Abstract 4727: Diastolic Untwisting Correlates Inversely with the End Systolic Area and Negative dP/dt in an Experimental Animal Model
Untwisting of the left ventricle (LV) has been shown to be related to early diastolic filling. We studied rotational dynamics of the LV in open chest rabbits at different loading conditions. Five rabbits (3–5 kg) were anesthetized and operated for midline sternotomy. A manometer tipped catheter was place on retrograde into the LV. Isotonic fluids were infused to increase the pre-load to a maximum of 20% of total blood volume (TBV). Similarly, blood was drawn in increments to reduce the preload to a maximum of 30% of TBV. Scanning was performed directly from the surface of the heart with a 10 MHz pediatric sector probe to acquire short axis views at the level just below the papillary muscle on a GE Vivid 7 ultrasound system at frame rates >150/sec. Image data was transferred to a Windows workstation for offline motion analysis in EchoPac using a speckle tracking based program to compute the degree and rate of rotation. End systolic area was computed by tracing endocardial border of the circumference of the short axis view. For all hemodynamic conditions, the peak rate of diastolic untwisting showed an inverse relationship with end systolic short axis cavity measurements (R2 = −0.78). Also, the peak rate of untwisting correlated well with peak −dP/dt (R2=0.80). Our study verifies that, as a function of twisting mechanics, early diastolic filling depends on the degree of systolic emptying.