IR Iran
IR Iran (إيران)
Iran enters the NephroWorldCup as a relative newcomer. Not known for its scientific prowess, this year's entry into the NephroWorldCup showcases the tremendous scientific advances made by the IR since the 2018 Tournament. This year's team focuses on an innovative way to predict arterial stiffness (AS) in hemodialysis patients. But before we get to the study, let's review AS.
AS is an independent cause of mortality in hemodialysis patients. Most folks believe its etiology has to do with uremic toxins, abnormal calcium-phosphate balance, and chronic inflammation: all of which are found in ESRD. The most common and perhaps best way of measuring AS is through the pulse wave velocity (PWV) (Figure 1). PWV is also the only measure of arterial stiffness that is correlated with clinical outcomes.
Carousel 1: Arterial stiffness in ESRD and non-ESRD patients | Courtesy of The European Renal Association and presented at the 2021 European Renal Association meeting | Courtesy of ISN Education and presented at the 2018 Renal Research Institute meeting | Courtesy of Gary Mitchell and presented at the 2019 Hypertension meeting (zoom in for details)
Figure 1: Ways to assess pulse wave velocity | Courtesy of The European Renal Association and presented at the 2021 European Renal Association meeting (zoom in for details)
We know that ESRD patients have higher arterial stiffness - that's pretty well established. And the AS increases the risk of mortality - not new either (Carousel 1).
So what is Iran fielding on the pitch this year? Even though measuring the pulse wave velocity is one of the best ways to measure arterial stiffness, it's not easy to do in a hemodialysis unit. Machines are expensive and there's a lot of operator-dependence. Together, these two features make measuring the PWV out of reach for many dialysis teams.
So what makes this year's Iranian team different? The researchers acknowledge that, in lieu of using the PWV to assess arterial stiffness, a easily measurable surrogate is needed: blood pressure response during hemodialysis treatment.
Figure 2: Baseline characteristics. Is your patient represented?
This is a 5-year prospective study of 51 hemodialysis patients receiving 4 hours per treatment thrice-weekly (Figure 2). Blood pressure readings were taken pre- and post-treatment for three consecutive treatments. Anyone whose intradialytic mean arterial pressure (MAP) decreased by > 5% were defined as "hemodialysis responsive". All PWV measurements were done during the mid-week dialysis treatment (Video 1).
Video 1: Measuring the carotid-femoral pulse wave velocity using the SphygmoCor instrument (as performed in the study) | Courtesy of CardieX Limited
Using modeling equations, the following predictor variables were found to predict arterial stiffness: intradialytic BP response during treatment, calcium x phosphate product and the log of the PTH (R-squared 0.69, p < 0.05) (Figure 3). The final predictive equation is:
AIx = 56.62 - 0.60 (BP response in HD) + 0.43(calcium x phosphate product) - 2.95(logPTH)
where AIx is the Augmentation Index: a quantitative measure of arterial stiffness.
Figure 3: Predictor variables in the multiple regression model to predict arterial stiffness
The Iranian team holds its own in this year's NephroWorldCup. Identifying an easily measurable surrogate for arterial stiffness (AIx) is a brilliant idea and one that we would expect from this increasingly talented team.