Low potassium cardioplegia: its effect on the incidence of complete heart block following cardiac surgery.

To investigate whether the concentration of potassium ion in cardioplegic solution was related to the incidence of complete heart block in patients undergoing myocardial revascularisation 163 consecutive cases were studied. Cardiac arrest was with St. Thomas' hospital cardioplegic solution in all patients. Ongoing myocardial protection was provided with St. Thomas' hospital solution (potassium concentration 20 mmol/l) in 56 patients (group A) and with Ringer's injection (potassium concentration 4 mmol/l) in 107 patients (group B). These two groups were studied sequentially. The incidence of complete heart block was higher in group A than in group B. Following aortic unclamping, 27 per cent of patients in group A compared to 14 per cent in group B exhibited the phenomenon (p less than 0.05). At the time of weaning from cardiopulmonary bypass the incidence was 20 per cent in group A compared to 10 per cent in group B (p less than 0.1). No differences were demonstrated between the two groups in terms of myocardial recovery, morbidity or mortality.