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Clinical evaluation of the Omniscience cardiac valve prosthesis
Clinical evaluation of the Omniscience cardiac valve prosthesis Follow-up of up to 6 years From January 1984 to June 1989, 259 Omniscience valve prostheses were implanted in 225 patients. Of the 225 patients; 143 (63.6 %) received mitral, 48 (21.3%) aortic, and 34 (15.1 %) double valve replacements. The early mortality rate was 8.9%; 97.6% of the patients were included in this study. These patients represent a cumulative follow-up of 407.9 patient-years, with a mean follow-up of 2.03 ± 0.1 (standard error) years. The late mortality rate was 4.03 % overall, which corresponds to 2.0% ± 0.7%/pt-yr (SE). The annual rate of valve endocarditis was 1.0% ± 0.5%/pt-yr (SE). The linearized rate of thromboembolism was 1.2 % ± 0.5 % /pt-yr (SE). Anticoagulant-related hemorrhage occurred in 15 patients with an annual rate of 3.7% ± 0.9% /pt-yr (SE). The linearized rate of valve thrombosis was 0.2 % ± 0.2 % / pt-yr (SE). By echocardiography the mean mitral valve opening was 75.9 ± 3.1 degrees (standard deviation) for 27 patients. During follow-up study, 136 (70.8 %) patients were in New York Heart Association class I, 44 (22.9%) were in class II, and 12 (6.3%) were in class III; there were 25 (11.1 %) patients in class II, 166 (73.8 %) in class III, and 34 (15.1 %) in class IV preoperatively. Actuarial freedom from thromboembolism was 94.5% ± 3.6% (SE); freedom from endocarditis, 97.8% ± 1.0% (SE); freedom from anticoagulant-related hemorrhage, 91.5% ± 2.0% (SE); freedom from valve thrombosis 99.1 % ± 0.8 % (SE); and freedom from hemolysis 985% ± '1.2% (SE). Actuarial survival at 6 years is 94.0% + 2.3% (SE) overall. In conclusion, the overall rate of valve-related complications with this valve is low. (J THORAC CARDIOVASC SURG 1992;103:259-66)
Hakki Akalin, MD,a E. Turner Corapcioglu, MD,a Omit Ozyurda, MD,a Kemalettin Ucanok, MD,a Adnan Uysalel, MD,a Biilent Kaya, MD,a N. Tuncay Eren, MD,a and Cetin Erol, MD,b Ankara, Turkey
Since the 1960s, replacement of diseased heart valves with prostheses has extended and improved life for a large number of patients. However, inasmuch as prosthetic heart valves are naturally susceptible to thrombosis, thromboembolism, endocarditis, valve deterioration, and the complications of anticoagulation, the ideal cardiac valve prosthesis has not yet been invented. I Various modifications of cardiac valve prostheses have been made to From the Departments of Cardiovascular Surgery" and Cardiology," Ankara University, Ibn-i Sina Hospital, Ankara, Turkey. Received for publication March 29, 1990. Accepted for publication Nov. 5, 1990. Address for reprints: Hakki Akalin, MD, Director, Department of Cardiovascular Surgery, Ankara University, Ibn-i Sina Hospital, 06100 Ankara, Turkey.
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improve the hemodynamic performance and to decrease the complications of the valve substitutes. Omni design is one of the best examples of such improvements.v 3 The Omniscience cardiac valve prosthesis (Medical Inc., Inver Grove Heights, Minn.) was developed from the LilleheiKaster valve, and a third-generation valve, the Omnicarbon, with the same geometric configuration as the Omniscience valve, was created. The Omniscience is a lowprofile and central-flow valve. It has a concavo-convex pivoting occluder disc made of pyrolytic carbon. The disc is free floating within a one-piece titanium frame. The sewing ring is rotatable and made of polytetrafluoroethylene. The first Omniscience cardiac valve prostheses were implanted by Dr. Richard DeWall at Kettering Medical Center in Dayton, Ohio, in August 1978.4 We began implanting the Omniscience valve in 1984. From January 259
The Journal of
260
Akalin et al.
Thoracic and Cardiovascular Surgery
N
100 , - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ,
84 72
80
60
49
40 19
20 2 O'------~
23
21
19
25
valve size _
AORTI C
27
29
31
33
mm TAD) MI TRAL
Fig. 1. Distribution of valve sizes (225 patients). TAD, Tissue anulus diameter.
Table I. Additional major cardiac procedures MVR
Procedure
Tricuspid annuloplasty Mitral commissurotomy Resection of sinus of valsalva aneurysm Repair of aorta-left ventriculartunnel Repair of atrial septal defect Ascending aortic graft Aorta-coronary bypass graft Total
In =
/43)
AVR
In =
48)
9 (6.3)*
9 (18.8)* I ( 2.1) I ( 2.1)
2 (1.4) I ( 2.1) I (0.7) 12 (8.4)
J..11:!2
13 (27.1)
Table II. Early mortality (225 patients) Cause
No.
%
Lowcardiac output Arrhythmia Cardiac arrest/sudden death Hepatic coma Cerebrovascular All causes
II 3 I I
4.9
Overall
In = 225) 9 ( 4.0)* 9 ( 4.0)
2 ( 0.9) I ( 0.4)
2 ( 0.9) I ( 0.4) ~ 26 (11.6)
*Numbers in parentheses are percents.
1984 to June 1989, 554 patients had valve replacement in our department; 259 Omniscience cardiac valve prostheses were implanted in 225 patients, representing 40.6% of our total valve replacement series during this period. Although there are few reports about this mechanical valve prosthesis, these reports have led to confusion in the literature."? Moreover, some of these reports available on the Omniscience valve have not been encouraging.v": 10 Therefore in this retrospective study we present our experience with the Omniscience valve prosthesis.
Patients and methods Between January 1984 and June 1989, 225 patients underwent cardiac valve replacement with an Omniscience prosthesis at Ankara University. All operations were performed with cardiopulmonary bypass, hemodilution, nonpulsatile flow, and
4
20
1.3 0.4 0.4 1.8 8.9
mostly a bubble oxygenator. Potassium crystalloid cardioplegic solution, moderate systemic hypothermia (26° and 28° C), and topical cooling were used in all patients. The prostheses were placed in all positions with interrupted horizontal mattress sutures buttressed with Teflon pledgets. The large orifice of the valve was oriented anteriorly, toward the aortic outflow tract, in the mitral position. The orientation was anterior to slightly right anterior in the aortic position. In all patients oral anticoagulant therapy was generally started on the second postoperative day. Our anticoagulant therapy protocol is as follows: early starting and the combination of aspirin (100 mg/day) plus dipyridamole (150 mg/day) plus warfarin. Anticoagulation was continued indefinitely in all patients, and prothrombin time ratio was kept at 2 to 2.5 times the control in seconds. Checkups were performed postoperatively at 6-week intervals and then annually. During July and November 1989, all patients were recalled, and a patient follow-up study was completed. Complete physical and laboratory examination, x-ray examination, electrocardiographic examination, and echocardiography were done to evaluate the patients' postoperative status. The definitions of complications of valve replacement are as
follows'':
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Omniscience cardiac valve prosthesis
February 1992
26 1
Table III. Late mortality AVR
MVR
Cause
In = 128)
Endocarditis Valve thrombosis Cerebral embolism Sudden unexplained deaths All causes
2 (1.6)* I (0.8)
DVR 28)
In = 44)
Overall
In = 200)
In =
I (3.6)
3 I I 3 8
I (3.6)* I (0.8) 4 (3.\)
2 (4.5)* 2 (4.5)
2 (7. I)
(1.5)* (0.5) (0.5) (1.5) (2.0)/pt-yr
*Numbers in parentheses are percents.
Table IV. Valve-related complications (according to implantation site) and late deaths AVR
MVR
Cause
In = 128)
Thromboembolism Valve thrombosis Hemolysis Endocarditis Reoperation Anticoagulant-related bleeding Perivalvular leak Structural failure Sudden-unexplained death All complications
4 (1.0%)* 1(0.2%) 2 (0.5%) 2 (0.5%)
In = 44)
I (0.2%)
II (2.7%)
1(0.2%)
2 (0.5%)
In = 28)
DVR
In = 200)
Overall
Deaths
I (0.2%)t
1(0.2%)
5 (1.2%)t I (0.2%) 2 (0.5%) 4 (1.0%)
4 (1.0%)
15 (3.7%)
I I 0 3 0 0 0 0 3 8 (2.0%)
3 (0.7%) 27 (6.6%)+
In)
*Two transient ischemic attack, two femoral embolism. tNumbers in 'parentheses are linearized rate (%/pt-yr). tSudden unexplained deaths are excluded.
I. All deaths more than 30 days after operation, whether valve related or not and irrespective of the cause, were considered late deaths. 2. All episodes of endocarditis were considered to be valve related even in patients in whom valve replacement was performed for native or previous prosthetic valve endocarditis. 3. Thromboembolism included all new cerebrovascular episodes, irrespective of possible associated cerebrovascular disease, reported on clinical grounds with or without radiologic documentation, and all peripheral emboli found at operation or autopsy. 4. All hemorrhages occurring later than 72 hours after operation were identified as anticoagulant related. They were classifiedas fatal, serious (causing permanent disability or necessitating operation, blood transfusion, or hospitalization), or minor (easily bruised or traumatic or nontraumatic cutaneous bleeding). 5. Periprosthetic leak included leaks that were hemodynamically significant, required operation, or were demonstrated at autopsy. 6. Valve thrombosis was diagnosed at operation or autopsy. 7. Hemolysis was considered on hematologic grounds in patients requiring treatment for anemia. 8. Valve failure was defined broadly if any of the complications just listed prompted reoperation or caused death, including operation for anticoagulant-related hemorrhage. Data analysis. Survival curves were plotted by the life-table method, and valve-related events were analyzed by the methods described by Grunkemeier and Starr I I and Anderson and col-
leagues.'? Results are expressed as mean ± standard deviation (SD) or mean ± standard error (SE).
Results Patient demographics. There were 121 (53.8%) male and 104 (46.2%) female patients, whose ages ranged from 13 to 65 years, with an average of 34.4 ± 10.3 (SD) years. Rheumatic heart disease was the underlying pathologic condition in most of the patients (79.3%). Of the 225 patients, 143 (63.6%) had mitral (MVR), 48 (21.3%) had aortic (A VR), and 34 (15.1 %) had double (i.e., aortic plus mitral) (DVR) valve replacements. Preoperatively 15.1% were in New York Heart Association functional class IV, 73.8% in class III, and only 11.1% in class II. Twelve (5.3%) patients had undergone previous cardiac operations (closed or open mitral commissurotomy). Additional procedures were performed in 26 (11.6%) patients (Table I). The distribution of Omniscience valve size in 225 patients is shown in Fig. 1. Operative mortality. In our study the operative or early mortality can be defined as the deaths that occurred during the first 30 postoperative days or those that occurred during the same hospitalization period as the operation; for the whole group the operative mortality was 8.9% (20/225). Early mortality for MVR was
The Journal of
2 6 2 Akalin et al.
Thoracic and Cardiovascular Surgery
\
... '.
I
\
\ \
,. .
.....\.. V,?9;. .
(:
Fig. 2. One of the example s of two-dimensional (apical two-chamber view) imagings and its diagram . The opened valve is shown by the arrow. The measured mitral valve opening a ngle is 80 degrees . LV, Left ventricle: LA, left atrium.
8.4% (12/143), for AVR 6.3% (3/48) and for DVR 14.7% (5/34). None of the earl y deaths were valve related . The causes of operative mortality are shown in Table II. Follow-up. There were 20 early deaths (8.9%) among the 225 patients; 205 patients were discharged from the hospital. At the time of this follow-up study five patients could not be contacted. Thus 97.6% of the patients were included in this study. These patients represent a cumulative follow-up of 407.9 patient-years, with a mean follow-up of 2.03 ± 0.1 (SE) years and with the longest follow-up being 5.7 years. Late mortality. The late mortality rate was 4.03% (8/200) overall, which corresponds to 2.0% ± 0.7%/ptyr (SE): four in the MVR group (3.1% ofMVR patients), two in the AVR group (4.5% of AVR patients), and two in the DVR group (7.1% ofDVR patients). Causes oflate deaths were valve related in five patients, and sudden-unknown death (because of lack of autopsy) in three patients. Table III presents a summary of the causes for the late deaths. Valve-related complications. Regarding the complications of valve replacement, valve-related complications were seen in 27 patients (I 3.5%), with a total of 6.6% ± 1.2%/pt-yr (SE). The causes of valve-related deaths and complications are listed in Table IV.
Prosthetic valve endocarditis. Prosthetic valve endocarditis was encountered in four patients at an annual rate of 1.0% ± 0.5%/pt-yr (SE). Two had had MVR, one AVR, and one DVR. Three of 'the four patients died of their infection (75%). Thromboembolism. Thromboembolic complications occurred in five patients (four MVR, one DVR). Two of them required femoral arterial embolectomy. One patient died of cerebral emboli 16 months after DVR. Two patients had transient ischemic attack without any sequelae. The linearized rate of thromboembolism of the whole group was 1.2% ± 0.5%/pt-yr (SE). Anticoagulant-related hemorrhage. Anticoagulantrelated hemorrhage was noted in a total of 15 patients in our series of 193 patients. The linearized rate of anticoagulant-related hemorrhage was 3.7% ± 0.9%/pt-yr (SE). None of the patients had fatal hemorrhage. All these patients were on a regimen of warfarin, aspirin, and dipyridamole therapy, and their prothrombin times were higher than the therapeutic range. Periprosthetic leak. There were no periprosthetic leaks in our series. Valve thrombosis. Valve thrombosis occurred in only one patient 13 months after MVR (29 mm tissue anulus diameter [TAD]). This patient died before reoperation, and valve thrombosis was confirmed at autop-
Volume 103 Numbe r 2
Omniscience cardiac valve prosth esis
February 1992
26 3
POSTOPERATIVE
PREOPERATIVE
NYHA III
NYHA II
6 .2%
11.1%
NYHA II
NYHA IV
22. 9%
15. 1%
192 Patients
22 5 Patients
Fig. 3. Preoperative and postoperative New York Heart Association functional classification.
100%
PERCENT FREE
H
VT
- --- - - ~
' '0 - - ----
A H
90%
----*-- HEMOLYSIS =9 S.5 ±1. 2 %
VALVE THRO=99.1±0.8% - {]- - P.V.ENDOCA =97 .8±1.0% Patients .t risk OVERALL
205
o
195
1115
2
110
3
44
25
4
5
YEARS POST IMPLANT
-4-
AN.REL HEM=91.5±2.0%
-- ~ - -
THROMBOEMB =94.5±3.6%
II
6
verticsl lines 95.. CL.
Fig. 4. Actuarial freedom from each complication. TE , Thromboembolism; A RH, anticoagulant-related hemorrhage; PVE, prosthetic valve endocarditis; VT, valve thrombosis; H , hemolysis, CL, confidence limits.
sy. Th e lineari zed rate of valve thrombosis of the entire group was 0.2% ± 0.2%/pt-yr (SE). Hemolysis. Hemolysis was significantly noticed in one patient after M VR. This pati ent refu sed reoperation. M ild hemolysis occurred in a nother one, a nd he requ ired only medica l treatment. Th e linearized rat e of hemol ysis was 0.5% ± 0.3%jpt-yr (SE). Valve failure. Valve failure was de tected in six pati ents (endoca rditis in three, valve thrombosis in one, hemol ysis
in one, thromboembolism in one) . The lineari zed rate was 1.5% ± 0.6%/pt-yr (SE) . Val ve opening. By two-dimensional echoca rdiogra phy a t a pical two- a nd four-chamber views, the mean mitral valve openin g angle was 75.9 ± 3.1 (S O ) degrees for 27 pat ients ( Fig. 2), Clinical improvement. During this follow-up study, 136 (70.8%) patients wer e in class I, 44 (22.9%) patients were in class II, and 12 (6. 3%) pat ients were in class III ;
The Journal of
2 6 4 Akalin et al.
Thoracic and Cardiovascular Surgery
PERCENT FREE
'~:: ~'""<::_-:" ..----i---:~-L- -i--- -.- . -.-~- - _.--.--.i MVR- 75.4 % + 5.5 % (SE) NR- 92.5 % ~ 4.0 % (SE)
50%
OVERALL- 77.0 % :!: 4.0 % (SE)
25%
Plltianta at riak 131 45 205
"VR AIR OVERALL
0%
0
126 42 185
105 37 185
54 19 80
24 16 44
14 11 25
2
3
4
5
YEARS POST IMPLANT --4-
OVERALL(AlR+MVR+DVR)
-*-
AIR
H-
4 4 8
6 vertical linaa 85.. CL
MVR
Fig. 5. Rates for actuarial freedom from all valve-relatedcomplications and deaths at 6 years for patients at risk.
there were 25 (11.1%) patients in class II, 166 (73.8%) in class III, and 34 (15.1 %) in class IV preoperatively (Fig. 3). Patients free from complications. Actuarial freedom from thromboembolism at 6 years for patients at risk was 94.5% ± 3.6% (SE) overall: freedom from endocarditis, 97.8% ± 1.0% (SE); freedom from anticoagulant-related hemorrhage, 91.5% ± 2.0% (SE); freedom from valve thrombosis, 99.1 % ± 0.8% (SE); and freedom from hemolysis, 98.5% ± 1.2% (SE) overall. Actuarial freedom from each complication is shown in Fig. 4. The rates for actuarial freedom from complications and deaths at 6 years is shown in Fig. 5. Survival. Actuarial survival at 6 years for patients at risk is 94.0% ± 2.3% (SE) overall, 95.0% ± 2.5% (SE) for the MVR group, and 95.6% ± 3.4% (SE) for the A VR group. Survival curves, including early mortality, for patients at risk are shown in Fig. 6. Discussion The first clinical implantation of the Omniscience valve occurred in 1978. 4 In 1981 Scotten and coworkers' ' found that, regarding transvalvular energy loss, the Omniscience valve was superior in performance to the other new tilting disc cardiac valve prostheses, and also the initial clinical evaluation of this valve showed that the results were acceptable.i-? Unfortunately, between the years 1983 and 1986, sharply contrasting short- and
medium-term results were published in the literature.f- 6, 7, 9,10,14-16 These interesting discussions between the opposite groups also continued in more recently published articles.!" 18 For these reasons we tried to present our experience with this "fairly judged" I 7 valve prosthesis. The 8.9% operative mortality rate for the wh'ole group is similar to that reported by others.r- 5, 8,19 It is closely related with additional procedures and previous cardiac operations. In our series no operative death was a result of valve-related complications. Factors such as age, associated disease, and advance in New York Heart Association functional class was associated with the causes of late mortality. Our results for late mortality (2.0% jpt-yr) are at marked variance with those reported by Carrier, Damle, and Cortina and their colleagues- 8. I because of the younger ages in our series. The prevalence of prosthetic valve endocarditis in our series (1.0%jpt-yr) is equal to the prevalences reported in the Iiterature.s- 8, LO but the high mortality rate of prosthetic valve endocarditis encountered in our series reflects our conservative management. Our results for thromboembolism (1.2%jpt-yr) and valve thrombosis (0.2%jpt-yr) are better than those of Carrier, Rabago, and Fananapazir and their colleagues.v? The reported extremely high rates of valve thrombosis are multifactorial. 10, 16, 17 Posterior orientation, oversizing, nonaggressive anticoagulant regimen,
°
Volume 103 Number 2
Omniscience cardiac valve prosthesis
February 1992
100%
PROBABILITY OF SURVIVAL
75%
MVR- 87.0 % :!: 3.6 % (SE) NR- 89.6 % ± 4.5 % (SE) OVERALL- 85.6 %
50%
25%
265
'!:
2.8 % (SE)
tlenta at rlak
MVR
143/131
126
105
54
AIR
48145
42
37
19
OVERALL
225/205
195
80
0%
185 I
11 1 2
2
0
24 16
14 11
4
I
44 I
25 I
8 I
3
4
5
YEARS POST IMPLANT -~-
OVERALL(AVR+MVR+DVR)
-8---
4
6 Vertical linea 95'5 CL.
MVR
Fig. 6. Survival (including early mortality) for patients at risk. and patient cardiac status (rhythm, etiology, pathology) also play an important role in valve thrombosis. Our better results are directly related to valve size (mean for mitral, 28.2 ± 1.4 [SO] mm TAD and for aortic, 23.0 ± 1.7 [SO] mm TAD), anterior orientation in mitral position, and our very aggressive anticoagulant therapy. Also, thromboembolic complications with mechanical prostheses are less prevalent in younger patients because of decreased coagulability/"; more than half of our patients were younger than 35 years. In an attempt to reduce thromboembolism without increasing bleeding problems, some investigators" recommend both platelet inhibitors and warfarin. Altman, Banllon, and Rouvier-? found that the addition of aspirin to warfarin (Coumadin) reduced the prevalence of thromboembolism from ll%/pt-yr to 3.5%/pt-yr; Sullivan, Harken, and Gorlin-' found that antiplatelet aggregates reduced the prevalence of thromboembolism from 14% to 1.3%/pt-yr. Dosage schedules and amounts of dipyridamole achieve only partial inhibition.I! Our anticoagulant therapy protocol is as follows:early starting and the combination of aspirin (100 mg/day) plus dipyridamole (150 rug/day) plus warfarin. In our series anticoagulant-related hemorrhage (3.7%/pt-yr) is more prevalent than in other series.> 8,10 Despite the frequency of bleeding complications of our protocol, there were no deaths related to this anticoagulant therapy. Perivalvular leak is an avoidable complication of valve
replacement and generally is related to the surgeon's technique. Our better results for perivalvular leak reflect our technique of routinely using horizontal mattress sutures buttressed with pledgets. Our results for hemolysis (0.5%/pt-yr) are similar to those of Carrier and Damle and their coworkers. 5, 8 Valve failure (any complication resulting in death or reoperation, including that for anticoagulant-related hemorrhage) occurred in six patients (one cerebral embolism, one valve thrombosis, one hemolysis, three cases of prosthetic valve endocarditis). Although there are some reports on the insufficient valve opening angle of Omniscience valves,s, 24 we showed and measured excellent mitral valve opening angles by two-dimensional echocardiography at apical two- and four-chamber views, which are the best views for measurement of the angles. The mean mitral valve opening was 75.9 ± 3.1 (SO) degrees for 27 patients. The actuarial rate of freedom from all complications, including late deaths, was 77.0% ± 4.0% (SE) overall. According to New York Heart Association functional class, 93.7% of the patients are now in class I and II. In conclusion, the search for an ideal valve prosthesis will continue as Omni design. The overall prevalence of valve-related complications with this valve, however, is low. Also, the quality of life and expectation for survival are excellent. Our results with this valve have been favorable.
2 6 6 Akalin et al.
REFERENCES 1. Morgan RJ, Davis JT, Fraker TD. Current status of valve prostheses. Surg Clin North Am 1985;65:699-720. 2. DeWall RA, Raggio JMC, Guilmet D, Morea M, Thevenet A. The Omni design: evolution of a valve. J THORAC CARDIOVASC SURG 1989;98:999-1007. 3. Callaghan JC, Damle A. Clinical experience with the Omnicarbon valve. In: Allessandro LC, ed. Heart surgery. 1st ed. Rome: Casa Editrice Scientifica Internazionale, 1989:341-4. 4. DeWall RA, Pelletier LC, Panebianco A, et al. Five year clinical experience with the Omniscience cardiac valve. Ann Thorac Surg 1984;38:275-80. 5. Carrier M, Martineau JP, Bonan R, Pelletier LC. Clinical and hemodynamic assessment of the Omniscience prosthetic heart valve. J THORAC CARDIOVASC SURG 1987; 93:300-7. 6. Rabago G, Martinell J, Fraile J, Andrade IG, Montenegro R. Results and complications with the Omniscience prosthesis. J THORAC CARDIOVASC SURG 1984;87:136-40. 7. Fananapazir L, Clarke DB, Dark JF, Lawson RAM, Moussalli H. Results of valve replacement with the Omniscience prosthesis. J THORAC CARDIOVASC SURG 1983; 86:621-5. 8. Damle A, Coles J, Teijeira J, Pelletier C, Callaghan JA. A six-year study of the Omniscience valve in four Canadian Centers. Ann Thorac Surg 1987;43:513-21. 9. Alstrup P, Rygg IH. Experience with Omniscience and Lillehei-Kaster valves [Letter]. J THORAC CARDIOVASC SURG 1984;87:940. 10. Cortina JM, Martinell J, Artiz V, Fraile J, Rabago G. Comparative clinical results with Omniscience (STM 1), Medtronic-Hall, and Bjork-Shiley convexo-concave (70 degrees) prostheses in mitral valve replacement. J THORAC CARDIOVASC SURG 1986;91:174-83. 11. Grunkemeier GL, Starr A. Actuarial analysis of surgical results: rationale and method. Ann Thorac Surg 1977; 24:404-8. 12. Anderson RP, Bonchek LI, Grunkemeier GL, Lambert LE, Starr A. The analysis and presentation of surgical results by actuarial methods. J Surg Res 1974;16:22430.
The Journal of Thoracic and Cardiovascular Surgery
13. Scotten LN,Racca RG,NugentAH, WalkerDK,BrownleeRT. New tilting disc cardiac valve prostheses. J THORAC CARDIOVASC SURG 1981;82:136-46. 14. Caffarena Raggio RJM, Luna D, Garcia Sanchez F. Long-term follow-up of patients implanted with the Omniscience cardiac valve prosthesis. J Cardiovasc Surg 1985;26:91-2. 15. Mestres CA, Igual A, Murtra M. Clinical performance of the Omniscience prosthetic heart valve with Dacron sewing ring. Thorac Cardiovasc Surg 1985;33:296-9. 16. Mikhail AA. A scientific critique of an Omniscience clinical paper. J THORAC CARDIOVASC SURG 1984;88:307-8. 17. DeWall RA. Thrombotic complications with the Omniscience valve: a current review [Letter]. J THORAC CARD10VASC SURG 1989;98:298-300. 18. Edmunds LH. Reply to the Editor. J THORAC CARDIOVASC SURG 1989;98:300. 19. Callaghan JC. Mitral valve replacement. In: Adams AS, Roberts AJ, eds. Cardiac colloquy. 1st ed. Boston: Adams, 1987:93-9. 20. Pass HJ, Crawford FA, Hohn AR. Cardiac valve replacement in children without anticoagulation. J THORAC CARD10VASC SURG 1984;87:832-5. 21. Chesebro JH, Fuster V, Elveback LR. Trial of combined warfarin plus dipyridamole or aspirin therapy in prosthetic heart valve replacement. Am J Cardiol 1983;51:153744. 22. Altman R, Banllon F, Rouvier J. Aspirin prophylaxis of thromboembolic complications in patients with substitute heart valves. J THORAC CARDIOVASC SURG 1976;72:1279. 23. Sullivan JH, Harken DE, Gorlin R. Pharmacologic control of thromboembolic complications of cardiac valve replacement. N Engl J Med 1971;284:1391-4. 24. Cordoba M, Almeida P, Martinez P, Maravi C, Ramirez JA, Rabago G. Invasive assessment of mitral valve prostheses. In: Rabago G, Cooley DA, eds. Heart valve replacement and future trends in cardiac surgery. 1st ed. Mount Kisco, N.Y.: Futura, 1987:375-89.
Hakki Akalin, MD,a E. Turner Corapcioglu, MD,a Omit Ozyurda, MD,a Kemalettin Ucanok, MD,a Adnan Uysalel, MD,a Biilent Kaya, MD,a N. Tuncay Eren, MD,a and Cetin Erol, MD,b Ankara, Turkey
Since the 1960s, replacement of diseased heart valves with prostheses has extended and improved life for a large number of patients. However, inasmuch as prosthetic heart valves are naturally susceptible to thrombosis, thromboembolism, endocarditis, valve deterioration, and the complications of anticoagulation, the ideal cardiac valve prosthesis has not yet been invented. I Various modifications of cardiac valve prostheses have been made to From the Departments of Cardiovascular Surgery" and Cardiology," Ankara University, Ibn-i Sina Hospital, Ankara, Turkey. Received for publication March 29, 1990. Accepted for publication Nov. 5, 1990. Address for reprints: Hakki Akalin, MD, Director, Department of Cardiovascular Surgery, Ankara University, Ibn-i Sina Hospital, 06100 Ankara, Turkey.
12/1/26541
improve the hemodynamic performance and to decrease the complications of the valve substitutes. Omni design is one of the best examples of such improvements.v 3 The Omniscience cardiac valve prosthesis (Medical Inc., Inver Grove Heights, Minn.) was developed from the LilleheiKaster valve, and a third-generation valve, the Omnicarbon, with the same geometric configuration as the Omniscience valve, was created. The Omniscience is a lowprofile and central-flow valve. It has a concavo-convex pivoting occluder disc made of pyrolytic carbon. The disc is free floating within a one-piece titanium frame. The sewing ring is rotatable and made of polytetrafluoroethylene. The first Omniscience cardiac valve prostheses were implanted by Dr. Richard DeWall at Kettering Medical Center in Dayton, Ohio, in August 1978.4 We began implanting the Omniscience valve in 1984. From January 259
The Journal of
260
Akalin et al.
Thoracic and Cardiovascular Surgery
N
100 , - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ,
84 72
80
60
49
40 19
20 2 O'------~
23
21
19
25
valve size _
AORTI C
27
29
31
33
mm TAD) MI TRAL
Fig. 1. Distribution of valve sizes (225 patients). TAD, Tissue anulus diameter.
Table I. Additional major cardiac procedures MVR
Procedure
Tricuspid annuloplasty Mitral commissurotomy Resection of sinus of valsalva aneurysm Repair of aorta-left ventriculartunnel Repair of atrial septal defect Ascending aortic graft Aorta-coronary bypass graft Total
In =
/43)
AVR
In =
48)
9 (6.3)*
9 (18.8)* I ( 2.1) I ( 2.1)
2 (1.4) I ( 2.1) I (0.7) 12 (8.4)
J..11:!2
13 (27.1)
Table II. Early mortality (225 patients) Cause
No.
%
Lowcardiac output Arrhythmia Cardiac arrest/sudden death Hepatic coma Cerebrovascular All causes
II 3 I I
4.9
Overall
In = 225) 9 ( 4.0)* 9 ( 4.0)
2 ( 0.9) I ( 0.4)
2 ( 0.9) I ( 0.4) ~ 26 (11.6)
*Numbers in parentheses are percents.
1984 to June 1989, 554 patients had valve replacement in our department; 259 Omniscience cardiac valve prostheses were implanted in 225 patients, representing 40.6% of our total valve replacement series during this period. Although there are few reports about this mechanical valve prosthesis, these reports have led to confusion in the literature."? Moreover, some of these reports available on the Omniscience valve have not been encouraging.v": 10 Therefore in this retrospective study we present our experience with the Omniscience valve prosthesis.
Patients and methods Between January 1984 and June 1989, 225 patients underwent cardiac valve replacement with an Omniscience prosthesis at Ankara University. All operations were performed with cardiopulmonary bypass, hemodilution, nonpulsatile flow, and
4
20
1.3 0.4 0.4 1.8 8.9
mostly a bubble oxygenator. Potassium crystalloid cardioplegic solution, moderate systemic hypothermia (26° and 28° C), and topical cooling were used in all patients. The prostheses were placed in all positions with interrupted horizontal mattress sutures buttressed with Teflon pledgets. The large orifice of the valve was oriented anteriorly, toward the aortic outflow tract, in the mitral position. The orientation was anterior to slightly right anterior in the aortic position. In all patients oral anticoagulant therapy was generally started on the second postoperative day. Our anticoagulant therapy protocol is as follows: early starting and the combination of aspirin (100 mg/day) plus dipyridamole (150 mg/day) plus warfarin. Anticoagulation was continued indefinitely in all patients, and prothrombin time ratio was kept at 2 to 2.5 times the control in seconds. Checkups were performed postoperatively at 6-week intervals and then annually. During July and November 1989, all patients were recalled, and a patient follow-up study was completed. Complete physical and laboratory examination, x-ray examination, electrocardiographic examination, and echocardiography were done to evaluate the patients' postoperative status. The definitions of complications of valve replacement are as
follows'':
Volume 103 Number 2
Omniscience cardiac valve prosthesis
February 1992
26 1
Table III. Late mortality AVR
MVR
Cause
In = 128)
Endocarditis Valve thrombosis Cerebral embolism Sudden unexplained deaths All causes
2 (1.6)* I (0.8)
DVR 28)
In = 44)
Overall
In = 200)
In =
I (3.6)
3 I I 3 8
I (3.6)* I (0.8) 4 (3.\)
2 (4.5)* 2 (4.5)
2 (7. I)
(1.5)* (0.5) (0.5) (1.5) (2.0)/pt-yr
*Numbers in parentheses are percents.
Table IV. Valve-related complications (according to implantation site) and late deaths AVR
MVR
Cause
In = 128)
Thromboembolism Valve thrombosis Hemolysis Endocarditis Reoperation Anticoagulant-related bleeding Perivalvular leak Structural failure Sudden-unexplained death All complications
4 (1.0%)* 1(0.2%) 2 (0.5%) 2 (0.5%)
In = 44)
I (0.2%)
II (2.7%)
1(0.2%)
2 (0.5%)
In = 28)
DVR
In = 200)
Overall
Deaths
I (0.2%)t
1(0.2%)
5 (1.2%)t I (0.2%) 2 (0.5%) 4 (1.0%)
4 (1.0%)
15 (3.7%)
I I 0 3 0 0 0 0 3 8 (2.0%)
3 (0.7%) 27 (6.6%)+
In)
*Two transient ischemic attack, two femoral embolism. tNumbers in 'parentheses are linearized rate (%/pt-yr). tSudden unexplained deaths are excluded.
I. All deaths more than 30 days after operation, whether valve related or not and irrespective of the cause, were considered late deaths. 2. All episodes of endocarditis were considered to be valve related even in patients in whom valve replacement was performed for native or previous prosthetic valve endocarditis. 3. Thromboembolism included all new cerebrovascular episodes, irrespective of possible associated cerebrovascular disease, reported on clinical grounds with or without radiologic documentation, and all peripheral emboli found at operation or autopsy. 4. All hemorrhages occurring later than 72 hours after operation were identified as anticoagulant related. They were classifiedas fatal, serious (causing permanent disability or necessitating operation, blood transfusion, or hospitalization), or minor (easily bruised or traumatic or nontraumatic cutaneous bleeding). 5. Periprosthetic leak included leaks that were hemodynamically significant, required operation, or were demonstrated at autopsy. 6. Valve thrombosis was diagnosed at operation or autopsy. 7. Hemolysis was considered on hematologic grounds in patients requiring treatment for anemia. 8. Valve failure was defined broadly if any of the complications just listed prompted reoperation or caused death, including operation for anticoagulant-related hemorrhage. Data analysis. Survival curves were plotted by the life-table method, and valve-related events were analyzed by the methods described by Grunkemeier and Starr I I and Anderson and col-
leagues.'? Results are expressed as mean ± standard deviation (SD) or mean ± standard error (SE).
Results Patient demographics. There were 121 (53.8%) male and 104 (46.2%) female patients, whose ages ranged from 13 to 65 years, with an average of 34.4 ± 10.3 (SD) years. Rheumatic heart disease was the underlying pathologic condition in most of the patients (79.3%). Of the 225 patients, 143 (63.6%) had mitral (MVR), 48 (21.3%) had aortic (A VR), and 34 (15.1 %) had double (i.e., aortic plus mitral) (DVR) valve replacements. Preoperatively 15.1% were in New York Heart Association functional class IV, 73.8% in class III, and only 11.1% in class II. Twelve (5.3%) patients had undergone previous cardiac operations (closed or open mitral commissurotomy). Additional procedures were performed in 26 (11.6%) patients (Table I). The distribution of Omniscience valve size in 225 patients is shown in Fig. 1. Operative mortality. In our study the operative or early mortality can be defined as the deaths that occurred during the first 30 postoperative days or those that occurred during the same hospitalization period as the operation; for the whole group the operative mortality was 8.9% (20/225). Early mortality for MVR was
The Journal of
2 6 2 Akalin et al.
Thoracic and Cardiovascular Surgery
\
... '.
I
\
\ \
,. .
.....\.. V,?9;. .
(:
Fig. 2. One of the example s of two-dimensional (apical two-chamber view) imagings and its diagram . The opened valve is shown by the arrow. The measured mitral valve opening a ngle is 80 degrees . LV, Left ventricle: LA, left atrium.
8.4% (12/143), for AVR 6.3% (3/48) and for DVR 14.7% (5/34). None of the earl y deaths were valve related . The causes of operative mortality are shown in Table II. Follow-up. There were 20 early deaths (8.9%) among the 225 patients; 205 patients were discharged from the hospital. At the time of this follow-up study five patients could not be contacted. Thus 97.6% of the patients were included in this study. These patients represent a cumulative follow-up of 407.9 patient-years, with a mean follow-up of 2.03 ± 0.1 (SE) years and with the longest follow-up being 5.7 years. Late mortality. The late mortality rate was 4.03% (8/200) overall, which corresponds to 2.0% ± 0.7%/ptyr (SE): four in the MVR group (3.1% ofMVR patients), two in the AVR group (4.5% of AVR patients), and two in the DVR group (7.1% ofDVR patients). Causes oflate deaths were valve related in five patients, and sudden-unknown death (because of lack of autopsy) in three patients. Table III presents a summary of the causes for the late deaths. Valve-related complications. Regarding the complications of valve replacement, valve-related complications were seen in 27 patients (I 3.5%), with a total of 6.6% ± 1.2%/pt-yr (SE). The causes of valve-related deaths and complications are listed in Table IV.
Prosthetic valve endocarditis. Prosthetic valve endocarditis was encountered in four patients at an annual rate of 1.0% ± 0.5%/pt-yr (SE). Two had had MVR, one AVR, and one DVR. Three of 'the four patients died of their infection (75%). Thromboembolism. Thromboembolic complications occurred in five patients (four MVR, one DVR). Two of them required femoral arterial embolectomy. One patient died of cerebral emboli 16 months after DVR. Two patients had transient ischemic attack without any sequelae. The linearized rate of thromboembolism of the whole group was 1.2% ± 0.5%/pt-yr (SE). Anticoagulant-related hemorrhage. Anticoagulantrelated hemorrhage was noted in a total of 15 patients in our series of 193 patients. The linearized rate of anticoagulant-related hemorrhage was 3.7% ± 0.9%/pt-yr (SE). None of the patients had fatal hemorrhage. All these patients were on a regimen of warfarin, aspirin, and dipyridamole therapy, and their prothrombin times were higher than the therapeutic range. Periprosthetic leak. There were no periprosthetic leaks in our series. Valve thrombosis. Valve thrombosis occurred in only one patient 13 months after MVR (29 mm tissue anulus diameter [TAD]). This patient died before reoperation, and valve thrombosis was confirmed at autop-
Volume 103 Numbe r 2
Omniscience cardiac valve prosth esis
February 1992
26 3
POSTOPERATIVE
PREOPERATIVE
NYHA III
NYHA II
6 .2%
11.1%
NYHA II
NYHA IV
22. 9%
15. 1%
192 Patients
22 5 Patients
Fig. 3. Preoperative and postoperative New York Heart Association functional classification.
100%
PERCENT FREE
H
VT
- --- - - ~
' '0 - - ----
A H
90%
----*-- HEMOLYSIS =9 S.5 ±1. 2 %
VALVE THRO=99.1±0.8% - {]- - P.V.ENDOCA =97 .8±1.0% Patients .t risk OVERALL
205
o
195
1115
2
110
3
44
25
4
5
YEARS POST IMPLANT
-4-
AN.REL HEM=91.5±2.0%
-- ~ - -
THROMBOEMB =94.5±3.6%
II
6
verticsl lines 95.. CL.
Fig. 4. Actuarial freedom from each complication. TE , Thromboembolism; A RH, anticoagulant-related hemorrhage; PVE, prosthetic valve endocarditis; VT, valve thrombosis; H , hemolysis, CL, confidence limits.
sy. Th e lineari zed rate of valve thrombosis of the entire group was 0.2% ± 0.2%/pt-yr (SE). Hemolysis. Hemolysis was significantly noticed in one patient after M VR. This pati ent refu sed reoperation. M ild hemolysis occurred in a nother one, a nd he requ ired only medica l treatment. Th e linearized rat e of hemol ysis was 0.5% ± 0.3%jpt-yr (SE). Valve failure. Valve failure was de tected in six pati ents (endoca rditis in three, valve thrombosis in one, hemol ysis
in one, thromboembolism in one) . The lineari zed rate was 1.5% ± 0.6%/pt-yr (SE) . Val ve opening. By two-dimensional echoca rdiogra phy a t a pical two- a nd four-chamber views, the mean mitral valve openin g angle was 75.9 ± 3.1 (S O ) degrees for 27 pat ients ( Fig. 2), Clinical improvement. During this follow-up study, 136 (70.8%) patients wer e in class I, 44 (22.9%) patients were in class II, and 12 (6. 3%) pat ients were in class III ;
The Journal of
2 6 4 Akalin et al.
Thoracic and Cardiovascular Surgery
PERCENT FREE
'~:: ~'""<::_-:" ..----i---:~-L- -i--- -.- . -.-~- - _.--.--.i MVR- 75.4 % + 5.5 % (SE) NR- 92.5 % ~ 4.0 % (SE)
50%
OVERALL- 77.0 % :!: 4.0 % (SE)
25%
Plltianta at riak 131 45 205
"VR AIR OVERALL
0%
0
126 42 185
105 37 185
54 19 80
24 16 44
14 11 25
2
3
4
5
YEARS POST IMPLANT --4-
OVERALL(AlR+MVR+DVR)
-*-
AIR
H-
4 4 8
6 vertical linaa 85.. CL
MVR
Fig. 5. Rates for actuarial freedom from all valve-relatedcomplications and deaths at 6 years for patients at risk.
there were 25 (11.1%) patients in class II, 166 (73.8%) in class III, and 34 (15.1 %) in class IV preoperatively (Fig. 3). Patients free from complications. Actuarial freedom from thromboembolism at 6 years for patients at risk was 94.5% ± 3.6% (SE) overall: freedom from endocarditis, 97.8% ± 1.0% (SE); freedom from anticoagulant-related hemorrhage, 91.5% ± 2.0% (SE); freedom from valve thrombosis, 99.1 % ± 0.8% (SE); and freedom from hemolysis, 98.5% ± 1.2% (SE) overall. Actuarial freedom from each complication is shown in Fig. 4. The rates for actuarial freedom from complications and deaths at 6 years is shown in Fig. 5. Survival. Actuarial survival at 6 years for patients at risk is 94.0% ± 2.3% (SE) overall, 95.0% ± 2.5% (SE) for the MVR group, and 95.6% ± 3.4% (SE) for the A VR group. Survival curves, including early mortality, for patients at risk are shown in Fig. 6. Discussion The first clinical implantation of the Omniscience valve occurred in 1978. 4 In 1981 Scotten and coworkers' ' found that, regarding transvalvular energy loss, the Omniscience valve was superior in performance to the other new tilting disc cardiac valve prostheses, and also the initial clinical evaluation of this valve showed that the results were acceptable.i-? Unfortunately, between the years 1983 and 1986, sharply contrasting short- and
medium-term results were published in the literature.f- 6, 7, 9,10,14-16 These interesting discussions between the opposite groups also continued in more recently published articles.!" 18 For these reasons we tried to present our experience with this "fairly judged" I 7 valve prosthesis. The 8.9% operative mortality rate for the wh'ole group is similar to that reported by others.r- 5, 8,19 It is closely related with additional procedures and previous cardiac operations. In our series no operative death was a result of valve-related complications. Factors such as age, associated disease, and advance in New York Heart Association functional class was associated with the causes of late mortality. Our results for late mortality (2.0% jpt-yr) are at marked variance with those reported by Carrier, Damle, and Cortina and their colleagues- 8. I because of the younger ages in our series. The prevalence of prosthetic valve endocarditis in our series (1.0%jpt-yr) is equal to the prevalences reported in the Iiterature.s- 8, LO but the high mortality rate of prosthetic valve endocarditis encountered in our series reflects our conservative management. Our results for thromboembolism (1.2%jpt-yr) and valve thrombosis (0.2%jpt-yr) are better than those of Carrier, Rabago, and Fananapazir and their colleagues.v? The reported extremely high rates of valve thrombosis are multifactorial. 10, 16, 17 Posterior orientation, oversizing, nonaggressive anticoagulant regimen,
°
Volume 103 Number 2
Omniscience cardiac valve prosthesis
February 1992
100%
PROBABILITY OF SURVIVAL
75%
MVR- 87.0 % :!: 3.6 % (SE) NR- 89.6 % ± 4.5 % (SE) OVERALL- 85.6 %
50%
25%
265
'!:
2.8 % (SE)
tlenta at rlak
MVR
143/131
126
105
54
AIR
48145
42
37
19
OVERALL
225/205
195
80
0%
185 I
11 1 2
2
0
24 16
14 11
4
I
44 I
25 I
8 I
3
4
5
YEARS POST IMPLANT -~-
OVERALL(AVR+MVR+DVR)
-8---
4
6 Vertical linea 95'5 CL.
MVR
Fig. 6. Survival (including early mortality) for patients at risk. and patient cardiac status (rhythm, etiology, pathology) also play an important role in valve thrombosis. Our better results are directly related to valve size (mean for mitral, 28.2 ± 1.4 [SO] mm TAD and for aortic, 23.0 ± 1.7 [SO] mm TAD), anterior orientation in mitral position, and our very aggressive anticoagulant therapy. Also, thromboembolic complications with mechanical prostheses are less prevalent in younger patients because of decreased coagulability/"; more than half of our patients were younger than 35 years. In an attempt to reduce thromboembolism without increasing bleeding problems, some investigators" recommend both platelet inhibitors and warfarin. Altman, Banllon, and Rouvier-? found that the addition of aspirin to warfarin (Coumadin) reduced the prevalence of thromboembolism from ll%/pt-yr to 3.5%/pt-yr; Sullivan, Harken, and Gorlin-' found that antiplatelet aggregates reduced the prevalence of thromboembolism from 14% to 1.3%/pt-yr. Dosage schedules and amounts of dipyridamole achieve only partial inhibition.I! Our anticoagulant therapy protocol is as follows:early starting and the combination of aspirin (100 mg/day) plus dipyridamole (150 rug/day) plus warfarin. In our series anticoagulant-related hemorrhage (3.7%/pt-yr) is more prevalent than in other series.> 8,10 Despite the frequency of bleeding complications of our protocol, there were no deaths related to this anticoagulant therapy. Perivalvular leak is an avoidable complication of valve
replacement and generally is related to the surgeon's technique. Our better results for perivalvular leak reflect our technique of routinely using horizontal mattress sutures buttressed with pledgets. Our results for hemolysis (0.5%/pt-yr) are similar to those of Carrier and Damle and their coworkers. 5, 8 Valve failure (any complication resulting in death or reoperation, including that for anticoagulant-related hemorrhage) occurred in six patients (one cerebral embolism, one valve thrombosis, one hemolysis, three cases of prosthetic valve endocarditis). Although there are some reports on the insufficient valve opening angle of Omniscience valves,s, 24 we showed and measured excellent mitral valve opening angles by two-dimensional echocardiography at apical two- and four-chamber views, which are the best views for measurement of the angles. The mean mitral valve opening was 75.9 ± 3.1 (SO) degrees for 27 patients. The actuarial rate of freedom from all complications, including late deaths, was 77.0% ± 4.0% (SE) overall. According to New York Heart Association functional class, 93.7% of the patients are now in class I and II. In conclusion, the search for an ideal valve prosthesis will continue as Omni design. The overall prevalence of valve-related complications with this valve, however, is low. Also, the quality of life and expectation for survival are excellent. Our results with this valve have been favorable.
2 6 6 Akalin et al.
REFERENCES 1. Morgan RJ, Davis JT, Fraker TD. Current status of valve prostheses. Surg Clin North Am 1985;65:699-720. 2. DeWall RA, Raggio JMC, Guilmet D, Morea M, Thevenet A. The Omni design: evolution of a valve. J THORAC CARDIOVASC SURG 1989;98:999-1007. 3. Callaghan JC, Damle A. Clinical experience with the Omnicarbon valve. In: Allessandro LC, ed. Heart surgery. 1st ed. Rome: Casa Editrice Scientifica Internazionale, 1989:341-4. 4. DeWall RA, Pelletier LC, Panebianco A, et al. Five year clinical experience with the Omniscience cardiac valve. Ann Thorac Surg 1984;38:275-80. 5. Carrier M, Martineau JP, Bonan R, Pelletier LC. Clinical and hemodynamic assessment of the Omniscience prosthetic heart valve. J THORAC CARDIOVASC SURG 1987; 93:300-7. 6. Rabago G, Martinell J, Fraile J, Andrade IG, Montenegro R. Results and complications with the Omniscience prosthesis. J THORAC CARDIOVASC SURG 1984;87:136-40. 7. Fananapazir L, Clarke DB, Dark JF, Lawson RAM, Moussalli H. Results of valve replacement with the Omniscience prosthesis. J THORAC CARDIOVASC SURG 1983; 86:621-5. 8. Damle A, Coles J, Teijeira J, Pelletier C, Callaghan JA. A six-year study of the Omniscience valve in four Canadian Centers. Ann Thorac Surg 1987;43:513-21. 9. Alstrup P, Rygg IH. Experience with Omniscience and Lillehei-Kaster valves [Letter]. J THORAC CARDIOVASC SURG 1984;87:940. 10. Cortina JM, Martinell J, Artiz V, Fraile J, Rabago G. Comparative clinical results with Omniscience (STM 1), Medtronic-Hall, and Bjork-Shiley convexo-concave (70 degrees) prostheses in mitral valve replacement. J THORAC CARDIOVASC SURG 1986;91:174-83. 11. Grunkemeier GL, Starr A. Actuarial analysis of surgical results: rationale and method. Ann Thorac Surg 1977; 24:404-8. 12. Anderson RP, Bonchek LI, Grunkemeier GL, Lambert LE, Starr A. The analysis and presentation of surgical results by actuarial methods. J Surg Res 1974;16:22430.
The Journal of Thoracic and Cardiovascular Surgery
13. Scotten LN,Racca RG,NugentAH, WalkerDK,BrownleeRT. New tilting disc cardiac valve prostheses. J THORAC CARDIOVASC SURG 1981;82:136-46. 14. Caffarena Raggio RJM, Luna D, Garcia Sanchez F. Long-term follow-up of patients implanted with the Omniscience cardiac valve prosthesis. J Cardiovasc Surg 1985;26:91-2. 15. Mestres CA, Igual A, Murtra M. Clinical performance of the Omniscience prosthetic heart valve with Dacron sewing ring. Thorac Cardiovasc Surg 1985;33:296-9. 16. Mikhail AA. A scientific critique of an Omniscience clinical paper. J THORAC CARDIOVASC SURG 1984;88:307-8. 17. DeWall RA. Thrombotic complications with the Omniscience valve: a current review [Letter]. J THORAC CARD10VASC SURG 1989;98:298-300. 18. Edmunds LH. Reply to the Editor. J THORAC CARDIOVASC SURG 1989;98:300. 19. Callaghan JC. Mitral valve replacement. In: Adams AS, Roberts AJ, eds. Cardiac colloquy. 1st ed. Boston: Adams, 1987:93-9. 20. Pass HJ, Crawford FA, Hohn AR. Cardiac valve replacement in children without anticoagulation. J THORAC CARD10VASC SURG 1984;87:832-5. 21. Chesebro JH, Fuster V, Elveback LR. Trial of combined warfarin plus dipyridamole or aspirin therapy in prosthetic heart valve replacement. Am J Cardiol 1983;51:153744. 22. Altman R, Banllon F, Rouvier J. Aspirin prophylaxis of thromboembolic complications in patients with substitute heart valves. J THORAC CARDIOVASC SURG 1976;72:1279. 23. Sullivan JH, Harken DE, Gorlin R. Pharmacologic control of thromboembolic complications of cardiac valve replacement. N Engl J Med 1971;284:1391-4. 24. Cordoba M, Almeida P, Martinez P, Maravi C, Ramirez JA, Rabago G. Invasive assessment of mitral valve prostheses. In: Rabago G, Cooley DA, eds. Heart valve replacement and future trends in cardiac surgery. 1st ed. Mount Kisco, N.Y.: Futura, 1987:375-89.