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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3752_Библиотеки_им_академика_М_И_Перельмана
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As patients having CCTA for arrhythmia applications
often undergo electrophysiology procedures which may
require fl uoroscopy, techniques to limit radiation dose are
extremely important. Dose reductions can be achieved
through limitation of fi eld of view to essential structures and
use of dose limiting imaging protocols. Prospective gating
techniques or retrospective gating with dose modulation can
be used in some circumstances, but these techniques can be
more limited in the setting of irregular rhythms.
Gated imaging can be problematic in the setting of the
rhythm irregularity and elevated heart rate, but is feasible in
some scenarios. Problems with irregularity can lead to
“step ladder” artifact limiting the ability to obtain diagnostic assessment of segments of the coronary arteries [ 2 , 3 ].
This artifact can be minimized using volume scanners
which can image the fi eld of view in a single heartbeat.
With retrospective gating, cardiac structures including each
coronary artery segment can be analyzed in the most optimal phase, but at the cost of an increased radiation dose.
Assessment of the coronary arteries with retrospective gating is achievable in patients in atrial fi brillation prior to
ablation [ 4 ]. With prospective gating, algorithms rejecting
beats outside of a specifi ed range have been developed for
patients with irregular rhythms [ 5 , 6 ]. In the setting of atrial
fi brillation with higher average ventricular rate response,
end-systole may be a more optimal phase of image reconstruction than end diastole [ 7 , 8 ].
In patients with pacemakers and ICDs and higher programmed pacing rates the pacing rate can be transiently
programmed down to the optimal rate for imaging, such as
60 bpm, if the patient’s native underlying heart rate is below
this value and the patient’s underlying condition allows this
change in programming. Reprogramming pacing function
to a non-rate responsive modes can be helpful as the breath
hold process can trigger a rate response with some devices.
The presence of pacemakers or ICDs can also lead to beam
hardening artifacts which can impact image quality.
Decisions as to the use of CCTA versus CMR in patients
with pacemakers and ICDs depend on device specifi cs. The
application of CMR for patients with cardiac pacemakers and
ICDs has undergone evolution with the advent of MR conditional devices which allow for the use of MR imaging under
specifi ed conditions [ 9 – 12 ]. Even in scenarios where CMR
can be performed, imaging artifacts can be problematic. Novel
algorithms to decrease artifact are being developed [ 13 , 14 ].
CCTA for Cardiovascular Diagnostic
Assessment and Procedural Facilitation
for Atrial Arrhythmias
Atrial Fibrillation Ablation
The potential mechanisms of initiation and perpetuation of
atrial fi brillation are multiple, with their relative roles still
being investigated. These potential mechanisms affecting
arrhythmia initiation and perpetuation include premature
atrial foci from the pulmonary veins and atria, autonomic
infl uences, rotors defi ned by atrial anatomic and electrophysiologic substrate, and reentrant atrial fl utter and atrial tachycardia circuits defi ned by regional electrophysiology, cardiac
structure, and myocardial fi brosis. Given these multiple
mechanisms, a variety of approaches to ablation target atrial
anatomy and electrophysiology, including catheter-based
segmental or complete circumferential electrical isolation of
the pulmonary veins, ablation of ectopic atrial foci, long linear lesions providing pathways of preferential conduction,
ablation of autonomic input, antral lesions targeting anatomy
related to rotors, and ablation of reentrant circuits.
Percutaneous catheter-based approaches are used to access
the left atrium via either a single or double transseptal technique depending on the number and types of left atrial catheters employed.
The performance of atrial fi brillation ablation requires
defi nition of an individual patient’s presence and degree of
atrial myopathy as well as characterization of the relationships between the left atrium and the surrounding cardiac
and thoracic structures. A pre-procedure study serves multiple purposes, acting as a means to decide whether to proceed
with ablation based on the degree of atrial myopathy, a roadmap for procedural planning, a 3-D data set for intra-procedure electroanatomic mapping and ablation, and a template
for comparison to future potential studies assessing for complications such pulmonary vein stenosis. CCTA characterization of the left atrium and pulmonary veins is achieved
through multiple modalities of evaluation including multiplane 2-D views, volumetric quantifi cation of the atria, 3-D
reconstructions, and virtual endovascular atrial views.
Left Atrial Myopathy: Left Atrial Size,
Morphology and Function
Atrial morphology is complex and therefore characterization
of the presence and degree of atrial myopathy based on volumetric assessment of size and function is of paramount
importance. Left atrial volume is an important predictor of
procedural success with atrial fi brillation ablation, as recurrence of atrial fi brillation is associated with an increased left
atrial volume (Fig. 24.2 ) [ 15 , 16 ].
CCTA left atrial indexed volume reference values have
been reported [ 17 – 19 ]. In patients in sinus rhythm at the
time of the CCTA, atrial ejection fraction can be calculated
with retrospective gating (Fig. 24.3 ) [ 20 ]. CCTA left atrial
volumes correlate with CMR volumes [ 21 ]. Preprocedure
assessment of left atrial size and pulmonary vein anatomy
and size are similar for CMR and CCTA, although cumulative radiation dose is decreased with CMR for image guided
ablation [ 22 ]. Variation in pulmonary vein anatomy branch-
ing patterns can be characterized [ 23 ]. Assessment of atrial
24 CCTA Cardiac Electrophysiology Applications: Substrate Identifi cation, Virtual Procedural Planning, and Procedural Facilitation
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wall thickness can be performed at multiple relevant locations including at the pulmonary veins, left pulmonary
vein/ left atrial appendage ridge and posterior left atrium
[ 24 , 25 ]. Thicker left pulmonary vein/left atrial appendage
ridges as assessed by CCTA are associated with a higher
rate of atrial fi brillation recurrence and therefore have
potential implications for ablation approach to this anatomy (Fig. 24.4 ) [ 25 , 26 ]. CCTA provides volumetric evi-
dence of reverse remodeling with successful atrial
fi brillation ablation [ 27 ]. Successful ablation is associated
ab
Fig. 24.2 Axial ( a ) and sagittal ( b ) views demonstrating profound atrial enlargement in a patient with atrial fi brillation. The left atrial volume was
greater than 450 cc
ab
Fig. 24.3 Assessment of left
atrial volume during atrial systole
( a ) and diastole ( b )
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with changes in atrial morphology with reversal of spherical remodeling [ 28 ]. In patients with paroxysmal atrial
fi brillation, reverse remodeling with improvement of atrial
transport function has been demonstrated by CCTA with
successful ablation [ 29 ].
In addition to atrial size and function, the visualization of
atrial fi brosis is important to assessment for atrial myopathy.
CMR has been the primary imaging modality for this assessment through characterization of focal fi brosis with late
gadolinium enhancement and diffuse fi brosis with T1 mapping. Challenges exist though as left atrial wall thickness is
at the limit of the spatial resolution of CMR. Atrial fi brosis
can be characterized by CMR delayed gadolinium enhancement [ 30 ]. The degree of left atrial fi brosis has been associ-
ated with sick sinus syndrome, history of stroke, and
decreased atrial pump function [ 31 – 33 ]. The degree of
preablation late gadolinium enhancement fi brosis has been
associated with arrhythmia recurrence [ 34 – 36 ]. Post abla-
tion left atria have increased scar density compared to preablation native fi brosis [ 37 ]. Delayed gadolinium enhancement
can assess the adequacy of lesion sets associated with pulmonary vein isolation. Identifi cation of gaps in lesion sets
may be the substrate post ablation arrhythmias and therefore
serve as targets for subsequent ablation therapy [ 38 ]. The
completeness of pulmonary vein isolation as well as posterior and septal wall debulking lesions as assessed by CMR
are markers of greater ablation success, particularly in the
setting of higher pre- ablation scar burden [ 39 , 40 ]. Patients
diagnosed with “lone” atrial fi brillation have evidence of
atrial fi brosis on CMR and procedural outcome of atrial
fi brillation ablation for “lone” atrial fi brillation demonstrated similar ablation results to those with comorbidities,
with the degree of fi brosis being the determining factor of
success [ 41 ]. Post contrast T1 assessment of diffuse fi brosis
correlates with decreased tissue voltage, and presence of
atrial fi brillation. It also predicts success of ablation [ 42 ].
CCTA fi rst pass attenuation can identify areas of atrial low
voltage areas, but requires further investigation [ 43 ].
Left Atrial Anatomy Relevant to Atrial
Fibrillation Ablation
Pulmonary venous anatomy demonstrates great variability
regarding vein number, location, size, shape, and ostial
complexity. CCTA can visualize these pulmonary vein characteristics and can defi ne the relationship between veins as
well as between the left upper pulmonary vein and left atrial
appendage (Figs. 24.5 , 24.6 , and 24.7 , Video 1). Workstation
software can be used to quantify characteristics of the pulmonary vein ostia, including area, maximum diameter, minimum diameter, and eccentricity. Key to these measurements
is identifi cation of the left atrial/pulmonary vein interface,
determination of the long axis of the vein at the ostium, and
recognition that the vein ostium is often an ovoid rather than
circular shape (Fig. 24.8 ). Three-D reconstructions can
serve as a roadmaps for ablation as well as templates for
post ablation changes [ 44 , 45 ]. In relation to other modali-
ties, CCTA and CMR offer similar ability to assess pulmonary vein morphology [ 46 ]. CCTA in comparison to invasive
venography, intracardiac echo, and transesophageal echo
performed during the procedure was superior to all of these
other modalities in identifying veins. CCTA and intracardiac echo provided comparable assessment of pulmonary
vein diameter, while diameters were larger based on venography and smaller based on transesophageal echo [ 47 , 48 ].
Pulmonary vein stenosis is a potential complication of
atrial fi brillation ablation [ 49 , 50 ]. The reported incidence
is dependent on imaging technique, defi nition of a signifi cant stenosis, and degree of surveillance [ 51 ]. As tech-
niques have evolved with recognition of the need to ablate
in the atrium outside of the pulmonary veins, the incidence
of pulmonary vein stenosis has signifi cantly decreased.
Stenosis can occur when ablation lesions are applied
directly to the pulmonary veins [ 52 ]. Imaging technologies
which can visualize the atrial/pulmonary vein interface are
therefore important to ablation lesion application within
the atria rather than the pulmonary veins. CCTA integration
with catheter-based mapping has also been shown to
decrease the incidence of pulmonary vein stenosis [ 53 ]. As
pulmonary vein stenosis can preexist ablation due to either
extrinsic compression by other thoracic structures or due to
a congenital etiology, the preprocedure study serves as a
Fig. 24.4 Endovascular view showing a prominent ridge ( arrows )
between the left atrial appendage and left upper pulmonary vein. LAA
left atrial appendage, LUPV left upper pulmonary vein, LLPV left lower
pulmonary vein
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template appropriate interpretation of pulmonary vein fi ndings post ablation [ 54 ]. Although CCTA is superior for pul-
monary vein identifi cation, transesophageal echo can be a
complementary modality for assessment of the pathophysiologic signifi cance of stenosis [ 52 ]. The incidence of pul-
monary vein stenosis is decreasing, but establishment of
screening algorithms and guidelines to assess the true current incidence and time course of the development of pul-
monary vein stenosis after atrial fi brillation ablation is
necessary [ 55 ]. CCTA is useful for the recognition of the
anatomic degree of pulmonary vein stenosis (Fig. 24.9 )
[ 56 ]. In scenarios with moderate stenosis, the functional
signifi cance of the pulmonary vein stenosis can be assessed
by transesophageal echo and lung perfusion via assessment
with V/Q scan [ 57 ]. CCTA integration with fl uoroscopy
can also facilitate procedural performance of pulmonary
Fig. 24.6 Characterization of the left atrium and pulmonary veins demonstrated through double oblique thick MIP ( left panel ), and a 3-D endo-
cardial view demonstrating 3-right sided pulmonary veins ( right panel )
Fig. 24.5 Characterization of the left atrium and pulmonary veins
demonstrated through 2-D axial views and 3-D volumetric reconstruction, demonstrating 2 left-sided pulmonary veins and variant anatomy
with 3-right sided pulmonary veins. LAA left atrial appendage, LUPV
left upper pulmonary vein, LLPV left lower pulmonary vein, RUPV
right upper pulmonary vein, RMPV right middle pulmonary vein, and
RLPV right lower pulmonary vein
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vein stenting [ 58 ]. The patency of pulmonary vein stents
can also be visualized with CCTA (Fig. 24.10 ).
Atrial anatomy other than the pulmonary veins important
to facilitation of atrial fi brillation ablation can be defi ned by
CCTA. Atrial septal characteristics important to transseptal
puncture include defi nition of the location and size of the
fossa ovalis, presence of a patent foramen ovale, and presence and degree of lipomatous hypertrophy of the atrial septum (Fig. 24.11 ). Atrial masses and thrombi can be identifi ed,
which could contraindicate transseptal catheterization.
CCTA can display the location of and wall thickness of left
atrial diverticulae (Fig. 24.12 , Video 2). CCTA has shown
these structures to have thinner walls than atrial myocardium
with frequent location near pulmonary veins and atrial
appendage ostia [ 59 ]. Atrial diverticulae could potentially
complicate catheter placement and manipulation if they are
mistaken for the orifi ces of pulmonary veins. Defi nition of
anatomy of the mitral isthmus is important as ablation lines
are sometimes applied to this region. The 3-D relationship of
the circumfl ex coronary artery, coronary sinus/great cardiac
vein in relation to the left atrium and mitral annulus can be
defi ned by CCTA [ 60 ]. Given these anatomic relationships,
there is the potential for coronary artery damage with the
application of ablation lesions in this area, potentially leading to myocardial infarction with the need for emergent
stenting. Additionally, sinus node dysfunction may occur as
a left sinus node artery can course in this space [ 61 ].
Bachmann’s bundle is an interatrial muscle band providing a
pathway of preferential conduction between the atria. This
bundle and its vascular supply can be visualized with CCTA
and could potentially be in the path of a left atrial ablation
roof line [ 62 ].
Thoracic Anatomy Relevant to Atrial
Fibrillation Ablation
Thoracic anatomy relevant to ablation includes the relationship of the esophagus and aorta to the posterior left atrium
and pulmonary veins. Left atrial-esophageal fi stula has been
reported as a fatal complication of atrial fi brillation ablation
[ 63 ]. The relationship between the thin wall of the posterior
left atrium, pulmonary veins, esophagus and aorta can be
visualized prior to ablation (Figs. 24.13 and 24.14 ). There is
variability of the course of the esophagus and degree of contact between the posterior left atrium/pulmonary veins,
esophagus and aorta [ 64 , 65 ]. Barium swallow at the time of
CT has been used to opacify the esophagus for electroanatomic image integration with ablation procedures [ 66 ].
Esophageal motility, change of the position of the esophagus
with respiration, and patient position, can change the spatial
relationship of the esophagus to the posterior left atrium
from the CCTA to the procedure as well as during the ablation procedure [ 67 , 68 ].Additionally a variable layer of a
Fig. 24.7 Characterization of the relationship between and ostial characteristics of a right upper and right middle pulmonary vein on a 3-D
endocardial view
Fig. 24.8 Identifi cation the left atrial/pulmonary vein interface, determination of the long axis of the vein at the os, and en face visualization of
an ovoid pulmonary vein os.
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Fig. 24.10 Curved
multiplanar views of
pulmonary vein stents
ab
Fig. 24.9 2-D ( a ) and 3-D ( b ) volume rendered images demonstrating signifi cant pulmonary vein stenosis ( arrow ) of a left lower pulmonary vein
(Courtesy of Dr. Jeffrey Schussler, Baylor University Medical Center, Dallas, Texas)
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pericardial fat pad can be visualized around the pulmonary
veins and posterior left atrium with CT which could conceivably provide some insulation to the esophagus with application of ablation lesions in the left atrium [ 64 , 69 ]. CCTA
identifi cation of the coronary venous system is important for
catheter placement, mapping, and for ablation lines [ 70 ]. The
relationship between the upper pulmonary veins and the
bronchi can be characterized by CCTA and is important to
understand in order to avoid the rare but possible complication of atrio- bronchial fi stula with ablation [ 71 – 73 ]. The
phrenic nerve has been visualized with CCTA, which can be
important to avoid diaphragmatic paralysis with atrial fi brillation ablation [ 74 ]. Epicardial adipose tissue can be quanti-
fi ed and has been associated with atrial fi brillation [ 75 ].
Incidental thoracic fi ndings visualized on CCTA have also
been demonstrated to infl uence decisions regarding proceeding with atrial fi brillation ablation [ 76 ].
CCTA Image Integration for Procedural
Facilitation of Atrial Fibrillation Ablation
Electroanatomic mapping with CCTA image integration
has revolutionized catheter–based therapies by allowing
for electrical mapping and ablation to occur on a 3-D map
of the patient’s individual endocardial left atrial anatomy
(Figs. 24.15 , 24.16 , 24.17 , and 24.18 , Videos 3, 4, 5, 6). The
process involves importation of the unprocessed DICOM
images into the electrophysiology mapping system, use of
Fig. 24.11 3-D double oblique view demonstrating lipomatous hypertrophy of ther inter-atrail septum ( arrows )
ab
Fig. 24.12 2-D double oblique ( a ) and 3-D ( b ) views demonstrating an atrial diverticulum ( arrows ) located on the anterior superior portion of the
left atrium
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edge detection software to delineate and edit down to relevant
cardiac and vascular structures including the left atrium and
in some electrophysiology laboratories the aorta and esophagus. Subsequently, a separate catheter-based anatomic map is
created using fi duciary landmark points in the left atrium followed by registration of surface points defi ning the endocardial boundaries of the left atrium. The anatomic catheter-based
map is then integrated with the CCTA images with assessment
of markers of successful integration defi ned by an acceptable
catheter to endocardium distances which have been demonstrated to be accurate [ 77 , 78 ]. If registration is inadequate,
catheter based points are edited and new points registered to
ensure that the atrial endocardial surface has been adequately
mapped. Atrial size is important to integration techniques as
greater misregistration occurs with larger dimensions [ 79 ].
Electroanatomic mapping with image integration
allows for arrhythmia activation and propagation, voltage
maps, catheter position, and ablation lesion set location to
be displayed on the 3-D CCTA reconstruction. Ablation
guided by integration of pre-procedure CCTA with real
time catheter- based electroanatomic maps can increase
the effi cacy of and decrease complications associated
with atrial fi brillation ablation. This technique has been
shown to be helpful in increasing restoration of sinus
rhythm and decreasing recurrence of atrial fi brillation
compared to electroanatomic mapping alone [ 53 , 80 ].
Clinical outcome though is still dependent on achieving
successful pulmonary vein isolation [ 81 ]. The localization
of the ablation catheter tip on the endocardial left atrial
reconstruction can help to ensure that radiofrequency
abc
Fig. 24.13 3-D reconstructions ( a and b ) demonstrating the relationship of the aorta to the posterior left atrium and left lower pulmonary vein. A
double oblique view ( c ) demonstrating the relationship of the esophagus and aorta to the posterior left atrium and pulmonary veins
ab c
Fig. 24.14 3-D reconstructions ( a and b ) demonstrating the relation-
ship of the aorta to the posterior left atrium and left lower pulmonary
vein. A 2-D axial view ( c ) demonstrates the relationship of the esopha-
gus and aorta to the posterior left atrium and pulmonary veins. In this
case, the esophagus ( arrow ) is “sandwiched” between spine and aorta at
the level of the left lower pulmonary vein.
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ab
Fig. 24.15 Initial image processing for electroanatomic mapping with
CCTA image integration showing segmentation of vascular structures
( a ) with the aorta ( green ), pulmonary arteries ( orange ), right atrium and
right ventricle ( yellow ) edited out, with the left atrium ( purple ) subse-
quently rotated to demonstrate the posterior left atrium ( b )
ab
Fig. 24.16 Image processing for electroanatomic mapping with CCTA image integration with a catheter-based anatomic map of the left atrium
( a , upper image ) and the 3-D volume rendered CT image of the left atrium ( a , lower image ) with integration of these images ( b )
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applications are placed in the atrium and not in the pulmonary veins or ostia to avoid pulmonary vein stenosis.
Subsequent to ablation, mapping using this system can be
performed to ensure electrical isolation of the pulmonary
veins.
Placement of uninterrupted ablation lines around pulmonary veins and as long linear lesions within the atrium are
important to the performance of atrial fi brillation ablation,
as gaps within these lesion lines can lead to unsuccessful
procedures. Gaps within ablation lines can also serve as a
substrate for post-ablation atrial fl utter reentry [ 82 , 83 ].
Image integration allows for registration of the position of
ablation lesions, therefore facilitating placement of lesion
sets to create continuous lines.
CCTA or CMR image integration with catheter-based
intracardiac maps can be additionally merged with intracardiac echocardiography, providing real time visualization of
the esophagus, visualization of transseptal puncture, appendage thrombi, ablation catheter contact and lesion depth, pulmonary vein stenosis, and pericardial effusion (Figs. 24.19
and 24.20 ) [ 84 – 89 ]. Multimodal imaging with integration of
CCTA images and real-time fl uoroscopy is also being preliminarily investigated [ 90 ]. The integration of cone beam
CT obtained at the time of ablation with electroanatomic
mapping has also been performed [ 91 ].
ab
Fig. 24.18 Electroanatomic mapping with image integration demonstrating mapping of arrhythmia electrical activation ( a ) and arrhythmia wave-
front propagation ( b )
Fig. 24.17 Electroanatomic mapping with image integration demonstrating an endocardial view of the left upper pulmonary vein after
radiofrequency catheter isolation of the vein with encircling radiofrequency energy applications ( red spheres )
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