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J Thorac Cardiovasc Surg 1995;110:663-0671
© 1995 Mosby, Inc.

SURGERY FOR ACQUIRED HEART DISEASE

Comparative results with the St. Jude Medical and Medtronic Hall mechanical valves

Ottawa, Ontario, Canada

From the Departments of Surgery, Pathology, and Laboratory Medicine, University of Ottawa Heart Institute, Ottawa Civic Hospital, Ottawa, Ontario, Canada.

Received for publication July 25, 1994. Accepted for publication Dec. 22, 1994. Address for reprints: Roy G. Masters, MD, University of Ottawa Heart Institute, Ottawa Civic Hospital, 1053 Carling Ave., Ottawa, Ontario, Canada K1Y-4E9.

Abstract

This study compared the clinical performance of the St. Jude Medical and Medtronic Hall mechanical valves in isolated aortic or mitral valve replacement. From 1984 to 1993, 349 St. Jude Medical valves (aortic 237, mitral 112) and 465 Medtronic Hall valves (aortic 272, mitral 193) were implanted in 814 patients at the University of Ottawa Heart Institute. The patients had similar preoperative characteristics. The hospital mortality rate for aortic valve replacement was 3.4% with the St. Jude Medical valve and 5.8% with the Medtronic Hall valve (p = 0.26) and the rate for mitral valve replacement was 8.9% with the St. Jude Medical valve and 11.9% with the Medtronic Hall valve (p = 0.54). Actuarial estimates of survival and freedom from complications were calculated. At 5 years the actuarial probability of survival (including hospital deaths) for aortic valve replacement was 86% ±3% with the St. Jude Medical valve and 68%±4% with the Medtronic Hall valve (p = 0.0001) and for mitral valve replacement was 75%±7% with the St. Jude Medical valve and 70%±4% with the Medtronic Hall valve (p = 0.54). The most common cause of late death was cardiac failure and no deaths were caused by structural failure. The 5-year probability of freedom from bleeding after aortic valve replacement was 99%±1% with the St. Jude Medical valve and 95%±2% with the Medtronic Hall valve (p = 0.06) and after mitral valve replacement 99%±1% with the St. Jude Medical valve and 97%±2% with the Medtronic Hall valve (p = 0.37). The 5-year probability of freedom from thromboembolism after aortic valve replacement was 88%±4% with the St. Jude Medical valve and 81%±3% with the Medtronic Hall valve (p = 0.08) and after mitral valve replacement was 85%±7% with the St. Jude Medical valve and 77%±5% with the Medtronic Hall valve (p = 0.17). Reoperation was uncommon and there were no cases of structural valve failure. The 5-year actuarial estimate of freedom from reoperation therefore for aortic valve replacement was 99%±1% with the St. Jude Medical valve and 96%±2% with the Medtronic Hall valve (p = 0.09) and for mitral valve replacement was 98%±2% with the St. Jude Medical valve and 95%±3% with the Medtronic Hall valve (p = 0.40). We concluded that the St. Jude Medical and Medtronic Hall mechanical valves offered similar clinical performance in isolated aortic or mitral valve replacement. J THORACCARDIOVASCSURG1995;110:663-71)

The St. Jude Medical and Medtronic Hall mechanical heart valves (St. Jude Medical, Inc., St. Paul, Minn.; Medtronic, Inc., Minneapolis, Minn.) were introduced for clinical use in 1977 and 1978, respectively. The bileaflet construction of the former and the tilting-disc assembly of the latter purportedly offer specific hemodynamic advantages. Although controversy exists as to the relative merits of each clinically, there are few studies from a single center that compare these two prostheses. We report a study of the relative clinical performances of these two mechanical valves in the setting of isolated aortic valve replacement (AVR) or mitral valve replacement (MVR).

PATIENTS AND METHODS

From May 1984 to December 1993, 349 St. Jude Medical and 465 Medtronic Hall mechanical valves were implanted in 814 patients at the University of Ottawa Heart Institute. There were 509 single valve replacements in the aortic position of which 237 were done with the St. Jude Medical valve and 272 were done with the Medtronic Hall valve. There were 305 single valve replacements in the mitral position of which 112 were done with the St. Jude Medical valve and 193 were done with the Medtronic Hall valve.

The choice of valve was made at the surgeon's discretion and the surgical technique and follow-up were similar for all patients. In general each surgeon used one brand throughout the study period. Operative technique included cardiopulmonary bypass with moderate hypothermia, topical cooling with saline solution, and cold crystalloid cardioplegic solution administered in the antegrade fashion. The implantation technique consisted of the use of interrupted horizontal mattress sutures reinforced with Teflon pledgets. Warfarin sodium administration was started within 72 hours after operation. During the initial years of the study the target prothrombin time ratio was 1.5 to 2.0 and most recently the target International Normalized Ratio (INR) was set at 2.5 to 3.5. Regulation of anticoagulation therapy after discharge from the hospital was by the patient's family physician or cardiologist after initial stabilization of the therapeutic results by the surgeon.

Follow-up
All patients who underwent valve replacement were registered with the Valve Clinic of the Ottawa Heart Institute. Survivors were evaluated annually and the closure date for this study was March 1, 1994. Of the 814 patients, 12% were considered lost to follow-up. There were 1172 patient-years of follow-up for the AVR group and 599 patient-years of follow-up for the MVR group.

Statistical analysis
Data are presented in strict accordance with the Guidelines for Reporting Morbidity and Mortality After Cardiac Valvular Operations. ¹ In addition we further defined major bleeding according to these Guidelines (as bleeding that caused death, stroke, operation, or hospitalization or that necessitated transfusion) and all other bleeding as minor.

Comparisons between the preoperative characteristics of the patient groups were made by the ² test or Fisher's exact test where appropriate for discrete variables and Student's t test for continuous variables. Late survival (freedom from death) and event-free probabilities were calculated by means of the life-table technique with SPSS statistical data analysis software (SPSS Inc., Chicago, Ill.) and are reported with 95% confidence limits. Comparisons between groups were made with the formula

which is defined in Colton. ² Results were considered statistically significantly at the p < 0.05 level.

RESULTS

Clinical characteristics
In both the AVR and MVR groups the average age of the patients at the time of implantation was similar: in the AVR group it was 58.5 ± 0.9 years in patients with the St. Jude Medical valve and 57.8 ± 0.8 years in patients with the Medtronic Hall valve (p = 0.31) and in the MVR group it was 58.2 ± 1.2 years in patients with the St. Jude Medical valve and 57.9 ± 0.9 years in patients with for the Medtronic Hall valve (p = 0.49). In the AVR group the proportion of male patients was 70% for the St. Jude Medical valve and 68% for the Medtronic Hall valve (p = 0.70), whereas in the MVR group there was a greater proportion of female patients in the Medtronic Hall valve group (67%) than in the St. Jude Medical valve group (56%) (p = 0.04). In the AVR group previous valve operations had been done in 23% of patients who received the St. Jude Medical valve and 34% of the patients who received the Medtronic Hall valve (p = 0.005), whereas in the MVR group previous operations had been done in 30% of the St. Jude Medical valve group and 32% of the Medtronic Hall valve group (p = 0.80).

Concomitant operations were done in 22% of patients: in the AVR group in 27% of patients receiving the St. Jude Medical valve and 21% receiving the Medtronic Hall valve (p = 0.19) and in the MVR group in 22% of patients receiving the St. Jude Medical valve and 16% receiving the Medtronic Hall valve (p = 0.22). Coronary artery bypass was the most common associated procedure, being and it was done in 93% of patients with a similar distribution among all four groups.

Before operation most patients were in New York Heart Association functional class III or IV. For AVR this included 60% and 66% (p = 0.17) and for MVR 68% and 68% (p = 0.99) of patients with the St. Jude Medical valve and Medtronic Hall valve, respectively. After operation, however, few were in class III or IV. For AVR this included 7% and 8% (p = 0.81) and for MVR 9% and 9% (p = 0.84) of patients with the St. Jude Medical valve and Medtronic Hall valve, respectively (Table I).

Late survival
There were a total of 51 late deaths recorded after AVR: 12 in patients receiving the St. Jude Medical valve and 39 in patients receiving the Medtronic Hall valve. Cardiac failure, not related to prosthetic valve dysfunction, was the most common cause of these late deaths, accounting for 33% and 41%, respectively, of these late deaths. Valve-related deaths accounted for three late deaths in the group having AVR with the St. Jude Medical valve and six late deaths in the group having AVR with the Medtronic Hall valve. These included death from thromboembolism, endocarditis, or hemorrhage. The actuarial probability of survival to 5 years after AVR with the St. Jude Medical valve was 86% ± 3% and 68% ± 4% after AVR with the Medtronic Hall valve (p = 0.0001) (Fig. 1).

View larger version (14K): [in this window] [in a new window]   Fig. 1. Actuarial survival (freedom from death): AVR. SJM-AVR, AVR with the St. Jude Medical valve; MH-AVR, AVR with the Medtronic Hall valve.

View larger version (14K): [in this window] [in a new window]   Fig. 2. Actuarial survival (freedom from death): MVR. SJM-MVR, MVR with the St. Jude Medical valve; MH-MVR, MVR with the Medtronic Hall valve.

View larger version (15K): [in this window] [in a new window]   Fig. 3. Actuarial freedom from thromboembolism: AVR. SJM-AVR, AVR with the St. Jude Medical valve; MH-AVR, AVR with the Medtronic Hall valve.

View larger version (13K): [in this window] [in a new window]   Fig. 4. Actuarial freedom from thromboembolism: MVR. SJM-MVR, MVR with the St. Jude Medical valve; MH-MVR, MVR with the Medtronic Hall valve.

Reoperation after discharge was uncommon with either valve in either position. There were no cases of structural dysfunction in this study. Reoperation was required for two patients having AVR with the St. Jude Medical valve and seven patients having AVR with the Medtronic Hall valve. Both patients in the former group required reoperation because of prosthetic valve endocarditis and there was one resultant death. In the latter group reoperation was required because of endocarditis in three patients, nonstructural failure (paravalvular leaks) in two, and iatrogenic ventricular septal defect in one case and in one patient where there was thought to be a high transvalvular gradient. There was only one death among these patients, and it occurred in the patient with a ventricular septal defect in whom multiorgan failure developed after-operation. The 5-year actuarial freedom from reoperation in patients having AVR was 99% ± 1% with the St. Jude Medical valve and 96% ± 2% with the Medtronic Hall valve (p = 0.09) (Fig. 5).

View larger version (14K): [in this window] [in a new window]   Fig. 5. Actuarial freedom from reoperation: AVR. SJM-AVR, AVR with the St. Jude Medical valve; MH-AVR, AVR with the Medtronic Hall valve.

View larger version (14K): [in this window] [in a new window]   Fig. 6. Actuarial freedom from reoperation: MVR. SJM-MVR, MVR with the St. Jude Medical valve; MH-MVR, MVR with the Medtronic Hall valve.

The St. Jude Medical and the Medtronic Hall prosthetic valves remain the most widely used mechanical valves in North America. Although a number of authors have reported their experience with one of these valves, there are few studies from a single center that compare the relative efficacy of both. This may be important because referral patterns may vary from one institution to another, as may operative techniques and postoperative management, which often makes comparisons difficult.

Though the hospital mortality reported here was lower for AVR with the St. Jude Medical valve this difference did not reach statistical significance. Before operation both groups of patients having AVR were similar though there was a greater proportion of reoperations in the group having AVR with the Medtronic Hall valve. In this study previous operation was not a risk factor for hospital mortality after AVR. Factors that have previously been noted as independent determinants of survival for AVR have included the urgency of operation, the presence of endocarditis, previous valve operation, concurrent coronary artery disease, and patient age. ^3,4 Previously reported hospital mortality rates for AVR with the St. Jude Medical valve have been 2.4%, ⁴ 3.2%, ⁵ 3.6%, ⁶ 5.2%, ⁷ 5.8%, ⁸ and 7%. ⁹ For AVR with the Medtronic Hall valve early mortality rates of 1.7%, ¹⁰ 3.8%, ¹¹ 4.2%, ¹² and 9.3% ¹³ have been reported. The hospital mortality rate reported here was lower for MVR with the St. Jude Medical valve but again this did not reach statistical significance. In this study there was a greater proportion of female patients in the group having MVR with the Medtronic Hall valve; however, this was not a risk factor for early death. Independent determinants of survival for MVR from previous studies haved include urgency, endocarditis, coronary disease, age, and ventricular function. ^3,4 Gender, however, was also not a risk factor in these studies. Operative mortality rates of 4.3%, ³ 4.7%, ⁶ 7.4%, ⁸ 8%, ⁹ 9.9%, ⁵ and 11.9% ⁷ have been reported for MVR with the St. Jude Medical valve and 7.5%, ¹¹ 7.8%, ¹³ 8.4%, ¹⁰ and 13.1% ¹² for MVR with the Medtronic Hall valve.

Anthunes, ¹⁴ in 1990, reported the results of a prospective randomized comparison of the St. Jude Medical and Medtronic Hall valves. This study of isolated MVR and AVR did not include patients who had previous valvular operations and it grouped the aortic and mitral valve results together. The hospital mortality rate in that study was 3.2% (3 patients) for the 89 patients receiving the St. Jude Medical valve and 5.7% (5 patients) for the 80 patients receiving the Medtronic Hall valve. Similarly a 1992 prospective randomized study by Fiore and associates ¹⁵ compared the results of MVR with the St. Jude Medical and Medtronic Hall valves. The hospital mortality rate in that study, however, was higher for the 55 patients receiving a St. Jude Medical valve than for the 47 patients receiving a Medtronic Hall valve at 14.5% (8 patients) and 10.6% (5 patients), respectively. The early survival differences noted in both of these studies, however, did not reach statistical significance at the 0.05 level possibly because of the study sizes.

We have detected a late survival advantage with the St. Jude Medical valve for isolated AVR or MVR at 5 years; this difference only reaches statistical significance with the former. Beyond 5 years the number of patients at risk in this study is small, which makes comparisons inappropriate. Actuarial 5-year estimates of survival of 71% ± 3%, ⁷ 78%, ⁴ 78% ± 4%, ⁵ and 96% ¹⁶ for AVR with the St. Jude Medical valve and 70% ± 6%, ¹² 72% ± 5%, ¹³ 82%, ¹¹ and 89% ¹⁰ for AVR with the Medtronic Hall valve have previously been reported. Survival estimates of 59% ± 4%, ⁷ 64% ± 9%, ⁵ 78%, ⁴ and 88% ¹⁶ for MVR with the St. Jude Medical valve and 67% ± 6%, ¹² 72% ± 5%, ¹³ 74%, ¹¹ and 79% ¹⁰ for MVR with the Medtronic Hall valve have also been reported. In the study by Fiore and associates ¹⁵ the 3-year survival was lower for MVR withthe St. Jude Medical valve (79% ± 5%) than for MVR with the Medtronic Hall valve (87% ± 5%). Anthunes ¹⁴ also founda lower 5-year survival with St. Jude Medical valves (74% ± 6%) than Medtronic Hall valves (88% ± 5%) despite the higher hospital mortality rate with the latter. Late survival is dependent on many factors related to the individual patients' disease and to the complications of the prostheses. Most deaths in our study were a result of cardiac failure and were not related to prosthetic valve dysfunction or failure or its attendant complications.

At 5 years we could not detect large differences between these two valves in freedom from complications. In all cases, however, the actuarial estimate was higher with the St. Jude Medical valve for either AVR or MVR, though the differences were not significant statistically. The actuarial freedom from thromboembolism was higher for the St. Jude Medical valve in both the aortic and mitral positions in this study. The 5-year freedom from thromboembolism after AVR with the St. Jude Medical valve has previously been reported at 88% ± 3%, ⁷ 92%, ⁴ 92% ± 4%, ⁵ and 97% ± 6% ⁸ and after AVR with theMedtronic Hall valve at 82% ± 4%, ¹³ 92% ± 3%, ¹² and 95%. ¹⁰ After MVR with the St. Jude Medical valve 5-year actuarial estimates have been reported at 85%, ⁴ 89% ± 5%, ⁵ 92% ± 2%, ⁷ and 99% ± 1% ⁸ and after MVR with theMedtronic Hall valve at 85% ± 8%, ¹² 89% ± 3%, ¹³ and 94%. ¹⁰ Clearly the occurrence of thromboemboli and bleeding after heart valve replacement is related to the level of anticoagulation, which varies among studies. In our study the target levels of anticoagulation were the same for both the St. Jude Medical and Medtronic Hall valves. However, beyond the initial few weeks required for stabilization, control of anticoagulation was not centralized. Further, we do not have complete records of the actual level of prothrombin time or INR at the time of thromboembolism. Current recommendations are for a target INR of 2.5 to 3.5 for all mechanical valves. ¹⁷ The comparative study byAnthunes ¹⁴ did not detect a statistically significant difference in freedom from thromboembolism at 5 years between the St. Jude Medical valve (92% ± 4%) and the Medtronic Hall valve (89% ± 4%) with a prothrombin index of 35% to 45%. Similarly although there was an apparent advantage with the St. Jude Medical valve in the rate of thromboembolism at 3 years in the study of Fiore and associates ¹⁵ (98% ± 2% versus 88% ± 6%) in which a prothrombin ratio of 1.5 was used this did not reach statistical significance.

Serious bleeding was uncommon in our study with less bleeding noted with St. Jude Medical valves in both aortic and mitral positions. Previous studies have reported the freedom from hemorrhage after AVR with the St. Jude Medical valve to be 89% ± 2%, ⁷94%, ⁴ and 98% ± 2% ⁵ and that after AVRwith the Medtronic Hall valve to be 100%. ¹² After MVR with the St. Jude Medical valve freedom from hemorrhage has been reported as 87%, ⁴ 97% ± 3%, ⁵ and 92% ± 2% ⁷ and after MVR with the Medtronic Hall valve 100%. ¹² One study grouped AVR and MVR with the MedtronicHall valve and reported a combined 5-year estimate of 98% ± 1%. ¹³ Anthunes ¹⁴ did not find any cases of serious bleeding with either valve in either position, whereas Fiore and associates ¹⁵ did not detect any large differences in bleeding between MVR with the St. Jude Medical valve and the Medtronic Hall valve (91% ± 5% versus 94% ± 4%) with a target prothrombin ratio of 1.5.

As in most previous reports we noted a low rate of endocarditis with little difference between the two valves. Arom and colleagues ⁵ reported a 6-year actuarial freedom fromendocarditis of 99% ± 2% for AVR with the St. Jude Medical valve and 99% ± 1% for MVR with the Medtronic Hall valve. Similarly Keenan and associates ¹² reported 5-year estimates of 96% ± 2% for AVR with the Medtronic Hall valve and 99% ± 2% for MVR with the Medtronic Hall valve. Reoperation in our short-term follow-up study was also uncommon, which attests to the similar durability of these valves. Of note, there were no cases of structural failure in our series.

In summary, the results obtained from this study indicate that the St. Jude Medical and the Medtronic Hall prostheses offer similar excellent clinical performance for both AVR and MVR. Although our results suggest an advantage in favor of the St. Jude Medical valve both in terms of survival and complications these differences await further clarification with more patients followed up for a longer period of time.

Acknowledgments

We wish to acknowledge the capable assistance of Ms. Mary Thompson, Ms. Sharon Finlay, Mr. Daniel Duguay, Mr. Bill Stinson, and Research Systems Associates, Ottawa.

References

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