The use of enzyme activated milk for in vitro simulation of prosthetic valve thrombosis.
OBJECTIVE
Thrombosis remains a serious risk for patients with artificial heart valves and may be attributed in part to adverse blood flow patterns. Although the final assessment of a valve must follow years of clinical experience, in vitro flow analyses give valuable information prior to implantation. Laser Doppler velocimetry and computational fluid dynamics enable quantitative flow analyses to be made in vitro. Whilst these techniques highlight features such as areas of stasis, turbulence and high shear which may predispose to thrombus formation, the complex and time varying nature of the flow through valves makes it difficult to predict accurately potential sites of thrombus deposition and accumulation.


METHODS
A technique is described which uses enzyme activated milk as a coagulable blood analogue to indicate flow related clotting. Milk flowing past a test valve or object was activated to clot downstream of the test piece after a certain time period. Milk clot was deposited clot at sites determined by the local flow disturbances. Milk clotting patterns produced on and around standard objects were compared with the transient flow patterns predicted around identical configurations to test the validity of computational flow analyses for predicting flow disturbances leading to clotting. Milk clots on valves were compared with examples of thrombus found on explanted valves of the same design.


RESULTS
The sites of deposition were consistent with the predicted flow patterns around the two configurations of flow obstruction studied. Milk clotting patterns on valves corresponded with the early stages of thrombus on explanted valves of the same design.


CONCLUSIONS
Whilst a coagulable milk mixture may be used to evaluate the risk of flow induced clot adherence, care must be taken when extrapolating to the clinical situation as other factors such as material properties, blood chemistry and concomitant disease must also be considered.
Keggen
L A
LA
Department of Medical Physics, University of Sheffield, United Kingdom.
Black
M M
MM
Lawford
P V
PV
Hose
D R
DR
Strachan
J R
JR
D000818:Animals; D001705:Bioprosthesis; D001783:Blood Flow Velocity / Q000502:physiology*; D012085:Chymosin; D006350:Heart Valve Prosthesis; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D017078:Laser-Doppler Flowmetry; D008892:Milk; D008955:Models, Cardiovascular; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013927:Thrombosis / Q000503:physiopathology*
C025350:rennet; D012085:Chymosin