Theories and Controversies on Mechanism of Electrocardiographic Changes during Hemodialysis: Reply to Christov et al.

To the Editor,

We would like to thank the authors for their valuable comments. The procedure of hemodialysis (HD) exerts significant acute and chronic stress upon the cardiovascular system.1, 2 Lung congestion and pericardial and pleural effusions can cause attenuation in the electrocardiogram potentials; therefore, the HD has been associated with an increase in the amplitudes of P wave and QRS complexes but not T waves.3, 4 However, the mechanisms of these changes continue to be elusive, and whether they represent cardiac and/or extracardiac influences has not as yet been unraveled.5, 6 Although Christov et al. speculated that post‐HD increase in electrical impedance is not the reason for QRS and P‐ wave augmentation, Madias et al. reported that these changes are only apparent (not electrophysiologically real), representing an extracardiac phenomenon mediated by an increased electrical resistance of the passive body volume conductor, resulting in the measurement of augmented QRS complexes after fluid removal6, 7, 8, 9, 10, 11, 12 with subject‐specific dynamic profiles during HD.13 This thesis is supported by theoretical work, animal experimentation, and clinical evidence.9, 10, 11, 12 Unlike the other waves, decreased T‐ wave amplitudes after HD might be caused by decreased blood potassium levels after HD as T‐ wave amplitudes decrease with decreasing blood potassium.3 However, many studies have demonstrated silent ST‐ segment changes occurring during dialysis reporting the occurrence of dialysis‐induced ST depression at rates that vary between 15% and 40%.1 Although Christov et al. speculated that these amplitude changes inversely correlated to the change of the heart‐ preload; an interesting study14 using volumetric hemodynamic monitoring evaluated the changes in extravascular lung water index (EVLWI) and intrathoracic blood volume index (ITBVI) that were measured immediately before and after HD in addition to hemodynamic‐ and oxygenation‐related parameters; and found that although the EVLWI decreased significantly with fluid removal, ITBVI remained stable. Significant changes were also observed in stroke volume variation, cardiac index, and mean arterial pressure. EVLWI reduction with dialysis reflects the removal of excess body fluid, whereas preservation of cardiac preload is indicated by ITBVI stability.14 All these mechanisms in HD patients may explain the variable results in the literature, and further studies are required to better investigate the both short‐term and long‐term HD effects on human electrophysiology and to elucidate the pathophysiology involved and identify and select optimal therapies.