Biomedical subjects

M Minarini

Publications and source records attributed to M Minarini.

6 recordsLinked to original sources

PubMed1992

Long-term echocardiographic Doppler monitoring of Hancock bioprostheses in the mitral valve position.

Echocardiographic and Doppler studies were performed in 134 patients with a Hancock bioprosthesis in the mitral valve position during a follow-up period of 1 to 216 months. Among the xenografts, 57% were clinically normal and 43% had severe dysfunction. Among the normal bioprostheses, 35% had echocardiographically thickened mitral cusps (> or = 3 mm) with normal hemodynamic function; by setting the lower 95% confidence limit of valve area at 1.7 cm2 these patients had a significantly (p < 0.01) smaller valve area than that of normal control subjects. Evaluation of all thickened normal mitral valves showed the highest incidence of thickening at 9 years after implantation. Valve replacement surgery was subsequently performed in 33 patients with dysfunctioning bioprosthetic and echocardiographic diagnosis was confirmed in 91% of explanted valves (bioprosthetic stenosis 21%, incompetence 46%, and combined stenosis and regurgitation 33%). In 2 valves that were found to be stenotic on echocardiographic examination, a calcium-related commissural tear was also observed at reoperation, and in another, a paravalvular leak was found. Dystrophic calcification, isolated (64%) or occasionally associated with fibrous tissue overgrowth (21%), was the main cause of failure. Pannus was present in prostheses with longer satisfactory function (168 +/- 31 vs 124 +/- 21 months; p < 0.001). Long-term performance was evaluated by the Kaplan-Meier method for up to 18 years of follow-up. Freedom from structural valvular disfunction after mitral replacement was 89% at 6 years, 77% at 8 years, 56% at 10 years, 31% at 12 years, 16% at 15 years, and 15% at 18 years.

Actuarial Analysis↗

PubMed1992

The Meadox-Gabbay pericardial xenograft: failure of the unicusp principle.

Durability of a new bioprosthesis, the Meadox-Gabbay unileaflet pericardial xenograft, was evaluated by reviewing a series of 12 patients who received this device in the mitral position from 1983 to 1985. Bioprosthetic failure necessitated reoperation in 5 patients 21, 22, 53, 66, and 81 months after placement. Three patients died of cardiac failure after 31, 52, and 70 months; no postmortem examinations were done. In 2 of the 3 patients, an echocardiographic study had shown signs of valvular dysfunction. Pathological examination of five available explants revealed the presence of redundancy and stretching of the single pericardial leaflet in all of them; in one, this lesion alone caused severe prosthetic incompetence. Other pathological findings included cusp and commissural calcification and commissural tears with or without calcification. Histologic examination and electron microscopy showed intrinsic calcification involving both collagen bundles and cellular debris and various degrees of collagen disruption. In this limited series of patients, the Meadox-Gabbay pericardial xenograft demonstrated various modes of failure that markedly impair its durability and render it unsuitable as a cardiac valve substitute.

Adult↗

PubMed1992

Durability of glutaraldehyde-fixed pericardial valve prostheses: clinical and animal experimental studies.

Bovine pericardium has been widely employed as a xenograft tissue for the manufacture of bioprosthetic valve substitutes. Early three-leaflet valve models showed poor tissue preservation and shortcomings in valve design, which accounted for tissue wear and prosthesis failure due to cuspal tear. Reducing the number of cusps in the unicusp pericardial valve has proved unsuccessful due to stretching of the single pericardial leaflet with consequent valvular incompetence. The new generation of pericardial xenografts present basic changes in valve design and optimal tissue preservation after industrial processing, with no evidence of leaflet tear at medium term follow up. However, clinical experience is limited and, similarly to porcine xenografts, dystrophic calcification still appears to be a major problem.

Adult↗

PubMed1992

Heart valve bioprosthesis durability: a challenge to the new generation of porcine valves.

Long-term experience with first generation porcine valve xenografts enabled identification of the major limitations to their durability: (1) prosthetic-ventricular mismatch due to the high profile of the stent in patients with mitral stenosis and a small left ventricle; (2) high-pressure fixation with loss of natural collagen crimping in the fibrosa, and wash-out of proteoglycans in the spongiosa; (3) xenograft tissue autolysis, due to the long interval between animal slaughter and aortic valve removal fixation; (4) muscle shelf in the right coronary cusp, which created a gradient and could undergo accelerated calcification and/or spontaneous perforation with time; (5) a flexible polypropylene stent, which could creep or even fracture with consequent inward bending of the stent; (6) progressive time-related dystrophic calcification; (7) host fibrous tissue ingrowth. An awareness of these limitations stimulated technical modifications, which frequently brought about distinct improvements: (1) the reduction of the stent profile eliminated the problem of mismatch, but resulted in a higher tendency towards cusp prolapse and earlier commissural tearing; (2) natural collagen waviness, proteoglycans and cusp extensibility were preserved by employing low or even zero pressure during the fixation process; (3) earlier valve fixation enabled preservation of cell integrity; (4) a new orifice for small valves was designed by replacing the right muscular cusp, thus achieving less gradient and avoiding muscle-shelf-related complications; (5) polypropylene was replaced by Delrin as stent material; (6) calcium-retarding agents like T6 and toluidine blue were applied during commercial processing and storage in order to mitigate tissue mineralization.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioprosthesis↗

PubMed1991

[Structural changes in valve prostheses].

All available prostheses, either mechanical or biological, may undergo structural alterations which are cause of reoperation or death. Some of these complications are common to all valves, whereas some are specific for certain models. Modern mechanical prostheses usually are resistant to structural deterioration, but still thrombogenic thus requiring long-term anticoagulation therapy to avoid thrombotic and thromboembolic episodes, which implies the risk of anticoagulation related hemorrhages. Bioprostheses, on the other hand, present a lower thrombogenicity, however they undergo by definition structural degeneration, especially dystrophic calcification, which is usually cause of reoperation within 8-10 years from implantation. Other prosthetic complications, such as infective endocarditis and fibrous tissue overgrowth, are common to both types of prostheses.

Bioprosthesis↗

PubMed1990

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.

Bioprosthesis↗