2012 Proceedings - International Tissue Elasticity Conference

069 SHEAR WAVE VELOCITY ACQUIRED BY SHEAR WAVE ELASTICITY IMAGING INCREASES
WITH TIME IN NORMAL AND HYPO–PERFUSED LANGENDORFF RABBIT HEARTS.
M Vejdani–Jahromi 1 , DM Dumont 1 , A Kiplagat 1 , GE Trahey 1 , PD Wolf 1 – Presented by Y–J Kim .
1 Duke University, Durham, NC, USA.
Background: Heart Failure is a fatal disease in which mechanical properties of the cardiac tissue are
affected. Currently, there is no widely used noninvasive technique to evaluate the changes in mechanical
properties of cardiac tissue. Shear Wave Elasticity Imaging (SWEI) is an ultrasound technique that can be
used to evaluate the stiffness of tissue by acquiring shear wave speed of propagation measurements. It is
known that all isolated heart preparations continuously deteriorate and standard measures of cardiac
function such as developed pressure or maximum dp/dt can be expected to deteriorate 5–10% per hour
[1]. The Langendorff preparation provides valuable information on left ventricular systolic and diastolic
pressures and their derivatives in hearts subjected to ischemia or hypoxia [2].
Aims: To evaluate the capability of SWEI in determining changes in functionality and mechanical
properties of the cardiac tissue.
Methods: Langendorff preparation is a method by which an isolated heart is kept alive for several hours by
retrograde perfusion of the coronaries through the aorta. Three rabbit hearts were isolated on a Langendorff
preparation, perfused with Tyrode solution and submerged in a designed bath with acoustic walls suitable for
ultrasound imaging to prevent reflections from the wall. Data were acquired using a VF10–5 linear transducer
on a Siemens SONOLINE Antares ultrasound system (Siemens Healthcare, Ultrasound Business Unit,
Mountain View, CA, USA) with focal point of 1.6cm, transmit frequency of 5.7MHz and F# of 2. The probe was
fixed approximately 1cm from the left ventricular free wall along the short axis and acquired data from the
same location through time. One rabbit was perfused under normal conditions and two were hypo–perfused
by allowing air bubbles to enter the coronaries at the time of cannulation. The ECG and aortic pressure were
recorded with PowerLab/Labchart data acquisition system (ADInstruments, Colorado Springs, CO, USA).
Results: Initial results showed that diastolic and systolic stiffness increased over time. This increase was
significantly higher in the ischemic hearts compared to the normally perfused heart. Shear wave velocity
increased by 56.5±0.71% and 19±1.4% in diastole and systole respectively in the two ischemic hearts and
14% both in systole and diastole in the normally perfused heart. The ratio of systolic stiffness to diastolic
stiffness expresses the effectiveness of ventricular function as a balance between its systolic contractility
and diastolic stiffness [3]. In our experiments, systolic to diastolic ratio showed 41±12.7% and 4% decrease
in the ischemic and normal hearts respectively, indicating decreased functionality in the ischemic hearts.
Conclusions: From this preliminary data, we conclude that shear wave velocity recorded by SWEI shows
a decrease in compliance and functionality in an isolated heart similar to the decrease, other researchers
have reported in the literature for normal and hypo–perfused hearts, using different methods. This
imaging modality can help us better assess and characterize the mechanical properties of the cardiac
tissue noninvasively and in real time.
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Figure 1: Systolic and Diastolic stiffness versus time in
three Langedorff rabbit hearts. Rabbit 1 and 2
were ischemic and rabbit 3 was normal. Solid
lines are Systolic shear wave velocity and
dashed lines are diastolic values.
Acknowledgements: The authors would like to thank Ellen Dixon Tulloch and Young–Joong Kim for their help in
this project. This work was supported by Medtronic Fellowship and NIH Grants R01EB012484 and R01HL096023.
References:
[1] D.R. Gross: Animal Models in Cardiovascular Research. Third edition, p. 123, 2009.
[2] M.Skzypiec–Spring, B. Grotthus: Isolated Heart Perfusion According to Langendorff–Still Viable in the New
Millennium. Journal of Pharmacological and Toxicological Methods, 55, pp. 113–126, 2007.
[3] J.N. Amoore: Theoretical Analysis of the Relationship between the Ratio of Ventricular Systolic Elastance to
Diastolic Stiffness and Stroke Volume. Med Bio Eng Comput, 30(6); p. 605–12, 1992.
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