CLINICAL RESEARCH: SAFETY ISSUE
Fluoroscopically Guided Implantation of Modern Cardiac Resynchronization Devices
Radiation Burden to the Patient and Associated Risks
Kostas Perisinakis, PhD*,*,
Nicholas Theocharopoulos, MSc*, ,
John Damilakis, PhD*,
Emmanouel Manios, MD ,
Panayiotis Vardas, MD, PhD, FESC, FACC and
Nicholas Gourtsoyiannis, MD, PhD
* Department of Medical Physics, Faculty of Medicine, University of Crete, Iraklion, Greece
Department of Cardiology, Faculty of Medicine, University of Crete, Iraklion, Greece
Department of Radiology, Faculty of Medicine, University of Crete, Iraklion, Greece
Department of Natural Sciences, Technical Education Institute of Crete, Iraklion, Greece
Manuscript received August 5, 2004;
revised manuscript received January 13, 2005,
accepted January 17, 2005.
* Reprint requests and correspondence: Dr. Kostas Perisinakis, Medical Physics Department, Faculty of Medicine, University of Crete, P.O. Box 2208, 71003 Iraklion, Crete, Greece (Email: perisina{at}med.uoc.gr).
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Abstract
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OBJECTIVES: To establish radiation risks for patients undergoing fluoroscopically guided cardiac resynchronization device implantation.
BACKGROUND: Cardiac resynchonization therapy (CRT) may be associated with extended fluoroscopic exposure.
METHODS: The fluoroscopy time, dose-area product (DAP), exposure parameters, and percentage contribution of the fluoroscopic projections commonly used were recorded in a series of 14 consecutive patients referred for cardiac resynchronization device implantation and compared to corresponding data obtained from a control group of 20 patients who underwent a conventional rhythm device implantation operation. The DAP to peak skin dose, DAP to effective dose, and DAP to gonadal dose conversion factors were determined for biventricular pacing and conventional rhythm device implantation using a humanoid phantom and thermoluminescence dosimetry.
RESULTS: The mean total fluoroscopy time and DAP values were 35.2 min and 4,765 cGy cm2, respectively, for biventricular pacing and 8.2 min and 1,106 cGy cm2, respectively, for conventional rhythm device implantation. Patient skin dose from biventricular pacing procedures requiring extended fluoroscopic exposure may exceed threshold dose for the induction of skin effects only if X-ray source-to-skin distance is kept low. The risk values for fatal cancer and severe hereditary disorders, respectively, associated with a typical CRT procedure were 273 per million and 0.2 per million treated patients.
CONCLUSIONS: Radiation risks associated with fluoroscopically guided CRT procedures may be considerable. Present data may be used for the estimation of patient radiation risks from CRT procedures performed in other institutions.
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Abbreviations and Acronyms
| | cGy cm2 = centigray x centimeter2 | | CRT = cardiac resynchronization therapy | | DAP = dose-area product | | ICD = implantable cardioverter-defibrillator | | ICRP = International Commission on Radiological Protection | | LAO = left-anterior oblique | | PA = posteroanterior | | RAO = right-anterior oblique | | SSD = source-to-skin distance | | TLD = thermoluminescence dosimeter | | Sv–1 = sievert–1 | | Gy–1 = gray–1 |
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Cardiac resynchronization therapy (CRT) is a proven additive therapeutic option for patients with severe and drug-refractory heart failure because it has been found to result in considerable symptomatic improvement and might increase survival rates in many patients (1–6). Recent technologic advances in leads and generators, coupled with rapidly expanding clinical indications, have resulted in a continuous increase in the number of modern resynchronization device implantation procedures (7). Implantation procedures for cardiac resynchronization are commonly performed in the electrophysiologic laboratory under fluoroscopic guidance (8). Owing to complexity, these procedures may be prolonged, resulting in considerable fluoroscopic exposure (9). The mean total fluoroscopic exposure involved in CRT with biventricular pacing has been reported to exceed one hour (10). In recent years, there is growing anxiety regarding radiation-induced detrimental effects associated with fluoroscopically guided interventional procedures that involve extended fluoroscopic exposure (11). Electrophysiologists and cardiologists are often unaware of the magnitude of the radiation dose to the skin delivered during cardiac interventional procedures. Besides, apart from increased entrance skin dose, extended fluoroscopic exposure may result in high patient effective dose and increased risk for radiation-induced carcinogenesis and genetic effects that should not be overlooked, especially when treated patients are young individuals with long remaining life expectancy (12). To our knowledge, there are no data in the literature on patient radiation burden and the associated radiogenic risks following fluoroscopically guided implantation of modern cardiac resynchronization devices.
The aim of the present study was to determine peak skin dose, effective dose and gonadal dose delivered to patients undergoing fluoroscopically guided modern cardiac resynchronization device implantation procedures and evaluate the radiogenic risk for skin injury, genetic effects, and carcinogenesis associated with typical CRT procedures. Radiation dose burden and associated risks from CRT were compared to corresponding values from conventional rhythm device implantation.
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Methods
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Patient study.
The fluoroscopy time, dose-area product (DAP) and exposure parameters for the posteroanterior (PA), the 30° left-anterior oblique (LAO), and the 30° right-anterior oblique (RAO) projections were recorded in a series of 14 consecutive patients referred for CRT in the electrophysiology laboratory of our institution. Dosimetric data were also recorded in a control group of 20 patients who underwent conventional pacemaker implantation or an implantable cardioverter-defibrillator (ICD) for antibradycardia or antiarrhythmia indications. Implantation procedures were performed by experienced medical personnel who are involved in more than 250 implantations per year. There had been 21 resynchronization devices implanted at the beginning of the present study. In all study cases, leads, devices, and implanting materials used were from Medtronic (St. Paul, Minnesota). Access to the coronary sinus was performed after cannulation of the left subclavian vein using the dedicated tools. Because operators are also experienced ablationists, the coronary sinus was rather easily cannulated in most cases by the use of a specially designed steerable electrophysiology catheter (Livewire; St. Jude Medical, Sylmar, California). Of the 15 consecutive patients that were scheduled to be included in the study a satisfactory left ventricular (LV) lead position was achieved in 14 patients. In a single patient, angiographic anatomy of the coronary sinus was not considered appropriate for LV lead implantation. This patient was excluded from our analysis. The CRT ICD was implanted in five and CRT pacemaker in the other nine treated patients. In two patients of the CRT group no atrial lead was implanted because of persistent atrial fibrillation. A single-lead device was implanted in four and a dual-lead device in the remaining 16 patients of the control group.
All studies were performed on a Philips BV-300R2 (Best, the Netherlands) C-arm fluoroscope. Patient age, height, and weight were recorded. The mean percentage contribution of PA, LAO, and RAO fluoroscopic exposures in total DAP was determined for each group of treated patients. The current study was approved by the local ethics committee, and informed consent was obtained from all participants.
Radiation dose measurements.
Dosimetric data were obtained using an anthropomorphic Rando phantom and thermoluminescence dosimetry (TLD). The phantom was loaded with 520 TLD chips to allow for the acquisition of dosimetric data for all radiosensitive organs/tissues as defined by the International Commission on Radiological Protection (ICRP) (12). Entrance skin dose was monitored with use of a 5 x 10 array of TLDs interspaced by 3 cm attached on the beam entrance surface on the posterior of the phantom thorax with the long side of the array perpendicular to phantom axis.
The phantom was exposed to separate fluoroscopy courses using the average contribution of PA, RAO, and LAO projections for each group of participants. Thus, organ and effective dose values were separately determined for: 1) biventricular pacing procedures, and 2) conventional pacemaker or ICD implantation procedures. Each time, the phantom was exposed to 10,000 cGy cm2 in total, to increase TLD signal and thus reduce the statistical error of our measurements.
The DAP to organ dose (dT) conversion factors were determined for all radiosensitive organs, and DAP to effective dose ( ) conversion factors were estimated according to recommendations of ICRP (12) and previously published data (13). The effective dose, gonadal dose, and peak skin dose to a patient undergoing a cardiac device implantation procedure may be estimated from:
 | (1) |
 | (2) |
 | (3) |
where E is the effective dose, GD is the gonadal dose, PSD is the peak skin dose, DAP is the total DAP value, and SSD and SSDph is the source-to-skin distance during patient and phantom exposure, respectively.
Risks for radiation-induced effects.
To evaluate the risk for radiation-induced skin effects following a device implantation procedure, the peak-skin dose resulting from a typical procedure in our institution was compared to 2 Gy, which is the threshold dose for the induction of skin erythema (14). The risk for fatal carcinogenesis following a fluoroscopically guided device implantation was estimated by multiplying patient effective dose by an average cancer excess mortality factor of 5 x 10–2 Sv–1 as recommended by the ICRP (12). The risk for severe hereditary effects was estimated by multiplying gonadal dose by a risk factor of 10–2 Gy–1, as recommended by ICRP (12).
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Results
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Patient demographic data, total fluoroscopy time, total DAP, and percentage contribution of each fluoroscopic exposure to total DAP are shown in Table 1 for each group of treated patients. The mean total fluoroscopy time and mean total DAP values were, respectively, 35.2 min and 4,765 cGy cm2 for biventricular pacing and 8.2 min and 1,106 cGy cm2 for conventional rhythm device implantation procedures.
Exposure parameters of phantom exposures are shown in Table 2. Total DAP to organ dose conversion factors obtained from phantom exposure measurements are presented in Table 3 for all radiosensitive organs/tissues. The peak skin, effective, and gonadal dose values delivered to a patient undergoing typical cardiac rhythm device implantation procedure in our institution are shown in Table 4. The 2-Gy threshold for skin effects is 11 and 44 times higher than patient peak-skin dose following a typical biventricular pacing procedure and a conventional cardiac rhythm device implantation procedure, respectively. The risk values for fatal cancer and severe hereditary disorders associated with a typical fluoroscopically guided resynchronization device implantation procedure as performed in our institution are shown in Table 5 for female and male patients.
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Table 4. Patient Peak Skin Dose, Effective Dose, and Gonadal Dose Following Typical Cardiac Rhythm Device Implantation Procedures
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Table 5. Risks for Fatal Carcinogenesis and Severe Hereditary Disorders Following Resynchronization Device Implantation Procedures
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Discussion
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Electrophysiologists rely heavily on fluoroscopy for the implantation of modern CRT devices. The current study was motivated by the absence of dosimetric data regarding patients undergoing modern fluoroscopically guided CRT procedures. Peak skin dose, gonadal dose, and effective dose associated with patients undergoing CRT procedures were determined and the corresponding radiation risks were evaluated. Radiation burden and associated risks resulted from CRT procedures were compared to corresponding data from conventional rhythm device implantation procedures. Present data may be used for the estimation of patient radiation risks from fluoroscopically guided CRT and conventional rhythm device implantation procedures performed in other institutions.
Quantitation of radiation risks associated with CRT procedures.
According to our findings, radiation burden and associated risks to patients undergoing CRT procedures are four times the corresponding values for patients undergoing conventional rhythm device implantation procedures. Radiation skin injuries following typical fluoroscopically guided CRT procedures are rather improbable in our institution because the fluoroscopy time threshold for the induction of skin lesions was estimated to be 5 h. However, large patients are associated with high exposure rate and consequently higher radiation burden. Especially, peak-skin dose would be much higher in large patients because the increased DAP rate is coupled with a lower SSD. Decreasing SSD from 64 cm to 44 cm increases entrance skin dose by 110%. Thus, radiogenic skin injuries might be induced in the case of biventricular pacing performed in large patients with SSD kept erroneously low during the procedure course. The nominal risk for cancer induction and genetic disorders has been reported to be 20% (200,000/million) and 6% (60,000/million), respectively (15). Compared to nominal risk, the stochastic radiation risk for hereditary effects following a cardiac rhythm device implantation procedure may be considered trivial. Patients with severe heart failure have a limited life expectancy and therefore radiogenic stochastic effects may not appear before the patient succumbs to heart failure. However, the risk for carcinogenesis associated with typical fluoroscopically guided CRT procedures should not be disregarded when treated patients are young individuals.
Uncertainties in the evaluated radiation risks.
The small number of patient procedures monitored to obtain data for the estimation of radiation risks constitutes a limitation for the current study. Error in the estimated radiation risks may be attributed to errors associated with thermoluminescence dosimetry and discrepancies between patient fluoroscopic exposure course and the considered phantom exposure course used to derive conversion factors. The error introduced by thermoluminescence dosimetry has been previously estimated to be <15% (13), whereas the error due to deviations between patient and phantom exposure was estimated to be <10%. The estimated overall error is not expected to exceed 20%, which may be considered acceptable in evaluating theoretical radiation risks.
The need for universally applicable dosimetric data.
Mean fluoroscopy time for conventional cardiac rhythm device implantation or extraction has been reported from 3.54 ± 2.3 min by Wiegand et al. (16) to 35 ± 22 min by Tse et al. (17), depending on the device implanted. Mean fluoroscopy time for biventricular pacing has been reported as 77 ± 19 min by Izutani et al. (10). Apparently, the variability in fluoroscopy times associated with cardiac rhythm device implantation procedures reported by different investigators is considerable. Consequently, there is a need for normalized dosimetric data universally applicable for the estimation of patient radiation risk following such procedures. The DAP-normalized dosimetric data presented here may be used to estimate patient radiation burden from CRT as well as conventional device implantation procedures performed at different institutions with use of different equipment and technique.
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Conclusions
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Radiation skin injuries are not to be expected following fluoroscopically guided cardiac resynchronization device implantation unless there is inappropriate use of fluoroscopy. The radiogenic risk for cancer induction should not be disregarded when treated patients are young individuals.
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References
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Abstract
Methods