British Journal of Radiology (2003) 76, 473-477
© 2003 British Institute of Radiology
doi: 10.1259/bjr/21553230
Factors influencing fluoroscopy time and dose–area product values during ad hoc one-vessel percutaneous coronary angioplasty
F Larrazet, MD1,
A Dibie, MD1,
F Philippe, MD1,
R Palau, MD2,
R Klausz3 and
F Laborde, MD1
Department of 1 Cardiology and 2 Radiology, Institut Mutualiste Montsouris, Paris and 3 General Electric Medical System, Buc, France
Correspondence: Dr Fabrice Larrazet, L'Institut Mutualiste Montsouris, 42 Boulevard Jourdan, 75674 Paris cedex 14, France
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Abstract
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X-ray exposure during radiologically guided interventional procedures may have some deleterious effects. The aim of our study was to analyse the factors affecting patient dose during percutaneous coronary angioplasty (PTCA). We evaluated radiation dose during coronary angiography followed by one-vessel PTCA in 402 consecutive patients who were treated by three experienced physicians using both femoral and radial techniques. Fluoroscopy time (t) and patient dose measured by a dose–area product (DAP) meter were recorded. A good correlation was observed between t and the DAP (r=0.78, p<0.001). To assess the factors affecting radiation exposure, we studied the differences between operators, arterial catheterization access and stenting strategy. Median (25th to 75th percentiles) values for t were 19 (13 to 26) min and for DAP were 191 (145 to 256) Gy cm2 for operator 3 compared with t=12 (9 to 18) min and DAP=137 (91 to 208) Gy cm2 for operator 2 (p<0.005 versus operator 3) and t=13 (9 to 17) min, and DAP=134 (93 to 190) Gy cm2 for operator 1 (p<0.001 versus operator 3). Differences between the radial and the femoral techniques were: t=17 (13 to 24) min versus 12 (8 to 17) min, (p<0.001) and DAP=175 (128 to 246) Gy cm2 versus 138 (93 to 197) Gy cm2, (p<0.001). In comparison with stenting without pre-dilation, direct stenting significantly reduced t and DAP [t=12 (9 to 16) min versus 16 (11 to 22) min, (p<0.001) and DAP=130 (95 to 186) Gy cm2 versus 163 (119 to 230) Gy cm2, respectively, (p<0.01)]. Radiation exposure to patients and staff are strongly dependent on operators, stenting strategy and the arterial access chosen for ad hoc one-vessel PTCA.
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Introduction
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Coronary angiography followed by angioplasty gives rise to high dose levels for staff and patients [1, 2]. In spite of the improvement of protective devices, long-term radiation effects remain a concern for patients, staff members and physicians. New strategies have been developed in order to improve patient comfort. Direct stenting is safe and feasible in native coronary arteries. It allows short procedures in more than 90% of eligible patients [3–5]. The transradial approach also appears to improve patients' comfort and to reduce nurses' and physicians' workload [6–10].
The radiation dose may be estimated from the fluoroscopy time (t), measured with dosimeters and transmission ion chambers and expressed in terms of the dose–area product (DAP). Our study was designed to investigate how these new approaches in interventional cardiology might affect patient radiation dose during ad hoc one-vessel percutaneous coronary angioplasty (PTCA). The role of the operator was also studied.
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Materials and methods
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The study population consisted of 402 patients out of 701 referred to our cathlab for coronary angioplasty during the same period. The mean age was 65±11 years and 115 (29%) were females. Coronary lesions were classified as type A, B1 and B2 [11]. This study was prospectively planned. 128 (32%) patients had a recent myocardial infarction (MI) with 66 (16%) acute MI, 165 (41%) had unstable angina and 80 (20%) had stable angina. The mean left ventricular ejection fraction was 54±13%. The procedure was performed via the transfemoral or the transradial approach by three experienced physicians (>100 angioplasty operations per operator per year) from September 1999 to April 2001. The body mass index (weight/height2) was calculated for each patient. Operators 1 and 3 preferentially used the transradial cannulation and often performed an additional ventriculography. Operators 1 and 2 used large intensifier fields with collimation. Operator 1 avoided angulated beams during procedures. The image intensifier was positioned as close to the chest wall as possible.
We excluded type C lesions, multivessel angioplasty, planned angioplasty, angioplasty performed by visiting cardiologists and the brachial approach.
The majority of patients had PTCA followed by stent implantation (n=340, 85%). 15% of patients had balloon angioplasty without stent placement because of a stentlike result or failure to stent the artery. Aspirin (250 mg) was given 24 h before the procedure and on the day of the procedure. Heparin (2000 IU) was administered intravenously during the procedure and isosorbide dinitrate was injected before baseline coronary angiography was performed with a 4 French (Fr) coronary catheter using the femoral approach. Transradial coronary angiography was performed through a short 4 Fr sheath after the arterial infusion of heparin (3000 IU) and verapamil (3–5 mg). We used a 5 Fr or 6 Fr guiding catheter for angioplasty. Intravenous administration of heparin was completed to 70 IU kg-1. Balloon angioplasty was performed by standard techniques. An additional stent was deployed if a suboptimal result after PTCA, defined as a residual stenosis of >30%, was obtained. The Bx Velocity stent (Cordis Europa, the Netherlands) was preferentially used for direct stenting. The stents were positioned under fluoroscopic guidance and deployed with a pressure ranging from 8 to 16 atmospheres and a duration ranging from 20 s to 45 s.
Platelet glycoprotein IIb/IIIa receptor inhibitor was administered after the coronary angiography was performed in 78 (19%) patients.
We have a laboratory equipped with a single plane angiocardiographic system (General Electrics (Milwaukee, WI) LCV+, installed in August 1999), equipped with a four-field 32 cm image intensifier (32 cm / 22 cm / 16 cm / 12 cm), continuously adjustable rectangular and circular field limitations and two-blade contour filters. The image intensifier dose rate for a 16 cm field and normal rate option is 0.83 µGy s-1. This figure has been corrected for the anti-scatter grid transmission factor. Dose rate options are available (high, normal and low for fluoroscopy; A, B, C and D for cine). All operators preferentially use the normal system for fluoroscopy with the C cine option. Fluoroscopy was exclusively performed in grid pulsed operation. After calibration of the apparatus, the DAP was measured with an ionization chamber mounted directly at the end of the collimator (Diamentor M4, PTW, Freiburg, Germany). This device is a microprocessor-controlled measuring system featuring two independent channels. The DAP measured was for the complete examination and therefore included radiation delivered during both acquisition runs and fluoroscopy. DAP measurements were expressed in units of Gy cm2.
Quantitative angiographic analysis obtained before, at the conclusion of the procedure and if necessary at follow-up, was performed on-line, using the catheter for calibration. Only end-diastolic frames were analysed. The single view showing the most severe degree of stenosis was used for analysis. A thrombotic aspect of the lesion was noticed if the patient had an acute coronary event (recent myocardial infarction or unstable angina with troponin I elevation), or if a filling defect surrounded by contrast at the site of the culprit lesion was observed. Complex lesions (type B2) were compared with simple lesions (type A and B1). Patients with coronary angiography were distinguished from patients with coronary angiography and adjunctive ventriculography and/or bypass graft angiography. Procedural complications included bailout stenting, no-reflow phenomenon and side branch occlusion.
Continuous variables are expressed as mean±SD except t and DAP which did not follow a normal distribution. t and DAP are expressed as the median value together with the 25th and 75th percentiles. Once a logarithmic transformation was applied to the t values, we used the general linear model procedure to study the factors influencing this variable. As the Levene test for equal variances remained not significant after the logarithmic transformation of DAP, we compared the rank distribution of this variable separately in each group by using Mann–Whitney and Games–Howell non-parametric tests. A multivariate regression analysis was performed to distinguish the operator-dependent factors (SPSS 10.0, Chicago, USA). A p-value<0.05 was considered statistically significant.
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Results
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The majority of patients suffered from an acute coronary syndrome or de novo angina pectoris. Baseline characteristics of lesions are listed in Table 1
. Most lesions were classified as type B2. Quantitative angiographic analysis and procedural measurements are listed in Table 2.
A good correlation was observed between t and DAP (Figure 1). A mild correlation was found between the body mass index and DAP (r=0.46, p<0.001). No correlation was found between the body mass index and t.
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Figure 1. Correlation between the fluoroscopy time and the dose–area product in 402 patients who underwent ad hoc one-vessel percutaneous transluminal coronary angioplasty.
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The number of lesions treated per patient was similar between the three operators (1.28 for operator 1, 1.25 for operator 2 and 1.24 for operator 3). Qualitative operator-dependent variables included adjunctive ventriculography, arterial access and the direct stenting approach (p<0.001 by multivariate regression analysis). Operator 3 performed 147 (91%) transradial procedures compared with 57 (46%) for operator 1 and 12 (10%) for operator 2 (p<0.01 between operators).
We identified numerous factors influencing t and DAP. Figure 2 shows comparison of median and 25th to 75th percentile dose level between operators (t=19 (13 to 26) min and DAP=191 (145 to 256) Gy cm2 for operator 3, t=12 (9 to 18) min and DAP=137 (91 to 208) Gy cm2, for operator 2, p<0.005 compared with operator 3 and t=13 (9 to 17) min, and DAP=134 (93 to 190) Gy cm2 for operator 1, p<0.001 compared with operator 3).
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Figure 2. Boxplot graphical comparison of fluoroscopy time and dose–area product between three operators (p<0.001 between operator 3 and others). Operator 1 is on the left, operator 2 is in the middle and operator 3 is on the right. Boxplot explanation: upper horizontal line of box, 75th percentile; lower horizontal line of box, 25th percentile; horizontal bar within box, median; upper horizontal bar outside box, 90th percentile; lower horizontal bar outside box, 10th percentile. Open circles (O) represent values more than 1.5 box-lengths from 75th percentile (outliers). Asterisks (*) represent values more than 3 box-lengths from 75th percentile (extremes).
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The radial approach was associated with higher radiation doses than the femoral approach (Figure 3), independently of other factors (t=17 (13 to 24) min versus 12 (8 to 17) min (p<0.001) and DAP=175 (128 to 246) Gy cm2 versus 138 (93 to 197) Gy cm2, p<0.001, respectively).
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Figure 3. Boxplot graphical comparison of fluoroscopy time and dose–area product between the femoral and the radial approach (p<0.001). Boxplot explanations are as given in the legend to Figure 2 .
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We observed a significant influence of direct stenting (n=88) compared with the standard approach (n=314) (t=12 (9 to 16) min versus 16 (11 to 22) min and DAP=130 (95 to 186) Gy cm2 versus 163 (119 to 230) Gy cm2, respectively, p<0.001).
Adjunctive ventriculography and/or bypass graft angiography (n=201) increased patient dose (t=16 (12 to 22) min versus 13 (9 to 19) min, and DAP=179 (128 to 240) Gy cm2 versus 148 (94 to 200) Gy cm2, p<0.001). Complex lesions also lengthened t and DAP in comparison with simple lesions (t=16 (11 to 22) min versus 13 (10 to 18) min, and DAP=167 (116 to 240) Gy cm2 versus 146 (100 to 195) Gy cm2, p<0.05). Although the lesion location was not included in our linear model procedure, a comparison between the three major coronary vessels revealed that left anterior coronary angioplasty was less time consuming than other locations (p<0.02 compared with the right artery for t as well as p<0.005 compared with both the right artery and the left circumflex for DAP). 27 (7%) procedural complications occurred with a weak increase in t (17 (12 to 26) min versus 15 (10 to 20) min) and DAP (167 (123 to 267) Gy cm2 versus 157 (107 to 219) Gy cm2). t and DAP was not significantly higher in patients referred to our cathlab for angiographic restenosis and target vessel repeat revascularization (n=37) compared with other patients (t=18 (11 to 26) min versus 15 (10 to 20) min, and DAP=183 (103 to 242) Gy cm2 versus 157 (108 to 217) Gy cm2).
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Discussion
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We identified factors influencing t and DAP in patients who had a coronary angiography followed by one-vessel PTCA. Some variables such as the body mass index, the adjunction of a ventriculography and/or bypass graft angiography and the treatment of complex lesions were obviously associated with higher radiation dose [12]. The study showed that the radiation dose was dependent on operators, on arterial access chosen for catheterization and on the methods of stenting. Angioplasty of lesions located on the right coronary artery and the left circumflex also seemed to be associated with higher radiation dose delivering procedures than PTCA of the left anterior descending artery.
Koenig et al [1, 2] recently reviewed 73 patients with skin injuries from fluoroscopically guided procedures and proposed recommendations for minimizing the dose delivered to patients. The majority of patients had a coronary angiography and intervention (n=47, 64%) with t ranging from 19 min to 172 min and an average time of about 60 min. Coronary angiography fluoroscopy times usually ranged from 2 min to 10 min with a mean value of 4.5 min [13, 14]. Values of t for staged angioplasty are much longer and reportedly ranges from 10 min to 20 min [9, 13–15]. Benardi et al recently reported DAP mean values ranging from 66 Gy cm2 to 117 Gy cm2 in patients with staged PTCA, according to the complexity of the procedure [12]. Patient dose levels were lower than in our study probably because all patients had staged PTCA (which does not take into account diagnostic coronary angiogram and ventriculography) performed by the femoral access.
The difference observed between operators was not related to their experience but to their wish to optimize radiation protection. To minimize the radiation delivery during coronary angiography followed by ad hoc PTCA, we recommend operators to use the femoral approach, to avoid angulation of the beam (especially on the left side), to use large field settings with additional collimation, to zoom the region of interest after first acquisitions, to review the previous run rather than repeating it, to avoid ventriculography and to directly stent the target lesion. We found that the arterial access was also a determining factor for t and DAP. 10 years ago, the transradial percutaneous approach was introduced with good safety and feasibility. However, this approach was associated with a steep learning curve [6–10]. Kiemeneij et al [9] did not observe a significant difference between the radial and the femoral approach although a trend toward shorter t was observed for transfemoral staged PTCA (11±10 min versus 13±11 min).
In our group of patients, the transradial approach involved longer fluoroscopic times than the transfemoral approach. This difference was not operator dependent and reflected the technical difficulties encountered in diagnostic coronary angiography combined with ad hoc angioplasty even in experienced hands (>500 transradial coronary angioplasties).
Direct stenting has been shown to reduce the duration of the procedure and the radiation exposure to patients in previous studies [3–5]. This new approach appears to be a determining factor in the reduction of t and DAP in our study group.
Clark et al observed a weak relation between DAP reading and body mass index (r=0.3) in 1627 procedures of which 219 were angioplasties [16]. We observed the same correlation in our study group (r=0.4).
We used two different methods to quantify radiation delivery. A good correlation was observed between both measurements (t and DAP). DAP is a good indicator of effective dose (risk of stochastic effects). Since the area being irradiated expands at the same rate as the radiation intensity decrease, the DAP remains independent of distance. It can be reduced by choosing large field settings and then collimating down. No general correlation was observed between DAP and the maximum entrance skin dose, a parameter which was not measured in our laboratory [17]. However, Katritsis et al found a linear relationship of the DAP and the dose at the coronary arteries measured by thermoluminescent dosimeters, mounted on a catheter that was advanced to the left or right sinus of valsalva [18]. t and, a fortiori, the duration of the procedure are unsatisfactory indicators of the radiation exposure of patients and staff during radiovascular intervention. Optimization of radiation protection should include on-line DAP measurements and cumulative skin dose estimates. No attempt was made to model or directly measure skin dose in our cathlab. The cineangiographic runs were not separately taken into account but their contributions to the patient dose was included in the DAP measurement.
More complex PTCA will develop over the next few years with the development of new-coated stents [19]. Physicians should keep in mind that excessive radiation dose might be deleterious for the patients.
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Conclusions
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Numerous factors influence patient dose during ad hoc one-vessel PTCA. In particular, t and DAP were operator dependent and influenced by the arterial access chosen for catheterization and the stenting strategy.
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Acknowledgments
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Special thanks to Karine Cognasse, Isabelle Legal and Evelyne Chandelon for their helpful technical assistance.
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Footnotes
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Current address for Remy Klausz: 283, rue de la Minière, 78533 Buc Cedex, France. 
Received for publication June 17, 2002.
Revision received January 15, 2003.
Accepted for publication March 31, 2003.
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Abstract
Introduction
