patient?

Anwer: In a digitalized patient

Digoxin inhibits the Na⁺/K⁺-ATPase(exchanges 2 K for 3Na) in the cardiac myocyte by competing with potassium,and causes intracellular sodium concentration to increase. This then leads to an accumulation of intracellular calcium by blocking the Na⁺-Ca⁺⁺ exchange system.

In patients on Digoxin, if more calcium is given it can lead to more intracellular calcium in mycocyte leading to what has been described as cardiac tetany due to prolonged depolarisation.