Intradialytic Cardiac Magnetic Resonance Imaging to Assess Cardiovascular Responses in a Short-Term Trial of Hemodiafiltration and Hemodialysis

Effect of isolated ultrafiltration and isovolemic dialysis on myocardial perfusion and left ventricular function assessed with 13N-NH3 positron emission tomography and echocardiography

Hemodialysis is associated with a fall in myocardial perfusion and may induce regional left ventricular (LV) systolic dysfunction. The pathophysiology of this entity is incompletely understood, and the contribution of ultrafiltration and diffusive dialysis has not been studied. We investigated the effect of isolated ultrafiltration and isovolemic dialysis on myocardial perfusion and LV function. Eight patients (7 male, aged 55 ± 18 yr) underwent 60 min of isolated ultrafiltration and 60 min of isovolemic dialysis in randomized order. Myocardial perfusion was assessed by ¹³N-NH₃ positron emission tomography before and at the end of treatment. LV systolic function was assessed by echocardiography. Regional LV systolic dysfunction was defined as an increase in wall motion score in ≥2 segments. Isolated ultrafiltration (ultrafiltration rate 13.6 ± 3.9 ml·kg^-1·h^-1) induced hypovolemia, whereas isovolemic dialysis did not (blood volume change -6.4 ± 2.2 vs. +1.3 ± 3.6%). Courses of blood pressure, heart rate, and tympanic temperature were comparable for both treatments. Global and regional myocardial perfusion did not change significantly during either isolated ultrafiltration or isovolemic dialysis and did not differ between treatments. LV ejection fraction and the wall motion score index did not change significantly during either treatment. Regional LV systolic dysfunction developed in one patient during isolated ultrafiltration and in three patients during isovolemic dialysis. In conclusion, global and regional myocardial perfusion was not compromised by 60 min of isolated ultrafiltration or isovolemic dialysis. Regional LV systolic dysfunction developed during isolated ultrafiltration and isovolemic dialysis, suggesting that, besides hypovolemia, dialysis-associated factors may be involved in the pathogenesis of hemodialysis-induced regional LV dysfunction.

Controversies in the management of the haemodialysis-related arteriovenous fistula following kidney transplantation

Arteriovenous fistula (AVF) is regarded as the best vascular access for chronic haemodialysis (HD). Still, AVF inherently causes significant haemodynamic changes. Although the necessity for vascular access despite its putative cardiovascular complications favours AVF creation in patients under chronic HD, one may question whether sustaining a functional AVF after successful kidney transplantation extends the haemodynamic threat. Small prospective series suggest that AVF ligation causes rapid and sustained reduction in left ventricular hypertrophy. Still, the benefits of such a cardiac remodelling in long-terms of cardiovascular morbi-mortality still need to be proven. Furthermore, the elevation of diastolic blood pressure and arterial stiffness caused by AVF ligation may blunt the expected cardio-protection. Finally, the closure of a functioning AVF may accelerate the decline of kidney graft function. As a whole, the current management of a functioning AVF in kidney transplant recipients remains controversial and does not rely on strong evidence-based data. The individual risk of graft dysfunction and a return to chronic HD also needs to be balanced. Careful pre-operative functional assessments, including cardio-pulmonary testing and estimated glomerular filtration rate slope estimation, may help better selection of who might benefit the most from AVF closure. Large-scale prospective, ideally multi-centric, trials are essentially needed.

Intradialytic Central Venous Oxygen Saturation is Associated with Clinical Outcomes in Hemodialysis Patients

Central venous oxygen saturation (ScvO₂) in the superior vena cava is predominantly determined by cardiac output, arterial oxygen content, and oxygen consumption by the upper body. While abnormal ScvO₂ levels are associated with morbidity and mortality in non-uremic populations, ScvO₂ has received little attention in hemodialysis patients. From 1/2012 to 8/2015, 232 chronic hemodialysis patients with central venous catheters as vascular access had their ScvO₂ monitored during a 6-month baseline period and followed for up to 36 months. Patients were stratified into upper and lower two tertiles by a ScvO₂ of 61.1%. Survival analysis employed Kaplan-Meier curves and adjusted Cox proportional hazards models. Patients in the lower tertiles of ScvO₂ were older, had longer hemodialysis vintage, lower systolic blood pressure, lower ultrafiltration rates, higher leukocyte counts and neutrophil-to-lymphocyte ratios. Kaplan-Meier analysis indicated a shorter survival time in the lower tertiles of ScvO₂ (P = 0.005, log-rank test). In adjusted Cox analysis, a 1 percent point decrease in mean ScvO₂ was associated with a 4% increase in mortality (HR 1.04 [95% CI 1.01-1.08], P = 0.044), indicating that low ScvO₂ is associated with poor outcomes. Research on the relative contributions of cardiac output and other factors is warranted to further elucidate the pathophysiology underlying this novel finding.