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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
| Abstract |
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| Introduction |
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The radiation dose may be estimated from the fluoroscopy time (t), measured with dosimeters and transmission ion chambers and expressed in terms of the dosearea 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.
| Materials and methods |
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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 (35 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 MannWhitney and GamesHowell 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.
| Results |
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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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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).
| Discussion |
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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, 1315]. 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 [610]. 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 [35]. 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.
| Conclusions |
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| Acknowledgments |
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| Footnotes |
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Received for publication June 17, 2002. Revision received January 15, 2003. Accepted for publication March 31, 2003.
| References |
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