Mechanical Mitral Prosthesis Research Articles

Ventricular assist device support in patients with mechanical heart valves

Background. Due to potential thromboembolic complications, mechanical valves within the native heart are often considered contraindications to ventricular assist device (VAD) support.Methods. A retrospective review of VAD cases between June 1982 and March 1998 showed 8 patients with mechanical valves who were supported with Thoratec (Pleasanton, CA) VADs.Results. There were 6 males and 2 females ranging in age from 20 to 69 years (mean 49.8 ± 5.6). Four patients were supported when they could not be weaned from cardiopulmonary bypass after reparative procedures and were thought to have reversible injuries. Four patients were supported as a bridge-to-cardiac transplantation. Two patients had mechanical mitral valves, 2 had aortic valve replacements, 1 had an aortic homograft and mechanical mitral valve, 2 had mechanical aortic and mitral prosthesis, and 1 patient had aortic, mitral, and triscupid valves. The types of valvular prostheses were St. Jude (5 patients) and Bjork-Shiley (3 patients). Duration of support ranged from 3.0 to 150 days (mean 34 days). Four patients were supported with biventricular assist devices and 4 had left VADs. Dextran and intravenous heparin anticoagulation were used in the shorter duration patients, with warfarin being used in the bridge patients. One patient received warfarin and aspirin. At the time of autopsy or device removal, only 1 of the 12 mechanical intracardiac valves showed any evidence of thrombosis, including the aortic valves in 2 patients supported for 2 and 5 months. There were no clinical thromboembolic events. Four patients (50%) were discharged (1 weaned, 3 transplanted).Conclusions. The 50% (4 of 8) survival rate compares favorably with the 44% (41 of 92) overall survival rate for our Thoratec patients (bridge plus recovery) who did not have mechanical prosthetic valves. These data suggest that patients with mechanical intracardiac valves can be supported for short durations with some additional risk, which is yet to be determined.

Bacillus cereus prosthetic valve endocarditis

Bacillus cereus is a ubiquitous organism that often contaminates microbiological cultures but rarely causes serious infections. Reports of B cereus endocarditis are infrequent. Infection in patients with valvular heart disease is associated with significant mortality and morbidity. We describe a case of B cereus endocarditis involving a mechanical mitral prosthesis that resolved after replacement of the prosthetic valve. We also review the previous cases reported in the literature.

Microbubbles and mitral valve prostheses — transesophageal echocardiographic evaluation

Objective: To assess whether microbubbles are associated with a specific type of mitral valve prosthesis and to investigate the relationship of microbubbles to ventricular function and mitral regurgitation. One of the types of spontaneous echocardiographic contrast observed in patients with prosthetic heart valves has been described as microbubbles. Methods: Clinical data and videotapes of patients with a prosthetic mitral valve who had undergone transesophageal echocardiography at the UCLA Medical Center between May 1989 and February 1995 were retrospectively reviewed. There were 109 studies (74 patients) available for review by two independent observers. Results: Microbubbles occurred in 49 of the 66 studies of St. Jude valves ( 74%), eight of the 12 studies of Bjork Shiley valves (67%), four of four studies of Medtronic valves (100%) and zero of 23 studies of tissue valves (0%). Patients with an estimated ejection fraction greater than 45% were found to have a much higher likelihood of having microbubbles observed. There was no statistically significant association between the degree of mitral regurgitation and the observation of microbubbles. Conclusions: Microbubbles are a common phenomenon occurring in patients with mechanical mitral prostheses compared with tissue mitral valve prostheses. Their formation depends on the systolic ventricular function, suggesting a cavitation-like phenomenon participating in their formation perhaps due to the rate or velocity of the valve closure.

Microbubbles associated with mitral valve prostheses in pediatric patients

Objectives: To assess whether microbubbles are associated with mitral valve prostheses in children and to investigate their relationship to exercise. Background: Bright, highly mobile echoes are seen in left heart chambers of patients with mechanical mitral valve prostheses. The clinical importance of those microbubbles is not yet known but they survive long enough to reach the cerebral circulation. No such studies have been reported in children. Methods: There were 20 male and 10 female patients with a mean age of 10.4 years (range 2–16 years). Transthoracic echocardiography with calculation of cardiac output and ejection fraction was performed at baseline and after exercise following mechanical mitral valve replacement. Studies were evaluated for the presence of microbubbles. The mean time from operation to time of study was 18 months (range 0.2–89 months) Results: Of the 30 children evaluated, 28 (93%) had evidence of microbubbles. Exercise increased the number of microbubbles in 15 of the 26 children. This was positively associated with an increase in cardiac output. Conclusions: (1) Microbubbles are common observed in children with mechanical mitral prostheses and are augmented by exercise. (2) This phenomenon is of a special concern in children due to their expected longevity with the prosthesis.

Left ventricular outflow tract obstruction with mitral mechanical prosthesis

Left ventricular outflow tract obstruction after mitral valve replacement may occur when the native mitral apparatus is preserved intact. Although it has usually been reported using bioprostheses, we present one case using a low-profile mechanical prosthesis. The reduction of left ventricular dimensions and valvular redundancy contributed to this complication. We obtained definitive relief of left ventricular outflow tract obstruction by transaortic exposure and partial resection of the obstructing tissue with the help of video-assisted cardioscopy.

Obstruction of Mechanical Mitral Prostheses: Analysis of Pathologic Findings

Background. The pathologic and echocardiographic findings observed in 87 patients with mitral valve obstruction were reviewed to ascertain the incidence of pannus formation versus that of thrombosis, the relationship between the two, and the time to the occurrence of pannus versus the time to thrombosis.Methods. Pannus morphology (concentric or eccentric), its location on the valve (atrial, ventricular, atrioventricular), and the presence and relationship of associated thrombi (atrial, ventricular, atrioventricular) were analyzed. The times between valve replacement and the occurrence of obstruction were also compared.Results. There were 10 caged-ball valves, 65 tilting-disc valves, and 12 bileaflet valves. Seventy-two patients underwent prosthetic replacement, and 15 underwent thrombolysis. Pannus alone was found in 27, pannus and thrombus in 39, and thrombus alone in 21. Primary thrombosis occurred earlier than pannus formation (p = 0.04); this was true for patients with bileaflet valves (p = 0.006) and those with tilting-disc valves (p = 0.04). Pannus was atrial in 19.7% (13/66), ventricular in 21.2% (14/66), and atrioventricular in 59.1% (39/66). Pannus morphology was concentric in 22.7% (15/66) and eccentric in 77.3% (51/66). Atrial secondary thrombi occur more often in patients with atrioventricular pannus (p = 0.04). Eight patients had reobstruction; this was caused by pannus formation in 5 and by thrombosis in 3. Five underwent reoperation, and 3 underwent thrombolysis. Reobstruction occurred earlier than the first event.Conclusions. The frequency of pannus formation is much higher than that of thrombus formation, but thrombosis is of earlier onset than pannus formation. Thrombosis is due to the deposition of clots on the prosthesis, and a pannus occurs as the result of an inflammatory reaction developing on both valve surfaces.(Ann Thorac Surg 1997;63:1101–6)

Transesophageal Doppler Echocardiography in the Evaluation of Mitral Bileaflet Mechanical Prostheses: Comparative Studies between Sorin Bicarbon and ATS Valve Prostheses in Mitral Valve Replacement

Transesophageal Doppler Echocardiography in the Evaluation of Mitral Bileaflet Mechanical Prostheses: Comparative Studies between Sorin Bicarbon and ATS Valve Prostheses in Mitral Valve Replacement

Video-Assisted Cardiac Surgery: Preliminary Experience in Reoperative Mitral Valve Surgery

Video-assisted endoscopic techniques had been applied in the surgical correction of patent ductus arteriosus, vascular ring, or coronary artery disease. However, it has been used only recently in the correction of reoperative mitral valve lesions. Video-assisted cardiac operations were performed on four patients who had received surgical interventions on their mitral valves and needed emergent reoperation. Four patients (3 men and 1 woman) received emergency surgery from September to December 1995 for thrombosis of mechanical mitral prosthesis (2 patients) and severe mitral regurgitation with previously failed mitral valve repair (2 patients). Six previous operations had been performed on these mitral valves. Patient ages ranged from 26.7 to 68.1 years (mean, 47.3 years). Preoperatively, acute pulmonary edema occurred in two patients, cerebral emboli occurred in one patient, and sepsis was found in one patient. Mechanical ventilatory support was used in two patients before operation. The operations were performed through right anterior minithoracotomy, guided by video-assisted endoscopic techniques with femoro-femoral extracorporeal circulation. The operative procedures were thrombectomy of mitral prosthesis in two patients, mitral valve repair in one patient, and mitral valve replacement in one patient. The duration of extracorporeal circulation was 166 to 320 min (222 +/- 67 min) and the operation time was 4.6 to 6.8 h (6.1 +/- 1.0 h). All patients recovered from the operations rapidly with uneventful postoperative courses except 1 patient who had sepsis preoperatively and died 2 months later. Our experience demonstrates that video-assisted cardiac surgery is technically feasible and could be performed in reoperation of the mitral valve.

Relationship Between Intravascular Hemolysis and Bright Sparkling Echoes Detected by TEE in the Vicinity of Mechanical Mitral Prosthesis.

The significance of abnormal bright and sparkling echoes in patients with mechanical mitral prosthetic valves (MMPV) has yet to be established. In the present study, the incidence of this phenomenon and its relationship with hemolysis was evaluated. Thirty-five consecutive patients with MMPV, each examined by transesophageal echocardiography (TEE), were divided into four groups: (1) no bright echoes (n = 11 patients); (2) minor echoes (+) (n = 11 patients); (3) moderate echoes (++) (n = 7 patients); and (4) numerous echoes (+++) (n = 6 patients). Hemolysis was evaluated from assays of serum haptoglobin, serum lactic dehydrogenase (LDH) and hydrobutyric dehydrogenase (HDH), plasma hemoglobin, indirect bilirubin, and LDH1 and LDH2 isoenzymes. Serum haptoglobin was significantly lower in the patients with bright echoes (0.17 vs 0.63; P < 0.05). In patients with (++) and (+++) bright echoes, the plasma hemoglobin levels and indirect bilirubin levels were significantly higher than the levels found in those patients with minor echoes or with no echoes. These results suggest that bright echoes in patients with MMPV are related to intravascular hemolysis, and the more intense the echo the more severe the hemolysis. Furthermore, there was a higher incidence of bright echoes in the patients with bileaflet prosthetic valves than in those fitted with the Björk valve (84.6% vs 22%). (ECHOCARDIOGRAPHY, Volume 13, July 1996)

Significance of "Strands" on Mitral Mechanical Prostheses During Late Follow-Up After Surgery.

The presence of "strands" on mitral mechanical prostheses (MMP) has been described, although their significance has yet to be established. The aim of this study was to determine the incidence and clinical implications of "strands" on MMP in late follow-up by a retrospective analysis of 320 consecutive patients who had undergone a transesophageal echocardiographic (TEE) examination under standardized conditions 7 +/- 6 years after mitral surgery. Twenty patients (6.25%) with "strands," defined as highly mobile linear echogenic densities, were identified. This group was compared with a control group of 38 patients, matched for age, sex, and interval between surgery and TEE study, selected at random from this population. Patients with MMP dysfunction were excluded. Type of prosthesis, echographic characteristics (left atrial diameter, spontaneous echo contrast, ejection fraction), and anticoagulant status were not found to bear any relationship to the presence of strands. However, the prevalence of previous embolic events was significantly higher in the "strand" group (10/20 [50%]) than in the control group (7/38 [18.4%]) (P < 0.05). The "strand" group also contained more patients with a prior history of mitral prosthesis thrombosis (7/20 [35%] vs 1/30 [2.6%]; P < 0.05). However, long-term follow-up (1-4 years) was uneventful. These results suggest that: (1) in late follow-up, strands are rare in patients with MMP (6%); and (2) strands were related to previous thromboembolic episodes. (ECHOCARDIOGRAPHY, Volume 13, May 1996)

Diagnosis of intermittent obstruction off mechanical mitral valve prostheses by Doppler echocardiography

In summary, this is a report on 5 various malfunctioning mechanical monocuspid mitral prostheses in which Doppler demonstrated intermittent restriction to the prosthetic disc opening, resulting in intermittent obstruction. In all 5 patients, it was mainly this abnormal Doppler signal that alerted us to the presence of prosthetic valve malfunction. In the 3 asymptomatic patients, the variable and intermittent increased delay in prosthetic valve opening was shown to be an early and sensitive echocardiographic sign of prosthesis malfunction in the absence of any significant increase in pressure gradients.

Variability of mitral valve area by Gorlin formula after replacement by a caged-ball prosthesis

The hemodynamically effective orifice size for valve prostheses is calculated using the modified Gorlin formula 1,2 in the same way as for native valves. The comparison of hemodynamic performance of different types of biological and mechanical prostheses has relied on the values obtained in this way, 3,4 although there are obvious anatomic and flow pattern differences with the native valves. Caged-ball prostheses have a fixed, nondistensible, maximal anatomic orifice area and therefore are generally thought to have also a constant Gorlin mitral area. Considerable variability of the Gorlin mitral area in patients with these prostheses is difficult to explain in the absence of obstruction by tissue or thrombus and provokes questions in regard to the use of this calculation for assessment of the performance of the mechanical valves. It is conceivable that the mitral area calculated by the Gorlin formula is variable and dependent on flow in mechanical ball prostheses. We tested this hypothesis by determining the Gorlin mitral area of mechanical mitral prostheses at rest and after an increase in transvalvular flow.

Comparison of Transesophageal Color Flow Doppler Imaging of Normal Mitral Regurgitant Jets in St. Jude Medical and Medtronic Hall Cardiac Prostheses

Transesophageal color flow Doppler imaging of mitral mechanical prostheses is now widely used. This method eliminates the frequent problems of acoustic shadowing and flow masking that are commonly seen with a transthoracic Doppler study of mechanical mitral prostheses. Transesophageal color flow Doppler imaging was performed postoperatively in seven patients who had received St. Jude Medical mitral prostheses (St. Jude Medical, Inc., St. Jude, Minnesota) and in six patients who received Medtronic Hall mitral valves (Medtronic, Inc., Minneapolis, Minnesota). Maximal systolic regurgitant jet length and area determinations were obtained in all patients. A comparison of maximal jet lengths and areas for each type of mechanical prosthesis demonstrated that the Medtronic Hall prostheses produced longer maximal jet lengths (p = 0.0001) and larger jet areas (p = 0.0009) than those produced by the St. Jude Medical mitral valves. Medtronic Hall prostheses produce a large centrally directed jet, whereas St. Jude Medical prostheses typically generate three smaller jets. Recognition of these differences in transesophageal color flow Doppler images in these commonly used cardiac valve prostheses is necessary to avoid misinterpretation of the normally large systolic regurgitant jet of the Medtronic Hall prosthesis as representing prosthetic dysfunction.

Acute thrombosis of prosthetic valves: a multivariate analysis of the risk factors for a lifethreatening event.

In 3231 prosthetic valves implanted between January 1975 and November 1990, we observed 61 cases of prosthetic obstruction of biological origin with clinical and laboratory findings of severe functional impairment which required surgery as emergency treatment. The hospital mortality was 19.67% (12/61). The obstruction was due to a primary thrombosis in all 5 bioprostheses which were not anticoagulated and in 11/56 (19.64%) mechanical prostheses of which 3 were not anticoagulated and 4 were not properly anticoagulated. The obstruction was due to fibrous tissue overgrowth in the other 45 mechanical prostheses (80.35%) with secondary thrombosis in 34 cases (60.71%) and no thrombosis in 11 (19.64%); 71.11% of these prostheses were adequately anticoagulated. Of the 61 obstructed prostheses, 53 were mitral and 8 were aortic. No tricuspid obstruction was observed. A statistical assessment by multiple correspondence, cluster and chi square analysis was performed in two groups of patients with different models of mechanical mitral prostheses. The 5-year actuarial incidence of obstruction was 6.08%. Significant risk factors were: tilting disc prostheses, prostheses without pyrocarbon coating, large prostheses, tilting disc prostheses with a small orifice posteriorly oriented, atrial fibrillation, enlarged left atrium, time from implant greater than 4 years, age between 40 and 50 years. In our opinion, prosthetic obstruction may be referred to a primary thrombosis only in cases where it may be prevented by adequate anticoagulation. In most cases, the obstruction is produced by periprosthetic fibroblastic proliferation which may develop in spite of adequate anticoagulation in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Doppler color flow mapping in the evaluation of prosthetic mitral and aortic valve function

Doppler color flow mapping and color-guided conventional Doppler studies were performed on 119 patients with 126 prosthetic valves (mitral alone in 60, aortic alone in 52 and both mitral and aortic in 7 patients) within 2 weeks of the catheterization study or surgery, or both. The mean pressure gradients derived by color-guided continuous wave Doppler ultrasound correlated well with those obtained at catheterization for both the tissue and mechanical mitral and aortic prostheses (r = 0.85 to 0.87). For the effective prosthetic orifice areas, better correlation with catheterization results were obtained with the tissue mitral (r = 0.94) and tissue aortic (r = 0.87) prostheses than with the mechanical mitral (r = 0.79) and mechanical aortic (r = 0.76) prostheses. The maximal width of the color flow signals at their origin from the tissue mitral prostheses also correlated well with the effective prosthetic orifice area at catheterization (r = 0.81).Doppler color flow mapping identified prosthetic valvular regurgitation with a sensitive and specificity of 89% and 100%, respectively, for the mitral and 92% and 83% for the aortic prostheses. There was complete agreement between the Doppler color flow mapping and angiographic grading of the severity of prosthetic valvular regurgitation in 90% of mitral and 73.5% of the aortic regurgitant prostheses with under- or overestimation by > 1 grade in only two cases. Valvular and paravalvular regurgitation was correctly categorized by Doppler color flow mapping in relation to the surgical findings in 94% of the mitral and 80.5% of the aortic prostheses.

Comparison of outcome after valve replacement with a bioprosthesis versus a mechanical prosthesis: Initial 5 year results of a randomized trial

The Veterans Administration Cooperative Study on Valvular Heart Disease was organized to compare survival and incidence of valve-related complications between patients receiving a bioprosthesis (the Hancock porcine heterograft) and a mechanical prosthesis (the Björk-Shiley spherical disc valve). Five hundred seventy-five patients undergoing single aortic or mitral valve replacement were randomized at surgery to one of the two valve types. At an average follow-up of 5 years (range 3 to 8) there are no statistically significant differences in survival between patients with the two valve types in the aortic valve replacement group. There is a statistically nonsignificant trend toward improved survival in patients undergoing mitral valve replacement with a bioprosthesis compared with a mechanical prosthesis (5 year survival probability was 0.70 +/- 0.05 and 0.58 +/- 0.06, respectively). Fatal and nonfatal valve-related complications occurred significantly less frequently in patients with a bioprosthesis compared with a mechanical prosthesis for both mitral and aortic valve replacement. Five year complication-free probability was 0.67 +/- 0.05 and 0.45 +/- 0.06, respectively, for patients with mitral valve replacement and 0.63 +/- 0.04 and 0.53 +/- 0.04, respectively, for those with aortic valve replacement. The difference in overall complication rates was largely due to the increased number of clinically significant but nonfatal bleeding episodes in patients receiving a mechanical prosthesis. Adjustment for differences in baseline characteristics between patients receiving a mitral mechanical prosthesis and a mitral bioprosthesis reduced the statistical significance of the difference in both mortality and complications.

Aortic and Mitral Valve Replacement in Children

This article presents a retrospective review of 20 aortic and 43 mitral prosthetic valves in 47 children over a 21-year period. The authors discuss the problems encountered during the early years of mechanical valve replacement in children, the enthusiasm for tissue valves in the mid to late 1970s as well as the early failure of these valves, and their current preference for mechanical aortic and mitral prostheses for children in most clinical situations.

Left Ventricular Outflow Tract Obstruction Related to a Valve Prosthesis: Case Caused by a Low-Profile Mitral Prosthesis

Mechanical and bioprosthetic mitral prostheses may have many potential complications. In patients with isolated mitral stenosis and a small left ventricular cavity, low-profile prostheses are recommended to avoid myocardial impingement that can result from a high-profile valve and lead to possible left ventricular inflow or outflow obstruction or ventricular arrhythmias. This case report illustrates that left ventricular outflow obstruction may also result from a low-profile mitral valve prosthesis. This obstruction was not diagnosed before cardiac catheterization. Assessment of patients with suspected prosthetic valve dysfunction is difficult and may necessitate cardiac catheterization or even direct surgical inspection for conclusive information.

A hemodynamic study of the Carpentier-Edwards and Hancock porcine xenografts in the mitral position.

A hemodynamic study was performed on 11 female and 3 male patients with porcine xenograft (9 Carpentier-Edwards, 5 Hancock) in mitral position on average 32.5 months (range 10-65 months) after the operation. In comparison with the preoperative values, the following parameters showed statistically significant post-operative decrease (mean values): wedge pressure (from 22.9 to 13.7 mmHg), pulmonary artery pressure (33.6-21.7), right atrial pressure (7.1-4.2) and pulmonary vascular resistance (3.6-1.9 mmHg/l/min). In a supine bicycle exercise test the mean wedge pressure rose to 27.8 (range 15-44) mmHg. The transvalvular average diastolic gradient showed a mean value of 6.9 (range 4-12 mmHg). The corresponding figures for the calculated valve area were 2.0 (1.0-3.5) cm2. A biplane left ventriculography showed no valvular or paravalvular regurgitation to the left atrium in any patient. The wedge pressures during exercise were significantly correlated with graft diameters. The results were compared with previous reports on mechanical and biological mitral prostheses, and it was concluded that implantation of a porcine xenograft in the mitral position is a satisfactory procedure in severe mitral disease.

Mechanical valves: A comparative analysis of the Starr-Edwards and Björk-Shiley prostheses

Despite the requirement of anticoagulation, mechanical valve prostheses offer the advantage of proven durability. We have compared the long-term results of 467 aortic valve replacements and 342 mitral valve replacements using the Starr-Edwards prosthesis with 110 aortic valve replacements and 105 mitral valve replacements using the Björk-Shiley prosthesis from 1973 through 1977. Improvement in New York Heart Association (NYHA) class was noted in greater than 80% of patients in all four groups. Long-term survival with mean follow-up over 5 years was not significantly different between respective groups. The probability of thromboembolic complications, however, was significantly higher (p less than 0.05) with the Starr-Edwards prosthesis in both the aortic and mitral positions. The probability of valve failure, although low for all groups, was significantly higher (p less than 0.05) in the Björk-Shiley mitral group due to late thrombotic occlusion. Use of the Starr-Edwards and Björk-Shiley prostheses is associated with satisfactory functional improvement and similar long-term survival rate. However, the increased risk of valve failure due to late thrombotic occlusion of the Björk-Shiley prosthesis should be considered when choosing a mechanical mitral prosthesis.