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

Chronic haemodynamic performance of a biorestorative transcatheter heart valve in an ovine model

BACKGROUND

The Xeltis biorestorative transcatheter heart valve (BTHV) leaflets are made from an electrospun bioabsorbable supramolecular polycarbonate-urethane and are mounted on a self-expanding nitinol frame. The acute haemodynamic performance of this BTHV was favourable.

AIMS

We sought to demonstrate the preclinical feasibility of a novel BTHV by evaluating the haemodynamic performances of five pilot valve designs up to 12 months in a chronic ovine model.

METHODS

Five design iterations (A, B, B', C, and D) of the BTHV were transapically implanted in 46 sheep; chronic data were available in 39 animals. Assessments were performed at implantation, 3, 6, and 12 months including quantitative aortography, echocardiography, and histology.

RESULTS

At 12 months, greater than or equal to moderate AR on echocardiography was seen in 0%, 100%, 33.3%, 100%, and 0% in the iterations A, B, B', C, and D, respectively. Furthermore, transprosthetic mean gradients on echocardiography were 10.0±2.8 mmHg, 19.0±1.0 mmHg, 8.0±1.7 mmHg, 26.8±2.4 mmHg, and 11.2±4.1 mmHg, and effective orifice area was 0.7±0.3 cm2, 1.1±0.3 cm2, 1.5±1.0 cm2, 1.5±0.6 cm2, and 1.0±0.4 cm2 in the iterations A, B, B', C, and D, respectively. On pathological evaluation, the iteration D demonstrated generally intact leaflets and advanced tissue coverage, while different degrees of structural deterioration were observed in the other design iterations.

CONCLUSIONS

Several leaflet material iterations were compared for the potential to demonstrate endogenous tissue restoration in an aortic valve in vivo. The most promising iteration showed intact leaflets and acceptable haemodynamic performance at 12 months, illustrating the potential of the BTHV.

Approach to the analysis of cardiac valve prostheses as surgical pathology or autopsy specimens

Pathologists are likely to encounter substitute heart valves with increasing frequency. Informed evaluation of such valves provides valuable information that contributes to both patient care and our understanding of the pathobiology of host interactions with mechanical devices. This article summarizes the most important considerations underlying such analyses-including valve identification, common morphologic features and modes of failure, technical details of evaluation, and potential pitfalls.

Successful treatment of failing biological prosthesis because of "Stent creep" with valve-in-valve transcatheter aortic valve implantation

INTRODUCTION

Stent creep is an uncommon mode of structural deterioration of bioprosthetic heart valves defined by a permanent inward deflection of the stent posts. This may occur because of valve over-sizing and leads to intrinsic valve stenosis. It has been described in older generation of bioprosthesis and was thought not to occur in modern devices.

METHODS

We describe three patients who were referred for bioprosthetic valve degeneration with presumed aortic stenosis. Investigations demonstrated mid valvular gradient predominantly because of stent creep. We performed valve-in-valve TAVI with Edward SAPIEN prosthesis.

RESULTS

Median age was 84 and logistic EuroSCORE 34.4. All patients had degenerated bioprosthesis with mean implant duration of 5.6 years. Two patients had Carpentier Edwards Perimount prosthesis (19 and 23 mm) and one patient had a Mitroflow (21 mm). Mean gradients were 33, 54, and 22 mm Hg. About 23 mm Edward SAPIEN valve was implanted in all cases with immediate improvement in haemodynamics with mean gradient reduction to 10, 17, and 8 mm Hg, respectively. The mean aortic valve area increased from 0.63 to 1.76cm(2) . There were no serious adverse events. The patients improved from NYHA III/IV to I/II post procedure and remain well at median follow-up of 24-months.

DISCUSSION

Stent creep is an uncommon mode of structural deterioration in bioprosthetic heart valves. It has been described in the previous generation of bioprosthesis. It is important to distinguish leaflet dysfunction and stent creep. By forcing the stent posts outwards a balloon expandable TAVI device can be used to treat this condition.

Hancock II bioprosthesis: a glance at the microscope in mid-long-term explants

BACKGROUND AND OBJECTIVES

The Hancock II bioprosthesis is a second-generation porcine valve xenograft treated with the detergent sodium dodecyl sulphate (T6) to retard calcification. The aim of this investigation was to study the gross and microscopic features in Hancock II explants to assess the structural changes occurring with time.

METHODS

Among 1382 Hancock II bioprostheses (701 isolated aortic, 421 isolated mitral, 130 double) implanted from 1983 to 1997 in 1252 patients, 22 (16 mitral, 6 aortic) were removed at reoperation until 1999 and were available for pathological investigation: infective endocarditis occurred in 5 and structural deterioration in 8, whereas in the remaining 9 xenografts reoperation was performed for nonstructural valve deterioration (paravalvular leak in 4 and prophylactic replacement in 5). Morphological investigation consisted of gross examination and x-ray, histologic, immunohistochemistry, electron microscopic, and atomic absorption spectroscopic examination.

RESULTS

The cause of structural valve deterioration was dystrophic calcification in 4 cases (1 aortic, 3 mitral; range of time graft was in place, 101 to 144 months), non-calcium-related tears in 3 cases (all mitral, range 121 to 163 months), and commissural dehiscence in 1 (aortic, range 156 months). Five of the nonstructural valve deterioration explants (range 42 to 122 months) showed only pinpoint mineralization at the commissures. Mean calcium content in nonstructural deterioration explants was 14.70 +/- 22.33 versus 99.11 +/- 81.52 mg/g in explants with structural valve deterioration. Electron microscopic examination showed early nuclei of mineralization mostly consisting of calcospherulae upon cell debris. Local or diffuse lipid insudation was observed in all but 2 explants and consisted of cholesterol clefts, lipid droplets, and lipid-laden macrophages featuring foam cells. The lipid insudation was the most plausible cause of tearing in 2 explants.

CONCLUSIONS

These pathologic findings support the clinical results of a delayed occurrence of structural failure of Hancock II bioprostheses and a mitigation of mineralization by the anti-calcification treatment. However, other factors such as lipid insudation may come into play in the long term.

Stent fracture in Wessex porcine heart valve bioprostheses

By January 1994, a total of 40 Wessex porcine bioprostheses (21 mitral, 18 aortic, and 1 tricuspid) were explanted from 31 subjects. They belonged to a series of 150 patients who received 184 of such prostheses in our unit. Seventeen of these explanted prostheses were available for study, and 11 of them presented some sort of stent fracture or fissuring (mean of 3.6 +/- 1.6 fractures per prosthesis). The disruption occurred in all cases at the base of the commissural arch or at the commissural bar of the stent. The fractures were not detected clinically nor echo-cardiographically before reoperation, and most valves were explanted for reasons other than the stent rupture itself. The actuarial probability of freedom from stent fracture in our series is 66 +/- 12% at 9 years of follow-up. In our experience, fracture of the stent is an important mode of structural dysfunction of the Wessex porcine bioprostheses.

Hancock II porcine bioprosthesis: excellent durability at intermediate-term follow-up

OBJECTIVES

This study aimed to assess the clinical performance and durability of a new generation of porcine valve, the Hancock II bioprosthesis, at intermediate-term follow-up.

BACKGROUND

Standard porcine bioprostheses undergo progressive structural deterioration, mainly due to cusp and commissural calcification, affecting durability and requiring reoperation. The Hancock II bioprosthesis, which is currently undergoing clinical investigation, is made from a porcine aortic valve treated with a calcium-retarding agent (sodium dodecyl sulfate [T6]), which should delay onset of calcification and increase durability.

METHODS

From May 1983 to December 1992, we used the Hancock II bioprothesis in aortic (59 patients), mitral (101 patients) and mitral-aortic (25 patients), valve replacement procedures. Postoperative follow-up ranged from 0.1 to 8.7 years (mean [+/- SD] 4.5 +/- 2.6 years) and was 100% complete. Freedom from major postoperative events was calculated at 7 years for patients with aortic valve replacement and at 8 years for those with mitral and mitral-aortic valve replacement.

RESULTS

The actuarial survival rate was 48 +/- 10%, 76 +/- 3% and 63 +/- 6%; freedom from valve-related mortality was 91 +/- 4%, 94 +/- 2% and 89 +/- 6%; freedom from thromboembolism was 80 +/- 11%, 90 +/- 2% and 79 +/- 7%; and freedom from reoperation was 100%, 97 +/- 1% and 89 +/- 6% after aortic, mitral and mitral-aortic valve replacement, respectively. No structural valve deterioration occurred.

CONCLUSIONS

At intermediate-term follow-up the Hancock II bioprosthesis showed excellent durability in all positions. However, the effectiveness of anticalcification treatment must be assessed with longer follow-up studies.

The pathology of Hancock standard porcine valve prosthesis: a 20-year span of experience

A spectrum of events leading to tissue failure is responsible for late dysfunction of Hancock porcine valve xenografts: (a) Primary failure: dystrophic calcification, thrombosis, fibrous tissue overgrowth, primary tears, cuspal hematomas, and stent postbending. (b) Secondary failure: endocarditis and paravalvular leak. Dystrophic calcification is the main factor influencing long-term durability and accounts in our experience for 88% of primary failure, through different clinical presentations; particularly, incompetence by cusp tearing and egg-shell fragmentation is by far the most frequent mode of failure. Cusp degeneration by primary tears (in the absence of dystrophic calcification) is an uncommon event, due to lipid infiltration or to right coronary muscle shelf spontaneous or immuno-related disruption.

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.

Cardiac valve prostheses: pathological and bioengineering considerations

Cardiac valve replacement with mechanical prosthetic or bioprosthetic devices enhances patient survival and quality of life. Nevertheless, prosthesis-associated complications are frequent and contribute significantly to outcome. Thromboembolic complications are the most important problems in patients with mechanical valves, necessitating chronic anticoagulation in all patients receiving them. In contrast, patients with bioprosthetic valves, composed of chemically treated animal tissues, generally do not require anticoagulants. However, bioprostheses fail frequently by degeneration, especially that involving cuspal calcification. This paper reviews the pathological and bioengineering considerations in the selection of cardiac prosthetic valves and the management of patients who have received these devices. The significance, morphology, and pathogenesis of the observed major complications and other alterations during function are described in detail. Contemporary investigative trends are summarized, including studies of inhibition of mineralization and other degenerative changes in bioprostheses, improved design rigid mechanical valves with pyrolytic carbon occluders and the development of central-flow, flexible polymeric leaflet valves.