Posts Tagged ‘vWF multimers’

Impact-R and Heyde Syndrome

Thursday, December 29th, 2011

This is a case of a 79-year old man with severe aortic stenosis and recurrent GI bleeding. This case study by Schmid, proposes that Impact-R to determine platelet function may be more time- and cost-effective compared to electrophoretic analysis of vWF multimers.

Severe aortic stenosis with bleeding diathesis is also known as Heyde syndrome. The pathophysiology: loss of high molecular weight vWF multimers in high shear stress conditions leads to a platelet type von Willebrand disease (acquired vWD, vWD type 2B) which can explain the bleeding tendencies of a patient with severe aortic stenosis.


Impact-R and Acquired von Willebrand Disease in Severe Aortic Stenosis

Wednesday, December 21st, 2011

The aortic valve is the valve between the left ventricle and the aorta, the main artery. It has three leaflets (tricuspid). When the left ventricle contracts, it pushes blood through the valves and into the aorta. When the left ventricle relaxes, the valves close, preventing the blood from flowing back into the left ventricle.

When the aortic opening becomes constricted or stenotic, the blood in the left ventricle cannot be pumped effectively into the aorta. Aortic stenosis (AS) is usually age-related and is caused by progressive calcification of any of the three leaflets of the valve.

Severe aortic stenosis also causes an acquired form of von Willebrand disease (vWD type 2A). This is due to breakdown of the von Willebrand factor (vWF) by the increased turbulence around the stenotic valve. The increased turbulence causing high shear stress conditions predisposes the vWF to cleavage by an enzyme, ADAMTS-13. This enzyme is the 13th member of the class of enzymes known as a disintegrin and metalloproteinase with a thrombospondin type 1 motif also known as von Willebrand factor-cleaving protease (vWFCP).

This acquired form of vWD causes bleeding in the AS patient. Whether the bleeding is due to platelet adhesion or to platelet aggregation has not been determined. This is the subject of the study done by Panzer, using the IMPACT-R machine. The study concludes that reduced levels of large vWF multimers associated with severe AS leads to impairment of both adhesion and aggregation of platelets. An abstract of the study can be found here.