INTERVENTION IN PERIPHERAL VASCULAR DISEASE

Interventional and Peripheral Vascular Procedures Using Contrast Management: Tips and Techniques

Morton J Kern, MD
Morton J Kern, MD
The following special CME section is underwritten through an educational grant from Bracco Diagnostics The first cardiac catheterization reported occurred in 1929 in Germany, performed by Dr. Werner Forssmann.1 After anesthetizing his own arm and performing a cut-down on the brachial vein, he inserted a urologic catheter, passed it up to the heart, and then walked down two flights to stand in front of an X-ray machine, where he took the first catheterization radiograph.2 The image detail was relatively poor. The selective injection of radiographic contrast media (also known as X-ray dye) for injection into coronary arteries was first described in the 1950s and 1960s by Melvin Judkins and Mason Sones. The imaging system they used was a very large, cumbersome X-ray machine eventually equipped with a cineangiographic system recording the angiographic information on motion picture film.3 The first imagers used 16 mm film; later 35 mm film was used. Since the X-ray tube was fixed to the floor, the patient had to be rotated under the image intensifier to get proper views of the structures from different angles; today, the image intensifier rotates over the patient who remains comfortably in place. In those early systems, the patient was typically positioned lying on his left side, right side forward and one arm up while a power injection of contrast media was administered through relatively large catheters into the coronary arteries. The initial injection systems had fixed settings for rate and flow. Dr. J. G. Mudd, the first director of the St. Louis University cath lab (the first such lab west of the Mississippi River) performed 32,000 coronary angiograms himself, all using just such a power injection system. Power injection was later supplemented by hand-injection through plastic valved manifolds, which were designed specifically to address the needs of small-vessel (coronary) angiography. In fact, manual contrast injection is the most commonly used technique today. Although operator-dependent, manual injection is regarded as practical, simple, reliable and highly functional.4 In 1977, Dr. Andreas Gruentzig revolutionized cardiology through the development of angioplasty, first introduced to the United States two years later in 1979.5 At that time, coronary angiography and balloon angioplasty were performed with large guiding catheters, of 9 Fr and 10 Fr diameter to accommodate balloon catheters of 4 Fr or 5 Fr diameter which is considered quite large compared to today’s devices (6 Fr guides using sub-3 Fr angioplasty equipment). Angioplasty drove the need for better imaging systems to perform balloon dilations and assess results inside small arteries. This, in turn, led to the most dramatic advances in angiographic technique, improving all related devices including catheters, balloons, stents, injection systems and vascular closure devices. At the beginning of angioplasty, lesions could not be well visualized using existing imaging systems, so it was extremely difficult for physicians to determine the balloon catheter position within the vessel. The early large balloon dilation catheters had pressure holes on the ends to measure pressure across a stenosis as a way of evaluating the correct position before dilating the narrowing. Thus, it was the pressure gradient that guided those earlier procedures. Techniques for coronary angiography, contrast injection, imaging, and contrast agent composition have advanced considerably since those early efforts. Today, contrast injection in the modern vascular laboratory is performed using either power injection, manual injection, or a combination of both.4 Manual Injection Systems The manual injection system is comprised of three main components: the injection syringe, the manifold with multiple stopcocks, and the pressure transducer system, which the operator uses to monitor catheter tip pressure. Although simple in design, each component brings with it the potential for some difficulty. Typical problems that may occur with manual injectors include leaks in the connections, loose fittings, and frequently needed forceful hand injections, especially when small-caliber catheters are used. These systems are simple, straightforward, and practical. However, they require a level of expertise on the part of the operator and may be associated with time-consuming adjustments or breakdowns. They also can require an “extra pair of hands” during the procedure. Defining the Optimal System There are three major issues involved in the pursuit of optimal coronary angiography. The first is obtaining adequate vessel opacification with small-diameter catheters. For diagnostic studies, most clinicians prefer to use catheters no larger than 5 Fr diameter in order to facilitate early ambulation. However, these small-diameter catheters can make opacification more challenging. The second concern in optimal coronary angiography is adequate personnel to assist the operator. If the operator is injecting with two hands, another person is needed to pan the table or hold the catheter. In interventional procedures, the operator uses both hands to guide the angioplasty equipment, while another person does the injecting and possibly yet another person pans the table. The third issue involves flexibility in contrast delivery.6 Since left ventriculography, aortography, and peripheral vascular angiography may all be performed as part of a coronary angiographic procedure, power injection is required. A variable, flexible power injector system is ideal, but is not available in many facilities. Most currently available power injectors function with off-table adjustments of the injection settings, meaning that clinicians must program and set the desired injection rate and volume. Syringe volume on such systems may be limited to 7 This system can facilitate procedures by freeing ancillary personnel attending to the injection and reducing the need for contrast wastage. This system is highly effective for angiographic procedures using small (8 An on-table touch screen with inputs for rate and flow allow rate and flow to be changed quickly without any additional help from a technician or nurse. The injection syringe on this system is angled upward and de-bubbled automatically, a feature which was designed to enhance patient safety and save time during procedures. The system connects the syringe to the patient with in-line bubble detectors, and a one-way valve linking pressure tubing to injection tubing which permits pressure for monitoring to be transmitted at all times except during an injection. The contrast reservoir is large enough to accommodate up to 500 ml of contrast; 5 or 6 patients can be treated before a refill is required. This method saves contrast, particularly when compared to the manual systems. The operator can control the flow and pressure settings with a touch-screen interface available in the sterile field. The operator controls the injection rate using a pressure-sensitive trigger with their thumb that operates like a gas pedal. The harder it is pressed, the faster the delivery. This allows for variable rate flows with an intuitive control. The touch-pad screen allows the operator to track contrast amounts (how much was delivered, how much remains).9 This system also offers a separate button for a saline flush. First described by Hopper et al9 this so-called “saline chaser” helps clear lines and reduces the amount of contrast media required. While not used by all operators, the ACIST system makes this option available. The need to reduce the amount of contrast used extends beyond cost controls. Excess contrast media may cause renal failure in some patients. To date, there is no definitive single method to reduce contrast-induced nephropathy other than properly hydrating the patient and generally reducing the volume of contrast used. In a study performed several years ago with the ACIST device, a 6 Fr standard manual injection with the hand manifold was compared to a 4 Fr ACIST angiography in routine coronary angiography and left ventriculography.10 A total of 101 patients were examined, with data taken of left ventricular contrast volume used during the procedure. The total contrast volume was reduced in the ACIST group, because there were better pictures of the coronaries without streaming, back up or false injections by hand.11 In another study, the 4 Fr ACIST device was compared to a 4 Fr manual injection system.12 The 96 patients included in this study produced quality scores comparable to those of the former study, in that the ACIST injector reduced contrast volume used and provided better imaging than the manual system. The need for multiple injections was eliminated with the power injector. Complications were about equal for both systems and would be considered low. When making a buying decision for an injector system, one of the key factors is the programmability and adjustability of flow controls and volume ranges as well as delivery pressures. Excessive contrast flow can damage the vessel and harm the patient. Insufficient flow provides poor images. Optimal Use of ACIST System There were some problems with coronary opacification in some patients with the ACIST injector, when using a 4 Fr catheter.13 Fortunately, the adjustable injection rate (controlled by the touch-pad) helped regulate this and address the problem. In our experience, the left ventricle appeared to be under filled and the injection rate through 4 Fr and 5 Fr catheters was too high; the 13 cc per second rate was reduced and maximal delivered pressure increased to overcome resistance through a 4 Fr catheter. A similar phenomenon occurred with aortography, which required moving up from a 4 Fr catheter to a 5 Fr or even 6 Fr catheter. The ACIST injector prompted frequent refilling of contrast medium if the contrast reservoir was small or the sensor on the contrast bottle was not clean. Fifty or 100 ml bottles require frequent replacement. Larger bottles (200 ml or more) avoid this issue, save time, minimize change-outs, and waste less medium. In our examination, we found that the ACIST touch screen connections required some tightening and replugging over time. Dirt or contrast media that drips into the sensor can negatively affect the warning system for low contrast. This problem was addressed by wiping off and cleaning the sensor. Pressure tubing for the bubble sensors requires careful placement. Pressure can build up in the injection syringe and block off the pathway to pressure; in this case, pressure must be released back into the reservoir. Precise hemodynamic waveforms were of variable quality with the ACIST system, mainly because of over damping, especially with 5 Fr catheters filled with viscous contrast media. A few simple steps with the ACIST injector could prevent this. First, operators should verify that the transducer is locked completely into the appropriate slot. Contrast will damp virtually all catheter waveforms, especially when using the smallest-diameter catheters. Contrast must be flushed out of the system when using a 4 Fr catheter to avoid an over damped signal. Issues of pressure waveform damping can be important for coronary angiographers, but were not a significant problem when using the system. The Illumena injector system from Liebel-Flarsheim (Mallinc-krodt, Hazelwood, Missouri) avoids this issue with front-loading prefilled syringes. This eliminates any need to decant contrast media and minimizes both the risk of introducing bubbles and the possibility of contamination with a toxic substance if there is any leakage during reconnection. Prefilled syringes are available only for the Illumena system in single-dose, prelabeled units. Some clinics have reported a cost savings as well as a savings in time and shelf-space because syringes and contrast are packaged together, can be easily stored and identified, and media easily prepared.13 The American Society of Radiologic Technologists has found that prefilled syringes in this system saved time, reduced costs, improved the quality of patient care and enhanced patient safety.14 Prefilled syringes are not available with ACIST or other injector systems. Other hardware concerns can occur across all systems from all manufacturers. It is important to maintain tight connections, especially with tubing, to keep sensors clean, and to keep the system in generally good working order with recommended routine maintenance. Conclusion Every capital acquisition represents a major investment on the part of a facility, and costs are best offset when a reliable, versatile system can be found to handle the range of procedures typically done at the facility in a safe, reliable, and time-efficient way.15 For those involved with coronary and other vascular angiography, features such as programmability of flow and volume ranges, adjustable delivery pressures, touch-screen controls and methods to minimize air bubbles are important. Unique features in the ACIST system are the pressure-sensitive flow control (gas-pedal system), the sterile touch pad, and saline flush options, all of which we found to be very useful. The pressure-sensitive flow control, in particular, shortens the learning curve in getting used to the equipment. On the other hand, the prefilled syringes of the Illumena system, the voice prompts and extravasation detection of the EmpowerCT system from E-Z-EM and the small footprint SpectrisMR are all unique features to those particular systems and may be of special interest to certain clinicians.
References
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