Multicenter Prospective Cohort on Aortic Valve Stenosis in Japanese Patients With End Stage Kidney Disease in Tokai Region (ASKIT)

This multicenter, prospective cohort study included 2,786 patients on dialysis who underwent transthoracic echocardiography between July 1, 2017 and June 30, 2018. Patients with a maximum aortic jet velocity (Vmax) ≥ 2.0 m/s, pressure gradient (PG) between the left ventricle and ascending aorta (mean PG) ≥ 20 mmHg, or aortic valve area (AVA) ≤ 1.0 cm 2 were categorized into the AS group. Of these, patients with Vmax ≥ 3.0 m/s, mean PG ≥ 20 mmHg, or AVA ≤ 1.0 cm 2 were categorized into the severe AS group. The AS and severe AS groups were then compared with the non-AS group to identify the risk factors for AS using multivariate logistic analysis. We also compared the risk factors for AS with and without aortic valve calcication, which is the stage prior to age-related AS.

Association/American College of Cardiology (AHA/ACC) Guidelines for the Management of Patients with Valvular Heart Disease. AS was de ned as 1) Vmax ≥2.0 m/s, or 2) Mean PG ≥20 mmHg, or 3) AVA ≤1.0 cm 2 . The patients who met any of the criteria were classi ed into the AS group; otherwise, they were classi ed into the non-AS group. Of 555 patients in the AS group, 514 (92.6%) met the condition of Vmax ≥2.0 m/s, 107 (19.3%) met mean PG ≥20 mmHg, and 102 (18.6%) met AVA ≤1.0 cm 2 . Based on this result, we newly classi ed the severe AS group, which changed the standard of Vmax from ≥2.0 m/s to ≥3.0 m/s without changing the standard of mean PG and AVA. Of 193 patients in the severe AS group, 98 (50.8%) met Vmax ≥3.0 m/s, 107 (55.4%) met mean PG ≥20 mmHg, and 102 (52.8%) met AVA ≤1.0 cm 2 . Figure 1 shows the process of the enrollment and classi cation of the patients into the different groups.

Statistics
Baseline data were presented as mean (standard deviation), median (interquartile range), or percentage for categorical measures in patients. We used Fisher's exact test for nominal variables and the Mann-Whitney U test for continuous variables to compare the baseline data of the AS group with that of the non-AS group, and that of the severe AS group with that of the non-AS group. For the multivariate Cox regression, we performed a univariate analysis to extract factors associated with AS and added factors associated with MBD to them. We de ned a model that included the gender, age, duration of dialysis, nephrosclerosis as the primary cause of CKD, diabetes mellitus as a comorbidity, use of calcimimetics, use of vitamin D receptor activators, use of phosphate binders, serum albumin level, serum corrected calcium level, serum phosphorus level, serum intact parathyroid hormone level, serum C-reactive protein level, and serum hemoglobin level. For the strati ed multivariate Cox regression, we divided the patients into 4 categories based on their age: <60, 60-69, 70-79, and ≥80 years. We also divided the patients into 4 categories based on their dialysis duration and serum phosphorus level: <5, 5-9, 10-14, and ≥ 5 years, and <4.0, 4.0-4.9, 5.0-5.9, and ≥6.0 mg/dL, respectively. All statistical analyses were performed using EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), which is a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria).(29) Two-sided values of p <0.05 were considered statistically signi cant in all analyses.

Baseline characteristics
A total of 2,786 patients were enrolled; 555 patients (20.0%) were de ned as the AS group and 2,231 (80.0%) were de ned as the non-AS group. Among the patients in the AS group, 193 patients (6.9%) were classi ed into the severe AS group. Table 1 shows the baseline characteristics of the patients. The median ages of the AS, severe AS, and non-AS groups were 75, 77, and 68 years, respectively. The median hemodialysis duration of the AS, severe AS, and non-AS groups were 8.0, 7.4, and 6.2 years, respectively. The prevalence rates of diabetes mellitus in the AS, severe AS, and non-AS groups were 36.0%, 39.9%, and 46.0%, respectively. There was no signi cant difference in the average serum phosphorus and serum-corrected calcium levels among the three groups. For the TTE results, the aortic valve calci cation rates in the AS and severe AS groups were 80.7% and 83.8%, respectively, which were higher than the 53.3% in the non-AS group. Data are presented as the mean ± standard deviation or percentages. Age, dialysis duration, intact PTH, and C-reactive protein are expressed as the median (interquartile range). Abbreviations: Admission due to HF < 1 year, admission due to heart failure within 1 year before echocardiography; LVDd, left ventricular end-diastolic diameter; LVDs, left ventricular end-systolic diameter.

Multivariate analysis for AS
We included the aforementioned 14 items, which we predicted to be related to AS, as the multivariable adjusted model's factors. We performed a multivariate analysis comparing the AS and severe AS groups with the non-AS group (  Analyses were performed using the multivariable adjusted model. Abbreviations: OR, odd ratio; CI, con dence interval, CKD, chronic kidney disease; VDRA, Vitamin D receptor activator. In addition, we divided the patients into two groups (with and without aortic valve calci cation) and performed multivariate analysis ( Table 3). The results showed that aortic valve calci cation was associated with aging, long-term dialysis, diabetes mellitus, Vitamin D receptor activators (VDRA) administration, elevated serum calcium level, and anemia, but not with elevated serum phosphorus level.

Comparison of AS parameters with and without aortic valve calci cation
The mean PG, AVA, and Vmax as measured using TTE were compared between the patients with and without aortic valve calci cation ( Table 4). The results signi cantly showed that those with aortic valve calci cation had characteristics of AS in all parameters.

Discussion
In the results of this study, the prevalence of AS in dialysis patients was as high as 20.0%, similar to previous reports. It was also observed that aortic valve calci cation and AS are closely related. Aging had a strong effect on the development of AS in patients undergoing dialysis as well as the general population. Notably, hyperphosphatemia and long-term dialysis were found to be associated with AS. studies have been performed that investigated the association between hyperphosphatemia and AS. In our study, an elevated serum phosphorus level was not associated with aortic valve calci cation but was associated with AS. On the other hand, an elevated serum calcium level was not associated with AS but was associated with aortic valve calci cation. Although we could not prove the hypothesis that hyperphosphatemia causes AS after calci cation of the aortic valve, MBD, including hypercalcemia and hyperphosphatemia, was suspected to be strongly associated with aortic valve calci cation and AS. Further, it is interesting to note that the group of patients with a serum phosphorus level ≥5.0 mg/dL, which is lower than the upper limit of 6.0 mg/dL as per the Japanese guidelines, was associated with AS. This ongoing cohort study will assess the prognosis of patients with AS and concomitant hyperphosphatemia and hypercalcemia. We hope that it will help in setting target values not only for serum phosphorus levels and serum calcium levels but also in selecting phosphorus binders.
Our study showed that long-term dialysis was associated with both AS and aortic valve calci cation by multivariate analysis, including aging and MBD-related factors. Because long-term dialysis involves various factors that affect the cardiovascular system, such as uid retention, chronic in ammation, and uremic toxins, it is di cult to identify which factors induce the development of AS.(43-48) Although we cannot measure them directly, we will investigate the types of dialysis methods, such as hemodialysis, on-line hemodia ltration, and intermittent hemodia ltration, and the dialysis time per week to evaluate their effects on the progression of AS.

Limitations
This present study has some limitations. First, since we excluded patients having a history of aortic valve surgery, this study may have overlooked a serious risk factor for AS. Second, since we only evaluated one baseline point, the baseline results alone did not adequately assess the prognosis of AS and AS-related factors in patients undergoing dialysis. Third, because this study was a multicenter study, the accuracy of TTE was not consistent. All the above problems may be solved by comparing the annual results with the baseline results.

Conclusion
Patients on maintenance dialysis have a high prevalence of AS and a high rate of aortic valve calci cation, which were associated with hyperphosphatemia and duration of dialysis. We will continue our prospective studies to evaluate the factors involved in the development and prognosis of AS in patients undergoing dialysis.  Figure 1 A ow diagram of the present study Abbreviations: Vmax, Velocity max; PG, pressure gradient; AVA, aortic valve area Figure 2 Multivariate-adjusted odds ratio (MOR) for AS between the categories of age, duration of dialysis, and serum phosphorus level The graph on the left was a comparison between the AS group and the non-AS group, and the graph on the right was a comparison between the severe AS group and the non-AS group.