Narrow limits of agreement, high correlations and small effect size suggest that the Polar V800 is a valid tool for the analysis of heart rate variability in athletes while running high endurance events such as marathon, trail, and ultra-trail races.

We investigated the ability of time-warping-based ECG-derived markers of T-wave morphology changes in time ($$d_{w}$$ d w ) and amplitude ($$d_a$$ d a ), as well as their non-linear components ($${d_w^{{\mathrm{NL}}}}$$ d w NL and $${d_a^{\mathrm{NL}}}$$ d a NL ), and the heart rate corrected counterpart ($$d_{w,c}$$ d w , c ), to monitor potassium concentration ($$[K^{+}]$$ [ K + ] ) changes ($$\Delta [K^+]$$ Δ [ 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 $$[K^{+}]$$ [ K + ] markers, such as T-wave width ($$T_w$$ T w ) and T-wave slope-to-amplitude ratio ($$T_{S/A}$$ 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 w , $$d_a$$ d a , $${d_w^{\mathrm{NL}}}$$ d w NL , $${d_a^{\mathrm{NL}}}$$ d a NL and $$d_{w,c}$$ 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 $$T_w$$ T w and $$T_{S/A}$$ T S / A were also extracted. Similarly, $$\Delta [K^+]$$ Δ [ K + ] was calculated as the difference between the $$[K^{+}]$$ [ K + ] values at each hour and the $$[K^{+}]$$ [ K + ] reference level at the end of the HD session. We found that $$d_{w}$$ d w and $$d_{w,c}$$ d w , c showed higher correlation coefficients with $$\Delta [K^+]$$ Δ [ K + ] than $$T_{S/A}$$ T S / A —Spearman’s ($$\rho$$ ρ ) and Pearson’s (r)—and $$T_w$$ T w —Spearman’s ($$\rho$$ ρ )—in both SL and PCA approaches being the intra-patient median $$\rho \ge 0.82$$ ρ ≥ 0.82 and $$r \ge 0.87$$ r ≥ 0.87 in SL and $$\rho \ge 0.82$$ ρ ≥ 0.82 and $$r \ge 0.89$$ r ≥ 0.89 in PCA respectively. Our findings would point at $$d_{w}$$ d w and $$d_{w,c}$$ d w , c as the most suitable surrogate of $$\Delta [K^+]$$ Δ [ 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 $$[K^{+}]$$ [ K + ] monitoring of ESRD-HD patients and flagging risk of $$[K^{+}]$$ [ K + ] -related cardiovascular events.

Background-The arrhythmogenesis of ventricular myocardial ischemia has been extensively studied, but models of atrial ischemia in humans are lacking. This study aimed at describing the electrophysiological alterations induced by acute atrial ischemia secondary to atrial coronary branch occlusion during elective coronary angioplasty. Methods and Results-Clinical data, 12-lead ECG, 12-hour Holter recordings, coronary angiography, and serial plasma levels of high-sensitivity troponin T and midregional proatrial natriuretic peptide were prospectively analyzed in 109 patients undergoing elective angioplasty of right or circumflex coronary arteries. Atrial coronary branches were identified and after the procedure patients were allocated into two groups: atrial branch occlusion (ABO, n=17) and atrial branch patency (non-ABO, n=92). In comparison with the non-ABO, patients with ABO showed: (1) higher incidence of periprocedural myocardial infarction (20% versus 53%, P=0.01); (2) more frequent intra-atrial conduction delay (19% versus 46%, P=0.03); (3) more marked PR segment deviation in the Holter recordings; and (4) higher incidence of atrial tachycardia (15% versus 41%, P=0.02) and atrial fibrillation (0% versus 12%, P=0.03). After adjustment by a propensity score, ABO was an independent predictor of periprocedural infarction (odds ratio, 3.4; 95% confidence interval, 1.01-11.6, P<0.05) and atrial arrhythmias (odds ratio, 5.1; 95% confidence interval, 1.2-20.5, P=0.02). Conclusions-Selective atrial coronary artery occlusion during elective percutaneous transluminal coronary angioplasty is associated with myocardial ischemic damage, atrial arrhythmias, and intra-atrial conduction delay. Our data suggest that atrial ischemic episodes might be considered as a potential cause of atrial fibrillation in patients with chronic coronary artery disease.