Asian Cardiovasc Thorac Ann 2003;11:309-313
© 2003 Asia Publishing EXchange Ltd
Thrombectomy With Disc Rotation of Medtronic Valves
Suresh B Kale, MS,
Devendra S Saksena, FACS,
Yeshwant C Agnihotri, MCh,
Kalyan H Ayyer, DM
Department of Cardiovascular Thoracic Surgery, Bombay Hospital Institute of Medical Sciences, Mumbai, India
For reprint information contact: Devendra S Saksena, FACS Tel: 91 22 2215 0814 Fax: 91 22 2208 1313 email: saksenad{at}bom3.vsnl.net.in Department of Cardiovascular Thoracic Surgery, Bombay Hospital Institute of Medical Sciences, New Marine Lines, Mumbai 400002, India.
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ABSTRACT
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Thrombotic obstruction of prosthetic valves is a serious problem. Early diagnosis and prompt treatment are life-saving in these cases. Three patients presented with subacute and chronic symptoms of prosthetic valve thrombosis of varying duration (7 days to 2 years). All 3 had a Medtronic Hall tilting disc valve implanted in a previous operation in the aortic or mitral position. Diagnosis was established by 2-dimensional echocardiography. Under cardiopulmonary or femorofemoral bypass, thrombectomy and rotation of the disc within the valve housing were performed through a median sternotomy. All the patients had an uncomplicated postoperative course. Pressure gradients fell markedly at discharge 8 to 10 days after surgery. The patients were followed up for between 3 and 11 months, during which they showed excellent prosthetic valve function and reduced gradients. The ability to rotate the valve within the housing allows adequate thrombectomy and pannus excision. Even several years after implantation (more than 10 years in 2 cases), the valve could still be rotated readily to obtain optimum flow and low pressure gradients.
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INTRODUCTION
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Thrombotic obstruction of mechanical prostheses is a rare but potentially fatal complication. Earlier studies had shown that it occurred more frequently with the tilting disc variety than with any other valve designs.1 Some of the early tilting disc valve designs were more prone to valve thrombosis. It is still commonly assumed that this problem afflicts all tilting disc designs, but available data do not support this assumption.2 Bileaflet designs are considered by many as more modern, third-generation, and less susceptible to valve thrombosis and thromboembolism. However, certain varieties of bileaflet valve prostheses may be more prone to thrombosis than do tilting disc valves, especially so in developing countries.3 The main cause of valve thrombosis has been attributed to inadequate systemic anticoagulation.4 In view of the sudden precipitous deterioration in hemodynamic functions and the high mortality associated with reoperation in these critically ill patients, an easy and safe procedure is required. The surgical option available for thrombosed tilting disc valves is thrombectomy or replacement of the prosthesis or both.5 We describe the treatment of 3 patients by thrombectomy and rotation of the disc within the valve housing several years after valve implantation.
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PATIENTS AND METHODS
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The 3 patients in this report presented with features of prosthetic valve thrombosis on follow-up between August 2000 and April 2001, with subacute and chronic symptoms. All of them had dyspnea on exertion with palpitation that had lasted between 7 days and 2 years. The other symptoms were orthopnea, paroxysmal nocturnal dyspnea, and chest pain (Table 1
). One patient had a thromboembolic event in 1991 resulting in hemiplegia, from which he completely recovered later. In all the patients, the valve sound had changed and the valve click was absent. They all had a Medtronic Hall tilting disc prosthesis (Medtronic, Inc., Minneapolis, MN, USA) implanted, in the aortic position in 2 patients and in the mitral position in the 3rd patient. Data on the patients’ previous valve surgery are shown in Table 2.
Diagnosis was established by 2-dimensional echocardiography in all the patients. In addition, cinefluoroscopy, transesophageal echocardiography, and angiography were undertaken (Table 3 and Figure 1). Under conventional cardiopulmonary bypass (in 2 patients) or femorofemoral bypass (in 1 patient) and through a median sternotomy, thrombectomy was performed and the tilting disc was rotated within the valve housing while flow dynamics were monitored to ensure low pressure gradients across the prosthesis and a maximum effective orifice area. Even many years after implantation, in 2 cases more than 10 years, the disc could be readily rotated.
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RESULTS
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Postoperatively, all the patients had an uncomplicated course and were discharged after 8 to 10 days. Prior to discharge, all of them underwent 2-dimensional echocardiography using a 3-MHz transducer, which showed the prosthetic valve functioning normally with decreased gradients across the valve (Table 4). The patients were put on anticoagulation with oral nicoumalone to maintain an international normalized ratio (INR) of 2.0 to 2.5 in the patients with an aortic valve prosthesis and 2.5 to 3.0 in the patient with a mitral valve prosthesis.
The patients were closely monitored for between 3 and 11 months, during which there was no evidence of thromboembolic episodes. Excellent prosthetic valve function and low gradients were shown by echocardiography. The patients’ functional capacity improved from New York Heart Association class III to class I, and their INR was in the acceptable range.
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DISCUSSION
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In clinical practice, native cardiac valves, which are considered to be "perfect" in design, have been found with inherent complications such as degeneration and thrombus deposition.2 Most of the complications are traditionally attributed to prosthetic valves. The most important factors, which are also indicators of prosthetic valve performance, that influence survival and the quality of life after valve replacement are mechanical integrity, hemodynamic characteristics, and thrombogenicity. The incidence of thromboembolism and thrombosis of prosthetic valves varies between series using the same type of prosthesis,6 indicating that the difference may lie in the patient population and in anticoagulation management. The rate of valve thrombosis gives a better indication of prosthesis thrombogenicity, although patient-related factors (age, ethnicity, diet, geographical location, and concomitant diseases) and antithrombotic management also play some role.7,8 Prosthetic valve thrombosis in various series ranged in rate from 1% to 8%.1 Sudden thrombosis in the absence of anticoagulation occurs at a rate of 3% per year. Despite anticoagulation, 1% of the patients with a tilting disc valve in the mitral position may have this complication.9 The cumulative risk for thrombosis of tilting disc valves at 5 years is 3%, 13%, and 13% after aortic, mitral, and combined aortic and mitral valve replacement, respectively, with an overall incidence of 8.6%.10
Butchart and colleagues,7 in their 20-year experience with the Medtronic Hall valve, showed that the design of the valve improves durability and hemodynamic performance and reduces thrombogenicity. Many reports indicated that patients with this valve may present with sudden deterioration in hemodynamics, and nonspecific symptoms may be present in 86% of patients for 1 week or more.11,12 Our 3 patients were symptomatic for 1 week to 2 years before they underwent reoperation, and they were in New York Heart Association class III at the time of hospital admission. They presented mainly with dyspnea on exertion and palpitation. Hence, during follow-up of patients with prosthetic valves, minor symptoms related especially to pulmonary congestion should prompt a careful cardiological evaluation to exclude the possibility of valve thrombosis. An associated change in valve sound or the absence of a metallic valve click is the most significant finding and deserves prompt investigation, particularly by echocardiography.
Transthoracic echocardiography and cinefluoroscopy can correctly detect prosthetic valve thrombosis in 85% of cases.11 Echocardiography in our 3 patients revealed restricted disc excursion, increased echo density of the prosthesis, and elevated gradient across the valve. Cinefluoroscopy in 1 patient showed restricted disc movement. Transesophageal echocardiography is regarded by some authors as the gold standard in diagnosis.11 However, cardiac catheterization remains the most sensitive diagnostic procedure, which is reserved for patients with unconfirmed diagnosis. Prosthetic leaflet dysfunction and high gradients were observed by cineangiography in 1 of our patients.
One of our patients had a low INR (1.3), while the other 2 were documented to have had adequate anticoagulation at the time of admission. Increased incidence of thromboembolic complications has been attributed to irregular anticoagulation therapy, which might have been associated with a rebound hypercoagulable state;2 while inadequate anticoagulation is considered the main cause of valve thrombosis.4
Surgical treatment of prosthetic valve thrombosis has been by thrombectomy or replacement of the prosthetic valve or both.4,5 Thrombectomy was considered the procedure of choice in many series12 because it is easy and fast to perform and is a safe procedure in critically ill patients. Thrombectomy and pannus excision from the downstream side of the valve are often difficult. In our 2 patients with aortic valve prostheses, the disc was rotated such that the major orifice of the prosthesis was oriented towards the greater curvature of the ascending aorta, or slightly deviated from this position if the disc was impinging on the septum. This valve position provided optimum blood flow and improved valve performance. In addition, thrombi and panni were readily removable from both valve surfaces through a left atriotomy and aortotomy. Orienting the larger orifice towards the greater curvature of the ascending aorta creates a near-physiological, or laminar, flow pattern.13 This is possible only with tilting disc prostheses as they have 2 orifices and hence experience less turbulence. The same cannot be achieved with bileaflet valves because they have 3 orifices. Consequently, gradients across the Medtronic Hall valve in the optimum position will be lower compared to bileaflet valves (such as the St. Jude Medical valve) of the same size in any orientation.7,14 This design also causes less hemolysis than the bileaflet design.15
In patient 3, who had a mitral valve prosthesis, the larger orifice of the prosthesis was oriented posteriorly. This orientation allows near-physiological flow patterns within the left ventricle.16 It also contributes to a normal rate of ventricular filling with improved cardiac output. Studies have shown that an INR of 3.0 normally effectively prevents thromboembolic events in most patients with a Medtronic Hall valve.17
We would like to highlight that disc rotation is possible even many years after implantation. Metallic instruments, such as forceps or an artery clamp, should not be used to rotate the disc as they would damage the pyrolitic carbon surface of the valve. This surface is biocompatible and prevents blood cell sludging and thrombus formation. A valve rotator was used in our cases. It is also important to take note of the type of instrument used for thrombectomy. A plastic scoop is highly recommended as it avoids abrasion of the valve surface. We used a conventional valve tester to check the undersurface of the valve.
Follow-up of our 3 patients showed excellent performance of the valve prostheses with decreased gradients and reduced left ventricular dimensions.
To summarize, nonspecific cardiac symptoms along with minor changes in physical findings should be sufficient to suspect possible prosthetic valve thrombosis, and thorough evaluation should be undertaken to confirm the diagnosis. Thrombectomy along with rotation of the disc within the valve housing is an easy, safe, and economical procedure for critically ill patients. We recommend rotating the disc to a position that provides low gradients across the valve with a maximum effective orifice area and better flow dynamics.
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REFERENCES
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ABSTRACT
INTRODUCTION
