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Radiopaque marker in the tilting disc of the Björk-Shiley heart valve
Radiopaque marker in the tilting disc of the Bjork-Shiley heart valve Evaluation of in vivo prosthetic valve function by cineradiography This paper describes a new, noninvasive method for evaluating the in vivo function of the Bjbrk-Shiley tilting disc valve in the aortic, mitral, and tricuspid positions. The tilting disc was equipped with a ring-shaped radiopaque marker, which permits visualization of the motion of the disc by both cineradiographic and fluoroscopic studies. A beam direction corresponding to the axis of motion of the disc should be sought for calculation of the prosthetic opening angle, whereas prostehtic valve closure is demonstrated by a beam direction deviating 20 to 30 degrees from the valve ring plane. Complete opening to 60 degrees and closure of the prosthetic valve, indicating free motility of the tilting disc, were confirmed by cineradiograms. The error of estimation of the in vivo opening angle is small with deviations of less than 15 degrees from the ideal beam direction and negligible for opening angles approaching 60 degrees. Deviations in two planes simultaneously cause less error than deviation in one plane. The radiopaque marker was designed to detect mechanical valve failure owing to thrombotic obstruction. The incidence of this particular complication was 8.1 per 100 patient-years after aortic valve replacement without anticoagulation treatment. With anticoagulation, this incidence was zero after aortic and 2.5 after mitral valve replacement. In our clinical experience to date, which comprises over 1,250 implants, we have not encountered a single case of primary mechanical valve dysfunction. Our current program includes a change-over to the radiopaque tilting-disc model of the Bjork-Shiley prosthesis, which was introduced at this clinic in March, 1975.
V. O. Bjork, M.D., A. Henze, M.D., and T. Hindmarsh, M . D . , Stockholm,
A hrombosis limiting the function of the Bjork-Shiley tilting disc valve has been a rare occurrence in our seven-year clinical experience with more than 1,250 consecutive implants. The risk of prosthetic encapsulation by thrombosis is obviously related to defects in anticoagulation therapy. 3-5 We4 recently reported upon eight cases of thrombosed aortic prostheses. The complication was recognized in five of the patients and emergency thrombectomy was successful in all of them. In addition, a patient with massive thrombosis of the mitral prosthesis was saved by emergency reoperation at this clinic in 1974. The fundamental pathology of thrombotic encapsulation of the prosthetic valve is twofold: obstruction of From the Thoracic Surgical Clinic and the Department of Thoracic Radiology, Karolinska sjukhuset, Stockholm, Sweden. Received for publication May 21, 1976. Accepted for publication Sept. 24, 1976.
Sweden
the prosthetic orifice and impaired or abolished motility of the tilting disc (Fig. 1). Patients with prosthetic thrombosis may be in very poor condition when hospitalized and should undergo operation with the least possible delay. On the other hand, a careful examination by heart catheterization and cardioangiograms is inevitable in patients with minimal symptoms but suspected thrombosis or dysfunction of the prosthetic valve.5 Direct visualization of the motion of the tilting disc would therefore be a valuable aid in the clinical evaluation of such patients. This report deals with our early experience with the radiopaque tilting-disc model Bjork-Shiley prosthesis and describes a simple, noninvasive method for in vivo evaluation of prosthetic valve function. Methods Radiopaque marker. Different types of radiopaque markers were tested by the General Atomic Company, 563
5 64
Bjork, Henze, Hindmarsh
Fig. 1. Thrombotic obstruction of the prosthetic orifice with abolished motility of the tilting disc.
Fig. 2. Bjork-Shiley aortic prosthesis with axis of motion of tilting disc indicated. San Diego, California. The first marker consisted of a mixture of fine tungsten powder and resin, which was filled into a ring-shaped groove in the graphite substrate before the latter was coated with Pyrolite carbon. However, aggregates of tungsten particles migrated into the depth of the coating and, because of the unknown effect of this migration on the wear of the disc,
The Journal of Thoracic and Cardiovascular Surgery
Fig. 3. The strut which slightly protrudes over the inflow profile of the prosthetic ring (top) served as a guide for proper adjustment of the projection. The beam direction corresponded to the axis of motion of the tilting disc as soon as the strut legs became coincident (bottom). this method had to be abandoned. The second type of marker, a metal wire in the shape of a ring, was fitted into the groove of the graphite substrate. Finally, this ring-shaped marker was modified by a metal foil instead of a wire and, after tests with tungsten and tantalum, the latter material was chosen. The dimensions of the tantalum foil ring marker were 0.020 inch (height) by 0.005 inch (thickness) by 0.500 inch (ring diameter). A corresponding groove was machined into the graphite substrate, the marker inserted, and thereafter the substrate coated with Pyrolite carbon. This procedure provided an excellent coating integrity, and no further migration of particles into the coating was observed. However, the shape of the disc with a foil ring marker was changed from a flat to a round back configuration. This spherical design of the inflow portion of the tilting disc permitted uniform surface polishing by using lens grinding techniques, but it slightly increased the thickness at the center of the disc and thereby the weight by 6 per cent. The radiopaque marker also increased the weight somewhat. The strength of the disc with a radiopaque marker is slightly increased and its parts will not become separated if the disc is fractured in a test machine. The graphite substrate serves as a body for the coating, and the groove with the marker does not weaken the structural integrity of the disc. Furthermore, the groove is
Volume 73 Number 4 April, 1977
Bjork-Shiley heart valve
565
* >
Fig. 4. A beam direction deviating 20 to 30 degrees from the valve ring plane was utilized in order to confirm closure of the prosthetic valve.
located near the outlet side of the disc opposite the area of critical wear or stress. Cineradiographic examination. Six patients, who had previously undergone isolated valve replacement with the radiopaque-disc model Bjork-Shiley prosthesis (four aortic, one mitral and one tricuspid), were examined by cineradiography at a frame speed of 24 exposures per second. A beam direction corresponding to the axis of motion of the tilting disc was sought (Fig. 2). The strut, which slightly protrudes over the inflow profile of the prosthetic ring, served as a guide, and proper adjustment of the projection was obtained as soon as the strut legs became coincident (Fig. 3). 6 The opening angle of the prosthetic valve, i.e. the angle between the plane of the tilting disc and that of the valve ring, was calculated from separate tracings or photographs of single exposures on appropriate parts of the cineradiographic film. A beam direction deviating 20 to 30 degrees from the valve ring plane was utilized in order to confirm closure of the prosthetic valve (Fig. 4). Considerations concerning projection. It was usually possible to obtain a beam direction corresponding to the axis of motion of the tilting disc (Fig. 2), provided that this axis did not diverge more than 45 degrees from the horizontal plane of the patient. The Bjork-Shiley prosthesis is preferably oriented in such a way that in the aortic position the bigger portion of the tilting disc opens against the commissure between the right and left coronary sinuses and in the tricuspid and mitral positions against the dorsal plane. The resulting
Fig. 5. Sketch of Bjork-Shiley prosthesis with the tilting disc in the open position. M, Axis of motion of the tilting disc. R, Axis corresponding to the valve ring plane diameter perpendicular toM. D, Axis corresponding to the disc plane diameter perpendicular to M. CR, Central perpendicular axis of the valve ring plane. V, Prosthetic opening angle, i.e., angle between D and R. divergence of the axis of motion of the tilting disc from the horizontal plane of the patient will therefore still permit proper adjustment of the projection. However, other orientations may be required for reasons of free disc motion in narrow aortic roots, small left ventricles, or multivalvular replacements and may later involve difficulties in obtaining optimal projection. Furthermore, cardiac action and respiratory movements will
The Journal of Thoracic and Cardiovascular Surgery
5 6 6 Bjork, Henze, Hindmarsh
Fig. 6. This drawing illustrates how inclination (see text) influences the relationship between the prosthetic opening angle seen on cineradiograms (v J and the in vivo opening angle (v). tg v tg v, = 5 ; cos a = 7 . Thus tg v = tg \Jcos a. a = Angle of inclination. Inclination takes place around the axis corresponding to the valve ring plane diameter, which is perpendicular to the axis of motion of the tilting disc (Fig. 5). Rotation takes place around the central perpendicular axis of the valve ring plane (Fig. 5). The influence of inclination and rotation upon the relationship between the prosthetic opening angle seem on cineradiograms (v^ and the in vivo opening angle (v) is clarified in Figs. 6 and 7. Inclination (Fig. 6) is given by the formula tg v = tg Vj/cos a and rotation by the formula tg v = tg vt • cos /3
Fig. 7. This drawing explains how rotation (see text) influences the relationship between the prosthetic opening angle seen on cineradiograms (vj and the in vivo opening angle (v). tg v = *; tg v, = g; cos /3 = 7. Thus tg v = tg Vj • cos /3. /3 = Angle of rotation. interfere with the maintenance of the projection during serial exposures. The axis of motion of the tilting disc is likely to deviate from the beam direction as a compound movement consisting of inclination and rotation of the prosthetic valve.
where a is angle of inclination and /3 is angle of rotation. For the compound deviation tg v = tg vt
cos ft
cos a v = v, if a = |8.
The relationship between v and Vj at different a and /8 is illustrated in Fig. 8. It is obvious that the error of estimation of the in vivo opening angle by cineradiography is low with deviations of less than 15 degrees and negligible for opening angles approaching 60 degrees. Compound deviations cause a lesser error than inclination or rotation alone. These considerations do not take into account distortion in the roentgen film. However,
Volume 73
Bjdrk-Shiley
Number 4
heart valve
567
April, 1977
Fig. 8. Diagram illustrating the relationship between prosthetic opening angle seen on cineradiograms (v-J and the in vivo opening angle (v). a = Angle of inclination. /3 = Angle of rotation.
such distortion is unlikely to occur when a small object, such as a prosthetic valve, is examined with the central beam. Results The motion of the tilting disc was clearly demonstrated in the 6 patients examined by cineradiography. Appropriate projections on serial heart cycles were obtained in 2 patients and the opening angle was calculated to be 60 degrees, which indicated full opening of the prosthetic valve in both cases. The sequence of the disc motion shown in Fig. 9 may serve as an illustration. Case reports CASE 1. U. P., a 31-year-old woman, had undergone tricuspid valve replacement with a 31 mm. Bjork-Shiley radiopaque-disc prosthesis because of Epstein's disease 2 weeks before the cineradiographic examination (Fig. 9). The heart was now in sinus rhythm. Full opening of the valve prosthesis was reached within 0.083 second, and valve closure, i.e., the downward motion of the tilting disc, was completed within 0.097 second at a heart rate of 65.5 beats per minute or 1.1 beats per second and at a frame speed of 24 exposures per second. CASE 2. V. S., a 63-year-old man, underwent aortic valve replacement with a 25 mm. Bjork-Shiley radiopaque-disc prosthesis on account of aortic valvular disease. Cineradiographic examination 2 weeks later showed full opening of the prosthesis within 0.056 second and closure completed within 0.069 second during sinus rhythm, 78.7 beats per minute or 1.3 beats per second at a rate of 24 exposures per second. Closure of the prosthetic valve was confirmed by a beam
Table I. Incidence of mechanical valve failure owing to thrombotic obstruction after isolated aortic and mitral valve replacements with the Bjork-Shiley prosthesis Anticoag.
No. of patients Total follow-up (patient-years) Mean follow-up per patient (yr.) No. of patients with thrombotic obstruction Thrombotic obstruction per 100 patient—years
No anticoag.
AVR
MVR
AVR
108 540 5.0 0
203 482 2.4 12
91* 61 0.7
0
2.5
MVR
5t 8.1*
-
*No medication in 27 patients. Persantine-acetylsalicylic acid in 64 patients. tAU 5 patients survived reoperation. $Most patients in this series are now taking anticoagulants because of this unacceptable incidence of thrombotic obstruction.
direction deviating 20 to 30 degrees from the valve ring plane. Under these circumstances, the valve ring and radiopaque marker form an elliptical double contour with coincident long axes. Fig. 4 shows two exposures from the same heart cycle in this projection and also demonstrates that deviation occurred during this short period, probably as a result of cardiac action and respiratory movements. Discussion The concept of providing the tilting disc of the Bjork-Shiley prosthesis with a radiopaque marker is not original. Bjork and Ovenfors 1 (1971) employed this
5 6 8 Bjork, Henze, Hindmarsh
The Journal of Thoracic and Cardiovascular Surgery
Fig. 9. Sequence showing motion of tilting disc of 31 mm. Bjork-Shiley prosthesis in the tricuspid position (Patient U. P.). Cineradiographic examination at a rate of 24 exposures per second. Sinus rhythm, 65.5 beats per minute or 1.1 beats per second. Maximal opening angle = 60.1 ± S.D. 1.0 degrees. method in order to study the disc rotation in patients operated upon with the Bjork-Shiley tilting disc valve. Four radiopaque markers were arranged in the tilting disc like the dials in the face of a watch, and this particular design permitted cineradiographic studies of the in vivo disc rotation. With the introduction of the Pyrolite carbon disc,2 it became possible to study the opening and closing motion of the tilting disc by cineradiography. This type of investigation, however, made heavy demands on the radiologist, as the disc could be visualized only in the ideal projection, i.e., with a beam direction coincident with the axis of motion of the tilting disc. The ring-shaped radiopaque marker in the tilting disc made it possible to obtain valuable information about the in vivo function of the Bjork-Shiley prosthesis by routine cineradiographic examination. An ideal projection is not essential for clinical evaluation, although deviations exceeding 15 degrees should not be accepted for determination of the opening angle. We have already pointed out that prosthetic valve closure is most easily confirmed by a beam direction deviating 20 to 30 degrees from the valve ring plane, and this part of the investigation is usually performed without difficulties. This projection is very informative, as thrombotic encapsulation always interferes with prosthetic valve closure. Complete opening to 60 degrees, and closure of the prosthetic valve, indicating free motility of the tilt-
ing disc, were confirmed in the 6 patients examined by cineradiography. Fluoroscopic studies may be employed in clinical work if cineradiographic examination is not available. These noninvasive procedures are well tolerated, even by the critically ill patient. The radiopaque marker was designed for detection of mechanical valve failure caused by thrombotic obstruction. Actual incidences of this particular complication after isolated aortic and mitral valve replacements are shown in Table I. We would emphasize that in our clinical experience to date, comprising more than 1,250 consecutive implants, we have not encountered a single case of primary mechanical valve dysfunction. Our current program includes a transfer to the radiopaque tilting-disc model of the Bjork-Shiley prosthesis, which has been in use at this clinic since March, 1975. REFERENCES 1 Bjork, V. O., and Ovenfors, C. O.: The Disc Rotation in Patients Operated Upon With the Bjork-Shiley Tilting Disc Valves With Radiopaque Markers, Scand. J. Thorac. Cardiovasc. Surg. 5: 83, 1971. 2 Bjork, V. O.: The Pyrolytic Carbon Occluder for the Bjork-Shiley Tilting Disc Valve Prosthesis, Scand. J. Thorac. Cardiovasc. Surg. 6: 109, 1972. 3 Bjork, V. O., and Henze, A.: Encapsulation of the BjorkShiley Aortic Disc Valve Prosthesis Caused by the Lack of
Volume 73 Number 4 April, 1977
Anticoagulation Treatment, Scand. J. Thorac. Cardiovasc. Surg. 7: 17, 1973. 4 Bjork, V. O., and Henze, A.: Management of Thromboembolism After Aortic Valve Replacement With the Bjork-Shiley Tilting Disc Valve, Scand. J. Thorac. Cardiovasc. Surg. 9: 183, 1975.
Bjork-Shiley
heart valve
569
5 Byrd, C. L., Yahr, W. Z., and Greenberg, J. J.: LongTerm Results of "Simple" Thrombectomy for Thrombosed Bjork-Shiley Aortic Valve Prostheses, Ann. Thorac. Surg. 20: 265, 1975. 6 Landou, C , and Hindmarsh, T.: Personal communication, Swedish Soc. Med. Radiol. 4: 49, 1975.
V. O. Bjork, M.D., A. Henze, M.D., and T. Hindmarsh, M . D . , Stockholm,
A hrombosis limiting the function of the Bjork-Shiley tilting disc valve has been a rare occurrence in our seven-year clinical experience with more than 1,250 consecutive implants. The risk of prosthetic encapsulation by thrombosis is obviously related to defects in anticoagulation therapy. 3-5 We4 recently reported upon eight cases of thrombosed aortic prostheses. The complication was recognized in five of the patients and emergency thrombectomy was successful in all of them. In addition, a patient with massive thrombosis of the mitral prosthesis was saved by emergency reoperation at this clinic in 1974. The fundamental pathology of thrombotic encapsulation of the prosthetic valve is twofold: obstruction of From the Thoracic Surgical Clinic and the Department of Thoracic Radiology, Karolinska sjukhuset, Stockholm, Sweden. Received for publication May 21, 1976. Accepted for publication Sept. 24, 1976.
Sweden
the prosthetic orifice and impaired or abolished motility of the tilting disc (Fig. 1). Patients with prosthetic thrombosis may be in very poor condition when hospitalized and should undergo operation with the least possible delay. On the other hand, a careful examination by heart catheterization and cardioangiograms is inevitable in patients with minimal symptoms but suspected thrombosis or dysfunction of the prosthetic valve.5 Direct visualization of the motion of the tilting disc would therefore be a valuable aid in the clinical evaluation of such patients. This report deals with our early experience with the radiopaque tilting-disc model Bjork-Shiley prosthesis and describes a simple, noninvasive method for in vivo evaluation of prosthetic valve function. Methods Radiopaque marker. Different types of radiopaque markers were tested by the General Atomic Company, 563
5 64
Bjork, Henze, Hindmarsh
Fig. 1. Thrombotic obstruction of the prosthetic orifice with abolished motility of the tilting disc.
Fig. 2. Bjork-Shiley aortic prosthesis with axis of motion of tilting disc indicated. San Diego, California. The first marker consisted of a mixture of fine tungsten powder and resin, which was filled into a ring-shaped groove in the graphite substrate before the latter was coated with Pyrolite carbon. However, aggregates of tungsten particles migrated into the depth of the coating and, because of the unknown effect of this migration on the wear of the disc,
The Journal of Thoracic and Cardiovascular Surgery
Fig. 3. The strut which slightly protrudes over the inflow profile of the prosthetic ring (top) served as a guide for proper adjustment of the projection. The beam direction corresponded to the axis of motion of the tilting disc as soon as the strut legs became coincident (bottom). this method had to be abandoned. The second type of marker, a metal wire in the shape of a ring, was fitted into the groove of the graphite substrate. Finally, this ring-shaped marker was modified by a metal foil instead of a wire and, after tests with tungsten and tantalum, the latter material was chosen. The dimensions of the tantalum foil ring marker were 0.020 inch (height) by 0.005 inch (thickness) by 0.500 inch (ring diameter). A corresponding groove was machined into the graphite substrate, the marker inserted, and thereafter the substrate coated with Pyrolite carbon. This procedure provided an excellent coating integrity, and no further migration of particles into the coating was observed. However, the shape of the disc with a foil ring marker was changed from a flat to a round back configuration. This spherical design of the inflow portion of the tilting disc permitted uniform surface polishing by using lens grinding techniques, but it slightly increased the thickness at the center of the disc and thereby the weight by 6 per cent. The radiopaque marker also increased the weight somewhat. The strength of the disc with a radiopaque marker is slightly increased and its parts will not become separated if the disc is fractured in a test machine. The graphite substrate serves as a body for the coating, and the groove with the marker does not weaken the structural integrity of the disc. Furthermore, the groove is
Volume 73 Number 4 April, 1977
Bjork-Shiley heart valve
565
* >
Fig. 4. A beam direction deviating 20 to 30 degrees from the valve ring plane was utilized in order to confirm closure of the prosthetic valve.
located near the outlet side of the disc opposite the area of critical wear or stress. Cineradiographic examination. Six patients, who had previously undergone isolated valve replacement with the radiopaque-disc model Bjork-Shiley prosthesis (four aortic, one mitral and one tricuspid), were examined by cineradiography at a frame speed of 24 exposures per second. A beam direction corresponding to the axis of motion of the tilting disc was sought (Fig. 2). The strut, which slightly protrudes over the inflow profile of the prosthetic ring, served as a guide, and proper adjustment of the projection was obtained as soon as the strut legs became coincident (Fig. 3). 6 The opening angle of the prosthetic valve, i.e. the angle between the plane of the tilting disc and that of the valve ring, was calculated from separate tracings or photographs of single exposures on appropriate parts of the cineradiographic film. A beam direction deviating 20 to 30 degrees from the valve ring plane was utilized in order to confirm closure of the prosthetic valve (Fig. 4). Considerations concerning projection. It was usually possible to obtain a beam direction corresponding to the axis of motion of the tilting disc (Fig. 2), provided that this axis did not diverge more than 45 degrees from the horizontal plane of the patient. The Bjork-Shiley prosthesis is preferably oriented in such a way that in the aortic position the bigger portion of the tilting disc opens against the commissure between the right and left coronary sinuses and in the tricuspid and mitral positions against the dorsal plane. The resulting
Fig. 5. Sketch of Bjork-Shiley prosthesis with the tilting disc in the open position. M, Axis of motion of the tilting disc. R, Axis corresponding to the valve ring plane diameter perpendicular toM. D, Axis corresponding to the disc plane diameter perpendicular to M. CR, Central perpendicular axis of the valve ring plane. V, Prosthetic opening angle, i.e., angle between D and R. divergence of the axis of motion of the tilting disc from the horizontal plane of the patient will therefore still permit proper adjustment of the projection. However, other orientations may be required for reasons of free disc motion in narrow aortic roots, small left ventricles, or multivalvular replacements and may later involve difficulties in obtaining optimal projection. Furthermore, cardiac action and respiratory movements will
The Journal of Thoracic and Cardiovascular Surgery
5 6 6 Bjork, Henze, Hindmarsh
Fig. 6. This drawing illustrates how inclination (see text) influences the relationship between the prosthetic opening angle seen on cineradiograms (v J and the in vivo opening angle (v). tg v tg v, = 5 ; cos a = 7 . Thus tg v = tg \Jcos a. a = Angle of inclination. Inclination takes place around the axis corresponding to the valve ring plane diameter, which is perpendicular to the axis of motion of the tilting disc (Fig. 5). Rotation takes place around the central perpendicular axis of the valve ring plane (Fig. 5). The influence of inclination and rotation upon the relationship between the prosthetic opening angle seem on cineradiograms (v^ and the in vivo opening angle (v) is clarified in Figs. 6 and 7. Inclination (Fig. 6) is given by the formula tg v = tg Vj/cos a and rotation by the formula tg v = tg vt • cos /3
Fig. 7. This drawing explains how rotation (see text) influences the relationship between the prosthetic opening angle seen on cineradiograms (vj and the in vivo opening angle (v). tg v = *; tg v, = g; cos /3 = 7. Thus tg v = tg Vj • cos /3. /3 = Angle of rotation. interfere with the maintenance of the projection during serial exposures. The axis of motion of the tilting disc is likely to deviate from the beam direction as a compound movement consisting of inclination and rotation of the prosthetic valve.
where a is angle of inclination and /3 is angle of rotation. For the compound deviation tg v = tg vt
cos ft
cos a v = v, if a = |8.
The relationship between v and Vj at different a and /8 is illustrated in Fig. 8. It is obvious that the error of estimation of the in vivo opening angle by cineradiography is low with deviations of less than 15 degrees and negligible for opening angles approaching 60 degrees. Compound deviations cause a lesser error than inclination or rotation alone. These considerations do not take into account distortion in the roentgen film. However,
Volume 73
Bjdrk-Shiley
Number 4
heart valve
567
April, 1977
Fig. 8. Diagram illustrating the relationship between prosthetic opening angle seen on cineradiograms (v-J and the in vivo opening angle (v). a = Angle of inclination. /3 = Angle of rotation.
such distortion is unlikely to occur when a small object, such as a prosthetic valve, is examined with the central beam. Results The motion of the tilting disc was clearly demonstrated in the 6 patients examined by cineradiography. Appropriate projections on serial heart cycles were obtained in 2 patients and the opening angle was calculated to be 60 degrees, which indicated full opening of the prosthetic valve in both cases. The sequence of the disc motion shown in Fig. 9 may serve as an illustration. Case reports CASE 1. U. P., a 31-year-old woman, had undergone tricuspid valve replacement with a 31 mm. Bjork-Shiley radiopaque-disc prosthesis because of Epstein's disease 2 weeks before the cineradiographic examination (Fig. 9). The heart was now in sinus rhythm. Full opening of the valve prosthesis was reached within 0.083 second, and valve closure, i.e., the downward motion of the tilting disc, was completed within 0.097 second at a heart rate of 65.5 beats per minute or 1.1 beats per second and at a frame speed of 24 exposures per second. CASE 2. V. S., a 63-year-old man, underwent aortic valve replacement with a 25 mm. Bjork-Shiley radiopaque-disc prosthesis on account of aortic valvular disease. Cineradiographic examination 2 weeks later showed full opening of the prosthesis within 0.056 second and closure completed within 0.069 second during sinus rhythm, 78.7 beats per minute or 1.3 beats per second at a rate of 24 exposures per second. Closure of the prosthetic valve was confirmed by a beam
Table I. Incidence of mechanical valve failure owing to thrombotic obstruction after isolated aortic and mitral valve replacements with the Bjork-Shiley prosthesis Anticoag.
No. of patients Total follow-up (patient-years) Mean follow-up per patient (yr.) No. of patients with thrombotic obstruction Thrombotic obstruction per 100 patient—years
No anticoag.
AVR
MVR
AVR
108 540 5.0 0
203 482 2.4 12
91* 61 0.7
0
2.5
MVR
5t 8.1*
-
*No medication in 27 patients. Persantine-acetylsalicylic acid in 64 patients. tAU 5 patients survived reoperation. $Most patients in this series are now taking anticoagulants because of this unacceptable incidence of thrombotic obstruction.
direction deviating 20 to 30 degrees from the valve ring plane. Under these circumstances, the valve ring and radiopaque marker form an elliptical double contour with coincident long axes. Fig. 4 shows two exposures from the same heart cycle in this projection and also demonstrates that deviation occurred during this short period, probably as a result of cardiac action and respiratory movements. Discussion The concept of providing the tilting disc of the Bjork-Shiley prosthesis with a radiopaque marker is not original. Bjork and Ovenfors 1 (1971) employed this
5 6 8 Bjork, Henze, Hindmarsh
The Journal of Thoracic and Cardiovascular Surgery
Fig. 9. Sequence showing motion of tilting disc of 31 mm. Bjork-Shiley prosthesis in the tricuspid position (Patient U. P.). Cineradiographic examination at a rate of 24 exposures per second. Sinus rhythm, 65.5 beats per minute or 1.1 beats per second. Maximal opening angle = 60.1 ± S.D. 1.0 degrees. method in order to study the disc rotation in patients operated upon with the Bjork-Shiley tilting disc valve. Four radiopaque markers were arranged in the tilting disc like the dials in the face of a watch, and this particular design permitted cineradiographic studies of the in vivo disc rotation. With the introduction of the Pyrolite carbon disc,2 it became possible to study the opening and closing motion of the tilting disc by cineradiography. This type of investigation, however, made heavy demands on the radiologist, as the disc could be visualized only in the ideal projection, i.e., with a beam direction coincident with the axis of motion of the tilting disc. The ring-shaped radiopaque marker in the tilting disc made it possible to obtain valuable information about the in vivo function of the Bjork-Shiley prosthesis by routine cineradiographic examination. An ideal projection is not essential for clinical evaluation, although deviations exceeding 15 degrees should not be accepted for determination of the opening angle. We have already pointed out that prosthetic valve closure is most easily confirmed by a beam direction deviating 20 to 30 degrees from the valve ring plane, and this part of the investigation is usually performed without difficulties. This projection is very informative, as thrombotic encapsulation always interferes with prosthetic valve closure. Complete opening to 60 degrees, and closure of the prosthetic valve, indicating free motility of the tilt-
ing disc, were confirmed in the 6 patients examined by cineradiography. Fluoroscopic studies may be employed in clinical work if cineradiographic examination is not available. These noninvasive procedures are well tolerated, even by the critically ill patient. The radiopaque marker was designed for detection of mechanical valve failure caused by thrombotic obstruction. Actual incidences of this particular complication after isolated aortic and mitral valve replacements are shown in Table I. We would emphasize that in our clinical experience to date, comprising more than 1,250 consecutive implants, we have not encountered a single case of primary mechanical valve dysfunction. Our current program includes a transfer to the radiopaque tilting-disc model of the Bjork-Shiley prosthesis, which has been in use at this clinic since March, 1975. REFERENCES 1 Bjork, V. O., and Ovenfors, C. O.: The Disc Rotation in Patients Operated Upon With the Bjork-Shiley Tilting Disc Valves With Radiopaque Markers, Scand. J. Thorac. Cardiovasc. Surg. 5: 83, 1971. 2 Bjork, V. O.: The Pyrolytic Carbon Occluder for the Bjork-Shiley Tilting Disc Valve Prosthesis, Scand. J. Thorac. Cardiovasc. Surg. 6: 109, 1972. 3 Bjork, V. O., and Henze, A.: Encapsulation of the BjorkShiley Aortic Disc Valve Prosthesis Caused by the Lack of
Volume 73 Number 4 April, 1977
Anticoagulation Treatment, Scand. J. Thorac. Cardiovasc. Surg. 7: 17, 1973. 4 Bjork, V. O., and Henze, A.: Management of Thromboembolism After Aortic Valve Replacement With the Bjork-Shiley Tilting Disc Valve, Scand. J. Thorac. Cardiovasc. Surg. 9: 183, 1975.
Bjork-Shiley
heart valve
569
5 Byrd, C. L., Yahr, W. Z., and Greenberg, J. J.: LongTerm Results of "Simple" Thrombectomy for Thrombosed Bjork-Shiley Aortic Valve Prostheses, Ann. Thorac. Surg. 20: 265, 1975. 6 Landou, C , and Hindmarsh, T.: Personal communication, Swedish Soc. Med. Radiol. 4: 49, 1975.