Abstract 3167: Effects of Left Ventricular Untwisting on Intraventricular Flow: New Insights from the Use of High Frame Rate Ultrasonic Digital Particle Imaging Velocimetry
Background: Left ventricular (LV) untwisting during the isovolumic periods may produce spiral flows within the LV cavity. The objectives of the present study were to correlate the intracavitary flow and LV untwisting sequence using a high-temporal resolution imaging technique.
Methods: The sequence of LV untwisting was explored in 10 porcine beating hearts using ultrasound speckle tracking (2-D strain, GE Healthcare). Changes in LV intracavitary flow were recorded using Doppler and contrast particle imaging velocimetry (PIV). The duration and magnitude of apical untwisting was modified using right atrial and LV epicardial pacing.
Results: Initial LV untwisting occurred during isovolumic contraction (IVC, peak clockwise untwist: −3.2 ± 2.6 degrees) and was associated with acceleration of flow from LV apex with formation of a vortex across the edge of anterior mitral leaflet (Figure 1⇓). A second sequence of untwisting coincided with isovolumic relaxation and was associated with flow that was initially directed toward the apex and then swirled backward towards the base. Epicardial pacing altered the sequence of untwisting and vortex formation and delayed mitral valve closure (28 ± 14 ms vs 61 ± 13 ms, P < .001) and aortic valve opening (77±18 ms vs 111±18 ms, P = .004).
Conclusion: LV untwisting causes flow redirection and a vortical flow momentum that optimizes a smooth transition for subsequent LV suction or ejection. Aberrant electrical activation delays the sequence of untwisting during IVC and disrupts the formation of blood flow vortex. Tracking the sequence of LV untwisting and vortex formation is a novel approach for combined assessment of LV mechanical and flow dyssynchrony.