Digital Imaging for the EP Lab: A guiding tool for the electrophysiology lab

This author offers his opinion on how to purchase a fixed-base imaging system. You can use the money you saved to purchase other tools on your lab's wish list!
Larry W. Brown, Seattle, WA

EP Lab at Memorial Hospital of South Bend, Indiana: (Front row, left to right): Michele Thielka, LeeAnn Czajkowski, Carol Nick, Cathy Bringedahl, Mike Goldenstern. (Back row, left to right): Aaron O'Dell, Jason Shruff.

With the development and introduction of newer devices for pacing, internal cardioversion, mapping, ablating, and real-time anatomic visualization, the important task of evaluating and selecting an X-ray imaging system sometimes takes a back seat. This is possibly due to several reasons. The development and evaluation of elegant tools to assist in the analysis, diagnosis, and treatment of arrhythmia focuses appropriately on the patient's clinical arrhythmia and conduction system rather than the technical aspects of imaging.

Fluoroscopy has long been available as a guiding tool and a number of manufacturers produce X-ray imaging systems for cardiac labs. However, in many cases, electrophysiology (EP) labs have had to employ fluoroscopy imaging systems designed for use in the cardiac catheterization laboratory, despite the unique requirements of imaging in the EP lab. Notwithstanding this momentum of the traditional cath lab X-ray imaging system, many dedicated EP labs are discovering the advantages of purchasing a fixed-base imaging system designed to meet the demands of interventional electrophysiologists. These specialized EP imaging systems can produce economic and as well as work flow benefits.

Getting the Pulses in Shape

Simplicity of production and effectiveness of the X-ray have stimulated its proliferation in cardiology and radiology. As cardiac intervention came of age, the 30 frame-per-second cardiac cine became the standard. However, the radiation dose during extended cardiac procedures became a major negative factor. Thus, in 1995, the FDA suggested guidelines for estimating and reducing patient-absorbed radiation during procedures involving extended fluoroscopic exposure times. Pulsed fluoroscopy, developed previously, was introduced into EP lab systems by Omega Medical Imaging in 1991. It quickly became the preferred method for reducing dose during longer EP procedures. Manufacturers achieve "pulse shaping" through various methods. In addition, the number of pulses per second was also reduced to 30, 15, 7.5, and lower, while attempting to keep the image quality at acceptable levels for the clinician. The pulse-shaping process makes the pulse wave as square as possible for shorter times, with real time adjustments to the pulse widths (time) and X-ray current (mA or milliAmperes) to maintain image quality at acceptable levels.

Due to the nature of electrical components and circuitry, pulsing requires elegant design because pulses don't start and stop sharply and cleanly without help. John Grady, the former President of XRE, provides an excellent review of the various methods of pulsing along with a frank discussion of the "hype, smoke, mirrors, and ethics" surrounding this topic in his publication, Pulsed Fluoroscopy. In it he states, "The essence of pulsing technology is that the fluoroscopic X-ray is emitted in very short bursts (pulsed) for each frame. The image quality perceived is a direct function of the total amount of X-ray used". Pulsed fluoroscopy mode is imperative for EP labs to reduce dose. A significant advantage of pulsing is that the individual cardiac image is sharper because the pulse width is shorter, allowing less motion to occur during the exposure than in continuous fluoroscopy. This is analogous to fast shutter speed in photography.

Knowledge Is Power

The evolving clinical knowledge and experience of electrophysiologists and their staffs, and increased dependence upon computerized systems for real-time analysis of intra-cardiac electrophysiology data, have combined to reduce the role played by X-ray imaging in electrophysiology. More accurate methods of measurement, mapping, and localization inside the chambers are also becoming available. However, electrophysiologists are reluctant to eliminate the use of fluoroscopic imaging in the EP lab because of its versatility and ease of use. Initial catheter placement during the EP study is more easily accomplished using fluoroscopic guidance. The ability to "see" the placement of the catheter is also very important during anatomical ablations, such as slow pathway ablation for AVNRT or right atrial isthmus ablations for atrial flutter. In addition, biplane viewing of catheter placement in slow pathway ablations can substantially reduce fluoro time.

During the last few years, certain methods have changed the presentation of the anatomical "shadow" produced by the X-rays. In general, the better the presentation of the image, the better our visualization of the anatomy. Possibly the most obvious change has been digital imaging, the process by which an analog image is changed into discrete electronically tagged pieces and made transportable. Though EP labs have not typically used recording techniques of the cath lab, the advantages of digital recording now benefit EP as well. Digital recording and storage brings advantages such as electronic transfer and reconstruction of images, more convenient storage and viewing, elimination of chemical processing, and reduction in cost over time. Another benefit is the ability to post-process the images. This does not alter the information in the image, yet can sometimes make the image more useful if done correctly. As mentioned earlier, methods of X-ray pulsing have been developed, allowing a reduction in the amount of radiation delivered per frame or pulse while maintaining the energy required to produce a good image. With the exception of this dose management technique, the improvements in X-ray imaging have been mostly in the presentation and handling of an image that is still produced in essentially the same way.

Digital Dynamics

It took some years to make the digital process consistently good. However, it has been accomplished to an acceptable point with the implementation of the 1024 x 1024 x 12 bit digital process. This gives the practitioner sufficient resolution and contrast for diagnosis. A receptor turns the X-ray field into an image that can be digitized and presented on a monitor. This image may also be recorded on film, but film is being replaced by digital systems as reliability has increased. Digital systems are available from a variety of manufacturers today. Original problems of noise associated with digital camera systems have been addressed successfully.

Features often include special effects and filters, edge enhancement, windowing and level, pan and zoom, loop store, and instant review. Other digital features are available, so EP lab managers and physicians can consider the ones that will benefit electrophysiology. Compatibility with your other equipment should be explored with any system purchase. DICOM (a medical standard for digital information communication) is sometimes made optional, so be sure you know whether this is the case. Features specially designed for EP labs are a part of some X-ray systems available today. EP lab managers should ask about special features when selecting a system. With the demands on the electrophysiologist, it is increasingly important to have excellent image quality. Under limited dose fluoro procedures, it is a necessity to have an excellent digital system to perform the image magic that transforms detail into definition. EP can be demanding enough without having to be frustrated by an inferior imaging system. Before you buy, verify that the selected company will guarantee total integration of the digital system. An EP imaging system manufacturer should allow you or your selected representative to attend the staging of your system before shipment. This provides the opportunity for technical cooperation and verification.

Frugality is Featured for EP

Features for the EP lab digital imaging system focus on economics of motion, space, and cost, while affording generosity to digital imaging technology and quality. Simplicity of design in the EP lab walks hand-in-hand with ease of use. This philosophy, if followed in the vendor selection process, will translate to large savings in acquisition cost, room support structure, and installation costs. It also enhances serviceability. The production of high-quality fluoroscopic images using reputable high-quality components and digital systems is currently available.

Features that add cost to the simplest of EP imaging systems will be the bi-plane and the digital spot image features. These represent added capability. However, an EP imaging system that has a digital spot-imaging capability is considerably less expensive than a cath lab system with digital cine mode, and is usually less expensive than a cath lab system sold as an EP system. The icing on the cake: your lab can use the money saved to purchase other tools on your wish list!

The Golden Era

What has been dubbed a "Golden Era of Pacing and Electrophysiology" is at hand. The dedication of the pioneers and those who continue to improve the clinical practice in the labs every day can be appreciated by anyone close to electrophysiology. The days are long but the satisfactions are great. The challenges continue, as more codified approaches and methods are employed to diagnose and treat more daunting arrhythmias. Pathways to more accurate observation are being widened. Such breakthrough technologies, along with digital imaging designed for the EP lab, can help you reach these high goals.

Acknowledgment. Grateful acknowledgement for this manuscript review goes to Michael Lauer, MD, PhD, Rick Hood, CVT, RCIS, NASPE Testamur, Chris Stapleton, RN, BSN, and to James Princehorn, Consultant.