Longitudinal changes in kidney function following heart transplantation: Stanford experience

Abstract

Many heart transplant recipients experience declining kidney function following transplantation. We aimed to quantify change in kidney function in heart transplant recipients stratified by pre-transplant kidney function. A total of 230 adult heart transplant recipients between May 1, 2008, and December 31, 2014, were evaluated for up to 5 years post-transplant (median 1 year). Using 19 398 total estimated glomerular filtration rate (eGFR) assessments, we evaluated trends in eGFR in recipients with normal/near-normal (eGFR ≥45 mL/min/1.73 m² ) vs impaired (eGFR <45 mL/min/1.73 m² ) kidney function and the likelihood of reaching an eGFR of 20 mL/min/1.73 m² after heart transplant. Baseline characteristics were similar. Immediately following heart transplant, the impaired pre-transplant kidney function group showed a mean eGFR gain of 9.5 mL/min/1.73 m² (n = 193) vs a mean decline of 4.9 mL/min/1.73 m² (n = 37) in the normal/near-normal group. Subsequent rates of eGFR decline were 2.2 mL/min/1.73 m² /y vs 2.9 mL/min/1.73 m² /y, respectively. The probability of reaching an eGFR of 20 mL/min/1.73 m² or less at 1, 5, and 10 years following heart transplant was 1%, 4%, and 30% in the impaired group, and <1%, <1%, and 10% in the normal/near-normal group. Estimates of expected recovery in kidney function and its decline over time will help inform decision making about kidney care after heart transplantation.

Keywords: combined/dual heart-kidney transplant; heart transplant; kidney transplant; kidney/renal function.

Figure 1

depicts the longitudinal changes of eGFR and serum creatinine over time stratified by baseline kidney function. Kidney function declined in both groups over time, but the group with impaired pre-transplant kidney function demonstrated improvement in kidney function in the first month following transplant with an average eGFR gain of 9.5 (95% CI: 6.6, 12.6) ml/min/1.73m² compared with a decline of 4.9 (95% CI: 3.2, 6.6) ml/min/1.73m² in the normal/near-normal kidney function group (p<.001). Estimated glomerular filtration rate subsequently declined at a rate of 2.9 (95% CI: 2.8, 3.0) mL/min/1.73m²/year in the normal/near-normal group and 2.2 (95% CI: 1.8, 2.6) mL/min/1.73m²/year in the impaired group. The probability of reaching an eGFR of 20 ml/min/1.73m² or below (a point at which patients are eligible for kidney transplant listing) at 1, 5, and 10 years after heart transplant was <1%, 4%, and 30% in the impaired group and <1%, <1% and 10% in the normal/near normal group. In Table 2 we present some hypothetical cases with baseline eGFR’s of 22, 33, 44, and 66. The patients with baseline values between 22 and 44 show an immediate increase in eGFR 1 month post transplant but a more rapid decline out to 10 years post transplant compared to the patient with a baseline eGFR of 66. To quantify the regression to the mean effect, we measured the overall mean (3.996) standard deviation (.437), and correlation (0.18) among log eGFR measurements in our cohort. This gave a regression to the mean effect on the log eGFR of only 0.07 (this translates to a difference in eGFR of 1.07 units).

Figure 2

shows the cumulative incidence of CKD stage 5, ESRD (top) and death (bottom) for abnormal and normal kidney function at baseline over the 5 years of follow-up. The figures are adjusted for competing risk of death and CKD and show the p-value for the Grays test of homogeneity. Patients with an abnormal baseline eGFR have a higher incidence of CKD (p=0.01) and a similar incidence of death (p=0.9) when compared to patients with normal or near normal kidney function at baseline.