At what level in mmol/l does low potassium have the potential to cause dangerous heart arythmias? less than 2.5? etc

Critically low: Normal serum potassium levels are generally considered to be between 3.5 and 5.0 mEq/L. Levels above 5.0 mEq/L indicate hyperkalemia, and those below 3.5 mEq/L indicate hypokalemia. A very low potassium level (less than 2.5 mmol/L) can be life-threatening and requires urgent medical attention. It is worse if the person is taking digoxin.