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The effect of a single dialysis session on spatial QRS-T angle in haemodialysis patients.

BACKGROUND
Abnormal values of the spatial angle between the directions of ventricular depolarization and repolarization (QRS-T) reflect the action potential inhomogeneities and predict cardiac events and mortality in various patient groups. The study was designed to (i) compare QRS-T in haemodialysis (HD) patients and healthy subjects, (ii) assess the influence of HD on QRS-T and (iii) evaluate the possible associations between QRS-T and echocardiography, haemodynamic as well as biochemical parameters.


METHODS
The angular differences between the maximum spatial QRS and T vectors were measured in 73 HD patients and in 57 controls. QRS-T in patients was estimated pre- and post-dialysis together with the evaluation of blood chemistry and haemodynamic parameters.


RESULTS
Pre-dialysis QRS-T was higher compared with controls (30.18 ± 9.84 and 13.65 ± 7.23, respectively; P < 0.001). HD induced an increase of QRS-T (41.09 ± 11.74; P < 0.001). Pre-dialysis QRS-T adjusted for left ventricular mass index correlated with troponin T (r = 0.398, P = 0.001) and HDL (r = -0.270, P = 0.043). The differences between pre- and post-dialysis (Δ) QRS-T correlated with Δ potassium (r = 0.453, P < 0.001), Δ calcium (r = -0.309, P = 0.011) and Δ stroke index (SI; r = 0.311, P = 0.017). On multivariate analysis, troponin T was found to be an independent predictor of pre-dialysis QRS-T, whereas independent predictors of the HD-induced increase in QRS-T were potassium and cardiac index changes.


CONCLUSIONS
QRS-T is high in HD patients. HD enhances the inhomogeneities of action potential. Pre-dialysis QRS-T is mainly associated with troponin T elevation. HD-induced increase in QRS-T is mainly associated with potassium and SI changes. The possible clinical importance of the higher QRS-T in HD patients remains to be confirmed in further studies.