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 (λ^t, λ^wt) and a divergence-related index (η). 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 η and d_w 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.