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Comparative Doppler evaluation of the monostrut and older convexo-concave Björk-Shiley mitral prosthetic valve
Internattonal Elsevier
CARD10
Journal of Cardialog),
355
24 (1989) 355-358
00924
Comparative Doppler evaluation of the monostrut and older convexo-concave BjiSrk-Shiley mitral prosthetic valve S. Radhakrishnan, Department
V. Dev, Anita Saxena, V.K. Bahl, P. Venugopal
of Cardiology and Cardiothoracic (Received
and S. Shrivastava
Surgery, All India Institute of Medical Sciences, New Delhi, India
4 July 1988; revision
accepted
6 April 1989)
Radhakrishnan S, Dev V, Saxena A, Bahl VK, Venugopal P, Shrivastava S. Comparative Doppler evaluation of the monostrut and older convexo-concave Bjiirk-Shiley mitral prosthetic valve. Int J Cardiol 1989;24:355-358. Doppler echocardiography was performed in 104 patients with a Bjiirk-Shiley prosthetic valve in the mitral position. Valves of size 25 mm and 27 mm were inserted in 39 and 65 patients, respectively. Each valve had two models; the older convexo-concave model (22 and 40, of 25 and 27 mm size, respectively). Inflow velocities were recorded using Doppler techniques and the gradients calculated using the Bernoulli principle. The area of the mitral valve was determined by the T1,2 method. Comparison of the two models for both sizes did not reveal any significant differences in either the gradients across the valves or the area of the valve. Trivial mitral regurgitation was detected in a higher percentage of monostrut valves (18% and 20% for the 25 and 27 mm older convexo-concave models and 59.9% and 52% for the 25 and 27 mm monostrut valve). We conclude that the newer monostrut model of the BjGrk-Shiley valve in the mitral position does not offer any additional haemodynamic benefit. Key words:
Bjiirk-Shiley
prosthetic
valve;
Monostrut
Introduction Prosthetic heart valves are commonly used for the treatment of valvar heart diseases. In our institution, the Bjiirk-Shiley prosthetic valve continues to be used with good results [l]. Because of ever growing technologic advances, newer models of prosthetic valves are being evaluated in order to improve haemodynamics, to decrease the rate of thrombosis or thrombo-embolism and to improve
Correspondence to: S. Shrivastava, M.D., Dept. of Cardiology, All India Institute of Medical Sciences, New Delhi-110029, India. 0167-5273/89/$03.50
6 1989 Elsevier Science
Publishers
valve:
Doppler
echocardiography
durability. The Bjork-Shiley prosthetic valve has undergone several such changes since its introduction in 1969 [2]. The most recent of these changes is the introduction of a model based on a monostrut. In vitro studies [3,4] and clinical experience [5] have shown favourable reports when compared to the older models. Haemodynamic evaluation from patients, however, comparing the monostrut valve with the older models inserted in mitral position, is not yet available. Since Doppler echocardiography has been used increasingly in the evaluation of prosthetic valves, and since gradients measured in this way have been found to correlate well with haemodynamic studies [6], we have evaluated ve-
B.V. (Biomedical
Division)
356 TABLE
size. Each size had two models. In the 25 mm size there were 17 monostrut and 22 of the older convexo-concave models, respectively. In the 27 mm size, 25 were of the monostrut variety and 40 were of the older convexo-concave model (Table
1
Number and models of the BjGrk-Shiley prosthetic and incidence of preoperative aortic regurgitation Convexo-concave
Monostrut
models
(mm)
No. of patients
Preoperative AR (8)
No. of patients
Preoperative AR (S)
25 27
17 25
12/22 21/40
22 40
6/X 12/25
Valve size
models
valve studied (AR).
(54) (52.5)
1). Rheumatic heart disease was the underlying cause for replacement of the valve in all cases. Mitral regurgitation was the predominant lesion in 38 patients (34.65%). Forty-two patients (40.3%) had a combination of mitral stenosis and regurgitation and 26 (25%) patients had predominant valvar stenosis. As assessed by preoperative angiography, trivial to mild aortic regurgitation was observed in a total of 51 cases; for this no surgical intervention was attempted. There was no significant difference in the incidence of aortic regurgitation in patients with different size and models of the prosthesis inserted (Table 1).
(13.2) (48)
locities measured by Doppler echocardiography and used them to calculate gradients across BjbrkShiley prostheses inserted in mitral position. In this way, we have compared the monostrut valves with the older convexo-concave model. Materials
and Methods
Patients Doppler echocardiographic evaluation was conducted in 104 patients in whom the mitral valve had been replaced using a Bjork-Shiley prosthesis. Normal prosthetic valvar function was established by clinical, fluoroscopic and M-mode echocardiographic examination. Patients with reduced left ventricular function on echocardiography (ejection fraction less than 55%) were not included in the study. The age of the patients ranged from 16 to 48 years (mean 30.2 years). The mean period of study from the time of operation onwards was 19.6 months.
Doppler Study Doppler echocardiography was performed with the ATL Ultramark 8 machine which is equipped with both pulsed and continuous wave Doppler systems. M-mode echocardiographic examination was performed to determine the size and function of the left ventricle and motion of the disc. Velocity profiles across the prosthetic valves were studied initially in the pulsed Doppler mode in apical four chamber view, with the sample volume in the left ventricle. Subsequent measurements of velocities and gradients were obtained from signals of the
Valve sizes and models. Of the prostheses inserted, 39 were of 25 mm size and 65 of the 27 mm TABLE
2
Doppler
velocity,
Valve size and models
gradients
and area of different
models
of Bjark-Shiley
prosthetic
valve.
No. of patients
Peak velocity
Peak gradient
EDG
MVA
(m/xc)
(mm Hg)
(mm Hg)
(mm Hg)
MR (%) (Trivial)
MBUC MBUMS 21 mm
22 17
1.6 k 0.3 1.6 f 0.3
10.5 f 4.5 10.3 f 3.7
2.4 f 1.8 2.4 + 1.7
2.5 f 0.3 2.8 f 0.3
18 59
MBUC MBUMS
40 25
1.5 f 0.2 1.6 f 0.3
9.3 f 2.8 10.0 + 4.5
2.6 * 1.9 2.1 * 2.1
2.6 i 0.3 2.5 k 0.4
20 52 *
25 mm
* P -C0.05. MBUC = older convexo-concave valvar area; MR = mitral regurgitation.
models:
MBUMS
= monostrut
valves;
EDG = end diastolic
gradients;
MVA = mitral
357
continuous wave technique using the same view. Those signals with the most clearly defined envelope and highest velocities were chosen for calculation of gradients, using the modified Bernoulli principle ( p = 4 X V’). The values were expressed in millimeters of mercury. The area of the prosthetic valve was calculated using the T,,, method and expressed as centimeters squared. Calculations were done by averaging the calculations for three beats in patients in sinus rhythm and five beats in patients in atria1 fibrillation. Mitral regurgitation was evaluated from the apical and parasternal windows in four chamber and long axis views. It was graded as mild if the jet extended only at or within two centimeters of the prosthetic valve and significant if detected in the left atria1 cavity beyond this distance. Statistical comparison of the two valve models was done using the Student’s r-test. The differences in incidence of mitral regurgitation were calculated by the chi-square test.
Results Velocity
and gradients
Peak velocity at early and end-diastole and the corresponding calculations of gradients and valve area are shown in Table 2. For the 25 mm size, the peak gradient, end-diastolic gradient and valvar area were 10.4 + 4.2 mm Hg, 2.4 k 1.8 mm Hg and 2.7 + 0.4 cm2, respectively. For the 27 mm size these values were 9.6 + 3.6 mm Hg, 2.4 + 2.1 mm Hg and 2.6 + 0.3 cm2, respectively. There was no significant difference between these values. When the two models of the same size were compared, there was no difference in the peak and end-diastolic gradients nor in the area of the valve. Mitral regurgitation was detected in a total of 34 cases (32.6%). It was found in 13 patients (33.3%) with the 25 mm size and 21 patients (32.2%) with the 27 mm size prosthesis. In all cases, it was localized to the site of valves, never extending beyond 1 cm of the valve. Comparison of the incidence of mitral regurgitation in the two models of 25 mm and 27 mm revealed a higher incidence for the monostrut valves. In the 25 mm size, it was 59 and 18% and
for the 27 mm size 52 and 20% for the monostrut and older convexo-concave models, respectively. These values reached statistical significance only for the 27 mm size valve (P < 0.05).
Discussion The Bjiirk-Shiley monostrut prosthetic heart valve was introduced in 1982 in an attempt to decrease mechanical dysfunction. The valve is made of a pyrolite carbon disc and the outflow strut has been made an integral part of the valve ring, taking the form of a monostrut [4]. The opening angle of the convexo-concave disc was increased to 70 o instead of the 60 o which existed in the older models. In-vitro studies showed that the increased angles significantly improved characteristics of flow, the turbulence and vortex formation which had indicated impairment of flow through the smaller orifice being reduced [4]. Studies have also shown that these valves create less resistance to flow as compared to the 60” convexo-concave model when inserted both in mitral and aortic positions [3,4]. Stevenson et al. [4] reported an average improvement in pressure drop calculated in vitro of 30-40 and 20-30% for steady and pulsatile flow, respectively [4]. Bjork et al. [5], in a study of 79 patients in whom a monostrut Bjiirk-Shiley prosthesis had been inserted in mitral position and followed for 2-3 years, found a negligible incidence of intravascular hemolysis and complete absence of valvar thrombosis [5]. Haemodynamic studies performed during life are not available for patients in whom the monostrut valves have been inserted in mitral position. Since gradients across a prosthetic valve inserted in mitral position and measured by Doppler techniques have been shown to correlate well with haemodynamic measurements [6], we conducted the present study to compare such gradients calculated for the monostrut valve with the older convexo-concave models. In a previous communication we have established norms for the older models of the Bjbrk-Shiley prosthesis inserted in mitral position and found no significant difference in gradients and areas between the two sizes (25 mm and 27 mm) [7]. The present study did not
358
show any significant difference between the older convexo-concave models and the monostrut valves with respect to Doppler derived gradients and areas. The incidence of mitral regurgitation, although trivial, was higher in the monostrut valves. This is unlikely to produce any significant haemodynamic compromise. but it is noteworthy that a similar higher incidence of regurgitation has been reported in in-vitro studies of the monostrut valves [4]. Within the limitations of the Doppler technique used, and its observed insensitivity of distinguishing between prostheses of different size (25 mm vs 27 mm), our initial experience suggests that the newer monostrut Bjork-Shiley prosthesis does not seem to offer any significant haemodynamic advantage when inserted in the clinical setting over the older convexo-concave model.
Acknowledgements The authors wish to thank their surgical colleagues from the Department of Cardiovascular and Thoracic Surgery for providing us with the cases. We also wish to thank our echocardio-
graphic technician Miss Rita Mohla, for her invaluable assistance in this study.
References Balram A, Kaul U. Rao RBV et al. Thrombotic obstruction of Bjiirk-Shiley valves. Diagnostic and surgical consideration. Int J Cardiol 1984;6:61-69. Bjiirk VO. A new tilting disc valve prosthesis. Stand J Thorac Cardiovasc Surg 1969;3:1-10. Bruss KH, Renl H, Van Gilse F, Knoth E. Pressure drop and velocity yields of mechanical heart valve prosthesis: Bjork-Shiley standard. BjGrk-Shiley concave-convex, Hall Laster, St. Judge. Life Support Syst 1983;1:3-22. Stevenson DM, Yoganathan AP, Francn RH. The BjBrk-Shiley heart valve prosthesis: flow characteristics of the new 70 o model. Stand J Thorac Cardiovasc Surg 1982;16:1-7. BjBrk VO. Lindblom D. The monostrut Bjiirk-Shiley heart valve. Seminars on cardiac valve replacement. II. J Am Co11 Cardiol 1985:6:1142-1148. Sagar KB, Wann S. Paulsen WH, Romhilt DW. Doppler echocardiographic evaluation of Hancock and Bjork-Shiley prosthetic valve. J Am Co11 Cardiol 1986;7:681-687. Radhakrishnan S, Behl VK. Bajaj R. Bhatia ML. Shrivastava S. Doppler echocardiographic evaluation of normal and thrombosed Bjiirk-Shiley mitral prosthetic valves. Int J Cardiol 1989:20:3X7-394.
CARD10
Journal of Cardialog),
355
24 (1989) 355-358
00924
Comparative Doppler evaluation of the monostrut and older convexo-concave BjiSrk-Shiley mitral prosthetic valve S. Radhakrishnan, Department
V. Dev, Anita Saxena, V.K. Bahl, P. Venugopal
of Cardiology and Cardiothoracic (Received
and S. Shrivastava
Surgery, All India Institute of Medical Sciences, New Delhi, India
4 July 1988; revision
accepted
6 April 1989)
Radhakrishnan S, Dev V, Saxena A, Bahl VK, Venugopal P, Shrivastava S. Comparative Doppler evaluation of the monostrut and older convexo-concave Bjiirk-Shiley mitral prosthetic valve. Int J Cardiol 1989;24:355-358. Doppler echocardiography was performed in 104 patients with a Bjiirk-Shiley prosthetic valve in the mitral position. Valves of size 25 mm and 27 mm were inserted in 39 and 65 patients, respectively. Each valve had two models; the older convexo-concave model (22 and 40, of 25 and 27 mm size, respectively). Inflow velocities were recorded using Doppler techniques and the gradients calculated using the Bernoulli principle. The area of the mitral valve was determined by the T1,2 method. Comparison of the two models for both sizes did not reveal any significant differences in either the gradients across the valves or the area of the valve. Trivial mitral regurgitation was detected in a higher percentage of monostrut valves (18% and 20% for the 25 and 27 mm older convexo-concave models and 59.9% and 52% for the 25 and 27 mm monostrut valve). We conclude that the newer monostrut model of the BjGrk-Shiley valve in the mitral position does not offer any additional haemodynamic benefit. Key words:
Bjiirk-Shiley
prosthetic
valve;
Monostrut
Introduction Prosthetic heart valves are commonly used for the treatment of valvar heart diseases. In our institution, the Bjiirk-Shiley prosthetic valve continues to be used with good results [l]. Because of ever growing technologic advances, newer models of prosthetic valves are being evaluated in order to improve haemodynamics, to decrease the rate of thrombosis or thrombo-embolism and to improve
Correspondence to: S. Shrivastava, M.D., Dept. of Cardiology, All India Institute of Medical Sciences, New Delhi-110029, India. 0167-5273/89/$03.50
6 1989 Elsevier Science
Publishers
valve:
Doppler
echocardiography
durability. The Bjork-Shiley prosthetic valve has undergone several such changes since its introduction in 1969 [2]. The most recent of these changes is the introduction of a model based on a monostrut. In vitro studies [3,4] and clinical experience [5] have shown favourable reports when compared to the older models. Haemodynamic evaluation from patients, however, comparing the monostrut valve with the older models inserted in mitral position, is not yet available. Since Doppler echocardiography has been used increasingly in the evaluation of prosthetic valves, and since gradients measured in this way have been found to correlate well with haemodynamic studies [6], we have evaluated ve-
B.V. (Biomedical
Division)
356 TABLE
size. Each size had two models. In the 25 mm size there were 17 monostrut and 22 of the older convexo-concave models, respectively. In the 27 mm size, 25 were of the monostrut variety and 40 were of the older convexo-concave model (Table
1
Number and models of the BjGrk-Shiley prosthetic and incidence of preoperative aortic regurgitation Convexo-concave
Monostrut
models
(mm)
No. of patients
Preoperative AR (8)
No. of patients
Preoperative AR (S)
25 27
17 25
12/22 21/40
22 40
6/X 12/25
Valve size
models
valve studied (AR).
(54) (52.5)
1). Rheumatic heart disease was the underlying cause for replacement of the valve in all cases. Mitral regurgitation was the predominant lesion in 38 patients (34.65%). Forty-two patients (40.3%) had a combination of mitral stenosis and regurgitation and 26 (25%) patients had predominant valvar stenosis. As assessed by preoperative angiography, trivial to mild aortic regurgitation was observed in a total of 51 cases; for this no surgical intervention was attempted. There was no significant difference in the incidence of aortic regurgitation in patients with different size and models of the prosthesis inserted (Table 1).
(13.2) (48)
locities measured by Doppler echocardiography and used them to calculate gradients across BjbrkShiley prostheses inserted in mitral position. In this way, we have compared the monostrut valves with the older convexo-concave model. Materials
and Methods
Patients Doppler echocardiographic evaluation was conducted in 104 patients in whom the mitral valve had been replaced using a Bjork-Shiley prosthesis. Normal prosthetic valvar function was established by clinical, fluoroscopic and M-mode echocardiographic examination. Patients with reduced left ventricular function on echocardiography (ejection fraction less than 55%) were not included in the study. The age of the patients ranged from 16 to 48 years (mean 30.2 years). The mean period of study from the time of operation onwards was 19.6 months.
Doppler Study Doppler echocardiography was performed with the ATL Ultramark 8 machine which is equipped with both pulsed and continuous wave Doppler systems. M-mode echocardiographic examination was performed to determine the size and function of the left ventricle and motion of the disc. Velocity profiles across the prosthetic valves were studied initially in the pulsed Doppler mode in apical four chamber view, with the sample volume in the left ventricle. Subsequent measurements of velocities and gradients were obtained from signals of the
Valve sizes and models. Of the prostheses inserted, 39 were of 25 mm size and 65 of the 27 mm TABLE
2
Doppler
velocity,
Valve size and models
gradients
and area of different
models
of Bjark-Shiley
prosthetic
valve.
No. of patients
Peak velocity
Peak gradient
EDG
MVA
(m/xc)
(mm Hg)
(mm Hg)
(mm Hg)
MR (%) (Trivial)
MBUC MBUMS 21 mm
22 17
1.6 k 0.3 1.6 f 0.3
10.5 f 4.5 10.3 f 3.7
2.4 f 1.8 2.4 + 1.7
2.5 f 0.3 2.8 f 0.3
18 59
MBUC MBUMS
40 25
1.5 f 0.2 1.6 f 0.3
9.3 f 2.8 10.0 + 4.5
2.6 * 1.9 2.1 * 2.1
2.6 i 0.3 2.5 k 0.4
20 52 *
25 mm
* P -C0.05. MBUC = older convexo-concave valvar area; MR = mitral regurgitation.
models:
MBUMS
= monostrut
valves;
EDG = end diastolic
gradients;
MVA = mitral
357
continuous wave technique using the same view. Those signals with the most clearly defined envelope and highest velocities were chosen for calculation of gradients, using the modified Bernoulli principle ( p = 4 X V’). The values were expressed in millimeters of mercury. The area of the prosthetic valve was calculated using the T,,, method and expressed as centimeters squared. Calculations were done by averaging the calculations for three beats in patients in sinus rhythm and five beats in patients in atria1 fibrillation. Mitral regurgitation was evaluated from the apical and parasternal windows in four chamber and long axis views. It was graded as mild if the jet extended only at or within two centimeters of the prosthetic valve and significant if detected in the left atria1 cavity beyond this distance. Statistical comparison of the two valve models was done using the Student’s r-test. The differences in incidence of mitral regurgitation were calculated by the chi-square test.
Results Velocity
and gradients
Peak velocity at early and end-diastole and the corresponding calculations of gradients and valve area are shown in Table 2. For the 25 mm size, the peak gradient, end-diastolic gradient and valvar area were 10.4 + 4.2 mm Hg, 2.4 k 1.8 mm Hg and 2.7 + 0.4 cm2, respectively. For the 27 mm size these values were 9.6 + 3.6 mm Hg, 2.4 + 2.1 mm Hg and 2.6 + 0.3 cm2, respectively. There was no significant difference between these values. When the two models of the same size were compared, there was no difference in the peak and end-diastolic gradients nor in the area of the valve. Mitral regurgitation was detected in a total of 34 cases (32.6%). It was found in 13 patients (33.3%) with the 25 mm size and 21 patients (32.2%) with the 27 mm size prosthesis. In all cases, it was localized to the site of valves, never extending beyond 1 cm of the valve. Comparison of the incidence of mitral regurgitation in the two models of 25 mm and 27 mm revealed a higher incidence for the monostrut valves. In the 25 mm size, it was 59 and 18% and
for the 27 mm size 52 and 20% for the monostrut and older convexo-concave models, respectively. These values reached statistical significance only for the 27 mm size valve (P < 0.05).
Discussion The Bjiirk-Shiley monostrut prosthetic heart valve was introduced in 1982 in an attempt to decrease mechanical dysfunction. The valve is made of a pyrolite carbon disc and the outflow strut has been made an integral part of the valve ring, taking the form of a monostrut [4]. The opening angle of the convexo-concave disc was increased to 70 o instead of the 60 o which existed in the older models. In-vitro studies showed that the increased angles significantly improved characteristics of flow, the turbulence and vortex formation which had indicated impairment of flow through the smaller orifice being reduced [4]. Studies have also shown that these valves create less resistance to flow as compared to the 60” convexo-concave model when inserted both in mitral and aortic positions [3,4]. Stevenson et al. [4] reported an average improvement in pressure drop calculated in vitro of 30-40 and 20-30% for steady and pulsatile flow, respectively [4]. Bjork et al. [5], in a study of 79 patients in whom a monostrut Bjiirk-Shiley prosthesis had been inserted in mitral position and followed for 2-3 years, found a negligible incidence of intravascular hemolysis and complete absence of valvar thrombosis [5]. Haemodynamic studies performed during life are not available for patients in whom the monostrut valves have been inserted in mitral position. Since gradients across a prosthetic valve inserted in mitral position and measured by Doppler techniques have been shown to correlate well with haemodynamic measurements [6], we conducted the present study to compare such gradients calculated for the monostrut valve with the older convexo-concave models. In a previous communication we have established norms for the older models of the Bjbrk-Shiley prosthesis inserted in mitral position and found no significant difference in gradients and areas between the two sizes (25 mm and 27 mm) [7]. The present study did not
358
show any significant difference between the older convexo-concave models and the monostrut valves with respect to Doppler derived gradients and areas. The incidence of mitral regurgitation, although trivial, was higher in the monostrut valves. This is unlikely to produce any significant haemodynamic compromise. but it is noteworthy that a similar higher incidence of regurgitation has been reported in in-vitro studies of the monostrut valves [4]. Within the limitations of the Doppler technique used, and its observed insensitivity of distinguishing between prostheses of different size (25 mm vs 27 mm), our initial experience suggests that the newer monostrut Bjork-Shiley prosthesis does not seem to offer any significant haemodynamic advantage when inserted in the clinical setting over the older convexo-concave model.
Acknowledgements The authors wish to thank their surgical colleagues from the Department of Cardiovascular and Thoracic Surgery for providing us with the cases. We also wish to thank our echocardio-
graphic technician Miss Rita Mohla, for her invaluable assistance in this study.
References Balram A, Kaul U. Rao RBV et al. Thrombotic obstruction of Bjiirk-Shiley valves. Diagnostic and surgical consideration. Int J Cardiol 1984;6:61-69. Bjiirk VO. A new tilting disc valve prosthesis. Stand J Thorac Cardiovasc Surg 1969;3:1-10. Bruss KH, Renl H, Van Gilse F, Knoth E. Pressure drop and velocity yields of mechanical heart valve prosthesis: Bjork-Shiley standard. BjGrk-Shiley concave-convex, Hall Laster, St. Judge. Life Support Syst 1983;1:3-22. Stevenson DM, Yoganathan AP, Francn RH. The BjBrk-Shiley heart valve prosthesis: flow characteristics of the new 70 o model. Stand J Thorac Cardiovasc Surg 1982;16:1-7. BjBrk VO. Lindblom D. The monostrut Bjiirk-Shiley heart valve. Seminars on cardiac valve replacement. II. J Am Co11 Cardiol 1985:6:1142-1148. Sagar KB, Wann S. Paulsen WH, Romhilt DW. Doppler echocardiographic evaluation of Hancock and Bjork-Shiley prosthetic valve. J Am Co11 Cardiol 1986;7:681-687. Radhakrishnan S, Behl VK. Bajaj R. Bhatia ML. Shrivastava S. Doppler echocardiographic evaluation of normal and thrombosed Bjiirk-Shiley mitral prosthetic valves. Int J Cardiol 1989:20:3X7-394.