Prolonged haemodialysis increases the risk of the impairment of global longitudinal strain in patient after kidney transplantation and a preserved ejection fraction of left ventricle

Background. Patients with chronic kidney disease, including these after kidney transplantation (KTx), have higher cardiovascular mortality. Global longitudinal strain (GLS) detects subtle changes in the left ventricle (LV) and is more sensitive predictor of cardiovascular mortality than the LV ejection fraction (LVEF).The aim of this study was to assess the prevalence of impaired GLS among kidney transplant recipients with preserved LVEF. We also aimed to identify possible clinical factors responsible for GLS impairment. Methods. A total of 79 patients following KTx with preserved LVEF and no history of cardiac disease were evaluated. We assessed echocardiogram parameters with the calculation of GLS, laboratory parameters, presence of diabetes, hypertension, duration of haemodialysis (HD) and time after KTx. An impaired GLS value was set on ≥-18%. The multivariate stepwise logistic regression analysis were used to identify the factors related to impaired GLS. Results. Among 79 (42 females, mean age 60.3) kidney transplant recipients with preserved LVEF, 39% had impaired GLS. ROC analysis revealed that the cut-off point for the prediction GLS ≥-18 % by HD duration is more than 28 months (AUC 0.67 (95%CI 0.545-0.79; P=0.007). In multivariate stepwise logistic regression analysis for variables related to impaired GLS duration of HD more than 28month is associated with GLS ≥-18( OR 4.06; 95CI (1.45-11.34) P=0.008). Conclusions. In our study group, a total of 39% of KTx patients with preserved LVEF had impaired GLS. The risk factor of GLS impairment was a prolonged duration of HD (>28months) prior to the transplantation procedure.


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GLS is a percentage change in length of myocardial segment in systole and is presented as negative value. The prognostic value of impaired GLS of LV is well documented among patients with various cardiovascular diseases. In recent years some studies have confirmed impaired GLS as a predictor of all-cause and cardiovascular mortality among patients with CKD [6,7]. So far, there have been no studies on clinical factors affecting GLS impairment in kidney transplant recipients.
The aim of the study was to assess the prevalence of impaired GLS among kidney transplant recipients with preserved LVEF and to identify the clinical factors for reduced GLS in these patients.

Patient population
We performed a retrospective analysis of patients after a successful KTx. The patients were derived from the Transplant Outpatient Clinic, which come from the Department of analyzed. From this study group, patients who underwent echocardiographic examination with GLS assessment in the central echo room of the hospital were selected. The indication for the echocardiographic examination was usually physical dyspnea reported by the patient.Inclusion criteria were ejection fraction above 50%, presence of sinus rhythm and good visualization enabling GLS assessment. Exclusion criteria were severe or moderate valvular pathology, presence of atrial fibrillation or coronary artery disease in medical history. Finally, 79 patients were included in the study. Patients' demographic and clinical data were extracted from the patient's electronic medical records and then verified with paper charts. Demographic and clinical data included: age, gender, body 5 mass index (BMI), presence of diabetes (DM), hypertension (HTN), duration of haemodialysis (HD) before and after KTx. In addition, the type of immunosuppressive regimen based on the mammalian target of rapamycin inhibitors (mTORi) or calcineurin inhibitors (CNI) has been reported. Each patient had their blood pressure measured prior to echocardiography. Laboratory variables included both serum lipid concentration and assessment of renal graft function (e.g. serum creatinine, estimated glomerular filtration rate (eGFR), and uric acid). The eGFR was calculated based on the Modification of Diet in Renal Disease formula. In the case of GFR, a mean GFR was used for the analysis, which was obtained from the previous 3 tests conducted every 3 months in the last six months before the echocardiographic examination. The last collected variables refer to the date of the echocardiographic examination.

Echocardiography
Transthoracic echocardiography examination was performed for each patient for clinical indications using a high-resolution ultrasound machine (GE Vivid E 9, Horten, Norway) in accordance with the European Society for Echocardiography recommendations. All measurements and STE analysis were performed by an experienced echocardiographer (O.M). The linear measurements of the LV, such as end-diastolic diameter (LVEDd), intraventricular end-diastolic diameter (IVDd), posterior end-diastolic wall thickness diameter (PWTd), were obtained by using the M-mode ultrasound imaging. Based on these measurements the LV mass (LVM) was calculated and then indexed to the body surface area (BSA).
The upper limit of the LV mass index (LVMI) was set on 115g/m 2 for men and 95g/m 2 for women. Severe LVH was considered as LVMI≥149/m 2 and ≥122/m 2 for men and women, respectively. The relative wall thickness (RWT) was calculated for classified LV geometry, 6 using the following formula: RWT = (2PWTd)/LVEDd). The concentric LVH was diagnosed in the presence of the following factors: increased LVMI, normal LV size and RWT>0.42, whereas the eccentric LVH was diagnosed in the presence of an increased LVMI, increased LV size, and RWT≤0.42. The LVEF and was measured using the modified Simson's rule. A similar formula was used for measured left atrium volume which was then indexed by BSA.
The Doppler echocardiography was used to evaluate the diastolic function of LV such as the early diastolic mitral inflow (E) and late diastolic mitral inflow (A) in order to derive E/A ratio and deceleration time. Doppler tissue imaging was performed in a four-chamber view to measure lateral and septal velocities of the mitral annulus, such as the peak early diastolic filling velocity (e) and the peak late diastolic filling velocity (a). Therefore, the ratio of E to average e (lateral+septal/2) was evaluated. GLS was measured using a twodimensional STE and was then provided by the software as the average peak systolic longitudinal strain value of the three apical views and expressed as a negative value. The normal value of GLS was considered below -18%. [8,9]. This value as a cut-off point was also adopted in studies of subclinical systolic dysfunction in patients with diabetes [10].Basically, the more negative the GLS value, the better cardiac function. Additionally, our study population was divided into two groups according to LV GLS <-18% (with normal GLS) and ≥-18% (with impaired GLS).

Statistical analysis
Continues variables were presented as mean and standard deviation or medians and interquartile ranges depending on their distribution and compared with Student's T-test or Mann Whitney U test as appropriate. The Shapiro-Wilk test was used to assess the variables' distribution. The discrete variables were presented as nouns and percentages and were compared with the Chi-square test with Yates correction when indicated. The duration of HD before KTX and time elapsed after KTx were analysed both as continuous 7 variables and were dichotomised using ROC curve analysis for prediction of GLS ≥ 18%.
The multivariate stepwise logistic regression analysis was performed to find independent variables related to GLS ≥-18%. The factors which in univariate analysis differ between groups with P less than 0.15 and variables of clinical significance were used as independent variables. A P-value of less than 0.05 was regarded as statistically significant.

Results
A total of 79 (53% females) kidney transplant recipients at mean (SD) age 60.3 (11.5) were included in the study. Among the reasons of KTx were: glomerulonephritis in 28 The demographic and clinical characteristic of the two groups is shown in Table 1. Both groups were similar in terms of age, women's presence and BMI.
The frequency of administration of the mTORi-based immunosuppressive regimen was similar in two groups. Only 2 patients from Group 1 and 4 patients from Group 2 received mTORi de novo after KTx as a protocol drug. While 10 patients from Group1 and 16 from Group2 were converted from immunosuppressive regimen based on CNI to mTORi due to 8 neoplastic disease or signs CNI nephrotoxicity treatment.. There were no significant differences between groups in the incidence of DM, HTN. The laboratory results were similar in both groups and are presented in Table 2.Althought all patients had preserved LVEF, Group 1 had significant higher LVEF. Echocardiographic parameters in study groups are shown in Table 3 LVH was observed in 65 (82%) patients. The incidence of severe LVH as well as concentric and eccentric LVH were similar in both groups. There was no significant difference between groups in Doppler parameters assessing the diastolic function of LV. The mean

Discussion
This study demonstrates that impaired GLS occurs in nearly 40% of KTx patients with preserved LVEF and that GLS impairment is related to the duration of HD before KTx 9 In our study, the majority of KTx patients had severe LVH. The LVH did not correlate with the impaired GLS. LVMI was comparable in patients with or without impaired GLS.
Although patients with damaged GLS had a statistically lower EF, both groups had preserved EF, which is considered a good prognosis. Impaired GLS in CKD patients is an indicator of decreased LV contractility probably due to LV remodelling with increased accumulation of extracellular matrix and myocardial fibrosis. Recently, Sandal et al. found that congestive heart failure, but not coronary artery disease, is the most common cause of cardiovascular events following KTx [11].

That finding confirms earlier outcomes of studies based on the United States Renal Data
System conducted on thousands of patient [12]. The consensus was that the KTx is a state of "accelerated heart failure" rather than "accelerated atherosclerosis".
The advantages of LV GLS over LVEF in the assessment of LV systolic function have been demonstrated in several studies in the general population as well as cardiac disease and in CKD patients. The previously reported prevalence of impairment of LV GLS in CKD patients with preserved LVEF ranged from 17 to 60%.The differences can be attributed to the selection of CKD patients for the studies (with various stages of CKD from 1 to 5, including patients with cardiac morbidity, e.g. history of myocardial infarction, CABG, atrial fibrillation, heart failure), and various cut-off values of GLS (-18 to -15%). Panoulas et al. in their study carried out on 106 CKD patients with LVEF≥55% and no history of cardiovascular disease or its symptoms, defined the GLS impairment as values greater than -16% [13]. The incidence of impaired GLS was dependent on the CKD stage and was only 3.4% in stage 1 or 2, 39.5% in stage 3, and 25.6% in stage 4 and 5. While the greatest LVMI was observed in patient 4-5 stage. In patients with impaired GLS, the authors observed an increased rate of adverse cardiovascular events (including general mortality, coronary artery disease, and length of hospitalization for heart failure) during follow-up of 30.7±11.7 months. They also suggested that impaired GLS may be a result of microvascular ischemia and myocardial fibrosis as the studied group did not have an evident disease in epicardial arteries, which had been confirmed by elective angiography.Hensen et al. showed LV systolic dysfunction defined by LV GLS ≤15.2%. in 32% of predialysis and dialysis patients with LV ejection fraction ≥50%. The cut-off value for impaired GLS was obtained from 2 standard deviations below the mean LV GLS value derived from healthy controls [14]. Ravera  In prospective observational studies of patients with hypertension or diabetes, the cut-off points for GLS described as LV systolic dysfunction and associated with adverse cardiovascular events were similar. The Lee et al study of 94 patients with hypertension showed that GLS> 17.6% was associated with cardiovascular adverse events [17] In Holland et al. study, with asymptomatic patients with diabetes and preserved LVEF, the all-cause mortality was related with GLS above 18.9% [18] Based on oncological studies with cardiotoxicity of chemotherapy, it was established that not a specific threshold but decrease in GLS by more than 15% from the baseline statement is associated with significant LV systolic dysfunction, which requires cardioprotective treatment [19].
Many previous studies have shown that KTx has a beneficial effect on LV structure and function compared to dialysis. The studies based on a series of conventional 11 echocardiograms showed an improvement in LVEF after KTx. Ravinder et al. showed improvement not only in LVEF but also in functional status of heart failure and increased survival rate after KTx [20]. Paoletti et al. in their study also proved that the LVH regression following KTx was a predictor of a better long-term clinical outcome [21].
However, the LVM regression has not been confirmed by CMR what may raise doubts about the reversibility of LVH in transplant patients [22]. LVEF and LV volumes improved, pointing to a reduction of LVH [25].
Our study indicates that the duration of HD longer than 28months leads to 4-fold increase of impaired GLS. This results may suggest that the structural abnormalities of myocardium progress on HD and fail to subside after KTx. Our study for the first time showed the relation of subclinical LV systolic dysfunction with a duration of HD before KTx.
Relationship between LVH and duration of HD was reported. Foley et al. showed that after 18 months of dialysis 62% of the patients had increased LV mass volume index and 49% of them developed overt LV failure [26].
Many studies showed, that long time on HD before transplantation is associated with Their retrospective study confirmed that preemptive KTx, as well as a short time of dialysis <1 year prior to transplantation in recipients of living kidney donor were associated with higher 5-year patient survival. During the last 2 decades, the percentage of patients with preemptive KTx raised from 10.9% to 17% [28].
During HD the patients are exposed to multiple factors such pressure and volume overload, activation of renin-angiotensin system chronic inflammation, 13 hyperhomocysteinemia, advanced glycosylation end products, anaemia, endothelial dysfunction, oxidative stress, arteriovenous access. The cumulative effect of these factors leads to cardiac and vascular damage. Dialysis treatment compared to preemptive KTx was associated with increased stiffness and reduced vascular compliance. Yet, the important role of FGF23 should emphasized, which serum level increase over 400 times in hemodialysed patients. FGF23 levels are associated with LVH, and myocardial fibrosis, and increased cardiovascular mortality [29].
Ten patients in our study with preemptive KTx had normal GLS, although they were mean 95 months after transplantation and had lower eGFR (41.3 mL/min/1.73m 2 ) This outcome emphasises the most harmful role of HD on systolic function on LV.

Study Limitation
The first limitation is the lack of comparison with echocardiograms before and after hemodialysis. Such a comparison would provide more information about the course and possible reversibility of GLS damage. The second limitation is the evaluation of only longitudinal strain, which only evaluates subendocardial myofibres without assessment of radial and circumferential strain, that evaluate midwall myofibres.

Conclusions
In total, 39% of kidney transplant patients with preserved LVEF and no history of ischemic heart diseases had reduced LV contractility defined as impaired GLS.
The main risk factor of GLS impairment was a long period of HD (>28) prior to the transplantation procedure. The consent for publication

Availability of data and materials
The datasets used and analysed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.

Funding.
The study was conducted by employees of the Wroclaw Medical University as part of scientific activity.

Authors' contributions
OM performed the echocardiography examinations and was a major contributor in writing the manuscript. OM, GA, SM contributed to the design of the research. SM BM, LK KM analyzed and interpreted the patients' data regarding haemodialysis and transplantation.
All the authors were involved in data collection. OM, ZD performed statistical analysis. All authors read and approved the final version of the manuscript.