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A Comparison of Image Quality Using Radial vs Femoral Approaches in Patients Undergoing Diagnostic Coronary Angiography
Abstract: Introduction. Radial access for diagnostic coronary angiography (CAG) has gained traction in recent years over the femoral artery approach, but difference in image quality has not been extensively studied. This study aims to compare image quality and diagnostic value in radial vs femoral access in patients undergoing invasive CAG. Methods. This is a retrospective study of 200 patients (100 radial and 100 femoral) undergoing CAG at an experienced center from 2014 to 2015. The primary endpoint was angiographic image quality, and secondary endpoints were proportion of non-diagnostic images and patient radiation dose. Image quality was assessed by four experienced angiographers using a quantitative scale. Mean differences in scores were compared as well as proportion of non-diagnostic images produced. Results. Radial access produced images that were significantly poorer than femoral access when viewing the left coronary artery (2.65 ± 0.04 vs 2.79 ± 0.03; P<.01). This difference remained significant after adjusting for age, gender, and catheter size (P=.04). There was no significant difference in image quality between the radial and femoral group when viewing the right coronary artery (2.91 ± 0.03 vs 2.84 ± 0.04; P=.11). There was a higher proportion of non-diagnostic images produced by radial access than femoral (3.23% vs 2.02%; P<.01) and radial access resulted in higher patient radiation doses (832.81 ± 49.59 mGy vs 645.69 ± 35.46 mGy; P<.01). Conclusion. Radial access produces poorer angiographic image quality and exposes patients to greater radiation compared to femoral access in contemporary practice. An awareness of these limitations is important when selecting mode of access in patients undergoing diagnostic CAG.
J INVASIVE CARDIOL 2018;30(11):411-415. Epub 2018 August 15.
Key words: coronary angiography, CAG, image quality, radial access
Radial access for diagnostic coronary angiography (CAG) is associated with several benefits, including reduced mortality rates,1,2 reduced vascular complications,3,4 improved patient quality of life,5 early discharge,3,6 and lower cost7,8 when compared to femoral access. As a result, many institutions have gradually shifted away from the traditional femoral artery approach, embracing the radial approach as the first choice for coronary catheterization where possible.9
However, there remains some evidence that femoral access has advantages over radial access, such as lower access-site failure rate,10 shorter procedural time,7,11 and less radiation exposure,12,13 although these effects seem to diminish with increasing radial access training and experience.14-16
One comparison that has not been thoroughly explored is the difference in CAG image quality produced from femoral vs radial access. The two previous studies addressing this question provide conflicting evidence.7,17 Therefore, the aim of the present study was to compare the clinical diagnostic value of image quality in radial vs femoral access in patients undergoing invasive CAG.
Methods
Study population. Patient data and angiograms were retrospectively collected from inpatients undergoing diagnostic CAG at a tertiary referral public hospital. Diagnostic CAGs meeting inclusion criteria were consecutively identified from December 2014 to June 2015. The sample size required was 100 for each group, with access gained via the femoral artery (femoral group) or the radial artery (radial group).7
Inclusion/exclusion criteria. All patients who underwent CAG with adequate clinical data were considered for inclusion in this study. In order to standardize the number of runs and view orientation for each patient’s angiogram to be analyzed, uncomplicated CAGs of the left coronary artery (LCA) and right coronary artery (RCA) were included. Any CAGs involving percutaneous intervention, fractional flow reserve measurement, or coronary artery bypass graft (CABG) were excluded. Radial-to-femoral crossovers were also excluded. Non-coronary artery images, such as ventriculograms or aortograms, were also excluded from analysis. While the left radial approach was explored in a previous study,7 it is an uncommonly used approach at our tertiary center (usually reserved for post-CABG cases), and was therefore excluded from this analysis.
Data collection method. Baseline characteristics for comparison between the two groups were collected through medical records and catheterization lab reports. This included age, gender, angiographic diagnosis, performing operator, catheter size, smoking status, history of hypertension, diabetes, hyperlipidemia, previous myocardial infarction or ischemic heart disease, and previous CAG.
The primary endpoint for this study was the angiographic image quality. Four clinicians experienced in viewing CAGs were trained to analyze the image quality of each angiogram run based on a score of 0-3, using a scoring system adapted from a 2004 study by Reddy and colleagues,17 which designated 0 = picture non-diagnostic; 1 = moderate opacification of the vessel only in systole or diastole and the picture was diagnostic; 2 = complete opacification of the vessel but not throughout systole and diastole or moderate opacification of the vessel throughout systole and diastole; and 3 = complete opacification of the entire length of the vessel throughout systole and diastole (Figure 1).
Each patient was given an average score for the angiographic views of the LCA, and one for the RCA from each assessor. The final score was a mean of the four assessors’ scores. Each access site was also graded based on the proportion of images that were non-diagnostic (ie, score = 0) for clinical implication of the ability to produce diagnostic images. The assessors were told this was a quality assurance study only, and were thus blinded to the purpose of the study, because blinding to patient access site was not possible as it was apparent in the CAG images.
The secondary endpoint was patient radiation dose. These data were acquired retrospectively from cath lab records, which were directly recorded from the radiation software output.
Statistical analysis. The sample size was determined based on previous published studies on CAG image quality,7 which indicated that 100 patients in each group were required to achieve a statistical power of >80% in detecting a mean difference in the primary endpoint of 10%. Continuous variables are presented as mean ± standard deviation, and compared between study groups using the independent t-test. Categorical variables are expressed as frequencies and percentages, and compared using the Pearson’s Chi-squared test. Primary outcomes were adjusted for age, sex, and catheter size using multivariable modeling. A subgroup analysis in patients who underwent CAG with 6 Fr catheters was performed to determine if the effect of access site persisted when catheter size was standardized. A P-value <.05 was considered statistically significant. Statistical analysis was performed using the SPSS version 23.0 (IBM Corporation, 2015).
Results
Baseline characteristics (Table 1) were overall similar between the radial and femoral groups. Patients undergoing CAG with radial access were more likely to be current smokers than the femoral group (23.5% vs 10.0%; P=.02) and less likely to suffer from hypertension (57.0% vs 72.7%; P=.02). Radial procedures were more likely to be performed using a 5 Fr catheter than a 6 Fr catheter (28.2% vs 5.2%; P<.001). In the radial group, 94 angiograms were noted to have used the radial-specific Tiger catheter (Terumo), of which 29 required other additional catheters. Femoral procedures were all performed using Judkins catheters (Boston Scientific).
The CAG image quality when viewing the LCA was significantly poorer when performed via the radial approach compared to femoral access (2.65 vs 2.79; P<.01) (Table 2). This difference remained statistically significant after adjusting for age, gender, and catheter size (P=.04) (Table 3). Radial access produced better image quality when viewing the RCA compared to femoral access, but this disparity was not statistically significant (2.91 vs 2.84; P=.11) (Table 2) and remained so after adjustment (P=.12) (Table 3).
In a separate subgroup analysis to negate the impact of catheter size on image quality, we included only patients who underwent CAG with 6 Fr catheters. There were no significant differences in baseline characteristics between the radial and femoral group (Supplementary Table S1). Angiographic image quality when viewing the LCA in this subgroup remained poorer via the radial approach compared to femoral (2.65 vs 2.79; P=.04) (Supplementary Table S2). Although statistically non-significant, this trend favoring the femoral approach remained after adjusting for age and gender (P=.06) (Supplementary Table S3). There was no significant difference in image quality between the two groups when viewing the RCA (2.91 vs 2.83; P=.17) (Supplementary Table S2), even after adjusting for age and gender (P=.15) (Supplementary Table S3).
Figure 2 demonstrates the proportion of non-diagnostic images from each group. Imaging of the LCA via the radial route was more likely to be non-diagnostic than images obtained following femoral access (4.02% vs 1.00%; P<.001). Conversely, when viewing the RCA, the proportion of non-diagnostic images was lower in the radial group compared to the femoral group (1.44% vs 4.17%; P<.001). When assessing overall performance of all runs (viewing either the LCA or RCA), the transradial approach produced a higher proportion of non-diagnostic images compared to the transfemoral approach (3.23% vs 2.02%; P<.01).
Patients were exposed to a higher radiation dose when the procedure was performed using radial access compared to femoral access (832.81 mGy vs 645.69 mGy; P<.01) (Table 4). This remained statistically significant after adjustment for age and gender (P<.01) (Table 5).
Supplemental Tables
Discussion
In this carefully conducted analysis of contemporary diagnostic CAG, we found that the radial route resulted in poorer quality images than those obtained following femoral access. There was a greater likelihood of non-diagnostic images of the left coronary system, and the patient was exposed to greater radiation during the procedure.
To our knowledge, this present study is only the third to compare the angiographic image quality between radial and femoral access, the last of which was published in 2004.7,17 In 2001, Louvard et al reported similar findings in their analysis, where poorer radial image quality was restricted to the LCA. On the other hand, in 2004, Reddy et al found no difference in image quality between radial and femoral access when viewing either LCA or RCA. However, this study was limited by a small sample size (n = 50) and therefore underpowered. A limitation of both these studies was the use of a single assessor for the determination of image quality.
The availability of radial-specific catheters such as the Tiger, which was used in 94% of our radial cases, has been shown to improve image quality and reduce radiation dose of radially produced images compared to the non-specific Judkins catheter.18 Our data indicate that this improvement is reflected solely in images of the RCA, where there was a trend toward better image quality and significantly fewer non-diagnostic images, perhaps due to the tendency for the Tiger catheter to engage the RCA deeply. Images of the prognostically more important left coronary system were, however, inferior via the radial approach. This was despite the fact that our operators had equal experience in both femoral and radial cases, and have consistently performed radial access since 2010. During the period of the study, the ratio of radial to femoral cases was approximately 2 to 1. Increased operator experience has been shown to reduce procedure time, screening time, and total radiation exposure in radial access cases.15,19,20 Therefore, given the greater experience of our operators with the radial approach, we believe this makes our findings more robust by shedding light on the shortcomings of the radial approach due to equipment and anatomical limitations. The radial approach may continue to be challenged by the tortuosity of the subclavian artery and arterial vasospasm, with the memory in the catheter curvature making it difficult to firmly engage the LCA ostium. This argument has been proposed in previous studies, and appears not to have been adequately addressed by the currently available radial-specific catheters.18
Differences in image quality in the past has been attributable to catheter size. Downsizing catheters from 6 Fr to 4 Fr reduces the image quality in transfemoral angiograms due to greater resistance to contrast injection.17,21 The smaller 5 Fr catheters more commonly used in the radial group in our study may have had a similar impact. However, this did not account for differences in image quality in our study, as the results persisted after adjustment for catheter size in the multivariable analyses. Our subgroup analysis of patients who underwent CAG with 6 Fr catheter only was limited by a reduced sample size, potentially under-powering our findings. Nonetheless, the subgroup analysis results reinforced the findings shown in our multivariable analyses, suggesting that radial access site remains a limiting factor to angiographic image quality.
Assessing the proportion of non-diagnostic images arguably has more immediate clinical relevance than our semiquantitative measure of image quality and has not been reported before. In this study, radial access was associated with significantly greater incidence of non-diagnostic images overall, primarily driven by failure to adequately opacify the left system in 4% of cases. While the absolute difference between radial and femoral scores appears small, our study likely under-estimates both the magnitude and the real inconvenience of this limitation, as we excluded angiograms with more than 10 runs to standardize our analysis process.
The finding that patients undergoing CAG with radial access were exposed to a higher radiation dose is consistent with evidence from a meta-analysis of 24 published randomized controlled trials, placing this analysis in a contemporary context.13
Study limitations. Our study is limited by its retrospective nature. As such, there was missing information on clinical characteristics for some patients, which may have compromised our adjusted analyses, including patient data on weight and body mass index. It is possible that patients with higher body mass index were preferentially selected for a radial approach. While it has been previously shown that increased body mass index correlates with increased radiation dose during coronary angiograms,22 there is no evidence of the impact of body mass index on our primary endpoint of image quality using contemporary imaging systems. We elected to limit our study to simple diagnostic angiograms, excluding the more complicated procedures, which may have limited the applicability of our findings. However, we believed this consistency was important to safeguard the robustness of our methodology, which is a unique strength of this analysis. In particular, the use of data from four independent assessors blinded to the purpose of the study reduced subjective observer bias, which is the most common limitation of this study type.
Conclusion
Contemporary radial access does produce poorer angiographic image quality compared to femoral access, driven by poorer images of the left coronary system, both when measured objectively using an image quality score, and when determining the proportion of non-diagnostic images. The enthusiastic uptake of radial access worldwide reflects reduced access complication rates in the ST-elevation myocardial infarction population, with less consistent evidence in the broader acute coronary syndrome populations, and limited evidence in stable patients.1,3,23-25 Our data suggest that this enthusiasm should be tempered by a realistic assessment of the fundamental limitations radial access places on the primary objective of the procedure, which is obtaining high-quality diagnostic images.
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From the 1Department of Cardiology, Concord Hospital, The University of Sydney, Australia; and 2Concord Clinical School, University of Sydney, NSW, Australia.
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 May 21, 2018, provisional acceptance given May 31, 2018, final version accepted June 18, 2018.
Address for correspondence: David Brieger, MD, Cardiology Department, Concord Hospital, The University of Sydney, Hospital Road, Concord 2139, NSW, Australia. Email: david.brieger@health.nsw.gov.au
