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Optimal shape of prosthesis for tricuspid valve replacement
Optimal shape of prosthesis for tricuspid valve replacement To develop an optimal prosthesis for use in the tricuspid valve, we determined the change in cardiac performance associated with the change in shape of the anulus of the tricuspid valve using a metal ring of variable flat ratio (defined as the long/short axis). In experiment I in an isolated autoperfusion model with six dogs, the left ventricular stroke work under a constant left atrial pressure of 7 mm Hg were, in grams per beat per minute, 11.88 ± 0.52 with a flat ratio of 1.0, 11.88 ± 0.70 with a flat ratio of 1.3, 16.23 ± 0.61 with a flat ratio of 1.6, and 11.22 ± 0.38 with a flat ratio of 2.3 (mean ± standard error of the mean). The volume was significantly higher with a flat ratio of 1.6 than with the other ratios (p < 0.05). In experiment II with six dogs in vivo, the blood flow of the pulmonary trunk artery was 0.57 ± 0.03 L/min with a flat ratio of 1.0, 0.66 ± 0.03 Lzmln with a flat ratio of 1.6, and 0.58 ± 0.03 L/min with a flat ratio of 2.3; the flow was significantly larger with a ratio of 1.6 than with the other ratios (p < 0.05). Right ventriculography was performed in five dogs. The percentage of radial shortening of the apex close to the acute margin was 19.4 % ± 3.1 % with a flat ratio of 1.0 and 49.2 % ± 5.1 % with a flat ratio of 1.6 (p < 0.05). In conclusion, the best hemodynamic results were obtained with a flat ratio of 1.6, which showed more advantageous hemodynamics than do the ratios of conventional circular prostheses. (J THORAC CARDIOVASC SURG 1993;106:1166-72)
Yasunori Fukushima, MD,a Yasunori Koga, MD,a Koichiro Shibata, MD,a Toshio Onitsuka, MD,a Mitsuhiro Hachida, MD,b Hitoshi Koyanagi, MD,b and Nobuo Kitamura, MD,c Miyazaki, Tokyo, and Osaka, Japan
AthOugh valve replacement is often the treatment of choice for patients with tricuspid valvular disorders, surgeons now make use of prosthetic valves designed for the mitral valve, not for the tricuspid valve. Replacing the flat tricuspid valve with a round prosthesis may impair the contraction of the right ventricle (RV).' In this study, we tested cardiac performance associated with various shapes, round to oval, of the tricuspid anulus and determined the optimal conformation of a prospective prosthesis for the tricuspid valve.
From the SecondDepartmentof Surgery,MiyazakiMedical College, Miyazaki"; the Department of Cardiovascular Surgery, Tokyo Women'sMedical College, Tokyob; the Department of Cardiovascular Surgery, Osaka National Hospital, Osaka," Japan. Received for publication March 6, 1992. Accepted for publication Feb. 17, 1993. Address for reprints: Yasunori Fukushima, MD, The Second Department of Surgery, Miyazaki Medical College, 5200 Kihara Kiyotake, Miyazaki, 889-16, Japan. Copyright © 1993 by Mosby-Year Book, Inc. 0022-5223/93 $1.00 +.10
I 1 66
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Materials and methods For the present experiment, a metal ring of variable flat ratio was designed and prepared (Fig. I). The ring was made of iron and was resistant to the deforming force of myocardial contraction. The axle of the ring was screwed so that the ring shape could be changed from round to elliptic by turning the axle without affecting the circumference. The ring itself had several holes for suturing to the tricuspid anulus. Fig. 1 shows the elliptic shape of the metal ring. The flat ratio was defined as the long/short axis length ratio. The metal ring was placed on the tricuspid anulus with the use of six mattress sutures. Two stitches were placed in the septal leaflet, one each in the anterior and posterior leaflets and one each into the commissures between the anterior and septal leaflets and between the posterior and septal leaflets. One end of the axle was put through the atrial wall outside the heart so that the ring shape could be adjusted externally (Fig. 2). The study was conducted in two stages. In experiment I, the optimal ring conformation was determined in an autoperfusion model of isolated heart and lung. In experiment II, cardiac performance was reevaluated in vivo, on the basis of the results of experiment I, with various flat ratios of the ring. Right ventriculography was also performed to determine the grounds of the results. Experiment I. Six mongrel adult dogs (10 to 15 kg body weight) were used. After intravenous injection of sodium pen-
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Fukushima et al.
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Fig. 1. Metal ring, whose shape can be changed from round to elliptic by turning the axle of the ring, has holes for suture fixation.
screw clamp
® flow meter Stroke Work=flow (ml/min)x (AOH-RLA) xO.0136
(s-m/beet)
Fig. 3. Autoperfusion model used for experiment I. Ao, Aorta; HR, heart rate. Fig. 2. Fixation of metal ring to tricuspid valve. Ring is placed with axle perpendicular to atrial free wall. tobarbital, 20 rug/kg, the trachea was intubated and respiration was controlled with a ventilator (volume-controlled, respiratory rate of 18 breaths/min, 10 ml/kg tidal volume, room air). The dog was placed in a supine position, and the thoracic cavity was opened bilaterally through the fourth intercostal space to expose
the heart and lungs. After intravenous injection of sodium heparin, 2 rug/kg, the left brachiocephalic artery was cannulated, the superior vena cava, inferior vena cava, and descending aorta were ligated, and the trachea was cut. The heart and lungs were removed en bloc. Fifty milliliters of Young's solution was injected through the ascending aorta to induce cardiac arrest. Ventilation was then terminated. Subsequently, the right atrium (RA) was opened, and the size of the tricuspid valve was
The Journal of Thoracic and Cardiovascular Surgery December 1993
1 1 6 8 Fukushima et al.
Fig. 4. Right ventriculography. Diastolic phase (left panel); systolic phase (right panel). Metal ring is sutured to tricuspid anulus.
PA
20 gm/beat/min
* * -" ,--
* ,,---,
:.:: a:
3
~
RA
~
oa:
10
I-
en
o
1.3
1.6
2.3
FLAT RATIO
Fig. 6. Stroke work associated with various flat ratios experiment I.
7
6
Fig. 5. Fractioning of RV wall. For each fraction of ventricle, percentage of diastolic-to-systolic shortening of distance from center of gravity of ventricle to ventricle wall was determined. Fractions 0 to 3, portions of PA, were not evaluated for percentage of radial shortening. measured. A suitable metal ring was adjusted and then sutured to the tricuspid anulus. The RA was then closed. The autoperfusion circuit system (Fig. 3) was established, and heartbeat and controlled ventilation were then reinstituted. When respiration
In
and cardiac contraction had been stabilized, the aortic pressure, mean left atrial (LA) pressure, heart rate, and cardiac output were measured with flat ratios of 1.0, 1.3, 1.6, and 2.3. The stroke work was calculated for each flat ratio. Cardiac performance, defined as the stroke workofthe left ventricle (LV) with a constant left atrial pressure of 7 mm Hg, was compared between each flat ratio. Experiment II. Six mongrel adult dogs, weighing 10 to 15 kg, were prepared in a manner similar to that in experiment I. With both venae cavae intermittently blocked with the use of the umbilical tapes, the RA was opened, the metal ring was sutured onto the tricuspid anulus, and the RA was then closed. When
The Journal of Thoracic and Cardiovascular Surgery Volume 106, Number 6
Fukushima et al.
I I69
ECG
200ft-f.~;;*~ml~'111
mmHg!
AoP
;.+"
: :.. ~
:
Oltt:U::i.::I:t::tt::t:t:tt:t:tIi::tt::t:
::r
..",.:--
I j
''1
-r
r
1,~-
RVP
1.
"
)
Fig. 7. Running chart from experiment II. No tricuspid dysfunction is indicated by RA pressure wave. ECG, Electrocardiogram; AoP, aortic pressure; RAP, right atrial pressure; RVP, right ventricular pressure.
the hemodynamic state became stable, the flat ratio was set at 1.0, 1.6, and 2.3. Aortic pressure, RA pressure, RV pressure, and blood flow of the pulmonary trunk artery (PA) were measured as indicators. We performed ventriculography to determine the motion of the RV wall for flat ratios of 1.0 and 1.6. A similar experimental modelwasused in fiveadditional dogs. Contrast medium was injected into the RA with an automatic injector. Roentgenography was performed at right angles to the metal ring plane and axle to produce a frontal viewof the RV (Fig. 4). The ventriculogramwas fractioned equally into 12 parts around the center of gravity of the RV (Fig. 5). For each fraction of the ventricle, percentage of diastolic-to-systolic shortening of the distance from the center of gravity of the ventricle to the ventricular wall was determined. Analysis of variance was used to compare groups statistically, and differences were considered significant if p < 0.05. Results Experiment I. The diameter of the tricuspid valve ring was 23 mm in three heart specimens and 25 mm in the other three. The peak or plateau stroke work of the LV (grams per beat per minute) was 11.88 ± 0.52 (mean ± standard error of the mean) with a flat ratio of 1.0, 11.88 ± 0.70 with 1.3, 16.23 ± 0.61 with 1.6, and 11.22 ± 0.38 with 2.3. LV stroke work with a flat ratio of 1.6 was significantly more than that with other flat ratios (p < 0.05). No significant differences in LV stroke
work were found among flat ratios of 1.0, 1.3, and 2.3 (Fig. 6). Experiment II. The diameter of the tricuspid valve ring was 27 mm in three dogs and 25 mm in the other three. During the experiment, the mean heart rate was 116.7 ± 10.3 beats/min, and sinus rhythm was maintained in all the animals. Ringer's lactate solution was intravenously infused to ensure stability of RA pressure. The mean RA pressure was 11.3 ± 3.3 mm Hg. A running chart from experiment II is shown in Fig. 7. For each flat ratio in obtained RA pressure patterns, fewer aberrations were found that indicated the presence of severely damaged tricuspid valve, especially insufficiency. Hemodynamics. Differences in the aortic pressure and the RV pressure were not significant in the three groups (Table I). The maximum rate of R V pressure rise was 2558.5 ± 353.2 mm Hg/sec with a flat ratio of 1.0, 2938.8 ± 396.9 mm Hg/sec with a ratio of 1.6, and 2800.0 ± 378.9 mm Hg/sec with a ratio of 2.3. The maximum rate of R V pressure rise with the use of the elliptic metal ring was significantly higher with the flat ratio of 1.6 compared with the flat ratios of 1.0 and 2.3 (p < 0.05), and the flat ratio of 2.3 achieved a higher rate than did the flat ratio of 1.0 (p < 0.05).
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Table I. Hemodynamics in experiment II Flat ratio 1.6
1.0 Aortic pressure (mm Hg) RV pressure (mm Hg) RV max dP/dt (rnm Hg/sec) PA blood flow (Lyrnin)
105.0 47.8 2558.5 0.57
± 7.1 ± 2.6 ± 353.2 ± 0.03
107.5 49.0 2938.8 0.66
± 7.1
± 2.6 ± 396.9 ± 0.03
2.3 105.8 47.7 2800.0 0.58
± 7.0 ± 2.6 ± 378.9 ± 0.03
p Value
NS NS p<0.05* p<0.05t
NS, Not significant; max dPjdt, maximum rate of pressure rise.
*p Value for 1.0 versus 1.6, 1.6 versus 2.3, and 1.0 versus 2.3 flat ratios. tp Value for 1.0 versus 1.6 and 1.6 versus 2.3 flat ratios.
Table II. Wall motion of the RV Percentage of radial shortening Segment 4 5
6 7 8
9 10 II
Flat ratio 1.0
Flat ratio 1.6
6.7 ± 23.2 ± 20.2 ± 19.4 ± 16.5 ± 36.1 ± 34.2 ± 31.4 ±
36.9 45.9 48.3 49.2 44.8 43.9 40.5 36.6
2.6 3.7 3.9 3.1 4.9 2.3 1.8 1.6
± 4.5 ± 4.4 ± 4.7 ± 5.1 ± 5.0 ± 5.0 ± 5.2 ± 5.2
p Value
NS NS NS p<0.05
NS NS NS NS
NS, Not significant.
The blood flow in the PA was 0.57 ± 0.03 L/min with a flat ratio of 1.0, 0.66 ± 0.03 L/min with a ratio of 1.6, and 0.58 ± 0.03 Lyrnin with a ratio of 2.3. The PA blood flow was significantly higher with the flat ratio of 1.6 than with 1.0 or 2.3 (p < 0.05). No significant differences between flows were found with ratios of 1.0 and 2.3. Ventriculography. The obtained right ventriculograms are presented in Fig. 4, and the fractioning of the ventricular wall was as indicated in Fig. 5. The percentage of radial shortening was examined for each fraction of the ventricular wall. In fraction 7, there was significant difference in percentage of radial shortening obtained with flat ratios of 1.0 and 1.6 (19.4% ± 3.1% versus 49.2% ± 5.1%, respectively; p < 0.05). The t test was used to determine the statistical significance of differences between means of the two groups (Table II). This fraction corresponds to the region of the apex of the heart close to the R V acute margin. Fractions 0 to 3, corresponding to portions of the PA, were not evaluated for percentage of radial shortening.
Discussion Repair of secondary tricuspid valve regurgitation remains a major therapeutic problem. In the case of surgical therapy of the mitral valve, it is recommended that
active surgical treatment is added to operative therapy for tricuspid valve disorders.r However, for patients with tricuspid valvular disorders, surgeons now make use of prostheses designed for the mitral valve not for the tricuspid valve. The use of mechanical prostheses in the tricuspid position in multivalvular procedures is associated not only with a high early mortality': 4 but also with a prevalence of thrombotic complications.r? Therefore, mild tricuspid regurgitation should be corrected at the initial operative procedurev'' by means of some form of annuloplasty technique." 10 The long-term survival of patients appears to be satisfactory I I and comparable with that of patients undergoing tricuspid annuloplasty." 12 Valvuloplasty rather than valve replacement has been the mainstay of treatment of patients with tricuspid valve disorders.P Peterffy, Jonasson, and Henze l 4 reported that high RA pressure, which indicates the presence of functional stenosis, occurred after tricuspid valve replacement. Symptoms of heart failure transiently develop in some patients with tricuspid valve replacement when they are febrile or during exercise, even if they have no symptoms at rest. This suggests that the increase in cardiac output during exercise is inadequate in patients with tricuspid valve replacement; this deterioration in cardiac function may provide evidence that fixation of the tricuspid anuIus by a round prosthesis impairs the contractility of the RV. I Tricuspid valvuloplasty is frequently performed with a Carpentier ring. This is a rigid ring designed for tricuspid valvuloplasty, with a conformation similar to that of the tricuspid anulus.? and there are many reports of satisfactory valvuloplasty achieved with it. 12 , 15, 16 Assuming the findings of these reports are correct, fixation of the tricuspid anulus with a rigid ring might not prove disadvantageous if the ring shape were chosen correctly. An optimally designed prosthesis for use at the tricuspid anulus might be one which improves cardiac function. The present study was an attempt to devise an effective method of repair of the tricuspid anulus in hemodynamic state.
The Journal of Thoracic and Cardiovascular Surgery Volume 106, Number 6
Rushrner '? has divided RV contraction into the following four aspects: (I) a bellowslike movement in which the free wall of the R V approaches the ventricular septum; (2) shortening of the RV in the direction of the long axis as a result of papillary muscle contraction; (3) protrusion of the ventricular septum into the RV cavity as a result of LV contraction; and (4) shortening of the free wall of the R V in association with LV contraction. Of these four factors, the bellowslike movement of the free wall of the R V toward the ventricular septum is thought to be the principal contributor to R V contraction. With the tricuspid anulus fixed in a round shape, this bellowslike movement and the protruding movement of the ventricular septum into the R V is impaired, resulting in decreased RV ejection power. If the tricuspid anulus is fixed in a suitable elliptic shape, however, the R V free wall and the ventricular septum will remain close to each other, and the bellowslike movement will not be impaired. The tricuspid anulus is a nearly circular fibrous structure and is much less prominent than the mitral valve anulus. The three leaflets are termed anterior, posterior, and septal. The posterior leaflet comprises the largest portion of anulus, with the remainder divided between the anterior and septal leaflets," In this study, various round-to-elliptic configurations were studied to quantify the hemodynamic effects of fixation of the tricuspid valve, and ventricular function, especially that of the RV, was assessed with metal rings of various flat ratios. In experiment I, a comparison of several metal ring ellipsoids demonstrated that best results were obtained with a flat ratio of 1.6. Therefore, ellipsoids with flat ratios of 1.0 (round), 1.6, and 2.3 were selected for testing in experiment II. To evaluate R V function, we measured P A blood flow, PA pressure, RV pressure, and motion ofthe RV wall. Results indicated that contraction and function of the R V were preserved well when the tricuspid anulus was fixed at a flat ratio of 1.6. The effect of the ring on cardiac function was more obvious in experiment I, in which the heart and lungs moved relatively freely. The results of right ventriculographic studies indicated that the movement on the acute margin of the RV apex was affected by changes of the fixed shape of the anulus between flat ratios of 1.0 and 1.6. However, the effects must be discussed, especially the RV wall motions, because the heart tested in our model was not in failure, and was neither dilated nor distended. During right heart failure, the expansion of the R V and dilation of the tricuspid anulus can commonly be observed. 19. 20 Whichever surgical treatment is performed, the tricuspid anulus will be plicated to its ordinary size. We have assumed that the extent of inter-
Fukushima et al.
117 1
vention of such a procedure corresponds to that of the insertion of an ordinary-sized metal ring. For each flat ratio, RA pressure patterns were without sufficient aberration to demonstrate the presence of tricuspid disorder. The results of experiments indicated that a flat ratio of 1.6 is better for tricuspid fixation than a ratio of 1.0 with respect to maintenance of R V function. A prosthesis for tricuspid valve replacement should be durable, of low profile, nonobstructive, and nonthrombogenic.P We suggest that the conformation of the prosthesis must be such that the influence of annular deformity on R V function is minimized and that the shape of the prosthesis should be ellipsic with a flat ratio of 1.6. Tricuspid valve prostheses might therefore be designed with these considerations in mind. REFERENCES I. Kozawa S, Matsumori M, Yamashita C, et al. Long term results of tricuspid valve replacement. Jpn J Artif Organs 1982;11:1192-5. 2. King RH, Schaff HV, DanielsonGK, et al. Surgery for tricuspid regurgitation late after mitral valve replacement. Circulation 1984;70: 1193-7. 3. Stephenson LW, Kouchoukos NT, Kirklin JW. Triplevalve replacement: an analysis of eight years' experience. Ann Thorac Surg 1977;23:327-32. 4. Boyd AD, Engelman RM, Isom OW, Reed GE, Spencer Fe. Tricuspid annuloplasty: five and one-half years' experience with 78 patients. J THORAC CARDIOVASC SURG 1974;68:344-51. 5. Macmanus Q, Grunkemeier G, Starr A. Late resultsof triple valvereplacement: a 14-yearreview. Ann Thorac Surg 1978;25:402-6. 6. Boskovic D, Elezovic I, Boskovic D, Simin N, Rolovic Z, Josipovic V. Late thrombosis of the Bjork-Shiley tiliting discvalvein the tricuspidposition. J THORAC CARDIOVASC SURG 1986;91: 1-8. 7. Eng J, Ravichandran PS, Kay PH, Murday AJ. Long-term resultof Ionescu-Shiley valvein the tricuspid position. Ann Thorac Surg 1990;51 :200-3. 8. Weerasena N, Spyt TJ, Pye M, Bain WHo Clinical evaluationof the Bjork-Shileydiscvalvein the tricuspid position: long-term results. Eur J Cardiothorac Surg 1990;4:19-23. 9. Carpentier A, DelocheA, Hanania G, et al. Surgical management of acquired tricuspid valve disease. J THORAC CARDIOVASC SURG 1974;67:53-65. 10. Gordin P, Meere C, Limet R, Lopez-Bescos L, Delcan JL, Rivera R. Carpentier's annulus and DeVega's annuloplasty: the end of the tricuspid challenge. J THORAC CARDIOVASC SURG 1975;70:852-61. II. Cohen SR, Sell JE, Mcintosh CL, Clark RE. Tricuspid regurgitationin patients with acquired, chronic,pure mitral regurgitation. I. Prevalence, diagnosis, and comparison of preoperativeclinicaland hemodynamicfeatures in patients
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12.
13.
14.
15.
with and without tricuspid regurgitation. J THoRAc CARDIOVASC SURG 1987;94:481-7. Kratz JM, Crawford FA Jr, Stroud MR, Appleby DC Jr, Hanger KH. Trends and results in tricuspid valve surgery. Chest 1985;88:837-40. Breyer RH, McClenathan JH, Michaelis LL, Mclntosh CL, Morrow AG. Tricuspid regurgitation: a comparison of nonoperative management, tricuspid annuloplasty, and tricuspid valve replacement. J THORAC CARDIOVASC SURG 1976;72:867-74. Peterffy A, Jonasson R, Henze A. Haemodynamic changes after tricuspid surgery: a catheterization study in fortyfive patients. Scand J Thorac Surg 1981;15:161-70. Sanfelippo PM, Giuliani ER, Danielson GK, Wallace RB, Pluth JR, McGoon DC. Tricuspid valve prosthetic replacement. J THORAC CARDIOVASC SURG 1976;71:441-5.
The Journal of ThoraciC and Cardiovascular Surgery December 1993
16. Rivera R, Duran E, Ajuria M. Carpentier's flexible ring versus De Vega's annuloplasty: a prospective randomized study. J THORAC CARDIOVASC SURG 1985;89:196-203. 17. Rushmer RF. Cardiovascular dynamics. 4th ed. Philadelphia: WB Saunders, 1976:91. 18. Waller BF. Etiology of pure tricuspid regurgitation: the right heart. Philadelphia: F A Davis, 1987:53-95. 19. Tanaka M, Matsubara 0, Hatakeyama S, Kajita A. Morphometrical analysis of autopsy hearts of congestive cardiomyopathy. Bull Tokyo Med Dent Univ 1983;30:73-94. 20. Hachida M, Kurosawa H, Fujiwara T, Sinoka T, Fukushima Y, Koyanagi H. Assessment of annular dilatation in secondary tricuspid valve insufficiency. Nippon Kyobu Geka Gakkai Zasshi 1986;34:77-84.
Yasunori Fukushima, MD,a Yasunori Koga, MD,a Koichiro Shibata, MD,a Toshio Onitsuka, MD,a Mitsuhiro Hachida, MD,b Hitoshi Koyanagi, MD,b and Nobuo Kitamura, MD,c Miyazaki, Tokyo, and Osaka, Japan
AthOugh valve replacement is often the treatment of choice for patients with tricuspid valvular disorders, surgeons now make use of prosthetic valves designed for the mitral valve, not for the tricuspid valve. Replacing the flat tricuspid valve with a round prosthesis may impair the contraction of the right ventricle (RV).' In this study, we tested cardiac performance associated with various shapes, round to oval, of the tricuspid anulus and determined the optimal conformation of a prospective prosthesis for the tricuspid valve.
From the SecondDepartmentof Surgery,MiyazakiMedical College, Miyazaki"; the Department of Cardiovascular Surgery, Tokyo Women'sMedical College, Tokyob; the Department of Cardiovascular Surgery, Osaka National Hospital, Osaka," Japan. Received for publication March 6, 1992. Accepted for publication Feb. 17, 1993. Address for reprints: Yasunori Fukushima, MD, The Second Department of Surgery, Miyazaki Medical College, 5200 Kihara Kiyotake, Miyazaki, 889-16, Japan. Copyright © 1993 by Mosby-Year Book, Inc. 0022-5223/93 $1.00 +.10
I 1 66
12/1/46701
Materials and methods For the present experiment, a metal ring of variable flat ratio was designed and prepared (Fig. I). The ring was made of iron and was resistant to the deforming force of myocardial contraction. The axle of the ring was screwed so that the ring shape could be changed from round to elliptic by turning the axle without affecting the circumference. The ring itself had several holes for suturing to the tricuspid anulus. Fig. 1 shows the elliptic shape of the metal ring. The flat ratio was defined as the long/short axis length ratio. The metal ring was placed on the tricuspid anulus with the use of six mattress sutures. Two stitches were placed in the septal leaflet, one each in the anterior and posterior leaflets and one each into the commissures between the anterior and septal leaflets and between the posterior and septal leaflets. One end of the axle was put through the atrial wall outside the heart so that the ring shape could be adjusted externally (Fig. 2). The study was conducted in two stages. In experiment I, the optimal ring conformation was determined in an autoperfusion model of isolated heart and lung. In experiment II, cardiac performance was reevaluated in vivo, on the basis of the results of experiment I, with various flat ratios of the ring. Right ventriculography was also performed to determine the grounds of the results. Experiment I. Six mongrel adult dogs (10 to 15 kg body weight) were used. After intravenous injection of sodium pen-
The Journal of Thoracic and Cardiovascular Surgery Volume 106, Number 6
Fukushima et al.
I I67
Fig. 1. Metal ring, whose shape can be changed from round to elliptic by turning the axle of the ring, has holes for suture fixation.
screw clamp
® flow meter Stroke Work=flow (ml/min)x (AOH-RLA) xO.0136
(s-m/beet)
Fig. 3. Autoperfusion model used for experiment I. Ao, Aorta; HR, heart rate. Fig. 2. Fixation of metal ring to tricuspid valve. Ring is placed with axle perpendicular to atrial free wall. tobarbital, 20 rug/kg, the trachea was intubated and respiration was controlled with a ventilator (volume-controlled, respiratory rate of 18 breaths/min, 10 ml/kg tidal volume, room air). The dog was placed in a supine position, and the thoracic cavity was opened bilaterally through the fourth intercostal space to expose
the heart and lungs. After intravenous injection of sodium heparin, 2 rug/kg, the left brachiocephalic artery was cannulated, the superior vena cava, inferior vena cava, and descending aorta were ligated, and the trachea was cut. The heart and lungs were removed en bloc. Fifty milliliters of Young's solution was injected through the ascending aorta to induce cardiac arrest. Ventilation was then terminated. Subsequently, the right atrium (RA) was opened, and the size of the tricuspid valve was
The Journal of Thoracic and Cardiovascular Surgery December 1993
1 1 6 8 Fukushima et al.
Fig. 4. Right ventriculography. Diastolic phase (left panel); systolic phase (right panel). Metal ring is sutured to tricuspid anulus.
PA
20 gm/beat/min
* * -" ,--
* ,,---,
:.:: a:
3
~
RA
~
oa:
10
I-
en
o
1.3
1.6
2.3
FLAT RATIO
Fig. 6. Stroke work associated with various flat ratios experiment I.
7
6
Fig. 5. Fractioning of RV wall. For each fraction of ventricle, percentage of diastolic-to-systolic shortening of distance from center of gravity of ventricle to ventricle wall was determined. Fractions 0 to 3, portions of PA, were not evaluated for percentage of radial shortening. measured. A suitable metal ring was adjusted and then sutured to the tricuspid anulus. The RA was then closed. The autoperfusion circuit system (Fig. 3) was established, and heartbeat and controlled ventilation were then reinstituted. When respiration
In
and cardiac contraction had been stabilized, the aortic pressure, mean left atrial (LA) pressure, heart rate, and cardiac output were measured with flat ratios of 1.0, 1.3, 1.6, and 2.3. The stroke work was calculated for each flat ratio. Cardiac performance, defined as the stroke workofthe left ventricle (LV) with a constant left atrial pressure of 7 mm Hg, was compared between each flat ratio. Experiment II. Six mongrel adult dogs, weighing 10 to 15 kg, were prepared in a manner similar to that in experiment I. With both venae cavae intermittently blocked with the use of the umbilical tapes, the RA was opened, the metal ring was sutured onto the tricuspid anulus, and the RA was then closed. When
The Journal of Thoracic and Cardiovascular Surgery Volume 106, Number 6
Fukushima et al.
I I69
ECG
200ft-f.~;;*~ml~'111
mmHg!
AoP
;.+"
: :.. ~
:
Oltt:U::i.::I:t::tt::t:t:tt:t:tIi::tt::t:
::r
..",.:--
I j
''1
-r
r
1,~-
RVP
1.
"
)
Fig. 7. Running chart from experiment II. No tricuspid dysfunction is indicated by RA pressure wave. ECG, Electrocardiogram; AoP, aortic pressure; RAP, right atrial pressure; RVP, right ventricular pressure.
the hemodynamic state became stable, the flat ratio was set at 1.0, 1.6, and 2.3. Aortic pressure, RA pressure, RV pressure, and blood flow of the pulmonary trunk artery (PA) were measured as indicators. We performed ventriculography to determine the motion of the RV wall for flat ratios of 1.0 and 1.6. A similar experimental modelwasused in fiveadditional dogs. Contrast medium was injected into the RA with an automatic injector. Roentgenography was performed at right angles to the metal ring plane and axle to produce a frontal viewof the RV (Fig. 4). The ventriculogramwas fractioned equally into 12 parts around the center of gravity of the RV (Fig. 5). For each fraction of the ventricle, percentage of diastolic-to-systolic shortening of the distance from the center of gravity of the ventricle to the ventricular wall was determined. Analysis of variance was used to compare groups statistically, and differences were considered significant if p < 0.05. Results Experiment I. The diameter of the tricuspid valve ring was 23 mm in three heart specimens and 25 mm in the other three. The peak or plateau stroke work of the LV (grams per beat per minute) was 11.88 ± 0.52 (mean ± standard error of the mean) with a flat ratio of 1.0, 11.88 ± 0.70 with 1.3, 16.23 ± 0.61 with 1.6, and 11.22 ± 0.38 with 2.3. LV stroke work with a flat ratio of 1.6 was significantly more than that with other flat ratios (p < 0.05). No significant differences in LV stroke
work were found among flat ratios of 1.0, 1.3, and 2.3 (Fig. 6). Experiment II. The diameter of the tricuspid valve ring was 27 mm in three dogs and 25 mm in the other three. During the experiment, the mean heart rate was 116.7 ± 10.3 beats/min, and sinus rhythm was maintained in all the animals. Ringer's lactate solution was intravenously infused to ensure stability of RA pressure. The mean RA pressure was 11.3 ± 3.3 mm Hg. A running chart from experiment II is shown in Fig. 7. For each flat ratio in obtained RA pressure patterns, fewer aberrations were found that indicated the presence of severely damaged tricuspid valve, especially insufficiency. Hemodynamics. Differences in the aortic pressure and the RV pressure were not significant in the three groups (Table I). The maximum rate of R V pressure rise was 2558.5 ± 353.2 mm Hg/sec with a flat ratio of 1.0, 2938.8 ± 396.9 mm Hg/sec with a ratio of 1.6, and 2800.0 ± 378.9 mm Hg/sec with a ratio of 2.3. The maximum rate of R V pressure rise with the use of the elliptic metal ring was significantly higher with the flat ratio of 1.6 compared with the flat ratios of 1.0 and 2.3 (p < 0.05), and the flat ratio of 2.3 achieved a higher rate than did the flat ratio of 1.0 (p < 0.05).
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Table I. Hemodynamics in experiment II Flat ratio 1.6
1.0 Aortic pressure (mm Hg) RV pressure (mm Hg) RV max dP/dt (rnm Hg/sec) PA blood flow (Lyrnin)
105.0 47.8 2558.5 0.57
± 7.1 ± 2.6 ± 353.2 ± 0.03
107.5 49.0 2938.8 0.66
± 7.1
± 2.6 ± 396.9 ± 0.03
2.3 105.8 47.7 2800.0 0.58
± 7.0 ± 2.6 ± 378.9 ± 0.03
p Value
NS NS p<0.05* p<0.05t
NS, Not significant; max dPjdt, maximum rate of pressure rise.
*p Value for 1.0 versus 1.6, 1.6 versus 2.3, and 1.0 versus 2.3 flat ratios. tp Value for 1.0 versus 1.6 and 1.6 versus 2.3 flat ratios.
Table II. Wall motion of the RV Percentage of radial shortening Segment 4 5
6 7 8
9 10 II
Flat ratio 1.0
Flat ratio 1.6
6.7 ± 23.2 ± 20.2 ± 19.4 ± 16.5 ± 36.1 ± 34.2 ± 31.4 ±
36.9 45.9 48.3 49.2 44.8 43.9 40.5 36.6
2.6 3.7 3.9 3.1 4.9 2.3 1.8 1.6
± 4.5 ± 4.4 ± 4.7 ± 5.1 ± 5.0 ± 5.0 ± 5.2 ± 5.2
p Value
NS NS NS p<0.05
NS NS NS NS
NS, Not significant.
The blood flow in the PA was 0.57 ± 0.03 L/min with a flat ratio of 1.0, 0.66 ± 0.03 L/min with a ratio of 1.6, and 0.58 ± 0.03 Lyrnin with a ratio of 2.3. The PA blood flow was significantly higher with the flat ratio of 1.6 than with 1.0 or 2.3 (p < 0.05). No significant differences between flows were found with ratios of 1.0 and 2.3. Ventriculography. The obtained right ventriculograms are presented in Fig. 4, and the fractioning of the ventricular wall was as indicated in Fig. 5. The percentage of radial shortening was examined for each fraction of the ventricular wall. In fraction 7, there was significant difference in percentage of radial shortening obtained with flat ratios of 1.0 and 1.6 (19.4% ± 3.1% versus 49.2% ± 5.1%, respectively; p < 0.05). The t test was used to determine the statistical significance of differences between means of the two groups (Table II). This fraction corresponds to the region of the apex of the heart close to the R V acute margin. Fractions 0 to 3, corresponding to portions of the PA, were not evaluated for percentage of radial shortening.
Discussion Repair of secondary tricuspid valve regurgitation remains a major therapeutic problem. In the case of surgical therapy of the mitral valve, it is recommended that
active surgical treatment is added to operative therapy for tricuspid valve disorders.r However, for patients with tricuspid valvular disorders, surgeons now make use of prostheses designed for the mitral valve not for the tricuspid valve. The use of mechanical prostheses in the tricuspid position in multivalvular procedures is associated not only with a high early mortality': 4 but also with a prevalence of thrombotic complications.r? Therefore, mild tricuspid regurgitation should be corrected at the initial operative procedurev'' by means of some form of annuloplasty technique." 10 The long-term survival of patients appears to be satisfactory I I and comparable with that of patients undergoing tricuspid annuloplasty." 12 Valvuloplasty rather than valve replacement has been the mainstay of treatment of patients with tricuspid valve disorders.P Peterffy, Jonasson, and Henze l 4 reported that high RA pressure, which indicates the presence of functional stenosis, occurred after tricuspid valve replacement. Symptoms of heart failure transiently develop in some patients with tricuspid valve replacement when they are febrile or during exercise, even if they have no symptoms at rest. This suggests that the increase in cardiac output during exercise is inadequate in patients with tricuspid valve replacement; this deterioration in cardiac function may provide evidence that fixation of the tricuspid anuIus by a round prosthesis impairs the contractility of the RV. I Tricuspid valvuloplasty is frequently performed with a Carpentier ring. This is a rigid ring designed for tricuspid valvuloplasty, with a conformation similar to that of the tricuspid anulus.? and there are many reports of satisfactory valvuloplasty achieved with it. 12 , 15, 16 Assuming the findings of these reports are correct, fixation of the tricuspid anulus with a rigid ring might not prove disadvantageous if the ring shape were chosen correctly. An optimally designed prosthesis for use at the tricuspid anulus might be one which improves cardiac function. The present study was an attempt to devise an effective method of repair of the tricuspid anulus in hemodynamic state.
The Journal of Thoracic and Cardiovascular Surgery Volume 106, Number 6
Rushrner '? has divided RV contraction into the following four aspects: (I) a bellowslike movement in which the free wall of the R V approaches the ventricular septum; (2) shortening of the RV in the direction of the long axis as a result of papillary muscle contraction; (3) protrusion of the ventricular septum into the RV cavity as a result of LV contraction; and (4) shortening of the free wall of the R V in association with LV contraction. Of these four factors, the bellowslike movement of the free wall of the R V toward the ventricular septum is thought to be the principal contributor to R V contraction. With the tricuspid anulus fixed in a round shape, this bellowslike movement and the protruding movement of the ventricular septum into the R V is impaired, resulting in decreased RV ejection power. If the tricuspid anulus is fixed in a suitable elliptic shape, however, the R V free wall and the ventricular septum will remain close to each other, and the bellowslike movement will not be impaired. The tricuspid anulus is a nearly circular fibrous structure and is much less prominent than the mitral valve anulus. The three leaflets are termed anterior, posterior, and septal. The posterior leaflet comprises the largest portion of anulus, with the remainder divided between the anterior and septal leaflets," In this study, various round-to-elliptic configurations were studied to quantify the hemodynamic effects of fixation of the tricuspid valve, and ventricular function, especially that of the RV, was assessed with metal rings of various flat ratios. In experiment I, a comparison of several metal ring ellipsoids demonstrated that best results were obtained with a flat ratio of 1.6. Therefore, ellipsoids with flat ratios of 1.0 (round), 1.6, and 2.3 were selected for testing in experiment II. To evaluate R V function, we measured P A blood flow, PA pressure, RV pressure, and motion ofthe RV wall. Results indicated that contraction and function of the R V were preserved well when the tricuspid anulus was fixed at a flat ratio of 1.6. The effect of the ring on cardiac function was more obvious in experiment I, in which the heart and lungs moved relatively freely. The results of right ventriculographic studies indicated that the movement on the acute margin of the RV apex was affected by changes of the fixed shape of the anulus between flat ratios of 1.0 and 1.6. However, the effects must be discussed, especially the RV wall motions, because the heart tested in our model was not in failure, and was neither dilated nor distended. During right heart failure, the expansion of the R V and dilation of the tricuspid anulus can commonly be observed. 19. 20 Whichever surgical treatment is performed, the tricuspid anulus will be plicated to its ordinary size. We have assumed that the extent of inter-
Fukushima et al.
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vention of such a procedure corresponds to that of the insertion of an ordinary-sized metal ring. For each flat ratio, RA pressure patterns were without sufficient aberration to demonstrate the presence of tricuspid disorder. The results of experiments indicated that a flat ratio of 1.6 is better for tricuspid fixation than a ratio of 1.0 with respect to maintenance of R V function. A prosthesis for tricuspid valve replacement should be durable, of low profile, nonobstructive, and nonthrombogenic.P We suggest that the conformation of the prosthesis must be such that the influence of annular deformity on R V function is minimized and that the shape of the prosthesis should be ellipsic with a flat ratio of 1.6. Tricuspid valve prostheses might therefore be designed with these considerations in mind. REFERENCES I. Kozawa S, Matsumori M, Yamashita C, et al. Long term results of tricuspid valve replacement. Jpn J Artif Organs 1982;11:1192-5. 2. King RH, Schaff HV, DanielsonGK, et al. Surgery for tricuspid regurgitation late after mitral valve replacement. Circulation 1984;70: 1193-7. 3. Stephenson LW, Kouchoukos NT, Kirklin JW. Triplevalve replacement: an analysis of eight years' experience. Ann Thorac Surg 1977;23:327-32. 4. Boyd AD, Engelman RM, Isom OW, Reed GE, Spencer Fe. Tricuspid annuloplasty: five and one-half years' experience with 78 patients. J THORAC CARDIOVASC SURG 1974;68:344-51. 5. Macmanus Q, Grunkemeier G, Starr A. Late resultsof triple valvereplacement: a 14-yearreview. Ann Thorac Surg 1978;25:402-6. 6. Boskovic D, Elezovic I, Boskovic D, Simin N, Rolovic Z, Josipovic V. Late thrombosis of the Bjork-Shiley tiliting discvalvein the tricuspidposition. J THORAC CARDIOVASC SURG 1986;91: 1-8. 7. Eng J, Ravichandran PS, Kay PH, Murday AJ. Long-term resultof Ionescu-Shiley valvein the tricuspid position. Ann Thorac Surg 1990;51 :200-3. 8. Weerasena N, Spyt TJ, Pye M, Bain WHo Clinical evaluationof the Bjork-Shileydiscvalvein the tricuspid position: long-term results. Eur J Cardiothorac Surg 1990;4:19-23. 9. Carpentier A, DelocheA, Hanania G, et al. Surgical management of acquired tricuspid valve disease. J THORAC CARDIOVASC SURG 1974;67:53-65. 10. Gordin P, Meere C, Limet R, Lopez-Bescos L, Delcan JL, Rivera R. Carpentier's annulus and DeVega's annuloplasty: the end of the tricuspid challenge. J THORAC CARDIOVASC SURG 1975;70:852-61. II. Cohen SR, Sell JE, Mcintosh CL, Clark RE. Tricuspid regurgitationin patients with acquired, chronic,pure mitral regurgitation. I. Prevalence, diagnosis, and comparison of preoperativeclinicaland hemodynamicfeatures in patients
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16. Rivera R, Duran E, Ajuria M. Carpentier's flexible ring versus De Vega's annuloplasty: a prospective randomized study. J THORAC CARDIOVASC SURG 1985;89:196-203. 17. Rushmer RF. Cardiovascular dynamics. 4th ed. Philadelphia: WB Saunders, 1976:91. 18. Waller BF. Etiology of pure tricuspid regurgitation: the right heart. Philadelphia: F A Davis, 1987:53-95. 19. Tanaka M, Matsubara 0, Hatakeyama S, Kajita A. Morphometrical analysis of autopsy hearts of congestive cardiomyopathy. Bull Tokyo Med Dent Univ 1983;30:73-94. 20. Hachida M, Kurosawa H, Fujiwara T, Sinoka T, Fukushima Y, Koyanagi H. Assessment of annular dilatation in secondary tricuspid valve insufficiency. Nippon Kyobu Geka Gakkai Zasshi 1986;34:77-84.