Monitoring blood potassium concentration in hemodialysis patients by quantifying T-wave morphology dynamics.

We investigated the ability of time-warping-based ECG-derived markers of T-wave morphology changes in time ( $$d_{w}$$ ) and amplitude ( $$d_a$$ ), as well as their non-linear components ( $${d_w^{{\mathrm{NL}}}}$$ and $${d_a^{\mathrm{NL}}}$$ ), and the heart rate corrected counterpart ( $$d_{w,c}$$ ), to monitor potassium concentration ( $$[K^{+}]$$ ) changes ( $$\Delta [K^+]$$ ) in end-stage renal disease (ESRD) patients undergoing hemodialysis (HD). We compared the performance of the proposed time-warping markers, together with other previously proposed $$[K^{+}]$$ markers, such as T-wave width ( $$T_w$$ ) and T-wave slope-to-amplitude ratio ( $$T_{S/A}$$ ), when computed from standard ECG leads as well as from principal component analysis (PCA)-based leads. 48-hour ECG recordings and a set of hourly-collected blood samples from 29 ESRD-HD patients were acquired. Values of $$d_w$$ , $$d_a$$ , $${d_w^{\mathrm{NL}}}$$ , $${d_a^{\mathrm{NL}}}$$ and $$d_{w,c}$$ were calculated by comparing the morphology of the mean warped T-waves (MWTWs) derived at each hour along the HD with that from a reference MWTW, measured at the end of the HD. From the same MWTWs $$T_w$$ and $$T_{S/A}$$ were also extracted. Similarly, $$\Delta [K^+]$$ was calculated as the difference between the $$[K^{+}]$$ values at each hour and the $$[K^{+}]$$ reference level at the end of the HD session. We found that $$d_{w}$$ and $$d_{w,c}$$ showed higher correlation coefficients with $$\Delta [K^+]$$ than $$T_{S/A}$$ —Spearman’s ( $$\rho$$ ) and Pearson’s (r)—and $$T_w$$ —Spearman’s ( $$\rho$$ )—in both SL and PCA approaches being the intra-patient median $$\rho \ge 0.82$$ and $$r \ge 0.87$$ in SL and $$\rho \ge 0.82$$ and $$r \ge 0.89$$ in PCA respectively. Our findings would point at $$d_{w}$$ and $$d_{w,c}$$ as the most suitable surrogate of $$\Delta [K^+]$$ , suggesting that they could be potentially useful for non-invasive monitoring of ESRD-HD patients in hospital, as well as in ambulatory settings. Therefore, the tracking of T-wave morphology variations by means of time-warping analysis could improve continuous and remote $$[K^{+}]$$ monitoring of ESRD-HD patients and flagging risk of $$[K^{+}]$$ -related cardiovascular events.