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Minimally Invasive Replacement Of The Pulmonary Valve: Histological Effects Of Non-orthotropical Placement Of The Valve Carrying Stent

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Minimally invasive percutaneous transluminal replacement of the pulmonary valve:
histological effects of non-orthotopic placement of the valve carrying stent
Richter D., Pokorny S., Haben I., Metzner A., Haupt J., Lutter G.

The minimally invasive replacement of heart valves enters the daily clinical practice more and more. The experimental percutaneous, transluminal replacement of the pulmonary valve with tissue engineered heart valves carried in a nitinol-stent is focus of recent research. Due to the size of the stent and the fact, that the position of a once placed stent cannot be corrected anymore, the positioning is difficult and could be non-orthotopic. This study focuses on the histological consequences of such an incorrect positioning.

In this study ten pulmonary valved stents were implanted in sheep – five were placed correctly and in the remaining five cases the stent was in a non-orthotopic position after placement. After 3-6 months the animals were sacrificed. The histological architecture and amount of collagen was analyzed and evaluated using the Movat's pentachrome, van Gieson and immunohistochemical staining of collagen I and III. On the basis of native valves a classification for the amount of collagen, cell wealth and development of the architecture was defined.

The amount of collagen I and the heart valve's layering, which is the core architecture of the valves, were in both groups identical and were therefore not modified because of the non-orthotopic positioning. However, the amount of collagen III, the most important structure protein in the heart valve, was lower in the valves that were placed incorrectly than in the orthotopic cases. Furthermore, the amount of cells was much higher in the valves that were placed non-orthotopically.

At first sight, in both experimental groups (orthotopic vs. non-orthotopic) the tissue engineered heart valves seem to develop their layering in a normal way even when the conditions are not ideal. Furthermore, there was no difference in the amount of collagen I. More particularly, there was an underproduction of collagen III and a higher amount of cells. The last one is known from hyperplasia or inflammation. So both observations seem to be a result of the incorrect placement of the valve which therefore has not only haemodynamic effects, but the development of the histological structure of the valve is effected as well.
In conclusion, the correct positioning of the stent is very important for the success of the replacement of heart valves and should be improved to guarantee a well outcome of our future patients.

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