Tomizawa Y

Right ventricular dynamics during left ventricular assistance in closed-chest dogs.

To determine the effects of left ventricular assist device (LVAD) support on global right ventricular (RV) systolic mechanics, 8 closed-chest, conscious, sedated dogs were studied after placement of an LVAD (left ventricle to femoral artery bypass) and implantation of 27 tantalum markers into the left ventricular and RV walls for computation of biventricular volumes and geometry. Biplane cinefluoroscopic marker images and hemodynamic parameters were recorded during transient vena caval occlusion at various levels of LVAD support. Right ventricular contractility was assessed using end-systolic elastance and preload recruitable stroke work, and the myocardial (pump) efficiency of converting mechanical energy to external work (stroke work/total pressure-volume area) was calculated. With full LVAD support, RV end-diastolic volume increased from 60 +/- 15 to 62 +/- 17 mL (p < 0.002), pulmonary artery input impedance decreased from 940 +/- 636 to 587 +/- 347 dyne.s/cm5 (p < 0.007), and measurement of RV and left ventricular septal-free wall dimensions demonstrated a significant leftward septal shift (p < 0.0005). Global RV end-systolic elastance and preload recruitable stroke work decreased from 2.4 +/- 1.0 to 1.7 +/- 0.7 mm Hg/mL (p < 0.004) and 14.1 +/- 3.3 to 12.1 +/- 3.9 mm Hg (p < 0.02), respectively; however, RV power output and myocardial efficiency did not change significantly (p > 0.74 and p > 0.33, respectively). Therefore, during LVAD support, global RV contractility is impaired with leftward septal shifting, but RV myocardial efficiency and power output are maintained through a decrease in RV afterload and an increase in RV preload.

Development and evaluation of a pliable biological valved conduit. Part II: Functional and hemodynamic evaluation.

Many congenital cardiac malformations may require a valved conduit for the reconstruction of the right ventricular outflow tract. In spite of many endeavors made in the last 25 years, the clinical results of right ventricular outflow tract reconstruction with currently available valved conduits are still not satisfactory. Specific problems encountered clinically include suboptimal hemodynamic performance, conduit kinking or compression, and fibrous peeling from the luminal surface. To address these deficiencies, we undertook the development of a biological valved conduit: a bovine external jugular vein graft with a retained native valve cross-linked with a diglycidyl ether (DE). This study, using a canine model, was to evaluate the functional and hemodynamic performance of this newly developed valved conduit. Three 14 mm conduits, implanted as bypass grafts, right ventricle to pulmonary artery, were evaluated. The evaluation was conducted with a noninvasive color Doppler flow mapping system at pre-implantation, immediately post implantation, one- and three-months post implantation, and prior to retrieval (five-months post implantation). The two-dimensional tomographic inspection of the leaflet motion at various periods post implantation showed that the valvular leaflets in the DE treated conduit was quite pliable. No cardiac failure or valvular dysfunction was observed in any of the studied cases. The color Doppler flow mapping study demonstrated that the valve in the DE treated conduit was competent, with no conduit kinking or compression observed in any of the three cases. The spectral Doppler velocity study evidenced that the transvalvular pressure gradients of the DE treated conduit were minimal as compared to those of the currently available conduits. In conclusion, from the functional and hemodynamic performance points of view, this newly developed valved conduit is superior to those currently available.

Development and Evaluation of a Pliable Biological Valved Conduit. Part I: Preparation, Biochemical Properties, and Histological Findings

Different types of external valved conduits have been used for the repair of complex congenital cardiac anomalies that may have otherwise been inoperable. However, an ideal conduit has yet to be found due to complications such as stenosis, thrombosis, calcification of the valve and graft wall, and “peeling” of the neointima. To address those problems, a new extracardiac valved conduit made of bovine jugular vein was developed and evaluated in a preliminary animal study. Harvested bovine vein containing a naturally existing valve was initially incorporated with protamine on the inner surface and then was cross-linked in diglycidyl ether (DE). Fixation with DE allowed the vein and its leaflets to retain a tissue-like elasticity. To provide antithrombogenicity to the graft, heparin was introduced into the lumen to bind ionically to the pre-entrapped protamine. The biological valved conduit of approximately 14 mm diameter was implanted from the right ventricle to pulmonary artery as bypass graft in three dogs. After implantation, the native main pulmonary artery was ligated between the anastomotic sites of the bypass conduit. No anticoagulant or antiplatelet drugs were administered after surgery. One DE-fixed valved conduit was retrieved at 3 months, and the others were removed at 5 months. Only small thrombus areas were found on the white luminal surfaces. The valves and the conduits maintained softness and pliability, similar to before implantation. Additionally, the collagen content, shrink temperature, and tanning index of this newly developed biological valved conduit before and after fixation were measured in the study. These preliminary results suggest that the new valved conduit fixed with DE and heparinized on the lumen may help mitigate the problems observed in the currently available conduits.

Exploring better methods to preserve the chordae tendineae during mitral valve replacement

BACKGROUND It is not known how best to resuspend the mitral chordae tendineae during mitral valve replacement to optimize postoperative left ventricular (LV) systolic and diastolic function. METHODS Six different techniques to preserve the chordae during mitral valve replacement were compared in 12 dogs using a nondistorting isovolumic technique: conventional, all chordae severed; anterior, all chordae preserved anteriorly; partial, anterior papillary muscle chordae preserved anteriorly; posterior, all chordae preserved posteriorly; oblique, anterior papillary muscle chordae directed anteriorly and posterior papillary muscle chordae posteriorly; and counter, opposite of oblique chordal direction. Control measurements (no chordal tension) were recorded between each experimental condition. RESULTS The oblique method tended to have the best LV systolic function versus the conventional method (Emax = 4.0 +/- 1.8 versus 3.3 +/- 1.2 mm Hg/mL [mean +/- standard deviation]; p = 0.08 by repeated-measures analysis of variance; physiologic intercept Ees100 = 20.3 +/- 8.6 mL [p < 0.05 versus control]), with no major change in LV diastolic stiffness. The posterior method had a lower Emax (3.3 +/- 1.2 mm Hg/mL) than the oblique method, but a similar Ees100 (20.8 +/-8.1 mL; p < 0.05 versus control) and the best diastolic LV performance (LV diastolic stiffness = 0.46 +/- 0.23 mm Hg/mL). The counter method also had good systolic function (Emax = 3.8 +/- 1.2 mm Hg/mL; Ees100 = 19.7 +/- 7.5 mL; p < 0.05 versus control), but had less favorable diastolic properties (0.65 +/- 0.37 mm Hg/mL; p < 0.05 by repeated-measures analysis of variance versus posterior). CONCLUSIONS In this isovolumic preparation in normal canine hearts, the oblique method of chordal resuspension was associated with the best LV systolic function, whereas the counter technique impaired LV diastolic function. These preliminary results warrant further study in ejecting and failing hearts to determine conclusively which chordal orientation best preserves LV performance after mitral valve replacement.

Rapid neointima formation with elastic laminae similar to the natural arterial wall on an adipose tissue fragmented vascular prosthesis

A vascular prosthesis that can induce a neointima similar to a natural arterial wall is reported. The authors have developed a sealing method using autologous tissue fragments. The sealed graft showed many advantages, with characteristic neointima formation in an animal study. The grafts were implanted in the thoracic descending aortae of 40 dogs and were removed from 1 hour to 608 days after implantation. Another 40 dogs, used as controls, had a fabric graft implanted using the preclotting method. The luminal surface of the sealed graft was completely endothelialized and the original adipose tissue fragments were absorbed within 1 month. Smooth muscle cells infiltrated and proliferated at the same time as endothelialization took place. Most of the smooth muscle cells were arranged in parallel rows and oriented circumferentially within the graft. At 1 month, elastic fibers appeared around the smooth muscle cells near the anastomotic sites. In the long-term specimens, these elastic fibers constituted a fine lamina in the neointima. Intimal hyperplasia and degenerative changes in the neointima were not observed. These results indicated that the sealing method could induce a very stable neointima with a smooth muscle cell layer and elastic laminae similar to a natural arterial wall within a short period of time throughout the graft wall, with maintenance of the neointima for a long period of time after implantation.

A method to reduce thrombogenicity of a graft for small diameter arterial substitution seeded with autologous venous tissue fragments.

The authors successfully applied a method to accelerate endothelialization by tissue fragmentation to a small diameter fabric vascular prosthesis. Tissue fragment seeded grafts showed rapid healing of the neointima. The thrombogenicity of the collagen fibrils in the fragments, however, caused major problems when the method was applied to small diameter grafts: the positively charged collagen fibrils aggregated the negatively charged platelets. The authors masked the fibrils electrostatically with heparin molecules, which are negatively charged. A canine jugular vein was resected, minced into tissue fragments, and suspended in the heparin solution; it then was sieved through the wall of a fabric prosthesis. The grafts (4 mm internal diameter and 3.5 cm in length) were implanted into both carotid arteries of six dogs (12 grafts). Tissue fragment seeded grafts without heparin also were implanted into six dogs. As a control, preclotted fabric grafts were implanted into six dogs (12 grafts). These grafts occluded within 1 week, whereas all the masked grafts were patent without thrombi. In vitro examination of heparin release revealed that approximately 92% of heparin in the graft was released during the first 5 hr, but approximately 6% remained after 25 hr. These results indicate that the method is applicable to small diameter arterial grafts.