Noninvasive quantification of blood potassium concentration from ECG in hemodialysis patients

Figures

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  Figure 1. A qualitative example of ECGs (8 independent leads, from 12-lead Holter recordings) acquired in a real patient at the initial (left) and final (right) stages of a dialysis session, demonstrating the correspondence between ECG-based TS/A parameter and T-wave morphology.

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  Figure 2. Preliminary results from the first attempt to derive an ECG-based [K+] estimator (KECG1 = 0.66* TS/A+2.72) by inverting the relation between the ECG-based TS/A parameter and the corresponding lab measurements of [K+] (KLAB), without any patient-specific calibration. Black dots are from sessions in which a systematic error (bias) was present all along the session, causing clustering of estimates far from the linear relationship.

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  Figure 3. Examples from three different sessions, for two different patients: one showing good agreement (left panels) and another showing systematic error (right panels) between the KECG1 (black circles) and KLAB (gray circles).

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  Figure 4. Left. When a patient-specific bias (PB2), estimated from the first dialysis session of each patient, is subtracted from the data, a nonlinear relationship can be observed between KLAB and TS/A, assessed in the remaining sessions. This observation led to the definition of the final ECG-based [K+] estimator (KECG = 0.36*TS/A2 + 0.22*TS/A + PB). This quadratic relationship is very similar to the one describing the dependence of the maximal conductance of IKr and IK1 currents on extracellular [K+] at the cellular level (inset panel24). Right: Bland-Altman plot of [K+] obtained applying the quadratic estimator and the reference values for [K+].

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  Figure 5. Results of the simulations performed using different potassium concentration levels. Top panels: membrane potentials for endocardial, M, and epicardial cells; middle panels: corresponding pseudo-ECGs clearly showing the differences in T-wave morphology; bottom panel: relationship between TS/A and [K+] in control (squares) and LQT2 (circles) conditions.

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  Figure 6. A typical QRS-T-wave complex from an idealized electrocardiogram together with the schematic explanation of the negative slope and the amplitude of the T wave used to compute TS/A for [K+] estimation.