The relationship between serum potassium and cardiac arrhythmias following cardiac infarction in patients aged over 65 years.

A retrospective analysis was performed of 405 patients, over the age of 65 years, who had been admitted with proven myocardial infarction to a coronary care unit, to investigate the relationship between the serum potassium level on admission and the incidence of cardiac arrhythmias. On admission, 173 (42.7%) patients had a serum potassium of less than 4.0 mmol/l. During the first 24 hours in hospital, 57% of all patients exhibited a disturbance of cardiac rhythm. The incidence of total arrhythmias was independent of the initial serum potassium level, but the mortality rate was 46.2% in those patients with a serum potassium less than 4.0 mmol/l while it was 34.5% in those with a potassium of 4.0 mmol/l or greater. Twelve patients with a serum potassium less than 4.0 mmol/l experienced at least one episode of ventricular fibrillation (6.9%), but only 1 patient with a serum potassium of 4.0 mmol/l or greater had this arrhythmia. The difference in incidence of this arrhythmia was highly significant (p less than 0.001). No patient who experienced ventricular fibrillation was on existing cardiac medication with either a diuretic, beta-adrenoreceptor blocking drug or digoxin. There was no significant difference in the occurrence of other cardiac arrhythmias between low and normal serum potassium groups.