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BRIEF RAPID COMMUNICATION

Transvascular Intracardiac Applications of a

Miniaturized Phased-ArrayUltrasonic Endoscope

Initial Experience With Intracardiac Imaging in Piglets

Lilliam M. Valdes-Cruz, MD; Eleftherios Sideris, MD; David J. Sahn, MD;

Azucena Murillo-Olivas, MD; Ole Knudson, BS, RDMS; Ryozo Omoto, MD;

Shunei Kyo, MD; and Robert Gulde, MD

Background. Recent advances in miniaturization of phased-array and mechanical ultrasounddevices have resulted in exploration of alternative approaches to cardiac and vascular imagingin the form of transesophageal or intravascular imaging. Preliminary efforts in adaptingphased-array endoscopes designed for transesophageal use to a transvascular approach haveused full-sized phased-array devices introduced directly into the right atrium in open-chestedanimals. The purpose of this study was to assess the feasibility of using a custom-made, very

small phased-array endoscope for intracardiac imaging introduced intravascularly through a

jugular venous approach in young piglets.Methods and Results. Experimental atrial septal defects created in four piglets (3-4 weeks old)

had been closed with a buttoned atrial septal defect closure device consisting of an occluder inthe left atrium and a counteroccluder in the right atrium. Five to 15 days after atrial septaldefect closure, the piglets were returned to the experimental laboratory, where a 6.3-mm,17-element, 5-MHz phased-array probe mounted on a 4-mm endoscope was introduced througha cutdown incision of the external jugular vein and advanced to the right atrium. From the rightatrium all four cardiac chambers, their inflows and outflows, and all four valves were wellimaged with minimal superior and inferior rotation. High-resolution imaging of the atrialseptum defined with anatomical accuracy, later verified by autopsy, the exact placement of boththe occluder and counteroccluder in the left and right sides of the atrial septal defects and theabsence of any shunting across the atrial septum in any of the four animals.

Conclusions. Our efforts indicate that transvascular passage of small phased-array probescan be easily accomplished and is a promising technique for detailed visualization of cardiacstructures. This approach may provide an alternative to transesophageal echocardiography,particularly for guiding interventional procedures such as placement of transcatheter closuredevices in pediatric patients. (Circulation 1991;83:1023-1027)

Recent advances in miniaturization of bothphased-array and mechanical ultrasounddevices has resulted in exploration of alter-

native approaches to cardiac and vascular imagingand has led to an increasing interest in the potentialsof "invasive" echocardiography, that is, transesoph-

From the Department of Pediatrics, Division of Pediatric Car-diology (L.M.V-C., D.J.S., A.M-O., O.K.), University of Califor-nia, San Diego Medical Center, San Diego, Calif.; the Departmentof Surgery (R.O., S.K.), Saitama Medical School, Saitama, Japan;and the Pediatric Cardiology and Heart Institute for CARE (E.S.,R.G.), Amarillo, Tex.Address for correspondence: Lilliam M. Valdes-Cruz, MD,

Division of Pediatric Cardiology, 225 Dickinson Street (H-814-A),San Diego, CA 92103

Received August 22, 1990; revision accepted November 20, 1990.

ageal and intravascular windows for echocardio-graphic and Doppler interrogation.1-4Although intracoronary imaging has been viewed as

an important aid to making decisions about modes oftreatment for coronary disease and can provide guid-ance during or after coronary balloon angioplasties orperformance of other atherotomy techniques, pediat-ric cardiologists have been more interested in explor-ing imaging technologies that would be more feasiblein the guidance of interventional catheterization pro-cedures such as balloon valvuloplasties, dilatations ofaortic coarctations or other central vascular stenoses,and placement of transcatheter devices used for clos-ing patent ductus arteriosus and atrial and ventricularseptal defects. To assess its use for intracardiac imag-

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1024 Circulation Vol 83. No 3 Mar/i 199]

ing and for monitoring the position of previously placedatrial septal defect closure devices, we used a custom-made very small phased-array endoscope introducedintravascularly through a jugular vein in young piglets.

MethodsAnzimal Model

As part of an ongoing protocol to test a transvas-cular method for closing atrial septal defects, fourpiglets (3-4 weeks old) had an atrial septal defectcreated by balloon dilatation of the fossa ovalis. Thedefects had been closed with a "buttoned" devicethat consisted of an occluder advanced into the leftatrium, a counteroccluder in the right atrium, and abuttoning mechanism that attached both compo-nents.) The piglets were then allowed to recover andwere sent back to the farm. Five to 15 days later, thepiglets (8-11 kg) were returned to the laboratory,where transesophageal and transvascular imagingwere performed to judge the adequacy of deviceplacement and defect closure before postmortempathologic examination.

Transvascullar Imaging MethodsTransvascular intracardiac imaging was performed

using a 6.3-mm-diameter, 17-element, 5-MHzphased-array probe mounted on a 4-mm endoscope(with scanning performed on an Aloka model 870,Aloka Co. Ltd., Tokyo). The probe scanned in a singletransverse plane and could be angled superiorly andinferiorly using a cable mechanism. It had capabilitiesfor two-dimensional imaging and pulsed wave Dopp-ler and color Doppler flow mapping at 5 MHz.

ResultsStudies were performed in close-chest piglets that

lay on their backs while anesthetized with ketamine(10-20 mg/kg); breathing was spontaneous, withoutendotracheal intubation or mechanical ventilation.The imaging probe was advanced through a cut-

down incision of the external jugular vein and intothe right atrium without difficulty. Once in the rightatrium, the probe required minimal rotation superi-orly and inferiorly to visualize all intracardiac struc-tures and flows with excellent resolution.Both atria, atrioventricular valves, and ventricles

were imaged in detail. Flows were recorded from thevena cava and the pulmonary veins, across bothatrioventricular valves, and through both ventricularoutflows and great vessels (Figure 1).

In all four piglets, the atrial septal defect closuredevices were identified, and the position of eachwithin the atrial septum was defined easily. Thedevice was positioned well in three of the four piglets(Figure 2A). Flow was recorded with color Dopplermapping around the tips of both the occluder andcounteroccluder in two of the piglets (Figures 2B and2C). In the fourth piglet, the occluder was partiallypulled through the defect into the right atrium, and asmall clot was seen at the bottom of the device just

FIGURE 1. Stillframes slowing nortnal Doppler spectral andcolorflow maps obtainied from initravascular approach. PanelA: Normal ascenzding aortic (AO) flow. Panels B and C:Normal mitt-al (MV) and tricuspid (TV) flows, re.spectively.RA, tight atriulm; RV, tigh1t ventricle; LV left ventrcle.

above the tricuspid valve. No residual flow throughthe atrial septal defects was recorded in any of thefour piglets.

All findings related to device placement wereconfirmed by fluoroscopy and postmortem examina-tion of the heart. No damage was found in the heartor veins as a result of the probe.

DiscussionOur efforts indicate that transvascular passage of

small phased-array probes is an easily accomplishedand promising technique for detailed visualization of

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Valdes-Cniz et al Intracardiac Imaging 1025

FIGURE 2. Panel A: Four-chamber view of the heart obtainedfrom an intracardiac iight atnral (RA) view. The atrial septal defectcloslure device is seen as atn unulisulally thick interatrial septum. The occluderpositioned itl the left atrium (LA) is not distinguishablefiom the couinterocclilder in the RA. At postmortem, bothl parts of the device, placed 2 weeks before this study, were completelyendothelialized and barely differenitiated from the suirrounding atrial tissuie. R, righlt ventricle; L V left ventricle. Panels B, C, andD: Two-dimensional image, color flow image, an:d diagramn, respectively, of an evrpanded view (of the atria. The occluder (OCC)is seen in the LA side of the septlum attached finmly to the atrial wall. Oni the right side of the septuim the c.ountzteroccluder (COC)is seeni with its superior end still not completely endothelialized onito the atrial septal tissue. Flow is seeni around the COC tip onthe color flow image; however, nio residual atrial shlunt was detected.

cardiac structures; this technique should serve toguide interventional catheterization procedures withgreat accuracy and ease.

Intravascular imaging catheters to date have beenused to obtain high-resolution images of vessellumina and vessel walls for purposes of guiding

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1026 Circulation Vol 83, No 3 March 1991

coronary angioplasties and valvuloplasties, for intra-coronary imaging and tissue characterization of ath-erosclerotic plaques, for guiding mechanical and laseratherectomies, and for preventing the complicationsassociated with these invasive procedures.6 Becausetheir primary applications have been vascular, thesecatheters have been optimized for the extreme nearfield, affording only a limited view of intracardiac,valvular, and septal structures.7-9 Furthermore, theyare mostly strictly imaging catheters without the capa-bility of interrogating flow velocity information.

Transesophageal echocardiography has been sug-gested for guiding interventional procedures and as-sessing placement of transcatheter closure devices.10The disadvantages of the transesophageal approachinclude the following: patient discomfort during manip-ulation of the transesophageal echocardiographicprobe, leading to the need for general anesthesia (inchildren) when patient immobility is required duringinterventional procedures; the risk of vagal stimulation,which can be a serious complication in the cardiaccatheterization setting; and problems with visualizationof cardiac structures and flows when overlapping lungstructures obscure or limit the echocardiographic win-dow. Further, the orientation of transesophageal scan-ning may be inadequate for imaging or flow interroga-tion of specific cardiac structures.

Preliminary efforts in adapting phased-array endo-scopes for transvascular use have involved the intro-duction of full-sized phased-array devices directlyinto the right atrium in open-chest animals.1" Withthe recent success in further miniaturizing thesephased-array probes, investigators have turned theirattention to assessing the feasibility of introducingthese probes transvascularly. Seward et al12 describedpreliminary findings with intracardiac imaging ob-tained by manipulating a small esophageal echocar-diographic transducer within the aorta and the infe-rior vena cava of normal pigs. Introduction of thesecatheters through the external jugular venous systemwould make this procedure somewhat analogous tothat used with bioptomes to perform endocardialbiopsies, although the sizes of these imaging endo-scopes still exceed those of biopsy catheters.A number of technological advances expected to

be available within the near future should facilitatesignificant miniaturization of these probes. Increas-ing transducer interrogation frequency to 7.5 andpotentially 10 MHz for sector scan-format phased-array technologies would result in a 30% to 50%decrease in array size, even with the same number ofelements, such that a 3-mm, 20-element phasedarray could be built for longitudinal scanning. Effortsin our laboratory on a National Institutes of Health-sponsored technology development program areaimed in that direction. 13 Further, in addition tochanges in the configuration of the phased-array scanhead itself, there are also new, smaller, more denselypacked and shielded coaxial cables that might aid inreducing shaft diameter.13 For intracardiac scanningfrom the right atrium, it is still probably advisable to

have steerability to aim the array at different areas ofthe heart, but metallic alloy materials that changeshape when temperature varies or when low-voltageelectrical current is applied could be used to bend orflex the tip of the probe. This system would be lesscumbersome and smaller than the cable system pres-ently used in ultrasonic esophagoscopes. Last, radi-ally arranged arrays or mechanically steered single-crystal catheters are available at 20 MHz and at lowerfrequencies,1415 but these technologies have not beenimplemented with the capability of color flow imag-ing or waveform Doppler. There are technical diffi-culties related to the coded aperture reconstructionsused for radial array catheter scanners that may limithigh spatial resolution at larger distances from thetransducer or limit their capability for deriving wave-form or color Doppler. We expect, however, thatminiaturization of probes and increases in frequen-cies to 7.5-10 MHz should permit the eventualintroduction of phased-array devices through a fem-oral venous approach; these improvements shouldincrease the ease of use of this type of intravascularultrasonic monitoring in the cardiac catheterizationlaboratory and allow for human application, eventu-ally even in children.

References1. Seward JB, Khandheria BK, Oh JK, Abel MD, Hughes RW Jr,

Edwards WD, Nichols BR, Freeman WK, Tajik AJ: Trans-esophageal echocardiography: Technique, anatomic correla-tions, implementation, and clinical applications. Mayo ClinProc 1988;63:649-680

2. Cyran SE, Kimball TR, Meyer RA, Bailey WW, Lowe E,Balisteri WF, Kaplan S: Efficacy of intraoperative transesoph-ageal echocardiography in children with congenital heartdisease. Am J Cardiol 1989;63:594-598

3. Bom N, Roelandt J: Intravascular Ultrasound: Techniques,Developments, Clinical Perspectives. Dordrecht, the Nether-lands, Kluwer Academic Publishers, 1989

4. Pandian NG: Intravascular and intracardiac ultrasound imag-ing: An old concept, now on the road to reality. Circulation1989;80:1091-1094

5. Sideris EB, Sideris SE, Fowlkes JP, Ehly RL, Smith JE, GuldeRE: Transvenous atrial septal defect occlusion in piglets witha "buttoned" double-disk device. Circulation 1990;81:312-318

6. Pandian NG, Weintraub A, Schwartz S, Kumar R, Kusay B, KatzS, Aronovitz M, Udelson J, Konstam M, Salem D, Kreis A:Intravascular and intracardiac ultrasound imaging: Currentresearch and future directions. Echocardiography 1990;7:377-387

7. Isner JM, Losordo DW, Rosenfield K, Ramaswamy K, Kelly S,Pastore JO, Kosowsky BD: Catheter-based intravascular ultra-sound discriminates bicuspid from tricuspid valves in adults withcalcific aortic stenosis. JAm Coll Cardiol 1990;15:1310-1317

8. Harrison JK, Sheikh KH, Davidson CJ, Kisslo KB, Leithe ME,Himmelstein SI, Kanter RJ, Bashore TM: Balloon angioplastyof coarctation of the aorta evaluated with intravascular ultra-sound imaging. JAm Coll Cardiol 1990;15:906-909

9. Pandian NG, Weintraub A, Kreis A, Schwartz SL, Konstam MA,Salem DN: Intracardiac, intravascular, two-dimensional, high-frequency ultrasound imaging of pulmonary artery and itsbranches in human and animals. Circulation 1990;81:2007-2012

10. Hellenbrand WE, Fahey JT, McGowan FX, Weltin GG,Kleinman CS: Transesophageal echocardiographic guidanceof transcatheter closure of atrial septal defect. Am J Cardiol1990;66:207-213

11. Schwartz SL, Pandian NG, Kusay BS, Kumar R, Weintraub A,Katz S, Aronovitz M: Real-time intracardiac two-dimensionalechocardiography: An experimental study of in vivo feasibility,

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imaging planes and echocardiographic anatomy. Echocardiog-raphy 1990;7:443-455

12. Seward JB, Khandheria BK, McGregor CGA, Locke TJ, TajikAJ: Transvascular and intracardiac two-dimensional echocar-diography. Echocardiography 1990;7:457-464

13. Sahn DJ, Tasker D, Hagen-Ansert S, Brisken A, Corbett S:Miniaturized high frequency phased array devices for highresolution neonatal and intraoperative imaging (abstract). JAm Coll Cardiol 1990;15:10A

14. Pandian N, Katz S, Kumar R, Tutar A, Schwartz S, WeintraubA, Gillam LD, McKay RG, Konstam M, Salem D, Connolly R,Aronovitz M: Enhanced depth of field in intracardiac 2-D

echocardiography with a new, prototype, low frequency (12MHz, 9 French) ultrasound catheter (abstract). Circulation1990;82:III-442

15. Hodgson J McB, Graham SP, Savakus AD, Dame SG,Stephens DN, Dhillon PS, Brands D, Sheehan H, Eberle MJ:Clinical percutaneous imaging of coronary anatomy using anover-the-wire ultrasound catheter system, in Bom N, RoelandtJ (eds): Intravascular Ultraound. Dordrecht, the Netherlands,Kluwer Academic Publishers, 1989, pp 187-193

KEY WORDS echocardiography, intracardiac atrial septaldefect * cogenital heart defects * transcatheter closure devices

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GuldeL M Valdes-Cruz, E Sideris, D J Sahn, A Murillo-Olivas, O Knudson, R Omoto, S Kyo and R

endoscope. Initial experience with intracardiac imaging in piglets.Transvascular intracardiac applications of a miniaturized phased-array ultrasonic

Print ISSN: 0009-7322. Online ISSN: 1524-4539 Copyright © 1991 American Heart Association, Inc. All rights reserved.

is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231Circulation doi: 10.1161/01.CIR.83.3.1023

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