|Year : 2015 | Volume
| Issue : 6 | Page : 1130-1134
|Predictive factors for increased aortic pulse wave velocity in renal transplant recipients and its relation to graft outcome
Muazam Ayub, Kifayat Ullah, Imtiaz Masroor, Ghias Uddin Butt
Department of Nephrology, Pakistan Institute of Medical Sciences, Islamabad, Pakistan
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|Date of Web Publication||30-Oct-2015|
| Abstract|| |
To evaluate aortic stiffness in renal transplant patients and to determine the correlation of renal insufficiency and estimated glomerular filtration rate (eGFR) with aortic pulse wave velocity (APWV), we studied 96 renal transplant patients followed-up at our center. We measured the APWV using transcutaneous Doppler flow recordings and the foot-to-foot method, and calculated the eGFR using the Modification of Diet in Renal Disease equation. The study included 81 (84.4%) males and 15 (15.6%) females. The mean age of the patients was 37.84 ± 10.10 years. The mean duration of transplant was 47.90 ± 34.40 months. The eGFR of the patients ranged from 1 to 120 mL/min, with a mean GFR of 72.6 ± 23.2 mL/min. Sixty-seven (69.8%) patients had eGFR > 60 mL/min and hence had stages 1 and 2 chronic kidney disease (CKD), 27 (28.1%) patients had eGFR 30-60 mL/min and hence had stage 3 CKD and two (2.1%) patients had eGFR <30 mL/min and hence had stages 4 and 5 CKD. The APWV of the patients ranged from 4 to 14.2 m/s, with a mean of 7.49 ± 2.47 m/s. A significant inverse correlation was found between the APWV and eGFR (Pearson correlation coefficient, -0.427, P = 0.00). The mean APWV was significantly higher among patients with higher CKD stage, P = 0.004. We conclude that the APWV is related to the renal graft dysfunction as measured by eGFR. The poorer the renal function, the higher was the APWV. Determination of the APWV may be helpful in predicting the outcome in renal transplant recipients.
|How to cite this article:|
Ayub M, Ullah K, Masroor I, Butt GU. Predictive factors for increased aortic pulse wave velocity in renal transplant recipients and its relation to graft outcome. Saudi J Kidney Dis Transpl 2015;26:1130-4
|How to cite this URL:|
Ayub M, Ullah K, Masroor I, Butt GU. Predictive factors for increased aortic pulse wave velocity in renal transplant recipients and its relation to graft outcome. Saudi J Kidney Dis Transpl [serial online] 2015 [cited 2021 Nov 29];26:1130-4. Available from: https://www.sjkdt.org/text.asp?2015/26/6/1130/168581
| Introduction|| |
Successful renal transplantation confers significant survival advantage compared with dialysis. , Nevertheless, mortality from cardiovascular disease (CVD) still remains at least three-to five-times higher in renal transplant recipients than in the general population.  Traditional risk factors do not fully explain the excess CVD risk in renal transplant patients, and accurate identification of the CVD risk in this population is warranted because of the longer potential life-time exposure owing to the improved graft survival. Large-artery damage is one of the most important factors responsible for the high prevalence of CVD in renal patients. Evaluation of central arterial stiffening can be helpful for more accurate risk stratification at a stage when intervention may still modify this risk. 
When the aorta stiffens,  the forward pulse wave travels faster and the arterial waves reflected from the periphery reach the heart early during systole, which leads to higher systolic and lower diastolic blood pressure with an increased cardiac workload and a decreased coronary perfusion pressure.  Accordingly, the aortic pulse wave velocity (APWV) is a predictor of cardiovascular outcome in patients with hypertension, ,, diabetes,  end-stage renal disease and elderly hospitalized subjects. 
The predictive value of the APWV is becoming increasingly recognized and is one of the classical indices of arterial stiffness, and can be directly measured by non-invasive techniques such as computerized oscillometry, tonometry and ultrasonography. The high diagnostic accuracy of the APWV ranks it as the gold standard method for assessing the central arterial stiffness. ,,
In milder forms of renal insufficiency, APWV is inversely related.  However, the impact of renal transplantation on recipient aortic stiffness remains poorly defined. Some studies in transplant patients have shown associations between the APWV and the outcome of transplantation. ,,,,
The aim of our study was to determine the factors related to increased APWV in transplant recipients and to evaluate the correlation of values of aortic PWV with the renal insufficiency (GFR estimates) in renal transplant patients.
| Materials and Methods|| |
This descriptive one-point study was conducted at the Department of Nephrology, Pakistan Institute of Medical Sciences (PIMS), Islamabad over six months (June-December 2013). We studied 96 stable renal transplant patients visiting our transplant clinic. The study was performed in accordance with the principles laid down in the declaration of Helsinki.
For each patient, the APWV was determined using transcutaneous Doppler flow recordings and the foot-to-foot method. The pressure wave-form was recorded non-invasively with a high-fidelity strain gauge transducer (SPT-301, Millar Instruments, Houston, Texas, USA). The aortic flow velocity and pressure were simultaneously recorded with a muti-sensor catheter that has an electromagnetic velocity probe and a pressure sensor mounted at the same location. Another pressure sensor at the catheter tip provided left ventricular pressure or a second aortic pressure to determine the APVW. The Flick cardiac output was used to scale the velocity signal to instantaneous volumetric flow.
Using pulse wave velocity, the effective reflection site distance was determined from both pressure and impedance data, implying that the region of the terminal abdominal aorta acts as the major reflection site in the normal adult man.
The augmented pressure was determined as the height of the late systolic peak above the inflection and the ratio of augmented pressure to the augmentation index. Left ventricular ejection time was determined from the foot of the pressure wave to the diastolic incisura. Augmented index ranged from 10 to 12 successive waves. Two simultaneous Doppler flow tracings were taken at the aortic arch and femoral artery in the groin using a non-directional Doppler unit with a hand-held probe, and were recorded at a speed of 100-200 mm/s. For aortic flow, the transducer was placed in the supra-sternal notch. The time delay (t) was measured between the feet of the flow waves recorded at these different points and averaged over ten beats. The distance (D) travelled by the pulse wave was measured over the body surface as the distance between the two recording sites. The APWV was calculated as pulse wave velocity = D/t and was expressed in m/s. The same specialist doctor performed all the measurements. All the data were collected on a performa.
| Statistical analysis|| |
Data were analyzed using SPSS version 15. The descriptive analysis was carried out and reported as means, with standard deviations and medians for continuous variables such as age of patients. For categorical variables such as gender, acute rejection, smoking, causes of renal diseases for transplantation and aortic stiffness, frequencies and percentages were reported. To determine the correlation of renal insufficiency (estimated GFR) with the APWV, the Pearson correlation coefficient was calculated. P-values <0.05 were considered significant.
| Results|| |
The study included 81 (84.4%) males and 15 (15.6%) females. The age of the patients ranged from 18 to 60 years, with a mean of 37.8 ± 10.1 years. The post-renal transplant duration ranged from eight to 132 months, with a mean of 47.9 ± 34.4 months.
The weight of the patients ranged from 48 to 70 kg, with a mean of 57.5 ± 5.3 kg. The height of the patients ranged from 150 to 167.50 cm, with a mean of 158± 3.36 cm. The body mass index of the patients ranged from 17.6 to 33.8, with a mean of 23.3 ± 2.83 [Table 1].
The reasons for renal transplant were as follows: Diabetes (35%), chronic glomerulonephritis (20%), polycystic kidney disease (3%), nephrosclerosis (hypertensive) (12%), systemic lupus erythematosis (SLE) (2.3%), stone disease (5%) and idiopathic (22.7%).
The eGFR of the patients ranged from 16 to 120 mL/min, with a mean GFR of 72.6 ± 23.2 mL/min [Table 1].
Depending on the eGFR using the MDRD equation, the patients were categorized into stages 1-5 chronic kidney disease (CKD). Sixtyseven (69.8%) patients had eGFR >60 mL/min and hence were in stages 1 and 2 CKD. Twenty-seven (28.1%) patients had eGFR 30- 60 mL/min and hence were in stage 3 CKD. Two (2.1%) patients had eGFR <30 mL/min and hence were in stages 4 and 5 CKD.
The APWV of the patients ranged from 4 to 14.2 m/s, with a mean of 7.49 ± 2.47 m/s, and the mean increased with the more advanced stage of CKD [Figure 1]. The APWV and the estimated GFR were inversely correlated (Pearson correlation coefficient was -0.427), and this correlation was statistically significant (P = 0.00) [Figure 2].
|Figure 1: The means of the aortic pulse wave velocity (APWV) among different chronic kidney disease (CKD) stages.|
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|Figure 2: The estimated glomerular filtration rate (eGFR) and the inverse correlation with the aortic pulse wave velocity (APWV).|
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The duration of transplant and the APWV was directly correlated (Pearson correlation coefficient was -0.103), but the correlation was not statistically significant (P = 0.361).
The mean blood pressure and the APWV were directly correlated (Pearson correlation coefficient was 0.176), and the relation was statistically significant (P = 0.05).
| Discussion|| |
Damage to the large arteries is a major factor in the high cardiovascular morbidity and mortality of patients with end-stage renal disease (ESRD). 
Bahous et al  demonstrated that in patients with ESRD, there was an increased prevalence of aortic stiffness determined by the measurement of APWV, which was a strong independent predictor of all-cause and cardiovascular mortality.
Verbeke et al attributed the increased arterial stiffness and wave reflections in renal transplant recipients to incomplete restoration of GFR and the presence of subclinical inflammation.  Zoungas et al and Kneifel et al found that impairment of the renal allograft function is associated with an increased arterial stiffness in renal transplant recipients. , Mitchell et al demonstrated that the impact of kidney transplantation on recipient aortic stiffness is dependent on donor age and suggest that ongoing damage to large arteries might contribute to the mechanism underlying the association of olddonor kidneys and increased cardiovascular mortality.  In our study, we found that APWV was significantly higher among patients with higher CKD stages and that the APWV and eGFR inversely correlated. Accordingly, the APWV correlated inversely with worsening of renal graft dysfunction.
Stiffness markers are increasingly used in population studies to evaluate cardiovascular morbidity and mortality. Our data suggest that in renal transplant subjects, stiffness markers may also be used as tools for the prediction of all-cause mortality. However, more studies on a larger scale are required to document the clinical utility of APWV in predicting the outcome in renal transplant recipients.
We conclude from our study that the APWV correlated with the renal graft dysfunction as measured by eGFR. The poorer the renal function, the faster was the APWV. Hence, the determination of the APWV can be helpful in predicting the outcome in renal transplant recipients.
Conflict of interest: None declared.
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Department of Nephrology, Pakistan Institute of Medical Sciences, Islamabad
[Figure 1], [Figure 2]
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