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(Circulation. 2000;102:698.)
© 2000 American Heart Association, Inc.
Basic Science Reports |
Visualization and Temporal/Spatial Characterization of Cardiac Radiofrequency Ablation Lesions Using Magnetic Resonance Imaging
From the Departments of Radiology (A.C.L., E.R.M.), Medicine (A.C.L., P.J., R.D.B., H.C., J.L., H.R.H.), Biomedical Engineering (A.C.L., E.R.M., H.R.H.), and Surgery (A.C.L.), Johns Hopkins University School of Medicine, Baltimore, Md.
Correspondence to Albert C. Lardo, PhD, Johns Hopkins School of Medicine, 601 N Caroline St, 4242 JHOC, Baltimore, MD 21287. E-mail alardo{at}mri.jhu.edu
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Abstract |
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Background—The purpose of this study was to describe a system and method for creating, visualizing, and monitoring cardiac radiofrequency ablation (RFA) therapy during magnetic resonance imaging (MRI).
Methods and Results—RFA was performed in the right
ventricular apex of 6 healthy mongrel dogs with a custom 7F
nonmagnetic ablation catheter (4-mm electrode) in a newly developed
real-time interactive cardiac MRI system. Catheters were positioned to
intracardiac targets by use of an MRI fluoroscopy sequence, and ablated
tissue was imaged with T2-weighted fast spin-echo and contrast-enhanced
T1-weighted gradient-echo sequences. Lesion size by MRI was determined
and compared with measurements at gross and histopathological
examination. Ablated areas of myocardium appeared as
hyperintense regions directly adjacent to the catheter tip and could be
detected 2 minutes after RF delivery. Lesions reached maximum size 
5
minutes after ablation, whereas lesion signal intensity increased
linearly with time but then reached a plateau at 12.2±2.1 minutes.
Lesion size by MR correlated well with actual postmortem lesion size
and histological necrosis area (55.4±7.2 versus
49.7±5.9 mm2, r=0.958,
P<0.05).
Conclusions—RFA can be performed in vivo in a new real-time interactive cardiac MRI system. The spatial and temporal extent of cardiac lesions can be visualized and monitored by T2- and T1-weighted imaging, and MRI lesion size agrees well with actual postmortem lesion size. MRI-guided RFA may be a useful approach to help facilitate anatomic lesion placement and to provide insight into the biophysical effects of new ablation techniques and technologies.
Key Words: catheter ablation • magnetic resonance imaging • histopathology • fluoroscopy
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Since its initial description in 1982,1 radiofrequency ablation (RFA) has evolved from a highly experimental technique to its present role as first-line therapy for most supraventricular arrhythmias, including atrioventricular nodal reentrant tachycardia, the Wolff-Parkinson-White syndrome, and focal atrial tachycardia.2 3 4 5 More recently, the clinical indications for RFA have expanded to include more complex arrhythmias that require accurate placement of multiple linearly arranged lesions rather than ablation of a single focus.6 In contrast to catheter ablation of accessory pathways and atrioventricular nodal reentrant tachycardia, for which detailed mapping is necessary to identify appropriate sites for energy delivery, sites for catheter ablation of atrial flutter and atrial fibrillation, for example, are identified almost entirely on an anatomic basis. Although the feasibility of anatomy-based catheter ablation has been demonstrated with standard catheter ablation techniques, these procedures are extremely time-consuming, require prolonged fluoroscopy exposure, and have been associated with a high incidence of complications. For these reasons, there is general agreement that new approaches to facilitate anatomy-based catheter ablation are needed.
The purpose of this study was to explore the potential role of MRI to guide a comprehensive interventional electrophysiology study in vivo. MRI offers several specific practical advantages over other imaging modalities for guiding and monitoring therapeutic interventions, including (1) real-time catheter placement with detailed endocardial anatomic information, (2) rapid high-resolution 3D visualization of cardiac chambers, (3) high-resolution functional atrial imaging to evaluate atrial function and flow dynamics during therapy, (4) the potential for real-time spatial and temporal lesion monitoring during therapy, and (5) elimination of patient and physician radiation exposure. No studies to date, however, have evaluated the potential use of MRI to guide ablation therapy in the heart. Accordingly, the purpose of this study was to (1) develop and characterize a novel MR ablation system capable of guidance, delivery, and monitoring of cardiac RF thermal therapy; (2) quantify temporal and spatial MR signal changes in cardiac tissue after RF-induced thermal damage; and (3) correlate MR lesion size with postmortem lesion size and quantitative histological markers of cell death.
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Methods |
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MRI System
Experiments were performed in a short 1.5-T closed-bore real-time interactive cardiac MRI system (Signa LX, General Electric Medical Systems) with a standard cardiac phased-array coil. This new system overcomes the limitations of conventional MR systems that rely on static scanning protocols by providing rapid data acquisition, data transfer, image reconstruction, and real-time interactive control and display of the imaging slice, while allowing for direct access to the groin or neck for catheter insertion and manipulation. The real-time hardware platform consists of a work station and bus adapter that can be added to conventional scanners. Details of this system have been described elsewhere.7 8
RFA System
RFA was performed with a standard clinical RF generator (Atakr,
Medtronic) with open-loop control. The generator was located outside
the scan room and was electrically interfaced to the animal via
nonmagnetic 7F ablation catheters (Bard Electrophysiology). These
custom catheters are fabricated with woven Dacron bodies, copper wires,
and 4-mm gold electrodes and therefore do not result in image
distortion.
A technical limitation of RF energy delivery and
electrophysiological signal acquisition in
the scanner is electromagnetic interference. Although the frequency of
the RF generation unit (500 kHz) is well below the 64-MHz proton
precession frequency at 1.5 T, higher harmonics of the RF signal can
produce significant image degradation. To overcome this problem,
special RF filters and shielding were designed and constructed to
suppress these harmonic signals and permit simultaneous RFA
and electrophysiological monitoring during
imaging. These multistage, low-pass filters consist of an arrangement
of nonmagnetic electrical components that achieve a cutoff frequency of
10 MHz. The output from the RF generator is directed to the ablation
catheter through these fully shielded filter assemblies that pass
through an electric patch panel between the scan and console rooms. The
dispersive ground electrode consists of a large conductive-adhesive pad
that is attached to the skin of the animal to complete the circuit.
Intracardiac electrogram (IEGM) tracings were acquired with the
same catheters via a similar 12-channel shielded filter box and were
recorded with automated data acquisition software. The effect of
the RFA signal on image quality is shown in Figure 1
. The left panel represents an
image acquired during RF delivery without filtering, and the image on
the right shows the same slice during RF delivery with filtering. Note
that there is no evidence of noise or artifact, and the tip of the
catheter is clearly visible in the right ventricular apex
(arrow).
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Animal Preparation and Experimental Protocol
All animal protocols were reviewed and approved by the Animal
Care and Use Committee at the Johns Hopkins University School of
Medicine and conformed to the guidelines published in the "Position
of the American Heart Association on Research Animal Use." Six
mongrel dogs weighing 28 to 36 kg were premedicated with a 10-mg
intramuscular injection of ketamine and maintained on 80%
oxygen and 1% isoflurane gas throughout the experiment by use of a
Narkomed Anesthesia ventilator (North American Draeger).
Surface ECG leads 1, 2, and 3 were monitored continuously throughout
the experiment. By standard techniques, 8F introducer sheaths were
placed in the right jugular vein for catheter access and in the right
femoral vein for administration of fluids and medication.
Under MR guidance, a 7F nonmagnetic single-electrode ablation catheter
was positioned at the inferior lateral wall of the right
atrium in 3 animals to determine the accuracy of catheter localization
under MR guidance (no ablation). In the same animals, 2 ablation sites
in the right ventricle (apex and free wall) were targeted for ablation
from a right jugular vein access with a fast gradient recall echo
(FGRE) sequence (TR=5 ms, TE=1.2 ms, field of view=22 cm, slice
thickness=7 mm, 256x128 matrix, tip angle=13°, readout
bandwidth=31.0 kHz). Once electrode-wall contact was visualized and
confirmed by IEGM tracings, the catheter was imaged to isolate the
optimal tomographic slice containing the catheter electrode. After
baseline images were acquired for this slice prescription, RFA was
performed in the right ventricle between the distal electrodes and a
large-surface-area skin patch at a power of 20 W for 60 seconds. To
avoid electrode coagulum formation, impedance was monitored by an
automatic open-loop feedback system that terminated RF delivery if the
impedance exceeded 220 
. The isolated slice and 2 immediately
adjacent slices were then subsequently imaged once every 2 minutes over
20 minutes with a T2-weighted fast spin-echo (FSE) sequence to monitor
temporal signal change and lesion growth over time (TR=5 ms, TE=68 ms,
echo train length=16, field of view=22 cm, slice
thickness=7 mm, 256x192 matrix, readout bandwidth=62.5 kHz).
After this imaging series (30 minutes after ablation), 0.3 mL/kg of
gadolinium-DTPA was administered as a bolus injection into an
intravenous line, and the same slice was imaged every 30
seconds over 12 minutes with the same T1-weighted gradient-echo
sequence as described above with a tip angle of 40°.
Postmortem Examination
After the experiment, the animals were killed by an overdose of
anesthesia, and the hearts were excised and sectioned
through the right ventricular lesion into slices
corresponding to the tomographic MR imaging slices. Lesion location,
morphology, width, length, and transmural extent were determined and
recorded at gross examination, and right ventricular
lesions were photographed for later comparison with MR images. Sections
from thermally damaged tissues were bisected longitudinally and
submitted for histological staining (Masson’s
trichrome and hematoxylin-eosin). Specimens were then analyzed
under light microscopy at x40 to characterize global morphological
changes9 (eg, delineated cell junctions and nuclei and
interstitial edema) for determination of the degree of
heat-induced cell damage and necrosis.
Data Analysis
To determine the temporal response of cardiac tissue after RF
delivery, lesion signal intensity, length, width, and area were
measured directly from MR images with an offline quantitative
analysis package (Scion Image for Windows). Each
parameter was measured 10 times for each time frame from
baseline to 20 minutes after ablation. Mean signal intensity from
region of interest (ROI) measurements was then normalized (mean ROI
signal intensity at time t divided by the baseline signal intensity)
and plotted as a function of time. A similar method was used after
gadolinium injection on T1-weighted imaging. In addition, IEGMs were
analyzed before and after ablation for changes in signal
amplitude and waveform shape. For accurate and consistent
determination of MR lesion size by free-hand planimetry, it was
necessary to establish quantitative exclusion criteria regarding the
spatial distribution of signal intensity through the lesion. This was
achieved by rejecting pixel values around the periphery of the lesion
that were less than the normal myocardium signal intensity
plus 1 SD of the background noise as determined from ROI intensity
measurements. Lesion parameters at gross examination were
measured independently of MR hand-planimetered lesion
parameters and compared.
Statistical Analysis
Changes in mean signal intensity and IEGM before and
after ablation were considered significant at a level of
P<0.05 in a paired t test. Lesion area
measurement comparisons between MR and gross examination were
analyzed by linear regression with a paired t test
at a level of P<0.05.
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Results |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Catheter Placement
An MR fluoroscopy sequence was used to successfully position the nonsteerable catheter at atrial and ventricular target sites in all animals. In 3 animals, MR-guided catheter placement was attempted to target the inferior lateral wall of the right atrium from a jugular access (Figure 2
).
Images were acquired without breath-hold once every heartbeat with
1-second updates. Details of the right atrial anatomy could be
appreciated in all animals, and several major endocardial anatomic
landmarks were successfully identified, including the superior and
inferior venae cavae, atrial septum, right atrial
appendage, coronary sinus, eustachian ridge, fossa ovalis, and
tricuspid valve. The catheter remained in the imaging plane throughout
the entire navigation sequence in 2 of 3 animals. Contact between the
electrode and tissue could be visualized without significant electrode
artifact (Figure 2f), and inferolateral wall catheter
localization was successful and reproducible in each animal. Right
ventricular ablation sites were successfully targeted in
all animals, and the electrode-tissue interface was clearly visualized
during FGRE imaging (Figure 3a),
with visual catheter stability confirmed by high-fidelity IEGMs
(amplitude=10.7 mV) as shown in Figure 3b.
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MRI Lesion Visualization and Temporal Signal Response
Lesions were successfully created and visualized at right
ventricular target sites in all animals.
Ventricular lesions appeared as clearly delineated
hyperintense regions directly adjacent to the ablation catheter tip and
were detectable 2 minutes after RFA (Figure 4). The lesion signal intensity response
is shown in Figure 4c at a temporal resolution of 2 minutes,
with the first 3 time points representing baseline
myocardial signal intensity before ablation. Mean intensity increased
linearly over the first 10 minutes and was then followed by a plateau.
Mean FSE signal intensity 15 minutes after ablation was 1.9±0.4 times
greater than the baseline myocardial intensity (P<0.05),
and the mean time to signal plateau was 12.2±2.1 minutes. FSE imaging
time averaged 1.7±0.3 minutes for a 2-slice acquisition. Approximately
30 minutes after this imaging protocol, FGRE images of the same
tomographic slice were acquired before and after injection of 7 mL
peripheral gadolinium (Figure 5a and 5b). The lesion border was clearly
demarcated 60 seconds after contrast injection. Intensity-versus-time
data for the contrast-enhanced lesion (temporal resolution=30 seconds)
indicated a rapid initial uptake of gadolinium and a gradual washout
over the next several minutes (Figure 5c). Data for an adjacent
region of native myocardium indicated a significantly lower
level of enhancement that followed a similar temporal course over the
imaging interval (1.13±0.12 versus 1.55±0.16, P<0.05).
Under MR fluoroscopy guidance, the catheter was moved from the right
ventricular apex and repositioned on the right
ventricular free wall. FSE images before and after RF
delivery are shown in Figure 6 with the
respective IEGM tracings. A large lesion was visualized directly
adjacent to the ablation catheter tip and demonstrated a temporal
response similar to those measured in right ventricular
apex lesions, with peak intensity occurring 11 minutes after
ablation. IEGM amplitude decreased from a mean preablation value of
10.3±3.1 mV to 2.2±3.3 mV after RF delivery (P<0.05).
Figure 7 is a series of lesion
profile plots that characterize the spatial and temporal formation of
ventricular lesions. A lesion profile is simply a plot of
signal intensity over a fixed spatial domain passing though the lesion,
as illustrated by Figure 7a for a single time frame. The 3D
surface plot represents a series of these profiles in time,
where the z axis represents the color-coded signal
intensity and the x and y axes represent
position and time after RF delivery, respectively. The lesion grew
dramatically in signal intensity and size from the baseline level shown
by the arrow. Maximum signal intensity and lesion area were achieved
12.2±2.1 and 5.3±1.4 minutes after RF delivery, respectively.
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Correlation With Gross and Histopathological Examination
Direct visual comparison of right ventricular lesions
at gross examination and those derived by MR 10 minutes after ablation
demonstrated similar lesion geometries (Figure 8). Lesion width and length measured at
gross examination correlated well with MR-derived measurements (width:
6.7±0.5 versus 7.1±0.9 mm, P<0.05; length: 9.4±1.5
versus 9.9±0.9 mm, P<0.05). MR lesion depth could be
assessed quantitatively in 3 animals and also agreed well with gross
examination measurements (depth: 3.4±2.1 versus 3.1±1.2 mm,
P<0.05). All lesions were composed of a series of 3
concentric elliptical zones of damage: a dark inner portion
representing a region of coagulative necrosis (zone 1), a
surrounding pale peripheral circular zone of
hemorrhage that extended 4 mm from the center of the
lesion (zone 2), and an outermost area consisting of a thin purple rim
extending an additional 2 to 3 mm (zone 3). Low-power
trichrome-stained histological specimens clearly
demarcated the pathological lesion from native undamaged tissue in all
animals. A strong agreement and correlation were observed (Figure 9) between the spatial extent of right
ventricular MRI-derived lesions and the actual extent of
damage measured at gross and histopathological examination (55.4±7.2
versus 49.7±5.9 mm, r=0.958, P<0.05).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Main Findings
In this study, we describe a novel MRI-compatible interventional electrophysiology hardware system used in conjunction with a newly developed real-time interactive cardiac MRI system to characterize the temporal and spatial development of cardiac lesions after RFA. Our findings indicate that (1) MR images and IEGMs can be acquired during RFA therapy by use of specialized RF filters, (2) nonmagnetic MR-compatible catheters can be successfully placed at right atrial and right ventricular targets by use of fast MR imaging sequences with interactive scan plane modification, (3) regional changes in ablated cardiac tissue are detectable and can be visualized with FSE and FGRE images, and (4) the spatial extent of heat-induced necrosis can be accurately quantified by MRI immediately after thermal damage. These results may have significant implications for the guidance, delivery, and monitoring of cardiac ablation therapy by interventional MRI.
MR-Guided Catheter Placement
Right atrial and ventricular sites were successfully
targeted in all animals by use of nonsteerable catheters with real-time
MR fluoroscopy pulse sequences. The high-resolution images of
endocardial anatomy combined with the ability to interactively
modify the scan plane considerably improved targeting and accurate
lesion placement, because standard fluoroscopic views could be defined
in real time by use of a graphical interface. Accurate atrial catheter
placement has clinical importance for the study of a variety of
supraventricular arrhythmias as the relationship
between endocardial anatomy and arrhythmia substrate
becomes increasingly appreciated. Current techniques to map and
identify arrhythmogenic foci are based on low-resolution voltage maps
generated by catheter movements under x-ray fluoroscopy. In addition to
limited anatomic information, catheter manipulation under x-ray
fluoroscopy can be arduous and poorly reproducible. Anatomic MRI-guided
electrophysiological mapping may
significantly improve the localization accuracy of critical
arrhythmogenic substrate and allow acquisition of true electroanatomic
data.
Another important feature of MR-guided catheter placement is the ability to visualize the electrode–endocardial tissue interface, which has been shown to increase lesion size by improving the efficiency of RF tissue delivery.10 Although traditional indicators of electrode contact, such as fluoroscopic catheter stability and IEGM amplitude, are useful, these parameters are relatively insensitive indicators of electrode-tissue contact.10 An important limitation of passive MR catheter tracking, however, is the need to manipulate the catheter within the imaging slice (typically 5 to 10 mm wide), which may be especially difficult during catheter placement in geometrically complex vessels and cardiac chambers, in which catheter curvature and loops are common. To improve the accuracy of MRI catheter positioning, we are currently developing active tracking techniques that provide the x, y, z space coordinates of the ablation catheter tip, which can then be superimposed on interactive 3D images of the atrial chambers.
In Vivo Lesion Visualization
Perhaps one of the greatest advantages of MRI-guided therapy is
the ability to visualize and monitor lesion formation with high
temporal and spatial resolution. In this study, right
ventricular lesions were created and visualized with both a
T2-weighted FSE sequence and a gadolinium-enhanced T1-weighted FGRE
sequence. Lesions imaged with FSE appeared immediately as elliptical,
hyperintense regions directly adjacent to the catheter tip; however,
zones of reversible and irreversible damage were not visible. FGRE
contrast-enhanced lesions 30 minutes after ablation showed rapid uptake
of gadolinium after injection and represented the affected
area similar to FSE images. The mechanisms of lesion enhancement for
these 2 sequences are quite different and may lend insight into the
biophysics of in vivo tissue damage and lesion formation.
FSE Imaging
MRI is able to detect 1 or more specific changes in T1 and T2
relaxation parameters resulting from heat-induced
biophysical changes in cardiac tissue, such as interstitial
edema, hyperemia, conformational changes, cell shrinkage, and
tissue coagulation. Reviewing this general inventory of effects in the
context of parameters detectable by MRI, acute
interstitial edema is most likely responsible for the
hyperintense regions representing the area of damage
observed by T2-weighted FSE imaging. The edema response is mediated by
the release of vasoactive polypeptides from local inflammatory cells
within seconds of the injury, which causes water and proteins to escape
through gaps in the endothelial cells lining the vessel
and enter the interstitial space. This nearly instantaneous
local increase in the number of unbound protons increases the T2
relaxation constant of the tissue and gives rise to the hyperintense
regions that appear to represent the spatial extent of the
anatomic lesion. The delayed lesion response after ablation over 10 to
12 minutes is consistent with the temporal physiology of local
acute interstitial edema and probably represents
the time required for hydrostatic and osmotic capillary pressures to
equilibrate.
Contrast-Enhanced FGRE Imaging
Although ablation lesions were not visible by T1-FGRE imaging
alone, the spatial extent of the lesion was clearly demarcated with
this sequence after peripheral administration of
gadolinium-DTPA. This enhancement is distinctly different from the
dynamic lesion detection described for T2-FSE images and can be
explained by considering the physical and
physiological mechanisms by which gadolinium
achieves enhanced signal intensity in injured myocardium.
Gadolinium-DTPA exerts its signal-enhancing effect by interacting with
water protons and inducing a shorter T1 relaxation time. In uninjured
myocardium, this large molecule cannot penetrate cell
membranes and is therefore restricted to the extracellular space.
After endocardial ablation, however, damaged/ruptured cell membranes
allow diffusion and penetration of the contrast agent into the
intracellular space, significantly increasing the volume of
distribution for the contrast agent and resulting in a "brighter"
voxel of tissue on T1-weighted images. For practical implementation,
FGRE imaging is preferable to FSE for cardiac ablation therapy, because
imaging times are decreased significantly and quality images may be
acquired without cardiac and respiratory gating.
Comparison With Other Imaging Modalities
Several studies have demonstrated the utility of intracardiac
ultrasound for guiding cardiac ablation therapy11 12 13 and
visualizing thermal lesions in vitro.10 14 A recent study
by Epstein and colleagues15 compared intracardiac
ultrasound to fluoroscopy guidance for creating linear right atrial
lesions in a canine model and showed that intracardiac ultrasound
significantly improved targeting, energy delivery, and lesion
formation. Although these reports are promising, the limitations of
this approach include relatively poor spatial resolution, only limited
views of the left and right atrium, the inability to distinguish
multiple intracardiac catheters, the need for complementary x-ray
fluoroscopy, and the inability to accurately quantify the spatial
extent of the thermal damage in vivo. Direct in vivo visualization of
right atrial anatomy and RF lesions with fiberoptic probes, in
which thermal damage is monitored on the basis of heat-induced
myocardial color changes, has also been performed
successfully.16 17 In addition to the relatively small
field of view produced by the probe, this methodology is subjective and
does not accurately represent irreversibly damaged tissue.
MRI is not subject to the aforementioned limitations, but it does have
a number of technical challenges to overcome before widespread use can
be realized. Specialized hardware required for MRI-guided
interventional electrophysiology studies, such as nonmagnetic
catheters, monitoring equipment, and electromagnetic filtering systems,
is generally not commercially available. In addition, although new
advances in scanner hardware have allowed for real-time MR imaging (20
frames per second), passive catheter tracking can be confounded by
complex catheter movements that cause the catheter to leave the imaging
plane. Finally, the delayed nature of lesion formation after the
initial RF delivery may confound instantaneous online assessment of
lesion size. Online assessment of lesion size is possible during
MRI-guided ablation but would require 3- to 5-minute pauses between
RF deliveries to allow the lesion to reach maximum size. Despite these
limitations, MRI offers several unique advantages for guiding cardiac
interventions and may improve both the efficacy and safety of cardiac
ablation therapy.
Clinical Implications
Although the approach described in this report has application for
all cardiac arrhythmias curable by RFA, it may be particularly
well suited for more complex arrhythmias that require the
accurate placement of multiple, linearly arranged lesions (eg, atrial
flutter, ventricular tachycardia complicating
coronary artery disease, and reentrant atrial
tachycardia after surgery for congenital cardiac
disease) rather than ablation of a single focus. The area of highest
potential impact for MR-guided interventional electrophysiology,
however, is in the management of atrial fibrillation. In addition to
improved anatomic targeting of critical focal sites, the ability to
directly visualize the spatial extent of atrial lesions with high
spatial resolution may help facilitate the placement of linear
transmural atrial lesions and allow for real-time interactive detection
and elimination of skip lesions. This potential may have particular
importance, because it has been shown that ablation lines with skip
lesions are not only ineffective but possibly
arrhythmogenic.18 In addition, the ability to characterize
the temporal evolution of lesions can be used for therapy titration and
avoidance of damage to tissue outside the ablation target volume
(although the observed delayed biophysical response of the lesion may
confound instantaneous assessment of lesion size). These combined
advantages may reduce the number of lesions required for conduction
block, procedure times, and the risk of perforation, all without
ionizing radiation.
Conclusions
These studies have, for the first time, demonstrated that RF
cardiac ablation can be performed under MRI guidance in vivo. Catheters
are clearly defined and easily positioned in gradient-echo images, and
the spatial and temporal extent of ventricular ablation
lesions can be accurately visualized by T2-weighted FSE imaging and
T1-weighted contrast-enhanced fast-gradient-echo imaging with a
standard cardiac phased-array thoracic coil. In addition, lesion size
by MRI agrees well with actual postmortem lesion size, and
high-fidelity intracardiac
electrophysiological signals can be
acquired and monitored during imaging. MRI-guided cardiac ablation may
be a useful technique to guide interventional electrophysiology studies
that will eliminate ionizing radiation exposure; will help provide
accurate therapy titration and facilitate the creation of linear,
contiguous, and transmural lesions; and may lend insight into the
physiological effects of novel ablation techniques
and technologies.
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Acknowledgments |
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This work was funded in part by NIH grant HL-45683, an American Heart Association Beginning Grant-in-Aid, and the Whitaker Foundation. Drs McVeigh and Halperin are Established Investigators of the American Heart Association. Dr Halperin is the recipient of the McClure Fellowship in Biomedical Engineering from the Johns Hopkins Applied Physics Laboratory.
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Footnotes |
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Funding was provided in part by Surgi-Vision, Inc. Drs Lardo, McVeigh, Berger, and Halperin are paid consultants for Surgi-Vision. The terms of this arrangement are managed by Johns Hopkins University in accordance with its conflict of interest policies.
This work was presented in the Young Investigator Competition at the 20th Scientific Sessions of the North American Society for Pacing and Electrophysiology (NASPE), May 12 through 15, 1999.
Received September 2, 1999; revision received March 13, 2000; accepted March 16, 2000.
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