Long-term hemodynamic assessment of the porcine heterograft in the mitral position. Late development of valvular stenosis

Stent creep of porcine bioprosthesis in the mitral position

Stent creep, often associated with valve malfunction, is said to play an important role in the long-term performance of a porcine bioprosthesis. We have measured the angle of the stent post showing maximal inward bending (IBA) on 44 mitral porcine bioprostheses. All of them were explanted 1 to 12 years (mean explant time, 7.8 years) postoperatively at reoperation. Patients included 19 men and 25 women, ranging in age from 24 to 66 years (mean age, 47.2 years). Mean IBA was 12.7 +/- 4.2 [SD] degrees in 14 valves implanted for 7 years or less and 16.4 +/- 5.8 degrees in 30 valves implanted 8 years or longer (p less than 0.05). There was no significant difference in IBA among valves based on type (25 Hancock valves, 15.0 +/- 4.7 degrees; 10 Angell-Shiley valves, 16.2 +/- 8.6 degrees; and 9 Carpentier-Edwards valves, 14.4 +/- 3.7 degrees). There was a significant difference in IBA based on valve size (37 valves measuring 25-29 mm in diameter, 16.3 +/- 5.1 degrees; and 7 valves measuring 31 mm in diameter, 9.9 +/- 5.1 degrees; p less than 0.05). IBA showed a tendency to have a large value in a heart with a small left ventricular end-systolic volume. We conclude that (1) stent creep is not related to the materials or designs of the stent post, but tends to increase with passage of time in place; and (2) compression of the left ventricular wall is one of the main causes of stent-post bending.

Intrinsic failure of Hancock mitral bioprostheses: 10- to 15-year experience

Hancock porcine bioprostheses have been implanted in the mitral position at the National Institutes of Health since July, 1970. Eight models (330, 330A, 330B, 330C, 332, 340, 341, and 342) were used during a 54-month period ending December, 1974, and 100 consecutive surviving patients were evaluated for subsequent bioprosthetic valve failure and prosthesis-related complications by annual clinic examinations and serial hemodynamic studies. Actuarial patient survival was 76 +/- 4%, 51 +/- 5%, and 30 +/- 6% after 5, 10, and 15 years, respectively. Intrinsic valve failure, defined as structural degeneration of bioprosthetic tissue or stent geometry alteration or both, in the absence of prior infection, occurred in 23 patients. The linear occurrence rate of bioprosthetic valve failure was 0.2%, 5%, and 15% per patient-year, and it affected 1 patient, 14 patients, and 8 patients at sequential 5-year milestones. The actuarial freedom from valve failure was 99 +/- 1%, 75 +/- 6%, 58 +/- 8%, and 40 +/- 12% after 5, 10, 12, and 14 years, respectively. The valve durability of early Hancock bioprostheses (models 330 through 341; N = 39) was not appreciably different from that of the current model 342 valves (N = 61). However, an increased incidence of intrinsic valve failure was observed for the first polypropylene-stented valve type (model 330) compared with the currently available model 342 valve (8/16, 50%, versus 12/61, 20%; p = 0.034). The yearly occurrence rate of prosthesis-related complications remained constant, but the rate of intrinsic valve failure increased in a progressive, nonlinear fashion. The high intrinsic failure rate of the Hancock porcine bioprosthesis after 10 to 12 years has moderated our initial enthusiasm for this valve in the mitral position, and has resulted in more frequent implantations of mechanical valve substitutes at this institution.

Mitral valvuloplasty is superior to valve replacement for preservation of left ventricular function: an intraoperative two-dimensional echocardiographic study

To investigate the mechanism and time of onset of ventricular dysfunction after mitral valve replacement, 18 patients with pure, severe mitral regurgitation (of whom 10 underwent mitral valve repair and 8 standard mitral valve replacement with papillary muscle excision) were studied by intraoperative two-dimensional echocardiography immediately before and immediately after the operative procedure. No patient sustained a perioperative myocardial infarction or had any residual mitral regurgitation. Although preoperative hemodynamics were similar, postoperatively the patients with valve repair had a lower pulmonary capillary wedge pressure than did the patients with valve replacement (8.6 +/- 1.9 versus 14.4 +/- 7.5 mm Hg, p less than 0.04). Although intraoperative echocardiographic ejection fraction fell significantly after mitral valve replacement (0.64 +/- 0.11 to 0.40 +/- 0.09, p less than 0.0001), it was maintained after valve repair (0.44 +/- 0.20 to 0.49 +/- 0.16, p = NS). Additionally, regional myocardial contractile abnormalities in the anterior and posterior septum were detected immediately after the procedure by intraoperative echocardiography in the patients with valve replacement, but not in those with repair. These postoperative regional contractile abnormalities after papillary muscle resection have not been described previously. Resection of the papillary muscles may disrupt the muscle bundle alignment and induce contractile abnormalities remote from the excised muscle. This study demonstrated that significant global and regional ventricular dysfunction develops immediately after removal of the papillary muscles, whereas myocardial contractility is preserved in patients undergoing mitral valve repair. Therefore, with intraoperative echocardiography to assure minimal residual regurgitation, surgeons should attempt to preserve ventricular function by performing mitral valve reconstruction in patients with mitral regurgitation.

Hemodynamic differentiation of pathologic and physiologic stenosis in mitral porcine bioprostheses

Porcine bioprostheses are physiologically stenotic valves. Degenerative calcification leading to pathologic stenosis is an increasingly recognized serious late complication of mitral valve replacement with a porcine bioprosthesis. Hemodynamic differentiation of pathologic from physiologic stenosis is important for identification of porcine bioprosthetic valve dysfunction. In 42 patients with a normal Hancock porcine bioprosthesis (standard model, sizes 27 to 33 mm), mean diastolic flow (65 to 461 ml/s), mean gradient (2.0 to 13.4 mm Hg) and effective orifice area (1.1 to 4.4 cm2) were determined at rest, during epicardial pacing (90, 110 and 130/min) and with isoproterenol infusion. A statistically significant increase in mean gradient occurred with increases in flow and decreases in valve size (p less than 0.05). Effective orifice area increased significantly as flow rate increased and as valve size increased (p less than 0.05). These measurements were compared with those in 16 patients with pathologically confirmed porcine bioprosthetic valve stenosis: 8 patients with reoperation (1.1% per patient-year) 3 to 8.5 years after mitral valve replacement and 8 previously reported abnormal cases. Stenotic failure rate was inversely related to valve size (2.1, 1.4, 0.5 and 0% per patient-year for sizes 27 to 33 mm). Stenotic and normal bioprostheses were not accurately differentiated on the basis of a single value for gradient or effective orifice area. A mathematical model that related flow to the square root of the mean gradient allowed complete separation of stenotic from normal prosthetic valve function, after valve size was accounted for and normal confidence limits were established (r = 0.74 to 0.94, sizes 27 to 33, p less than 0.0001). The effective orifice area-flow relation did not provide accurate differentiation of abnormal from normal function. Thus, normal mitral bioprostheses have significant transvalvular gradients whose magnitude depends on flow. Risk of stenotic failure is increased in the smaller valves, which have a larger gradient at implantation. Differentiation of pathologic from physiologic stenosis cannot be made on the basis of a single value for gradient or effective orifice area. Accurate hemodynamic differentiation is achieved by relating mean gradient to mean diastolic flow rate and valve size.

Quantitative anatomic analysis of "stent creep" of explanted Hancock standard porcine bioprostheses used for cardiac valve replacement

The degree of progressive inward deflection of the stent posts ("stent creep") during function of Hancock standard orifice porcine aortic valve bioprostheses is unknown. The present investigation determines, using a quantitative geometric analysis of clinically removed bioprostheses, the contribution of stent creep to progressive reduction in the outflow orifice area of these valves. Fifty-four Hancock standard orifice porcine aortic valve bioprostheses obtained at reoperation or at autopsy of 50 patients were studied; 47 of these were removed more than 21 months postoperatively. The projected geometric outflow orifice area of each prosthesis was planimetrically measured. To compare prostheses through the entire range of available sizes, this measured area was divided by that of an unimplanted valve of the same size to calculate a ratio designated the "normalized outflow area ratio" (NOAR). Thus, by definition, for all unimplanted standards, NOAR was 1.00. In 7 prostheses in place for less than 1 month, the NOAR was 1.00 +/- 0.03 (mean +/- standard deviation). In 47 prostheses removed 21 to 126 months postoperative, the NOAR was 0.91 +/- 0.08. The relation between NOAR and duration of function determined by linear regression was NOAR = 0.955 - 4.560 X 10(-4) X Duration (in months). The minimum NOAR found was 0.74; the NOAR was less than 0.80 in 4 prostheses (8% of long-term valves). Thus, stent creep is usually not prominent after long-term function of Hancock standard orifice procine bioprostheses and suggests that clinically important progressive reduction of the geometric outflow orifice is infrequent.

Underestimation of prosthetic mitral valve areas: role of transseptal catheterization in avoiding unnecessary repeat mitral valve surgery

In patients with symptoms of heart failure after mitral valve replacement, identification of a stenosed prosthesis may be difficult. Twelve such patients were evaluated, presenting at a mean of 8.4 years after mitral valve replacement (four mechanical, eight porcine). Transvalvular pressure gradients were obtained using both indirect (pulmonary capillary wedge) and direct (transseptal catheterization) measurements of left atrial pressure. In all 12 patients, the diastolic gradient across the prosthetic valve was overestimated when pulmonary wedge rather than transseptal measurements were used. Calculated mitral valve prosthetic area was underestimated by the pulmonary wedge determinations. These findings may be caused by either the phase delay of the pulmonary wedge V wave relative to the transseptal V wave, resulting in a higher diastolic mean left atrial pressure, or the faulty wedge determinations in the setting of pulmonary hypertension, or both. In patients being considered for repeat mitral valve replacement because of prosthetic valve stenosis, transseptal catheterization allows for more accurate determination of prosthetic valve area and more accurately defines the need for repeat mitral valve surgery.

Prosthetic heart valves: a review

There are a number of difficulties inherent in the analysis of such a large and diverse quantity of data. In a substantial number of clinical trials, there is no significant effort made to evaluate prosthetic performance as a function of preoperative cardiac anatomy. Hemodynamics have not been systematically studied in relation to preexisting left ventricular size, shape, or configuration, mitral annular orientation, or left atrial size. Postoperative anticoagulation protocols vary from one institution to another and occasionally within study groups themselves. Less tangible variables such as alteration in surgical technique over time and differential familiarity of cardiovascular surgeons with the prostheses employed are chronic problems in any study of this sort. Perhaps the greatest variable in evaluating the postoperative performance of valvular prostheses over the past 20 yr is the radical improvement in techniques of intraoperative myocardial preservation. Notwithstanding, comparisons are possible within the confines of certain criteria. The caged ball value remains in use after 20 years of clinical experience. It has sustained the greatest number of modifications, probably because it has been the most extensively studied. Hemodynamics are adequate although its centrally obstructed design is responsible for increased turbulence, hemolysis, and neointimal proliferation, particularly in the aortic position. The device has been shown to be durable with virtually no reports of ball variance since the alteration of the silicone curing procedure in 1965. Thromboembolic rates are acceptable in the anticoagulated patient while prosthetic thrombosis is not a grave threat in the non-close clearance device. Incidence of endocarditis is not particularly different from that associated with all nonbioprosthetic valves, although there is a much greater published volume of clinical experience concerning recognition and treatment of late prosthetic valve endocarditis in patients with caged ball valves than there is for any other replacement device. Perhaps the most serious disadvantage to caged ball design is its size. Its large spatial requirements have led to anatomic complications in patients with small aortic roots, isolated mitral stenosis, left ventricular hypertrophy, and double valve replacement, among others. Nevertheless, this is still the valve of choice in some centers.(ABSTRACT TRUNCATED AT 400 WORDS)

Long-term failure rate and morphologic correlations in porcine bioprosthetic heart valves

To ascertain relations among site, incidence, and mechanisms of clinically evident failure of porcine bioprosthetic heart valves, the frequency of failure of 1,110 valves in 1,001 adult operative survivors from January 1972 to January 1982 was reviewed and correlated with the pathologic features of 22 consecutive dysfunctional valves. There were 373 mitral, 519 aortic, and 109 double replacements, yielding for study 482 mitral and 628 aortic valves at risk. Infective endocarditis occurred in 1.9% (8 mitral, 7 aortic, and 4 double). Twenty-three valves (13 mitral and 10 aortic) with documented primary dysfunction were explanted, a mean of 55 months (range 9 to 94) after surgery. The primary dysfunction rate for the 333 valves implanted for greater than or equal to 5 years was 6.8% (11 of 161) for mitral and 4.1% (7 of 172) for aortic valves. Valves implanted for less than 5 years had a failure rate of 0.7%. The actuarially determined freedom from primary valve failure was 98 +/- 1% for mitral and 98 +/- 1% for aortic valves at 5 years and 79 +/- 7% for mitral and 91 +/- 4% for aortic valves at 10 years. Recovered valves (12 mitral and 10 aortic) with detailed morphologic analysis were functioning for a mean duration of 52 months (range 12 to 87). Causes of failure included calcification-related tears in 7 (4 mitral and 3 aortic, mean 66 months), tear without calcium deposits in 4 (4 mitral, mean 44 months), cuspal stiffening without tear but with calcium deposits in 2 (1 mitral and 1 aortic, mean 80 months) and thrombosis in 1 (aortic). Late primary dysfunction was most frequently a result of degenerative processes, especially calcification, often with secondary tears, but cuspal tears in the absence of calcium deposits and thrombosis predominated at shorter intervals.

Valvular heart disease: a perspective

Valve replacement has been one of the most important advances in the management of patients with valvular heart disease. The 10 and 15 year survival rate after isolated aortic and mitral valve replacement with the Starr-Edwards valve is 56 and 44%, respectively. At 5 and 7 years, survival with the Björk-Shiley, porcine bioprosthesis and the Starr-Edwards valve is similar. Patients operated on during the last 5 to 10 years have a much better survival rate than those operated on in the 1960s; therefore, the 10 and 15 year survival of those operated on recently should improve. All patients with a mechanical prosthesis need long-term anticoagulant therapy with drugs of the coumadin type. Porcine bioprostheses have a low failure rate up to 5 years after valve replacement; after this, valve failure occurs at an increasing rate, but the incidence at 10 and 15 years is not known. Valve replacement usually produces a marked improvement in the symptomatic status of the patient because of improved hemodynamics; ventricular function is improved in selected subsets of patients. The role of long-term vasodilator therapy has not been fully determined. Antibiotic prophylaxis for secondary prevention of rheumatic carditis and for prevention of infective endocarditis is important.

The clinical life history of explanted prosthetic heart valves

This report analyzes 118 prosthetic heart valves obtained from 97 patients at reoperation (96) or at postmortem examination (22). The number obtained from the mitral, aortic, and tricuspid positions were 78, 32, and 8, respectively. Duration of implant ranged from one day to 12.3 years. Valves showing the least long-term wear were the Starr-Edwards metal strut-silicone bell and the Björk-Shiley. Moderate long-term durability was provided by the Beall and Starr-Edwards cloth-covered composite-seat prostheses while short-term durability was given by Hancock and Carpentier valves. Reoperation for valve-related causes was performed for 46 of 47 Beall valves, which demonstrated stenosis, hemolysis, and incompetence from component wear, 6 of 27 Björk-Shiley prostheses for valve thrombosis or thromboembolism or both, and 11 of 17 porcine prostheses because of calcification (4) or cusp perforation or rupture. Analyses of wear and fatigue of mechanical valves demonstrated that use of ultrahard materials (pyrolyte carbon, titanium, stellite 21) provided superior durability in contrast to polymeric solids or fabrics with poor abrasion and impact characteristics. Further, cloth and disc wear were evident as early as 0.5 year after implant and appeared to be complete by 4 years. Completeness of healing after 24 months was not related to the type of fabric material used or its construction. This study suggests that mechanical valves made from hard materials have long durability when properly implanted and require fastidious prophylaxis against infection and thromboembolism. The findings of early cusp perforation or rupture in the aortic position and leaflet calcification, stiffening, or disruption in the mitral position for porcine prostheses suggest that frequent and careful examinations of patients with these prostheses are required to detect early signs of stenosis or incompetence and that early reoperation is required before catastrophic valve failure necessitates emergency prosthetic valve replacement.

Bioengineering aspects of heart valve replacement

Biomedical engineering inputs have been important in the design, development and testing of substitute heart valves as well as in the pre- and post-operative management of patients with cardiac valve disease. This paper is a review of heart valve replacement whose goal is the enhancement of future bioengineering contributions. We review the approach to the patient with valvular heart disease, and the sources of early and late postoperative pathology with emphasis on complications of the prostheses used. Major significant problem areas relate to the noninvasive evaluation of cardiovascular function (both before and after surgery), device design, hemodynamics, and the need for thromboresistant and durable materials.