Prosthetic valve obstruction is becoming a common clinical issue .It can be either acute, sub-acute or chronic . The pathology is usually thrombus formation , scar tissue growth (Pannus) or rarely a mechanical defect. Echocardiographic differentiation of thrombus from pannus can be difficult .Generally , pannus is smaller , linear (less round) ,encroach from the periphery to central , mean gradients are consistently lower than thrombus mediated obstruction. Clinically pannus related obstruction present less acutely and occur in-spite of good compliance of anticoagulant medication and a well maintained INR .
Trans thoracic (TTE) , Trans-esophagel (TEE ) echocardiography , and real time 3D TEE are useful imaging modalities .The value of cine fluroscopy should be never underestimated and it is probably still the the best way assess the struck metallic leaflet.
Though the pathogenesis of pannus and thrombus are considered different there is no reason they can’t occur in a given patient at the same time.We know at least one patient who had been referred to surgeon for mitral valve obstruction due to failed thrombolysis had showed heavy load of thrombus attached over a well formed pannus originating in medial sewing ring.
However intelligent one may be , human brain often tends to get skewed when confronted with a sudden query like “What is your diagnosis , This or that ? Pannus or thrombus ? .Most will go with any one of it ! However, cardiac physicians must be aware both pannus and thrombus can occur overlaid simultaneously in a given patient .The exact incidence of such “combined thrombo-pannus” is not known but bound to be higher as we look for it. In fact , many of the residual gradients after lysis is attributable to undiagnosed pannus. There is also a suggestion scarred , injured , rough surface of the pannus could be the initial trigger for thrombus formation .
1.Differentiating thrombus from pannus formation in obstructed mechanical prosthetic valves: an evaluation of clinical, transthoracic and transesophageal echocardiographic parameters J Am Coll Cardiol. 1998;32(5):1410-1417.