EFSUMB EUROPEAN FEDERATION OF SOCIETIES FOR ULTRASOUND IN MEDICINE AND BIOLOGY ‘Building a European Ultrasound Community’ Young Investigator’s Award WFUMB 2011 VIENNA AUSTRIA 28 August 2011 13.50 – 15.45 10 minutes each for presentation plus 3 minutes discussion
Hemodynamics and arterial wall histology in the arteriovenous shunt 1
1
2
3
2
2
2
1
Moschos I, Manos T, Giagini A, Kakisis JD, Sokolis DP, Varela AE, Davos CH, Tsangaris S
1
2
National Technical University of Athens, Foundation of Biomedical Research, Academy of Athens, University of Athens School of Medicine
3
ABSTRACT Introduction Frequent hemodialysis requires adequate blood flows, typically produced by an arteriovenous shunt. The disturbed hemodynamics, caused by this surgical intervention, affects adversely both the venous and arterial sides of the shunt. The irregular blood flow at the venous anastomosis and outflow has been studied extensively, being closely related to intimal hyperplasia development, a major cause of patency loss, yet, only few studies have examined the disturbed blood flow at the arterial anastomosis. Doppler ultrasound has proven an invaluable tool for diagnosis and management of such pathological vascular flow conditions. The purpose of this study was to analyze Doppler ultrasound flow variables, before and after arteriovenous shunt creation at the proximal and distal carotid segment, in addition to corresponding arterial histology. Methods An arteriovenous shunt was created in 14 healthy Landrace pigs (mean weight 70±8 kg) between the common carotid artery and ipsilateral internal jugular vein, using an expanded polytetrafluοroethylene synthetic graft. Before and after construction of the anastomoses, Doppler flow waveforms were recorded intraoperatively with a 5.7 MHz flow probe (Vivid7, GE Medical Systems) at the proximal and distal segment of the carotid artery. The flow parameters measured were: peak systolic velocity (PSV), minimum diastolic velocity (MDV), time-averaged maximum (TAmax) and mean velocity (TAmean), resistive index (RI=PSV-MDV/PSV), and flow rate (FR=TAmean×carotid cross-sectional area). After animal euthanasia, the shunted and contralateral carotids were excised and divided into two parts, according to topography (proximal and distal). These were submitted to histological analysis using image-processing software (Image-Pro Plus 6.0). The histometric parameters measured were: the dimensions of the tubular vessels and the content of certain structural components, such as collagen, elastin, and smooth muscle cells. Statistical Analysis Data were analyzed with GraphPad Prism Software. Statistical comparisons were performed using the paired Student’s t-test. A p value <0.05 was considered significant.
Results Doppler flow hemodynamics were deranged after the arteriovenous shunt creation with proximal flow indices increased as compared to distal or preoperative flow values. Histological parameters showed a tendency of the arterial wall to remodel. Wall thickness increased and there was accumulation of collagen at the expense of elastin and smooth muscle cells. Conclusions The arteriovenous shunt creation decreases the peripheral resistance and alters hemodynamics. Flow indices are increased at the proximal and a steal phenomenon developed at the distal side. The increased flow observed at the proximal region caused decreased distensibility and increased wall stiffness; similar results were noted for the distal segment. This paper is part of the 03ED 262 research project, implemented within the framework of the “Reinforcement of Human Research Manpower” (PENED) and co-financed by National and Community Funds (20% from Greek Ministry of Development – General Secretariat of Research and Technology and 80% from E.U. – European Social Fund).