Asian Cardiovasc Thorac Ann 2001;9:182-186
© 2001 Asia Publishing EXchange Pte Ltd
Fifteen-Year Experience With Shanghai Disc Valve Prosthesis
Zhu Ping, MD,
Feng Shu Sheng, MB
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Department of Cardiothoracic Surgery Zhujiang Hospital, First Military Medical University Guangzhou, Guangdong People's Republic of China
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For reprint information contact: Zhu Ping, MD Tel: 86 20 8514 3591 Fax: 86 20 8431 8440 email: Zhuyiwen{at}public.guangzhou.gd.cn Department of Cardiothoracic Surgery, Zhujiang Hospital, Zhuangtou, Haizhu District, Guangzhou, Guangdong 510282, People's Republic of China.
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Abstract
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Between 1983 and 1998, 168 Shanghai prosthetic heart valves were implanted in 122 patients (57 males, 65 females) aged 14 to 57 years (mean, 34 years). There were 69 mitral, 7 aortic, and 46 double valve replacements. Early mortality in each group was 8.7%, 14.3%, and 6.5%, respectively. Mean follow-up was 7.9 years (87.5% complete). There were 7 late deaths (5.7%); 2 in the mitral group, 5 in the double valve group. Five late deaths were considered valve-related. The 5-year actuarial survival rates were 96.8% for mitral, 100% for aortic, and 88% for double valve replacement. Preoperatively, 77.9% of patients were in New York Heart Association functional class III or IV, whereas postoperatively, 90.2% were in class I or II. No structural failure was observed. There were 3 cases of systemic and cerebral embolism, and 2 cases of valve thrombosis in patients who had ceased taking anticoagulants. Hemorrhage was the most frequent complication; 1 of 6 events was fatal. The very affordable Shanghai valve provided good hemodynamic performance with low thrombogenicity in patients receiving anticoagulants.
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Introduction
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The quality of life and long-term survival of patients with heart valve lesions are significantly improved after heart valve replacement. Mechanical valve prostheses have demonstrated superior durability compared to bioprostheses.1 All available mechanical valves carry a significant risk of complications such as thrombo-embolism and anticoagulant-induced hemorrhage.2 Thus, research efforts are now focused mainly on improving biological valve durability and reducing mechanical valve thrombogenicity.
In 1983, the Shanghai disc valve (Shanghai Medical Equipment Research Institute, Shanghai, China) was introduced into clinical practice at our institution (Figure 1
). The main goals were to offer improved hemodynamic properties, reduced thrombogenicity, and improved longevity. Thus, the valve housing was processed from one solid piece of chromium and nickel, without thrombogenic welds or bends, to ensure against mechanical breakdown. The disc allows a maximal opening angle of 60 to 70 degrees, as well as more central positioning of the orifice to provide unimpeded trans-valvular flow on both sides of the open disc. It was also hoped that this hemodynamic pattern along with further nonthrombogenic construction principles, in-cluding a Pyrolyte carbon-covered disc, would reduce valve thrombogenicity.3,4
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Patients and Methods
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From December 1983 to December 1998, 168 Shanghai prosthetic heart valves were implanted in 122 patients; 69 underwent mitral valve replacement, 7 underwent aortic valve replacement, and 46 underwent double (mitral and aortic) valve replacement. The study comprised 57 males and 65 females, with ages ranging from 14 to 57 years (mean, 33.9 ± 3.4 years). Most patients were in New York Heart Association functional class III or IV, and 14 (11.5%) had undergone previous open cardiac operations.
A Swan-Ganz catheter was placed into the pulmonary artery in 87 patients (of whom 47 had mitral, 4 had aortic, and 36 had double valve replacement). Pulmonary arterial, left atrial, and left ventricular end-diastolic pressures were measured continuously. Cardiac output and cardiac index were estimated by the Fick technique in the preoperative and postoperative periods.5 The distribution of valve sizes implanted in the aortic and mitral positions is shown in Figure 2. Ten patients had concomitant procedures: De Vega tricuspid annuloplasty in 10 cases, and atrial septal defect closure in 1 case. Clinical details are shown in Table 1. The standard technique of cardiopulmonary bypass with moderate systemic hypothermia (25°C to 26°C) was used. Cold potassium cardioplegia (St. Thomas' Hospital solution) or cold blood cardioplegia combined with topical hypothermia (iced saline) were used routinely for myocardial protection. The procedures were performed by the same group of surgeons using the same technique. All significant calcification was debrided from the native annulus. In cases of aortic valve replacement, the diseased valve was removed via a classical aortotomy. The prosthetic valves were secured with interrupted mattress sutures, with orientation of the large valve opening slightly to the right of the right coronary ostium. In mitral valve replacement, the Shanghai disc valve was implanted with a continuous polyester suture or interrupted mattress sutures, with Teflon pledgets on the atrial sides. The large opening of the valve was usually oriented posteriorly, but in a small number of cases, it was oriented anteriorly towards the septum. Anticoagulation with warfarin was routinely started between the 2nd and 4th postoperative day, and therapeutic levels were achieved on the 6th to 8th postoperative day. A prothrombin time (PT) of 1.5 to 2 times the control value (17 to 25 seconds) was considered adequate for single and double valve prostheses. PT was checked daily in the hospital until it was stable, then weekly until discharge, and monthly thereafter.
Hospital survivors were contacted yearly by means of a mailed questionnaire or telephone interview; most patients returned for follow-up examination. Patient-years of follow-up were 515 for mitral, 48 for aortic, and 219 for double valve replacement; total follow-up was 782 patient-years. Fourteen patients (11.5%) were lost to follow-up. Valve-related complications were defined as structural failure, valve thrombosis, embolism, anticoagulant-related bleeding, paravalvular leak, and infective endocarditis. Deaths were classified as early (within 30 days of the operation) or late (more than 30 days postoperatively). Valve-related mortality included death caused by structural deterioration, nonstructural valve dysfunction, thromboembolism, anticoagulant-related hemorrhage, prosthetic endocarditis, or death at reoperation (deaths due to heart failure in patients with advanced myocardial disease and satisfactorily functioning prosthetic valves, were excluded). Structural abnormality was any change in valve function due to an intrinsic abnormality. Nonstructural dysfunction was any abnormality resulting in stenosis or regurgitation not intrinsic to the prosthesis itself (fibrous tissue overgrowth or suture entrapment, paravalvular leak, or inappropriate sizing).
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Results
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The early mortality rate was 8.2% overall. The causes and details of these early deaths are shown in Table 2. None of the 10 early deaths was found to be valve-related, and 4 occurred in patients who had undergone a previous cardiac operation. There were 7 late deaths (late mortality, 5.7%) occurring between the 2nd and 48th postoperative months; the details are shown in Table 3. Five of the late deaths were considered valve-related; the other 2 were due to cardiac or respiratory failure. Hemodynamic data were recorded preoperatively and postoperatively; details are shown in Table 4.
Follow-up information was obtained for 98 of the 112 patients (87.5%) discharged from the hospital and operated on before December 1998, with a minimum follow-up period of 12 months (Table 5). Analysis of the late deaths showed that 85% occurred within the first 2 postoperative years. Therefore, at 5 years, early mortality excluded, the actuarial survival rate was 96.8% for mitral valve replacement, 100% for aortic valve replacement, and 88% for double valve replacement. Improvement in cardiac function was clearly demonstrated (Figure 3). This clinical improvement was attributed to the good hemodynamic performance of the Shanghai prosthetic valve. Preoperatively, 77.9% of patients were in New York Heart Association functional class III or IV, whereas postoperatively, 90.2% were in class I or II.
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Figure 3. Preoperative and postoperative functional status according to the New York Heart Association (NYHA) classification.
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Anticoagulant-related hemorrhage requiring transfusion or hospitalization occurred in 6 patients, more than 30 days postoperatively in all cases. There were 2 late episodes of hemorrhage (2 and 4 months) among the mitral and double valve replacement patients, respectively, one of which resulted in death. The hemorrhages were caused by cerebral, uterine, gum, or leg muscle bleeding. There was no correlation between the incidence of hemorrhage and valve position. Two patients with double valve prostheses developed prosthetic thrombosis at 11 and 13 months postoperatively. These patients, for unknown reasons, had stopped their anticoagulation regimen 6 to 8 weeks before admission to hospital in cardiac failure. Echocardiography showed decreased excursion of the leaflet in the mitral valve prosthesis, indicating a thrombus attached to the atrial side. In both instances, the patients died. Thrombi were found on the mitral and aortic valve prostheses at autopsy, especially the mitral valves. In both cases, a massive thrombus extended from the annulus through the periprosthetic tissue up towards the valve orifice on the left ventricular side, thus interfering severely with leaflet movement. No early or late mortality was related to valve malfunction.
Cerebral embolic events were observed in 2 patients 2 months and 4 months after mitral and aortic valve replacement, who had not taken warfarin for 2 weeks postoperatively. There were symptoms of hemiplegia, aphasia, and coma, with no evidence of infection or any other cause such as atrial myxoma or valve thrombolysis. Both patients died from respiratory failure. One thrombo-embolic episode occurred 42 months postoperatively in another patient with mitral valve replacement. Among 98 implants followed up, there was one paravalvular leak 2 months after mitral valve replacement. Reoperation and replacement of the mitral valve prosthesis were required. In the absence of paravalvular leak, clinically significant hemolysis occurred in 4 patients and resolved spontane-ously (Table 6). With regard to structural deterioration, no change in valve function resulting from an intrinsic abnormality was noted to cause stenosis or unusual regurgitation. Structural failure such as wear or stress fracture of any part of the prosthesis, was not observed in this series.
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Discussion
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The Shanghai disc valve prosthesis was first introduced into clinical practice in 1978. Since that time, more and more implants have been performed all over the country. In addition to the previously well-documented superior clinical results, good hemodynamic performance, and consequent functional improvement with the Shanghai valve, its durability is confirmed by this 15-year study without evidence of mechanical failure. Specifically, there were no incidences of escaped leaflets, breakdown of materials, or malfunction due to the valve itself.6 The early mortality in this study is higher than that in some other series. However, the majority of deaths occurred in patients who had pervious cardiac operations and the mortality rate in primary cardiac surgical patients is low when compared with other data.7 Our high patient survival rate based on the 15-year follow-up, is comparable with that of the St. Jude Medical valve.8
The most frequent valve-related complication in this study was hemorrhage. The 4 cases of hemorrhage that occurred within 2 months of surgery were in patients with poor hepatic function. The 3 surviving patients recovered well after hospitalization, transfusion, improvement in hepatic function, and regulation of warfarin dosage. Spontaneous fluctuations in the PT are a well-described occurrence in patients maintained on stable doses of warfarin. Unfortunately, these fluctuations may cause a significant shortfall or excesses of anticoagulation, which increase the risks of adverse clinical events such as thrombosis, embolism, or hemorrhage.9 Although frequent monitoring of the PT by venepuncture is essential to avoid anticoagulant-related complications, it is important to recognize the key role of hepatic function in anti-coagulation. It is necessary for patients receiving anticoagulants to have their hepatic function monitored and maintained in normal status.10
The other frequent valve-related complication was thromboembolism. It should be emphasized that both cases of valve thrombosis and the 3 cases of embolism occurred in patients with sub-therapeutic or no warfarin treatment. Similar findings were reported by Nair and colleagues11 for the St. Jude Medical valve. Because the thromboembolic risk is lower in patients maintained on warfarin, this anticoagulant continues to be recommended for all patients receiving mechanical valve implants.12 An additional risk factor for thromboembolism identified in this study was continued antibiotic treatment after discharge from hospital. PT can be prolonged when antibiotics and anticoagulants are used at the same time. The PT must be tested one month after discharge from hospital. The single case of paravalvular leak was not the result of prosthetic valve endocarditis but due to technical difficulties at the time of operation, residual calcification, and poor native tissue.
Good hemodynamic performance of the Shanghai heart valve was evident in the early postoperative period. Improvement in functional status is an important measure of valve performance.13,14 The postoperative functional status of the surviving valve recipients was markedly improved. Most of the patients were able to take part in activities that were impossible before the operation. Functional improvement appeared to be sustained for 15 years postoperatively, undoubtedly because of the good hemodynamic characteristics of the valve.
In view of such good hemodynamic performance, excellent functional improvement, and extensive durability, the Shanghai valve has become the mechanical prosthesis of choice for cardiac valve replacement in our institute. It appears to be one of the best performing mechanical prosthesis currently available in our country, and its low cost makes it more widely affordable.
Presented at the 8th Annual Meeting of The Asian Society for Cardiovascular Surgery, Fukuoka, Japan, September 6–8, 2000.
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References
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Abstract
Introduction
