OBSTRUCTION OF MECHANICAL MITRAL PROSTHESES - ANALYSIS OF PATHOLOGICAL FINDINGS

Background. The pathologic and echocardiographic findings observed in 87 patients with mitral valve obstruction were reviewed to ascertain t he incidence of pannus formation versus that of thrombosis, the relati onship between the two, and the time to the occurrence of pannus versu s the time to thrombosis. Methods. Pannus morphology (concentric or ec centric), its location on the valve (atrial, ventricular, atrioventric ular), and the presence and relationship of associated thrombi (atrial , ventricular, atrioventricular) were analyzed. The times between valv e replacement and the occurrence of obstruction were also compared. Re sults. There were 10 caged-ball valves, 65 tilting-disc valves, and 12 bileaflet valves. Seventy-two patients underwent prosthetic replaceme nt, and 15 underwent thrombolysis. Pannus alone was found in 27, pannu s and thrombus in 39, and thrombus alone in 21. Primary thrombosis occ urred earlier than pannus formation (p = 0.04); this was true for pati ents with bileaflet valves (p = 0.006) and those with tilting-disc val ves (p = 0.04). Pannus was atrial in 19.7% (13/66), ventricular in 21. 2% (14/66), and atrioventricular in 59.1% (39/66). Pannus morphology w as concentric in 22.7% (15/66) and eccentric in 77.3% (51/66). Atrial secondary thrombi occur more often in patients with atrioventricular p annus (p = 0.04). Eight patients had reobstruction; this was caused by pannus formation in 5 and by thrombosis in 3. Five underwent reoperat ion, and 3 underwent thrombolysis. Reobstruction occurred earlier than the first event. Conclusions. The frequency of pannus formation is mu ch higher than that of thrombus formation, but thrombosis is of earlie r onset than pannus formation. Thrombosis is due to the deposit deposi tion of clots on the prosthesis, and a pannus occurs as the result of an inflammatory reaction developing on both valve surfaces. (C) 1997 b y The Society of Thoracic Surgeons.