Abstract 2572: Relationship Between Circumferential and Radial Strain Rate in the Endocardium and the Epicardium: Validation Study Using an In-Vitro Pumped Pig Heart Model
Background: Various components of contraction occur simultaneously as myocardial layers shorten circumferentially. Doppler derived strain rate imaging (SRI) is inherently angle dependent. By scanning for strain rates in varying views, this study attempted to differentiate circumferential and radial SR in the epicardium and endocardium.
Methods: Five pig hearts explanted immediately after a terminal experiment were dissected to retain only the LV. A balloon was inserted into the LV cavity through the aorta and connected to a pulsatile pump. Using two orthogonal cross-sectional views, tissue Doppler imaging was obtained with a 5 MHz transducer (heart rate, 30 – 60 bpm; stroke volume, 20 –35 ml). High fidelity ventricular pressures and sonomicrometry with an array of 5 crystals placed either in the subendocardial or subepicardial layers was used as a reference for both circumferential and radial SR.
Results: Our results demonstrated good correlation between dP/dt and strain rate (r>0.9). Both sonomicrometry and ultrasound SRs in the radial direction were consistently higher than in the circumferential direction for the same dP/dt (p<0.0001), especially for the endocardium, where SRs were an average of 35% higher than circumferential SRs (mean=0.48 ± 0.22 s-1 versus -0.35 ± 0.17 s-1).
Conclusions: SR in this LV model was greatest in the radial direction. SRI is an effective method of evaluating global LV function that can bring new insight and understanding about cardiac mechanics.