Patricia A. Weber

Anterior mitral leaflet mobility is limited by the basal stay chords.

Background We hypothesize that 2 tendon‐like anterior basal stay chords, which remain taut during the entire cardiac cycle, limit the motion of the anterior mitral leaflet. Methods and Results Sonomicrometric crystals were implanted in 6 sheep at the insertion of stay chords at anterior mitral leaflet (S1 and S2), papillary muscle tips, fibrous trigones, mitral annulus, and the tip of the anterior leaflet (AL). Distances between crystals were recorded before and after section of stay chords. During the cardiac cycle, the angle &agr; between mitral annulus and AL changed by +54.2±12.4 degrees; the angles between mitral annulus and S1 (&bgr;1) changed by +25.7±14.6 degrees, and between mitral annulus and S2 (&bgr;2) by +20.4±7.8 degrees. During diastole, AL twice crossed the virtual plane formed by the stay chords: during E‐wave by a maximum of 6.5 mm (mean, 2.5±2.2 mm) and during A‐wave by a maximum of 3.2 mm (mean, 1.7±0.9 mm). After section of both stay chords, total anterior mitral leaflet motion increased as follows: AL, +6.9±3.4 degrees; S1, +13.1±4.4 degrees; and S2, +30.9±11.7 degrees (P<0.05). Conclusions Although the lateral movement of anterior mitral leaflet is limited by stay chords, the midportion moves unimpaired toward the septum, like a sail, between the 2 stay chords during diastole. A diastolic left ventricular‐inflow and systolic left ventricular‐outflow funnel mechanism is created. Stay chord section increased lateral anterior mitral leaflet movement. (Circulation. 2003;107:2969‐2974.)

Sutureless Stented Aortic Valve Implantation Under Direct Vision: Lessons From a Negative Experience in Sheep

Abstract  Background and Aim of the Study: Percutaneous aortic valve replacement has been proposed as a valid alternative to surgery in selected cases; however, it still has many problems. As a less radical preliminary step, we implanted a balloon‐expandable stented aortic valve under direct vision in sheep. Methods: Under cardiopulmonary bypass (CPB) and through a transverse aortotomy, an aortic valve mounted in a long tubular balloon‐expandable stent was implanted in six acute sheep. The leaflets were not excised and no anchoring sutures were used between stent and native annulus. Epicardial, two‐dimensional color Doppler echocardiography was used to assess the function of the stented valve followed by macroscopic inspection at necropsy. Results: Direct visualization of the entire annulus when the collapsed, valved stent was placed within the aortic root was difficult in all animals. Valve deployment took less than 1 minute. The surgical procedure resulted in major complications in all cases. Migration (3/6), paravalvular leak (2/6), mitral conflicts resulting in mitral regurgitation (1/6), and coronary ostia obstruction (2/6) were the major events at the origin of the failure. Only three animals could be weaned from CPB but did not recover enough to survive the procedure. Conclusions: Sutureless implantation of a stented aortic valve through standard CPB and aortotomy is far more complex than expected. Changes in stent design and surgical approach are indicated.

Kinking of the atrioventricular plane during the cardiac cycle.

Systolic descent of the atrioventricular plane toward the relatively stationary left ventricular apex is well described. As the atrioventricular plane includes two separate valvular units, systolic atrioventricular plane displacement should not be homogenous. In 6 sheep, sonomicrometric crystals were implanted at the base of the right coronary sinus, anterolateral and posteromedial fibrous trigones, posterior mitral annulus, left ventricular apex, and the tips of the anterior and posterior mitral leaflets. The aortomitral angle was calculated and related to simultaneous left ventricular and aortic pressures and mitral valve movement. The aortomitral angle was largest at end diastole (150.73° ± 15.48°). During isovolumic contraction, it narrowed rapidly to 144.90° ± 16.64°, followed by a slower narrowing during ejection until it reached its smallest angle at end systole (139.66° ± 16.78°). During isovolumic relaxation, the aortomitral angle increased to 143.66° ± 16.02° at the beginning of diastole. During the first third of diastole, it narrowed again to 141° ± 16.24° before re-expanding to maximum at end diastole. During systole, the atrioventricular plane descended non-homogeneously toward the apex, with kinking at the hinge between the aortic and mitral annulus plane. This deformation of the atrioventricular plane has relevance in valve surgery.

In vitro study of percutaneous aortic valve replacement: selection of a tissue valve.

Abstract  Background: Selection of the best tissue valve is an essential step before percutaneous aortic valve replacement (PAVR) becomes a clinical reality. The aim of this study was to evaluate in vitro three different tissue valves mounted within the same endovascular stent. Methods: Thirty stented valves (10 aortic porcine, 10 pulmonary porcine, and 10 pericardial tubular) were sutured within a 32‐mm long by 23‐mm diameter cobalt‐nickel stent. The porcine valves were trimmed down close to the cusps. All valves were delivered with a percutaneous valvuloplasty catheter and placed orthotopically in a latex root that was cast from a sheeps aorta. The roots were tested in a pulse duplicator at a rate of 60 beats per minute and 3.5 liters per minute. The transvalvular gradient, maximum valve orifice area, and presence of central and paravalvular leaks were recorded echocardiographically. Results: Within the limitations of implantation in a synthetic, noncalcified annulus, the pericardial valve performed best in terms of orifice area, transvalvular gradients, and tissue bulk; but four of the ten valves showed a central leak due to the type of stent used. Conclusion: The ideal valve for PAVR should collapse with minimal bulk to avoid coronary obstruction and central and paravalvular leaks. The tubular pericardial valve showed the lowest pressure gradients and was the most compressible, but was more open to manufacturing errors.

An in vitro model of pericardial tissue healing

INTRODUCTION A previous study in our laboratory showed that a flap of fresh autologous pericardium bisecting the aorta of sheep retracted and became fibrotic. Histologic analyses suggested that activated cells within the pericardium contributed to the retraction of the implant. Here we report the development of an in vitro model to investigate the effects of serum on cellular proliferation and cell-mediated tissue contraction. METHODS Sections of living and ethanol-treated sheep pericardium were incubated with 0.5%, 5%, 10%, 20%, and 50% serum in medium for up to 8 days and evaluated for cellular proliferation and tissue contraction. These serum-stimulated events were further evaluated in the presence of Mitomycin C, Cytochalasin B and D, Aphidicolin, AraC, and Cycloheximide. RESULTS Cellular proliferation and cell-mediated tissue contraction were induced by serum in a dose-dependent manner. Expression of PCNA was suppressed in the presence of Cytochalasin B, Cytochalasin D, Aphidicolin, and AraC. Tissue contraction was prevented by Cycloheximide. Mitomycin C inhibited both proliferation and tissue contraction. Ethanol-treated tissue, which was absent of living cells, did not respond to stimulation with serum. CONCLUSIONS An in vitro model was developed to study the responses of cells within pericardial tissues to stimulation by serum. In this model, serum induced cellular proliferation and tissue contraction. Different chemical inhibitors independently modulated these serum-stimulated events. Pre-existing cells within pericardial tissues might respond to stimulus through differential pathways. This model may help to develop methods to make autologous pericardium a clinically useful biomaterial.