DIFFERENTIATING THROMBUS FROM PANNUS FORMATION IN OBSTRUCTED MECHANICAL PROSTHETIC VALVES - AN EVALUATION OF CLINICAL, TRANSTHORACIC AND TRANSESOPHAGEAL ECHOCARDIOGRAPHIC PARAMETERS

Objectives. We sought to determine the clinical and echocardiographic parameters that differentiate thrombus from pannus formation as the et iology of obstructed mechanical prosthetic valves. Background. Distinc tion of thrombus from pannus on obstructed prosthetic valves is essent ial because thrombolytic ther spy has emerged as an alternative to reo peration. Methods. We analyzed clinical, transthoracic and transesopha geal echocardiography (TEE) data in 23 patients presenting with 24 obs tructed prosthetic valves and compared the findings to pathology at su rgery. Results. Fourteen valves had thrombus and 10 had pannus formati on. Patients with thrombus had a shorter duration from time of valve i nsertion to malfunction, shorter duration of symptoms, but similar New York Heart Association functional class at the time of operation. Pat ients with thrombus had a lower rate of adequate anticoagulation (21% vs. 89%; p = 0.0028). Pannus formation was more common in the aortic p osition (70% vs. 21%; p = 0.035). Abnormal prosthetic valve motion was detected by TEE in all cases with thrombus formation but in 60% with pannus (p = 0.0198). Thrombi were larger than pannuses (total length 2 .8 +/- 2.47 cm vs. 1.17 +/- 0.43 cm; p = 0.038). This was mostly due t o extension of thrombi into the left atrium in prosthetic mitral valve s. Thrombi appeared as a soft mass on the valve in 92% of cases, where as 29% of pannuses had a soft echo density (p = 0.007). Ultrasound vid eo intensity ratio, derived as the video-intensity of the mass to that of the prosthetic valve, was lower in the thrombus group (0.46 +/- 0. 14 vs, 0.71 +/- 0.17, p = 0.006). A videointensity ratio of < 0.70 had a positive predictive value of 87% and a negative predictive value of 89% for thrombus. Duration from onset of symptoms to reoperation of < 1 month separated thrombus from pannus formation. The best objective c linical parameter for prediction of thrombus was inadequate anticoagul ation, whereas the best TEE parameters were qualitative and quantitati ve ultrasound intensity of the mass. The presence of either inadequate anticoagulation or a soft mass by TEE improved the predictive power o f either parameter alone and was similar to that of ultrasound videoin tensity ratio. Conclusions. Duration of symptoms, anticoagulation stat us and qualitative and quantitative ultrasound intensity of the mass o bstructing a mechanical prosthetic valve can help differentiate pannus formation from thrombus and may therefore be of value in refining the selection of patients for thrombolytic therapy of prosthetic valve ob struction. (C) 1998 by the American College of Cardiology.