Negative impact of very mild volume overload on the heart function in patients on chronic hemodialysis

Heart failure is associated with higher mortality of hemodialysis patients. Fluid overload is a major risk factor for cardiovascular disease in these patients, but it is frequently clinically silent. The optimal assessment of ideal dry weight is still searched for. We hypothesized that even very mild fluid overload would be associated with the left ventricular ejection fraction and on the size of heart chambers.

Inclusion visit data of a cohort observation study were analyzed: bioelectrical impedance, echocardiography with hemodynamic estimations and basic laboratory tests. Fluid overload was defined by using the fluid overload/extracellular water index (FO/ECW, relative hydration index) > median value. Moreover, analyses according to FO/ECW quartiles were performed. All these measurements were done within an hour and at least 24 h after the previous hemodialysis.

We included 334 patients. FO/ECW median was 7%. Patients with fluid overload had lower left ventricular ejection fraction (median (interquartile range): 53(45-62) vs. 60(56-67)%, p = 0.0002), dilatation of all heart chambers, more pronounced hypertrophy of the left ventricle with higher NTproBNP, significantly lower serum albumin levels and lower body mass. The relationship between the relative hydration index and heart changes was gradual. Fluid overload, as defined by the mild criteria, was associated with a worse ejection fraction, but also with other functional and structural heart changes.

Our study demonstrates that in patients on dialysis, even mild (often subclinical) fluid overload is associated with structural and functional heart changes. Early identification of fluid overload with improved methods of volume assessment is thus warranted and especially in lean patients.