Background: Chronic kidney disease (CKD) affects more than 10% of the population worldwide and is associated with increased mortality and morbidity. In patients with CKD, cardiovascular diseases are the most common cause of death. The effects of CKD on cellular mechanisms in cardiomyocytes remain only partially understood. Thus, our goal was to investigate the influence of CKD on human ventricular myocardium.

Methods: Experiments were conducted using human left ventricular myocardium, which was acquired from patients with aortic stenosis and preserved LV function (EF ≥50%) undergoing surgical valve replacement. Based on the glomerular filtration rate (GFR), patients were divided into a control (C) group (GFR>60 ml/min/1,73m²) or CKD group (GFR<60 ml/min/1,73m²). Additionally, electrolyte imbalances as they occur in dialysis patients were simulated using a human ventricular induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) model to study the arrhythmic potential of CKD. Medium exchanges represented patient’s dialysis sessions with abrupt changes from high to low potassium and phosphate concentration. Epifluorescence microscopy for measuring Ca²⁺ homeostasis and detecting arrhythmias in the iPSC model was performed using the ratiometric Ca²⁺ dye Fura-2 AM. Action potential measurements were conducted using ruptured-patch whole-cell current clamp technique.

Results: Ventricular myocardium could be obtained from 11 patients with normal kidney function and 8 patients with CKD. Patients in the CKD group had markedly impaired GFR (35.1±15.8 ml/min/1,73m² CKD vs. 87.0±11.5 ml/min/1,73m² C, p<0,0001). LVEF was persevered in both groups (52.5±3.6% CKD vs. 54.1±4.7% C, p=0.474).

Epifluorescence microscopy demonstrated that a Ca²⁺ transient amplitude reduction could be observed in the CKD group which points to negative inotropic effects and contractile dysfunction in patients with CKD. Action potential measurements revealed an action potential duration (APD) prolongation when the CKD group was compared to the control group. Longer APD represents an arrhythmic trigger and may explain the increased amount of rhythm disorders seen in patients with CKD. Both reduced Ca²⁺ transient amplitudes as well as prolonged action potentials are also known as hallmarks of heart failure (figure 1).

Fig. 1: Effects of CKD on Ca²⁺ transients (A) and APD90 (B) at 30 bpm. Cells per group: (A) 43 vs. 55, (B) 23 vs. 14, ***p<0,001.

In addition, after one week of dialysis simulation using an iPSC model, more arrhythmias in the group undergoing a dialysis simulation were detected that in the control group. This indicates that the abrupt electrolyte changes occurring during dialysis may be responsible for the impaired prognosis of patients requiring dialysis (figure 2).

Fig. 2: Dialysis simulation leads to the occurrence of more arrhythmias in the dialysis group (21/48 cells with arrhythmic events) compared to the control group (5/47 cells with arrhythmic events), ****p<0,0001.

Conclusion: We could demonstrate that human ventricular cardiomyocytes isolated from patients with CKD show impaired cellular electrophysiological function and that an iPSC model identifies dialysis as an arrhythmogenic trigger. These findings have translational importance as in an aging population, CKD and cardiovascular diseases are going to increase. Thus, our results may be the first step in understanding the development of cardiorenal syndrome on a cellular myocardial level.