Potassium concentrations and ventricular ectopy: a prospective, observational study in post-cardiac surgery patients

To determine whether a correlation exists between concentrations of intracellular and extracellular potassium and to determine the frequency of ventricular ectopy in patients after cardiac operations.

Prospective, observational clinical evaluation.

Surgical-respiratory intensive care unit of a university-affiliated tertiary care center.

Continuous 24-hr electrocardiographic monitoring was performed, and serum (extracellular) and erythrocyte (intracellular) potassium concentrations ([K+]e and [K+]i) were determined, before cardiopulmonary bypass, immediately postoperatively, and at 2, 4, 12, and 20 hrs after elective coronary bypass grafting in 31 patients.

None. Potassium replacement was left to the discretion of the attending physicians.

Although the mean [K+]e varied significantly during the postoperative 24-hr period (p<.0001), the [K+]i did not (p = .953). No significant correlations were found between premature ventricular beats and [K+]i, [K+]e, or [K+]i/[K+]e (all p>.05). However, among the few patients who had one or more episodes of ventricular tachycardia (VT) within 30 mins of a study K+ sample, the mean [K+]e was significantly lower during the episode(s) of VT compared with the mean [K+]e in the absence of VT (p<.01).

Although it is clear that over the clinically acceptable range of [K+]e and [K+]i concentrations seen in this population, there is no correlation between potassium concentrations and the occurrence of premature ventricular beats, the infrequent association of more serious ventricular ectopy, VT, with lower [K+]e concentrations supports the practice of using serum potassium to guide potassium replacement in patients after cardiac operations.