Review Article
Intracardiac Echocardiography: Newest Technology*

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Abstract

Intracardiac echocardiography, defined as ultra-sonographic navigation and visualization within large blood-filled cavities or vessels of the cardio-vascular system, has recently undergone refinement as a clinical tool through technologic advances in transducer miniaturization. Intra-cardiac ultra-sound catheters image at lower frequencies than current conventional intravascular ultrasound catheters used for intracoronary imaging. The lower imaging frequency enables greater tissue penetration, permitting whole-heart evaluation from a right-sided catheter position. Newer devices are steerable, have variable imaging frequency (5.5 to 10 MHz), and full Doppler capability (pulsed, continuous wave, and tissue Doppler). These advances have made intracardiac high-resolution imaging as well as hemodynamic assessment possible. A historical perspective, current capabilities and limitations, and potential clinical and research applications of this new imaging technique are discussed. (J Am Soc Echocardiogr 2000;13:788-95.)

Section snippets

INTRODUCTION

Cardioscopy, or visualizing from within the heart and its conduits, has fascinated scientists and clinicians for decades.1, 2, 3 Ingenious methods have been used with limited success; however, only with the advent of invasive ultrasonography has actual visual navigation within the beating heart and vascular tree been possible.4, 5 Ultrasonography permits visualization not only of the vascular cavity and its walls but also across the walls and into surrounding contiguous structures. The physics

HISTORY

Cardioscopy devices were first proposed in the early 1920s.1, 6 One such early device consisted of a tube fitted with a glass or plastic window and illuminated by incident or transmitted light. The window was pressed against the cardiac structures being evaluated to eliminate blood from the field of view. Such tools were designed to perform limited surgical procedures such as mitral commissurotomy.6 Fiberoptics also were used to visualize within the heart;3, 7 however, this technique could be

TODAY

With advances in technology such as miniaturization of low-frequency transducers capable of enhanced tissue penetration, intracardiac imaging has become a clinical tool. Today, 2 introductory technologies have been used in human beings: (1) 9F (3.2-mm diameter), 9-MHz rotating ultrasound element catheter (EP Technologies, Boston Scientific Corp; San Jose, Calif)24 and (2) 10F (3.2-mm diameter), 5.5- to 10-MHz (ie, frequency agile), Doppler-capable vector phased-array ultrasound-tipped catheter

TOMORROW

Realization of the potential applications of intracardiac echocardiography depends on our ability to reduce the limitations of today’s technology. Current technology is unable to provide a wide field of view, which would facilitate user orientation within the heart and enhance navigation. Rotational (fan or toroidal),40 elevation defocusing,41 multiplane,42 and higher-dimensional transducer arrays have been proposed to expand the visual field (Figure 7).

. Unique imaging features of the

CONCLUSION

With advances in technology, including miniaturization of low-frequency transducers capable of enhanced tissue penetration, intracardiac imaging is now a clinical tool. With the introduction of the newest 5.5- to 10-MHz phased-array transducer (with full Doppler capability) mounted on a 10F catheter, intracardiac echocardiography has the potential to play an important role in diagnostic and therapeutic interventional procedures. The clinical application of these current devices in cardiology

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    *

    Reprint requests: James B. Seward, MD, Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic, 200 First Street SW, Rochester, MN 55905.

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