Background/Significance

Exposure to medical radiation is rising rapidly, increasing approximately sevenfold over 2 decades, with interventional procedures accounting for about 7%.^1,2 Consequently, there is heightened concern for increased cancer risk, particularly in those with genetic predisposition, repeated or prolonged exposure, women, and people over 40 years old.³ Cardiac catheterization is a common procedure due to the high burden of cardiovascular disease in the United States. Diagnostic catheterization was performed in over 1.2 million hospitalizations during 2011, the second and third most common procedure for middle-aged and older adults, respectively.⁴ The American College of Cardiology has identified radiation exposure from cardiovascular imaging as a concern.⁵ In conjunction with other governmental agencies and medical societies, the Food and Drug Administration (FDA) is working on tracking exposure, developing dose reference levels, providing feedback to physicians, generating a mechanism for reporting overexposure, and collecting epidemiologic data for research.⁶ Two overarching principles guiding patient safety have arisen from this work:

1. Justification for the use of radiation
2. Optimization of the technique to attain a dose as low as reasonably achievable (ALARA)

Shared decision-making by physician and patient contemplating invasive testing or therapy should take these principles into consideration.

Effects of Radiation Exposure

Background radiation exposure comes mostly from radon gas and for the United States is approximately 3.1 mSv/year (for perspective, 1 mSv is approximately 10 chest X-rays), but the exposure varies according to the altitude at which one lives, frequency of airplane travel, and proximity to other environmental sources.^2,7 Individuals can calculate their estimated annual exposure.⁸ Estimated doses of radiation delivered during common interventional cardiology procedures are listed in Table 1. For a review of X-ray physics specific to cardiac catheterization, see Hirshfeld et al.⁹ Deterministic effects from apoptosis occur when a threshold radiation dose has been achieved, such as cataracts, depilation, skin burn, or ulceration. Skin burn and ulceration have been reported with fluoroscopy directed to the same area for a prolonged period, typically >10 Gy (a measure of absorbed energy; 1 mSv = 1 Gy for cardiac catheterization).¹⁰ Patients who have undergone complex interventions with exposure >5 Gy should be counseled to check for a telltale erythematous square rash on their backs and proactively scheduled for examination.⁹ Referral to dermatology for protective dressings may be helpful because ulcers are difficult to treat and often require skin grafting.¹¹ Cancers are stochastic effects from radiation, occurring randomly due cumulative exposure and DNA damage. Stochastic effects have been largely extrapolated from environmental exposure to radiation disasters (like atomic bomb fallout and Chernobyl), with a threshold for cancer >100 mSv.⁹ The majority of patients will not achieve this threshold dose from cardiac catheterizations. The lifetime additional increased risk of cancer per examination from coronary stenting has been estimated as <1/1,000 when exposed to the equivalent of >500 chest X-rays during a procedure.¹²

Table 1: Estimated Radiation Exposure to Patients From Common Interventional Procedures^39-41

Procedure	mSv*
Diagnostic angiography	7.6 ± 6.0
Diagnostic angiography + percutaneous coronary intervention (PCI)	22.4 ± 16.5
PCI for chronic total occlusion	39.3 ± 30.1
Transcatheter aortic valve replacement (TAVR)	25.6 ± 6.2
*1 mSv = approximately 10 chest X-rays.7

Risk Factors for Increased Radiation Exposure in Cardiac Catheterization

Patient-level factors, including anatomic characteristics of coronary artery lesions, and physician and institutional practices have the potential to increase radiation exposure in cardiac catheterization. Lesion complexity and the number of patient co-morbidities have increased over time.¹³ Patients are being referred for surgical turn-down, revascularization of chronic total occlusions, bypass graft intervention, bifurcation lesions, atherectomy for calcified lesions, staged procedures, and hemodynamic support for high-risk PCI. Apart from complex coronary anatomy, obesity (body mass index >30 kg/m²) is a major patient-level risk factor for increased radiation exposure. In 2011, 45.9% of patients presenting for PCI included in the National Cardiovascular Data Registry were obese.¹⁴ Challenging coronary anatomy coupled with obesity raises the total radiation dose to the patient and the rapidity with which it is achieved during the procedure.

Physicians themselves vary in the use of fluoroscopy. Annual operator volume is inversely associated with fluoroscopy time.¹⁵ Interventionalists vary by which portions of the procedure they visualize versus those that they do intuitively by feel. Operators can opt to decrease radiation exposure by using fluoro-save to record the last sequence versus cine to store still images, adopting lower frame-rate settings, and using less high-frame rate ventriculography. Choice of access site plays a role as well. Interventional cardiologists are exponentially adopting radial access due to evidence of decreased mortality and reduced bleeding with this approach.^14,16 However, case volume affects fluidity with the radial versus femoral approach, prolonging fluoroscopy time early on. This is mostly overcome with experience as the operator progresses beyond 100-200 radial cases.¹⁷ The benefit of transradial access may outweigh the risk of increased radiation exposure to the patient and operator.¹⁸

Aside from coronary interventions, patients are increasingly coming to the catheterization laboratory for newer techniques. Peripheral interventions rely on digital subtraction angiography, which can have a 20-fold increased radiation dose per frame than conventional cine.⁹ Pre-operative planning and simulation for complex intervention may reduce exposure.¹⁹ Structural heart interventions rely heavily on intracardiac or transesophageal echocardiography. TAVR, specifically the transfemoral approach, is an outlier in that fluoroscopy is frequently employed for steps like sheath placement, valve crossing, balloon valvuloplasty, valve positioning, deployment, and vascular closure. If future iterations of TAVR or mitral valve technologies become more commonly used in younger, healthier individuals, then limiting fluoroscopy will become even more important. Lastly, training TAVR team members in radiation safety is useful because those from other departments may be new to the fluoroscopy suite and can have higher exposure.²⁰

There are also institutional factors that affect patient radiation doses. Teaching hospitals have longer fluoroscopy times, either due to fellows functioning as the primary operator or to referral of more complex cases to tertiary care.¹⁵ Strong administrative support at the hospital level is required for installation of new fluoroscopy suites when end-of-life has been reached or for purchase of radiation-reducing technology, like the Siemens Artis Zeego Hybrid (Siemens Medical Solutions; Malvern PA) or Philips AlluraClarity system (Philips Healthcare; Best, Netherlands), both of which reduce exposure in PCI and TAVR,^21-23 or a novel system that creates a visual color map of the skin dose for live physician feedback.²⁴

Strategies to Reduce Radiation Exposure in Cardiac Catheterization

The strategies to reduce radiation exposure in the laboratory largely lie in the hands of physicians and institutions. Operator and hospital factors account for 20% of the variability in fluoroscopy time.¹⁵ Operators are at the forefront here, challenged by the need to do increasingly complex work with shorter fluoroscopy times and decreased procedural complications. Operator training and feedback make an impact. Providing fluoroscopy times to surgeons improves performance and could likely impact interventional cardiologists in their practice as well.²⁵

Radiation reduction involves the physician's active awareness. The physician can collimate the image to focus on a smaller area, decrease the frame rate to halve the radiation dose, bring in wedge filters, keep the detector close to the patient, put the patient's arms up in the lateral projection, eliminate unnecessary high frame rate ventriculography, adopt fluoro-save for non-critical images, use anteroposterior and right anterior oblique views, use less magnification, avoid extreme angulation, change the projection frequently to distribute the radiation rather than concentrate it, and shield patients as needed to attain exposure ALARA.

Finally, hospital leadership can proactively invest and maintain technology to directly reduce radiation exposure to patients and physicians. Tracking cumulative individual exposure across different departments within one institution and even across different hospitals, as a "fifth" vital sign, should be possible in the era of electronic medical records but needs champions in administration and information technology. Until then, motivated patients can download a medical imaging record card from the FDA's website to track their own exposure.²⁶

Certainly a radiation-free technology that is applicable to the majority of patients and with quality imaging would be ideal. Magnetic resonance imaging-guided catheterization is under investigation, and right-heart catheterization can be performed this way, but coronary catheterization is challenged by development of completely new catheter technology and imaging coronary blood flow without iodinated contrast.^27-29

Special Populations in the Cardiac Catheterization Laboratory

Pregnant Patients

Women have an increased cancer risk from radiation exposure compared with men, including female fetuses.³ The National Council on Radiation Protection and Measurements recommends fetal exposure be limited to <5 mSv during the entire pregnancy, and some other countries have lower recommend levels.³⁰ In emergent cases of suspected spontaneous coronary artery dissection or acute myocardial infarction, pregnant women should be referred for cardiac catheterization. Although minimization of exposure is important, especially reducing the imaging field (collimation; see the "Strategies to Reduce Radiation Exposure" above), radiation exposure to the fetus is less concerning than the risk of maternal mortality in these cases, and catheterization should not be delayed or withheld.³¹ Ultrasound guidance can eliminate the need for fluoroscopy of the groin. Right-heart catheterization for pregnant patients with pulmonary hypertension can often be performed without fluoroscopy. The addition of lead shielding under the gravid uterus is a common practice, but more research is needed to understand how it compares with collimation and best practices alone.³²

Children and Adolescents

Radiation exposure in children and adolescents in the catheterization laboratory is beyond the scope of this discussion; however, more children with congenital heart disease are surviving into adulthood. Early exposure is a focus of quality improvement and research.^33-35 Considering stochastic effects from repeated procedures may factor into conversations with parents.

Cardiac Catheterization Laboratory Staff

Any discussion of radiation exposure would be incomplete without mentioning the laboratory staff member, who finds him- or herself in the role of patient at times. Operators can be exposed to >6 mSv per year, with a 4.5-fold increased risk of cancer and 9-fold higher odds of cataracts.^36,37 Thus, physicians and nursing and technical staff have distinct risks due to repeated exposure to workplace radiation, of which their physicians need to be cognizant. Distance from the source, properly fitting protective aprons, hats with shielding, and protective eyewear reduce exposure. Hands-free shielding can reduce orthopedic burden but can be clumsy in emergencies. Shielding draped over the patient reduces exposure to the operator but, paradoxically, may double the dose to the patient.³⁸ Robotic catheterization may reduce operator risk but is not yet in widespread use.

Pregnant physicians and staff desiring to work in the catheterization laboratory in pregnancy should have properly fitted shielding throughout the course of pregnancy. Half frontal aprons can be discreetly worn under usual lead when privacy may be a concern early on. In later trimesters, full maternity aprons or shortened tops and longer skirts may fit more comfortably over the gravid uterus, and the thickness of shielding can be tailored to be more protective in the front and side panels. A 1 mm material thickness maximally attenuates exposure.³⁰

Making a Shared Decision

In sum, interventional cardiologists, staff, and patients alike benefit from reducing radiation exposure in the cardiac catheterization laboratory. Applying the principles of patient safety to that end, the first consideration in shared decision-making should be this: is the procedure justified based on the evidence (Figure 1)? Here patients can provide perspectives on their symptoms, beliefs about the procedure, values, and goals for their medical care. Physicians can articulate benefit versus risks of catheterization, which should include a discussion of any perceived prolonged radiation exposure due to complex anatomy or obesity (regardless of whether the procedure is considered emergent, urgent, or elective), how much symptomatic relief is expected, and alternative medical or surgical therapies. Risk of radiation exposure can be articulated to patients in lay terms using chest X-ray equivalents and risk of cancer with repeated or prolonged exposure.¹² Physicians can help patients estimate cumulative doses by tallying exposure with an online calculator or a medical record card when counseling patients about individual risks for short- and long-term side effects of fluoroscopy.

Figure 1: Key Points for Physicians and Patients to Consider in Shared Decision-Making Regarding Radiation Exposure in Cardiac Catheterization

The second consideration is this: how can the procedure be optimized to reduce radiation exposure? This responsibility lies with operators and institutions. Physicians, invasive and non-invasive alike, can support each other in training and quality initiatives, and institutions can support operators by providing the most radiation-safe, modern equipment and shielding and adopting patient-centered protocols. With these principles guiding decision-making, physicians can confidently tell their patients that they will undergo an appropriate procedure with the patients' safety in mind.

References

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Keywords: Diagnostic Imaging, Angiography, Digital Subtraction, Atherectomy, Background Radiation, Cardiac Catheterization, Cardiovascular Diseases, DNA Damage, Echocardiography, Transesophageal, Fluoroscopy, Heart Diseases, Hemodynamics, Hypertension, Pulmonary, Magnetic Resonance Imaging, Mitral Valve, Myocardial Infarction, Patient Safety, Percutaneous Coronary Intervention, Radiation Protection, Risk Factors, Transcatheter Aortic Valve Replacement, X-Rays

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