Changes in kidney function among patients undergoing transcatheter aortic valve replacement

Implication for health policy/practice/research/medical education: Impact of transcatheter aortic valve replacement (TAVR) on renal function especially in patients with chronic kidney disease (CKD) is unclear. In this current study, we investigated the change in eGFR following TAVR in non-advanced CKD patients with severe aortic stenosis (AS) stratified by levels of eGFR (≥ 60, 30-59, and <30 mL/min/1.73m2). Our findings were as follows; 1) acute kidney injury (AKI) significantly decreased eGFR at 6 months after TAVR and 2) In patients with no AKI after TAVR, individuals with CKD (particularly eGFR <30 mL/min/1.73m2) had a significant increase in eGFR (decrease in SCr) at 6 months. Please cite this paper as: Thongprayoon C, Cheungpasitporn W, Kittanamongkolchai W, Srivali N, Greason KL, Kashani KB. Changes in kidney function among patients undergoing transcatheter aortic valve replacement. J Renal Inj Prev. 2017;6(3):216221. DOI: 10.15171/jrip.2017.4


Objectives
Little is known regarding the impact of TAVR on renal function especially in patients with CKD.Thus, we conducted this retrospective study to evaluate the change in eGFR after TAVR.

Patients and Methods
We conducted a retrospective observational study at Mayo Clinic Hospital, a quaternary referral hospital in Rochester, Minnesota.Adult patients (age ≥18 years) with AS, who underwent TAVR between January 1st, 2008 and June 30th, 2014 were enrolled.Exclusion criteria were: (a) patients who had advanced CKD stage 5 (eGFR <15 mL/min/1.73m 2 ), (b) patients who received dialysis (≤14 days prior to TAVR), and (c) patients without research authorization.Clinical, laboratory, pre-and post-procedural data were obtained from our institutional electronic medical record system.The Society of Thoracic Surgeons' (STS) adult cardiac surgery risk score was calculated for each patient as a surrogate for operative mortality risk (19)(20)(21).The eGFR was calculated using the CKD epidemiology collaboration equation (22).Primary outcomes were the changes in eGFR after TAVR; at the day of hospital discharge and at 6 months.We stratified patients based on AKI and CKD stages.AKI after TAVR was defined by an increase in serum creatinine (SCr) of ≥0.3 mg/dL (≥26.5 µmol/L) within 48 hours after TAVR or a relative increase of ≥50%) of the KDIGO definition (23).

Ethical issues
1) The research followed the tenets of the Declaration of Helsinki; 2) The Institutional Review Board affirmed our study and informed consent for patients with research authorization was waived; and 3) This study was approved by the Ethics Committee of Mayo Clinic.

Statistical analysis
To identify the differences in clinical characteristics between patients with and without AKI after TAVR, student's t test was used for continuous variables and the chi-squared test, or Fisher's exact test was used for categorical variables, as appropriate.The changes in eGFR and SCr before and after TAVR were tested using paired t test.A two-sided P value of <0.05 was considered statistically significant.All analyses were performed using JMP statistical software version 10 (SAS, Cary, NC).

Results
A total of 390 TAVR procedures for AS were conducted during the study time period.Three were excluded due to advance CKD stage 5 or receiving dialysis (≤14 days before TAVR).One patient had no research authorization and therefore was excluded.A total of 386 patients were included in the analysis.

Discussion
Previous studies have demonstrated an association between CKD and poor outcomes in patients undergoing TAVR (24,25).However, data on the change of renal function after relief of severe AS by TAVR are limited.
In the current study, we examined the change in eGFR following TAVR in non-advanced CKD patients with severe AS stratified by levels of eGFR (≥ 60, 30-59, and <30 mL/min/1.73m 2 ).Our findings were as follows; 1) AKI significantly decreased eGFR at six months after TAVR and 2) In patients with no AKI after TAVR, individuals with CKD (particularly eGFR <30 mL/min/1.73m 2 ) had a significant increase in eGFR (decrease in SCr) at 6 months.
Although the precise underlying mechanisms of recovery of kidney function among CKD patients after TAVR is still unclear, we believe that the increase in eGFR is likely attributed to an improvement in the cardiac forward flow after relief of severe AS resulting in a higher organ perfusion including kidneys (17,26).Also, improvement in a right heart function can lead to a decrease in renal venous congestion (17,27).As our finding of an increase in eGFR in CKD patients after TAVR, improvement in eGFR following SAVR has been demonstrated (17,18).Thus, improvement in cardiac functions after TAVR likely plays a significant role in an improvement in kidney function.
In patients with advanced CKD or dialysis dependence, studies have shown a higher rate of early and late mortality following TAVR (28,29).Despite having poorer outcomes after TAVR compared with non-dialysis patients, TAVR is comparable with SAVR in ESRD patients on dialysis based on a propensity-matched comparison of all Medicare feefor-service patients undergoing TAVR or SAVR (29).Data on renal function change after TAVR in advanced CKD (nondialysis stage 5 CKD) are limited.Unfortunately, the proportion of nondialysis stage 5 CKD undergoing TAVR at our institution during the study period was very small and thus we did not enroll in our study.Interestingly, a case of reversal of end-stage renal disease in a patient after TAVR was reported (30).Future studies are required to assess renal function change in this high-risk patient population.

Conclusion
In conclusion, our study demonstrates that change in eGFR is significantly related to baseline kidney function of patients undergoing TAVR.AKI significantly reduces eGFR at 6 months post TAVR.Without AKI after TAVR, patients with CKD, particularly baseline eGFR between 15 and 30 mL/min/1.73m 2 may benefit from TAVR by an improvement in eGFR at 6 months.

Limitations of the study
There are several limitations to our study.First, our study has a retrospective observational design and patients in our center are predominantly Caucasian populations, conceivably causing selection bias and restricting the generalizability of our findings.Second, the cause of a slight reduction in eGFR (approximately -4.0 mL/min/1.73m 2 ) at 6 months in non-AKI patients with baseline eGFR ≥ 60 mL/min/1.73m 2 is unclear.Calculating eGFR based on SCr has a few limitations (31,32).It is possible that patients after TAVR had improved function status and muscle mass, resulting in higher SCr levels (33).Unfortunately, our data regarding body mass index (BMI) at 6 months follow-up are limited.Future studies with a more accurate assessment of GFR are needed.

Table 1 .
Clinical characteristics and outcomes of TAVR a Continuous variables are reported as mean±standard deviation; b Categorical variables are reported as count (percentage).Abbreviations: ACEI, angiotensin-converting enzyme inhibitor; AKI, acute kidney injury; ARB, angiotensin II receptor blocker; CABG, coronary artery bypass graft surgery; eGFR, estimated glomerular filtration rate; NYHA, New York Heart Association; PCI, percutaneous coronary intervention; RBC, red blood cell; STS, Society of Thoracic Surgeons; TAVR, transcatheter aortic valve replacement.

Table 2 .
Change in eGFR at hospital discharge and 6 months after TAVR