2012 Proceedings - International Tissue Elasticity Conference

26
Session SAS: Oral Presentations of Finalists for Student Awards Session
Tuesday, October 2 2:30P – 4:30P
011 ELECTROMECHANICAL WAVE IMAGING OF BIOLOGICAL AND ELECTRONIC PACEMAKERS
IN CONSCIOUS DOGS IN VIVO.
Alexandre Costet 1 , Jean Provost 1 , Alok Gambhir 2 , Yevgeniy Bobkov 3 , Gerard J.J. Boink 3 ,
Peter Danilo Jr 3 , Michael R. Rosen 3 , Elisa E. Konofagou 1,4 .
1 Biomedical Engineering Department, 2 Medicine–Cardiology Department, 3 Pharmacology
Department, 4 Radiology Department, Columbia University, New York, NY, USA.
Background: Safe and real–time non–invasive imaging of cardiac electrical activation has been a long
term goal of clinicians and laboratory investigators. Standard methods currently available in the clinic
are all catheter–based and limited to epicardial or endocardial mapping. They are also time consuming
and costly. Electromechanical Wave (EW) Imaging (EWI) is a direct ultrasound–based imaging technique
that can map the transmural electromechanical activation in all four chambers in vivo [1].
Aims: In this study, we assessed the reproducibility of EWI in closed–chest, conscious dogs to determine
EWI’s potential for longitudinal animal studies. In order to show reproducibility in a variety of cases, we
mapped electromechanical activation in conscious animal during normal sinus rhythm (NSR) and during
idioventricular rhythm occurring in dogs in heart block, implanted with electronic and biological
pacemakers (EPM and BPM respectively).
Methods: Six different dogs (n=6) were used in this study. Four dogs underwent AV node ablation to
create heart block and were subsequently implanted with an EPM in the right ventricular (RV)
endocardial apex while two additionally received a BPM at the left ventricular (LV) epicardial base. A
Verasonics system (Verasonics, Redmond, WA) with a 2.5MHz phased array was used to perform EWI
transthoracically in conscious dogs using a flash beam sequence at 2000 frames/s in the apical 2 and
4–chamber views before and 7 days after implantation. In post–implantation animals, EWI was performed
during BPM pacing only and during EPM pacing only. Axial incremental displacements and strains were
estimated using radiofrequency (RF) cross–correlation with a window size of 9.2mm and a window shift of
0.385mm and a least–squares kernel size of 5.0mm, respectively. Isochrones of the electromechanical
activation were then generated in order to assess EWI reproducibility.
Results: During NSR, the EW originated at the right atrium (RA), propagated to the left atrium (LA) and
emerged from multiple sources in both ventricles. During BPM, the EW originated from the LV basal
lateral wall and subsequently propagated throughout the ventricles. During EPM, the EW originated at
the RV apex and propagated throughout both ventricles.
Conclusions: EWI was capable of adequately differentiating BPM from EPM and NSR and identified the
distinct pacing origins transthoracically and in conscious dogs These findings indicate the potential of
EWI to serve as a simple, direct and noninvasive imaging tool for monitoring of pacing therapies.
(a) (b)
Figure 1: EWI isochrones during NSR, biological and electronic pacing. The orgins of the isochrones correspond to the onset of the
P–wave (a) or the QRS (b, c). (a) EWI isochrone of normal sinus rhythm in one dog pre–surgery. Activation at the atria
originates from the RA and propagates to the LA. In the ventricles, arrows indicati the sites of early activation. (b) EWI
isochrone during biological pacing. Early activation is seen in the basal region of the lateral wall in the LV. (c) EWI
isochrone during electronic pacing. Early activation is seen near the apex of the RV.
Acknowledgements: Supported in part by NIH funding (R01EB006042, R01HL094410 and R01HL67101).
References:
[1] Provost J., Lee W–N., et al.: Imaging the Electromechanical Activity of the Heart In–Vivo. Proc. Natl. Acad. Sci.
U.S.A., Vol. 108, No. 21, pp. 8565–8570, 2011.
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