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

Objective: To determine whether a correlation exists between concentrations of intracellular and extracellular potassium and to determine the frequenc y of ventricular ectopy in patients after cardiac operations. Design: Prospective, observational clinical evaluation. Setting: surgical-respiratory intensive care unit of a university affiliate d tertiary care center. Patients: Continuous 24-hr electrocardiographic monitoring was performed, a nd serum (extracellular) and erythrocyte (intracellular) potassium concentr ations ([K+](e) and [K+](i)) were determined, before cardiopulmonary bypass , immediately postoperatively, and at 2, 4, 12, and 20 hrs after elective c oronary bypass grafting in 31 patients. Interventions: None. Potassium replacement was left to the discretion of th e attending physicians. Measurements and Main Results: Although the mean [K+](e) varied significant ly during the postoperative 24-hr period (p < .0001), the [K+](i) did not ( p = .953). No significant correlations were found between premature ventric ular 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 tachyca rdia (VT) within 30 mins of a study K+ sample, the mean [K+](e) was signifi cantly lower during the episode(s) of VT compared with the mean [K+](e) in the absence of VT (p < .01). Conclusions: 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 prematu re ventricular beats, the infrequent association of more serious ventricula r ectopy, VT, with lower [K+](e) concentrations supports the practice of us ing serum potassium to guide potassium replacement in patients after cardia c operations.