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Ann Thorac Surg 1997;63:1101-1106
© 1997 The Society of Thoracic Surgeons

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Original Article: Cardiovascular

Obstruction of Mechanical Mitral Prostheses: Analysis of Pathologic Findings

Departments of Cardiac Surgery and Statistics, University of Bari, and Departments of Cardiac Surgery and Pathology, Second University of Naples, Naples, Italy

Accepted for publication November 5, 1996.

	Abstract

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
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.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
Progress in the design and structure of mechanical prostheses over the years has led to a considerable improvement in their hemodynamic features and durability, such that they are now preferable to bioprostheses in most cases [1–7]. However, their use is still burdened with the risk of complications, among which thrombosis is the most dreaded. Such thrombosis is still associated with a high mortality, even if emergency medical or surgical treatment is promptly established [7].

Numerous studies have been carried out with the aim of identifying the risk factors for prosthetic thrombosis [2, 3]. Despite these studies, however, there is still little knowledge about the mechanisms of obstruction [4–6]. Although obstruction is most often thought to result from valve thrombosis, the role of chronic pannus formation in causing obstruction is less well established [7]. Furthermore, very little is known about the difference in the time between valve replacement and obstruction by thrombus versus obstruction by pannus [2]. Moreover, the relationship between thrombus and pannus formation on the valve has not been fully elucidated.

The aim of the present study was therefore to analyze the pathologic findings in patients with obstructed mechanical mitral prostheses in an attempt to determine the incidence of pannus formation versus thrombosis and the interaction of the two and to ascertain whether the time to the development of pannus and thrombosis differs. To do this, we reviewed our data for patients with an obstructed mitral prostheses treated from May 1981 to December 1994.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
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 of 87 patients, however, because 4 patients had undergone their mitral valve replacement at other centers. The breakdown of patients by prosthesis was as follows: 10 patients had caged ball valves (9 Starr-Edwards, 1 Smeloff-Cutter), 65 had tilting-disc valves (51 Sorin, 6 Björk-Shiley, 6 Lillehei-Kaster, 1 Omnicarbon, 1 Medtronic Hall), and 12 had bileaflet valves (6 CarboMedics, 2 St. Jude, 4 Jyros).

Until December 1990 it was our policy to perform emergency surgical intervention in all patients with prosthetic thrombosis. Until that time diagnosis of valve obstruction was established on the basis of either clinical or echocardiographic evidence of valve obstruction. Clinical criteria consisted of dyspnea of recent onset and loss of valve clicks; echocardiographic criteria consisted of block of the occluder and increased pressure half-time.

Since January 1991, thrombolytic treatment with recombinant tissue-type plasminogen activator has been used at our institutes. Therefore, beside diagnosing valve obstruction, our policy has also been to identify whether obstruction was caused by pannus, treatable only by operation, or by thrombus alone, treatable by thrombolysis, as reported previously [8].

The following criteria were used to select patients for thrombolysis: (1) onset of symptoms within 15 days of presentation, (2) transesophageal echocardiographic evidence of clots on the prosthesis or cardiac chambers, and (3) preserved excursion of either the disc or of at least one leaflet. All patients who did not satisfy these criteria were considered to have valve obstruction caused by pannus and were operated on accordingly [8]. Of these 87 patients, 72 underwent operation and 15 underwent thrombolysis.

There were 25 male and 62 female patients ranging in age from 17 to 71 years (mean, 46.9 ± 10.9 years). At hospital admission 23 patients were in New York Heart Association functional class II, 42 were in class III, and 22 were in class IV. Patients were kept in an anticoagulation range of between an INR of 2 to 3.5; 12 of the 87 patients were found to be inadequately anticoagulated at the time of treatment.

The operative technique for the placement of the mechanical valve at our institutions had consisted of the total excision of the native valve along with the subvalvular apparatus. Tilting-disc prostheses were positioned with the larger orifice oriented anteriorly until 1985 and with the larger orifice oriented posteriorly after this time. Bileaflet prostheses were implanted in the antianatomic position (ie, valve leaflets perpendicular to mitral commissures). Warfarin anticoagulation was started on the first postoperative day after chest drains were removed.

	Operative Technique and Patient Management

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
Reoperations were performed by the same group of surgeons using the same technique. In this technique the heart was completely mobilized through a repeat median sternotomy and the aorta and both venae cavae cannulated. Standard cardiopulmonary bypass was achieved with mild systemic hypothermia (28°C). Once the left atrium was opened, the obstructed prosthesis was carefully excised and atrial thrombectomy was carried out whenever necessary. In all cases care was taken during valve excision not to remove any obstructing material from prosthetic surfaces to ensure a complete and reliable pathologic evaluation. Prosthetic replacement was performed by implanting the valve at the suprannular level using Tevdek 2/0 mattress suture.

All patients were given dipyridamole orally in a dose of 400 mg daily, in addition to the warfarin, as recommended for patients with mechanical valves who suffer thromboembolic complications despite warfarin treatment at the recommended intensity [9].

	Pathologic Findings

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
The operating surgeon carefully examined the prosthesis before and after its removal from the tissue bed to determine the nature and location of the obstruction. The histologic examination of the obstructing material was carried out by the pathologist to confirm the surgical findings. The specimens used for these purposes consisted of samples of the prosthetic ingrowth that were embedded in paraffin and serially sectioned. The serial sections were then stained with hematoxylin and eosin, Van Gieson, and periodic-acid Schiff. Gram's and Grocott's stains were applied to sections to be used to search for evidence of bacterial or fungal vegetations. Microscopic features considered indicative of pannus were an exuberant overgrowth of fibroblastic tissue together with macrophages and interspersed capillary vessels, whereas those considered indicative of thrombus were fibrin masses in which erythrocytes, platelets, and leukocytes were enmeshed [10]. A thrombosis was considered the primary cause of the valve obstruction if there was only an isolated thrombus on the prosthesis. A thrombosis was regarded as the secondary cause if the thrombus occurred in association with pannus.

The nature of the obstruction was categorized as pannus alone, pannus and secondary thrombus, or thrombus alone. The pannus or thrombus, or both, was also categorized according to its location on the prosthetic surfaces as atrial, ventricular, or atrioventricular. The morphology of the pannus was classified as either concentric (ie, the regular and circular shape of the ingrowth tissue over the prosthesis) or eccentric (ie, the irregular and uncircular shape of the pannus over localized, protruding edges of the prosthesis). These morphologic patterns were analyzed in relation to their position (atrial, atrioventricular, ventricular) and the type of valve. The association of thrombi with concentric or eccentric pannus and their position on prosthetic surfaces were also analyzed.

	Thrombolysis

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
The protocol for the treatment with recombinant tissue-type plasminogen activation consisted of a 10-mg intravenous bolus, followed by a 50-mg infusion administered during the first hour and a 20-mg infusion administered during the second and third hours. The results of treatment were assessed on the basis of the clinical and auscultatory findings as well as the transthoracic and transesophageal echocardiographic findings 24 hours after the end of the infusion [8]. Thrombolysis was considered successful if the poppet excursions were seen to be completely restored and the thrombi were absent on the echocardiogram obtained both 24 hours and 3 months after treatment. According to Bodnar and associates [11], the echocardiographic finding of a normally functioning valve after thrombolysis is confirmation that the prosthetic occlusion was caused by thrombus alone. As a consequence, the locations of the thrombi on prosthetic surfaces detected during pretreatment echocardiograms were recorded and these data were included with the pathologic findings in the statistical analysis.

Patients reoperated on for a recurrent obstruction were again given dipyridamole at the same dose as before, and in addition to their warfarin [9]. Patients who suffered a recurrence of primary thrombosis underwent thrombolysis following the same protocol as used earlier.

	Statistical Methods

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
All the pathologic and echocardiographic findings and their relations were represented by means in contingency tables and analyzed with the two-tailed Fisher's exact test and the likelihood ratio test [12]. Freedom from obstruction curves for the two disorders were calculated separately using the Kaplan-Meier product-limit estimator and compared by means of the Wilcoxon and log-rank tests [13]. Additional nonparametric comparison of the times to the occurrence of the obstruction was done using the Mann-Whitney U test. These analyses were done for the whole group as well as for subgroups of patients grouped according to the type of prosthesis (caged-ball, tilting-disc, bileaflet) and the anterior or posterior orientation of the larger orifice for the tilting-disc valves. All data were analyzed using Statistical Analysis System software (version 6.10; SAS Institute Inc, Cary, NC).

	Follow-up

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
Patients were followed up at our outpatient clinic, with questionnaires sent to the general practitioners of all patients not seen at the outpatient clinic. Information was available for all patients, and thus the follow-up was 100% complete. The cumulative patient follow-up was 709 patient-years, with the period of follow-up ranging from 3.2 to 241.2 months (mean, 97.8 months) [14].

	Results

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

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

	Operation

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
Of the 72 patients operated on, 64 (88.8%) received a mechanical valve and 8 (11.1%) a bioprosthesis. Nine patients died within 30 days of operation, resulting in an operative mortality rate of 12.5%. The causes of death were low-output syndrome (7 patients), stroke (1 patient), and rupture of a mycotic cerebral aneurysm (1 patient).

	Thrombolysis

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
Thrombolysis was successful in all patients but 1, a patient who had a 2M Starr-Edwards valve. She was successfully reoperated on 3 days after thrombolysis; pannus overgrowth was found on the cage of the explanted prosthesis. Of the complications that arose in the course of treatment, a transient ischemic attack occurred in 3 patients and a transient peripheral embolism in 1.

	Follow-up

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
Eight deaths occurred during the follow-up period, and these were considered late deaths with respect to the first obstructive event; 3 patients died of progressive left ventricular failure, 2 patients died at the second reoperation for prosthetic obstruction, 1 patient died of gastric cancer, and 2 patients died suddenly of unexplained causes; permission for postmortem examination was denied in both cases.

Reobstruction occurred in 8 patients (9.1%) between 56 days and 3.1 years (mean, 1.27 ± 0.9 years) after prosthetic replacement. Five patients underwent repeat prosthetic replacement; 3 patients received a Sorin tilting-disc valve, 1 a Lillehei-Kaster valve, and 1 a St. Jude Medical valve. Operative death occurred in 2 of the 5 (40%) patients, and the cause was the low-output syndrome. The remaining 3 patients who suffered reobstruction had received a Starr-Edwards valve at the time of the previous obstruction and were treated successfully this time with thrombolysis, with no complications.

	Pathologic Findings

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
The histologic studies confirmed the surgical findings in all patients. Of the entire group of 87 patients, the obstruction was caused by pannus alone in 27 patients, pannus and secondary thrombus in 39, and thrombus alone in 21.

Table 1 shows the relationship between the location of the pannus and the secondary thrombi on prosthetic surfaces. A statistically significant relationship was found between the formation of thrombi on atrial prosthetic surfaces and the growth of pannus on atrioventricular prosthetic surfaces (p = 0.04, likelihood ratio test). Table 2 shows the morphology of pannus with regard to its location; eccentric pannus was found in far more cases than concentric pannus, and the morphology and the location of the pannus seemed to be related (p = 0.017, likelihood ratio test). Table 3 shows the morphology of pannus broken down by the type of prosthesis; the pannus in tilting-disc valves was mostly eccentric, but this was not so for caged-ball and bileaflet valves (p = 0.001, likelihood ratio test). The relationship between pannus morphology and secondary thrombosis for tilting-disc valves is presented in Table 4. Because no statistically significant difference in the relationship was found, eccentric and concentric pannus were considered to occur with equal frequency in association with thrombosis. The same was noted for caged-ball and bileaflet valves.

View larger version (15K): [in this window] [in a new window]   Fig 1. . Freedom from obstruction rates and obstruction times: use of the Kaplan-Meier estimator for uncensored data yields rates as estimated probabilities. The obstructions caused by thrombus alone occurred mostly within 4 years of operation (shown by curve and circles), whereas obstruction caused by pannus with or without secondary thrombi occurred more evenly throughout the observation period (shown by curve and triangles) (p = 0.04; Wilcoxon test).

During the 12-year observation time, there was a highly significant difference between the time to the first obstruction and the time to reobstruction, which suggests reobstruction occurs much earlier than the first event.

	Comment

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
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 prosthetic valve obstruction, in which fibrous tissue overgrowth is rarely mentioned [3–6]. Deviri and coworkers [2] reported a pannus ingrowth rate of 46%.

With regard to the time to the development of thrombus as opposed to pannus, our analysis showed that primary thrombosis occurs earlier than fibrotic overgrowth, with the difference being statistically significant. In our series, primary prosthetic valve thrombosis occurred within 4 years of valve replacement, whereas obstruction by pannus overgrowth occurred more evenly throughout the observation period. This was true both for patients with tilting-disc valves and for patients with bileaflet valves. Our data are somewhat at variance with those reported by Deviri and associates [2], who found no statistically significant difference between the time to pannus formation and the time to thrombus formation.

This difference in the time to obstruction stems from the difference in the pathogenic mechanisms underlying prosthetic obstruction. The thrombotic process begins with the intraoperative activation of platelets and the coagulation system [7]. Other factors contribute to the development of a thrombogenic milieu in the early postoperative period [7]. Furthermore, most of the thrombotic and thromboembolic events occurring several years after prosthetic valve implantation are related to an inadequate anticoagulation status existing for some time before the observed event, as demonstrated by the higher incidence of thromboembolism within the first 3 months of valve replacement [8].

The histologic features of pannus in our series consisted of a massive fibroblastic proliferation with interspersed blood vessels and capillary buds surrounding giant cells, which were found around and over the suture knots. Two inflammatory processes with common mechanisms and manifestations develop after valve replacement [10]. The first one, which is reparatory in nature, involves the replacement of damaged myocardium around the valve annulus with nonspecialized connective tissue scar. The second one is the foreign-body reaction to synthetic biomaterial, a special form of nonimmune inflammation [10]. The prolonged exposure to nondegradable synthetic material represents a persistent stimulus to macrophage infiltration and the proliferation of fibroblasts, both phenomena typical of chronic inflammation. In this reaction the most prominent cells are macrophages that are grouped as giant cells. The finding of these cells is considered evidence of a severe reaction in which the material is not well tolerated and these cells are presumably attempting to phagocytose material. New blood vessels form as the result of the budding or sprouting of preexisting vessels at the annular edges [10]. Furthermore, fibroblasts synthesize collagen and other extracellular tissue components [10]. Therefore it is likely that in some patients a stronger chronic inflammation develops in response to the foreign body so as to expand and rapidly envelop the valve orifice.

With this in mind, it can be speculated that the presence of pannus on the atrioventricular surfaces of 39 of the 66 prostheses obstructed by pannus in our series likely represents an advanced stage of exuberant tissue overgrowth, whereas those prostheses with pannus on just one surface are at an earlier stage of the same process.

Some coexisting factors may contribute to exuberant tissue overgrowth. The design and biocompatibility of the prosthesis; the presence of irregular endothelial surfaces at the time of original valve placement; the surgical technique used; low-output conditions; blood flow turbulence, especially in the mitral position; pregnancy; endocarditis; and inadequate anticoagulation may all play a role in the development of pannus [3–6, 8, 15].

Unfortunately, it is very difficult to assess the real role of these factors in pannus obstruction, either alone or in association, in most of the series described in the literature, because no distinction is made between pannus and thrombus [3–6, 16].

With regard to pannus morphology, eccentric pannus was found in far more patients (77.2%) than concentric pannus (22.8%), with the difference being statistically significant. Almost all of the prostheses showing eccentric pannus were tilting-disc valves (94%; 48/51) on which the protruding edges of the pannus were localized over the minor orifice area. Because this area is the site of low flow, it can be speculated that low flow contributes to the development of pannus. Moreover, there was a statistically significant relationship between the morphology and the position of pannus.

With regard to the relationship between thrombus and pannus, our analysis showed that there is a statistically significant relationship between atrioventricular pannus and atrial secondary thrombi. This is likely due to (1) the obstruction, which severely impairs atrial emptying, resulting in blood stagnation within the left atrium and the secondary deposition of clots on prosthetic surfaces, and (2) the well-described interactions between inflammation and thrombosis [10]. Furthermore, the equal frequency of secondary thrombi in association with concentric and eccentric pannus indicates that either type of pannus may trigger a thrombotic mechanism, especially if associated with inadequate anticoagulation.

Eight patients suffered reobstruction, 3 of whom were treated with thrombolysis and 5 of whom underwent reoperation. In all the thrombosis or obstruction occurred much sooner than the first event. In patients reoperated on pannus and secondary thrombus were found to have the same features as they did at the previous event. The addition of dipyridamole to warfarin therapy, as recommended in the literature [9], did not seem to be effective in reducing the risk of pannus recurrence. The reason for the earlier recurrence of obstruction and these pathologic findings may be that the insertion of a new mechanical prosthesis triggers a new, more rapid phlogistic reaction in a patient with a prosthesis-related inflammatory reaction already activated by the previous event. On the other hand, all of the patients who underwent thrombolytic treatment at the time of reobstruction had a Starr-Edwards valve, which is generally recognized to be associated with a higher incidence of clot deposition on the strut [19]. For this reason, prophylactic prosthetic valve replacement was proposed.

With regard to the other two types of prosthesis, the six Starr-Edwards prostheses with fibrous tissue overgrowth showed pannus accumulation along the struts and around the orifice. Concentric pannus was found on all the bileaflet valves explanted, a finding strongly indicating that it is very unlikely that the fibrous ingrowth began in the region of the hinge pockets, because in this situation even minimal pannus might have completely immobilized one or both leaflets.

The conclusions that can be drawn from the present study are that, unlike the findings from most other series, the incidence of pannus overgrowth on prosthetic valves is higher than that of thrombus formation. Pannus forms much faster than thrombus. However, thrombotic obstruction has an earlier onset than fibrotic overgrowth, and this is because different mechanisms underlie the obstruction. Thrombosis is solely caused by clot deposition on prosthetic surfaces, and it generally occurs within the first years after valve replacement. Conversely, pannus is the result of an exuberant healing process in response to a foreign body; it takes longer to become clinically manifest. Because the fibrotic overgrowth generally develops on both prosthetic surfaces, prosthetic replacement is preferred to debridement in patients with an obstruction caused by pannus.

It was also found that concentric and eccentric pannus occur with equal frequency in association with thrombi; for hemodynamic reasons, however, such secondary thrombi were situated predominantly on the atrial prosthetic surface.

There is general agreement on the causes of thrombotic obstruction, but the causes of pannus overgrowth are not defined yet. It is likely that a particular patient's more intense nonimmune reaction against a foreign body together with other contributory factors such as low transvalvular flow (ie, tilting-disc valves) trigger pannus growth.

More studies of patients with obstruction caused by pannus are necessary so that those who are prone to this reaction can be identified. The achievement of this goal, along with the use of more biocompatible material capable of better hemodynamic performance, will perhaps eradicate this dreadful complication of mechanical heart valves.

	Acknowledgments

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

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

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 
Address reprint requests to Dr Vitale, Residence Windsor, Parallela via Mauro Amoruso 62/7, 70124 Bari, Italy.

	References

Top Footnotes Abstract Introduction Material and Methods Operative Technique and Patient... Pathologic Findings Thrombolysis Statistical Methods Follow-up Results Operation Thrombolysis Follow-up Pathologic Findings Comment Acknowledgments References

 

1. Arom KV, Nicoloff DM, Kersten TE, Northrup WF III, Lindsay WG, Emery RW. Ten years experience with the St. Jude Medical valve prosthesis. Ann Thorac Surg 1989;47:831–7.[Abstract/Free Full Text]
2. Deviri D, Sareli P, Wisembaugh T, Cronje S. Obstruction of mechanical heart valve prostheses: clinical aspects and surgical management. J Am Coll Cardiol 1991;17:646–50.[Medline]
3. Kontos GJ, Schaff HV, Orszulak TA, Puga FJ, Pluth JR, Danielson GK. Thrombotic obstruction of disc valves: clinical recognition and surgical management. Ann Thorac Surg 1989;48:60–5.[Abstract/Free Full Text]
4. Venugopal P, Kaul U, Iyer KS, et al. Fate of thrombectomized Björk-Shiley valves. A long term cinefluoroscopic echocardiographic and hemodynamic evaluation. J Thorac Cardiovasc Surg 1986;91:168–73.[Abstract]
5. Copans H, Lakier JB, Kinsley RH, Colsen PR, Fritz VU, Barlow JB. Thrombosed Björk-Shiley mitral prostheses. Circulation 1980;61:169–74.[Free Full Text]
6. Wright JO, Hiratzka LF, Brandt B III, Doty D. Thrombosis of the Björk-Shiley prosthesis. J Thorac Cardiovasc Surg 1982;82:138–44.
7. Edmunds LH Jr. Thrombotic and bleeding complications of prosthetic heart valves. Ann Thorac Surg 1987;44:430–45.[Abstract/Free Full Text]
8. Vitale N, Renzulli A, Cerasuolo F, et al. Prosthetic valve obstruction: thrombolysis versus operation. Ann Thorac Surg 1994;57:365–70.[Abstract/Free Full Text]
9. Chesebro JH, Fuster V, Elveback LR, et al. Trial of combined warfarin plus dipyridamole or aspirin therapy in prosthetic heart valve replacement: danger of aspirin compared with dipyridamole. Am J Cardiol 1983;51:1537–41.[Medline]
10. Schoen FJ. General pathologic considerations. In: Schoen FJ, ed. Interventional and surgical cardiovascular pathology: clinical correlations and basic principles. Philadelphia: Saunders, 1989:1-58.
11. Bodnar E, Butchart EG, Bamford J, Besselaar AMPH, Grunkemeier GL, Frater RWM. Proposal for reporting thrombosis, embolism and bleeding after heart valve replacement. J Heart Valve Dis 1994;3:120–3.[Medline]
12. Kendall M, Stuart A. Robust and distribution free procedures. In: Kendall M, Stuart A, eds. The advanced theory of statistics. London: Griffin & Co., 1979:492-541.
13. Collet D. Some non parametric procedures. In: Collet D, ed. Modelling survival data in medical research. London: Chapman and Hall, 1994:15-51.
14. Edmunds LH Jr, Clark RE, Cohn LH, Miller DG, Weisel RD. Guidelines for reporting morbidity and mortality after cardiac valvular operations. Ann Thorac Surg 1988;46:257–9.[Free Full Text]
15. Renzulli A, de Luca L, Caruso A, Galzerano D, Verde R, Cotrufo M. Acute thrombosis of prosthetic valves: a multivariate analysis of the risk factors for a life-threatening event. Eur J Cardiothorac Surg 1992;6:412–21.[Abstract/Free Full Text]
16. Martinell J, Jimenez A, Rabago G, Artiz V, Fraile J, Farré J. Mechanical cardiac valve thrombosis: is thrombectomy justified? Circulation 1991;84(Suppl 3):70–5.
17. Yoganathan AP, Corcoran WH, Harrison EC, Carl JR. The Björk-Shiley aortic prosthesis: flow characteristics, thrombus formation and tissue overgrowth. Circulation 1978;58:70–6.[Abstract/Free Full Text]
18. De Luca L, Vitale N, Giannolo B, Cafarella G, Piazza L, Cotrufo M. Mid-term follow-up after heart valve replacement with CarboMedics bileaflet prostheses. J Thorac Cardiovasc Surg 1993;106:1158–65.[Abstract]
19. Fann CI, Moreno Cabral CE, Miller DV. Caged-ball valves: the Starr Edwards and Smeloff-Cutter prostheses. In: Bodnar E, Frater RWM, eds. Replacement cardiac valves. New York: Pergamon, 1991:149-86.

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				A. Vahanian, B. Iung, L. Pierard, R. Dion, and J. Pepper CHAPTER 21 Valvular Heart Disease ESC Textbook of Cardiovascular Medicine, January 1, 2009; 2(1): med-9780199566990-chapter - med-9780199566990-chapter. [Abstract] [Full Text] [PDF]

				L. S. Rallidis, C. Papadopoulos, J. Kanakakis, I. Paraskevaidis, and D. T. Kremastinos 'Obstruction alternans' of a Sorin tilting disc prosthetic mitral valve: a case of emergency action Eur Heart J Cardiovasc Imaging, September 1, 2008; 9(5): 704 - 706. [Abstract] [Full Text] [PDF]

				U. Dandekar, M. Kalkat, and C. Smallpeice Fatal early acute thrombosis of mechanical mitral prosthesis Interact CardioVasc Thorac Surg, August 1, 2006; 5(4): 460 - 461. [Abstract] [Full Text] [PDF]

				H. Teshima, N. Hayashida, S. Fukunaga, E. Tayama, T. Kawara, S. Aoyagi, and M. Uchida Usefulness of a multidetector-row computed tomography scanner for detecting pannus formation Ann. Thorac. Surg., February 1, 2004; 77(2): 523 - 526. [Abstract] [Full Text] [PDF]

				R. Roudaut, X. Roques, S. Lafitte, E. Choukroun, N. Laborde, F. Madona, C. Deville, and E. Baudet Surgery for prosthetic valve obstruction. A single center study of 136 patients Eur J Cardiothorac Surg, December 1, 2003; 24(6): 868 - 872. [Abstract] [Full Text] [PDF]

				H. Teshima, N. Hayashida, H. Yano, M. Nishimi, E. Tayama, S. Fukunaga, H. Akashi, T. Kawara, and S. Aoyagi Obstruction of St Jude medical valves in the aortic position: histology and immunohistochemistry of pannus J. Thorac. Cardiovasc. Surg., August 1, 2003; 126(2): 401 - 407. [Abstract] [Full Text] [PDF]

				H. Teshima, N. Hayashida, N. Enomoto, S. Aoyagi, K. Okuda, and M. Uchida Detection of pannus by multidetector-row computed tomography Ann. Thorac. Surg., May 1, 2003; 75(5): 1631 - 1633. [Abstract] [Full Text] [PDF]

				N. Vitale, A. Renzulli, L. de Luca Tupputi Schinosa, and M. Cotrufo Prosthetic valve obstruction: thrombolysis versus operation: Updated in 2000 Ann. Thorac. Surg., December 1, 2000; 70(6): 2182 - 2183. [Abstract] [Full Text] [PDF]

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