Clin Res Cardiol DOI 10.1007/s00392-015-0814-7
ORIGINAL PAPER
Reducing radiation exposure during invasive coronary angiography and percutaneous coronary interventions implementing a simple four-step protocol Moritz Seiffert • Francisco Ojeda • Kai Mu¨llerleile • Elvin Zengin • Christoph Sinning • Christoph Waldeyer • Edith Lubos • Ulrich Scha¨fer Karsten Sydow • Stefan Blankenberg • Dirk Westermann
•
Received: 14 December 2014 / Accepted: 13 January 2015 Ó Springer-Verlag Berlin Heidelberg 2015
Abstract Background With an increasing number of complex and repeated percutaneous coronary interventions (PCI), radiation-induced hazards for patients and operators remain an important issue in fluoroscopy-guided procedures. Our objective was to evaluate radiation exposure during coronary angiographic procedures and assess the efficacy of a four-step program to reduce radiation exposure during coronary angiography (CAG) and PCI. Methods and results A retrospective single-center analysis was performed in patients undergoing CAG or PCI in the first 6 months of 2012 vs. the first 6 months of 2014 (n = 3,107 procedures). During 2013, a four-step protocol was established in our hospital. It contained measures to reduce radiation exposure, including a frame rate reduction from 15 to 7.5 frames per second, the use of fluoroscopy storage, strict use of beam collimation, and repeat training on radiation safety. After adjustment for confounding variables, a dose-area product (DAP) reduction of 54.2 % was observed subsequent to implementation of the fourstep protocol. Independent predictors of DAP were age [odds ratio (OR) 1.01], body surface area (OR 5.47), prior coronary artery bypass grafting (OR 1.44), radial access (OR 1.16), PCI (OR 2.36), female gender (OR 0.91), and the implementation of the four-step program (OR 0.46). Conclusion A simple four-step protocol led to a significant reduction in radiation exposure in diagnostic and
M. Seiffert F. Ojeda K. Mu¨llerleile E. Zengin C. Sinning C. Waldeyer E. Lubos U. Scha¨fer K. Sydow S. Blankenberg D. Westermann (&) Department of General and Interventional Cardiology, University Heart Center Hamburg, Martinistrasse 52, 20246 Hamburg, Germany e-mail: [email protected]
interventional coronary procedures without significant drawbacks in image quality. Hence, radiation safety programs are of paramount importance and should be established to improve patient and operator safety with regard to radiation-induced hazards. Keywords Radiation Percutaneous coronary interventions Abbreviations CABG Coronary artery bypass grafting CAG Coronary angiography CFX Circumflex artery DAP Dose-area product LAD Left anterior descending coronary artery PCI Percutaneous coronary intervention RCA Right coronary artery
Introduction Radiation exposure during coronary angiography (CAG) and percutaneous coronary interventions (PCI) is associated with radiation-induced injuries. Deterministic and stochastic effects leading to skin injury and potential cancer have been described [1]. With an increasing number of complex and repeated PCI, radiation-induced hazards remain an important issue in fluoroscopy-guided procedures. In addition to the patients’ risk, radiation-induced damage has also been reported for interventional cardiologists [2] emphasizing the importance of reducing radiation exposure during procedures. However, several caveats challenge attempts to reduce radiation in the cardiac catheterization laboratory-first,
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sufficient image quality is of utmost importance and should not be compromised by reducing radiation. Second, attempts to reduce radiation should not result in extended procedure duration or increased contrast agent use with subsequent adverse impact on renal function. These aspects have also been the basis of the ALARA (as low as reasonably achievable) principle, guiding radiation use throughout all medical specialties. As cardiology has been identified as one of the specialties with the highest utilization of radiation [3], all measures to reduce radiation exposure are considered essential in this field [4, 5]. Radiation exposure is influenced by a variety of technical and clinical factors. While patient characteristics, e.g. body surface area (BSA), cannot be modified by the operator, procedural aspects can be adjusted to reduce radiation exposure during coronary procedures. Accordingly, we implemented a four-step program in our cardiac catheterization laboratory, sought to define radiation exposure of different strategies, and assess efficacy in reducing dose-area product (DAP).
Materials and methods Study design We conducted a retrospective analysis of all consecutive coronary angiograms and PCI performed at our institution from January 1st, 2012 through June 30th, 2012 and January 1st, 2014 through June 30th, 2014, respectively. Operators included experienced attending physicians and cardiology fellows in interventional training to evaluate the real-world scenario of a teaching hospital. Elective, urgent, and emergent procedures were included for the same reason. All procedures were performed using a flat panel detector X-ray system (Allura Xper FD10, Philips Medical, Eindhoven, The Netherlands). Radiation dose measurements Fluoroscopy time is the duration of fluoroscopy during the procedure. However, it does not include the energy dose utilized and is, therefore, not a useful descriptor of patient radiation. The cumulated DAP represents the absorbed energy dose delivered to the patient multiplied by the cross-sectional area irradiated and is given in cGy*cm2. It is measured by a transmission ionization chamber and is considered a surrogate measure of the patient’s risk of stochastic radiation effects. In contrast to the total air Kerma at the interventional reference point, an approximation to the deterministic effect, DAP is independent of
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the distance from the X-ray source in different c-arm angulations [1, 4]. Four-step plan to reduce radiation exposure During 2013, a simple four-step algorithm was established in our unit to reduce radiation exposure to patients and operators in CAG and PCI procedures. The changes implemented contained (1) a reduction from 15 to 7.5 frames per second for cineangiographic images, (2) the use of the last image hold or fluorostore feature to document stent expansion, balloon inflation, and guidewire position during PCI instead of cineangiographic imaging, (3) strict use of beam collimation to limit the exposed field, and (4) additional and repeat training on radiation safety to enhance awareness in this regard. In case of insufficient imaging quality, adjustment towards higher frame rates was left to the discretion of the operator. Data management and statistics All relevant patient demographics and procedural variables, including access choice, target vessel, contrast agent volume, fluoroscopy time, and DAP were documented in a dedicated database. Primary endpoint was DAP, secondary endpoints were fluoroscopy time and contrast volume. Data are grouped according to the date of the procedure performed (2012 vs. 2014) to investigate on the effect of measures taken to reduce radiation exposure during 2013. Categorical data are presented as counts (percentages); they were compared with the Chi-square test. Continuous data are presented as median (interquartile range); they were compared using Mann–Whitney U or Kruskal–Wallis tests. DAP was linearly regressed, after being log transformed to achieve an approximate normal distribution, on age, sex, BSA, access, PCI and year. Beta coefficients are given after re-transformation [exp(beta coefficient)] to describe the relative influence of each variable on DAP. P values are reported without correction for multiple testing. The level of statistical significance was set to twotailed P \ 0.05. Statistical analysis was performed using SPSS version 22 and R version 3.1 [6].
Results During the first half year of 2012 and 2014, a total of 3,107 patients underwent diagnostic CAG or PCI at our institution and were hence included into this retrospective analysis. Patient demographics with respect to age, gender and body mass index were similar in the respective groups with a majority of male patients (71.3 %) and a median age of 69 years (Table 1). A similar share of previous coronary
Clin Res Cardiol Table 1 Baseline and procedural characteristics
All patients (n = 3,107) Age (years) Sex (male)
2012 (n = 1,656)
69.0 (61.0–76.0) 2,216 (71.3 %)
69.0 (60.0–76.0) 1,185 (71.6 %)
2014 (n = 1,451)
P
70.0 (61.0–76.0)
0.36
1,031 (71.1 %)
0.76
BMI (kg/m2)
26.1 (24.2–29.4)
26.2 (24.2–29.4)
26.0 (24.1–29.4)
0.25
BSA (m2)
1.96 (1.81–2.08)
1.96 (1.81–2.08)
1.96 (1.81–2.08)
0.33
Prior CABG
311 (10.0 %)
155 (9.4 %)
156 (10.8 %)
0.21
421 (13.7 %)
163 (10.0 %)
258 (18.1 %)
2,631 (85.8 %)
1,466 (89.5 %)
1,165 (81.6 %)
\0.01
Access Radial Femoral Other
13 (0.4 %)
9 (0.5 %)
4 (0.3 %)
Procedure Values are presented as median (interquartile range) or frequencies and percentages BMI body mass index, BSA body surface area, CABG coronary artery bypass grafting, CAG coronary angiography, CFX circumflex artery, LAD left anterior descending artery, PCI percutaneous coronary intervention, RCA right coronary artery
0.82
CAG
1,848 (59.5 %)
988 (59.7 %)
860 (59.3 %)
PCI
1,259 (40.5 %)
668 (40.3 %)
591 (40.7 %)
79 (6.3 %)
50 (7.5 %)
29 (4.9 %)
LAD CFX
473 (37.6 %) 238 (18.9 %)
248 (37.1 %) 130 (19.5 %)
225 (38.1 %) 108 (18.3 %)
RCA
PCI—target vessel Left main stem
0.44
358 (28.4 %)
184 (27.5 %)
174 (29.4 %)
Bypass graft
48 (3.8 %)
26 (3.9 %)
22 (3.7 %)
Multiple vessels
63 (5.0 %)
30 (4.5 %)
33 (5.6 %)
Table 2 Procedural characteristics—before and after implementation of a four-step plan
Dose-area product (cGy*cm2) PCI Radial
All patients (n = 3,107)
2012 (n = 1,656)
2014 (n = 1,451)
P
2,017 (1,021–3,917)
2,754 (1,566–5,081)
1,300 (670–2,583)
\0.01
3,380 (1,826–5,990)
4,570 (2,872–7,774)
2,217 (1,259–3,972)
\0.01
3,463 (2,011–5,438)
4,825 (3,209–8,155)
2,442 (1,390–4,462)
\0.01
3,345 (1,808–6,008)
4,566 (2,843–7,758)
2,092 (1,252–3,841)
\0.01
1,404 (764–2,555)
1,992 (1,183–3,288)
940 (523–1,655)
\0.01
Radial
1,380 (747–2,756)
2,131 (1,225–3,980)
1,102 (599–1,926)
\0.01
Femoral
1,382 (757–2,478)
1,950 (1,163–3,184)
853 (492–1,499)
\0.01
Femoral CAG
Fluoroscopy time (min)
5.8 (2.5–11.3)
5.6 (2.4–11.0)
6.0 (2.6–11.9)
0.06
10.5 (6.9–17.3)
10.4 (6.5–16.6)
11.1 (7.2–18.1)
0.19
Radial
12.4 (8.3–18.1)
13.1 (8.6–18.6)
12.3 (8.1–18.1)
0.40
Femoral CAG
10.4 (6.5–17.0) 3.2 (1.9–6.3)
10.1 (6.4–16.4) 3.1 (1.8–6.1)
10.5 (7.1–18.1) 3.3 (1.9–7.0)
0.11 0.10
Radial
4.8 (3.0–9.1)
4.7 (3.0–9.8)
5.0 (3.0–8.7)
0.97
Femoral
2.8 (1.6–5.5)
2.7 (1.6–5.5)
2.8 (1.6–5.5)
0.97 \0.01
PCI
Contrast volume (ml)
90 (58–138)
94 (61–135)
84 (54–140)
140 (100–190)
139 (100–180)
147 (106–199)
Radial
142 (109–190)
140 (104–181)
143 (110–200)
0.80
Femoral
140 (100–190)
138 (100–180)
147 (105–199)
\0.01
67 (50–94)
74 (51–100)
60 (46–84)
\0.01
Radial
65 (48–85)
61 (46–89)
67 (50–81)
0.56
Femoral
67 (50–95)
75 (52–100)
59 (46–84)
\0.01
PCI
CAG
0.01
Values are presented as median (interquartile range) CAG coronary angiography, PCI percutaneous coronary intervention
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Fig. 1 Dose-area product before (2012) and after (2014) implementation of a four-step program to reduce radiation exposure (a) and stratified according to coronary angiography (CAG) or percutaneous coronary intervention (PCI) (b). *P \ 0.01
artery bypass surgery (CABG) was observed in both years. Access choice differed between both groups with 18.1 % of patients undergoing radial procedures in 2014 and 10.0 % in 2012. 40.5 % of overall procedures included coronary interventions, consistent in 2012 and 2014. Target vessels intervened upon included the LAD (37.6 %), RCA (28.4 %), CFX (18.9 %), and left main coronary artery (6.3 %). Bypass graft interventions were performed in 3.8 and 5.0 % of patients underwent PCI of more than one coronary artery. No differences in target vessels were observed between the 2 years. Patients with a femoral compared to radial procedure were more likely to have had previous CABG (10.9 vs. 4.5 %, P \ 0.01), to receive coronary intervention (42.1 vs. 34.4 %, P = 0.01), and to undergo PCI of the left main stem (7.0 vs. 1.4 %) or bypass grafts (4.2 vs. 0.7 %.). DAP was higher in PCI than CAG (median 3,380 vs. 1,404 Gy*cm2, P \ 0.01). Furthermore, it was reduced significantly from 2012 to 2014 in the overall patient population and in the respective subgroups of patients undergoing PCI or CAG through radial or femoral approaches (Table 2; Fig. 1). Although DAP was similar in the unadjusted comparison of patients undergoing radial and femoral procedures (Table 3), adjusted analysis showed an increase of 16.4 % in DAP using the radial approach (Table 4). In addition, fluoroscopy time was longer in radial PCI or CAG (16.1 and 41.7 %). A subsequent trend towards a longer median fluoroscopy time in 2014 compared to 2012 (6.0 vs. 5.6 min, P = 0.06) was observed in the light of an increasing share of radial procedures. Excluding multiple vessel interventions, no association of target vessels and DAP was observed (Table 5). Fluoroscopy time, however, differed significantly with the lowest values for treatment of LAD and CFX lesions and the highest for bypass graft PCI.
Table 3 Procedural characteristics—radial versus femoral approach
Dose-area product (cGy*cm2)
All patients (n = 3,052)
Radial (n = 421)
Femoral (n = 2,631)
P
2,017 (1,021–3,917)
1,981 (966–3,843)
2,007 (1,025–3,862)
PCI
3,359 (1,819–5,963)
3,463 (2011–5,438)
3,347 (1,808–6,020)
0.92
CAG
1,404 (764–2,555)
1,380 (747–2,756)
1,382 (757–2,478)
0.50
Fluoroscopy time (min)
0.56
\0.01
5.8 (2.5–11.3)
7.3 (3.4–12.8)
5.4 (2.3–11.0)
PCI
10.5 (6.9–17.3)
12.4 (8.3–18.1)
10.4 (6.5–17.0)
CAG
3.2 (1.9–6.3)
4.8 (3.0–9.1)
2.8 (1.6–5.5)
\0.01
Contrast volume (ml)
0.03
90 (58–138)
80 (56–129)
90 (58–140)
0.04
PCI
140 (100–190)
142 (109–190)
140 (100–190)
0.61
CAG
67 (50–94)
65 (48–85)
67 (50–95)
0.24
Values are presented as median (interquartile range) CAG coronary angiography, PCI percutaneous coronary intervention
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Clin Res Cardiol Table 4 Linear regression analysis Parameter
Beta coefficient (95 % CI)
Beta coefficient per SD (95 % CI)
P
Age (per year)
1.012 (1.010–1.014)
1.146 (1.116–1.176)
\0.01
Female gender (vs. male)
0.907 (0.850–0.969)
0.957 (0.930–0.986)
\0.01
BSA (per m2)
5.468 (4.763–6.278)
1.445 (1.403–1.489)
\0.01
Prior CABG
1.443 (1.327–1.570)
1.116 (1.089–1.146)
\0.01
Radial access (vs. femoral)
1.164 (1.082–1.253)
1.054 (1.027–1.081)
\0.01
PCI (vs. CAG)
2.356 (2.237–2.479)
1.523 (1.486–1.564)
\0.01
Year (2014 vs. 2012)
0.458 (0.426–0.482)
0.672 (0.660–0.695)
\0.01
Linear regression analysis for dose-area product (DAP). Beta coefficients reflect the relative influence of each variable on DAP and are given after re-transformation [exp(beta coefficient)] BSA body surface area, CABG coronary artery bypass grafting, CAG coronary angiography, CI confidence interval, PCI percutaneous coronary intervention, SD standard deviation
Contrast volume was reduced significantly from 2012 to 2014 (94 vs. 84 ml, P \ 0.01) due to a decrease in the femoral CAG subgroup (Table 2). In the femoral PCI and overall PCI subgroups, however, a more contrast medium was required in 2014 vs. 2012. Contrast use differed significantly with regard to target vessels: While the lowest volumes were utilized in LCA and RCA interventions, LAD and bypass graft PCI required the highest amounts of contrast agent (Table 5). Linear regression analysis identified age [odds ratio (OR) 1.01], body surface area (OR 5.47), prior CABG (OR 1.44), radial access (OR 1.16), and PCI (OR 2.36) as predictors of increased DAP during coronary procedures (Table 4). Female gender (OR 0.91) and the implementation of the four-step plan between 2012 and 2014 (OR 0.46) were associated with a decrease in radiation exposure.
Discussion In this retrospective analysis of 3,107 patients undergoing CAG and PCI, we observed a significant reduction of radiation exposure after initiating a simple four-step program. After adjustment for confounding variables, a DAP reduction of 54.2 % was observed, which corresponds to the radiation dose of approximately 400 chest X-rays saved per patient [3]. This effect was consistent among patients undergoing coronary angiography or PCI. Among the variables analyzed, the implemented changes led to the largest reduction in radiation exposure and yielded to the only parameter that was easily influenced by the operator. Importantly, the overall program was not associated with increased use of contrast medium, hence ruling out insufficient temporal resolution of the acquired images after implementation of the protocol. Patient demographics and baseline variables were similar among patients before and after implementation of the
program. Importantly, no differences were observed in body mass index and surface area, age, gender, and performed procedures—all of which were factors known to influence radiation exposure. This association has previously been described [7–11] and was reconfirmed in our linear regression analysis. Data are conflicting regarding the influence of access choice on radiation exposure [12]. While an increase in DAP and fluoroscopy time with radial access has been described [13], some authors link this effect primarily to lower volume centers with similar radiation exposure in high volume radial centers [10, 12, 14]. The results of our analysis are interesting in several regards—Radial access was used more frequently in 2014 compared to 2012, however, still performed in the minority of patients undergoing CAG or PCI. This may have been attributed to the setting of a teaching hospital and tertiary referral center with a large fraction of complex procedures. Operators tended towards a femoral approach in patients with patent bypass grafts, coronary interventions vs. diagnostic angiography, and treatment of lesions in the left main stem or bypass grafts, reflecting more complex procedures. After adjustment for confounding variables, radiation exposure was higher in radial procedures in our analysis. Explanations may refer to less radial experience in the described setting and the more complex placement of suitable diagnostic or guiding catheters, as has previously been described [14]. Little data are available for DAP with regard to target vessels. An association has been described [11] and may be linked to beam angulation [9], however, target vessels were not linked to higher DAP in our experience. The use of contrast agent was similar with different access routes and was also significantly reduced between 2012 and 2014 overall. This reduction was mainly attributed to a decrease in the femoral coronary angiography subgroup. In the femoral PCI subgroup, however, a larger amount of contrast agent was required in 2014 vs. 2012, possibly reflecting a higher fraction of complex procedures
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0.14
* Comparison was performed with the Kruskal–Wallis test excluding multiple vessel interventions
CFX circumflex artery, LAD left anterior descending artery, RCA right coronary artery
Radiation and contrast exposure during coronary interventions according to different target vessels. Values are presented as median (interquartile range)
\0.01 178 (145–240)
198 (150–246) 146 (100–200)
147 (100–181) 125 (90–170)
132 (98–178) 149 (110–193)
138 (95–175) 145 (106–184)
154 (110–200) 141 (90–190) 147 (106–199) 2014
120 (77–170) 139 (100–180) 2012
\0.01 190 (147–245) 146 (100–200) 130 (94–170) 140 (100–185) 150 (110–190) 130 (82–190) 140 (100–190) Contrast volume (ml)
\0.01
\0.01 12.5 (10.5–20.9)
15.0 (9.1–22.7) 17.2 (11.4–22.7)
14.4 (10.3–20.4) 10.9 (7.1–17.6)
12.5 (8.1–21.5) 9.8 (6.7–15.7)
8.6 (5.3–14.3) 9.9 (6.5–15.9)
9.9 (6.5–15.5) 11.9 (5.1–23.0) 11.1 (7.2–18.1) 2014
10.6 (6.3–19.8) 10.4 (6.5–16.6) 2012
0.09 \0.01
0.91 6,624 (4,553–10,797)
3,172 (2,432–6,896) 14.1 (9.8–21.0) 1,887 (1,229–4,603) 14.9 (10.4–22.2)
5,623 (3,369–7,065) 4,452 (2,774–7,450)
2,306 (1,349–3,636) 11.3 (7.3–19.3) 2,363 (1,509–4,396) 9.2 (6.0–15.1)
5,099 (2,726–7,613) 4,329 (2,814–7,768)
1,786 (1,028–3,380) 9.9 (6.5–15.6) 2,327 (1,072–4,948) 11.0 (5.4–21.1)
4,190 (2,643–8,312) 4,570 (2,872–7,774)
2,227 (1,259–3,994) 10.5 (6.9–17.4) 2014 Fluoroscopy time (min)
2012
0.26 4,591 (3,103–9,045) 4,195 (1,820–6,152) 3,242 (1,786–5,491) 3,681 (1,905–6,068) 3,063 (1,637–5,799) 3,676 (1,835–7,350) 3,387 (1,826–5,998)
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Dose-area product (cGy*cm2)
Left main stem (n = 79) All target vessels (n = 1,259)
Table 5 Target vessels
LAD (n = 473)
CFX (n = 238)
RCA (n = 358)
Bypass graft (n = 48)
Multiple vessels (n = 63)
P*
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in this group with less complex procedures being attributed to the growing radial group. Although the increase in contrast use was mild, future studies will have to evaluate its impact on renal function. A central part of our program was frame rate reduction from 15 to 7.5 frames per second for cine acquisitions. A significant reduction of radiation exposure to the patients and operators has recently been demonstrated [15, 16]. We confirm these findings in a larger patient cohort and demonstrate an even greater reduction by implementing a fourstep protocol. Importantly, the reduced frame rate was sufficient for the vast majority of our procedures and higher frame rates were only necessary in particular circumstances, e.g. to evaluate coronary stent overlap or exact placement of bioresorbable vascular scaffolds. A further reduction to even lower frame rates may be reasonable in certain cases but clearly reduces image quality. Consistent collimation to the region of interest was shown to effectively reduce radiation during three-dimensional rotational angiography [17] and was an essential component of a mini-course on radiation safety during CAG and PCI [18]. Although impossible to quantify, operators were educated on consequent collimation especially during PCI in our institution, in particular during balloon and stent placement with a known coronary anatomy and sufficient guidecatheter and guidewire control. Consistent collimation was shown to reduce radiation exposure by more than 65 % for PCI [19] as collimation reduces radiation by the inversesquare law. In a similar manner, we encouraged the fluorostore feature that enables storage of the last 20 s of fluoroscopy to document stent expansion, balloon inflation, and guidewire position during PCI instead of a new cineangiographic imaging with additional radiation. If the operator felt the need for better visualization, additional cineangiography runs were left at his discretion, e.g. in complex and severely calcified lesions. Extreme angulations were shown to be associated with higher radiation exposure [8, 9] and their use was discouraged in our program whenever feasible. As consistent data confirm the strong influence of individual operators on radiation doses, the clear need for physician education cannot be overemphasized [10, 11, 14, 20]. Several limitations need to be addressed with regard to the presented results: The study was set up as a single-center retrospective analysis and the results can, therefore, only be interpreted as hypothesis generating. Despite balanced baseline parameters, confounding variables not measured may have influenced the results presented. For example, data on beam angulation and lesion or procedure complexity were not available. As all four steps to reduce radiation exposure were integrated at once, it was impossible to evaluate the effect of each step alone. Furthermore, radiation exposure was approximated by DAP and
Clin Res Cardiol
fluoroscopy time. However, the patient’s exact skin dose can only be approximated at current [1]. In addition, operators’ radiation doses were not evaluated in this analysis. In conclusion, by implementing a simple four-step program into clinical routine at a teaching hospital and tertiary referral center, a significant reduction in radiation exposure was achieved for diagnostic and interventional coronary procedures without significant drawbacks to the image quality. In addition to technical advances and protection equipment, continuous physician education and benchmarking of radiation proved simple yet very effective in utilizing radiation exposure as low as reasonably achievable benefitting patients and operators alike. Acknowledgments D. W., K. M. and S. B. are funded by the DZHK (Deutsches Zentrum fu¨r Herz-Kreislauf-Forschung). Conflict of interest
None.
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Trevino-Frutos R (2013) Effect of physician training on the X-ray dose delivered during coronary angioplasty. J Invasive Cardiol 25:109–113 Agarwal S, Parashar A, Bajaj NS, Khan I, Ahmad I, Heupler FA Jr, Bunte M, Modi DK, Tuzcu EM, Kapadia SR (2014) Relationship of beam angulation and radiation exposure in the cardiac catheterization laboratory. JACC Cardiovasc Intervent 7:558–566 Delewi R, Hoebers LP, Ramunddal T, Henriques JP, Angeras O, Stewart J, Robertsson L, Wahlin M, Petursson P, Piek JJ, Albertsson P, Matejka G, Omerovic E (2013) Clinical and procedural characteristics associated with higher radiation exposure during percutaneous coronary interventions and coronary angiography. Circ Cardiovasc Intervent 6:501–506 Fetterly KA, Lennon RJ, Bell MR, Holmes DR Jr, Rihal CS (2011) Clinical determinants of radiation dose in percutaneous coronary interventional procedures: influence of patient size, procedure complexity, and performing physician. JACC Cardiovasc Intervent 4:336–343 Rao SV, Krucoff MW (2013) Radial first: paradox ? proficiency = opportunity. J Am Heart Assoc 2:e000281 Shah B, Bangalore S, Feit F, Fernandez G, Coppola J, Attubato MJ, Slater J (2013) Radiation exposure during coronary angiography via transradial or transfemoral approaches when performed by experienced operators. Am Heart J 165:286–292 Jolly SS, Cairns J, Niemela K, Steg PG, Natarajan MK, Cheema AN, Rao SV, Cantor WJ, Dzavik V, Budaj A, Sheth T, Valentin V, Fung A, Widimsky P, Ferrari E, Gao P, Jedrzejowski B, Mehta SR, Investigators R (2013) Effect of radial versus femoral access on radiation dose and the importance of procedural volume: a substudy of the multicenter randomized RIVAL trial. JACC Cardiovasc Intervent 6:258–266 Abdelaal E, Plourde G, MacHaalany J, Arsenault J, Rimac G, Dery JP, Barbeau G, Larose E, De Larochelliere R, Nguyen CM, Allende R, Ribeiro H, Costerousse O, Mongrain R, Bertrand OF, Interventional Cardiologists at Quebec Heart-Lung I (2014) Effectiveness of low rate fluoroscopy at reducing operator and patient radiation dose during transradial coronary angiography and interventions. JACC Cardiovasc Intervent 7:567–574 Wassef AW, Hiebert B, Ravandi A, Ducas J, Minhas K, Vo M, Kass M, Parmar G, Hussain F (2014) Radiation dose reduction in the cardiac catheterization laboratory utilizing a novel protocol. JACC Cardiovasc Intervent 7:550–557 Wielandts JY, Smans K, Ector J, De Buck S, Heidbuchel H, Bosmans H (2010) Effective dose analysis of three-dimensional rotational angiography during catheter ablation procedures. Phys Med Biol 55:563–579 Kuon E, Weitmann K, Hoffmann W, Dorr M, Reffelmann T, Hummel A, Riad A, Busch MC, Empen K, Felix SB (2014) Efficacy of a minicourse in radiation-reducing techniques in invasive cardiology: a multicenter field study. JACC Cardiovasc Intervent 7:382–390 Kuon E, Robinson DM, Empen K, Dahm JB (2005) Fluoroscopy time: an overestimated factor for patient radiation exposure in invasive cardiology. Rofo 177:812–817 Fazel R, Curtis J, Wang Y, Einstein AJ, Smith-Bindman R, Tsai TT, Chen J, Shah ND, Krumholz HM, Nallamothu BK (2013) Determinants of fluoroscopy time for invasive coronary angiography and percutaneous coronary intervention: insights from the NCDR((R)). Cathet Cardiovasc Intervent 82:1091–1105
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ORIGINAL PAPER
Reducing radiation exposure during invasive coronary angiography and percutaneous coronary interventions implementing a simple four-step protocol Moritz Seiffert • Francisco Ojeda • Kai Mu¨llerleile • Elvin Zengin • Christoph Sinning • Christoph Waldeyer • Edith Lubos • Ulrich Scha¨fer Karsten Sydow • Stefan Blankenberg • Dirk Westermann
•
Received: 14 December 2014 / Accepted: 13 January 2015 Ó Springer-Verlag Berlin Heidelberg 2015
Abstract Background With an increasing number of complex and repeated percutaneous coronary interventions (PCI), radiation-induced hazards for patients and operators remain an important issue in fluoroscopy-guided procedures. Our objective was to evaluate radiation exposure during coronary angiographic procedures and assess the efficacy of a four-step program to reduce radiation exposure during coronary angiography (CAG) and PCI. Methods and results A retrospective single-center analysis was performed in patients undergoing CAG or PCI in the first 6 months of 2012 vs. the first 6 months of 2014 (n = 3,107 procedures). During 2013, a four-step protocol was established in our hospital. It contained measures to reduce radiation exposure, including a frame rate reduction from 15 to 7.5 frames per second, the use of fluoroscopy storage, strict use of beam collimation, and repeat training on radiation safety. After adjustment for confounding variables, a dose-area product (DAP) reduction of 54.2 % was observed subsequent to implementation of the fourstep protocol. Independent predictors of DAP were age [odds ratio (OR) 1.01], body surface area (OR 5.47), prior coronary artery bypass grafting (OR 1.44), radial access (OR 1.16), PCI (OR 2.36), female gender (OR 0.91), and the implementation of the four-step program (OR 0.46). Conclusion A simple four-step protocol led to a significant reduction in radiation exposure in diagnostic and
M. Seiffert F. Ojeda K. Mu¨llerleile E. Zengin C. Sinning C. Waldeyer E. Lubos U. Scha¨fer K. Sydow S. Blankenberg D. Westermann (&) Department of General and Interventional Cardiology, University Heart Center Hamburg, Martinistrasse 52, 20246 Hamburg, Germany e-mail: [email protected]
interventional coronary procedures without significant drawbacks in image quality. Hence, radiation safety programs are of paramount importance and should be established to improve patient and operator safety with regard to radiation-induced hazards. Keywords Radiation Percutaneous coronary interventions Abbreviations CABG Coronary artery bypass grafting CAG Coronary angiography CFX Circumflex artery DAP Dose-area product LAD Left anterior descending coronary artery PCI Percutaneous coronary intervention RCA Right coronary artery
Introduction Radiation exposure during coronary angiography (CAG) and percutaneous coronary interventions (PCI) is associated with radiation-induced injuries. Deterministic and stochastic effects leading to skin injury and potential cancer have been described [1]. With an increasing number of complex and repeated PCI, radiation-induced hazards remain an important issue in fluoroscopy-guided procedures. In addition to the patients’ risk, radiation-induced damage has also been reported for interventional cardiologists [2] emphasizing the importance of reducing radiation exposure during procedures. However, several caveats challenge attempts to reduce radiation in the cardiac catheterization laboratory-first,
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sufficient image quality is of utmost importance and should not be compromised by reducing radiation. Second, attempts to reduce radiation should not result in extended procedure duration or increased contrast agent use with subsequent adverse impact on renal function. These aspects have also been the basis of the ALARA (as low as reasonably achievable) principle, guiding radiation use throughout all medical specialties. As cardiology has been identified as one of the specialties with the highest utilization of radiation [3], all measures to reduce radiation exposure are considered essential in this field [4, 5]. Radiation exposure is influenced by a variety of technical and clinical factors. While patient characteristics, e.g. body surface area (BSA), cannot be modified by the operator, procedural aspects can be adjusted to reduce radiation exposure during coronary procedures. Accordingly, we implemented a four-step program in our cardiac catheterization laboratory, sought to define radiation exposure of different strategies, and assess efficacy in reducing dose-area product (DAP).
Materials and methods Study design We conducted a retrospective analysis of all consecutive coronary angiograms and PCI performed at our institution from January 1st, 2012 through June 30th, 2012 and January 1st, 2014 through June 30th, 2014, respectively. Operators included experienced attending physicians and cardiology fellows in interventional training to evaluate the real-world scenario of a teaching hospital. Elective, urgent, and emergent procedures were included for the same reason. All procedures were performed using a flat panel detector X-ray system (Allura Xper FD10, Philips Medical, Eindhoven, The Netherlands). Radiation dose measurements Fluoroscopy time is the duration of fluoroscopy during the procedure. However, it does not include the energy dose utilized and is, therefore, not a useful descriptor of patient radiation. The cumulated DAP represents the absorbed energy dose delivered to the patient multiplied by the cross-sectional area irradiated and is given in cGy*cm2. It is measured by a transmission ionization chamber and is considered a surrogate measure of the patient’s risk of stochastic radiation effects. In contrast to the total air Kerma at the interventional reference point, an approximation to the deterministic effect, DAP is independent of
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the distance from the X-ray source in different c-arm angulations [1, 4]. Four-step plan to reduce radiation exposure During 2013, a simple four-step algorithm was established in our unit to reduce radiation exposure to patients and operators in CAG and PCI procedures. The changes implemented contained (1) a reduction from 15 to 7.5 frames per second for cineangiographic images, (2) the use of the last image hold or fluorostore feature to document stent expansion, balloon inflation, and guidewire position during PCI instead of cineangiographic imaging, (3) strict use of beam collimation to limit the exposed field, and (4) additional and repeat training on radiation safety to enhance awareness in this regard. In case of insufficient imaging quality, adjustment towards higher frame rates was left to the discretion of the operator. Data management and statistics All relevant patient demographics and procedural variables, including access choice, target vessel, contrast agent volume, fluoroscopy time, and DAP were documented in a dedicated database. Primary endpoint was DAP, secondary endpoints were fluoroscopy time and contrast volume. Data are grouped according to the date of the procedure performed (2012 vs. 2014) to investigate on the effect of measures taken to reduce radiation exposure during 2013. Categorical data are presented as counts (percentages); they were compared with the Chi-square test. Continuous data are presented as median (interquartile range); they were compared using Mann–Whitney U or Kruskal–Wallis tests. DAP was linearly regressed, after being log transformed to achieve an approximate normal distribution, on age, sex, BSA, access, PCI and year. Beta coefficients are given after re-transformation [exp(beta coefficient)] to describe the relative influence of each variable on DAP. P values are reported without correction for multiple testing. The level of statistical significance was set to twotailed P \ 0.05. Statistical analysis was performed using SPSS version 22 and R version 3.1 [6].
Results During the first half year of 2012 and 2014, a total of 3,107 patients underwent diagnostic CAG or PCI at our institution and were hence included into this retrospective analysis. Patient demographics with respect to age, gender and body mass index were similar in the respective groups with a majority of male patients (71.3 %) and a median age of 69 years (Table 1). A similar share of previous coronary
Clin Res Cardiol Table 1 Baseline and procedural characteristics
All patients (n = 3,107) Age (years) Sex (male)
2012 (n = 1,656)
69.0 (61.0–76.0) 2,216 (71.3 %)
69.0 (60.0–76.0) 1,185 (71.6 %)
2014 (n = 1,451)
P
70.0 (61.0–76.0)
0.36
1,031 (71.1 %)
0.76
BMI (kg/m2)
26.1 (24.2–29.4)
26.2 (24.2–29.4)
26.0 (24.1–29.4)
0.25
BSA (m2)
1.96 (1.81–2.08)
1.96 (1.81–2.08)
1.96 (1.81–2.08)
0.33
Prior CABG
311 (10.0 %)
155 (9.4 %)
156 (10.8 %)
0.21
421 (13.7 %)
163 (10.0 %)
258 (18.1 %)
2,631 (85.8 %)
1,466 (89.5 %)
1,165 (81.6 %)
\0.01
Access Radial Femoral Other
13 (0.4 %)
9 (0.5 %)
4 (0.3 %)
Procedure Values are presented as median (interquartile range) or frequencies and percentages BMI body mass index, BSA body surface area, CABG coronary artery bypass grafting, CAG coronary angiography, CFX circumflex artery, LAD left anterior descending artery, PCI percutaneous coronary intervention, RCA right coronary artery
0.82
CAG
1,848 (59.5 %)
988 (59.7 %)
860 (59.3 %)
PCI
1,259 (40.5 %)
668 (40.3 %)
591 (40.7 %)
79 (6.3 %)
50 (7.5 %)
29 (4.9 %)
LAD CFX
473 (37.6 %) 238 (18.9 %)
248 (37.1 %) 130 (19.5 %)
225 (38.1 %) 108 (18.3 %)
RCA
PCI—target vessel Left main stem
0.44
358 (28.4 %)
184 (27.5 %)
174 (29.4 %)
Bypass graft
48 (3.8 %)
26 (3.9 %)
22 (3.7 %)
Multiple vessels
63 (5.0 %)
30 (4.5 %)
33 (5.6 %)
Table 2 Procedural characteristics—before and after implementation of a four-step plan
Dose-area product (cGy*cm2) PCI Radial
All patients (n = 3,107)
2012 (n = 1,656)
2014 (n = 1,451)
P
2,017 (1,021–3,917)
2,754 (1,566–5,081)
1,300 (670–2,583)
\0.01
3,380 (1,826–5,990)
4,570 (2,872–7,774)
2,217 (1,259–3,972)
\0.01
3,463 (2,011–5,438)
4,825 (3,209–8,155)
2,442 (1,390–4,462)
\0.01
3,345 (1,808–6,008)
4,566 (2,843–7,758)
2,092 (1,252–3,841)
\0.01
1,404 (764–2,555)
1,992 (1,183–3,288)
940 (523–1,655)
\0.01
Radial
1,380 (747–2,756)
2,131 (1,225–3,980)
1,102 (599–1,926)
\0.01
Femoral
1,382 (757–2,478)
1,950 (1,163–3,184)
853 (492–1,499)
\0.01
Femoral CAG
Fluoroscopy time (min)
5.8 (2.5–11.3)
5.6 (2.4–11.0)
6.0 (2.6–11.9)
0.06
10.5 (6.9–17.3)
10.4 (6.5–16.6)
11.1 (7.2–18.1)
0.19
Radial
12.4 (8.3–18.1)
13.1 (8.6–18.6)
12.3 (8.1–18.1)
0.40
Femoral CAG
10.4 (6.5–17.0) 3.2 (1.9–6.3)
10.1 (6.4–16.4) 3.1 (1.8–6.1)
10.5 (7.1–18.1) 3.3 (1.9–7.0)
0.11 0.10
Radial
4.8 (3.0–9.1)
4.7 (3.0–9.8)
5.0 (3.0–8.7)
0.97
Femoral
2.8 (1.6–5.5)
2.7 (1.6–5.5)
2.8 (1.6–5.5)
0.97 \0.01
PCI
Contrast volume (ml)
90 (58–138)
94 (61–135)
84 (54–140)
140 (100–190)
139 (100–180)
147 (106–199)
Radial
142 (109–190)
140 (104–181)
143 (110–200)
0.80
Femoral
140 (100–190)
138 (100–180)
147 (105–199)
\0.01
67 (50–94)
74 (51–100)
60 (46–84)
\0.01
Radial
65 (48–85)
61 (46–89)
67 (50–81)
0.56
Femoral
67 (50–95)
75 (52–100)
59 (46–84)
\0.01
PCI
CAG
0.01
Values are presented as median (interquartile range) CAG coronary angiography, PCI percutaneous coronary intervention
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Fig. 1 Dose-area product before (2012) and after (2014) implementation of a four-step program to reduce radiation exposure (a) and stratified according to coronary angiography (CAG) or percutaneous coronary intervention (PCI) (b). *P \ 0.01
artery bypass surgery (CABG) was observed in both years. Access choice differed between both groups with 18.1 % of patients undergoing radial procedures in 2014 and 10.0 % in 2012. 40.5 % of overall procedures included coronary interventions, consistent in 2012 and 2014. Target vessels intervened upon included the LAD (37.6 %), RCA (28.4 %), CFX (18.9 %), and left main coronary artery (6.3 %). Bypass graft interventions were performed in 3.8 and 5.0 % of patients underwent PCI of more than one coronary artery. No differences in target vessels were observed between the 2 years. Patients with a femoral compared to radial procedure were more likely to have had previous CABG (10.9 vs. 4.5 %, P \ 0.01), to receive coronary intervention (42.1 vs. 34.4 %, P = 0.01), and to undergo PCI of the left main stem (7.0 vs. 1.4 %) or bypass grafts (4.2 vs. 0.7 %.). DAP was higher in PCI than CAG (median 3,380 vs. 1,404 Gy*cm2, P \ 0.01). Furthermore, it was reduced significantly from 2012 to 2014 in the overall patient population and in the respective subgroups of patients undergoing PCI or CAG through radial or femoral approaches (Table 2; Fig. 1). Although DAP was similar in the unadjusted comparison of patients undergoing radial and femoral procedures (Table 3), adjusted analysis showed an increase of 16.4 % in DAP using the radial approach (Table 4). In addition, fluoroscopy time was longer in radial PCI or CAG (16.1 and 41.7 %). A subsequent trend towards a longer median fluoroscopy time in 2014 compared to 2012 (6.0 vs. 5.6 min, P = 0.06) was observed in the light of an increasing share of radial procedures. Excluding multiple vessel interventions, no association of target vessels and DAP was observed (Table 5). Fluoroscopy time, however, differed significantly with the lowest values for treatment of LAD and CFX lesions and the highest for bypass graft PCI.
Table 3 Procedural characteristics—radial versus femoral approach
Dose-area product (cGy*cm2)
All patients (n = 3,052)
Radial (n = 421)
Femoral (n = 2,631)
P
2,017 (1,021–3,917)
1,981 (966–3,843)
2,007 (1,025–3,862)
PCI
3,359 (1,819–5,963)
3,463 (2011–5,438)
3,347 (1,808–6,020)
0.92
CAG
1,404 (764–2,555)
1,380 (747–2,756)
1,382 (757–2,478)
0.50
Fluoroscopy time (min)
0.56
\0.01
5.8 (2.5–11.3)
7.3 (3.4–12.8)
5.4 (2.3–11.0)
PCI
10.5 (6.9–17.3)
12.4 (8.3–18.1)
10.4 (6.5–17.0)
CAG
3.2 (1.9–6.3)
4.8 (3.0–9.1)
2.8 (1.6–5.5)
\0.01
Contrast volume (ml)
0.03
90 (58–138)
80 (56–129)
90 (58–140)
0.04
PCI
140 (100–190)
142 (109–190)
140 (100–190)
0.61
CAG
67 (50–94)
65 (48–85)
67 (50–95)
0.24
Values are presented as median (interquartile range) CAG coronary angiography, PCI percutaneous coronary intervention
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Clin Res Cardiol Table 4 Linear regression analysis Parameter
Beta coefficient (95 % CI)
Beta coefficient per SD (95 % CI)
P
Age (per year)
1.012 (1.010–1.014)
1.146 (1.116–1.176)
\0.01
Female gender (vs. male)
0.907 (0.850–0.969)
0.957 (0.930–0.986)
\0.01
BSA (per m2)
5.468 (4.763–6.278)
1.445 (1.403–1.489)
\0.01
Prior CABG
1.443 (1.327–1.570)
1.116 (1.089–1.146)
\0.01
Radial access (vs. femoral)
1.164 (1.082–1.253)
1.054 (1.027–1.081)
\0.01
PCI (vs. CAG)
2.356 (2.237–2.479)
1.523 (1.486–1.564)
\0.01
Year (2014 vs. 2012)
0.458 (0.426–0.482)
0.672 (0.660–0.695)
\0.01
Linear regression analysis for dose-area product (DAP). Beta coefficients reflect the relative influence of each variable on DAP and are given after re-transformation [exp(beta coefficient)] BSA body surface area, CABG coronary artery bypass grafting, CAG coronary angiography, CI confidence interval, PCI percutaneous coronary intervention, SD standard deviation
Contrast volume was reduced significantly from 2012 to 2014 (94 vs. 84 ml, P \ 0.01) due to a decrease in the femoral CAG subgroup (Table 2). In the femoral PCI and overall PCI subgroups, however, a more contrast medium was required in 2014 vs. 2012. Contrast use differed significantly with regard to target vessels: While the lowest volumes were utilized in LCA and RCA interventions, LAD and bypass graft PCI required the highest amounts of contrast agent (Table 5). Linear regression analysis identified age [odds ratio (OR) 1.01], body surface area (OR 5.47), prior CABG (OR 1.44), radial access (OR 1.16), and PCI (OR 2.36) as predictors of increased DAP during coronary procedures (Table 4). Female gender (OR 0.91) and the implementation of the four-step plan between 2012 and 2014 (OR 0.46) were associated with a decrease in radiation exposure.
Discussion In this retrospective analysis of 3,107 patients undergoing CAG and PCI, we observed a significant reduction of radiation exposure after initiating a simple four-step program. After adjustment for confounding variables, a DAP reduction of 54.2 % was observed, which corresponds to the radiation dose of approximately 400 chest X-rays saved per patient [3]. This effect was consistent among patients undergoing coronary angiography or PCI. Among the variables analyzed, the implemented changes led to the largest reduction in radiation exposure and yielded to the only parameter that was easily influenced by the operator. Importantly, the overall program was not associated with increased use of contrast medium, hence ruling out insufficient temporal resolution of the acquired images after implementation of the protocol. Patient demographics and baseline variables were similar among patients before and after implementation of the
program. Importantly, no differences were observed in body mass index and surface area, age, gender, and performed procedures—all of which were factors known to influence radiation exposure. This association has previously been described [7–11] and was reconfirmed in our linear regression analysis. Data are conflicting regarding the influence of access choice on radiation exposure [12]. While an increase in DAP and fluoroscopy time with radial access has been described [13], some authors link this effect primarily to lower volume centers with similar radiation exposure in high volume radial centers [10, 12, 14]. The results of our analysis are interesting in several regards—Radial access was used more frequently in 2014 compared to 2012, however, still performed in the minority of patients undergoing CAG or PCI. This may have been attributed to the setting of a teaching hospital and tertiary referral center with a large fraction of complex procedures. Operators tended towards a femoral approach in patients with patent bypass grafts, coronary interventions vs. diagnostic angiography, and treatment of lesions in the left main stem or bypass grafts, reflecting more complex procedures. After adjustment for confounding variables, radiation exposure was higher in radial procedures in our analysis. Explanations may refer to less radial experience in the described setting and the more complex placement of suitable diagnostic or guiding catheters, as has previously been described [14]. Little data are available for DAP with regard to target vessels. An association has been described [11] and may be linked to beam angulation [9], however, target vessels were not linked to higher DAP in our experience. The use of contrast agent was similar with different access routes and was also significantly reduced between 2012 and 2014 overall. This reduction was mainly attributed to a decrease in the femoral coronary angiography subgroup. In the femoral PCI subgroup, however, a larger amount of contrast agent was required in 2014 vs. 2012, possibly reflecting a higher fraction of complex procedures
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0.14
* Comparison was performed with the Kruskal–Wallis test excluding multiple vessel interventions
CFX circumflex artery, LAD left anterior descending artery, RCA right coronary artery
Radiation and contrast exposure during coronary interventions according to different target vessels. Values are presented as median (interquartile range)
\0.01 178 (145–240)
198 (150–246) 146 (100–200)
147 (100–181) 125 (90–170)
132 (98–178) 149 (110–193)
138 (95–175) 145 (106–184)
154 (110–200) 141 (90–190) 147 (106–199) 2014
120 (77–170) 139 (100–180) 2012
\0.01 190 (147–245) 146 (100–200) 130 (94–170) 140 (100–185) 150 (110–190) 130 (82–190) 140 (100–190) Contrast volume (ml)
\0.01
\0.01 12.5 (10.5–20.9)
15.0 (9.1–22.7) 17.2 (11.4–22.7)
14.4 (10.3–20.4) 10.9 (7.1–17.6)
12.5 (8.1–21.5) 9.8 (6.7–15.7)
8.6 (5.3–14.3) 9.9 (6.5–15.9)
9.9 (6.5–15.5) 11.9 (5.1–23.0) 11.1 (7.2–18.1) 2014
10.6 (6.3–19.8) 10.4 (6.5–16.6) 2012
0.09 \0.01
0.91 6,624 (4,553–10,797)
3,172 (2,432–6,896) 14.1 (9.8–21.0) 1,887 (1,229–4,603) 14.9 (10.4–22.2)
5,623 (3,369–7,065) 4,452 (2,774–7,450)
2,306 (1,349–3,636) 11.3 (7.3–19.3) 2,363 (1,509–4,396) 9.2 (6.0–15.1)
5,099 (2,726–7,613) 4,329 (2,814–7,768)
1,786 (1,028–3,380) 9.9 (6.5–15.6) 2,327 (1,072–4,948) 11.0 (5.4–21.1)
4,190 (2,643–8,312) 4,570 (2,872–7,774)
2,227 (1,259–3,994) 10.5 (6.9–17.4) 2014 Fluoroscopy time (min)
2012
0.26 4,591 (3,103–9,045) 4,195 (1,820–6,152) 3,242 (1,786–5,491) 3,681 (1,905–6,068) 3,063 (1,637–5,799) 3,676 (1,835–7,350) 3,387 (1,826–5,998)
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Dose-area product (cGy*cm2)
Left main stem (n = 79) All target vessels (n = 1,259)
Table 5 Target vessels
LAD (n = 473)
CFX (n = 238)
RCA (n = 358)
Bypass graft (n = 48)
Multiple vessels (n = 63)
P*
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in this group with less complex procedures being attributed to the growing radial group. Although the increase in contrast use was mild, future studies will have to evaluate its impact on renal function. A central part of our program was frame rate reduction from 15 to 7.5 frames per second for cine acquisitions. A significant reduction of radiation exposure to the patients and operators has recently been demonstrated [15, 16]. We confirm these findings in a larger patient cohort and demonstrate an even greater reduction by implementing a fourstep protocol. Importantly, the reduced frame rate was sufficient for the vast majority of our procedures and higher frame rates were only necessary in particular circumstances, e.g. to evaluate coronary stent overlap or exact placement of bioresorbable vascular scaffolds. A further reduction to even lower frame rates may be reasonable in certain cases but clearly reduces image quality. Consistent collimation to the region of interest was shown to effectively reduce radiation during three-dimensional rotational angiography [17] and was an essential component of a mini-course on radiation safety during CAG and PCI [18]. Although impossible to quantify, operators were educated on consequent collimation especially during PCI in our institution, in particular during balloon and stent placement with a known coronary anatomy and sufficient guidecatheter and guidewire control. Consistent collimation was shown to reduce radiation exposure by more than 65 % for PCI [19] as collimation reduces radiation by the inversesquare law. In a similar manner, we encouraged the fluorostore feature that enables storage of the last 20 s of fluoroscopy to document stent expansion, balloon inflation, and guidewire position during PCI instead of a new cineangiographic imaging with additional radiation. If the operator felt the need for better visualization, additional cineangiography runs were left at his discretion, e.g. in complex and severely calcified lesions. Extreme angulations were shown to be associated with higher radiation exposure [8, 9] and their use was discouraged in our program whenever feasible. As consistent data confirm the strong influence of individual operators on radiation doses, the clear need for physician education cannot be overemphasized [10, 11, 14, 20]. Several limitations need to be addressed with regard to the presented results: The study was set up as a single-center retrospective analysis and the results can, therefore, only be interpreted as hypothesis generating. Despite balanced baseline parameters, confounding variables not measured may have influenced the results presented. For example, data on beam angulation and lesion or procedure complexity were not available. As all four steps to reduce radiation exposure were integrated at once, it was impossible to evaluate the effect of each step alone. Furthermore, radiation exposure was approximated by DAP and
Clin Res Cardiol
fluoroscopy time. However, the patient’s exact skin dose can only be approximated at current [1]. In addition, operators’ radiation doses were not evaluated in this analysis. In conclusion, by implementing a simple four-step program into clinical routine at a teaching hospital and tertiary referral center, a significant reduction in radiation exposure was achieved for diagnostic and interventional coronary procedures without significant drawbacks to the image quality. In addition to technical advances and protection equipment, continuous physician education and benchmarking of radiation proved simple yet very effective in utilizing radiation exposure as low as reasonably achievable benefitting patients and operators alike. Acknowledgments D. W., K. M. and S. B. are funded by the DZHK (Deutsches Zentrum fu¨r Herz-Kreislauf-Forschung). Conflict of interest
None.
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