Impact of Multislice Computed Tomography to Estimate Difficulty in Wire Crossing in Percutaneous Coronary Intervention for Chronic Total Occlusion
ABSTRACT: Background. Percutaneous coronary intervention (PCI) for chronic total occlusions (CTO) remains a challenge. Multislice computed tomographic coronary angiography (CTCA) allows noninvasive evaluation of the coronary artery by visualizing vessel trajectory and morphological features at the occluded site. The aim of this study was to assess the value of CTCA to predict the success of guidewire crossing in PCI to treat CTOs.
Methods. We performed CTCA in patients with CTOs (of > 3 months’ duration); 110 lesions were scanned. Wiring success was defined as complete crossing of the guidewire past the occluded site. Correlation of the following morphological parameters with wiring success was analyzed: target vessel bending (defined as > 45º), shrinkage, severe calcification, presence of side branches, stump morphology, in-stent occlusion and occlusion length.
Results. Wiring success was obtained in 93 lesions (85%). In the unsuccessful group, bending, shrinkage and severe calcification were significantly higher compared to the successful group (76% vs. 18%, p Conclusion. Bending, shrinkage and severe calcification are significant predictors for wiring success. CTCA provides a practical determinant of the outcomes in PCI to treat CTOs.
J INVASIVE CARDIOL 2009;21:575–582
Key words: Multislice computed tomography, chronic total occlusion, percutaneous coronary intervention morphological assessment, wiring success
Indications for percutaneous coronary intervention (PCI) have continued to expand over the years. Particularly with the introduction of drug-eluting stents, it has reached into the area of chronic total occlusions (CTOs), which was often formerly considered a contraindication.1–5 Recent data have shown that successful PCI for CTOs results in improved survival rates as well as enhanced left ventricular function, reduced angina and improved exercise tolerance.4–12 However, despite technical progress and increased operator experience, PCI for CTO remains a challenge due to perceived procedural complexity. Failure of guidewire crossing is the most common reason for an unsuccessful procedure, and in most cases, its difficulty stems from a lack of morphological information of the occluded site on angiography: vessel tortuosity or bending, exact occlusion length or vessel diameter, localization of soft or calcified plaque, and so forth.
Considerable progress has recently been achieved in noninvasive imaging by computed tomography (CT). The high diagnostic accuracy of multislice CT in the detection of coronary artery disease is now well known.13–18 Computed tomographic coronary angiography (CTCA) allows the depiction of a three-dimensional trajectory of the occluded site, as well as soft plaque or calcium deposits in the vessel wall and surrounding tissue, and not just the “patent” portion filled with the contrast media as angiography does.19–21
Focusing on these advantages, we evaluated the impact of morphological features obtained by CTCA on wiring success rates in PCI to treat CTOs. The aim of this study was to investigate the potential of CTCA to predict procedural outcomes in PCI for CTO.
Methods
Population demographics. Between January 2006 and January 2008, 115 patients with CTO lesions underwent CTCA prior to PCI (median interval 7 days, mean 18 ± 41). Exclusion criteria for CTCA examination were as follows: renal insufficiency (serum creatinine > 1.5 mg/dl), allergy to contrast media, inability to hold breath and chronic atrial fibrillation or any other chronic rhythm irregularity. CTOs in native coronary arteries post coronary artery bypass graft (CABG) surgery were included, although CTOs in bypass grafts were ruled out of the population. CTO was defined as the absence of antegrade flow of contrast distal to the occlusion on catheter-based angiography with thrombolysis in myocardial infarction (TIMI) flow grade 0, which was deemed to be of > 3 months’ duration. Five images (4%) with inadequate quality for assessment due to severe motion artifact were ruled out of the population. Ultimately, 110 CTO lesions were included. All patients gave written informed consent, and the study protocol was approved by the hospital’s ethics committee.
Scan protocol for CTCA. All patients were scanned using a 64-slice SOMATOM Sensation 64 Cardiac Scanner (Siemens Medical Solutions, Forchheim, Germany). When the heart rate was ≥ 70 beats/minute, a beta-blocker (metoprolol 20–60 mg) was administered for heart rate control. Nitroglycerin was administered prior to the scan. A bolus of contrast media (370 mg iopamidol iodine/ml, Schering AG, Berlin, Germany; iopromide, 370 mg iodine/ml, Shering AG, Berlin, Germany; Omnipaque
®, 350 mg iodine/ml, Daiichi Pharmaceutical Co., Ltd., Tokyo, Japan) was injected into an antecubital vein, followed by flushing with 30 ml of saline. To reduce the incidence of adverse reactions, the type of contrast media selected for each patient took previous usage into consideration. The proper amount of contrast media and injection speed were determined according to the patient’s body weight, heart rate and scan time. The start delay was automatically defined using the scanner’s bolus tracking software. The region of interest was placed within the ascending aorta and the scan was started when the CT density reached 120 Hounsfield Units higher than the baseline CT density. The basic scan was performed between the tracheal bifurcation and the diaphragm (patients with the internal thoracic artery as bypass graft, from the ostium of the internal thoracic artery), utilizing the following parameters: collimation width 64 x 0.6 mm; rotation time 330 ms; tube voltage 120kV; effective tube current s800 mAs; table feed 11.5 mm/rotation and pitch 0.2.
Data acquisition and analysis of CTCA. Image reconstruction was retrospectively gated to the electrocardiogram (ECG), and the optimal cardiac phase displaying the minimum motion artifact was individually determined. Depending on the heart rate during the examination, axial slices were reconstructed synchronized to the ECG by a monophase (heart rate ®) kernel with a slice thickness of 0.6 mm (increment 0.3 mm).18 Spatial resolution was 0.33 mm.
CTCA datasets were transferred to workstations for image analysis. Maximum-intensity projection with 6–10 mm slice and multiplanar reformatted reconstructions were made utilizing the Wizard
® or Circulation
® workstation (Siemens Medical Solutions). The volume-rendering image and “angiographic image”, which visualizes the entire coronary tree, were made with Aquarius NetStation
® (TeraRecon, Inc., San Mateo, California). Figure 1 represents a typical CTO case on CTCA.
Two experienced reviewers blinded to the findings of the catheter-based angiography and clinical data analyzed the following seven parameters of each lesion on CTCA: 1) bending of the target vessel (defined as > 45 degree either in the occluded site or proximal of the occlusion, Figure 3); 2) shrinkage of the target vessel (defined as an abrupt narrowing or severe tapering of the distal portion, in which the cross-section showed less than 1 mm in vessel diameter, Figure 4); 3) severe transluminal calcification (defined as the presence of high-density plaques with > 500 HU which nearly or completely cover the circumference [360º] of the entire cross-section inside or at the either end of the occluded site; Figure 5); 4) side branches, which are located close to the entry point; 5) tapered stump morphology of the occluded end; 6) in-stent occlusion; and 7) occlusion length. Morphological features were evaluated to determine outcome predictors. Figure 1 represents examples of CTO images by CTCA.
Procedure of percutaneous coronary intervention. All PCI procedures for CTO were performed by highly skilled operators with experience of > 100 CTO procedures. The strategy for each case was selected at the operators’ discretion. Guidewires were used in a stepwise progression from soft and/or hydrophilic wires to stiffer wires. Some cases required several wiring techniques besides the single antegrade wire technique including the parallel wire technique, the intravascular ultrasound-guided technique or the retrograde approach.
3,5,22–27
Wiring success was defined as complete crossing of the guidewire through the occluded site.19 Treatment success was defined as restoration of anterograde flow, with TIMI grade 3 flow and a final residual stenosis ® software (Medis Holding, Leiden, the Netherlands).
Statistical analysis. Quantitative variables are described as mean ± standard deviation (SD). Categorical variables are presented as numbers and percentages. The chi-square test was used for comparing frequency of occurrence. Comparison of quantitative variables was performed by one-way analysis of variance for normally distributed variables. A probability value of ® version 5.0 (Abacus Concepts, Inc., Berkeley, California) was used for data analysis.
Results
Patient characteristics and scan condition. Among 110 CTO lesions, 93 (85%) were successfully crossed by the guidewire (wiring success). No significant difference between the successful and unsuccessful groups was shown in baseline patient characteristics, occluded vessel and left ventricular ejection fraction. Frequency of previous CABG was significantly higher in the successful group (Table 1).
Concerning scan condition, the mean heart rate was 63.0 beats/minute (range 44–94), with use of beta blocker in 34%, the mean scan time 12.5 seconds (range 10–21 seconds, the longest in a case post CABG), and the total amount of contrast media 73.7 ml (range 50–98). Rhythm irregularity occurred in 1 patient, in whom incidental extra beats appeared only during the scan. The estimated radiation exposure was 14.3 mSv for females and 13.2 mSv for males. No significant differences in scan condition parameters were observed between the groups (Table 1).
Morphological characteristics between successful and unsuccessful groups observed by CTCA. Table 2 represents the morphological characteristics of CTO lesions observed by CTCA. Comparing two groups, target-vessel bending was detected at a significantly higher frequency in the unsuccessful group (18% vs. 76%,
p p = 0.0005) and severe calcification (18% vs. 41%,
p = 0.0356). On the contrary, no significant differences were seen between groups concerning tapered stumps, significant side branches, in-stent occlusions or occlusion length.
PCI procedure. One patient ended up in a suboptimal state with TIMI grade 2 flow due to formation of a post-ballooning coronary dissection despite successful crossing with the guidewire (Table 3). No deaths or Q-wave myocardial infarctions occurred, although the rate of coronary perforations was significantly higher in the unsuccessful group (8% vs. 41%,
p = 0.0001). It took significantly longer in the unsuccessful group to complete the entire procedure (178 ± 74 minutes vs. 228 ± 78 minutes,
p = 0.0130). The number of wires used was significantly higher in unsuccessful cases (3.8 ± 2.0 vs. 5.1 ± 2.8,
p = 0.0255).
Impact of morphological features on wiring success. Table 4 demonstrates the impact of morphological features on wiring success rates. Patients with vessel bending, shrinkage and severe calcification showed significantly higher success rates than those without those features (57% vs. 95%,
p p = 0.0005 and 71% vs. 88%,
p = 0.0356, respectively).
Table 5 depicts the significant multivariate predictors of wiring failure in PCI for CTO. According to the odds ratio, vessel bending, vessel shrinkage and severe calcification remained significant following multivariable adjustment.
Presentation of typical cases. Figure 2 represents a CTO of the mid-left circumflex artery, with no severe vessel bending, shrinkage or severe calcification. The lesion length is measured as 22.9 mm. The overall procedure was completed successfully in 95 minutes. Figures 3–5 show the failed cases. Figure 3 represents a CTO of the right coronary artery. On the first attempt, cineangiography was unable to accurately depict the true course of the severely bended vessels. CTCA, which was performed before the second attempt, demonstrated the true vessel course as well as the exact occlusion length and diameter. Figure 4 shows a CTO case of the left anterior descending artery. The occluded site shows shrinkage, which looks smaller in vessel diameter than the distal portion. The occlusion length was 27.2 mm on CTCA. During the procedure, a dissection occurred at the occluded site, which led to failure to cross the guidewire. Figure 5 is also a CTO case of the left anterior descending artery. On CTCA, calcification appears to cover the entire cross-section. The guidewires via the antegrade and retrograde approaches both advanced into the subintimal space, and the operator ultimately abandoned the procedure.
Discussion
Recent data suggest that successful recanalization of coronary CTOs results in improved survival as well as enhanced left ventricular function and increased quality of life.
4–11 Various types of devices and techniques have been developed to improve success rates of PCI for CTO,
3,5,22–28 however, it is still regarded as a difficult procedure for many interventional cardiologists. Concerning CTOs, the lack of adequate morphological information provided by angiography is one of the most essential factors in making the procedure less reliable.
Today CTCA has won its position as a promising noninvasive diagnostic tool
13–18 that has begun to replace conventional catheter-based coronary angiography in some clinical scenarios. Providing information not only on the degree of stenosis, it allows for the visualization of the three-dimensional structure of the coronary tree. CTCA can depict the trajectory of an occluded lesion, the location of side branches, stump morphology, plaque mass and composition, calcium distribution, and so forth. In addition, CTCA provides accurate measurement of occlusion length without foreshortening vessel diameter and area.
19,20
The present data indicate the following: 1) Among 110 CTO lesions treated, 93 (85%) were successfully crossed by guidewire through the occluded site. Adequate TIMI flow failed to be achieved in only 1 patient due to coronary dissection, and this despite successful guidewire crossing. 2) Among vessel morphologies evaluated by CTCA, vessel bending, vessel shrinkage and severe calcification were frequently observed in the unsuccessful group compared to the successful group (76% vs. 18%,
p p = 0.0005, and 41% vs. 11%,
p = 0.0356, respectively). 3) Vessel bending, vessel shrinkage and severe calcification was related to a significant reduction of wiring success rate (57% vs. 95%,
p p = 0.0005 and 18% vs. 41%, p = 0.0356, respectively). 4) Multivariate regression analysis identified that vessel bending, shrinkage and severe calcification were independent predictors of the outcome of the procedure.
Some investigators reported that the use of CTCA, lack of stump morphology, occlusion length > 15 mm and severe calcification were independent predictors of procedural failure.
19 Others suggested that heavy transluminal calcification as assessed with CTCA was an independent predictor.
20 According to our data, however, bending of the target vessel is the most prominent predictor, followed by vessel shrinkage and severe calcium. Lesions with severe vessel bending would require skill and experience, even in a nonoccluded lesion in which the operator is able to identify the coronary tract. Vessel shrinkage, presumably reflecting the age of the CTO, often induces the guidewire to track outside the vessel (coronary perforation). Also, when the guidewire hits a superficial calcium deposit, the wire is apt to advance the subintimal space, let alone in cases of 360º calcification. Thus, our data clearly support the issues that operators often face in their real-world practice.
CTCA has great advantages within these parameters over other invasive and noninvasive modalities such as angiography or intravascular ultrasound. CTCA offers operators the evidence for therapeutic decision making. Proper selection of PCI candidates by utilizing CTCA would be the first step to improve success rates. In other words, when the vessel morphology turns out to be unsuitable for PCI, changing over to another strategy would be an option to achieve positive outcomes. In addition, during the procedure the operator can consult CTCA as a reliable guide successful guidewire crossing. It is also true that a larger dose of contrast media and a relatively high dose of radiation exposure remain matters of concern.
29,30 Nevertheless, various important morphological data would eventually allow improved safety and success rates by saving time, contrast media and reducing radiation exposure during PCI.
Study limitations. The procedure was not performed by a single operator, and the selection of device and strategy was at the operator’s discretion, which may have affected procedural outcomes. However, the most important factors were lesion morphology and characteristics because all of the operators were skilled and experienced. The impact of the exact occlusion period, which previous investigators mentioned as an outcome predictor,
5,19 was not evaluated because in most of our cases, as is typical in the clinical setting, such information was not known. The degree of bending may change according to the cardiac phase (systolic and diastolic), which often makes the procedure more complicated. Although the degree of bending changes during the cardiac cycle, only one phase was analyzed by CTCA. Also, the patient population was rather small and was neither consecutive nor randomized. A larger-scale, prospective investigation would be expected to investigate the true effectiveness of preprocedural CTCA.
Conclusion
CTCA noninvasively provides three-dimensional morphological information on the coronary tract. Vessel bending, shrinkage and severe calcification are independent predictors of procedural outcomes in PCI for CTO lesions. Proper patient selection and therapeutic decision making based on a universal, objective and scientific approach using CTCA will lead to an improvement in success rates of PCI for CTO.
Acknowledgement. The authors thank Mr. Wayne Smith for his assistance with the preparation of the manuscript.
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