Long-Term Results With the Medtronic-Hall Valvular Prosthesis

Transcription

1 Long-Term Results With the Medtronic-Hall Valvular Prosthesis Cary W. Akins, MD Cardiac Surgical Unit, Massachusetts General Hospital, Boston, Massachusetts Background. Although more than 170,000 Medtronic- Hall mechanical valvular prostheses have been inserted world-wide, long-term results are available on only a small percent of those valves inserted. Methods. A prospective data registry of all Medtronic- Hall cardiac prostheses inserted by one surgeon was used to identify 460 valves inserted during 391 operations from 1983 to 1994: single aortic (n = 210), single mitral (n = 115), or double aortic and mitral (n = 66) replacements, including three tricuspid valve replacements. Follow-up was sought five times in 10 years and was available for 280 (99%) of 283 survivors with only an isolated aortic or mitral Medtronic-Hall valve followed up for at least 1 year (1,246 patient-years). Results. Hospital mortality was 4.6% (18 patients). Of 40 late deaths, eight were valve-related (0.6% per patientyear). The linearized rates of complications for aortic and mitral valve replacements (percent per patient-year) were, respectively: structural deterioration, 0 and 0; nonstructural dysfunction, 0.1 and 2.1; thromboembolism, 1.3 and 2.1; thrombosis, 0 and 0.2; anticoagulant-related bleeding, 1.7 and 1.9; and prosthetic valve endocarditis, 0.6 and 1.0. Actuarial freedom from reoperation at 10 years was 97% for aortic and 88% for mitral valves. Conclusions. The Medtronic-Hall mechanical valvular prosthesis has excellent durability and acceptably low rates of valve-related complications and remains my mechanical prosthetic valve of choice for both aortic and mitral valve replacements. (Ann Thorac Surg 1996;61:806-13) cardiac surgeons choose a prosthesis for valular replacement, they are required to make a compromise between the excellent durability of approved mechanical prostheses and the greater freedom from thromboembolism and diminished requirement for anticoagulation associated with current bioprostheses. The Medtronic-Hall mechanical cardiac valvular prosthesis, one of the latest evolutionary designs of singledisc prostheses, offers a wider opening angle, a larger minor orifice, and translation as well as rotation of the disc on a central, machined strut. These features were developed to offer potentially greater durability, improved hemodynamics, and lower thromboembolic rates. This report documents the 10-year clinical experience with the Medtronic-Hall valve by one surgeon in one institution. The series is divided into two parts: (1) an in-hospital study, which details the preoperative information and operative result for all patients having insertion of a Medtronic-Hall valve, and (2) a long-term follow-up review for those patients having only an isolated aortic or mitral Medtronic-Hall valve for whom follow-up information was available for more than I year after hospitalization. Material and Methods Patients Beginning in October 1983, when the first Medtronic-Hall valve was implanted at the Massachusetts General Hospital, a registry of all patients having implantation of a Accepted for publication Oct 30, Address reprint requests to Dr Akins, Cardiac Surgical Unit, Massachusetts General Hospital, White 503, 32 Fruit St, Boston, MA Medtronic-Hall valve was begun. This prospective registry contains preoperative information on each patient, details of the operation, and a record of postoperative complications. All of the information about the patient's hospitalization for valve insertion was obtained by trained research personnel on a prospective basis. All patients who had a Medtronic-Hall valve implanted by one surgeon are the subject of this report. From October 1983 through December 1994, 460 Medtronic-Hall valvular prostheses were inserted during 391 operations, which constitute the in-hospital series. Valve implantation into only the aortic position (AVR) was performed in 210 operations, the mitral position (MVR) in 115 operations, and combined aortic and mitral positions (DVR) in 66 operations. In addition three valves were inserted into the tricuspid position during DVR. Demographic and clinical presentation characteristics of the patient population, segregated according to type of valve operation, are presented in Table 1. Aortic valve replacement was more commonly performed in men, and MVR and DVR in women. Most patients having MVR or DVR presented with congestive heart failure. Of the 391 total operations performed, 148 (37.9%) were valve reoperations. For the 210 patients having only an AVR, 51 (24.2%) were reoperations: first-time in 45 (21.4%), second-time in 5 (2.4%), and third-time in 1 (0.5%). For the 115 patients having only an MVR, 59 (51.3%) were reoperations: first-time in 42 (36.5%), second-time in 12 (10.4%), and third-time in 5 (4.3%). For the 66 patients having DVR, 38 (57.6%) were reoperations: first-time in 27 (40.9%), second-time in 9 (13.6%), and third-time in 2 (3.0%). Selected findings from cardiac catheterizations, ac by The Society of Thoracic Surgeons /96/$15.00 Published by Elsevier Science Inc SSDI (95)

2 Ann Thorac Surg AKINS ;61: MEDTRONIC-HALL VALVE Table 1. Demographic and Clinical Characteristics AVR MVR DVR Characteristic (210) (115) (66) Sex Male 160 (76.2%) 31 (27.0%) 22 (33.3%) Female 50 (23.8%) 84 (73.0%) 44 (66.7%) Age (mean, y) NYHA class (mean) Symptoms Congestive heart 110 (52.4%) 100 (86.9%) 58 (87.9%) failure Angina pectoris 85 (40.5%) 10 (8.7%) 13 (19.7%) Syncope 25 (11.9%) 2 (1.7%) 4 (6.1%) Endocarditis 23 (10.9%) 7 (6.1%) 5 (7.6%) Stroke 9 (4.3%) 25 (21.7%) 10 (15.1%) AVR - aortic valve replacement; MVR - mitral valve replacement; ation. DVR = double valve replacement; NYHA New York Heart Associ- cording to valve operation, are noted in Table 2. Coronary artery disease was present in 122 patients (31.2%). In one DVR reoperation an aortic bioprosthesis was removed only because it was 11 years old, and in another DVR reoperation a rnitral bioprosthesis was removed only because the patient had endocarditis on the aortic valve extending into the mitral annulus. Operative Techniques Operations were performed during standard cardiopulmonary bypass with moderate hypothermia (25 to 28 C). Venous cannulation was accomplished through the right atrium, or occasionally in addition via the femoral vein. Arterial cannulation was performed through the ascending aorta, although for some composite aortic valve and ascending aortic root replacements perfusion was performed through a femoral artery. Myocardial protection was achieved with either cold, oxygenated crystalloid cardioplegia or cold, oxygenated blood cardioplegia, instilled antegrade either into the aortic root or selectively into the coronary orifices. Valves were secured to the annulus with either figureof-8 sutures or pledgeted mattress sutures, if the annulus was friable. In the aortic position the greater orifice of the valve was aimed toward the greater curvature of the aorta, usually about the middle of the noncoronary sinus. In the mitral position the greater orifice of the valve was directed posteriorly, with the occluder of the prosthesis functioning essentially as an anterior mitral leaflet. In all cases complete freedom of motion of the occluder was obtained, even if it meant rotating the housing to a position somewhat different from that usually selected. The native mitral leaflets were not routinely preserved in this series for several reasons. In the first place 59 (51.3%) of the 115 isolated MVR and 38 (57.6) of the 66 DVR operations were reoperations. Second, virtually all native mitral valves replaced were rheumatically diseased or had active endocarditis and were completely excised to allow implantation of the largest possible prosthesis. (During these study years, I reconstructed 96% of mitral valves that presented with pure, nonrheumatic mitral regurgitation.) Anticoagulant Management Anticoagulant therapy with warfarin was begun as soon as the patient could receive oral medications, usually on the first postoperative day. The dosage of warfarin was adjusted to achieve target prothrombin times that differed by valve position and patient risk factors [1]. The target international normalized ratios sought were as follows: low-risk AVR patients, 2.0 to 2.5; high-risk AVR patients, 2.5 to 3.0; low-risk MVR patients, 2.5 to 3.0; and high-risk MVR patients, 3.0 to 3.5. If the prothrombin time was subtherapeutic on the fifth postoperative day, intravenous administration of low molecular weight dextran, or more recently heparin, was begun, and continued until the prothrombin time became therapeutic. Antiplatelet agents were not routinely administered to any patient. Follow-up During the 10 years of the study, complete follow-up was sought five times, on average every 2 years. Follow-up information about survival and valve-related events was obtained through direct communication with the patients by trained research personnel. If subsequent hospitalization, death, or valve-related events had occurred, the patient's physician or appropriate hospital record department was contacted to document the events and hospitalizations. All follow-up information was organized to conform with the published guidelines for reporting morbidity and mortality after cardiac valvular operations [2]. Specifically, operative mortality was defined as any death that occurred during the hospitalization in which valve implantation was performed, or death within 30 days of the operation if the patient was discharged before that time. Further, paravalvular leak was recorded not only for those patients who required reoperation because of Table 2. Catheterization Findings AVR MVR DVR Finding (210) (115) (66) Ejection fraction (mean) Valve lesion Aortic stenosis 108 (51.4%) (33.3%) Aortic regurgitation 74 (35.3%) (33.3%) Aortic stenosis and 28 (13.3%) (31.8%) regurgitation Mitral stenosis... 9 (7.8%) 17 (25.8%) Mitral regurgitation (52.2%) 31 (47.0%) Mitral stenosis and (40.0%) 17 (25.8%) regurgitation Coronary artery 82 (39.0%) 27 (23.5%) 13 (19.7%) disease AVR = aortic valve replacement; MVR - mitral valve replacement. DVR = double valve replacement;

3 808 AKINS Ann Thorac Surg MEDTRONIC-HALL VALVE 1996;61: the complication, but also for any patient who had a bland periprosthetic leak demonstrated by echocardiography, regardless of symptoms. All early and late valverelated events were counted. The most recent follow-up was performed between June 1993 and March 1994 and was recorded as of June 30, Follow-up was sought for those patients with only an isolated aortic or mitral Medtronic-Hall valve that had been in place for at least 1 year. Patients with multiple valve replacements or intracardiac valvular prostheses of another type were excluded from followup. Patients were included in follow-up if they had coronary artery bypass grafting (CABG), ascending aortic grafts, or suture repair of other intracardiac or aortic defects. Of the 177 AVR patients appropriate for longterm evaluation, only 1 patient was lost to follow-up, yielding complete follow-up in 99%. Average follow-up for AVR patients was 4.3 years, and cumulative follow-up was 765 patient-years. Of the 106 MVR patients appropriate for long-term study, only 2 patients were lost to follow-up, yielding complete follow-up in 98%. Average follow-up for the MVR patients was 4.6 years, and cumulative follow-up was 481 patient-years. Statistical Analysis All early and late episodes or events were included in the calculation of the linearized incidence of complications or events and were expressed as number of events per 100 patient-years of follow-up, segregated by valve position. To describe the long-term results in accordance with the guidelines and to compare those results between aortic and mitral valves, actuarial curves for mortality and late complications were obtained by the life-table method [3]. The significance of differences between the two groups was determined by means of the Mantel-Cox test in the BMDP program PIL [4]. To assess the impact of the valve position, age, and associated coronary artery disease on long-term survival, these factors were inserted into a multiple stepwise logistic regression algorithm, BMDP program PLR [4]. Results Operative Mortality Operative mortality for the total group was 4.6% (18/391). The operative mortality by valve position was 2.9% for AVR (0.9% for 110 isolated AVR), 4.3% for MVR (3.6% for 84 isolated MVR), and 10.6% for DVR (8.9% for 45 isolated DVR). Twelve of the 18 deaths occurred after the 148 reoperative valve replacements, yielding an operative mortality rate for reoperations of 8.1%, compared with 2.5% for first-time single or double valve replacements. Late Mortality Late deaths occurred in 40 (14.3%) of the 280 hospital survivors of AVR or MVR followed up long-term. Linearized mortality was 2.5% per patient-year for hospital survivors of AVR and 4.4% per patient-year for hospital survivors of MVR. The causes of late mortality are noted in Table 3. Table 3. Causes of Late Mortality Cause of Death AVR MVR Total Valve-related Thromboembolism Anticoagulant hemorrhage Prosthetic endocarditis Sudden, unexplained Other cardiac Heart failure Coronary artery disease Noncardiac AVR = aortic valve replacement; MVR = mitral valve replacement. Actuarial survival at 10 years, including operative mortality, was 72.4% % after AVR and 62.6% + 6.6% after MVR (p = not significant). Actuarial survival for AVR and MVR patients, separated according to the presence or absence of CABG, is depicted in Figure 1. At 10 years actuarial survival for the AVR patients was significantly better than for AVR + CABG patients: 79.3% % versus 58.1% ± 11.4%, respectively (p < 0.02). Actuarial survival at 10 years for MVR compared with MVR + CABG patients was 67.3% + 6.9% versus 41.5% % (p = 0.059). However, the mean ages of the patients in the AVR, AVR + CABG, MVR, and MVR + CABG subgroups were , 62 _~ 6, 62 _+ 9, and years, respectively. Therefore, to further delineate the true impact of CABG and age on actuarial survival for AVR and MVR patients, we employed a multiple stepwise logistic regression algorithm into which age, valve position, and CABG were inserted as variables. In univariate testing age was by far the strongest predictor of death (p < ), and CABG was a weaker predictor (p = 0.01). Valve position did not quite attain statistical significance as a predictor of death (p = 0.08). When interactions between effects of valve position and CABG on survival were sought, only in the case of MVR did adding CABG significantly decrease survival (p = 0.02). In the multivariate testing, when the patient population was corrected for age, valve position was not a significant predictor of death, and CABG just failed to attain statistical significance (p = 0.06). Valve-Related Complications Table 4 contains the incidence and linearized rates and Table 5 the 5-year, 8-year, and 10-year actuarial eventfree rates for valve-related complications and consequences for those patients followed up long-term. STRUCTURAL DETERIORATION. Structural deterioration did not occur in any patient in this study. NONSTRUCTURAL DYSFUNCTION. No patient in this study had clinically significant hemolysis that was not secondary to paravalvular leak. Nonstructural dysfunction occurred in only 1 AVR patient, who at 42 months postoperatively had removal of the valve at another hospital, where no abnormality of

4 Ann Thorac Surg AK1NS ;61: MEDTRONIC-HALL VALVE Fig 1. Actuarial survival for aortic (AVR) and mitral valve replacement (MVR) patients segregated according to the presence of coronary artery bypass grafting (CABG). 5o- = Avs ~ \1 4 $ -- Av~, r,u~ '/- 6.2 P<0.02 ~ ~ I~ l l I I I I I I I I l I $ 9 to YEAR the valve was reportedly identified except possibly for some pannus ingrowth. No AVR patient had a periprosthetic leak that was not due to endocarditis. The linearized rate for nonstructural dysfunction after AVR was 0.1% per patient-year, and the 10-year actuarial eventfree rate was 99.1% _+ 0.9%. Bland periprosthetic leak was documented in 10 patients after MVR, for a linearized rate of 2.1% per patientyear and a 10-year actuarial event-free rate of 83.0% + 5.5%. Of the 10 paravalvular leaks, eight occurred in patients after reoperative MVR (five first-time reoperations, three second-time reoperations) at a mean of 44 months postoperatively. Four asymptomatic patients had incidental leaks discovered by echocardiography and were followed up medically. Five patients required reoperation; all of these reoperations were successful. One patient was awaiting reoperation (which was performed Table 4. Incidence and Linearized Rates of Complications and Consequences AVR MVR Linearized Linearized Event Number Rate a Number Rate ~ Late death Nonstructural dysfunction Thromboembolism Thrombosis Anticoagulant bleeding Prosthetic endocarditis Reoperation Physical impairment Valve-related death All valve-related morbidity and mortality a Linearized rate expressed as percent per patient-year AVR = aortic valve replacement; MVR = mitral valve replacement. AVR AVR,CABG MVR MVR,CABG successfully after the closing date of the study). The linearized rate for nonstructural dysfunction requiring reoperation after MVR was 1.2% per patient-year. THROMBOEMBOLISM. Valvular thrombosis did not develop in any AVR patient in this study. Thromboembolism was documented in ten events in 10 patients after AVR: five after isolated AVR, four after AVR + CABG, and one after composite AVR + ascending aortic replacement. A history of atrial fibrillation could be documented in 6 of the patients. Only one event occurred during the valve replacement hospitalization at 5 days after AVR + CABG. The mean interval from operation to thromboembolism for the other 9 patients was 45 months. One late thromboembolic event was fatal. The linearized rate for thromboembolism after AVR was 1.3% per patient-year, and the 10-year actuarial eventfree rate was 87.3% ± 4.4% (Fig 2). Valvular thrombosis occurred in I MVR patient in this study, for a linearized rate of 0.2% per patient-year and a 10-year actuarial event-free rate of 99.0% ~+ 1.0%. The patient presented with gastrointestinal bleeding 6 months after MVR and was treated with fresh frozen plasma and vitamin K. He progressively lost crisp valve sounds and was then referred for reoperation, at which time his valve was successfully replaced with a bioprosthesis. Thromboembolism after MVR was reported on nine occasions in 8 patients, of whom 5 had atrial fibrillation. In all 5 of the patients for whom anticoagulation data were available, the prothrombin time was suboptimal. No event occurred during valve replacement hospitalization. The nine postoperative events were reported at a mean of 19 months postoperatively. One late thromboembolic event was fatal. The linearized rate for thromboembolism, including the valve thrombosis, after MVR was 2.1% per patient-year, and the 10-year actuarial event-free rate was 90.8% ± 3.2% (see Fig 2). ANTICOAGULANT-RELATED HEMORRHAGE. Anticoagulantrelated bleeding occurred in 13 patients after AVR. Gastrointestinal bleeding developed in 1 patient in the hospital 10 days after AVR + CABG. The remaining 12

5 810 AKINS Ann Yhorac Surg MEDTRONIC-HALL VALVE 1996;61: Table 5. Actuarial Event-Free Rates From Complications and Consequences AVR Event Five -Year Eight-Year Ten-Year Five -Year Eight-Year Ten-Year Death 86.1% _+ 3.4% 75.4% ± 5.1% 72.4% 5.7% Nonstructural dysfunction 99.1% +_ 0.9% 99.1% _+ 0.9% 99.1% +_ 0.9% Thromboembolism 95.4% +_ 1.9% 87.3% _+ 4.4% 87.3% +_ 4.4% Thrombosis 100% 100% 100% Anticoagulant bleeding 93.8% ± 2.8% 86.6% _+ 4.2% 80.0% % Prosthetic endocarditis 97.9% ± 1.2% 95.8% % 95.8% _+ 2.4% Reoperation 97.0% ± 1.5% 97.0% _+ 1.5% 97.0% _+ 1.5% Physical impairment 99.1% ± 0.9% 96.2% +_ 3.0% 96.2% % Valve-related death 99.2% _+ 0.8% 97.2% +_ 2.1% 97.2% _+ 2.1% All valve-related morbidity 87.2% +_ 3.0% 76.7% _+ 4.9% 70.8% % and mortality MVR 80.3% % 65.5% % 62.6% % 93.1% % 83.0% % 83.0% % 90.8% % 90.8% % 90.8% % 99.0% % 99.0% + 1.0% 99.0% ± 1.0% 91.2% % 85.6% % 85.6% % 95.2% ± 2.7% 88.2% ± 5.4% 88.2% % 93.1% + 2.8% 88.0% + 4.4% 88.0% % 96.8% % 96.8% + 1.8% 96.8% ± 1.8% 95.5% % 87.4% % 87.4% % 71.6% ± 5.1% 54.2% % 54.2% % AVR = aortic valve replacement; MVR = mitral valve replacement. events occurred at a mean of 45 months postoperatively. One patient died of intracranial hemorrhage secondary to trauma 25 months after AVR + CABG with composite ascending aorta and aortic arch replacement. The linearized rate for anticoagulant-related hemorrhage following AVR was 1.7% per patient-year, and the ten-year actuarial event-free rate was % (Figure 3). After MVR, 9 patients experienced anticoagulantrelated bleeding, including 2 patients who died of intracerebral hemorrhage at 20 and 66 months postoperatively. No event occurred during MVR hospitalization. The mean postoperative interval for the nine events was 32 months. The linearized rate for anticoagulant-related hemorrhage after MVR was 1.9% per patient-year, and the 10-year actuarial event-free rate was 85.6% ± 4.9% (Fig 3). PROSTHETIC ENDOCARDITIS. After AVR, endocarditis developed in 5 patients, early in none. The mean time to the complication was 46 months. All 5 patients required and survived reoperation, one of which was performed after the closing date for follow-up. The linearized rate for endocarditis after AVR was 0.6% per patient-year, and the 10-year actuarial event-free rate was 95.8% ± 2.4%. Prosthetic endocarditis occurred in 5 patients after MVR, early in none, at a mean postoperative interval of 59 months. Two patients survived reoperation, 2 died before operation could be undertaken, and I was treated successfully with antibiotics alone. The linearized rate for endocarditis after MVR was 1.0% per patient-year, and the 10-year actuarial event-free rate was 88.2% %. Valve-Related Consequences REOPERATION. Valve replacement after AVR was required in 5 patients: 4 for endocarditis and 1 for presumed pannus ingrowth. The mean interval to reoperation was 42 months. All patients survived reoperation. The linearized rate for reoperation after AVR was 0.6% per patientyear, and the 10-year actuarial event-free rate was 97.0% ± 1.5% (Fig 4). After MVR, 8 patients required reoperation at a mean postoperative interval of 29 months: 5 for periprosthetic leak 2 for endocarditis, and 1 for valve thrombosis. All patients survived reoperation. The linearized rate for reopera- Fig 2. Actuarial event-free rates for thromboembolism for aortic (AVR) and mitral valve replacement (MVR) patients. (NS = not significant.) 100 ~..~ - -,.,.., % [ PERCENT FREE 10 V~OtS -~ AVR /- 4.4% p:ns "--O--- MVR /- 3.2% 10 AVR 158 IM'W 86 o/ o l l I I I I I l YEAR

6 Ann Thorac Surg AKINS ;61: MEDTRONIC-HALL VALVE,oo % % Fig 3. Actuarial event-free rates for anticoagulantrelated bleeding for aortic (AVR) and mitral valve replacement (MVR) patients. (NS = not significant.) PERCENT FREE ~. AVR /- 7.5% p=ns ---'O'--- MVR /- 4.9% 20-10" ~VR 158 MVR89 0 I I I I I I I I I I l0 YEAR tion after MVR was 1.7% per patient-year, and the 10-year actuarial event-free rate was 88.0% + 4.4% (see Fig 4). PERMANENT PHYSICAL IMPAIRMENT. Permanent physical impairment after AVR occurred in 2 patients, both secondary to thromboembolism. The linearized rate for permanent physical impairment after AVR was 0.3% per patient-year, and the 10-year actuarial event-free rate was 96.2% + 3.0%. After MVR, permanent physical impairment developed in 3 patients, secondary to thromboembolism in all 3. The linearized rate for permanent physical impairment after MVR was 0.6% per patient-year, and the 10-year actuarial event-flee rate was 96.8% + 1.8%. VALVE-RELATED DEATH. After AVR, valve-related death occurred in 2 patients (see Table 3). The linearized rate for valve-related death after AVR was 0.3% per patientyear, and the 10-year actuarial event-free rate was 97.3% + 2.1%. Valve-related death occurred in 6 patients after MVR (see Table 3). The linearized rate for valve-related death after MVR was 1.2% per patient-year, and the 10-year actuarial event-free rate was 87.4% + 5.1%. ALL VALVE-RELATED MORBIDITY AND MORTALITY. The linearized rate for all mortality and valve-related morbidity, including hospital death, after AVR was 4.6% per patientyear, and the 10-year actuarial event-free rate was 70.8% + 7.3% (Fig 5). The linearized rate for all mortality and valve-related morbidity, including hospital death, after MVR was 8.1% per patient-year, and the 10-year actuarial event-free rate was 54.2% _+ 7.0% (see Fig 5). Comment Although more than 170,000 Medtronic-Hall valves have been inserted worldwide, follow-up data are available on only a small percent of valves implanted [5]. This report documents the clinical experience of one surgeon using this valve exclusively as a mechanical replacement for more than 10 years. The functional performance of the Medtronic-Hall % Fig 4. Actuarial event-free rates for reoperation for aortic (AVR) and mitral valve replacement (MVR) patients. b, O l0- AVR MVR I I PERCENT FREE 10 YEARS AVR /- 1.5% p = 0.06 MVR /- 4.4% I I I I I! I I YEAR

7 812 AKINS Ann Thorac Surg MEDTRONIC -HALL VALVE 1996;61: Fig 5. Actuarial event-free rates for all mortality and valve-related morbidity for aortic (AVR) and mitral valve replacement (MVR) patients. 1oo 9o 70.89t A w A v 10- AVR MVR i i PERCENT FREE lo YV.AltS AVR /- 7.3 p = MVR / I I I I I I I I % valve is notable for its low profile, rotatability, excellent gradient relief even in small sizes [6, 7], relatively low regurgitant fraction [8], and low incidence of hemolysis [9]. Its excellent durability, due in large part to the fact that the housing and strut mechanism are completely machined from one solid piece of titanium, led to its choice as the prosthesis for the Jarvik total artificial heart [10]. There has never been a report of the clinical loss of structural integrity of a standard Medtronic-Hall valve, the only model available in the United States. In prospective, randomized comparisons the Medtronic-Hall valve has been found to be at least comparable with the St. Jude Medical valve in terms of hemodynarnic performance and incidence of late valve-related complications in the rnitral position in one study [6] and in both aortic and mitral positions in another study [11]. In a prospective, randomized comparison with the Monostrut prosthesis the Medtronic-Hall valve was found to be somewhat better in terms of thrombogenicity and at least comparable in terms of other late valverelated complications for AVR, MVIL and combined valve replacements [12]. In a recent retrospective review of late results with Starr-Edwards models 1260 and 6120, St. Jude Medical, Omniscience, CarboMedics, and Medtronic-Hall mechanical valves, the Medtronic-Hall valve had the best freedom from combined thromboembolic and anticoagulant-related bleeding complications [13]. As noted in that review, the principal disadvantage of the Medtronic- Hall valve is the careful attention required of the implanting surgeon to ensure that the motion of the occluder is not impinged. Increasing experience with this prosthesis, however, has shown a dramatic decrease in the reported occurrence of that complication [5]. Although it is tempting to impugn the design features of a prosthetic valve when implantation complications occur, in most cases the problem is not related to the prosthesis but to the insertion technique. As with any prosthetic valve, the surgeon must be certain that the device is implanted properly, which means cutting the tails of sutures appropriately short and debriding any native valve remnants that might interfere with occluder func- tion. Rotatability of the housing within the sewing ring is a great advantage in helping to avoid intracardiac structures that might hinder normal disc motion. The orientation of the Medtronic-Hall valve that I prefer in the aortic position is to have the greater orifice of the prosthesis directed toward the greater curve of the ascending aorta, which usually means about the middle of the noncoronary sinus. In the rnitral position the valve should be oriented so that the occluder behaves like an anterior rnitral leaflet, that is, with the greater orifice directed posteriorly. This yields the normal flow of blood: first down the posterolateral wall of the left ventricle to the apex and then up the septum to the left ventricular outflow tract, as we have confirmed with intraoperative transesophageal echocardiography. Bioprostheses cannot mimic this flow [14], nor do bileaflet mechanical valves in our experience. The actuarial event-free rates in the current series demonstrate improved survival and significantly better event-free survival for AVR patients than for MVR patients (see Table 5). Of interest is that the actuarial event-free rates for thromboembolism and anticoagulant-related bleeding at 10 years, although not significantly different, favor the mitral prostheses over aortic prostheses, whereas the linearized rates are lower for aortic valve patients for both complications (see Table 4). Part of the reason for this apparent contradiction may lie with the fact that the majority of events in the mitral patients occurred in the earliest years after operation, whereas events in the aortic patients were spread more broadly through the follow-up period. Linearized calculations assume that the hazard function for any complication is a constant throughout the follow-up period, while actuarial determinations assess the risk over time. Furthermore, the two thromboembolic events that occurred in 1 MVR patient would be counted twice for the linearized rate but only once for the actuarial rate. Patients having MVR do have higher linearized rates for and poorer long-term freedom from nonstructural dysfunction, prosthetic endocarditis, reoperation, and valve-related death than do AVR patients (see Table 4). Of these complications, nonstructural dysfunction re-

8 Ann Thorac Surg AKINS ;61: MEDTRONIC-HALL VALVE quires some additional discussion. The linearized rate for nonstructural dysfunction for mitral valves of 2.1% per patient-year is higher than that reported in most other studies [5]. There are several possible reasons for this. In the first place all paravalvular leaks were counted in this study, not just those that required reoperation or led to death. Four of the ten leaks reported were minor asymptomatic leaks detected at late echocardiography. Counting only the six other leaks, the linearized rate for significant nonstructural dysfunction would be 1.2% per patient-year, a rate comparable with those reported in other published series. Also, of the ten leaks, eight occurred at a mean of 44 months postoperatively in patients whose MVR was a reoperation (five first-time and three second-time reoperations), despite the frequent use of pledgeted sutures. Poor tissue quality may have contributed to the late appearance of these complications. Fortunately all 6 patients who came to reoperation survived without complications. One other feature of this study that is worthy of comment is that complete follow-up was sought five times during the course of the study, or on average every 2 years, not just once at the end of the study interval. We know that the more often patients are interviewed for results, the more complications they will remember, and thus the greater will be the reported rates of complications. The impact of this message is well illustrated by the report of Horstkotte and associates [15] on the St. Jude Medical valve. Patients in their study, with its average follow-up of 114 months, were reexamined at a median interval of 8 months. This intense follow-up protocol yielded linearized thromboembolic rates of 2.7% and 4.4% per patient-year for aortic and mitral valves, respectively, and those rates do not include events that occurred within the first 3 months after valve implantation or more than the first event for patients who suffered multiple events. Similarly the linearized anticoagulantrelated bleeding rates for aortic and mitral valves in that study were 4.1% and 6.4% per patient-year, respectively. Thus, much of the importance of complication rates reported in any series is a function of the intensity with which reports of those complications are sought. The lowest complication rates would be measured when follow-up is sought only once after a long time interval. The impact of concomitant CABG on mortality is obvious, particularly in patients requiring MVR. As many late deaths were due to coronary disease as to valverelated complications (see Table 3). Even after patient subgroups were corrected for age, CABG just failed to be a significant predictor of death (p = 0.06). With a larger patient population the age-corrected impact of coronary disease would probably be significant, as would the differences between AVR and MVR patients. This deleterious impact of coronary disease on the long-term survival of valve replacement patients has been previously examined by Jones and associates [16]. The results in this study corroborate their findings and support the contention that associated coronary artery disease should be strongly considered when choosing a mechanical valve or bioprosthesis, particularly when the patient is more than 60 years of age and requires an MVR. As with Jones and associates' study, the current study found less impact of coronary disease in AVR patients. In summary, the long-term follow-up of patients who received the Medtronic-Hall prosthesis in this study revealed that the valve has superb durability and the incidence of valve-related complications was low and certainly comparable with those reported for other prostheses. These results support the continued use of the Medtronic-Hall valve as my prosthesis of choice when replacement of the aortic or mitral valve with a mechanical prosthesis is indicated. I thank Barbara Akins, BSN, and Annetta Boisselle, BSN, for help in data acquisition and John Newell, Director of the Cardiac Computer Center, Massachusetts General Hospital, for assistance with statistical evaluation. References 1. Butchart EG, Lewis PA, Bethel JA, Brechenridge IM. Adjusting anticoagulation to prosthesis thrombogenicity and patient risk factors. Circulation 1991;84(Suppl 3): Edmunds LH Jr, Clark RE, Cohn LH, Miller DC, Weisel RD. Guidelines for reporting morbidity and mortality after cardiac valvular operations. 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Am J Cardiol 1993;71: DeVries WC, Anderson JL, Joyce LD, et al. Clinical use of the total artificial heart. N Engl J Med 1984;310: Antunes MJ. Clinical performance of St. Jude and Medtronic-Hall prostheses: a randomized comparative study. Ann Thorac Surg 1990;50: Kim YI, Lesaffre E, Scheys 1, Stalpaert G, Flameng WJ, Daenen WJ. The Monostrut versus Medtronic-Hall prosthesis: a prospective randomized study. J Heart Valve Dis 1994;3: Akins CW. Results with mechanical cardiac valvular prostheses. Ann Thorac Surg 1995;60: McKenney PA, Davidoff R, Faxon DP, Shemin RJ. Reversal of left ventricular flow pattern following bioprosthetic mitral valve replacement [Abstract]. Circulation 1991;84(Suppl 2): Horstkotte D, Schulte HG, Bircks W, Strauer BE. Lower intensity anticoagulation therapy results in lower complication rates with the St. Jude Medical prosthesis. J Thorac and Cardiovasc Surg 1994;107: Jones EL, Weintraub WS, Craver JM, Guyton RA, Shen Y. 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