J A C C : C A R D I O V A S C U L A R I M A G I N G V O L . 8 , N O . 7 , 2 0 1 5

ª 2 0 1 5 B Y T H E A M E R I C A N C O L L E G E O F C A R D I O L O G Y F O U N D A T I O N I S S N 1 9 3 6 - 8 7 8 X / $ 3 6 . 0 0

P U B L I S H E D B Y E L S E V I E R I N C . h t t p : / / d x . d o i . o r g / 1 0 . 1 0 1 6 / j . j c m g . 2 0 1 5 . 0 5 . 0 0 1

CT Angiography forRevascularization of CTOCrossing the Borders of Diagnosis and Treatment

Maksymilian P. Opolski, MD,* Stephan Achenbach, MDy

ABSTRACT

Fro

of

Sp

rel

Ma

Coronary computed tomography angiography (CTA) is increasingly used to diagnose and rule out coronary artery

disease. Beyond stenosis detection, the ability of CTA to visualize and characterize coronary atherosclerotic plaque, as

well as to obtain 3-dimensional coronary vessel trajectories, has generated considerable interest in the context of pre-

procedural planning for revascularization of chronic total occlusions (CTOs). Coronary CTA can characterize features

that influence the success rate of percutaneous coronary intervention (PCI) for CTOs such as the extent of calcification,

vessel tortuosity, stump morphology, presence of multiple occlusions, and lesion length. Single features and combined

scoring systems based on CTA may be used to grade the level of difficulty of the CTOs before PCI and have been shown

to predict procedural success rates in several trials. In addition, the procedure itself may be facilitated by real-time

integration of 3-dimensional CTA data and fluoroscopic images in the catheterization laboratory. Finally, the ability of

coronary CTA to assess anatomy, perfusion, and viability in 1 single examination makes it a potential “one stop shop”

that predicts not only the likelihood of successful PCI but also the clinical benefit of CTO revascularization. Further

research is clearly needed, but many experienced sites have already integrated coronary CTA into the routine planning

and guiding of CTO procedures. (J Am Coll Cardiol Img 2015;8:846–58) © 2015 by the American College of Cardiology

Foundation.

C hronic total occlusions (CTOs), sometimesreferred to as the “final frontier in inter-ventional cardiology,” represent a major

challenge for percutaneous coronary intervention(PCI) (1). Although leaving CTOs untreated is associ-ated with poor prognosis (2,3), current PCI attemptrates for CTOs are surprisingly low, and most pa-tients are managed medically (4). To further compli-cate matters, success rates of PCI in CTOs areusually moderate (with higher success in some lumi-nary expert centers) (5,6), and failed revasculariza-tion increases the risk of adverse outcomes (7).Therefore, careful selection of patients in whichsuccessful PCI for CTOs can be expected is of highclinical relevance. Furthermore, a variety of modernimaging modalities, dedicated devices, and tech-niques have been developed in an effort to over-come difficulties encountered in percutaneous

m the *Department of Interventional Cardiology and Angiology, Institute

Internal Medicine 2 (Cardiology), University of Erlangen, Erlangen, Germ

eakers Bureau honoraria from Siemens Healthcare and Abbott Vasc

ationships relevant to the contents of this paper to disclose.

nuscript received April 4, 2015; revised manuscript received May 1, 2015,

treatment of CTOs (8–10). Coronary computed to-mography angiography (CTA) can characterize fea-tures that influence the success rates of PCI forCTOs (most of which are not readily seen on inva-sive coronary angiography), and it is thereforeincreasingly used to predict the likelihood of suc-cessful recanalization (10). The present review out-lines established and potential applications ofcoronary CTA for the pre-procedural planning andguidance of PCI for CTOs.

DEFINITION, PREVALENCE, AND CLINICAL

CHARACTERISTICS OF CTOs

A CTO of a coronary artery is defined as the totalocclusion of the vessel on invasive angiography withcomplete interruption of antegrade blood flow(Thrombolysis In Myocardial Infarction flow grade 0)

of Cardiology, Warsaw, Poland; and the yDepartment

any. Dr. Achenbach has received grant support and

ular. Dr. Opolski has reported that he has no

accepted May 5, 2015.

AB BR E V I A T I O N S

AND ACRONYM S

CT = computed tomography

CTA = computed tomography

angiography

CTO = chronic total occlusion

PCI = percutaneous coronary

intervention

J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 8 , N O . 7 , 2 0 1 5 Opolski and AchenbachJ U L Y 2 0 1 5 : 8 4 6 – 5 8 CTA for PCI of CTO

847

and an age of the occlusion $3 months proven byprior angiography or estimated from the clinicalcourse (11). Although the true prevalence of CTOs inthe general population is unknown, chronic occlu-sions are common among patients with known orsuspected coronary artery disease, and they are foundin 15% to 30% of all subjects undergoing coronaryangiography (1,4). CTOs are associated withadvancing age and cardiovascular risk factors, andthey are most prevalent in the right coronary artery,followed by the left anterior descending coronaryartery (4).

RATIONALE FOR CTO REVASCULARIZATION

The aim of CTO revascularization is the same as forcoronary stenoses, namely improvement in symp-toms or prognosis, which requires that a sufficientlylarge and CTO-specific territory of viable andischemic myocardium is present. There is conclusiveevidence indicating substantial symptomatic im-provement, recovery of left ventricular function, anda reduced need for bypass surgery among CTO pa-tients after successful PCI (1). In addition, survival isbetter after successful (compared with failed) PCI ofCTO lesions, which may, however, be partly attrib-uted to the deleterious effects of failed PCI (2,7).For these reasons, CTO revascularization is fullysanctioned according to current guidelines whenpersistent symptoms and/or objective evidence ofviability/ischemia exist (12).

CURRENT TRENDS IN THE

MANAGEMENT OF CTOs

Despite marked advances in endovascular tech-niques and device technology for PCI, most patientswith CTO are managed medically (4). The barriers tomore frequent application of PCI in CTOs arenumerous. First, percutaneous recanalization ofCTOs requires specific expertise and, even then, itremains technically challenging with lower proce-dural success rates (60% to 85%) compared withsubtotal stenoses (98%) (13). Second, the unpredict-able and often long procedural times complicate lo-gistics in the catheterization laboratories and maylimit physician willingness to attempt CTO recana-lization (14). Third, the incomplete visualization ofCTO on invasive angiography, with no objectivemeans to precisely identify the vessel trajectoryduring the “hit-or-miss” wire manipulation, in-creases the risk of serious complications (10). Thus,there is substantial interest to use imaging for pre-procedural CTO characterization, and coronary CTAis the prime candidate.

DIAGNOSIS OF CTO ON

CORONARY CTA

A CTO may be incidentally identified on adiagnostic coronary CTA, or a coronary CTAmay be specifically performed beforeattempting CTO recanalization. AlthoughCTOs are defined based on the angiographiccriterion of antegrade blood flow interruption,

coronary CTA typically replicates angiographic find-ings by demonstrating a complete lack of contrastopacification within the coronary occlusion on multi-planar reformations (Figure 1) (10). Until now, no sys-tematic computed tomography (CT) comparisonbetween the characteristics of acute versus chronictotal coronary occlusions has been available, andreliable identification of CTOs relies more on clinicalhistory than on specific CT morphological findings.However, typically, the distal vessel lumen of a CTO isopacified with contrast on coronary CTA, and acuteocclusions may exhibit a particularly pronounced de-gree of positive remodeling (10).

In fact, coronary CTA may have difficulty indifferentiating high-grade stenoses from completeocclusions, which is a consequence of its limitedspatial resolution (Figure 2). Lesion length can be anindicator of total occlusion, with lesions $9 mmregarded as likely to represent complete occlusion(15). Furthermore, the recently described “reverseattenuation gradient sign” has been proposed as ahighly specific feature of CTO on coronary CTA (16).

CHARACTERIZATION OF CTO ON

CORONARY CTA

Invasive coronary angiography provides incompleteinformation on vessel morphology in occluded coro-nary artery segments. Coronary CTA, on the otherhand, reliably visualizes the occluded coronarysegment and is able to identify and quantitativelyevaluate morphological (e.g., calcification) andanatomical (e.g., tortuosity, length) features of theocclusion (10). Similarly, the distal vessel territory isoften more clearly depicted on coronary CTA thanin invasive angiography (Figure 3) (17). Two- and3-dimensional reconstructions enable visualizationof the exact vessel trajectory with accurate mea-surement of the occlusion length and precise map-ping of vessel tortuosity (10). Coronary CTA canalso be used to identify ostial occlusions, a featurethat may be missed in invasive angiography(Figure 4). Advantages of coronary CTA over stan-dard, catheter-based angiography are most apparentin long and tortuous CTO lesions or when the distal

FIGURE 2 Challeng

(A) In coronary CTA,

rupted (arrow). (B) I

Abbreviation as in Fi

FIGURE 1 Chronic Total Occlusion in Coronary CTA

(A) Multiplanar reformation demonstrating noncalcified occlusion that lacks contrast

opacification in the mid-segment of the right coronary artery (arrow). The vessel distal

to the occluded segment is opacified with contrast. (B) Corresponding invasive angio-

graphic view. CTA ¼ computed tomography angiography.

Opolski and Achenbach J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 8 , N O . 7 , 2 0 1 5

CTA for PCI of CTO J U L Y 2 0 1 5 : 8 4 6 – 5 8

848

CTO segment cannot be visualized in invasive angi-ography (10,17).

PREDICTION OF PROCEDURAL OUTCOME

OF PCI BY CORONARY CTA

Angiographic studies have consistently reported thatpreviously failed recanalization, increasing age ofthe occlusion, presence of marked calcification, longocclusion length, a blunt proximal stump, excessivevessel tortuosity, presence of a side branch at theocclusion site, and antegrade bridging collateralsdecrease the likelihood of successful guidewire

ing Diagnosis of a High-Grade Stenosis in Coronary CTA

the lumen of the medial right coronary artery is completely inter-

nvasive angiography shows a short, very high-grade stenosis (arrow).

gure 1.

crossing in CTO (18). Recently, the J-CTO (MulticenterCTO Registry of Japan) score has been introduced asan accurate angiographic prediction rule for time-efficient guidewire crossing that determines the dif-ficulty level of CTOs (14). Importantly, with theavailability of improved techniques and devices forPCI, some of the historical predictors of failed revas-cularization (e.g., side branch at the occlusion entry,presence of antegrade bridging collaterals) no longerseem valid. Consequently, a number of CT featuresof CTO have been identified for the prediction ofPCI success by using contemporary percutaneoustechniques (Table 1).

CALCIFICATION. Calcification is the hallmark of ahigh difficulty level of CTOs. It poses difficulties at allsteps of the procedure, hampering successful guide-wire passage, lesion pre-dilation, and adequate stentexpansion (18). In this regard, an increase in calciumcontent over time may explain the progressive diffi-culty in successfully treating older occlusions (1). Ofnote, several studies have consistently indicated thatcoronary CTA is more sensitive to detect, quantify,and localize calcification compared with invasiveangiography (19–21).

The influence of CTA-derived calcification on PCIoutcome in CTO was first reported by Mollet et al.(22). They used 16-slice CT scan and demonstratedthat calcification involving >50% of the vesselcross-sectional area along with an occlusion length>15 mm were independent predictors of guidewirecrossing failure in a series of 47 lesions. Another smallCT study conducted by Soon et al. (19) included 39patients with 43 chronically occluded vessels; theyfound that calcification $50% of vessel cross-sectionwas the only independent correlate of unsuccessfulPCI, conferring a 10-fold higher risk for proceduralfailure.

Subsequently, a larger study using 64-detector rowCT scan in a series of 142 CTO lesions corroborated thedecisive role of calcification in reducing the proba-bility of successful PCI (17). Of note, Cho et al. (23)performed a comprehensive calcium quantificationassessment in a group of 64 patients with 72 CTOlesions and found that only the relative percentageof calcium area divided by the vessel area in thecross-section with the highest calcium content was anindependent determinant of PCI failure. Interest-ingly, they identified a cross-sectional calcium areaof 54% as the best cutoff value for predictingPCI failure. Hence, a simplified approach of visualcalcium assessment that uses a 50% cutoff valuemakes intuitive sense. Consequently, it is notthe length of calcium but rather the extent of

FIGURE 3 Visualization of the Distal Vessel Segment by Coronary CTA and Invasive Angiography in a Patient With

Chronically Occluded LAD

(A) Curved multiplanar reformat of the left anterior descending coronary artery (LAD), along with serial cross-sectional images in coronary CTA.

The short occlusion segment (black asterisk) is followed by a wide lumen of the mid- and distal LAD that terminates below the apex

(white asterisks). (B) A 3-dimensional reconstruction reveals the exact anatomical course of the LAD in coronary CTA. (C and D) In invasive

angiography, the mid-LAD is displayed via retrograde filling from the left circumflex coronary artery (white asterisks). Even by combining (C)

early and (D) late frames of the cine sequence, the length and the diameter of the LAD are significantly underestimated. Abbreviation as in

Figure 1.

J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 8 , N O . 7 , 2 0 1 5 Opolski and AchenbachJ U L Y 2 0 1 5 : 8 4 6 – 5 8 CTA for PCI of CTO

849

cross-sectional vessel calcification that indicatescrossing difficulty. Two additional studies have sug-gested that calcification at the entry (but not at theexit) site of CTO constitutes the major hurdle of suc-cessful guidewire crossing when using the antegradeapproach (17,24). It should be noted that Hsu et al.(25), in a group of 67 patients with 82 de novo CTOlesions, found that a calcification length ratio >0.5(defined as calcification length to occlusion length)was an independent predictor of failed PCI. How-ever, they did not account for the extent of cross-sectional calcification. Finally, although severaldifferent approaches for calcium quantification havebeen reported thus far, most of the CT studiesconsistently suggest the practical utility of severecalcification involving $50% of the vessel cross-sectional area for prediction of PCI failure in CTO(17,19,21,22).

TORTUOSITY. CTO interventions require negotiatingthe wire along the correct track of the occludedsegment. Marked vessel tortuosity (often referred toas bending) substantially increases the difficultyof this task and is associated with a greater riskof coronary injury, especially if stiffer wires areselected (18).

Yokoyama et al. (26) were the first to highlight theability of coronary CTA to depict marked CTObending that could not be identified on coronaryangiography. In a study by Ehara et al. (27) of 110patients with the same number of CTOs, bending(defined as an angle >45� either at the occlusion siteor proximal to the occluded segment) was the mostprominent independent predictor of wiring failure(followed by vessel shrinkage and severe calcium).Subsequently, García-García et al. (17) showed thatvessel tortuosity throughout the occluded segment

FIGURE 4 Visualization of an Ostial Occlusion by Coronary CTA

(A and B) Invasive angiography in a 53-year-old woman fails to visualize the large intermediate branch that is occluded at its origin. (C and D)

Visualization of the occluded intermediate branch by coronary CTA (arrows). LCX ¼ left circumflex coronary artery; other abbreviations as

in Figures 1 and 3.

Opolski and Achenbach J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 8 , N O . 7 , 2 0 1 5

CTA for PCI of CTO J U L Y 2 0 1 5 : 8 4 6 – 5 8

850

(but not proximal to the lesion) was associated withprocedural failure. In their study, however, tortuosityfailed to independently predict PCI success beyondsevere calcium.

OCCLUSION LENGTH AND MULTIPLE OCCLUSION

SITES. Historically, the Euro CTO Club consideredan occlusion length >20 mm as an important predic-tor of failed recanalization (18). Consequently, mul-tiple reports showed that accurate measurementof occlusion length is easily possible on coronaryCTA and that lesion length may be significantlyunderestimated in invasive angiography (19,20,22).However, the relevance of CTA-derived occlusionlength as an independent predictor of PCI failure isunclear. In some studies, the presence of a longoccluded segment on coronary CTA (defined as either>15 mm or >18 mm or $32 mm or as a continuousvariable) was found to be an independent predictor

of procedural failure (22,28–30), whereas other re-ports failed to demonstrate any relevant relationshipbetween CTA-derived occlusion length and PCI out-come (17,19,21,24,27). These findings suggest thatcontemporary PCI techniques may be less affectedby lesion length when attempting CTO recanalization.

Recently, it was shown that up to one-fourth of allCTO lesions include multiple occlusion sites, a char-acteristic clearly seen on coronary CTA but usuallymissed in invasive angiography (31). The influence ofthe presence of multiple occlusions on recanalizationsuccess was tested in the CT-RECTOR (CT-Registryof Chronic Total Occlusion Revascularization) regis-try. The presence of multiple occlusions showed arobust and independent association with guidewirecrossing, while occlusion length did not (21). Theunderlying reason for the negative effect of multipleocclusions on recanalization success is likely due tothe fact that multiple entry and exit sites increase

TABLE 1 Studies Investigating the Ability of Coronary CTA to Predict Successful PCI in CTOs

First Author, Year (Ref. #) Type of CT No. of CTO Study Endpoint Success Rate (%) Independent Predictors of PCI Failure

Mollet et al., 2005 (22) 16-slice 47 Guidewire crossing 55 Calcium >50% CSAOcclusion length >15 mm

Soon et al., 2007 (19) 16-slice 43 Guidewire crossing with stenting(TIMI flow grade 3 and <25% stenosis)

56 Calcium $50% CSA

Ehara et al., 2009 (27) 64-slice 110 Guidewire crossing 85 Bending (>45�)Shrinkage (<1 mm in vessel diameter)Severe calcium (w360� CSA)

García-García et al.,2009 (17)

16/64-slice 142 Guidewire crossing (TIMI flow grades 2–3and <50% stenosis)

63 Calcium >50% CSA

Cho et al., 2010 (23) 64-slice 72 Guidewire crossing with stenting(TIMI flow grade 3)

76 % Calcium area/CSA

Li et al., 2010 (30) 64-slicedual source

74 Guidewire crossing (TIMI flow grades 2–3and <20% stenosis)

77 Occlusion lengthSeverity of calcification (noncalcified,

spot-calcified, arc-calcified, circular-calcified)

Hsu et al., 2011 (25) 64-slice 82 Guidewire crossing (TIMI flow grades 2–3and <30% stenosis)

89 Calcification length ratio (calcificationlength/occlusion length) >0.5

Choi et al., 2011 (28) 64-slice 186 Guidewire crossing (TIMI flow grade 3and <30% stenosis)

77 Occlusion length >18 mmSegmental density >139 HUCTO duration >12 months or unknown

Martín-Yuste et al.,2012 (24)

64-slice 77 Guidewire crossing 62 Calcium arc/CSA

Li et al., 2013 (32) 64-slicedual source

88 Guidewire crossing (TIMI flow grade 3and <25% stenosis)

58 Linear intrathrombus enhancement

Opolski et al., 2015 (21) 64/128-slicedual source

240 Guidewire crossing within 30 min 62 Calcium $50% CSABending ($45�)Multiple occlusion sitesBlunt stumpCTO duration $12 months or unknownPreviously failed PCI at CTO

Luo et al., 2015 (29) 256-slice 108 Guidewire crossing (TIMI flow grade 3and <20% stenosis without MACE)

74 Negative remodelingOcclusion length $32 mm

CSA ¼ cross-sectional area; CT ¼ computed tomography; CTA ¼ computed tomography angiography; CTO ¼ chronic total occlusion; MACE ¼ major adverse cardiac events; PCI ¼ percutaneous coronaryintervention; TIMI ¼ Thrombolysis In Myocardial Infarction.

J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 8 , N O . 7 , 2 0 1 5 Opolski and AchenbachJ U L Y 2 0 1 5 : 8 4 6 – 5 8 CTA for PCI of CTO

851

the difficulty in achieving successful guidewirepassage into the distal true lumen.

STUMP MORPHOLOGY. In invasive coronary angiog-raphy, the presence of a blunt stump is related tofailed guidewire crossing, whereas a tapered shapeof the proximal stump is considered a key marker fora potentially patent residual lumen (“microchannel”)that facilitates guidewire negotiation across theproximal cap (18).

CTA studies have provided conflicting resultsregarding the influence of stump morphology on PCIsuccess rates in CTO. Two reports demonstrated asignificant influence of stump morphology on PCIsuccess based on multivariable regression analysesof CTO parameters (21,22). Conversely, several otherCTA studies failed to show any relevant relationshipbetween stump appearance and the procedural suc-cess of PCI (17,23,24,27). Interestingly, in a studyby Li et al. (32) including 88 CTO lesions, a CTA-visible linear intrathrombus enhancement withinthe occluded segment (reflecting the presence of“microchannels”) has been suggested as a robustpredictor of PCI success. Of note, according to

Rolf et al. (20), coronary CTA seems to be more sen-sitive for the detection of a blunt stump than invasiveangiography.

SHRINKAGE. Shrinkage is defined as an abrupt nar-rowing of the occluded segment of CTO to <1 mm invessel cross-sectional diameter and has been postu-lated to reflect the age of the occlusion (27).

The influence of vessel shrinkage (as definedearlier) on successful guidewire passage has thus faronly been investigated in a single CTA study. In aseries of 110 CTO lesions, shrinkage was the secondmost prominent and independent predictor of wiringfailure (27). Of note, a recent study using a 256-detector CT in a series of 108 CTO lesions foundthat negative remodeling (defined as the ratio ofthe diameter of the occluded vessel to the diameterof the adjacent normal vessel <1), reflecting vesselshrinkage, was the strongest predictor of failedantegrade PCI (29). As a potential limitation, it maybe difficult to reliably measure the vessel diameterof the occluded segment in CTA, given its typicallylow-contrast attenuation relative to the surroundingtissue.

FIGURE 5 Calculation Sheet for the CT-RECTOR Score With Illustrated Definitions of Each Variable and Listing of the Difficulty Groups

CTO ¼ chronic total occlusion; CT-RECTOR ¼ Computed Tomography Registry of Chronic Total Occlusion Revascularization; PCI ¼ percuta-

neous coronary intervention. Adapted with permission from Opolski et al. (21).

Opolski and Achenbach J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 8 , N O . 7 , 2 0 1 5

CTA for PCI of CTO J U L Y 2 0 1 5 : 8 4 6 – 5 8

852

CT-RECTOR SCORE. The CT-RECTOR score wasdeveloped as a noninvasive prediction tool thatcombines several CT-derived parameters to predictrecanalization success in CTO (21). It was derivedfrom 240 consecutive CTO lesions included in amulticenter registry, and the outcome variable wasthe ability to successfully cross the CTO with aguidewire within 30 min. The advantage of thisendpoint (as opposed to any success) is the fact that itprovides some independence from individual oper-ator skills (14). Multivariable analysis yielded 6 in-dependent and straightforward CTA-based andclinical variables that were associated with guidewirecrossing: the presence of multiple occlusions, a bluntstump, severe calcification, bending, a CTO age $12months, and previously failed PCI. The CT-RECTOR

score was calculated by assigning 1 point for eachindependent predictor and adding them per CTOlesion (Figure 5). With an increasing score, the likeli-hood of successful guidewire crossing within 30 mindecreased, ranging from 95% for a CT-RECTORscore of 0 to 22% for a CT-RECTOR score of $3(Table 2). Of note, the CT-RECTOR score exceededthe discriminatory performance of the angiography-based J-CTO score. In contrast to the J-CTO score,the CT-RECTOR score consists of 6 variables, in-cluding multiple occlusions and CTO duration, andexcluding the lesion length. Although the relativelysimple CT-RECTOR score gave equal weight to allpredictors of recanalization failure, a more refinedstratification may be achieved by putting more weighton strong predictors such as the cross-sectional

TABLE 2 Relationship Between the Difficulty Groups Derived From the

CT-RECTOR Score and the Likelihood of Successful Guidewire Crossing

Within 30 Minutes

CT-RECTOR Score No. of CTO CasesLikelihood of SuccessWithin 30 Min (%)

Easy 0 22 95

Intermediate 1 60 88

Difficult 2 67 57

Very difficult $3 91 22

CT-RECTOR ¼ Computed Tomography Registry of Chronic Total Occlusion Revascularization;other abbreviations as in Table 1.

J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 8 , N O . 7 , 2 0 1 5 Opolski and AchenbachJ U L Y 2 0 1 5 : 8 4 6 – 5 8 CTA for PCI of CTO

853

degree of calcification, but this remains to bedetermined in the future. Clinically, CT-based findingssuch as the CT-RECTOR score may be used to assessCTO difficulty level before PCI (Figures 6 and 7),both to help decide whether recanalization shouldbe attempted and to allocate resources (e.g.,particularly experienced operators, CTO-dedicateddevices, procedural time) specifically to complex CTOlesions.

PLANNING THE PROCEDURE WITH

CORONARY CTA

The availability of detailed anatomical information ofcoronary arteries before PCI is essential, and coronaryCTA has been shown to aid in procedural planningof CTOs. Indeed, the most optimal PCI techniquesand devices can be selected based on the morpho-logical and anatomical features of CTOs on coronaryCTA. For example, the depiction of severe calcium in

FIGURE 6 Difficult CTO From the Guidewire Failure Group

(A and B)Multiplanar reformations of a long and severely calcified CTO le

right coronary artery (RCA). (C) Cross-sectional view of the calcification

displaying marked bending ($45�) within the occlusion route. The calcul

attempt of guidewire penetration entering a false lumen of the RCA (bl

as in Figure 5.

the proximal CTO cap, together with a good retro-grade collateral flow, offers a reasonable justificationfor choosing the retrograde approach, especially afterpreviously failed PCI. In addition, focally distrib-uted severe calcium can lead to selection of stiff flator tapered wires, with a subsequent exchange tosoft polymeric wires once calcification is crossed.

sion (arrows) with blunt entry site in the mid-to-distal segment of the

occupying $50% vessel area. (D) A 3-dimensional reconstruction

ated CT-RECTOR score was 3. (E) Coronary angiography shows failed

ack asterisk) by using the parallel wire technique. Abbreviations

FIGURE 7 Easy CTO From the Guidewire Success Group

(A and B) Multiplanar reformations of a short noncalcified CTO lesion (arrow) with tapered entry site in the mid-segment of the RCA.

(C) Cross-sectional view of the noncalcified occlusion site. (D) A 3-dimensional reconstruction displaying nonrelevant bending within the

occlusion route. The calculated CT-RECTOR score was 0. (E) Coronary angiography shows successful recanalization of the RCA within 2 min of

guidewire manipulation (white asterisk). Abbreviations as in Figures 5 and 6.

Opolski and Achenbach J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 8 , N O . 7 , 2 0 1 5

CTA for PCI of CTO J U L Y 2 0 1 5 : 8 4 6 – 5 8

854

Similarly, for heavily calcified lesions, the needfor additional debulking devices (e.g., high-pressureballoons or rotablation) can be anticipated. Finally,3-dimensional coronary CTA may aid in the pre-procedural selection of the most suitable fluoro-scopic projection angles, thus minimizing additionalcontrast use during invasive angiography (10).

Of particular interest, coronary CTA can be directlyused in the catheterization laboratory during PCI.One approach has been to import the CTA datasetsdirectly to the catheterization laboratory with a pos-sibility of automatic alignment according to theangulation of the C-arm (10). This method allows theoperator to verify the direction of the guidewireadvancement relative to the course of the occludedvessel segment and to identify angulations of theC-arm that avoid foreshortening of the treated vesselsegment. This has been recently corroborated ina study by Rolf et al. (20), who reported signifi-cantly higher success rates for PCI with pre-procedural CTA displayed in the catheterization

laboratory compared with PCI without CTA. Alterna-tively, a more complex approach of real-time inte-gration of 3-dimensional coronary CTA data andfluoroscopic images in the catheterization laboratoryhas been proposed (Figure 8) (10). However, whilerecanalization of CTO based on CTA datasets incombination with magnetic navigation has alreadybeen reported in a small series of 43 patients (33),such an approach demonstrated only a moderatesuccess rate (44.2%). Indeed, fusion techniquesare hampered by patient, cardiac, and respiratorymotion artifacts and thus do not provide the sub-millimeter accuracy required to determine the exactwire position relative to the distal vessel lumen (e.g.,an intraluminal versus subintimal position of theguidewire).

STUDY LIMITATIONS

Obviously, pre-procedural coronary CTA adds con-trast and radiation exposure, and there is yet no

FIGURE 8 Image Fusion of Coronary CTA and Fluoroscopic Images

(A and B) Three-dimensional anatomy of the coronary arteries derived from CTA facilitates identification of projections without fore-

shortening for each respective vessel segment. (C and D) CTA and fluoroscopic data are combined to show coronary segments in green

(no foreshortening) or red (substantial foreshortening). Prototype, Siemens Healthcare, Erlangen, Germany. Abbreviation as in Figure 1.

J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 8 , N O . 7 , 2 0 1 5 Opolski and AchenbachJ U L Y 2 0 1 5 : 8 4 6 – 5 8 CTA for PCI of CTO

855

uniform policy among CTO operators (not to mentioncurrent guidelines) regarding whether coronary CTAshould be routinely recommended before attemptingCTO recanalization (11,34). Thus, for now, coronaryCTA should be specifically considered for patientswith challenging or ambiguous CTO lesions as eval-uated by using invasive coronary angiography. How-ever, strategies to limit radiation exposure areconstantly being refined, and ultra-low-dose pro-tocols with estimated effective radiation doses <1mSv and preserved image quality have been reported(35). Moreover, the contrast volume required forcoronary CTA can be effectively reduced (36), andscheduling the CT acquisition at least a few daysbefore the PCI attempt should not increase the risk ofcontrast nephropathy. Finally, given the additionalcost of pre-procedural CTA, an economic balance fornoninvasive optimization of patient referral patternsand allocation of resources during percutaneous

treatment of CTO should be addressed in futureCT trials.

CONCLUSIONS

Coronary CTA is uniquely suited to visualize theanatomical features of both the occluded and distalvessel segments in chronically occluded coronaryarteries. The value of coronary CTA to predict thesuccess of percutaneous recanalization of CTOshas been thoroughly studied in numerous trials(including a total of 1,269 CTO lesions), and severalrelevant predictors of PCI failure have been identi-fied. They include severe calcification, bending,blunt stump, the presence of multiple occlusions,and occlusion length. CTA-based scores thatcombine several such parameters may be particu-larly useful in differentiating between “easy” and“difficult” CTO lesions, and they further support

CENTRAL ILLUSTRATION Roles of Coronary CTA in the Management of CTO

The most important clinical applications of coronary computed tomography angiography (CTA) in the management of chronic total occlusion (CTO) include: 1) iden-

tifying the CTO; 2) predicting clinical benefit from revascularization; 3) predicting the difficulty level with which a CTO can be crossed; 4) pre-procedural planning; 5)

visualization during the procedure; and 6) long-term follow-up of the recanalized coronary segments. CSA ¼ cross-sectional area.

Opolski and Achenbach J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 8 , N O . 7 , 2 0 1 5

CTA for PCI of CTO J U L Y 2 0 1 5 : 8 4 6 – 5 8

856

J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 8 , N O . 7 , 2 0 1 5 Opolski and AchenbachJ U L Y 2 0 1 5 : 8 4 6 – 5 8 CTA for PCI of CTO

857

treatment decisions as well as allocation of re-sources in the catheterization laboratory. Of partic-ular interest, real-time integration of 3-dimensionalCTA datasets and fluoroscopic images may modifyand optimize recanalization strategy. The CentralIllustration summarizes the established and devel-oping roles of coronary CTA in the management ofCTOs. Although more data are needed to identifythe full potential of coronary CTA for planning

percutaneous intervention in CTO, coronary CTA israpidly gaining recognition as a highly useful tool ininterventional cardiology.

REPRINT REQUESTS AND CORRESPONDENCE: Dr.Maksymilian P. Opolski, Department of Interven-tional Cardiology and Angiology, Institute of Cardio-logy, Alpejska 42, 04-628 Warsaw, Poland. E-mail:opolski.mp@gmail.com.

RE F E RENCE S

1. Stone GW, Kandzari DE, Mehran R, et al. Per-cutaneous recanalization of chronically occludedcoronary arteries: a consensus document: part I.Circulation 2005;112:2364–72.

2. George S, Cockburn J, Clayton TC, et al. Long-term follow-up of elective chronic total coronaryocclusion angioplasty: analysis from the U.K.Central Cardiac Audit Database. J Am Coll Cardiol2014;64:235–43.

3. Carlino M, Magri CJ, Uretsky BF, et al. Treat-ment of the chronic total occlusion: a call to actionfor the interventional community. CatheterCardiovasc Interv 2015;85:771–8.

4. Fefer P, Knudtson ML, Cheema AN, et al.Current perspectives on coronary chronic totalocclusions: the Canadian Multicenter Chronic TotalOcclusions Registry. J Am Coll Cardiol 2012;59:991–7.

5. Galassi AR, Boukhris M, Tomasello SD, et al.Incidence, treatment, and in-hospital outcome ofbifurcation lesions in patients undergoing percu-taneous coronary interventions for chronic totalocclusions. Coron Artery Dis 2015;26:142–9.

6. Galassi AR, Ganyukov V, Tomasello SD, Haes B,Leonid B. Successful antegrade revascularizationby the innovation of composite core dual coil in athree-vessel total occlusive disease for cardiacarrest patient using extracorporeal membraneoxygenation. Eur Heart J 2014;35:2009.

7. Khan MF, Brilakis ES, Wendel CS, Thai H. Com-parison of procedural complications and in-hospital clinical outcomes between patients withsuccessful and failed percutaneous intervention ofcoronary chronic total occlusions: a meta-analysisof observational studies. Catheter CardiovascInterv 2015;85:781–94.

8. Galassi AR, Boukhris M, Tomasello SD, et al.Long-term clinical and angiographic outcomes ofthe mini-STAR technique as a bailout strategy forpercutaneous coronary intervention of chronictotal occlusion. Can J Cardiol 2014;30:1400–6.

9. Tomasello SD, Giudice P, Attisano T,Boukhris M, Galassi AR. The innovation of com-posite core dual coil coronary guide-wire tech-nology: a didactic coronary chronic total occlusionrevascularization case report. J Saudi Heart Assoc2014;26:222–5.

10. Magro M, Schultz C, Simsek C, et al. Computedtomography as a tool for percutaneous coronaryintervention of chronic total occlusions. Euro-Intervention 2010;6 Suppl G:G123–31.

11. Sianos G, Werner GS, Galassi AR, et al. Recan-alisation of chronic total coronary occlusions:2012 consensus document from the EuroCTO club.EuroIntervention 2012;8:139–45.

12. Montalescot G, Sechtem U, Achenbach S, et al.2013 ESC guidelines on the management of stablecoronary artery disease: the Task Force on themanagement of stable coronary artery disease ofthe European Society of Cardiology. Eur Heart J2013;34:2949–3003.

13. Grantham JA, Marso SP, Spertus J, House J,Holmes DR Jr., Rutherford BD. Chronic total oc-clusion angioplasty in the United States. J Am CollCardiol Intv 2009;2:479–86.

14. Morino Y, Abe M, Morimoto T, et al. Predictingsuccessful guidewire crossing through chronictotal occlusion of native coronary lesions within30 minutes: the J-CTO (Multicenter CTO Registryin Japan) score as a difficulty grading and timeassessment tool. J Am Coll Cardiol Intv 2011;4:213–21.

15. von Erffa J, Ropers D, Pflederer T, et al.Differentiation of total occlusion and high-gradestenosis in coronary CT angiography. Eur Radiol2008;18:2770–5.

16. Li M, Zhang J, Pan J, Lu Z. Obstructive coro-nary artery disease: reverse attenuation gradientsign at CT indicates distal retrograde flow—auseful sign for differentiating chronic total occlu-sion from subtotal occlusion. Radiology 2013;266:766–72.

17. García-García HM, van Mieghem CA,Gonzalo N, et al. Computed tomography in totalcoronary occlusions (CTTO registry): radiationexposure and predictors of successful percuta-neous intervention. EuroIntervention 2009;4:607–16.

18. Di Mario C, Werner GS, Sianos G, et al. Euro-pean perspective in the recanalisation of chronictotal occlusions (CTO): consensus document fromthe EuroCTO Club. EuroIntervention 2007;3:30–43.

19. Soon KH, Cox N, Wong A, et al. CT coronaryangiography predicts the outcome of percuta-neous coronary intervention of chronic totalocclusion. J Interv Cardiol 2007;20:359–66.

20. Rolf A, Werner GS, Schuhbäck A, et al. Pre-procedural coronary CT angiography significantlyimproves success rates of PCI for chronic totalocclusion. Int J Cardiovasc Imaging 2013;29:1819–27.

21. Opolski MP, Achenbach S, Schuhbäck A,et al. Coronary computed tomographic predic-tion rule for time-efficient guidewire crossingthrough chronic total occlusion. Insights fromthe CT-RECTOR (Computed Tomography Regis-try of Chronic Total Occlusion Revascularization)Multicenter Registry. J Am Coll Cardiol Intv2015;8:257–67.

22. Mollet NR, Hoye A, Lemos PA, et al. Value ofpreprocedure multislice computed tomographiccoronary angiography to predict the outcomeof percutaneous recanalization of chronic totalocclusions. Am J Cardiol 2005;95:240–3.

23. Cho JR, Kim YJ, Ahn CM, et al. Quantificationof regional calcium burden in chronic totalocclusion by 64-slice multi-detector computedtomography and procedural outcomes of percu-taneous coronary intervention. Int J Cardiol 2010;145:9–14.

24. Martín-Yuste V, Barros A, Leta R, et al. Factorsdetermining success in percutaneous revasculari-zation of chronic total coronary occlusion: multi-detector computed tomography analysis. Rev EspCardiol 2012;65:334–40.

25. Hsu JT, Kyo E, Chu CM, Tsuji T, Watanabe S.Impact of calcification length ratio on the inter-vention for chronic total occlusions. Int J Cardiol2011;150:135–41.

26. Yokoyama N, Yamamoto Y, Suzuki S, et al.Impact of 16-slice computed tomography inpercutaneous coronary intervention of chronictotal occlusions. Catheter Cardiovasc Interv 2006;68:1–7.

27. Ehara M, Terashima M, Kawai M, et al. Impactof multislice computed tomography to estimatedifficulty in wire crossing in percutaneous coro-nary intervention for chronic total occlusion.J Invasive Cardiol 2009;21:575–82.

28. Choi JH, Song YB, Hahn JY, et al. Three-dimensional quantitative volumetry of chronictotal occlusion plaque using coronary multi-detector computed tomography. Circ J 2011;75:366–75.

29. Luo C, Huang M, Li J, et al. Predictors ofinterventional success of antegrade percuta-neous coronary interventions for chronic totalocclusions. J Am Coll Cardiol Img 2015;8:804–13.

30. Li P, Gai LY, Yang X, Sun ZJ, Jin QH. Computedtomography angiography-guided percutaneouscoronary intervention in chronic total occlusion.J Zhejiang Univ Sci B 2010;11:568–74.

Opolski and Achenbach J A C C : C A R D I O V A S C U L A R I M A G I N G , V O L . 8 , N O . 7 , 2 0 1 5

CTA for PCI of CTO J U L Y 2 0 1 5 : 8 4 6 – 5 8

858

31. Opolski MP, Kepka C, Achenbach S, et al.Coronary computed tomographic angiographyfor prediction of procedural and intermediate out-come of bypass grafting to left anterior descendingartery occlusion with failed visualization on conven-tional angiography. Am J Cardiol 2012;109:1722–8.

32. Li M, Zhang J, Pan J, Lu Z. Coronary totalocclusion lesions: linear intrathrombus enhance-ment at CTpredicts better outcomeof percutaneouscoronary intervention. Radiology 2013;266:443–51.

33. Ramcharitar S, van der Giessen WJ, van derEnt M, de Feyter P, Serruys PW, van Geuns RJ.

The feasibility and safety of applying the Mag-netic Navigation System to manage chronicallyoccluded vessels: a single centre experience.EuroIntervention 2011;6:711–6.

34. Werner GS, Hecht H, Stone GW. Utility of CTangiography to guide coronary intervention ofchronic total occlusions. J Am Coll Cardiol Img2015;8:814–6.

35. Achenbach S, Marwan M, Ropers D, et al.Coronary computed tomography angiographywith a consistent dose below 1 mSv usingprospectively electrocardiogram-triggered high-

pitch spiral acquisition. Eur Heart J 2010;31:340–6.

36. Zhang LJ, Qi L, Wang J, et al. Feasibility ofprospectively ECG-triggered high-pitch coronaryCT angiography with 30 mL iodinated contrastagent at 70 kVp: initial experience. Eur Radiol2014;24:1537–46.

KEY WORDS chronic total occlusion,coronary angiography, coronary computedtomography angiography, percutaneouscoronary intervention