Platelet hyperaggregability, including Sticky Platelet Syndrome has been identified as a cause of thrombotic conditions including venous thrombosis and foetal loss. The laboratory diagnosis of classical Sticky Platelet Syndrome is based on enhanced platelet aggregation responses to submaximallevels of adenosine diphosphate and epinephrine by optical aggregometry techniques. This study sought to evaluate platelet hyperaggregability by Multiple Electrode Aggregometry, PFA-100 analysis and quantitative analysis of associated platelet parameters as an adjunct to thrombophilia screening. Forty nine patients and 50 control subjects (nonna! volunteers) were investigated in this study. Multiple Electrode Aggregometry was performed on all participants at standard and submaxima! concentrations of adenosine diphosphate, collagen, thrombin receptor agonist protein-6, arachidonic acid and epinephrine together with PFA-100 closure times, immature platelet fraction, mean platelet volume, plateletcrit, platelet distribution width and platelet-large cell ratio measurement. Statistically significant differences in PFA-100 (collagen/adenosine diphosphate cartridges) were observed between the test and control cohort. Observations of study results and clinical presentation in the test cohort identified results outside of reference ranges in symptomatic and asymptomatic test individuals in whom no abnormalities were recorded by conventional thrombophilia testing. Binary logistic regression models identified that mean platelet volume levels were found to contribute significantly to the prediction of whether an individual presented as a member of the test or control cohort. Mean platelet volume was also shown to contribute significantly to predicting whether a participant feU into test and control subgroups. Study results suggest that evaluation of platelet reactivity by whole blood platelet analysis may play a role as an adjunct to conventional laboratory investigation of patients who present for thrombophilia screening.

Background: Venous thromboembolism (VTE) in one of the leading causes of maternal morbidity and mortality in high income countries. However there is a surprising shortage of evidence which allows us to accurately predict which women are at high risk which has hindered prevention to date. Therefore the aim of this thesis is to measure the occurrence of and risk factors for VTE during the antepartum and postpartum periods. Methods: Electronic health records from women of childbearing age (15-44 years) were identified from two separate databases; The Health Improvement Network (THIN) between 1995 and 2009 and the Clinical Practice Research Datalink (CPRD) linked to Hospital Episode Statistics (HES) between 1997 and 2010. Five separate studies were then carried out to study the incidence and risk factors for VTE during antepartum and postpartum periods. In studies 1 and 2 I used the THIN database to assess the incidence of and risk factors for VTE during antepartum and postpartum periods separately. Studies 3, 4 and 5 incorporated the CPRD-HES linked data which enabled me to get better ascertainment of VTE and its potential risk factors. Using these data I externally validated my VTE definition which was followed by investigating the impact of non-delivery related hospitalisations on the incidence of antepartum VTE. I also examined the risk factors for postpartum VTE using a conceptual hierarchical analysis approach along with their impact on the timing of VTE during specific periods of postpartum. All results were presented in the form of absolute rates (AR) per 100,000 person-years and incidence rate ratios (IRR) were calculated using Poisson regression with adjustment for relevant covariates. Results: In THIN, there were a total of 1.7 million women of which 280,451 experienced 376,154 pregnancies resulting in live or stillbirths whereas the CPRD-HES linked data contained information on over 240,000 pregnancies among 204,929 women. Overall VTE rates were highest in the first few weeks postpartum. Women in their third trimester of antepartum were at a 5 fold increased risk of first VTE compared to their time outside pregnancy whereas in the first and second trimesters this rate was only marginally higher. However the use of CPRD-HES linked database gave me estimates of VTE risk with better precision in and around pregnancy that were comparable to the existing literature. For my risk factor analysis I found that the strongest risk factor for VTE during the antepartum period was hospitalisation corresponding to a 17-fold increase (IRR=17.7 95%CI=7.7-39.6) compared to time outside hospital. The rate of VTE was also high during the 28 days post-discharge (IRR=5.9; 95%CI=3.5-10.0; AR=646). These factors were not confounded by pregnancy related characteristics and complications, pre-existing medical co-morbidities or demographic or life style related characteristics. I also found that postpartum, women whose pregnancies resulted in stillbirth were at a 6- fold (IRR=6; 95%CI 3.17-14.6; AR=2570) increased risk of VTE. Those with caesarean delivery (elective or emergency), pre-term birth or postpartum haemorrhage had a 2-fold or higher risk of postpartum VTE compared to their respective baseline (AR>600/100,000 person-years). These findings were consistent across both the THIN and CPRD-HES linked data bases with respect women's risk factors for VTE. Finally the risk of VTE remains consistently high up to first six weeks postpartum (>700/100,000 person-years) for pregnancies of women complicated with BMI>30kg/m2 or caesarean delivery whereas risk of VTE was only high in the first three weeks postpartum (>1300/100,000 person-years) In those with pre-term birth or postpartum haemorrhage. Conclusion: I have provided some of the most precise estimates of absolute rates of VTE In and around pregnancy for better understanding of risks. The overall rate of antepartum VTE is substantially increased during non-delivery related hospitalisations and this increase is sustained in the 28 days post-discharge. Postpartum, delivery associated characteristics and complications including, stillbirth, caesarean delivery, BMI>30Kg/m2 postpartum haemorrhage are important risk factors for VTE particularly during the first three weeks postpartum. My analysis provides valuable information to clinicians for better decision making in terms of identifying high risk pregnant and postpartum women who may require some form of thromboprophylaxis.

Η θρόμβωση αποτελεί το πιο συχνό αίτιο δυσλειτουργίας της αγγειακής προσπέλασης, στους ασθενείς, με νεφρική ανεπάρκεια τελικού σταδίου, που υποβάλλονται σε αιμοκάθαρση. Σκοπός: Στόχος της παρούσας μελέτης είναι η εκτίμηση του ρόλου του προεγχειρητικού απεικονιστικού ελέγχου στη δημιουργία αγγειακής προσπέλασης και ο έλεγχος των παραγόντων που επηρεάζουν τη βιωσιμότητα της. Εκτιμήθηκε η επίδραση της διαμέτρου των αγγείων, που χρησιμοποιούνται στη δημιουργία αγγειακής προσπέλασης, στη βατότητα αυτής. Ελέγχθηκε ο ρόλος των γονιδιακών θρομβοφιλικών παραγόντων (FV Leiden, FII G20210A και MTHFR C677T→A) στην παρουσία θρόμβωσης και στην επιβίωση της ΑΦΕ. Τέλος ελέγχθηκε η δυνατότητα πρόβλεψης της θρόμβωσης με τη χρήση δημογραφικών, αιμοδυναμικών, αιματολογικών και βιοχημικών παραγόντων, αλλά και των θρομβοφιλικών γονιδιακών μεταλλάξεων. Μέθοδος- Υλικό: 137 συνεχόμενα περιστατικά, από Μάρτιο 2005 έως Δεκέμβριο 2006, προσήλθαν για δημιουργία αγγειακής προσπέλασης για αιμοκάθαρση και εντάχθηκαν στην παρούσα μελέτη. Μετά από φυσική εξέταση και λήψη ιστορικού, κατεγράφη το αιματολογικό- βιοχημικό τους προφίλ και η παρουσία θρομβοφιλικών μεταλλάξεων. Υπεβλήθηκαν σε χαρτογράφηση των αγγείων των άκρων με χρήση υπερήχων και φλεβογραφία και συνυπολογίζοντας όλα τα δεδομένα ακλούθησε η δημιουργία αγγειακής προσπέλασης. Δημιουργήθηκαν 26 περιφερικές ΑΦΑ, 74 κεντρικές ΑΦΑ, τοποθετήθηκαν 32 ΑΦΜ και σε 5 περιστατικά ετέθη μόνιμος καθετήρας. Εξαιρέθηκαν από τη μελέτη τα περιστατικά με πρώιμη θρόμβωση (9), τα περιστατικά που δεν χρησιμοποιήθηκε η αγγειακή προσπέλαση (11) και στα περιστατικά που χάθηκαν από την παρακολούθηση η απεβίωσαν πριν συμπληρωθούν τουλάχιστον 4 μήνες ελέγχου (14). Στα υπόλοιπα 102 περιστατικά έγινε υπερηχογραφικός έλεγχος της αγγειακής προσπέλασης στους 2, 6 και 12 μήνες και κλινική εκτίμηση έως το πέρας της μελέτης σε τακτά χρονικά διαστήματα. Αποτελέσματα: Η USVM άλλαξε το προεγχειρητικό σχεδιασμό σε 31 (22.6%) ασθενείς, χωρίς να αλλάξει η τελική αναλογία του τύπου σε σύγκριση με την αρχική εκτίμηση. 18 ασθενείς (36.7%) που τα υπερηχογραφικά ευρήματα άλλαξαν το σχεδιασμό ήταν διαβητικοί σε σύγκριση με το 14.8% (13) σε μη διαβητικούς (p<.001). Στα περιστατικά που άλλαξε το σχεδιασμό η USVM υπήρξαν για μεγαλύτερο χρονικό διάστημα σε πρόγραμμα αιμοκάθαρσης(2.7 vs. 0.9 έτη). Φλεβογραφικά αναγνωρίστηκαν 18 περιστατικά με κεντρική στένωση και σε 12 από αυτά άλλαξε ο σχεδιασμός. Σημαντική στένωση παρουσίασε το 93% των ασθενών που στο ιστορικό ανέφεραν πάνω από 2 τοποθετήσεις κεντρικών καθετήρων. Η διάμετρος της φλέβας στις αναστομώσεις που παρουσίασαν πρώιμη θρόμβωση υπήρξε μικρότερη από τις υπόλοιπες λιτουργικές ΑΦΑ (2.84 vs 3.94, p<.001). Οι ΑΦΕ που παρουσίασαν θρόμβωση παρουσίασαν αρχική παροχή (Qa) 558.13 ml/min σε σύγκριση με τα 821.26 ml/min των περιστατικών που δεν παρουσίασαν θρόμβωση. Τα περιστατικά που παρουσίασαν θρόμβωση είχαν υψηλότερη συγκέντρωση Lp(a), είχαν ενταχθεί για μεγαλύτερο χρόνο σε αιμοκάθαρση και παρουσίαζαν μετάλλαξη του MTHFR (R2=0.6, p<.001). Οι γυναίκες, τα μοσχεύματα, ο χαμηλότερος όγκος ροής και η παρουσία μετάλλαξης FV Leiden σχετίζονται με συχνότερη εμφάνιση θρόμβωσης (p<.05). Συμπεράσματα: Ο υπερηχογραφικός έλεγχος θα πρέπει να γίνεται συστηματικά στον προεγχειρητικό σχεδιασμό, με μεγαλύτερο όφελος στους διαβητικούς, σε άτομα με περισσότερο χρόνο σε αιμοκάθαρση, με ιστορικό άλλων επεμβάσεων αγγειακής προσπέλασης. Η φλεβογραφία θα πρέπει να γίνεται σε όλους τους ασθενείς με ιστορικό τοποθέτησης κεντρικής γραμμής στην πλευρά του χειρουργείου. Η πρώιμη θρόμβωση της ΑΦΕ συνδέεται με μικρότερη διάμετρο της φλέβας προς αναστόμωση. Ο Qa αποτελεί αξιόπιστο δείκτη καλής λειτουργίας της ΑΦΕ. Η θρόμβωση εμφανίζεται πιο συχνά στις γυναίκες, στους ασθενείς με αυξημένα επίπεδα Lp(a), σε ατόμα με περισσότερα χρόνια σε αιμοκάθαρση και στα ΑΦΜ. Τόσο ο FV Leiden όσο και το MTHFR φαίνεται να παίζουν ρόλο στην εμφάνιση θρόμβωσης στις ΑΦΑ. / Vascular access thrombosis (VAT) is one of the most common causes of morbidity in hemodialysis patients. Objective: In an effort to increase the prevalence of AV fistulae, ultrasound vessel mapping (USVM) and upper extremity venography (UEV) have been suggested; however the effectiveness of their combined use remains unknown. We studied the effect of such a combined protocol on AV access type change, compared to physical examination alone. The vascular access patency had been correlated to vessel diameter and to a number of thrombosis risk factors. Finally the role of genetic thrombophilic risk factors on vascular access thrombosis was studied. Methods: Consecutive cases with chronic kidney disease (n=137) after an initial estimation of the AV access type based on physical examination, had USVM and UEV, to detect vascular pathology that could potentially alter the original plan. 26 distal AVF, 74 central AVF, 32 AV grafts and 5 permanent catheters were placed. 9 cases presented early thrombosis, 11 cases had delayed first use or the access wasn’t used at all, 14 patients died or did not present at their follow up and were excluded from our study. On the remaining 102 cases an ultrasound control of the VA was performed on 2, 6 and 12 months and clinical evaluation of the VA was performed in a regular base. Results: USVM changed the preoperative plan in 22.6% (31) patients; this was 36.7% (n=18) in diabetics compared to 14.8% (n=13) in non-diabetics (p<.001). Patients that USVM changed the type of the planned AV access had been on hemodialysis significantly longer (2.7 years vs. 0.9 years, p<.001). Venography identified 18 patients with central vein stenosis that led to a site change in 12 of them. Significant venous stenosis in patients with history of two or more central catheters placed and without such was 93%.Original plan was revised in 31% and this rate was similar for distal AVFs, central AVFs and AV grafts (38%, 26% and 43%, respectively, all p>0.05). The internal vein diameter used in VA creation was significant smaller in cases of early thrombosis (2.84 vs 3.94, p<.001). Thrombosed VA presented with initial flow volume measurement (Qa) of 558.13 ml/min and was significantly lower than VA without thrombosis 821.26 ml/min. Thrombosis was more frequent in a) higher values of cholesterol and Lp(a), b) longer periods under hemodialysis, b) lower blood flow volume in initial testing and with existence of MTHFR mutations. VA was thrombosed sooner in women, when an AV graft was placed and in FV Leiden mutation (p<.05). Conclusions: A significant proportion of patients have vascular pathology severe enough to alter the access type as suggested by physical examination alone. USVM should be routinely performed, while UEV selectively in patients with history of surgery or instrumentation of their central veins. The early thrombosis of VA appears on a smaller vein diameter. The blood flow volume measurement is a reliable indicator in case of vascular access thrombosis. Thrombosis appears in greater proportion in women, in higher Lp(a) concentration, in AV grafts. Finally FV Leiden and MTHFR mutations seem to play a role in vascular access thrombosis.