Original Articles
Obstruction of Mechanical Mitral Prostheses: Analysis of Pathologic Findings

https://doi.org/10.1016/S0003-4975(96)01391-4Get rights and content

Abstract

Background. The pathologic and echocardiographic findings observed in 87 patients with mitral valve obstruction were reviewed to ascertain the incidence of pannus formation versus that of thrombosis, the relationship between the two, and the time to the occurrence of pannus versus the time to thrombosis.

Methods. Pannus morphology (concentric or eccentric), its location on the valve (atrial, ventricular, atrioventricular), and the presence and relationship of associated thrombi (atrial, ventricular, atrioventricular) were analyzed. The times between valve replacement and the occurrence of obstruction were also compared.

Results. There were 10 caged-ball valves, 65 tilting-disc valves, and 12 bileaflet valves. Seventy-two patients underwent prosthetic replacement, and 15 underwent thrombolysis. Pannus alone was found in 27, pannus and thrombus in 39, and thrombus alone in 21. Primary thrombosis occurred earlier than pannus formation (p = 0.04); this was true for patients with bileaflet valves (p = 0.006) and those with tilting-disc valves (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 was concentric in 22.7% (15/66) and eccentric in 77.3% (51/66). Atrial secondary thrombi occur more often in patients with atrioventricular pannus (p = 0.04). Eight patients had reobstruction; this was caused by pannus formation in 5 and by thrombosis in 3. Five underwent reoperation, and 3 underwent thrombolysis. Reobstruction occurred earlier than the first event.

Conclusions. The frequency of pannus formation is much higher than that of thrombus formation, but thrombosis is of earlier onset than pannus formation. Thrombosis is due to the deposition of clots on the prosthesis, and a pannus occurs as the result of an inflammatory reaction developing on both valve surfaces.

(Ann Thorac Surg 1997;63:1101–6)

Section snippets

Material and Methods

From May 1981 to December 1994, 1,878 patients underwent mitral valve replacement using mechanical prostheses at our institutions; of them, 479 (25.5%) received a caged-ball valve, 928 (49.4%) a tilting-disc valve, and 471 (25.1%) a bileaflet valve. During this time 83 (4.42%) of the 1,878 patients suffered prosthetic valve obstruction, 1.9% (9/479) with a caged-ball valve, 6.8% (63/928) with a tilting-disc valve, and 2.3% (11/471) with a bileaflet valve.

The entire study population was made up

Results

Obstruction occurred from 4 days to 14 years (mean, 4.3 ± 3.45 years) after valve replacement.

Comment

The first and most relevant finding in our series was the very high incidence of cases in which the moving element of the prosthesis was gradually blocked until complete arrest occurred as the result of an overgrowth of fibrous tissue that invaded the valve orifice. The presence of pannus, either alone or in association with secondary thrombi, was ascertained in 75.8% (66/87) of the patients. These findings are in contrast with those cited in reports of the major series of patients with

Acknowledgements

We gratefully thank Professor Gilda Caruso for reviewing the manuscript and Dr Domenico Paparella for collecting data.

References (19)

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