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Blood Flow Patterns in the Heart: Blood Flow Across Intracardiac Shunts
Blood flow through a shunt is small and difficult to detect. In addition, the shunt site itself may not be visible in the image, or multiple shunt sites may be present. The direction and velocities of blood flow, the timing, and the degree of turbulence vary significantly among shunt sites. Color reversal produced by frequency aliasing may make it impossible to determine shunt flow direction by relying on the colors. In many cases, you will have to determine the direction by watching the progression of the blood flow through the shunt, or by using PW or CW Doppler. Blood Flow Across Intracardiac Shunts: Ventricular Septal Defects Ventricular septal defect (VSD) flow jets image best in the parasternal, apical, and subcostal views. Blood flow through a VSD is turbulent and usually occurs in systole. Flow can be left-to-right, right-to-left, or bidirectional, depending on intracardiac pressures. This magnified parasternal long-axis view shows blood flow through a VSD using an enhanced color map. However, the shunt flow moves from the LV to the RV (toward the transducer), the very high velocities in the interventricular septum (IVS) images with aliased flow. After the blood emerges from the VSD, the velocities decrease, as indicated by a blue pattern in the RV. The red in the RV represents swirling of the VSD flow jet after it hits the RV wall. This end-systolic parasternal short-axis view shows a VSD flow jet. An enhanced velocity map is used. The VSD shunt flow moves from left to right, away from the transducer, as indicated by oranges, yellows, and aliased blues. Click below to view a real-time image of VSD. module230_VSD_2.AVI