Nature of cardiac arrhythmias and electrolyte disturbances. Role of potassium in atrial fibrillation.

Atrial fibrillation is highly favoured by an accelerated atrial muscle repolarization. In hyperthyroidism, this occurs without changes in resting membrane potential level of the atrial muscle cells and without changes in the ionic composition of the cell. In patients prone to atrial fibrillation but without signs of hyperthyroidism, accelerated atrial repolarization can also be demonstrated. In such patients, a decreased atrial muscle potassium content seems responsible for the electrophysiological changes that highly favours the occurrence of atrial fibrillation.