A juvenile sheep model for the long-term evaluation of stentless bioprostheses implanted as aortic root replacements.

BACKGROUND AND AIM OF THE STUDY: Orthotopic valve replacement in large animals is an important component of the preclinical assessment of bioprosthetic valves. To provide the most useful preclinical information, the development of models that parallel clinical practice patterns is essential. Therefore, we sought to develop a technically feasible and reproducible model for chronic evaluation of stentless bioprosthetic aortic valves implanted as aortic root replacements in juvenile sheep. METHODS: Juvenile domestic sheep (mean age 21+/-2.28 weeks; range: 17-26 weeks) underwent aortic root replacement using standard cardiopulmonary bypass (CPB) and surgical techniques. Animals were implanted with 19 mm (n = 21), 21 mm (n = 18) or 23 mm (n = 4) bioprostheses from two different manufacturers, and followed for 150 days. Animals surviving at least 150 days were considered long-term survivors; those which died prior to postoperative day (POD) 31 were considered operative deaths. RESULTS: Forty-three animals underwent aortic root replacement. The mean CPB time was 91+/-20 min (range: 62-149 min); mean cross-clamp time was 63+/-13 min (range: 39-95 min). Thirty-five animals (81%) survived the first 30 days of the study period. Five deaths occurred at POD 0 due to anastomotic complications. One death occurred each on POD 3, 6, and 26 as a result of prosthesis size mismatching, thromboembolic complications, and endocarditis, respectively. There were five late deaths. Twenty animals survived the minimum 150-day study period, and 12 were sacrificed at 183+/-17 days. Six animals remain alive at 151+/-0.98 days, and one animal died each on POD 184 and 190. The remaining 10 animals are not yet 150 days from their operation. Currently, all are well at 102+/-34 days (range: 33-140) days. CONCLUSION: These data suggest that long-term evaluation of stentless aortic bioprostheses implanted as aortic root replacements can be accomplished using juvenile sheep.

Mitral valve replacement with glutaraldehyde preserved aortic allografts.

OBJECTIVE: To present long-term results after mitral valve replacement with stent mounted glutaraldehyde preserved aortic allografts in patients older than 15 years. The clinical support for this study was to combine the glutaraldehyde technique of biological tissue preservation with the advantages of allografts when compared to xenografts. This was demonstrated in previous studies using other methods of tissue processing. METHODS: Between September 1984 and November 1994, 70 patients aged 16-77 years (mean 35.4 years) underwent mitral valve replacement with this preserved and mounted allograft. Of these, 40 patients (57.2%) were aged 16-35 years and 15 (21.4%) were 20 years old or younger; 46 (65.7%) were females and 24 (34.3%) males. Single mitral valve replacement was performed in 60 patients and 10 were also subjected to other combined cardiac procedures. Human aortic valves were obtained during routine autopsy, processed in glutaraldehyde and mounted into flexible stents, using the same technique as that used for porcine bioprostheses. RESULTS: Hospital mortality was 1.4%. Total follow-up was 543.1 patient-years, corresponding to a mean follow-up of 7.9 years per patient. Echocardiography demonstrated a hemodynamic performance similar to porcine bioprostheses. Late mortality was 0.7 +/- 0.6% per patient-year and the causes were congestive heart failure in 2, prosthetic endocarditis in 1 and acute myocardial infarction in 1. The 12-year actuarial survival was 92.4 +/- 3.2%. The incidence of late complications was 5.2 +/- 1.2% per patient-year, including congestive heart failure, prosthetic endocarditis, periprosthetic leak, thromboembolic episodes, recurrence of rheumatic disease, coronary artery disease and allograft failure. Complications related to heart disease represented 2.8 +/- 0.6% and allobioprosthesis-related 2.4 +/- 0.5% per patient-year. The 12-year actuarial freedom from primary valve failure was 81.0 +/- 15.0%. The incidence of reoperations was 1.5 +/- 0.8% per patient-year and the main indication was prosthetic endocarditis. Other causes were periprosthetic leak, aortic insufficiency in the native aortic valve and allobioprosthesis dysfunction. Functional results demonstrated a significant improvement in patients clinical condition. CONCLUSION: This 12-year follow-up shows a very low incidence of primary allograft failure for patients older than 15 years undergoing mitral valve replacement, and much superior than our results with porcine bioprosthesis in the same age group. This supports our assumption that this investigational valve represents a new advance in cardiac valve surgery.

The new Labcor-Santiago pericardial bioprosthesis.

The Labcor-Santiago pericardial valve has been designed to minimize mechanical stress and to avoid abrasion wear, at the same time preserving the concept of mounting the pericardium outside the posts for full orifice opening. The new design has preserved the traditional superior hemodynamic performance of pericardial valves, avoiding abrasion by careful padding of the stents and introducing a new concept of cusp attachment in order to increase mechanical durability. Since June 1990, 40 patients received 46 Labcor-Santiago valves: 29 in the aortic position and 17 in the mitral position. Mean age was 65.6 years. Eighty percent of the patients were women. New York Heart Association Functional Class III-IV was present in 76% of patients. Hospital mortality has been 12.5%, with 31% undergoing concomitant procedures. No anticoagulation was administered and there has been one thromboembolic event. Echo-Doppler assessment yielded the following in the aortic position: effective orifice area for 19-mm size = 1 cm2; for 21-mm size = 1.2 cm2. Mean systolic gradient for 19-mm size = 14.7 mmHg; for 21-mm size = 11.2 mmHg. In the mitral position: effective orifice area for 27-mm size = 2 cm2; for 29-mm size = 2.3 cm2. Mean diastolic gradients for 27-mm size = 4.6 mmHg; for 29-mm size = 3.3 mmHg. The low-profile flexible stent, the streamlined shape without outside prosthetic material, and the anatomical sewing rim allow a comfortable implantation of the Labcor-Santiago valve, particularly in the small aortic annulus. It is hoped that this new design will contribute to an increase in in vivo mechanical durability.

Early experience with crimped bovine pericardial conduit for arterial reconstruction.

A bovine pericardial conduit was developed in the laboratory incorporating the principle of crimping used for synthetic vascular prostheses. The pericardium was processed in glutaraldehyde and the tube was crimped by a technique which preserves the integrity of collagen fibres. This vascular substitute presents a non-thrombogenic and non-porous inner surface which does not require preclotting and does not leak. The material is very soft, easy to handle and suture, coapts nicely to suture lines resulting in a hemostatic anastomosis. The crimping design provides longitudinal elasticity and resistance to collapsing, retains its shape with bending and avoids kinking. Crimping provides a circular tube which makes the construction of the anastomosis easier. Experimental studies in dogs demonstrated absence of thromboembolism with the conduit implanted in the abdominal aorta. Fibrin accumulation was not noted in the convexities of the crimps. This conduit was designed for aortic and pulmonary reconstruction and available in different sizes with or without a biological valve. Initial clinical experience included its use in 10 patients with aortic dissections or aortic aneurysms from August 1989 to March 1990. A reconstruction of the abdominal aorta was performed in 2 patients, the descending thoracic aorta in 2, the ascending aorta in 2 and the ascending aorta including the aortic valve and reimplantation of coronary arteries in 4. For the latter 4, composite crimped pericardial tubes containing a porcine bioprosthesis were used. An additional patient with a single ventricle underwent a Fontan type operation also employing a valved crimped pericardial conduit.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac valve replacement with glutaraldehyde preserved aortic allografts.

From September 1984 to December 1988, 144 patients underwent cardiac valve replacement using glutaraldehyde preserved stent mounted aortic allografts. The mean age was 21.4 years (54.9% were 15 years old or younger). The mitral valve was replaced in 125 patients, the aortic valve in 7, the pulmonary valve in 3, the tricuspid in 1, the mitral and tricuspid in 1, and the aortic and mitral in 7. Hospital mortality was 2.8% (4 patients). Total follow-up was 396.3 patient-years and the mean follow-up was 2.8 years per patient. The 5-year actuarial survival was 73.8% +/- 11.9%. The 4-year actuarial survival for patients aged 15 or younger was 81.4% +/- 7.1%. The overall mortality was 2.8% +/- 0.8%/per patient-year. The incidence of valve-related complications was 4.8% +/- 1.1%/per patient-year, and the calcification rate was 3.0% +/- 0.9%/per patient-year and was the main complication reported in 12 patients, all under the age of 15 years. It occurred 14-47 months after implantation (mean 32.7 months). Five-year actuarial freedom from valve dysfunction due to calcification was 82.6% +/- 5.0% and for patients aged 15 or younger was 69.9% +/- 8.8%. The incidence of reoperation was 3.3% +/- 0.9%/per patient-year. These initial results demonstrate a 5-year actuarial freedom from primary valve failure due to fibrocalcification superior to the results obtained with xenobioprostheses in the paediatric age group.