Nonlinear T-Wave Time Warping-Based Sensing Model for Non-Invasive Personalised Blood Potassium Monitoring in Hemodialysis Patients: A Pilot Study

Abstract

Background: End-stage renal disease patients undergoing hemodialysis (ESRD-HD) therapy are highly susceptible to malignant ventricular arrhythmias caused by undetected potassium concentration ([K+]) variations (Δ[K+]) out of normal ranges. Therefore, a reliable method for continuous, noninvasive monitoring of [K+] is crucial. The morphology of the T-wave in the electrocardiogram (ECG) reflects Δ[K+] and two time-warping-based T-wave morphological parameters, dw and its heart-rate corrected version dw,c, have been shown to reliably track Δ[K+] from the ECG. The aim of this study is to derive polynomial models relating dw and dw,c with Δ[K+], and to test their ability to reliably sense and quantify Δ[K+] values. Methods: 48-hour Holter ECGs and [K+] values from six blood samples were collected from 29 ESRD-HD patients. For every patient, dw and dw,c were computed, and linear, quadratic, and cubic fitting models were derived from them. Then, Spearman’s (ρ) and Pearson’s (r) correlation coefficients, and the estimation error (ed) between Δ[K+] and the corresponding model-estimated values (Δ^[K+]) were calculated. Results and Discussions: Nonlinear models were the most suitable for Δ[K+] estimation, rendering higher Pearson’s correlation (median 0.77 ≤r≤ 0.92) and smaller estimation error (median 0.20 ≤ed≤ 0.43) than the linear model (median 0.76 ≤r≤ 0.86 and 0.30 ≤ed≤ 0.40), even if similar Spearman’s ρ were found across models (median 0.77 ≤ρ≤ 0.83). Conclusion: Results support the use of nonlinear T-wave-based models as Δ[K+] sensors in ESRD-HD patients.

Differences in ventricular wall composition may explain inter-patient variability in the ECG response to variations in serum potassium and calcium

“…Inter-patient variability in the relation between electrolytes and ECG markers has been reported by several authors ( Buemi et al, 2005 ; Montague et al, 2008 ; Severi et al, 2009b ; Alabd et al, 2011 ; Green et al, 2013 ; Corsi et al, 2017 ; Yoon et al, 2018 ; Pilia et al, 2020 ; Palmieri et al, 2021b ; Palmieri et al, 2022 ). We are not aware of previous work explaining this variability in terms of variations in ventricular wall composition, except for our previous study in simulated ventricular 1D fibers ( Bukhari et al, 2021 ).…”

“…Other studies have investigated model-based markers of T wave morphology ( Rodrigues et al, 2020 ), sympathetic activity-related T wave instability during HD ( Schüttler et al, 2021 ) and descriptors of the sine wave shape, amplitude and time voltage area of the QRS complex ( Ojanen et al, 1999 ; An et al, 2012 ; Curione et al, 2013 ; Pilia et al, 2020 ). To characterize overall variations in the morphology of the QRS complex and the T wave, in previous studies we have developed [K + ] and [Ca 2+ ] estimators using non-linear dynamics and time-warping techniques and we have evaluated them during and after HD in ESRD patients ( Bukhari et al, 2019 ; Srinivasan et al, 2020 ; Palmieri et al, 2021a ; Palmieri et al, 2021b ; Bukhari et al, 2021 ; Bukhari et al, 2022a ; Bukhari et al, 2022b ).…”

“…A common weakness of all the proposed markers is that their relationships with electrolyte concentrations vary strongly between patients ( Buemi et al, 2005 ; Montague et al, 2008 ; Alabd et al, 2011 ; Green et al, 2013 ; Pilia et al, 2020 ; Palmieri et al, 2022 ; Palmieri et al, 2021b ). The cause of this variability is presently unknown.…”

Monitoring of Serum Potassium and Calcium Levels in End-Stage Renal Disease Patients by ECG Depolarization Morphology Analysis

“…These studies, however, have not established a tight correlation between the proposed markers and [K + ], thus limiting their possibilities for ambulatory [K + ] monitoring. In previous studies, we used nonlinear dynamics and time-warping techniques to characterize changes in the whole T wave at varying [K + ] and [Ca 2+ ] in patients and simulated ECGs [28][29][30][31][32][33]. We found a strong relationship between [K + ] and T wave linear and nonlinear features.…”

“…We used linear estimators due to the small number of samples, particularly when using a patient-specific approach. Future work could investigate the use of nonlinear estimators [11,32], which could prove to be particularly relevant for the estimation of [K + ] and [Ca 2+ ] at the start of HD sessions when these take values far from those at other HD stages.…”