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Dialysis fistulas and heart failure

Defining the optimal care for patients reaching end-stage renal disease (ESRD) requiring haemodialysis continues to be a challenge for nephrologists, cardiologists, and vascular surgeons. It has been acutely recognized that temporary dialysis catheters used in 82% of those who start dialysis can be a nidus for intravascular infection and are associated with early mortality in ESRD. Accordingly, there has been a large emphasis on ‘fistula first’ or, in other words, having a permanent surgically created dialysis access conduit [arteriovenous fistula (AVF) or shunt with graft (AVG) material] and thus reducing the exposure to and the length of time with dialysis catheters. Permanent vascular access brings a new set of issues to the patient and physician, with complications such as low flow, clotting, infection, and need for revision. In this issue of the journal, Reddy and colleagues present data from 137 ESRD patients who underwent echocardiographic examinations before and 2.6 years after AVF/AVG creation. While there were modest improvements in left ventricular hypertrophy, access creation was associated with multiple adverse changes in right ventricular structure and function without a measurable increase in cardiac output. The consequences of these changes included a nearly four-fold increased risk of incident heart failure, which occurred in 43% of cases. It should be mentioned that in the overall Mayo ESRD cohort (n = 654) with paired echocardiograms, the development of right ventricular dysfunction irrespective of AVF/ AFG status was associated with mortality [hazard ratio (HR) 1.66, 95% confidence interval (CI) 1.34–2.06; P < 0.001]. So, it is not clear how much systemic shunting played a role in the outcomes of this study. Additionally, those who had their vascular access ligated and presumably went back to catheter access did not have dramatic improvements in right ventricular function, but modest stabilization. Thus, these data are suggestive but far from conclusive that AVF/ AFG and systemic shunting are causal in the development of right ventricular dysfunction and clinical heart failure. These caveats considered, the hypothesis is that the degree of systemic shunting of blood and recirculation creates a volume overload state on the right heart chambers, and in the milieu of ESRD leads to biventricular heart failure (Figure 1). Patients with ESRD already have the three central mechanisms of cardiac failure: pressure overload, systemic volume overload, and cardiomyopathy. Additional recirculation with systemic shunting works to accentuate volume overload without an improvement in tissue perfusion. This study brings to light an important clinical issue and a series of opportunities for future clinical research. The first research gap relates to the anatomical size of the arterial access at the inflow, needle insertion points, and outflow, predicted rates of flow during dialysis, location of the access (distal vs. proximal), and the final quantification of systemic shunting during off-dialysis periods. In the US Renal Data System, when compared with those with dialysis catheters, AVF/AVG was not associated with the development of heart failure or other cardiovascular events. So the risk appears to be concentrated in one or more subgroups potentially according to access variables, patient risk, and the modality of dialysis. The present study identified age as the only multivariate predictor of right ventricular dysfunction. McCullough and colleagues have recently demonstrated a large reduction in cardiovascular hospitalizations in patients who choose to undergo home haemodialysis on a more frequent basis than three times per week in a dialysis centre. Thus, the degree of systemic shunting and its influence on the right ventricle may be modified by the degree of chronic blood volume control. The second gap is the association between quantity of shunt or shunt fraction with the risk of right ventricular dilation and dysfunction. Can vascular surgeons use techniques to measure and more precisely control the degree of systemic shunting while still providing a durable access for dialysis? The third gap is the need for a more comprehensive understanding of the determinants of right ventricular failure in ESRD as the phenomenon can occur in the pre-dialysis phase before any access is created, in patients with dialysis catheters, and in patients with peritoneal dialysis. It is possible that in ESRD patients with pre-existing heart failure, the risks of systemic shunting outweigh the risks of catheter infection and that indeed a dialysis catheter would be the preferred mode of vascular access. There is great hope with leads from Reddy and colleagues that future research can guide physicians in how to create and manage the most ideal