Estimation of Potassium Levels in Hemodialysis Patients by T Wave Nonlinear Dynamics and Morphology Markers.

Objective: Noninvasive screening of hypo-and hyperkalemia can prevent fatal arrhythmia in end-stage renal disease (ESRD) patients, but current methods for monitoring of serum potassium ([K+]) have important limitations. We investigated changes in nonlinear dynamics and morphology of the T wave in the electrocardiogram (ECG) of ESRD patients during hemodialysis (HD), assessing their relationship with [K+] and designing a [K+] estimator. Methods: ECG recordings from twenty-nine ESRD patients undergoing HD were processed. T waves in 2-min windows were extracted at each hour during an HD session as well as at 48 h after HD start. T wave nonlinear dynamics were characterized by two indices related to the maximum Lyapunov exponent (lambda(t), lambda(wt)) and a divergence-related index (eta). Morphological variability in the T wave was evaluated by three time warping based indices (d(w), reflecting morphological variability in the time domain, and d(a) and d(a)(NL,) in the amplitude domain). [K+]was measured from blood samples extracted during and after HD. Stage-specific and patient specific [K+] estimators were built based on the quantified indices and leave-one-out cross-validation was performed separately for each of the estimators. Results: The analyzed indices showed high inter-individual variability in their relationship with [K+]. Nevertheless, all of them had higher values at the HD start and 48 h after it, corresponding to the highest [K+]. The indices eta and dw were the most strongly correlated with [K+] (median Pearson correlation coefficient of 0.78 and 0.83, respectively) and were used in univariable and multivariable linear [K+] estimators. Agreement between actual and estimated [K+] was confirmed, with averaged errors over patients and time points being 0.000 +/- 0.875 mM and 0.046 +/- 0.690 mM for stage-specific and patient-specific multivariable [K+] estimators, respectively. Conclusion: ECG descriptors of T wave nonlinear dynamics and morphological variability allow noninvasive monitoring of [K+] in ESRD patients. Significance: ECG markers have the potential to be used for hypo-and hyperkalemia screening in ESRD patients.