Energy loss is a well-established engineering concept that when applied to evaluating the performance of native heart valves and valvular prostheses has the potential for providing valuable information about the impact of valve function on myocardial performance. The concept has been understood for many years, but its routine application has been hindered not only by a lack of understanding of its meaning but also because of the lack of investigational tools to easily obtain the data necessary for its estimation. Today the gathering of that information is becoming easier, and thus the time has come to revisit the efficacy of energy loss for evaluating heart valve performance. This review defines what energy loss is, how it is measured, and how it might be applied to clinical situations of heart valve disease to better understand the impact of valvular disease on ventricular function.

The most widely implanted prosthetic valve is the mechanical bileaflet. Recent clinical experiences suggest that some designs are more prone to thromboembolic episodes than others. This study evaluated the hinge flow and near-field forward flow of the new St. Jude Medical Regent bileaflet mechanical heart valve. Laser Doppler velocimetry measurements were conducted within the hinge and near-field forward flow regions of the Regent valve. These pulsatile flow velocity measurements were animated in time to visualize the flow fields throughout the cardiac cycle. During forward flow, a recirculation region developed in the inflow pocket of the Regent hinge but was subsequently abolished by strong backflow during valve closure. Leakage velocities in the hinge region reached 0.72 m/s and Reynolds shear stresses reached 2,600 dyn/cm2. Velocities in the near-field region were highest in the lateral orifice jet, reaching 2.1 m/s. Small regions of separated flow were observed adjacent to the hinge region. Leaflet motion through the Regent hinge creates a washout pattern which restricts the persistence of stagnation zones in its hinge. Based upon the results of these studies, the hematological performance of the Regent series should be at least equivalent to the performance of the Standard series.

The clinical histories of the Medtronic Parallel (MP) and St. Jude Medical (SJM) Standard valves suggest pivot geometry influences the thrombogenic characteristics of bileaflet prostheses. This work studied the effects of various pivot geometries on markers of platelet damage in a controlled, in vitro apparatus. The Medtronic Parallel valve, two St. Jude Medical valves, and two demonstration prostheses were used to study the effects of bileaflet pivot design, gap width, and size on platelet secretion and anionic phospholipid expression during leakage flow. A centrifugal pump was used to drive blood through a circuit containing a bileaflet prosthesis. Samples were taken at set time intervals after the start of the pump. These samples were analyzed by cell counting, flow cytometry, and enzyme-linked immunosorbant assay. No significant differences were observed in platelet secretion or anionic phospholipid expression between experiments with the SJM 27 Standard regular leaker, the SJM 20 regular leaker, and the MP 27 valves. Significant differences in platelet secretion and anionic phospholipid expression were observed between a SJM 27 Standard regular leaker and a SJM 27 high leaker valve. These studies suggest that leakage gap width within bileaflet valve pivots has a significant effect on platelet damage initiated by leakage flow.

In this work, estimates of turbulence were made from pulsatile flow laser Doppler velocimetry measurements using traditional phase averaging and averaging after the removal of cyclic variation. These estimates were compared with estimates obtained from steady leakage flow LDV measurements and an analytical method. The results of these studies indicate that leakage jets which are free and planar in shape may be more unstable than other leakage jets, and that cyclic variation does not cause a gross overestimation of the Reynolds stresses at large distances from the leakage jet orifice.

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