QRS Slopes for Potassium and Calcium Monitoring in End-Stage Renal Disease Patients

Non-invasive estimation of serum potassium, [K⁺], and calcium, [Ca²⁺], are of major importance to prevent ventricular arrhythmias and sudden cardiac death, but current ambulatory estimation methods, mostly based on T wave properties, are limited. We present an analysis based on QRS slopes to detect and quantify electrolyte abnormalities in end-stage renal disease (ESRD) patients. We applied principal component analysis to 12-lead electrocardiograms (ECGs) of 29 ESRD patients undergoing hemodialysis (HD). In the first principal component, we analyzed two-minute segments at the end of each HD hour and computed a mean warped QRS complex (MWQRS) representing an optimal average of QRS complexes. We calculated the upward ($I_{\text{US}}$) and downward ($I_{\text{DS}}$) slope of the MWQRS and we quantified the relative slope changes with respect to the end of the HD session ($\Delta I_{\text{US}}$ and $\Delta I_{\text{DS}}$). $\Delta I_{\text{US}}$ and $\Delta I_{\text{DS}}$ significantly increased and decreased, respectively, during HD in association with decreasing [K⁺] and increasing [Ca²⁺]. The median correlation coefficients of $\Delta I_{\text{US}}$ and $\Delta I_{\text{DS}}$ with the change in [K⁺] were −0.84 and 0.88, respectively. Corresponding correlation coefficients with the change in [Ca²⁺] were 0.78 and −0.91. The quantified QRS slope changes were related to both amplitude and duration changes in the QRS complex during HD. Changes in QRS slopes are strongly related to variations in [K⁺] and [Ca²⁺] during HD and could be used to monitor electrolyte concentrations in ESRD patients.