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Mechanical prosthetic valve-associated strands: Pathologic correlates to transesophageal echocardiography
Mechanical Prosthetic Valve-associated Strands: Pathologic Correlates to Transesophageal Echocardiography John D. Rozich, MD, PhD, William D. Edwards, MD, Richard D. Hanna, MD, Dawn M. Laffey, RCS, Gilbert H. Johnson, PA-C, and Kyle W. Klarich, MD, Eau Claire, Wisconsin; and Rochester, Minnesota
Echocardiographic detection of prosthetic valve-associated strands has previously been reported, but their clinical relevance is unclear. Limited data are available regarding the cause, composition, and natural history of these strands. This report presents the gross and histopathologic findings of an ex-
planted mechanical prosthetic valve shown by transesophageal echocardiography to have several strands. The patient had not experienced prior neurologic symptoms. Potential causes of strand formation in various clinical settings are also discussed. (J Am Soc Echocardiogr 2003;16:97-100.)
A
CASE REPORT
From the Department of Cardiovascular Diseases, Luther Midelfort Clinic–Mayo Health System, Eau Claire, Wis; and the Divisions of Anatomic Pathology (W.D.E.) and Cardiovascular Diseases and Internal Medicine (K.W.K.), Mayo Clinic, Rochester, Minn. Reprint requests: John D. Rozich, MD, Luther Midelfort Clinic– Mayo Health System, 1400 Bellinger St, Eau Claire, WI 54702. Copyright 2003 by the American Society of Echocardiography. 0894-7317/2003/$30.00 ⫹ 0 doi:10.1067/mje.2003.36
A 76-year-old woman presented at our institution with progressive dyspnea, fatigue, and chest pain that was progressive during the preceding 6 months. She denied having had symptoms of a transient ischemic attack, and she had not had a focal stroke. She had a history of aortic valve replacement with a 21-mm Medtronic-Hall tilting disk mechanical valve 16 years earlier because of symptomatic aortic regurgitation. Coronary arteriography had revealed severe 3-vessel obstructive coronary artery disease. Echocardiographic interrogation of the aortic prosthesis revealed velocities by continuous wave Doppler of 4.8 m/s, with a mean gradient across the aortic prosthesis of 53.7 mm Hg. Previous Doppler studies had shown chronically increased transvalvular gradients, and fluoroscopy of the valve revealed normal disk motion within the prosthetic ring. Although the valve appeared to be functioning normally, it was decided to explant the aortic prosthesis at the time of coronary artery bypass grafting because of suspected patient-prosthesis mismatch. Preoperative TEE demonstrated normal motion of the prosthetic tilting disk without evidence of significant thrombus or obstruction. However, several linear echodense strands were seen in the left ventricular outflow tract. These filamentous strands appeared to be either adherent to the disk or associated with the prosthetic annulus. At least 1 larger strand (1 cm in length) was noted among the multiple strands. The larger strand appeared to move independently of the valve motion and could be seen in several different views (Figure 1). Importantly, this structure had not been visualized or commented on in previous reports. There was no evidence of vegetation, perivalvular leak, or excessive motion of the prosthetic annulus. The patient had experienced no fever, malaise, anemia, weight loss, or illness to suggest infective endocarditis.
s many as 30% of focal neurologic events have a cardiac source of embolism. Transesophageal echocardiography (TEE) has been widely accepted as an important imaging modality for the evaluation of patients suspected of having cardioembolic sequelae.1 This is especially true for patients with prosthetic heart valves because the prosthesis is often most precisely defined by TEE, and detection of prosthetic dysfunction and thrombus is thereby enhanced. More recently, filamentous strands of varying lengths attached to, or associated with, prosthetic heart valves have been described.2-5 However, their morphology, composition, and clinical significance are not well understood. Prosthetic valve-associated strands are likely to have multiple causes; previous reports have suggested either a fibrinous or a collagenous composition.6,7 These reports have also noted varying intervals, from days to years, between placement of a prosthesis and detection of strands; this finding also suggests various types of composition and causes.6,7 Although collagen strands may be relatively benign, anecdotal evidence, nonetheless, suggests that they may have embolic potential.6 This report provides gross and histopathologic descriptions of collagen strands in an explanted aortic Medtronic-Hall tilting disk prosthesis.
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extending into the cylinder of the valve orifice by less than 0.15 cm. The tissue was contiguous with the aortic intima and, on gross inspection, was not associated with thrombus; it was consistent with pannus formation. Inspection of the prosthetic annulus revealed a thin, translucent 1-cm filamentous structure that, with gentle agitation in saline, prolapsed into the orifice of the aortic prosthesis. The tissue filament was contiguous with the shelf-like outgrowth noted (Figure 2) and, depending on the force of agitation of saline, extended into and prolapsed through the aortic valve. This tissue filament appeared to be consistent with the large strand that was visualized by echocardiography in the left ventricular outflow tract (Figure 1). This mobile filamentous structure was removed and stained for collagen. A second wisp of tissue was found that measured 0.8 by less than 0.1 cm along its greatest dimensions. On histopathologic study, the strands stained positive with Masson trichrome strain, consistent with collagen. Hematoxylin and eosin staining was negative for fibrin, and staining for elastin was also negative. Figure 3 shows filamentous strands stained for collagen.
DISCUSSION
Figure 1 A, Image from transesophageal echocardiogram (TEE) taken before explantation of aortic prosthesis. Multiplane probe with circular transducer is positioned at 137 degrees. Filamentous echodense structure is clearly identified on left ventricular side of prosthesis and appears attached (arrow). B, Expanded image from TEE with arrow localizing most prominent strand. Strand was freely mobile, with its resultant motion often whipping in and out of image plane. This created real-time images of ribbon-like structure of varying lengths. Superior to large strand are numerous smaller filamentous strands also appearing attached or associated with prosthesis.
At operation, inspection of the valve was unremarkable, according to the surgeon, who had been told of the preoperative TEE findings. Intraoperative TEE again revealed filamentous stranding before incision of the aorta. The explanted prosthetic valve was immediately placed in cold saline and transported to surgical pathology. Gross inspection of the valve within 15 minutes of explantation revealed a small, shelf-like outgrowth of tissue on the aortic side of the prosthesis. It measured approximately 0.7 by 0.1 cm and extended over the “lip” of the sewing ring of the prosthesis, with its border
TEE is a valuable tool for the evaluation of potential sources of emboli, especially in patients with prosthetic heart valves.1,8 The finding of prosthetic valve-associated strands represents a clinical dilemma, because the composition, cause, and management of this finding have remained poorly defined.6,7 Prosthetic valvular strands are generally considered to be thin (⬍1-mm wide), mobile, linear, and echodense structures of varying length associated with the prosthesis.2-8 Interpretation of TEE images has often suggested that these structures are adherent to the leaflets or to the sewing ring, but direct visualization of the origins of these structures has been very limited. Furthermore, diagnostic criteria have not been developed, and there is marked interobserver variability.8 Considering this variability, defining the incidence of prosthetic strands is difficult, but it has been reported to be 18% to 43%.3-5 Strands appear to have been observed more commonly in association with mechanical, as compared with bioprosthetic, valves.4,5 Prosthetic valve strands have been observed as early as 2 hours after valve replacement operation and, in this setting, reports have suggested a fibrin composition.8 Strands have appeared after thrombolytic therapy for obstructive thrombosis of a mechanical valve, again suggesting that the strands are fibrinous.9 Pathologic examination, however, is rare, and strands in these reports may not be representative of those seen in other clinical settings. Isada et al4 examined 3 prosthetic valves at operation and noted thrombus in 1 case, but they did not specifi-
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Figure 2 Inspection of ventricular surface of prosthetic annulus revealed thin, translucent 1-cm filamentous structure, which, with gentle agitation in saline, prolapsed through orifice of aortic prosthesis into what, in situ, would be left ventricular outflow tract (wide arrow). Tissue filament was contiguous with shelf-like outgrowth (thin arrow).
Figure 3 Photomicrograph of aortic valvular strand. A, Low-power view, showing collagenous composition (blue material) (trichrome stain). B, High-power view, showing fibroblasts in dense collagenous extracellular matrix (hematoxylin and eosin).
cally identify the strands visualized on TEE. Orsinelli and Pearson5 described 3 cases involving StarrEdwards mitral valves that were removed because of recurrent emboli. Examination revealed thrombus and pannus on the explanted valves. Because this report showed both thrombus and pannus in the setting of recurrent neurologic injury, heterogeneous composition of the strands could not be excluded. In contrast, there have been 2 reports of prosthetic valve strands consisting primarily of collagen in a pattern similar to Lambl’s excrescences on native valves. Ionescu et al7 report such a strand attached to the atrial side of a leaflet of a bioprosthetic valve removed because of structural deterioration and regurgitation. Hutchinson et al6 reported on a patient with recurrent cerebral emboli and prominent strands associated with a Medtronic-Hall aortic mechanical prosthesis. Translucent white tissue similar to that described in the current report was attached to pannus on the ventricular side of the valve. This report raised the possibility that these lesions have significant embolic potential. The finding in our patient is unusual because the larger strand was contiguous with pannus on the
aortic side of the prosthesis and prolapsed through the orifice of the prosthesis into the left ventricular outflow tract. On gross inspection, it also appeared that the strand and pannus were contiguous with the intima of the aorta, not attached to the valve leaflets but overlying the sewing ring on the aortic surface. Strands have been found to be more common in patients undergoing TEE for evaluation of the source of embolism than in patients examined for other reasons.5 Although this association may imply an embolic potential, prospective follow-up is limited and the therapeutic implications of prosthetic valveassociated strands remain unclear. The pathologic feature described in the current report and that by Hutchinson et al6 is of thin, friable tissue that could conceivably embolize. Mechanical valve-associated embolic events have been reported to occur at rates of approximately 1% per year despite therapeutic anticoagulation.10 However, whether prosthetic valve-associated strands play a role in cardioembolic events remains speculative. Importantly, given the collagen composition of these strands, aggressive therapeutic anticoagulation is not likely to completely eliminate their embolic potential.
100 Rozich et al
This type of strand may easily be overlooked in an explanted valve at operation because it is nearly transparent and it adheres to the prosthesis. Thus, either use of agitated saline or removal with forceps is required for it to be completely visualized. These structures may, therefore, be present in cases of prosthetic valves removed because of recurrent cerebral emboli in which gross and pathologic examination revealed a normal valve. Careful inspection and handling of explanted valves is essential for proper documentation of these strands. The filamentous structures found in our patient were not visible on gross examination by an experienced surgeon. This finding parallels that in other reports, including that of Magarey,11 who observed that Lambl’s excrescences are often not visible in situ. The pearly white, nearly transparent characteristics of the filamentous structures make detailed gross inspection extremely difficult (Linden RP, personal communication, 2002) and may account for negative findings at the time of operation and explantation.6 Furthermore, discussions with our pathologists underscore the importance of direct communication among surgeon, echocardiographer, and pathologist, because gentle agitation of the explanted prosthesis was necessary to allow visualization of the filamentous structures that otherwise had become adherent to the sewing ring. Whether fixation in formalin complicates detection of these delicate structures is unclear, but it is recommended that at removal the explanted valves and associated tissue be transported immediately in cold saline to the pathologist. In summary, the current report provides additional insight into the origin of TEE-detected filamentous strands associated with mechanical prosthetic valves. Further study of the specific mechanisms of formation and the composition of these strands is needed to determine their natural history and the optimal clinical management.
Journal of the American Society of Echocardiography January 2003
John Rozich, MD, and Richard P. Linden, MD, provided the photograph of the explanted prosthetic valve. REFERENCES 1. Lee RJ, Bartzokis T, Yeoh TK, Grogin HR, Choi D, Schnittger I. Enhanced detection of intracardiac sources of cerebral emboli by transesophageal echocardiography. Stroke 1991; 22:734-9. 2. Stoddard MF, Dawkins PR, Longaker RA. Mobile strands are frequently attached to the St. Jude Medical mitral valve prosthesis as assessed by two-dimensional transesophageal echocardiography. Am Heart J 1992;124:671-4. 3. Iung B, Cormier B, Dadez E, Drissi MF, Tsezana R, Viguier E, et al. Small abnormal echos after mitral valve replacement with bileaflet mechanical prostheses: predisposing factors and effect on thromboembolism. J Heart Valve Dis 1993;2:259-66. 4. Isada LR, Torelli JN, Stewart WJ, Klein AL. Detection of fibrous strands on prosthetic mitral valves with transesophageal echocardiography: another potential embolic source. J Am Soc Echocardiogr 1994;7:641-5. 5. Orsinelli DA, Pearson AC. Detection of prosthetic valve strands by transesophageal echocardiography: clinical significance in patients with suspected cardiac source of embolism. J Am Coll Cardiol 1995;26:1713-8. 6. Hutchinson K, Hafeez F, Woods TD, Chopra PS, Warner TF, Levine RL, et al. Recurrent ischemic strokes in a patient with Medtronic-Hall prosthetic aortic valve and valve strands. J Am Soc Echocardiogr 1998;11:755-7. 7. Ionescu AA, Newman GR, Butchart EG, Fraser AG. Morphologic analysis of a strand recovered from a prosthetic mitral valve: no evidence of fibrin. J Am Soc Echocardiogr 1999;12: 766-8. 8. Ionescu AA, Moreno de la Santa P, Dunstan FD, Butchart EG, Fraser AG. Mobile echoes on prosthetic valves are not reproducible: results and clinical implications of a multicentre study. Eur Heart J 1999;20:140-7. 9. Narins CR, Eichelberger JP. The development of valvular strands during thrombolytic therapy detected by transesophageal echocardiography. J Am Soc Echocardiogr 1996;9:888-90. 10. Vongpatanasin W, Hillis LD, Lange RA. Prosthetic heart valves. N Engl J Med 1996;335:407-16. 11. Magarey FR. On the mode of formation of Lambl’s excrescences and their relation to chronic thickening of the mitral valve. J Pathol Bacteriol 1949;61:203-8.
Echocardiographic detection of prosthetic valve-associated strands has previously been reported, but their clinical relevance is unclear. Limited data are available regarding the cause, composition, and natural history of these strands. This report presents the gross and histopathologic findings of an ex-
planted mechanical prosthetic valve shown by transesophageal echocardiography to have several strands. The patient had not experienced prior neurologic symptoms. Potential causes of strand formation in various clinical settings are also discussed. (J Am Soc Echocardiogr 2003;16:97-100.)
A
CASE REPORT
From the Department of Cardiovascular Diseases, Luther Midelfort Clinic–Mayo Health System, Eau Claire, Wis; and the Divisions of Anatomic Pathology (W.D.E.) and Cardiovascular Diseases and Internal Medicine (K.W.K.), Mayo Clinic, Rochester, Minn. Reprint requests: John D. Rozich, MD, Luther Midelfort Clinic– Mayo Health System, 1400 Bellinger St, Eau Claire, WI 54702. Copyright 2003 by the American Society of Echocardiography. 0894-7317/2003/$30.00 ⫹ 0 doi:10.1067/mje.2003.36
A 76-year-old woman presented at our institution with progressive dyspnea, fatigue, and chest pain that was progressive during the preceding 6 months. She denied having had symptoms of a transient ischemic attack, and she had not had a focal stroke. She had a history of aortic valve replacement with a 21-mm Medtronic-Hall tilting disk mechanical valve 16 years earlier because of symptomatic aortic regurgitation. Coronary arteriography had revealed severe 3-vessel obstructive coronary artery disease. Echocardiographic interrogation of the aortic prosthesis revealed velocities by continuous wave Doppler of 4.8 m/s, with a mean gradient across the aortic prosthesis of 53.7 mm Hg. Previous Doppler studies had shown chronically increased transvalvular gradients, and fluoroscopy of the valve revealed normal disk motion within the prosthetic ring. Although the valve appeared to be functioning normally, it was decided to explant the aortic prosthesis at the time of coronary artery bypass grafting because of suspected patient-prosthesis mismatch. Preoperative TEE demonstrated normal motion of the prosthetic tilting disk without evidence of significant thrombus or obstruction. However, several linear echodense strands were seen in the left ventricular outflow tract. These filamentous strands appeared to be either adherent to the disk or associated with the prosthetic annulus. At least 1 larger strand (1 cm in length) was noted among the multiple strands. The larger strand appeared to move independently of the valve motion and could be seen in several different views (Figure 1). Importantly, this structure had not been visualized or commented on in previous reports. There was no evidence of vegetation, perivalvular leak, or excessive motion of the prosthetic annulus. The patient had experienced no fever, malaise, anemia, weight loss, or illness to suggest infective endocarditis.
s many as 30% of focal neurologic events have a cardiac source of embolism. Transesophageal echocardiography (TEE) has been widely accepted as an important imaging modality for the evaluation of patients suspected of having cardioembolic sequelae.1 This is especially true for patients with prosthetic heart valves because the prosthesis is often most precisely defined by TEE, and detection of prosthetic dysfunction and thrombus is thereby enhanced. More recently, filamentous strands of varying lengths attached to, or associated with, prosthetic heart valves have been described.2-5 However, their morphology, composition, and clinical significance are not well understood. Prosthetic valve-associated strands are likely to have multiple causes; previous reports have suggested either a fibrinous or a collagenous composition.6,7 These reports have also noted varying intervals, from days to years, between placement of a prosthesis and detection of strands; this finding also suggests various types of composition and causes.6,7 Although collagen strands may be relatively benign, anecdotal evidence, nonetheless, suggests that they may have embolic potential.6 This report provides gross and histopathologic descriptions of collagen strands in an explanted aortic Medtronic-Hall tilting disk prosthesis.
97
98 Rozich et al
Journal of the American Society of Echocardiography January 2003
extending into the cylinder of the valve orifice by less than 0.15 cm. The tissue was contiguous with the aortic intima and, on gross inspection, was not associated with thrombus; it was consistent with pannus formation. Inspection of the prosthetic annulus revealed a thin, translucent 1-cm filamentous structure that, with gentle agitation in saline, prolapsed into the orifice of the aortic prosthesis. The tissue filament was contiguous with the shelf-like outgrowth noted (Figure 2) and, depending on the force of agitation of saline, extended into and prolapsed through the aortic valve. This tissue filament appeared to be consistent with the large strand that was visualized by echocardiography in the left ventricular outflow tract (Figure 1). This mobile filamentous structure was removed and stained for collagen. A second wisp of tissue was found that measured 0.8 by less than 0.1 cm along its greatest dimensions. On histopathologic study, the strands stained positive with Masson trichrome strain, consistent with collagen. Hematoxylin and eosin staining was negative for fibrin, and staining for elastin was also negative. Figure 3 shows filamentous strands stained for collagen.
DISCUSSION
Figure 1 A, Image from transesophageal echocardiogram (TEE) taken before explantation of aortic prosthesis. Multiplane probe with circular transducer is positioned at 137 degrees. Filamentous echodense structure is clearly identified on left ventricular side of prosthesis and appears attached (arrow). B, Expanded image from TEE with arrow localizing most prominent strand. Strand was freely mobile, with its resultant motion often whipping in and out of image plane. This created real-time images of ribbon-like structure of varying lengths. Superior to large strand are numerous smaller filamentous strands also appearing attached or associated with prosthesis.
At operation, inspection of the valve was unremarkable, according to the surgeon, who had been told of the preoperative TEE findings. Intraoperative TEE again revealed filamentous stranding before incision of the aorta. The explanted prosthetic valve was immediately placed in cold saline and transported to surgical pathology. Gross inspection of the valve within 15 minutes of explantation revealed a small, shelf-like outgrowth of tissue on the aortic side of the prosthesis. It measured approximately 0.7 by 0.1 cm and extended over the “lip” of the sewing ring of the prosthesis, with its border
TEE is a valuable tool for the evaluation of potential sources of emboli, especially in patients with prosthetic heart valves.1,8 The finding of prosthetic valve-associated strands represents a clinical dilemma, because the composition, cause, and management of this finding have remained poorly defined.6,7 Prosthetic valvular strands are generally considered to be thin (⬍1-mm wide), mobile, linear, and echodense structures of varying length associated with the prosthesis.2-8 Interpretation of TEE images has often suggested that these structures are adherent to the leaflets or to the sewing ring, but direct visualization of the origins of these structures has been very limited. Furthermore, diagnostic criteria have not been developed, and there is marked interobserver variability.8 Considering this variability, defining the incidence of prosthetic strands is difficult, but it has been reported to be 18% to 43%.3-5 Strands appear to have been observed more commonly in association with mechanical, as compared with bioprosthetic, valves.4,5 Prosthetic valve strands have been observed as early as 2 hours after valve replacement operation and, in this setting, reports have suggested a fibrin composition.8 Strands have appeared after thrombolytic therapy for obstructive thrombosis of a mechanical valve, again suggesting that the strands are fibrinous.9 Pathologic examination, however, is rare, and strands in these reports may not be representative of those seen in other clinical settings. Isada et al4 examined 3 prosthetic valves at operation and noted thrombus in 1 case, but they did not specifi-
Journal of the American Society of Echocardiography Volume 16 Number 1
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Figure 2 Inspection of ventricular surface of prosthetic annulus revealed thin, translucent 1-cm filamentous structure, which, with gentle agitation in saline, prolapsed through orifice of aortic prosthesis into what, in situ, would be left ventricular outflow tract (wide arrow). Tissue filament was contiguous with shelf-like outgrowth (thin arrow).
Figure 3 Photomicrograph of aortic valvular strand. A, Low-power view, showing collagenous composition (blue material) (trichrome stain). B, High-power view, showing fibroblasts in dense collagenous extracellular matrix (hematoxylin and eosin).
cally identify the strands visualized on TEE. Orsinelli and Pearson5 described 3 cases involving StarrEdwards mitral valves that were removed because of recurrent emboli. Examination revealed thrombus and pannus on the explanted valves. Because this report showed both thrombus and pannus in the setting of recurrent neurologic injury, heterogeneous composition of the strands could not be excluded. In contrast, there have been 2 reports of prosthetic valve strands consisting primarily of collagen in a pattern similar to Lambl’s excrescences on native valves. Ionescu et al7 report such a strand attached to the atrial side of a leaflet of a bioprosthetic valve removed because of structural deterioration and regurgitation. Hutchinson et al6 reported on a patient with recurrent cerebral emboli and prominent strands associated with a Medtronic-Hall aortic mechanical prosthesis. Translucent white tissue similar to that described in the current report was attached to pannus on the ventricular side of the valve. This report raised the possibility that these lesions have significant embolic potential. The finding in our patient is unusual because the larger strand was contiguous with pannus on the
aortic side of the prosthesis and prolapsed through the orifice of the prosthesis into the left ventricular outflow tract. On gross inspection, it also appeared that the strand and pannus were contiguous with the intima of the aorta, not attached to the valve leaflets but overlying the sewing ring on the aortic surface. Strands have been found to be more common in patients undergoing TEE for evaluation of the source of embolism than in patients examined for other reasons.5 Although this association may imply an embolic potential, prospective follow-up is limited and the therapeutic implications of prosthetic valveassociated strands remain unclear. The pathologic feature described in the current report and that by Hutchinson et al6 is of thin, friable tissue that could conceivably embolize. Mechanical valve-associated embolic events have been reported to occur at rates of approximately 1% per year despite therapeutic anticoagulation.10 However, whether prosthetic valve-associated strands play a role in cardioembolic events remains speculative. Importantly, given the collagen composition of these strands, aggressive therapeutic anticoagulation is not likely to completely eliminate their embolic potential.
100 Rozich et al
This type of strand may easily be overlooked in an explanted valve at operation because it is nearly transparent and it adheres to the prosthesis. Thus, either use of agitated saline or removal with forceps is required for it to be completely visualized. These structures may, therefore, be present in cases of prosthetic valves removed because of recurrent cerebral emboli in which gross and pathologic examination revealed a normal valve. Careful inspection and handling of explanted valves is essential for proper documentation of these strands. The filamentous structures found in our patient were not visible on gross examination by an experienced surgeon. This finding parallels that in other reports, including that of Magarey,11 who observed that Lambl’s excrescences are often not visible in situ. The pearly white, nearly transparent characteristics of the filamentous structures make detailed gross inspection extremely difficult (Linden RP, personal communication, 2002) and may account for negative findings at the time of operation and explantation.6 Furthermore, discussions with our pathologists underscore the importance of direct communication among surgeon, echocardiographer, and pathologist, because gentle agitation of the explanted prosthesis was necessary to allow visualization of the filamentous structures that otherwise had become adherent to the sewing ring. Whether fixation in formalin complicates detection of these delicate structures is unclear, but it is recommended that at removal the explanted valves and associated tissue be transported immediately in cold saline to the pathologist. In summary, the current report provides additional insight into the origin of TEE-detected filamentous strands associated with mechanical prosthetic valves. Further study of the specific mechanisms of formation and the composition of these strands is needed to determine their natural history and the optimal clinical management.
Journal of the American Society of Echocardiography January 2003
John Rozich, MD, and Richard P. Linden, MD, provided the photograph of the explanted prosthetic valve. REFERENCES 1. Lee RJ, Bartzokis T, Yeoh TK, Grogin HR, Choi D, Schnittger I. Enhanced detection of intracardiac sources of cerebral emboli by transesophageal echocardiography. Stroke 1991; 22:734-9. 2. Stoddard MF, Dawkins PR, Longaker RA. Mobile strands are frequently attached to the St. Jude Medical mitral valve prosthesis as assessed by two-dimensional transesophageal echocardiography. Am Heart J 1992;124:671-4. 3. Iung B, Cormier B, Dadez E, Drissi MF, Tsezana R, Viguier E, et al. Small abnormal echos after mitral valve replacement with bileaflet mechanical prostheses: predisposing factors and effect on thromboembolism. J Heart Valve Dis 1993;2:259-66. 4. Isada LR, Torelli JN, Stewart WJ, Klein AL. Detection of fibrous strands on prosthetic mitral valves with transesophageal echocardiography: another potential embolic source. J Am Soc Echocardiogr 1994;7:641-5. 5. Orsinelli DA, Pearson AC. Detection of prosthetic valve strands by transesophageal echocardiography: clinical significance in patients with suspected cardiac source of embolism. J Am Coll Cardiol 1995;26:1713-8. 6. Hutchinson K, Hafeez F, Woods TD, Chopra PS, Warner TF, Levine RL, et al. Recurrent ischemic strokes in a patient with Medtronic-Hall prosthetic aortic valve and valve strands. J Am Soc Echocardiogr 1998;11:755-7. 7. Ionescu AA, Newman GR, Butchart EG, Fraser AG. Morphologic analysis of a strand recovered from a prosthetic mitral valve: no evidence of fibrin. J Am Soc Echocardiogr 1999;12: 766-8. 8. Ionescu AA, Moreno de la Santa P, Dunstan FD, Butchart EG, Fraser AG. Mobile echoes on prosthetic valves are not reproducible: results and clinical implications of a multicentre study. Eur Heart J 1999;20:140-7. 9. Narins CR, Eichelberger JP. The development of valvular strands during thrombolytic therapy detected by transesophageal echocardiography. J Am Soc Echocardiogr 1996;9:888-90. 10. Vongpatanasin W, Hillis LD, Lange RA. Prosthetic heart valves. N Engl J Med 1996;335:407-16. 11. Magarey FR. On the mode of formation of Lambl’s excrescences and their relation to chronic thickening of the mitral valve. J Pathol Bacteriol 1949;61:203-8.