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  • Title: The hemodynamic effects of mechanical prosthetic valve type and orientation on fluid mechanical energy loss and pressure drop in in vitro models of ventricular hypertrophy.
    Author: Travis BR, Heinrich RS, Ensley AE, Gibson DE, Hashim S, Yoganathan AP.
    Journal: J Heart Valve Dis; 1998 May; 7(3):345-54. PubMed ID: 9651851.
    Abstract:
    BACKGROUND AND AIMS OF THE STUDY: When choosing a prosthetic replacement for a natural heart valve, one objective should be to minimize the workload placed on the heart. This workload can be raised by fluid mechanical energy losses imposed by the valve. For a patient with left ventricular hypertrophy, certain aortic valve types and orientations could be hemodynamically superior to others. METHODS: This study used a control volume analysis to investigate the effects of prosthetic mechanical aortic valve type and orientation on fluid mechanical energy losses in four in vitro models of the left ventricular outflow/aortic inflow tract in various degrees of hypertrophy. Flow visualization studies were performed to qualitatively validate this analysis. The two most commonly used mechanical valve designs were studied: the St. Jude Medical (SJM) bileaflet valve and the Medtronic Hall (MH) tilting disk valve. Experiments were performed in pulsatile flow at a constant heart rate of 60 beats per min for five valve type/orientation combinations. The stroke volume was varied between 40 and 120 ml in five increments for each model and valve/orientation studied. RESULTS: Valve type and orientation was found to have a significant effect on energy losses in these models (p < 0.05). Valve/orientation combinations with leaflets or disks approximately parallel to the proximal flow direction created lower energy losses than others. The MH valve in the 180 degrees orientation caused significantly less energy losses and pressure drops (orifice and recovered) than any of the SJM valve/orientations studied (p < 0.05). The SJM and MH valves in the 0 degree orientation were responsible for significantly more energy loss than other valve/orientations studied (p < 0.05). An aortic inflow tract model with severe (45 degrees) curvature created significantly more energy loss (p < 0.05) than those with less curvature (15 and 30 degrees). However, the insertion of an obstruction simulating a hypertrophic tissue outgrowth caused much more energy loss than increasing the severity of outflow tract curvature from 15 to 45 degrees. Both orifice pressure drop and recovered pressure drop had excellent linear correlations with energy losses found in these models. CONCLUSIONS: These results imply that: (i) prosthetic valve type and orientation should be considered when replacing the aortic valve of a hypertropic patient; (ii) removal of obstructions within the aortic inflow tract will decrease ventricular workload; and (iii) the Doppler-estimated pressure gradients commonly use by cardiologists to assess the performance of a prosthetic valve, correlate very well with left ventricular energy loss and work load.
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