The increasing number and complexity of these procedures have led to a higher number of patients at risk for tissue reactions like skin injuries. Monitoring of their dose indicators is essential in recognizing these patients. The aim of this work was to determine local diagnostic reference levels (DRLs) for recanalization of chronic total occlusion (CTO) and other occlusions procedures. All data from patients who underwent cardiac procedures were reviewed and classified according to their complexity. Dose indicators such as fluoroscopy time (FT), dose area product (DAP), and air kerma at patient entrance reference point (AK r ) were recorded. Correlations with patient’s body mass index, operators, procedure strategy, and complexity were studied. For CTO, the mean DAP, AK r , and FT were 252 ± 234 Gycm 2 , 3,985 ± 3,579 mGy, and 47 ± 36 minutes, respectively. To better reflect the non-Gaussian distribution of data, the median and the 75th percentile values were also reported: median DAP, 172 Gycm 2 ; 75th percentile DAP, 350 Gycm 2 ; median AK r , 2,714 mGy; and 75th percentile AK r, 5,921 mGy. A tentative new set of values were suggested to take into account the complexity difference in recanalization of total occlusions according to their antegrade or retrograde approach. These approach-specific DRLs for total occlusions were mean DAP (120 ± 114 Gycm 2 ), mean AK r (1,789 ± 1,933 mGy), and mean FT (22 ± 18 minutes) for antegrade approach and mean DAP (459 ± 304 Gycm 2 ), mean AK r (6,881 ± 4,243 mGy), and mean FT (82 ± 40 minutes) for retrograde approach. The other significant values were median DAP (84 Gycm 2 ), 75th percentile DAP (147 Gycm 2 ), median AK r (1,160 mGy), and 75th percentile AK r (2,176 mGy) for antegrade approach and median DAP (422 Gycm 2 ), 75th percentile DAP (552 Gycm 2 ), median AK r (6,295 mGy), and 75th percentile AK r (8,064 mGy) for retrograde approach. In conclusion, a set of local DRL values from a large center were assessed. DRLs were provided for antegrade and retrograde approaches, reflecting the difference in difficulty from these 2 kinds of CTOs. The wide dose estimator values variations were explained through procedure complexity. The values obtained for the other more classic percutaneous coronary interventions were comparable with those found in the literature.
Diagnostic coronary angiographies have been used steadily for many years. PCIs including recanalization of chronic total occlusion (CTOs) are increasing in terms of volume and complexity. New stenting devices and more experienced operators allow for more difficult and complex procedures to be performed in patients on a short hospitalization basis, thus avoiding open bypass surgery for these patients. In contrast, concerns about possibly high levels of radiation exposure have been expressed, regarding both tissue reactions and cancer induction. Very few, if any, studies have been published on CTO doses. A survey of dose indicators leading to establishment of diagnostic reference levels (DRLs) for this rapidly expanding procedure will allow a better understanding of the distribution of doses, of their potential effects and risks on patients, and will initiate a possibility to undertake optimization actions to ensure conformity with the As Low As Reasonably Achievable (ALARA) principle. DRLs can also be used as a trigger tool for optimization, guidance for good practice, and patient follow-up. The consensus among the EuroCTO club is to define a CTO as “the presence of Thrombolysis In Myocardial Infarction (TIMI) 0 flow within an occluded arterial segment of >3 months standing.” Improvement of catheterization and dilating or de-occluding devices (catheter, guiding) and of approaches (antegrade/retrograde, self-standing, or complementary) have led to a high success rate even when used in anatomically complex situations or clinically complex patients.
Methods
The study was carried out at the Institut Cardiovasculaire Paris Sud, Hôpital Privé Jacques Cartier in Massy and Hôpital Privé Claude Galien in Quincy, 2 high-volume French cardiology centers located in the Parisian area. Both sites have the same patient population, with 9 senior interventional cardiologists and a number of resident cardiologists or trainees, and have the same type of equipment with >5,000 procedures performed each year. The equipment used during the study time consisted of 8 angiographic C-arms from 3 manufacturers (GE, Milwaukee, Wisconsin, Philips, Eindhoven, The Netherlands, and Siemens, Erlangen, Germany) in 5 cathlabs. All but 2 equipments have been replaced during the study period because of turnover of machines. All senior operators have performed all procedures included in the study.
A retrospective analysis of overall data (procedure-related data, gathered dose indicator values, patient-related data, operator experience, and equipment-related data) was performed from January 2013 to July 2014. In all, 8,931 procedures concerning 6,054 patients were included. The first step of the study dealt with defining the center’s local DRLs for coronary angiography (CA) and PCIs excluding CTOs, to benchmark them with published DRL, especially in the French context. The second phase was focused on analyzing the local practice to determine local DRLs for all CTOs and suggesting approach-specific DRLs for antegrade and retrograde CTOs.
Although some studies have tried to correlate the displayed air kerma at patient entrance reference point (AK r ) value to actual skin dose either by direct measurements or by calculation taking into account different factors influencing maximum skin dose location and value, the following dose indicators were used within this study: AK r (the easiest-to-obtain surrogate for maximum skin dose), dose area product (DAP), FT, number of series, and number of frames when available. DAP meters were calibrated taking into account tabletop and pad attenuation. All equipments were checked for DAP (table and pad included) and AK r accuracy during annual quality control according to the French regulatory protocols.
The procedure-related data dealt with the following items: the diagnostic or therapeutic nature (CA or PCI), routine angioplasties or occlusions and CTO, medical strategy and approach for CTOs (antegrade or retrograde), number and location of dilated segments, relative frequency of procedure types, complexity, success or failure, and operator. Duration of lesion (>3 months, <3 months, and unknown), artery access route, and adopted medical strategy (antegrade and retrograde) were tested as complexity components of CTOs.
The patient-related data were age, weight, height, and body mass index (BMI). Trigger levels have been defined to detect patients possibly at risk for tissue reactions. AK r levels of 5,000 mGy to 9,000 mGy with intervals of 1,000 mGy were used as on-line oral alert levels for operators; 7,000 mGy and 10,000 mGy were used, respectively, as triggers for follow-up of patients and “stop and get advice from senior colleague” before continuing the procedure. The value for individual calculation of maximum skin dose was locally set at 7,000 mGy as a more practical value because skin reactions were never observed at lower levels in patients who underwent a procedure in the center, despite regular follow-up of patients >5,000 mGy for 2 years. Consequently, trigger levels were raised from 5,000 mGy as recommended by Cardiovascular and Interventional Radiological Society of Europe (CIRSE) to 7,000 mGy, and first on-line alert level was set at 5,000 mGy. The patient population having undergone multiple procedures over the study period was analyzed to assess the cumulative dose received. Dose indicators per procedure were registered, and patients were followed up by phone or by visit if their cumulative AK r was more than the local trigger level of 7,000 mGy.
Statistical analysis was done using SAS for windows, version 8.2 (SAS Institute, Cary, North Carolina). This was an observational, nonrandomized study; therefore, the statistical analysis was based on descriptive statistical techniques. Categorical variables were presented as a rate with its 95% exact confidence interval, whenever appropriate. Continuous variables were presented as means ± 1 SD with their 95% confidence interval.
Results
Table 1 summarizes the procedures performed in 6,054 patients during the 18 months, split between 63% CA and 37% PCI. Out of this latter group, 29% were angioplasties in nonoccluded vessels and 8% total occlusions including 208 CTOs of >3-month duration, 182 occlusions of unknown duration (many of them likely or possible CTOs), and 320 occlusions of <3-month duration, the large majority of which were because of acute myocardial infarction. The ratio women/man ranged from 45% for CA to 29% for PCI and 25% for occlusions. Mean age, mean BMI, and mean weight did not show any significant difference (p = 0.6) in all 3 categories of procedures. The percentage of CTOs among the overall number of procedures (8% if all occlusions are taken into account and 2.3% if only total occlusions known as having been present for longer than 3 months) was much lower than that reported in another study.
| Procedure type | Number of procedures | Gender | Age Mean ± s.d. [year] | BMI Mean ± s.d. [kg/m 2 ] | Weight Mean ± s.d. [kg] | |
|---|---|---|---|---|---|---|
| Males | Females | |||||
| CA | 5,645 | 3,904 | 1,741 | 68 ± 12 | 27 ± 5 | 78 ± 16 |
| PCI | 2,576 | 2,003 | 573 | 68± 12 | 27 ± 4 | 78 ± 15 |
| All total occlusions | 710 | 568 | 142 | 64.± 12 | 28 ± 5 | 80 ± 16 |
| TOTAL | 8,931 | 6,475 | 2,456 | 67 ± 12 | 27 ± 5 | 78 ± 15 |
All statistical parameters markedly varied ( Table 2 ). Minimum-maximum differences were very wide (a range of ∼250 to 3,400), and SDs were even greater than their corresponding mean value confirming a broad distribution of dosimetry data. Maximum value of AK r was 24.5 Gy, a dose level likely to cause patient skin injuries, and maximum FT reached almost 3 hours. All dose-related values were systematically lower for CA than for angioplasties. Mean values were greater than median values for all dose indicators, likely to be reflecting a non-Gaussian skewed distribution of data. DAP, AK r, and FT values for CTOs were higher of approximately a factor of 2 than the corresponding ones for occlusions of unknown duration and again by a factor of 2 if occlusions <3 months were considered, thus implicitly illustrating their greater degree of complexity. Although occlusions of unknown duration are usually thought to be CTOs and a predictor of worse prognosis, the statistics for this group were intermediate between those of the proved CTO group and of occlusions <3-month duration. Number of series and frames were both significantly higher (p <0.001) for CTOs compared with angioplasties. Statistically significant difference (p <0.001) existed between DAP parameters in CTOs with proved occlusion duration of >3 months compared with the group of patients including occlusions of <3-month duration and of unknown duration. Median values of all dose indicators regularly increased with the increasing complexity of the procedure from routine diagnostic CA to CTO procedure dealing with complex lesions for CTO, and they were roughly 7 to 11 times higher than those for CA.
| Statistics | Procedure type | DAP [Gy.cm 2 ] | AK r [mGy] | FT [min] | Number of series ∗ | Number of frames ∗ |
|---|---|---|---|---|---|---|
| Min | CA | 0.3 | 7.2 | 0.52 | 3 | 205 |
| PCI | 2 | 27 | 0.37 | 4 | 105 | |
| CTOs >3 months | 10 | 132 | 1 | 16 | 619 | |
| Unknown duration | 12 | 125 | 1,1 | na | na | |
| <3 months | 7 | 84 | 1,1 | na | na | |
| Mean ± s.d. | CA | 32 ± 27 | 380 ± 302 | 5.2 ± 5.2 | 8.9 ± 4 | 494 ± 235 |
| PCI | 73 ± 77 | 1,024 ± 1,087 | 16 ± 14 | 12 ± 14 | 807 ± 940 | |
| CTOs >3 months | 252 ± 234 | 3,985 ± 3,579 | 47 ± 36 | 64 ± 25 | 4,255 ± 2,520 | |
| Unknown duration | 166 ± 175 | 2,575 ± 2,760 | 31 ± 24 | na | na | |
| <3 months | 87 ± 78 | 1,115 ± 1,020 | 15 ± 12 | na | na | |
| Median | CA | 25 | 306 | 3.3 | 8 | 429 |
| PCI | 50 | 670 | 12 | 13 | 517 | |
| CTOs >3 months | 172 | 2,729 | 36 | 64 | 3,861 | |
| Unknown duration | 106 | 1,762 | 23 | na | na | |
| <3 months | 63 | 786 | 11 | na | na | |
| 3d Quartile | CA | 39 | 472 | 6.3 | 9 | 576 |
| PCI | 91 | 1,277 | 21 | 22 | 939 | |
| CTOs >3 months | 350 | 5,779 | 61 | 77 | 5,704 | |
| Unknown duration | 189 | 2,939 | 39 | na | na | |
| <3 months | 108 | 1,347 | 18 | na | na | |
| Max | CA | 369 | 3,460 | 34 | 34 | 2,245 |
| PCI | 1,254 | 12,015 | 93 | 114 | 7,811 | |
| CTOs >3 months | 1,786 | 24,546 | 172 | 119 | 11,921 | |
| Unknown duration | 1,334 | 20,562 | 165 | na | na | |
| <3 months | 584 | 1,900 | 90 | na | na |
Radial artery access was preferred in 96% of cases (88% right and 7% left) over femoral, humeral, or cubital artery access for CA and in 93% (85% right and 8% left) for PCI. The success rate of procedures can be assessed in various ways, for example, according to the variation in the TIMI flow after and before the procedure. The overall success rate for occlusion procedures was 87%. For all 710 total occlusions with TIMI score of 0 at the start of the procedure, 90 (12%) were failures with no improvement of TIMI score, 30 (4%) showed mild-to-moderate improvement (TIMI score ranging from 1 to 2), and 594 (84%) reached a TIMI score of 3, indicating the complete recanalization of the artery. For 207 CTOs >3 months, 43 (21%) were failures, 7 (3%) were partial successes, whereas 157 (76%) were successes. The success rate for CTOs <3 months was rather high illustrating again that these procedures were less complex which is consistent with their lower observed dose indicators and that they were almost always acute infarctions. Occlusions of unknown duration were more successful than proved CTOs.
Differences in all 3 dose indicators between antegrade and retrograde approaches ( Table 3 ) were found to be highly significant (p <0.001), retrograde approach requiring systematically longer FT and leading to greater DAP values. Lesions in bifurcation and number of the segments involved in a given procedure were analyzed because they represent another complexity factor likely to affect patient dose. There were no significant differences in dose indicators (p >0.5). All CTO procedures (antegrade and retrograde) from the first 12 months of the study were classified according to the Japanese chronic total occlusion (J-CTO) score and mean dose indicators values ( Table 4 ). This score takes into account the length of the occlusion, the tortuosity, the blunt or tapered nature of the entry shape, and the presence or absence of calcifications and if there was a previous attempt at recanalization.
| Dose Indicator | Antegrade (n = 638) | Retrograde ( n = 72) |
|---|---|---|
| Mean ± s.d. | ||
| FT [min] | 22 ± 18 | 82 ± 40 |
| AK r [mGy] | 1,789 ± 1,933 | 6,881 ± 4,243 |
| DAP [Gy.cm 2 ] | 120 ± 114 | 459 ± 304 |
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