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Optical Coherence Tomography Imagingof the Purkinje Network

MICHAEL JENKINS, B.S., RYAN S. WADE, B.I.S., YUANNA CHENG, PH.D.,ANDREW M. ROLLINS, PH.D., and IGOR R. EFIMOV, PH.D.

From the Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA

Optical imaging of the conduction system with fluorescentpotentiometric probes has significantly advanced our under-signing of impulse initiation in the sino-atrial node,1 conduc-tion through the atrioventricular node,2 and synchronizationof contraction by the Purkinje system.3 However, further ad-vancement of our understanding of molecular and cellularmechanisms of cardiac conduction is hampered by the lim-ited experimental ability of existing imaging techniques tocorrelate functional and structural information in the complexthree-dimensional structure of the conduction system of theheart. We suggest that the combination of fluorescent poten-tiometric imaging with optical coherence tomography (OCT)can potentially provide a unique opportunity for structure-function studies at the cellular and tissue levels. In this study,we investigated the possibility of OCT imaging the three-dimensional (3D) structure of the Purkinje network. The fig-ure shows that OCT provides high-resolution 3D images ofthe complex morphology of the Purkinje network. OCT is apromising new tool for 3D structure-function imaging of thePurkinje network.

OCT is an emerging non-invasive diagnostic technologythat uses back-reflected infrared light (1,310 nm) to per-form 3D imaging at micron-scale resolution.4 The technol-ogy is based on low-coherence Michelson interferometry.Light back-scattered from the sample interferes with refer-ence light, allowing us to detect light reflected from a specificdepth determined by the reference light path length. By scan-

This work was supported by NIH grant HL58808 (to I.R.E) and a grantRG-02-0376 from the Whitaker foundation (to A.M.R.).

J Cardiovasc Electrophysiol, Vol. 16, pp. 559-560, May 2005.

Address for correspondence: Igor R. Efimov, Ph.D., Washington Univer-sity, Campus Box 1097, One Brookings Drive, St. Louis, MO 63130-4899.E-mail: igor@wustl.edu

doi: 10.1111/j.1540-8167.2005.30621.x

ning the reference path length, we obtain a scattering profileup to 1–3 mm in depth. Two-dimensional (2D) and 3D imagesare built by scanning the OCT beam laterally on the sample.For this study, we used a real-time OCT system describedpreviously.5

“A” represents a 2D OCT image (B-scan) of the endo-cardial surface of a rabbit heart. Individual 2D images weretaken 20 µm apart forming a 3D data set (image C). ThreePurkinje fibers are clearly visible above the endocardial sur-face. “B” shows a section of the same tissue sample stainedwith hematoxylin and eosin, which distinguishes the Purk-inje fibers from other cardiac muscle cells by staining themdark blue. Image B was taken from the same tissue sampleas A, but not necessarily the precise location. Because OCTimaging is performed on the fresh, intact tissue, OCT imagesare not subject to the distortions and artifacts inherent to thehistology preparation process. “C” presents a 3D OCT imageof the Purkinje fiber network on top of the endocardial sur-face. The 3D OCT volume is 2.8 mm × 3.6 mm × 4.3 mm.Three-dimensional (3D) structure was reconstructed, scaled,and visualized as an isosurface. “D” shows light photographand the field of view as the yellow box.

References

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2. Efimov IR, Mazgalev TN: High-resolution, three-dimensional fluores-cent imaging reveals multilayer conduction pattern in the atrioventric-ular node. Circulation 1998;98:54-57.

3. Rentschler S, Vaidya DM, Tamaddon H, Degenhardt K, Sassoon D, Mor-ley GE, Jalife J, Fishman GI: Visualization and functional characteriza-tion of the developing murine cardiac conduction system. Development2001;128:1771-1783.

4. Huang D, Swanson EA, Lin CP, Schuman JS, Stinson WG, ChangW, Hee MR, Flotte T, Gregory K, Puliafito CA, Fujimoto JG: Opticalcoherence tomography. Science 1991;254(5035):1178-1181.

5. Rollins AM, Kulkarni MD, Yazdanfar S, Un-arunyawee R, IzattJA: In vivo video rate optical coherence tomography. Opt Express1998;3(6):219-229.

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Figure 1. Optical coherence tomography (OCT) image of the Purkinje network.