Cardiac catheterization's side effects.
Cardiac function usually is evaluated by cardiac catheterization performed under fluoroscopic guidance. Approximately 80% of the patients who undergo cardiac catheterization have advanced coronary disease caused by the accumulation of fatty plaque on the vessels of the heart. (2) This condition is life threatening and can require open heart surgery or an interventional procedure. Cardiac catheterization is an essential tool for gathering information for interventional procedures or surgery.
The number of cardiovascular-interventional procedures performed annually is increasing and many patients have them more than once. These procedures are the only alternative to open heart surgery, and over the past 30 years cardiovascular-interventional radiology has proven to be a better, easier method of treatment than some conventional surgical techniques. (3) Interventional techniques are less invasive, lower risk, less costly and offer quicker recovery times.
Some common interventional procedures that involve extended fluoroscopic time are percutaneous transluminal coronary angioplasty (PTCA), radiofrequency cardiac catheter ablation, vascular embolization and stent and filter placements. (2) The primary method for treating stenosis and short occlusions is PTCA, also known as balloon angioplasty. In this technique, a catheter is introduced into the femoral artery and advanced to the stenosis in the coronary artery. A balloon then is dilated along the length of the stenosis, increasing blood flow to the heart muscle. Unfortunately, approximately 30% to 50% of these patients experience restenosis, thus requiring a second procedure. (2)
Sometimes a stent is placed inside the coronary artery at the point of stenosis. (2) Stent placement is performed in a manner similar to PTCA, but a metallic stent is mounted on the PTCA balloon. For optimum stent deployment, the stent is centered along the length of the stenosis. After the stent is deployed, the PTCA balloon is removed and a high-pressure balloon is advanced to the stent to set it within the artery. Restenosis rates are lower in patients who receive intracoronary stents than in those who undergo conventional PTCA.
Another procedure performed in the cardiac catherization radiology department is radiofrequency (RF) ablation. This procedure is performed at the time of a diagnostic electrophysiology study when an arrhythmogenic focus is identified. RF ablation is performed by delivering a low-voltage, high-frequency alternating current directly to the endocardial tissue through a specially designed ablation catheter. The current destroys the underlying abnormal myocardial conduction tissue and creates a small, discrete burn lesion. Localized RF lesions cause areas of tissue necrosis and scarring that subsequently destroy the arrhythmogenic focus. It may be necessary to create several RF lesions to eliminate the abnormality.
Digital fluoroscopy plays a major role in these exams due to the fact that it displays an image in real time on a monitor. Using fluoroscopy during cardiac procedures in interventional radiology has decreased the numbers of open heart surgeries. (3) However, depending on the complexity of the blockage, many of these procedures can take several hours, potentially exposing a patient to a significant amount of radiation. The question is: "Does this exposure rate pose a serious threat?"
The 2 main biological effects of ionizing radiation are deterministic and stochastic. Deterministic effects are those in which the number of cells lost in an organ or tissue is so great that there is also a loss of tissue function. Skin erythema and ulceration are examples of deterministic effects. These types of burns occur at a threshold exposure rate; above this threshold, the severity of the effect increases with dose (ie, exposure time.) (3) Considering the frequency of interventional procedures, it is very important to be aware of the base-line thresholds necessary for burns to appear. Because there are no specific dose limits for patients in the United States, the guiding principle is that all deterministic effects should be avoided while optimizing radiation exposure for maximum diagnostic accuracy with minimum dose. (3) Dose limits for these burns also are important due to the fact that they are delayed; physicians cannot determine the damage by observing the patient immediately after the procedure.
Table 1 lists the types of interventional procedures that have resulted in reports of skin injuries and the number of injuries reported to the FDA. It is probable that the reported injuries represent only a fraction of the total number of radiation-induced injuries associated with fluoroscopically guided procedures. The severity of the reported injuries ranged from erythema in a few cases through moist desquamation to skin necrosis requiring skin grafting in the most serious cases. (2)
One case reported to the FDA involved a 40-year-old male patient who underwent coronary angiography, coronary angioplasty and a second angiography procedure due to complications. These were followed by a coronary artery bypass graft, all performed on March 29, 1990. (2) This case is an example of a serious radiation-induced skin injury. Six weeks following the procedures, the area of injury was turning red. Approximately 8 weeks following the procedures, in mid May, second-degree burns had appeared. In late summer 1990, the area had the appearance of a healed burn, except for a small ulcerated area near the center. Skin breakdown continued over the following months with progressive necrosis. The injury eventually required a skin graft. The amount of the skin dose this patient received is unknown. However, from the nature of the injury, the dose probably exceeded 20 Gy. (2)
The radiation dose to an individual patient during an interventional procedure varies considerably depending on patient characteristics, distance from the radiation source, the tissue irradiated and magnification modes used during the procedure. The absorbed dose rate required to cause a skin injury depends on these factors, but typical threshold doses for various effects are about 3 Gy (300 rad) for temporary epilation, about 6 Gy (600 rad) for erythema and about 15 to 20 Gy (1500 to 2000 rad) for moist desquamation, dermal necrosis and secondary ulceration. (4)
Often during cardiovascular-interventional procedures the cardiologist uses a magnification mode on the fluoroscopy unit to best demonstrate the heart. Applying this mode during the procedure raises the patient's entrance skin dose by 4 times. A normal entrance skin dose rate from the direct beam of a fluoroscopy radiation source is between 0.02 Gy/min and 0.05 Gy/min (2 to 5 rad/min), but may be higher, depending on factors that increase the dose rate.
All hospitals and cardiology departments have a legal duty to comply fully with regulations intended to prevent radiation-induced skin injuries. The FDA suggests that facilities performing fluoroscopically guided procedures observe basic principles regarding patient selection, normal conduct of the procedure and limits on fluoroscopy exposure time. (2) Protocols should be modified, as appropriate, to limit the cumulative absorbed dose to any irradiated area of the skin to the minimum necessary for the clinical task and avoid approaching cumulative doses that would induce unacceptable adverse effects.
(1.) Burlington BD. FDA public health advisory: avoidance of serious x-ray-induced skin injuries to patients during fluoroscopically guided procedures. Available at: www.fda.gov/cdrh/fluor.html. Accessed March 5, 2002.
(2.) Thomson KR. Interventional radiology. The Lancet. 1997;350:354.
(3.) Wilde P, Pitcher BM. Radiation hazards for the patient in cardiological procedures. Heart. 2001;85:127.
(4.) U.S. Food and Drug Administration Center for Devices and Radiological Health. Recording information in the patient's medical record that identifies the potential for serious x-ray-induced skin injuries. Available at: http://fda.gov/cdrh/xray-inj.html. Accessed March 5, 2002.
Marie Martinez, R.T. (R), graduated from Santa Rosa Junior College in July 2002. She is employed by Kaiser Permanente of Santa Rosa in California.
Table 1 Skin Injuries from Fluoroscopy Reported to the FDA * Type of Procedure Number of Injuries RF Cardiac Ablation 12 Coronary Angioplasty 4 * Between January 1992 and October 1995. Some injuries occurred before 1992. Source: Shope TB. Radiation-induced skin injuries from fluoroscopy. Available at: www.fda.gov/cdrh/rsnaii.html.
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|Title Annotation:||STUDENT SCOPE|
|Date:||Sep 1, 2003|
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