Platelets and Patent Ductus Arteriosus: Is there a Any Association Really?

Patent Ductus Arteriosus (PDA) can cause mortality and morbidity such as respiratory distress syndrome (RDS), pulmonary hemorrhage, bronchopulmonary dysplasia (BPD), intraventricular hemorrhage (IVH), necrotizing enterocolitis (NEC), retinopathy of prematurity (ROP) [1]. For this reason, early diagnosis and treatment of PDA is the most important point. The main diagnostic method of PDA is Doppler echocardiography [2]. However, there is no clearly consensus on diagnosis of hemodynamically significant patent ductus arteriosus (hsPDA). Therefore, new diagnostic methods of PDA are needed. A great number of the studies have shown that platelets play a role in closure of the PDA [3-6]. The first of these studies, Echtler et al. studied the relationship between ductal closure and platelet parameters in animals [3]. In the same study, the ductus arteriosus did not close (thus, remained permanently open) in animals in which platelet functions were compromised. After this study, they studied on premature infants about relationship between ductal closure and platelet parameters. According to this study, a low platelet count and a low PDW were risk factors for PDA. However, studies that reported that platelet parameters were not associated with PDA were also published [7-11]. We also wanted to contribute to clarify the relationship between PDA and platelet parameters.


Introduction
Patent Ductus Arteriosus (PDA) can cause mortality and morbidity such as respiratory distress syndrome (RDS), pulmonary hemorrhage, bronchopulmonary dysplasia (BPD), intraventricular hemorrhage (IVH), necrotizing enterocolitis (NEC), retinopathy of prematurity (ROP) [1]. For this reason, early diagnosis and treatment of PDA is the most important point. The main diagnostic method of PDA is Doppler echocardiography [2]. However, there is no clearly consensus on diagnosis of hemodynamically significant patent ductus arteriosus (hsPDA). Therefore, new diagnostic methods of PDA are needed. A great number of the studies have shown that platelets play a role in closure of the PDA [3][4][5][6]. The first of these studies, Echtler et al. studied the relationship between ductal closure and platelet parameters in animals [3]. In the same study, the ductus arteriosus did not close (thus, remained permanently open) in animals in which platelet functions were compromised. After this study, they studied on premature infants about relationship between ductal closure and platelet parameters.
According to this study, a low platelet count and a low PDW were risk factors for PDA. However, studies that reported that platelet parameters were not associated with PDA were also published [7][8][9][10][11]. We also wanted to contribute to clarify the relationship between PDA and platelet parameters.

Materials and Methods
This observational, retrospective cohort study was conducted between August 2017 and 2018. Preterm infants that less than 34 gestational weeks were examined to echocardiography at the time of detected clinical findings or within 24-72 h after admission to our unit, routinely [12]. The patients were divided into two groups according to echocardiography findings randomly; hsPDA require ductal closure treatment and non-hsPDA. hsPDA was defined when at least one of the clinical findings associated with PDA was present: a hyperdynamic precordium; a sustained murmur; tachycardia; hypotension; oliguria; an increased pulse pressure; an increase in ventilation pressure and/or oxygen demand; and at least one echocardiographic finding: ductal diameter ≥1.5mm, left atrium/ aortic root ratio ≥1.5, and/or diastolic flow failure in the abdominal aorta or inverse flow. We applied intravenous or oral ibuprofen to close the hsPDA. Intravenous or oral paracetamol was given in cases who ibuprofen is unsuccessful or contraindicated. After treatment, echocardiography was performed again, and the PDA was classified as open or closed. We excluded those with conditions that might cause inflammation or affect platelet count and/or function

Statistical Analysis
Statistical analyses were performed using SPSS for Windows ver. 22.0 (SPSS Inc., Chicago, Illinois). The paired samples t-test and independent samples t-test were used to compare continuous variables. Continuous variables are presented as means ± SDs, and categorical variables are given as frequencies with percentages. A p-value less than 0.05 was considered statistically significant.

Results
258 newborns under 34 weeks were admitted to our unit, of whom 121 were excluded. The study group consisted of 72 premature infants with hsDPA who applied ductus closure treatment and 65 premature infants without hs DPA or spontaneously closed PDA consisted of the control group ( Figure   1). The demographic characteristics of both groups are shown in Table 1. The mean gestational age and the mean birth weight of the study and control groups were, respectively, 31.4±3.8 vs. 32.3±4.5 weeks (p=0.12); 1441±347 vs. 1,539±286g (p=0.08). There was no difference between two groups in perinatal parameters. The platelet parameters of both groups are shown in Table 2. There was no difference between the two groups in terms of MPV, Platelet count and Platelet mass index. However, PDW and PCT were statistically significantly in the study group than the control group.   As the ductus wall is thin, contraction is inadequate and endothelial damage and platelet aggregation thus develop because of vesselwall hypoxia. Based on this hypothesis, it was claimed that platelet counts were important in terms of DA closure in preterm infants, as they are in the pathophysiology of adult vascular diseases [14,15].
However, this hypothesis is not supported by the fact that platelet transfusion does not reduce the incidence of PDA in preterm newborns with immune thrombocytopenia and does not increase the PDA frequency in term newborns with severe thrombocytopenia secondary to Wiskott-Aldrich syndrome [16][17][18][19][20].
In Fujioka et al. [21][22][23]. the platelet count was not related to PDA diagnosis or treatment success. On the other hand, Echtler et al. [3,5,6] reported that a low platelet count increased the hsPDA incidence [24][25]. In some works performed after these contradictory studies, it was reported that large platelets create a greater potential risk of prothrombotic reactions; large platelets are more aggregated than small and normal platelets given the greater number of receptors such as thromboxane A2-B2 and glycoproteins IIb-IIIa on the surfaces of large platelets. It was suggested that the increased metabolic and enzymatic activities of dysfunctional thrombocytes, rather than the platelet count, were associated with PDA [26][27][28][29]. We sought to identify parameters related to platelet function associated with PDA. These remain controversial; all of MPV, PDW, PCT, and platelet mass index have been associated with cardiovascular diseases in adults [30][31][32][33][34][35]. In addition, in a limited number of studies on neonates, the MPV and PDW were shown to be associated with prematurity complications such as RDS and BPD [36][37].
In our study, no difference was found between the platelet counts of the hsPDA and control groups at 48-72 h and 7. day. In addition, there was no difference between the platelet counts of newborn who did and did not fail treatment. In conclusion, the platelet count was not a predictor of hsPDA diagnosis or treatment success. The results of our study contradict those of the two major meta-analyses conducted by Simon et al. and Mitra et al. but support the cohort study of Sallmon et al. [18][19][20]. PCT was lower and PDW was higher in the study groups than control groups and the difference between the two groups was statistically significant.
However, MPV and platelet mass index were similar in both groups.
Thus, we conclude that the PCT and PDW can be used to predict hsPDA but not treatment success. Demirel and Dizdar et al. [4].
reported that the PDW was higher in preterm infants with hsPDA than in control groups [38,39]. Bekmez et al [40]. reported that a low PCT increased the hsPDA incidence Demir et al. [41]. found a high MPV and a low platelet mass in the hsPDA group. We also excluded patients who received ibuprofen as ductus closure therapy because of potential effects on platelet count and functions. Infants born to mothers with prior pre-eclampsia, which affects platelet count and ductal flow because of the increased placental resistance, were also excluded [42][43][44]. We also excluded infants with perinatal asphyxia associated with an increased PDA, thrombocytopenia, and platelet dysfunction [45][46][47]. Newborns whose mothers had earlier received steroids were excluded because of possible effects on the platelet count. We thus excluded all pathologies that may affect platelet count and function and induce inflammation. There were some limitations of our study. The first limitation of our study is that it was retrospective in nature. The second limitation is modest sample size. As a result, according to our study, platelet count, MPV and platelet mass index cannot be used to predict either hsPDA or treatment success, but a low PCT and high PDW can be used predict hsPDA but not treatment success.