Systolic Dysfunction Portends Increased Mortality among Those Waiting for Renal Transplant
Angelo M. de Mattos*,
Andrew Siedlecki*,
Robert S. Gaston*,
Gilbert J. Perry,
Bruce A. Julian*,
Clifton E. Kew, II*,
Mark H. Deierhoi,
Carlton Young,
John J. Curtis* and
Ami E. Iskandrian
* Divisions of Nephrology, and Cardiology, Transplant Surgery, University of Alabama at Birmingham, Birmingham, Alabama
Correspondence: Dr. Angelo M. de Mattos, University of California, Davis, 2233 Stockton Boulevard, HSF Room 2014, Sacramento, CA 95817. Phone: 916-734-8620; Fax: 916-734-8351; E-mail: angelo.demattos{at}ucdmc.ucdavis.edu
Received for publication April 24, 2007.
Accepted for publication November 6, 2007.
Individuals waiting for a renal transplant experience excessivecardiovascular mortality, which is not fully explained by theprevalence of ischemic heart disease in this population. Overtheart failure is known to increase the mortality of patientswith ESRD, but the impact of lesser degrees of ventricular systolicdysfunction is unknown. For examination of the association betweenleft ventricular ejection fraction (LVEF) and mortality of renaltransplant candidates, the records of 2718 patients evaluatedfor transplantation at one institution were reviewed. During6355 patient-years (median 27 mo) of follow-up, 681 deaths occurred.Patients with systolic dysfunction (LVEF 0.40) had significantlylower survival than those with higher systolic function (median49 ± 3.1 versus 72 ± 4.0 mo; P < 0.001) buthad similar survival to patients with ischemia (48 ±2.5 mo). Multivariate modeling showed that those with systolicdysfunction were nearly twice as likely to die as those withnormal systolic function, adjusted for risk factors includingdiabetes, left ventricular hypertrophy, and ischemia (adjustedhazard ratio 1.7; 95% confidence interval 1.43 to 2.07). Inaddition, a graded, reverse association between LVEF and mortalitywas identified. In conclusion, systolic dysfunction is stronglyassociated with mortality, in a graded manner, in renal transplantcandidates.
Cardiovascular mortality is increased in chronic kidney disease(CKD).1 CKD has been proposed as an independent risk factorfor cardiac mortality,2 a phenomenon particularly evident amongdialysis patients.3 Reports on the mechanisms of cardiac deaththus far have drawn associations between CKD and outcomes ofatherosclerotic heart disease. Notwithstanding the high prevalenceof coronary artery disease in the dialysis population,4 ischemicevents would not account for most of the cardiac deaths reported.5An alternative explanation for the high mortality on the renaltransplant waiting list is needed. Overt heart failure (HF)is associated with high mortality rates in dialysis6 and posttransplantationpopulations.7 HF is commonly described as either diastolic orsystolic ventricular dysfunction (SD), the latter been gaugedby the left ventricular ejection fraction (LVEF). In the generalpopulation, all-cause and cardiac mortality risk increases withdeclining LVEF.8 Whether lesser degrees of SD, which are oftenasymptomatic, exert similar impact on mortality in patientswho have CKD and are awaiting transplantation is unknown. Furthermore,despite the association between ischemia and SD, previous reportshave not differentiated their specific roles to the prematurecardiac mortality in the CKD population.
Renal transplant candidates constitute an ideal population tostudy cardiac disease and mortality because (1) they are mostoften at stage 4 or 5 CKD at the time of evaluation, (2) theprevalence of cardiovascular disease is markedly increased,(3) follow-up is near complete while patients are on the waitinglist, and (4) mortality while on the waiting list is increased.Furthermore, the transplant evaluation process is fairly standardizedacross centers and focused on identifying cardiovascular disease.Most common, noninvasive techniques are used, including cardiacsingle-photon emission computed tomography (SPECT), which identifiescoronary artery disease by describing myocardial perfusion defects,9a procedure widely used and validated in the CKD population.10More recently, gated-SPECT imaging has allowed simultaneousmeasurement of LVEF and perfusion. This study describes therole of LVEF as an independent risk factor for all-cause andcardiac-related mortality in a population awaiting renal transplantation.
Between January 1, 1997, and June 30, 2004, 5305 individualswere evaluated for kidney transplantation at our institution.We excluded 76 recipients of previous nonrenal allografts and557 individuals with previous diagnosis of HF. In addition,458 patients were not considered transplant candidates and neverlisted. Of the remaining 4214 patients, 2718 (64.5%) fulfilledthe American Society of Transplantation guidelines criteriafor cardiac imaging and had stress-SPECT imaging completed andcomprise the final study cohort. Of these, 446 patients hadalso undergone two-dimensional echocardiogram (2DE). Demographicdata are depicted in Table 1. When compared with those withnormal LVEF, the SD group included more men, smokers, left ventricularhypertrophy (LVH), perfusion abnormalities, and longer exposureto dialysis. In contrast, patients with normal LVEF were older,had lower serum albumin and creatinine levels, and had higherbody mass index (BMI).
Table 1. Demographic data according to left ventricular systolic function
During 6355 patient-years of follow-up, 681 (25%) patients diedand 813 (30%) patients received a transplant. The median follow-upfor the entire cohort was 27 mo (range 0.3 to 95.8 mo). Deathwas due to a cardiac event in 43% of the known causes of death.Patients with normal LVEF survived substantially longer on thewaiting list than did those in the SD group (73 ± 4.3versus 44 ± 3.1 mo; P < 0.001). Further categorizationof the SD group by LVEF disclosed a stepwise relationship betweendegrees of SD and mortality (Figure 1A), which was also shownwhen cardiovascular death was the end point (Figure 2). Theproportion of patients removed from the waiting list withinthe first 2 yr as a result of transplantation was similar betweenthe SD (17%) and control subjects with normal LVEF (23%).
Figure 1. (A) Overall survival after evaluation according to categories of LVEF. (B) Overall survival according to presence of ischemia or systolic dysfunction (Systolic DF: left ventricular ejection fraction 40%) at the time of transplant evaluation.
Figure 2. Cardiovascular death survival after evaluation, according to categories of LVEF. All other causes of death were considered censoring events.
Univariate analysis of the stratified cohort disclosed a differencein longevity, with median waiting list survival for SD patientsof 49 ± 3.1 mo, significantly lower than 72 ±4.0 mo for control subjects (P < 0.001). Four-year mortalitywas 54.8% in the SD group. Patients with SD but no evidenceof coronary artery disease fared no better than patients inthe ischemia group, whose median survival was 48 ± 2.5mo (P = 0.8; Figure 1B). By excluding the 613 patients withischemia, a stepwise increase in all-cause mortality was documentedwith reduced LVEF (reference LVEF 51 to 60%; n = 800): Crudehazard ratio (HR) 2.9 (95% confidence interval [CI] 1.96 to4.27) for LVEF 30% (n = 60), 1.5 (1.09 to 2.09) for LVEF 31to 40% (n = 153), 1.3 (1.05 to 1.69) for LVEF 41 to 50% (n =436), and 0.9 (0.68 to 1.12) for LVEF >60% (n = 656). Thesame pattern was seen with cardiac mortality: Crude HR 6.4 (4.15to 10.01) for LVEF 30%, 3.5 (2.26 to 5.33) for LVEF 31 to 40%,1.8 (1.16 to 2.67) for LVEF 41 to 50%, and 0.8 (0.51 to 1.37)for LVEF >60%.
After accounting for the presence of ischemia and all otherrisk factors, the adjusted HR for SD was 1.7 (95% CI 1.43 to2.07), an independent association from diabetes, LVH, and abnormalperfusion (Table 2). A stepwise relationship is suggested bythe presence of a graded-reverse association between LVEF andmortality (Figure 3). This finding was further confirmed byentering LVEF into the models as a continuous variable (adjustedHR 0.975; 95% CI 0.968 to 0.981; P < 0.001; in other words,for each percent increment in LVEF, the adjusted mortality riskdecreased by 2.5%). Further analysis using cardiac death asthe outcome of interest showed similar results: adjusted HRfor SD 2.9 (95% CI 2.12 to 4.03). The models including the interactionterm "ischemia x SD" resulted in adjusted HR not different fromthe main-effect models. The models built across strata of riskfactors showed internal consistency because adjusted HR weresimilar across strata (dialysis and nondialysis, gender, race,age categories, and ischemia).
Figure 3. Adjusted HR for all-cause mortality, according to categories of LVEF. Adjustments were made for age, gender, SES, obesity, race, presence of diabetes, hypertension, LVH, preexisting ischemia, anemia, low albumin level, tobacco smoking, and duration of dialysis. **P < 0.001; *P = 0.02; #P = 0.1.
2DE was performed for 446 (16.4%) of the 2718 patients withSPECT data. There was a significant correlation between theLVEF measurements by SPECT and 2DE (r = 0.74, P < 0.001).The multivariable analysis confirmed the association betweenSD (LVEF 40%; n = 91) by 2DE and mortality (adjusted HR 1.8;95% CI 1.23 to 2.60) and cardiac mortality (adjusted HR 2.2;95% CI 1.29 to 3.91).
Although the prevalence of cardiovascular disease is markedlyincreased in the CKD population, a closer analysis of the mortalitydata suggests that ischemic events are not the predominant causeof death in this population, and other mechanisms may be operative.5Overt HF in the setting of ESRD portends a dismal outlook witha 3-yr mortality of 50% after diagnosis6 and 80% after hospitalizationfor HF.11 In a population-based study, the reported all-causemortality at 4 yr was 9.8% for individuals with LVEF 40%.12Little is known about mortality of patients with advanced-stageCKD and milder degrees of SD or regarding the relative importanceof ischemic and nonischemic causes. Unlike previous reports,this analysis focused on asymptomatic individuals without previousdiagnoses of HF: The sole reason for testing was to establishtransplantation candidacy. This approach allowed us to examinethe importance of lesser degrees of SD, adding a "dose-response"dimension that best described the continuum of exposure andavoiding arbitrary and potentially biased cutoff points forLVEF. This is the first work attempting to dissect the roleof an ischemic substrate in SD, by using stratified analysis,adjustments via multivariable modeling, and the analysis oftwo-way interactions. Finally, we used a single standardizedtechnique widely used clinically (SPECT) with validation byanother method (2DE), which allows for easy reproducibilityof our protocol.
The presence of a relationship between LVEF and mortality inour population was not unexpected; however, the magnitude ofsuch association was not anticipated, because we described analmost six-fold increase in mortality for transplant candidates(54.8% 4-yr all-cause mortality for individuals with LVEF 40%)when compared with the general population with similar degreeof SD.12 These findings offer clinically important observationsfor the care of patients with advanced-stages CKD. First, itprovides an alternative explanation to the ischemic model asthe leading mechanism resulting in the premature death of theseindividuals. Uremia has been associated with decrease in cardiaccontractility function in a rodent model.13 We hope that ourreport stimulates further research into the mechanisms and therapeuticstrategies focusing on myocardial contractility. Second, itidentifies a subset of the CKD population (those with SD, withor without ischemia) at significantly higher mortality riskwhile awaiting transplantation, where the role of medical interventionsand devices such as implantable cardiac defibrillators and pacemakersshould be studied. Transplantation is considered the therapyof choice for advanced stages of CKD, and improvements or evennormalization of LV function within the first year of engraftmenthave been described14,15; however, because of disparities inthe supply of organs and number of listed patients, transplantationis often delayed for months or years, which results in unacceptablyhigh mortality rates in individuals waiting for a kidney. Becausethe Centers for Medicare and Medicaid Services and the UnitedNetwork for Organ Sharing are currently evaluating kidney allocationpolicies in the light of "net benefit,"16 the significance ofLV function in influencing outcomes should be studied prospectively.
This observational study has limitations. Whereas ascertainmentof outcome was possible, specific causes of death were describedas "unknown" in one third of cases, which might have limitedsome of the analyses. Measurements of LVEF by two modalitieswere limited to the 446 patients who had undergone 2DE. Nonetheless,it is reassuring to find some correlation between the two techniques.LVEF measurements were not systematically repeated in a largeproportion of patients, and no adjustments for interim therapieshave been made. For full ascertainment of the presence of coronaryartery disease, angiograms should have been performed for allpatients with decreased LVEF; however, because of expenses andrisks associated with the procedure, this approach seems unfeasible.No assessment of diastolic dysfunction was obtained, therebypreventing the analysis of this contributing factor in mortality.Finally, our data were limited to the period spent on the waitinglist; therefore, the impact of transplantation on survival ofpatients with CKD and SD should be the focus of future research.
In conclusion, we reported a significant association betweenSD and mortality in patients awaiting renal transplantation.This association was independent of ischemia and other cardiovascularrisk factors. The cumulative mortality for patients who hadSD and were awaiting transplantation was almost six-fold higherthan the reported mortality for similar LVEF in the generalpopulation. Widely available and minimally invasive testingcould identify this high mortality risk subset of the CKD population.
This is a single-center observational study using data collectedprospectively in a large transplant center. The University ofAlabama at Birmingham (UAB) Renal Transplant Database containsdetailed information pertaining to all individuals seeking renaltransplantation at UAB since 1993. Three research nurses andone supervising data analyst continuously update the patients'files. Several sources of information, including contact withpatients and patients' families, referring physicians, UAB andother medical facilities records, death certificates, and theUS Social Security Death Master File are used to ascertain mortalitycorrectly.
We excluded all patients with previous heart, lung, or livertransplants and those not considered transplant candidates andthus never placed on the waiting list. Because we focused onpatients without clinically manifested HF, we excluded patientswith previous diagnosis of congestive HF, cardiomyopathy, orsignificant cardiac valvulopathy. For the purpose of this study,the evaluation date was the date of measurement of LVEF by SPECT.Survival time was estimated from the date of evaluation to thedate of death; date of transplantation; or until December 31,2005. Mortality as a result of cardiac event was defined bydeath certificates (primary or contributing cause) or medicalrecords and often confirmed with health care provider or familymembers.
Pharmacologic stress-SPECT perfusion imaging detects and quantifiesischemic and scar burden. From pooled data of 11 studies, thesensitivity and specificity were 85 and 91%, respectively, indetecting ischemia.9 Furthermore, at UAB since 1997, the SPECTimages were acquired in the gated mode, which allows measurementof LVEF. The EF, by gated SPECT, has in multiple studies correlatedwell with EF measured by other methods such as contrast angiography,2DE, and magnetic resonance imaging. It has the major advantageof being automated and reproducible.17 Cardiac ischemia andSD in combination portend a worse outcome. Presence of ischemiaor scar limits the capacity to recover LV function.18,19 Previouswork found that recipients with myocardial perfusion defectshad a higher cardiac event rate within 42 mo of transplantation.20Our institution follows the renal transplant candidates evaluationguidelines put forth by the American Society of Transplantation21;perfusion scans (stress-SPECT) are performed routinely in candidateswho are older than 50, in individuals with diabetes for longerthan 10 yr, in patients with previous cardiovascular events(CVE), and in patients with at least two of the following riskfactors: LVH, family history of ischemic heart disease, dyslipidemia,or significant smoking history. Perfusion scans were performedaccording to the Guidelines for Nuclear Cardiology Procedures22and were routinely scheduled at midweek to reduce the influenceof volume overload and uremia. All echocardiograms performedduring the evaluation period were retrieved.
Following the Guidelines for Nuclear Medicine Procedures,23LVEF 40% defined SD; for the purpose of this study, ischemiawas defined by either a stress-SPECT showing a perfusion abnormality(ischemia, scar, or both) or a history of previous CVE includingrevascularization. Anemia was defined by a hematocrit <33%;socioeconomic status (SES) was categorized by using educationallevel attained as a surrogate marker (<12 yr of schoolingdefined low SES); hypertension was defined by a systolic BP>140 mmHg, a diastolic BP >90 mmHg, or the use of antihypertensivedrugs. LVH was diagnosed by 12-lead electrocardiogram24 or 2DE.25BMI was calculated by weight (kg)/square of height (m). Durationof dialysis, age, gender, race, diabetes, serum albumin andcreatinine levels, and tobacco smoking history were extractedfrom the database. The study protocol was reviewed and approvedby the institutional review board for human use at UAB.
Statistical Analyses
Distribution of patients' characteristics at evaluation wastested by 2 analysis or t test as appropriate. Results weredescribed as means ± SD. Event-free survival curves wereconstructed using the product-limit method (Kaplan-Meier), anddifferences among survival curves were estimated by the log-ranktest. Cox regression modeling was used to estimate crude (univariate)and adjusted (multivariate) risks. Variables entered in themodels were the ones described as being associated with cardiovascularmortality: Age, gender, SES, obesity, race, presence of diabetes,hypertension, LVH, preexisting ischemia, anemia, low albuminlevel, tobacco smoking, and duration of dialysis. Direct visualizationof Log [–log (survival time)] versus log (survival time)plots and examination of Martingale residuals26 were used tovalidate the proportionality of hazard increments assumption.LVEF by SPECT, age, BMI, and duration of dialysis were testedin the models both as a continuous and as categorical variables(LVEF 30, 31 to 40, 41 to 50, 51 to 60, or >60%; age <50or 50; BMI <30, 30 to 35, or >35 kg/m2; dialysis >2,1 to 2, or <1 yr or no dialysis). The decision to describea variable either as continuous or categorical was based onthe best fit of the multivariable models. We attempted to distinguishthe impact of ischemia and SD on mortality by performing a stratifiedanalysis in which the study cohort was divided into three groups:(1) SD (LVEF 40%) without perfusion abnormality (ischemia orscar) or previous CVE, (2) ischemia (previous CVE or perfusionabnormalities), and (3) normal control subjects (LVEF >40%,no previous CVE, and normal perfusion pattern). We then performedmultivariable analysis in which the attributed risk for SD wasadjusted by the presence of ischemia and other cardiovascularrisk factors. In addition, models including the interactionterm "ischemia x LVEF" were built and their HR compared withmain-effect models. Subsequent analyses were conducted usingcardiac death as the outcome of interest. Internal consistencywas assessed by building several models across strata of riskfactor categories: Dialysis and nondialysis, male and female,older and younger than 50 yr, black and nonblack, with and withoutischemia. Estimated risks were reported as HR with corresponding95% CI. All P values reported were two-sided. SPSS 11.5 forWindows (SPSS, Chicago, IL) software was used in the analyses.
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