Prosthetic valve obstruction is an important complication of artificial valves.The incidence of prosthetic valve obstruction is estimated to be 4% per year.
- Pure thrombus 75%*
- Pure pannus 10%
- Combination of pannus and thrombus 12%
Data from Deviri (J Am Coll Cardiol, 1998; 32:1410-1417 )
*Note statistically you are going to be right 3 times out of 4 if you diagnose thrombus over pannus
Pannus literally means a hanging flap of tissue. It is is a membrane of granulation tissue as an response to healing.It can occur anywhere in the body. When it occurs in the prosthetic valve tissue interface it has important consequences.It is same as excessive scarring , ( something similar to keloid formation ) .
How do they clinically present ?
Prosthetic valve thrombosis is usually a acute or sub acute event as thrombus formation rapidly deteriorates the clinical situation.Pannus brings a patient with the complaints of chronic progressive dyspnea.(This rule is very subjective but . . .)
What are the determinants of pannus growth ?
Time is the major determinant. minimum period required is 12 months. It is a avascular mass.It should be noted a injured pannus can predispose a thrombotic process and a chronic thrombus can trigger intravascular growth factors that promotes pannus growth.
What is the direction of growth of pannus in prosthetic valve ?
The pannus grows , usually in the tissue valve interface.It tracks and creeps along the suture lines .Generally this does not encroach the valve orifice or chamber sapce , but occasionally the hanging edges can hit upon a leaflet.This is more common with tilting disc on the side of minor orifice. When excessive it can make a valve leaflet almost standstill.
How common is pannus formation in starr edwards valve?
Is relatively uncommon as the dynamic ball periodically interrupts the process of pannus in growth within the orifice.
Why is recognition of pannus important ?
Prosthetic valve thrombois is amenable to thrombolysis and it should be proptly differentiated for pannus.This is many times a difficult excercise, but the above observation will be helpful.