Transradial Access and Radiation Exposure in Diagnostic and Interventional Coronary Procedures

Abstract: Background. Although transradial access (TRA) is being increasingly used in interventional cardiology, there are concerns about a possible increase in radiation exposure (RE) as compared to transfemoral access (TFA). Methods. In this retrospective study, we aimed to compare RE during coronary angiography and percutaneous coronary intervention (PCI) according to the vascular access route (TRA vs TFA). We included all procedures performed in our laboratory, in which RE data (dose area product, cGy•cm²) were available, from May 2009 to May 2013. Both multiple linear regression analysis and propensity score matching were performed in order to compare RE between TRA and TFA after adjusting for clinical and procedural confounders. Results. DAP values were available for 1396 procedures; TRA rate was 82.6%. TRA patients were younger, less frequently female, and had higher body mass index as compared to TFA patients; the rates of PCI, ad hoc PCI, bypass angiography, thrombus aspiration, and primary angioplasty, as well as the number of stents implanted, fluoroscopy time, and contrast dose were significantly higher in TFA. Median DAP value was significantly higher in TFA than in TRA (9670 cGy•cm² vs 7635 cGy•cm²; P<.01). After adjusting for clinical and procedural confounders, vascular access was not found to be an independent predictor of RE at multiple regression analysis; this was also confirmed by stratified comparison of DAP values by quintiles of propensity score. Conclusion. After adjusting for clinical and procedural confounders, TRA was not found to be associated with increased RE as compared to TFA in an experienced TRA center.  

J INVASIVE CARDIOL 2014;26(9):469-474

Key words: radiation exposure, transradial intervention

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Transradial access (TRA) is being increasingly used worldwide for coronary angiography (CA) and percutaneous coronary intervention (PCI), since it offers several advantages as compared to transfemoral approach (TFA), such as significant reduction in vascular complications, increased patient comfort, reduced hospital stay, and lower cost.^1-3 Moreover, in the setting of ST-elevation myocardial infarction (STEMI), TRA is associated with reduced short-term mortality as compared to TFA, mainly mediated by a reduction in bleeding complications.^4,5 Nevertheless, TRA is technically more demanding than TFA and requires appropriate training and the completion of a learning curve to be mastered by the operator and to prove safe and effective.^6,7 Technical difficulties, especially at the beginning of the learning curve, are mainly represented by catheter manipulation and negotiation of coronary ostia; these maneuvers are usually not as straightforward as in TFA and may require more time and more fluoroscopic guidance, possibly leading to increased radiation exposure for both patients and operators. 

Medical exposure to x-ray in the field of interventional cardiology represents an important issue,⁸ since x-rays are associated with both deterministic effects, such as radiation-induced injuries in patients’ skin,⁹ and to stochastic effects, such as radiation-induced cancer.¹⁰

Whether TRA is associated with increased radiation exposure is still a matter of debate, since conflicting data have been reported.¹¹ Indeed, many studies were observational, excluded some procedure types (such as bypass angiography, and primary PCI), and included procedures performed by physicians in training or with initial experience in TRA. 

The aim of the present study is to investigate radiation exposure during CA and PCI in a moderate-volume center with high rate of TRA.

Methods

Setting. We designed a retrospective, single-center analysis of patient radiation exposure during diagnostic and interventional coronary procedures performed at our institution during a 4-year period (May 2009 to May 2013). Our hospital is a non-academic center with a catheterization laboratory performing more than 500 PCIs/year. TRA was introduced in our practice in 2003 and represents the default vascular access since 2007.

Study population. In order to assess the predictors of increased radiation exposure, we included in the study all procedures, performed either by TRA or TFA, in which radiation exposure data and fluoroscopy time were available. Emergency procedure and bypass study were included in the analysis; exclusion criteria were PCI attempts on chronic total occlusions, usually performed by bilateral TFA. Clinical and procedural data were retrieved from an electronic database in which all procedures are prospectively recorded. During the study period, there were some changes in the team of operators working in the laboratory; overall, there were seven different operators, all experienced in both TRA and TFA (mean caseload of 250 procedures/operator/year with a TRA rate ranging from 69%-90%); there were no fellows or physicians in training. CA and PCI were performed according to standard technique; vascular access site, devices, and pharmacotherapy were left to the operator’s discretion. All patients provided written informed consent to the procedure.

Diagnostic and interventional coronary procedures were defined as follows: bypass study was defined as a procedure in which angiography of at least one bypass conduit was performed; multivessel PCI was defined as a single procedure in which PCI on at least 2 different main coronary vessels was performed; ad hoc PCI was defined as a PCI performed immediately after CA; primary PCI was defined as a PCI performed during an acute STEMI (within 12 hours of symptom onset).

At the time of the study, conversions from one access to another (eg, from TRA to TFA in the case of puncture failure) were not recorded; therefore, the analysis was based on the final access route.

Radiation exposure measurement and angiographic equipment. Patient radiation exposure was measured by the dose area product (DAP), which is the product of the dose value of the incident radiation by the irradiated field and is measured in cGy•cm². Both DAP and fluoroscopy time are provided by built-in software of the angiography system, which is periodically calibrated by a technician to ensure reliability.

All procedures were performed in a single angiographic room equipped with a flat-panel Innova 2000 cardiac angiographic system (General Electric), which allows fluoroscopy and cine acquisition in four fields of view: 20, 17, 15, and 12 cm diagonal square. The number of frames is routinely set at 15 s^-1 frame rate both for fluoroscopy and cine acquisition. The interventional cardiologists use lead aprons and thyroid collars, as well as a ceiling-mounted glass shield and a lead skirt along the table to shield scattered radiations. A medical radiation technician operates the x-ray system and is responsible for patient and staff radioprotection.

Statistical analysis. Clinical and procedural characteristics were compared between patients treated by TRA (radial group) and TFA (femoral group). Categorical variables are expressed as percentages and were compared by chi-square test or Fisher’s exact test, as appropriate. Continuous variable were checked for normal distribution using histograms and Shapiro-Wilk’s test. The variables are expressed as mean ± standard deviation or median (interquartile range), and were compared by Student’s t-test or Mann-Whitney U-test, as appropriate. Correlations between continuous variables were obtained by the Pearson correlation coefficient or the Spearman correlation coefficient if variables were not normally distributed.

In order to compare radiation exposure between radial group and femoral group adjusting for clinical and procedural confounders, we performed both multiple linear regression analysis and propensity score matching.

In the regression model, the dependent variable was the natural logarithm of the radiation exposure (LnDAP) because the distribution of the DAP value was positively skewed. Several clinical and procedural characteristics known to be associated with radiation exposure, as well as vascular access site, were then forced into the model.

Propensity score indicating the likelihood of vascular access (TFA vs TRA) was calculated for each patient based on a non-parsimonious logistic regression model,¹² constructed with TFA as the dependent variable. The reliability of the model was evaluated using the Hosmer-Lemeshow goodness-of-fit statistical analysis. Patient and procedural variables were used to calculate the propensity score.

Then, the study population was stratified by quintiles of propensity score and DAP values in each quintile were compared according to vascular access. A P-value <.05 was considered statistically significant. The analyses were performed with SPSS 21.0 for Windows. 

Results

During the study period, a total of 4110 procedures were performed. Inclusion criteria, especially the availability of fluoroscopy times and DAP values, were met by 1396 procedures, which therefore represent the study cohort. TRA was used in 1153 procedures (82.6%) and was right-sided in 82.3% of cases. Clinical and procedural characteristics were different between radial group and femoral group (Table 1). Radial group patients were younger and had a higher mean body mass index (BMI), suggesting a bias toward the use of radial access in overweight patients. Femoral group patients were older, more frequently female, and had significantly higher rates of PCI, bypass angiography, multivessel PCI, ad hoc PCI, primary PCI, stent implantation, and thrombus aspiration, suggesting a bias toward the use of femoral access in sicker patients and in more complex procedures.

Indeed, DAP values were 7635 (range, 4393-12976)cGy•cm² in the radial group vs 9670 (range, 5555-14310) cGy•cm² in the femoral group (P=.01; Figure 1), fluoroscopy time (minutes:seconds) was 06:12 (range, 03:15-10:30) in the radial group vs 07:12 (range, 04:18-11:24) in the femoral group (P<.001), and contrast dose was 150.4 ± 88.2 mL in the radial group vs 189.5 ± 102.63 mL in the femoral group (P<.001).

We observed a strong correlation between fluoroscopy time and DAP (Spearman’s Rho, 0.761; P<.01) (Figure 2) and a weak, although statistically significant, correlation between BMI and DAP (Spearman’s Rho, 0.266; P<.01) (Figure 3). 

After adjusting for clinical and procedural confounders with multivariate analysis (Table 2), the following predictors of increased radiation exposure were identified: age, BMI, ad hoc PCI, number of stents implanted, bypass study, and the use of adjunctive diagnostic tools (pressure wire or intravascular ultrasound). On the contrary, female sex was a predictor of reduced radiation exposure. Moreover, there was a wide range of radiation exposure associated with each interventional cardiologist.

Vascular access site had no significant impact on radiation exposure. This finding was also confirmed by the results of propensity score analysis, which showed that no significant difference in DAP values was observed between the radial group and femoral group after stratification for quintiles of propensity score (Table 3). 

Discussion

The present study shows that TRA, compared to TFA, is not associated with increased DAP values in a moderate-volume laboratory where TRA represents the access of choice for a wide range of procedures. Given the observational design of the study and the presence of selection biases for vascular access, which are reflected by the heterogeneity of the radial group and femoral group in terms of clinical and procedural characteristics, we applied both multiple linear regression analysis and propensity score analysis in order to appraise the impact of vascular access on radiation exposure, thus obtaining consistent results after adjusting for a wide number of confounders, including the operators performing the procedure.

The issue of radiation exposure according to vascular access in interventional cardiology is still a matter of controversy. 

The majority of published studies are observational in nature and measure patient radiation exposure as assessed by fluoroscopy time, air kerma, or DAP, usually derived by the built-in software of the angiographic system. Only a few studies report data on operator radiation exposure,^13,14 although strong correlations between patient and operator exposure were observed,^13,15 so it is reasonable to assume that an increase in patient exposure will correlate with an increase in operator exposure as well.

Although many non-randomized studies reported increased patient radiation exposure with TRA,^13,16-18 TRA was not an independent predictor of radiation exposure at multiple regression analysis in two large, recently published registries.^19,20 This was confirmed by a recent meta-analysis including 11 observational and 3 randomized studies.²¹

As far as randomized comparisons are concerned, Lange et al¹⁵ observed a significant increase in fluoroscopy time and DAP with TRA as compared to TFA in diagnostic CA, but not in PCI. Brueck et al observed an increased DAP in TRA as compared to TFA, but the requested TRA experience for the operators to join the study was only 50 TRA catheterizations, whereas extensive experience in TFA was required.²²

Similar findings were observed in a substudy of the multicenter randomized RIVAL trial, which showed significantly higher fluoroscopy time and air kerma (but not DAP) values in TRA as compared to TFA, but also showed that these differences were no longer significant when analyzing high TRA volume centers and operators.²³ The impact of the learning curve on radiation exposure was also reported by Neill et al, who analyzed fluoroscopy times for diagnostic and interventional procedures during a transition phase from routine TFA to routine TRA in a single center. The authors found that although TRA was globally associated with an increase in fluoroscopy time, the time was decreasing with increasing operator experience in TRA.²⁴ A similar inverse association between increased TRA experience and fluoroscopy time was also reported by Kasasbeh et al²⁵ and Sciahbasi et al.²⁶

Our study has several areas of strength as compared to previously published studies. First, the operators participating to the study were all experts in both TRA and TFA; no fellows or physicians in training were working in the laboratory during the study period. Second, all procedures were performed in a single catheterization room with the same angiographic system; this eliminates the variability related to the inclusion of procedures performed with different angiographic systems or even different laboratories. Third, as opposed to other studies, we did not exclude some procedure types, such as primary PCI and procedures in patients with previous bypass surgery; we only excluded PCI attempts on chronic total occlusions. The inclusion of a real-world population in our study, although reflecting more closely the daily clinical practice, contributed to a quite large heterogeneity, both in clinical and procedural characteristics, between radial and femoral Groups. Indeed, as with previous studies, radial group patients had higher BMI, whereas femoral group patients were older and sicker. Interestingly, it was recently shown at a high-volume, predominantly TRA PCI center, the subset of patients undergoing PCI via TFA tended to have more challenging clinical and procedural characteristics, such as older age, female gender, higher rate of cardiogenic shock, and more complex procedures, including use of rotational atherectomy, saphenous vein graft PCI, and CTO PCI, when compared to TRA patients.²⁷

Study limitations. Our study presents several limitations, including the observational, retrospective design and only partial availability of radiation exposure parameters, which reduced the study cohort to 1396 procedures out of a total of 4110 procedures performed during the study period.

Moreover, as in most previously published studies, we did not measure operator radiation exposure and we did not consider in the analysis many technical factors and variables that can greatly influence patient exposure, such as the position of the x-ray tube, height of the table, distance between patient and image intensifier, and the fluoroscopic and cine acquisition dose rate setting. However, many of these factors are strictly related to the different mode of operation that is specific to each interventional cardiologist. 

Indeed, the heterogeneity in radiation exposure may also be influenced by other potential confounders, such as variable background and experience in TRA and different procedural complexities among the various operators. 

Therefore, after including the operators as a predictive variable in the multiple regression model, we found (consistent with previous studies)^19,20 a substantial variability in radiation exposure among them; this also provided an operator-adjusted estimate of the impact of vascular access choice on radiation exposure. 

Conclusion

In our study, TRA was not found to be associated with increased patient radiation exposure; this finding confirms the results of other studies performed in experienced TRA centers. Nevertheless, only adequately powered randomized comparisons of procedures performed by high-volume operators with experience in both access routes, possibly with measurements of both patient and operator exposure, will clarify this still-debated issue.²⁸

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From ¹Interventional Cardiology Unit, Sandro Pertini Hospital, Rome, Italy; ²Demography Unit, Stockholm University, Stockholm, Sweden; and ³Emergency Department, Sandro Pertini Hospital, Rome, Italy.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript submitted January 6, 2014, provisional acceptance given February 28, 2014, final version accepted March 18, 2014.

Address for correspondence: Dr Stefano Rigattieri, UOSD Emodinamica Interventistica, Ospedale Sandro Pertini, Via dei Monti Tiburtini 385, 00157 Roma, Italy. Email: stefanorigattieri@yahoo.it