Abstract 12661: A New Method to Visualize and Quantitate Intracardiac Vortex Based on the Continuity Equation and Speckle Tracking Echocardiography

Abstract

Background: Although intracardiac vortex is of interest in understanding cardiac function, an echocardiographic method (echo PIV) to assess it requires contrast injection which limits its clinical use. Vector Flow Mapping (VFM®, Hitachi-Aloka Medical) is a novel software to visualize intracardiac flow based on the continuity equation and speckle tracking echocardiography. In VFM, left ventricular (LV) cavity is divided into small square segments (figure). Because of the conservation of mass, blood influx to the segment is equal to the outflux. Vertical flow velocities (V_V1, V_V1’) can be measured by Doppler echocardiography. Horizontal velocity (V_H1) can be obtained by speckle tracking echocardiography. Then, V_H2 is determined as V_V1+V_H1-V_V1’, which is now a horizontal velocity to the next segment. Thus, intracardiac flow including vortex can be determined noninvasively without using contrast. We investigated whether VFM could reasonably show LV vortex in 8 dogs.

Methods: Color Doppler apical long-axis view was obtained for VFM analysis along with LV pressure measurement by a micromanometer before and after esmolol loading (250 μ g/kg/min). Circulation [cm²/s], an index of vortex magnitude, was measured for the maximum vortex during diastole.

Results: A large vortex in the anterior side and a small one in the posterior side were seen in diastole as previously reported. The area of the anterior vortex became maximum in mid diastole. Circulation decreased significantly by esmolol (baseline vs. esmolol: 57.2 ± 8.0 vs. 41.5 ± 8.1 cm²/s, p = 0.0002). Circulation correlated with early diastolic transmitral flow velocity (r = 0.70, p = 0.0018), but not with LV systolic and end-diastolic pressures, peak positive and negative dP/dt, and tau.

Conclusions: VFM is a promising noninvasive method to visualize and quantitate intracardiac vortex. It may be a good tool to assess LV function from the standpoint of blood flow.