CTA Can Help Identify True CTOs

 

Computed tomographic angiography (CTA) can be used to differentiate between a chronic total occlusion (CTO) and a subtotal occlusion (STO), according to a single-center study published in the August 17, 2015, issue of JACC: Cardiovascular Interventions. For lesions identified as CTOs, the noninvasive imaging also predicts lower likelihood of PCI success.

A different view:   CTA Can Help Identify True CTOs

Jin-Ho Choi, MD, PhD, of Samsung Medical Center (Seoul, South Korea), and colleagues looked at 486 consecutive patients (median age 63 years; 82% men) with at least 1 completely occluded artery (n = 553 lesions) on coronary CTA that was confirmed by subsequent angiography at their center between June 2006 and November 2013.

CTA was performed with a 64-slice scanner (Aquilion 64; Toshiba Medical Systems) in 236 patients and a 128-slice scanner (SOMATOM Definition; Siemens Medical Solutions) in 250 patients.

Invasive coronary angiography identified a CTO (defined as a completely interrupted lumen with TIMI flow grade 0) in 362 patients and an STO (defined as diameter stenosis ≥ 95% with TIMI flow grade 1-2) in 124 patients. Clinical risk factors were similar between the groups, except that CTO patients were more likely to have Q waves on ECG and silent ischemia and had lower LVEF and higher LV mass index. Prevalence of multivessel disease was also similar between the groups.

Different Types of Blockage Show Distinct Traits

On CTA, CTOs (n = 411) were more likely than STOs (n = 142) to be present in the RCA (P = .003). In addition, CTOs showed longer occlusion length, larger proximal reference luminal area, and larger vessel area in the occluded segment compared with STOs (P < .005 for all). The more severe blockages also had more side branches, a blunt stump, greater calcification, and more noninvasively visualized collateral vessels (P < .005 for all). In addition, the overall and distal transluminal attenuation gradients—which reflect the kinetics of intraluminal flow and collateral circulation, respectively—were higher in CTOs compared with STOs (both P < .01).

In comparison, on invasive angiography, CTOs again showed longer occlusion length and also more frequent side branches compared with STOs (both P < .001). Although a collateral vessel was seen in all CTOs and 67.6% of STOs, collaterals supplying arteries with CTOs were larger and had higher flow and more retrograde flow than those supplying arteries with STOs (P < .001 for all).

PCI was attempted less frequently in CTOs than in STOs (56.9% vs 76.1%) and the procedural success rate for CTO PCI was lower (75.2% vs 95.4%; both P < .001), driven by an inability to pass the wire across the occlusion. In addition, perforation was seen only in CTO cases (0.9%).

The power of individual CTA findings to predict the presence of an invasively confirmed CTO was moderate. However, a model combining the optimal cutoff values for multiple CTA metrics showed much higher discriminative power (P < .05), yielding a negative predictive value of 93% and a positive predictive value of 55% (both P < .001). The model consisted of:

  • Occlusion length ≥ 15 mm
  • Side branches
  • Blunt stump
  • Visualized collateral vessel
  • Cross-sectional calcification ≥ 50%
  • Distal transluminal attenuation gradient ≥ -0.9 Hounsfield units/10 mm

The model also predicted unsuccessful PCI better than did single CTA findings, with a positive predictive value of 91% and a negative predictive value of 31% (both P < .005).

CTO PCI: A Question Not of Whether But Where

“CTOs are the most challenging lesions in interventional cardiology, and outside of expert centers and expert operators, success rates remain disappointingly low,” Dimitrios Karmpaliotis, MD, PhD, of Columbia University Medical Center (New York NY), told TCTMD in a telephone interview. He cited a recent registry study in which CTO PCI was successful less than two-thirds of the time and about 1 out of 5 centers did not even perform the procedure. This rarity of CTO PCI is especially disheartening in light of accumulating evidence that successful cases can improve quality of life and potentially survival, he commented.

“In that context, trying to define the characteristics of a CTO that could predict the difficulty of the procedure would be desirable,” Dr. Karmpaliotis said. “And the present study suggests that preprocedural CT angiography may help” in that regard.

“But if a procedure is clinically indicated, the results of CT angiography should not dictate whether PCI is performed but rather who should do it,” he stressed.

Moreover, except for the ability to assess calcification, CTA adds little to the information provided by the specialized invasive angiography that is required in preparation for CTO PCI, Dr. Karmpaliotis pointed out. That is in part why CTA is rarely used by expert centers in the United States, where the success rate is now more than 90%, he noted. That being said, preprocedural CTA may give operators unfamiliar with the more complex invasive angiography needed for CTOs an indication of the difficulty of a case and prompt them to refer the patient to an experienced center rather than attempt it themselves with potentially disastrous results, he added.

“The 1 area where CT has an important role in CTO PCI is when you don’t see the target very clearly angiographically and you’re wondering whether or not to recanalize,” Emmanouil S. Brilakis, MD, PhD, of the Dallas VA Medical Center (Dallas, TX), told TCTMD in a telephone interview. Dr. Karmpaliotis agreed, adding that the problem arises more commonly in bypass patients, who frequently have multiple vascular connections.

On the whole, however, Dr. Brilakis said he was skeptical of the usefulness of CTA. The study findings are “very elegant” and “confirm what we knew from [invasive] angiography,” he said, “but on practical grounds, I’m puzzled as to what to make of them in the current era.”

 


Source: 
Choi J-H, Kim E-K, Kim SM, et al. Noninvasive discrimination of coronary chronic total occlusion and subtotal occlusion by coronary computed tomography angiography. J Am Coll Cardiol Intv. 2015;8:1143-1153.

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Disclosures
  • Dr. Choi reports no relevant conflicts of interest.
  • Dr. Brilakis reports receiving research grants from Boston Scientific and Infraredx.
  • Dr. Karmpaliotis reports serving on speakers bureaus for Abbott, Asahi, Boston Scientific, and Medtronic.

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