Hydrodynamic characteristics of prosthetic heart valves Cardiamed

Transcription

1 Hydrodynamic characteristics of prosthetic heart valves Cardiamed Hydrodynamic characteristics of blood flow passing through a prosthetic heart valve have profound effect on the activation of thrombus formation processes on it as well as on trauma of formed elements of blood. During laminar stream flow similar to physiological blood flow through cardiovascular system there is no trauma of formed elements of blood, i.e. of erythrocytes and thrombocytes (Fig.1) The flow stresses, occurring in the areas of separation of blood flow from the surface of prosthetic valve and in the areas of turbulence formation, can cause trauma of formed elements of blood. (Fig.2) This can lead to increased hemolysis or activation of thrombocytes. In areas adjacent to prosthetic valve, where stagnation zones in blood flow occur, there are suitable conditions for adhesion of thrombocytes and activation of thrombus formation process. (Fig.3). In order to eliminate the possibility of stable localization of blood stagnation zones, the leaflets of Cardiamed valve rotate around the central axis of the valve housing during its performance (Fig.4). The continuous change of orientation of valve leaflets triggers the change in the localization of blood stagnation zones, thus reducing the risk of thrombus formation.

2 In order to ensure a laminar blood flow and reduce flow stresses, the leaflets of Cardiamed valve in contrast with the leaflets of the known prosthetic valves from other valve manufacturers are not flat but have a special curved shape. This allows to improve flow structure and obtain more homogeneous distribution of velocities within flow. Fig.5 shows relative distribution of local velocity value V within flow passing through the valves with respect to mean flow velocity V o for the valve having common flat leaflets and for Cardiamed valve having curved leaflets. (The studies were carried out at the State Polytechnic University of St. Petersburg) The special aerodynamic shape of Cardiamed valve leaflets ensures the generation of a practically laminar blood flow passing through all valve orifice openings when the valve is in the open position. Fig.6 shows streamlines and velocity profile of blood flow passing through Cardiamed valve, visualized by hydrogen bubble method. The aerodynamic shape of Cardiamed valve leaflets not only generate a laminar blood flow, but also speeds up valve opening and closure. Fig.7 shows results of comparison test for modern prosthetic heart valves using pulse duplicator with the aim to determine the time of valve closure at various cycle frequencies. One of the most effective methods for reducing the risk of thrombus formation is to use regurgitant blood flow for proper washing of dangerous zones. In order to implement this method for Cardiamed valve, the valve has special slots in the area of hinge mechanism without any casual clearances between leaflets and valve housing in the closed position. Due to this local jets of blood, wh

3 ich wash hinge mechanism, are formed (Fig.8). While passing through the valve these jets move tangent to the valve housing. As a result these jets force blood rotate inside heart chambers, thus reducing the risk of formation of stagnation zones (Fig.9). The studies confirmed that the trauma of erythrocytes does not occur in the regurgitant jets and that regurgitant volume of blood passing through Cardiamed valves does not differ much from the corresponding values of modern heart valve prostheses.

4 Hemodynamic characteristics of prosthetic heart valves Cardiamed Hydrodynamic characteristics of prosthetic heart valves Cardiamed are in compliance with the current requirements of cardiac surgery. The numerous studies of pressure gradients of Cardiamed valves in vivo with the use of ultrasonic instruments confirm that the gradients are similar to those of modern mechanical prostheses (Fig.11 Fig.13). The physical status of the most patients who received Cardiamed valves correspond to functional class II (NYHA) (Fig.14, 15). Clinical investigations of prosthetic heart valves Cardiamed The most extensive clinical investigation was conducted at the Research Institute for Transplantology and Artificial Organs (Moscow) with more than 1500 implants of prosthetic heart valve CardiaMed during a period of 10 years. The statistically processed clinical data is given in Figs

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10 One feature of clinical use of CardiaMed valve was the prescription of the anticoagulant therapy with fenilin, an anticoagulant of indirect action, to most patients. Warfarin was prescribed in small number of cases because of difficulty of selecting the right dosage (patients were at higher risk of thromboembolic complications). Another feature of patient follow-up was a non-standard control of blood clotting. Control of PTI was used at the hematological laboratories and only in few cases they used INR control. Although there were no appropriate control for the level of blood clotting, it could be claimed that the level of blood clotting in patients was sufficiently high because there were no incidence of hemorrhagic complications. Despite this the level of

11 thromboembolic complications was sufficiently low, and that fact confirms good thromboresistance characteristics of the prosthesis The frequency of valve-related complications. Prosthetic heart valves CardiaMed (2000 patients for six-year follow-up period). Complications Thrombosis of prosthesis Thromboembolis m Prosthetic valve endocarditis Haemmorrhogic complications Aortic prostheses, % patient-years Mitral prostheses, % patient-years Total % patientyear 0,22 0,14 0,17 0, ,05 0,33 0,07 0,17 0,0 0,0 0,0