The development of modern angiography was enabled by one simple technique: the percutaneous introduction of devices into a blood vessel over a wire guide ( Fig. 2-1 ). Described by Sven Ivan Seldinger in 1953, this elegant innovation (now known by Seldinger’s name) eliminated the need for surgical exposure of a blood vessel before catheterization, thus allowing the transfer of angiography from the operating room to the radiology department. Virtually all vascular and many nonvascular invasive procedures are performed with Seldinger’s technique.

Figure 2-1
Seldinger technique. A, Percutaneous puncture of a blood vessel with a hollow needle. B, Introduction of an atraumatic guidewire through the needle into the blood vessel lumen. C, Needle is removed while guidewire remains in place. Compression over the puncture secures the guidewire and prevents bleeding. D, Angiographic catheter is advanced into vessel over the guidewire.

(From Kadir S. Diagnostic Angiography. Philadelphia: WB Saunders, 1986, with permission.)

Preprocedure Patient Evaluation and Management

Knowledge empowers, and in interventional radiology it is the difference between unthinking completion of an assigned task and meaningful participation in the care of a patient. As an interventional radiologist, you should not only be skilled with a catheter, but also be a specialist in the diseases that you treat. Ideally, you will have seen the patient previously in consultation and selected which procedure to perform. The evaluation is the same in clinic or at the bedside, and begins with a review of the clinical issue. Do you understand the diagnostic questions and the information needed? Do you understand the different therapeutic options? A brief, directed history should be obtained. In particular, the symptoms or signs that precipitated the consultation are important, as this knowledge may impact the course of the subsequent examination and interpretation of the images. Other essential areas to cover in the history include prior surgical procedures (especially vascular); evidence of atherosclerotic disease (e.g., prior myocardial infarction or stroke) in “index” vascular beds; diabetes, with attention to medications; status of renal function; allergies; and known previous exposure to iodinated contrast agents. When available, office records or the patient’s chart should be reviewed for similar information. Operative notes and reports from previous angiograms provide valuable information that may alter the entire approach to the procedure. Most important, personal review of noninvasive vascular studies, prior angiograms, and correlative imaging is essential before embarking upon any invasive procedure.

The immediate preprocedural physical examination is focused on the overall status of the patient and selection of a vascular access site. Introduce and identify yourself before examining the patient. The pulse examination should be conducted by the person who will perform the angiogram. A general assessment of risk for the procedure and sedation should be made. The American Society of Anesthesiologists (ASA) classification, though designed for surgical patients, is a simple way to categorize and communicate procedural risk ( Table 2-1 ). Equally important, the patient’s understanding of the procedure, ability to cooperate, current level of pain, and ability to lie on a procedure table in the position necessary for the procedure should be considered before going forward.

Table 2-1
American Society of Anesthesiologists Classification for Preoperative Risk
Class Definition
1 A normal healthy patient
2 A patient with mild systemic disease
3 A patient with severe systemic disease
4 A patient with severe systemic disease that is a constant threat to life
5 A moribund patient who is not expected to survive without the operation
6 A declared brain-dead patient whose organs are being removed for donor purposes

The strength of the pulses and the presence of peripheral aneurysm (as suggested by a broad, prominent pulse) should be recorded using a consistent system. Cellulitis, fresh surgical incisions, a large abdominal pannus, or a dense scar over the vessel all influence selection of an access site. Pulses distal to the anticipated access site must be evaluated and recorded. This baseline information is useful if an occlusive complication occurs or to determine success of a revascularization procedure. The physical examination should include both sides of the patient in case an alternate or additional access is required during the procedure. When an upper extremity approach is anticipated, blood pressures in both arms must be obtained.

Evidence of vascular disease such as trophic skin changes, hair loss, cool skin temperature, dependent rubor, delayed capillary refill, ulceration, and gangrene should be noted. Classification systems for acute and chronic ischemia have been devised, which serve to decrease ambiguity when describing a patient, have prognostic implications, and allow assessment of outcomes of interventions (see Table 15-6, Table 15-11 ).

Patients should be well hydrated prior to the procedure. Outpatients who will have conscious sedation should not be instructed to fast after midnight, but rather encouraged to drink clear liquids (no solid food) until 2 hours before their scheduled appointment. Medications can be taken with a sip of water. Patients for whom general anesthesia will be required should follow local anesthesiology department guidelines, usually fasting for 6 hours. Before the procedure, an intravenous infusion of (D5/0.5NS or 0.9NS) should be begun at a rate that sustains hydration (about 100 mL/hr) for adults with normal renal and cardiac function. Inpatients who will have conscious sedation should stop solid food 6 hours before the procedure, but can be given clear liquids until 2 hours before. An intravenous infusion should be established before arriving in the angiographic suite. Most hospitals have guidelines for oral intake before invasive procedures; however, these are generally not designed for patients about to receive large doses of nephrotoxic contrast.

There are no laboratory studies that are absolutely mandatory before conducting an angiogram. However, because the procedure involves making a hole in a blood vessel and administering nephrotoxic contrast material, reasonable laboratory tests in patients at risk include coagulation studies (international normalized ratio [INR] or prothrombin time (PT), activated partial thromboplastin time [aPTT]), platelet count, and serum creatinine (Cr). Routine laboratory studies can be safely omitted in young patients without known coagulation disorders or renal dysfunction.

A prolonged PT or INR is usually the result of warfarin therapy, liver disease, or poor nutritional status. Femoral arterial access is safe when the INR is 1.5 or less (or the PT less than 15 seconds). Coagulation studies should be normal for axillary, high brachial, or translumbar aortic access. Fresh frozen plasma (FFP) is used to rapidly normalize the INR or PT before a procedure. Vitamin K (phytonadione) administration for reversal of coagulopathy caused by warfarin, liver disease, or vitamin K deficiency is effective but can require a day or more to work. FFP contains normal quantities of all coagulation factors. The effect of FFP is fast but volume related; 10-20 mL per kg is usually required to normalize a coagulopathic patient (each bag contains 200-300 mL). The half-life of some of the coagulation factors in FFP is short (e.g., 3-5 hours for factor VII), so continuation of transfusion during or even after the procedure may be necessary in severely coagulopathic patients.

A prolonged aPTT is usually due to administration of unfractionated heparin (low-molecular-weight heparin does not alter the aPTT), which can be turned off when the patient arrives in the angiography suite. FFP is not indicated for reversal of heparin-induced coagulopathy. Because the half-life of heparin is roughly 60 minutes, most patients will be sufficiently reversed to allow manual compression by the end of the procedure.

Platelets have an extremely important role in hemostasis after angiographic procedures. Even in the presence of normal coagulation studies, thrombocytopenia carries a high risk of bleeding complications. Angiography is safe in patients with platelet counts greater than 50,000/mm 3 ; venous procedures are safe when platelet counts are greater than 30,000/mm 3 (assuming normal platelet function). Placement of implanted venous access ports requires platelet counts greater than 50,000/mm 3 . Platelet transfusion, with infusion continuing through the procedure for patients with severe consumptive thrombocytopenia, should be considered for patients with low platelet counts. Most angiographic procedures can be safely performed in patients taking platelet-inhibiting agents such as aspirin or clopidogrel. Interruption of these medications is not necessary before diagnostic angiography, and preprocedural administration of platelet inhibitors is often desirable in patients undergoing arterial interventions.

In the presence of an abnormal serum Cr, the risk of renal failure after the procedure should be weighed against the benefits of the examination. Prophylactic measures should be followed to maximize renal protection (see Contrast Agents). During the procedure, dilution of contrast in a ratio of 1:2 or even 1:1 (NS:contrast), limited use of hand injections, digital capture of fluoroscopic images, and liberal use of roadmap images to guide catheter positioning are all useful techniques to minimize contrast use.

Basic Safety Considerations

Interventional radiology must be safe for patients and providers. Precautions against exposure to body fluids should be exercised at all times, even when working with patients with no known risk factors. Consistent use of masks, face shields or other protective eyewear, sterile gloves, and impermeable gowns should be routine. Closed flush and contrast systems minimize the risk of splatter. All materials used during the case should be discarded in receptacles designed for biological waste.

Needles, scalpels, or any other sharp device used during a case should be carefully stored on the work surface in a red sharps container or removed immediately after use. Recapping is not advised. Verbal communication when handling sharps is essential. The best sharps containers contain a foam block in which the point of the sharp can be embedded. At the end of the case, it is the responsibility of the physician to dispose of the sharps in the appropriate receptacle. Puncture wounds from contaminated sharps are not only painful, but also potentially life-altering. If an accidental splash, puncture, or other exposure occurs, immediate consultation with individuals responsible for the management of occupational exposures is essential.

Radiation exposure to the patient and the staff should be kept to minimum. Use fluoroscopy only as needed. Last image hold, the ability to store and review fluoro loops, and imaging with pulse-mode fluoro (3-7.5 frames per second as compared to 15) all reduce patient and operator exposure. Prolonged fluoroscopy at high magnification with the x-ray tube in one position can cause cutaneous radiation burns to the patient. Cumulative exposure to physicians from scatter, especially when standing at the side of the patient during imaging, can be substantial. Wraparound lead, thyroid shields, and leaded glasses should be worn. Leaded table drapes, careful coning of the beam, minimizing the air-gap between the image-intensifier and the patient, and use of boom-mounted x-ray shields are all means to decrease physician exposure to scatter. The operator’s hands should never be visible on the image screen. Although it is tempting to remain at the patient’s side during angiography in order to save time, this is a bad habit. Radiation badges should be worn at all times.

Many interventional radiologists report degenerative neck and back problems over time. Careful design of angiographic suites with attention to positioning of controls and monitors can reduce twisting and bending. In the future, robotically assisted or performed procedures will further decrease operator risk.

Tools

Access Needles

All percutaneous angiographic procedures begin with an entry needle. There is great variety in vascular access needles, but all have a central channel for introduction of a guidewire ( Fig. 2-2 ). Needles with a central sharp stylet that obturate the lumen have a blunted, atraumatic tip when the stylet is removed. The stylet allows the needle to puncture the vessel, but once removed theoretically reduces the risk of trauma. The stylet may be solid or hollow. In the latter case, blood can be visualized on the stylet hub once the vessel lumen is entered. The stylet must be removed in order to insert the guidewire. Needles with stylets are generally used only for arterial punctures. Needles without stylets have very sharp beveled tips, a quality that is useful when attempting to puncture small, mobile, or low-pressure vessels. The guidewire is introduced directly through the needle once the tip is fully within the vessel lumen. This style of needle is used for venous as well as arterial punctures.

Figure 2-2, Typical access needles. A, From left: 18-gauge Seldinger needle with hollow, sharp central stylet that extends beyond the blunt tip of the needle; stylet; Seldinger needle with stylet removed; 18-gauge sharp hollow (one-wall) needle; 21-gauge microaccess needle. B, Microaccess system. From left: 21-gauge needle; 0.018-inch guidewire for insertion through needle; 5-French dilator with central 3-French dilator tapered to 0.018-inch guidewire; 5-French dilator with 3-French dilator removed (accepts an 0.038-inch guidewire); 3-French dilator.

The most common sizes for vascular access needles are 18- to 21-gauge in diameter and 2¼-5 inches in length. The lower the gauge number, the larger the diameter of the needle will be. The 18-gauge needles accommodate standard diameter guidewires. The 21-gauge needles are often packaged as part of a microaccess system that includes a small guidewire and coaxial dilators that convert the puncture to a standard-sized guidewire. These needles are designed to be highly visible under ultrasound to facilitate image-guided access. Microaccess techniques can be used for all arterial and venous punctures.

Guidewires

Guidewires are available in a wide variety of thicknesses, lengths, tip configurations, stiffnesses, coatings, and materials of construction ( Fig. 2-3 ). In general, the guidewire thickness (always referred to in hundredths of an inch; e.g., 0.038 inch) should match the diameter of the lumen at the tip of the catheter or device that will slide over it. Guidewires that are too big will jam inside the catheter. However, if a guidewire is much smaller than the hole at the tip of the catheter or device there will be an abrupt transition or step-off that creates a gap that can trap subcutaneous tissue and cause the catheter to “stick” on the wire. The gap can also cause the catheter tip to “hang-up” on plaque or at branch points as it is advanced along the guidewire ( Fig. 2-4 ).

Figure 2-3, Common guidewires. From left: Straight 0.038-inch; J-tipped 0.038-inch with introducer device (arrow) to straighten guidewire during insertion into needle hub; angled high-torque 0.035-inch; angled hydrophilic-coated 0.038-inch nitinol wire with pin vise (curved arrow) for fine control; 0.018-inch platinum-tipped microwire.

Figure 2-4, Catheter and guidewire mismatch. The catheter is tapered to 0.038 inch, but the guidewire is 0.018 inch in diameter. The tip of the catheter can “hang-up” on vessel wall, plaque, or the ostium of a branch vessel.

The most commonly used type of guidewire has a central stiff core around which is tightly wrapped a smaller wire, just like a coiled spring ( Fig. 2-5 ). The outer wire is welded to the core at the back end, but not at the tip. The purpose of the coiled wrap is to decrease the area of contact between the surface of the guidewire and the tissues. Between the inner core wire and the outer wrap is a fine safety wire that runs along the length of the guidewire and is welded to the outer wrap at both ends. The safety wire prevents the wrap from unwinding. This is where the term safety guidewire originates. The thickness and composition of the inner core determines the degree of guidewire stiffness ( Table 2-2 ). Flexible guidewires are important for negotiating tortuous or diseased vessels, but stiff guidewires (“working” wires) provide the most support for introducing catheters and devices. The ultimate variable-stiffness guidewire is one in which the core can be slid in and out of the spring wrap (“movable core guidewire”) as needed. An important variation in guidewire design is the mandril wire, in which the springlike soft tip is limited to the tip, with the remainder of the guidewire consisting of a solid wire. This is a common construction for small-diameter guidewires, or extra rigid large-diameter guidewires.

Figure 2-5, Basic construction of common guidewires. 1 and 2, The straight and curved safety guidewires are basic tools. These are constructed of an outer coiled spring wrap, a central stiffening mandril welded to the outer wrap at the back end only, and a small inner safety wire (arrow) welded to the outer wrap at both ends. 3, Movable core guidewire. The inner mandril slides back and forth, and can be removed entirely, using the handle at the back end of the guidewire (arrow) . This changes the stiffness of the wire tip. 4, Low-profile mandril guidewire, in which the soft spring wrap is limited to one end of the guidewire (arrow) . The remainder of the guidewire is a plain mandril. 5, Mandril-guidewire coated with a hydrophilic substance (arrow) that reduces friction and increases ability to select tortuous vessels.

Table 2-2
Guidewire Stiffness
Guidewire Stiffness
Movable core 0 (when core removed)
Standard 0.035-inch ++
Standard 0.038-inch +++
Rosen ++++
Amplatz +++++
Amplatz Super-Stiff ++++++
Lunderquist +++++++

The taper of the core at the leading end of the guidewire determines the softness or “floppiness” of the tip. The length and rate of transition of the taper defines the characteristics of the tip. Bentson guidewires, or movable core guidewires with the core retracted, have the softest tips. During diagnostic procedures, the soft end of the guidewire goes inside the patient. During interventions, the stiff back end of a guidewire can be a useful recanalization tool.

A curve in the end of the guidewire provides an additional degree of safety in diseased vessels. As the curved guidewire is advanced, the round presenting part deflects away from plaque, whereas the tip of a straight guidewire could burrow under it. A curve can be added to a straight guidewire by gently drawing the floppy tip across a firm edge (e.g., a fingernail or closed hemostat), much like curling a ribbon. In some instances, adding a curve to the body of the guidewire (especially stiff working wires) can be very useful for positioning a wire across the aortic bifurcation or in the thoracic aortic arch. Tip-deflecting guidewires allow variation in the radius of the curve while in the patient, but these guidewires have stiff tips and should never be advanced beyond the end of the catheter ( Fig. 2-6 ).

Figure 2-6, Tip deflecting guidewire. This wire has a stiff tip that is used to direct a catheter. A, The guidewire and the preattached handle. B, Deflection of the guidewire tip. The deflection is performed inside the catheter lumen. The catheter is then advanced off of the guidewire; the guidewire is never advanced beyond the tip of the catheter.

Specialty guidewires, such as wires coated with slippery hydrophilic substances, highly torqueable guidewires, kink-resistant nitinol-based wires, and microwires are widely available. These guidewires are the difference between routine success and failure in the more challenging cases. Fine manipulation is often best with a small pin vise or other device (a “torque handle”) that slides on and off of the external portion of the guidewire. Hydrophilic-coated guidewires are especially useful, because they can easily reach previously inaccessible places. This type of guidewire has a central core that is coated with an outer layer of hydrophilic material (see Fig. 2-5 ). These guidewires should not be inserted through access needles, because the non-radiopaque coating is easily sheared off by the metal edge at the tip of the needle when the guidewire is withdrawn. Also, unless kept moist, hydrophilic guidewires quickly become sticky. When this happens, it is difficult to advance a catheter over the guidewire. Furthermore, the entire guidewire may be pulled inadvertently out of the patient if it sticks to a gloved hand or gauze. To stabilize a hydrophilic guidewire during a catheter exchange, grip the wire with wet gauze. This allows a secure hold without drying out the guidewire.

The length of most guidewires used in routine angiography is 145-180 cm. When more guidewire is needed inside the body, or when the devices and catheters to be placed over the guidewire are long, an “exchange length” guidewire (260-300 cm) is used. This length is not used for routine cases because the length of guidewire outside the body is unwieldy and easily contaminated.

Dilators

Vessel dilators are short tapered catheters usually made of a stiffer plastic than diagnostic angiographic catheters ( Fig. 2-7 ). The sole purpose of a dilator is to spread the soft tissues and the wall of the blood vessel to make passage of a catheter or device easier. By inserting sequentially larger dilators over a guidewire, a percutaneous access with a 21-gauge needle can be increased to almost any size. Sequential dilatation minimizes the risk of trauma to the vessel and tissues because incremental steps in size (1- to 2-French) can be accomplished with little force. The first dilator size after puncture with an 18-gauge access needle is usually 5-French. Larger dilators can then be used as needed. Do not dilate an access site to more than 50% of the diameter of the artery if hemostasis with manual compression is anticipated; when the diameter of the hole in the wall approaches the diameter of the artery, the puncture becomes a partial transection.

Figure 2-7, Vascular dilators. Standard taper (arrow) and longer taper (arrowhead) “Coons” tip. The latter is useful when more gradual dilatation is required.

Catheters

Angiographic catheters are made of plastic (polyurethane, polyethylene, Teflon, or nylon). The exact catheter material, construction, coatings, inner diameter, outer diameter, length, tip shape, and side-hole configuration are determined by the intended use ( Fig. 2-8 ). Catheters for aortography are thick walled to handle large-volume, high-pressure injections, and often curled at the tip (“pigtail”), which keeps the tip of the catheter away from the vessel wall, with multiple side holes proximal to the curl such that the majority of the contrast exits the catheter in a diffuse cloud. Conversely, selective catheters are thinner walled for lower volume injections, shaped to seek branches off the main vessel, and tapered at the tip to advance smoothly into the branch vessel, with a single end hole to direct contrast in a specific direction. Precise control of the tip of the selective catheter is a top priority. Selective catheters therefore usually have fine metal or plastic strands incorporated into the wall (“braid”) so that the tip is responsive to gentle rotation of the hub ( Fig. 2-9 ).

Figure 2-8, Pigtail flush catheter (left) with multiple side holes. Selective catheter (right) with a single end hole.

Figure 2-9, Drawing illustrating the fine wire braid in the shaft of a selective catheter. The dark color at the end of the catheter is radiopaque, facilitating visualization of the catheter.

Many different units and systems are used to describe a single catheter. The outer size is measured in French (3 French = 1 mm), while the diameter of the end hole (and therefore the maximum size guidewire that the catheter will accommodate) is described in hundredths of an inch. The length of the catheter is in centimeters (usually between 65 and 100 cm). The maximum flow rates are in milliliters per second (mL/sec), and maximum injection pressures are in pounds per square inch (PSI). The shape of the tip is named for either something that the catheter looks like (“pigtail,” “cobra,” “hockey-stick”, “shepherd’s crook”), the person who designed it (Simmons, Rösch, Sos, Binkert), or the intended use (celiac, left gastric, internal mammary) ( Fig. 2-10 ). There are so many different catheters that no one department can or need stock them all. The shape of some catheters may be modified by bending into the desired configuration while heating in steam and then rapidly dunking in cool sterile water ( Fig. 2-11 ).

Figure 2-10, Common catheter shapes. 1, Straight. 2, Multipurpose (hockey-stick). 3, Davis. 4, Binkert. 5, Headhunter (H1). 6, Cobra-2 (cobra-1 has a tighter curve, cobra-3 has a larger and longer curve). 7, Rösch celiac. 8, Sos. 9, Mickaelson. 10, Simmons-2 (the downgoing segment is shorter in the Simmons-1 and longer in the Simmons-3). 11, Pigtail. 12, Tennis racket.

Figure 2-11, Steaming a catheter. The catheter is held in steam for 30-60 seconds, then dunked in cool sterile water to “fix” the new shape.

Complex catheter shapes must be reformed inside the body after insertion over a guidewire. The catheter will resume its original configuration if there is sufficient space within the vessel lumen and memory in the catheter material. Some catheter shapes cannot reform spontaneously, in particular the larger recurved designs such as the Simmons. There are a number of ways to reform these catheters ( Figs. 2-12 to 2-16 ). A recurved shape can also be created from an angled selective catheter by forming a Waltman loop ( Fig. 2-17 ).

Figure 2-12, Branch technique for reforming a Simmons catheter. 1, The catheter is advanced into the branch over a guidewire (dashed line). Aortic bifurcation is shown in this illustration. 2, The guidewire is withdrawn proximal to the origin of the branch but still in the catheter. One may also remove the guidewire and reinsert the stiff end to the same point. The catheter is then simultaneously twisted and advanced. 3, Reformed catheter.

Figure 2-13, Aortic spin technique for reforming a Simmons catheter (works best for Simmons 1). 1, The catheter is simultaneously twisted and advanced in the proximal descending thoracic aorta. Note the wire is withdrawn below the curved portion of the catheter . 2, Reformed catheter.

Figure 2-14, Cope string technique, which easily reforms any recurved catheter. 1, Approximately 3-4 cm of 4-0 Tevdek II (Deknatel Inc., Fall River, Mass.) suture material (curved arrow) has been backloaded into the catheter tip. The catheter is then loaded onto a floppy-tipped guidewire (dashed line) and advanced (arrow) into the patient. 2, The catheter has been advanced over the guidewire into the aorta, with trailing suture material exiting the groin adjacent to the catheter. The floppy portion of the guidewire still exits the catheter, “locking” suture material in catheter tip. Suture material is pulled gently (black arrow) as slight forward force applied to catheter (gray arrow) . 3, Simmons has been reformed. 4, Suture is removed by first retracting the guidewire into the catheter (dashed arrow), “unlocking” the suture material. Suture material can then gently be pulled out (black arrow).

Figure 2-15, Ascending aorta technique for reforming a Simmons catheter. 1, Floppy-tipped 3-J guidewire reflected off of the aortic valve. The catheter is advanced over the guidewire. 2, The catheter is advanced around a bend in the guidewire. 3, Retraction of the guidewire completes the reformation.

Figure 2-16, Deflecting wire technique (unsafe in small or diseased aortas). 1, Deflecting wire is positioned near the tip of the catheter. 2, Wire is deflected, curving the catheter as well. 3, With the guidewire fixed, the catheter is advanced (arrow) to reform Simmons.

Figure 2-17, The Waltman loop, which can be formed in any major aortic branch vessel with braided selective catheters. A, An angled catheter positioned over the aortic bifurcation. Note the stiff end of the guidewire at the catheter apex (arrow) . B, The catheter is advanced and twisted, forming the loop. C, Looped catheter has been used to select the ipsilateral internal iliac artery (arrow) .

Straight and pigtail catheters are generally used for nonselective injections. Straight catheters should only be advanced over a guidewire; pigtail catheters can be safely advanced in normal vessels once the pigtail has reformed. Before removal of a pigtail catheter from the body, the tip is usually straightened with a guidewire. Straight catheters can be removed without a guidewire.

Selective catheters are chosen based upon the anatomy of the vessel of interest ( Fig. 2-18 ). The technique for selecting a branch vessel with a catheter varies with the type of catheter ( Figs. 2-19 and 2-20 ). Aggressive probing with the catheter or guidewire, or advancing the catheter into the branch without leading with at least 1-2 cm of soft guidewire, can result in arterial dissection or perforation. The Waltman loop is particularly useful in the pelvis for selection of branches of the internal iliac artery on the same side as the arterial puncture.

Figure 2-18, Choosing a selective catheter shape. A, Angled catheter when angle of axis of branch vessel from aortic axis is low. B, Curved catheter (e.g., cobra-2 or celiac) when angle of axis of branch vessel is between 60 and 120 degrees. C, Recurved catheter (e.g., Sos or Simmons) when angle of axis of branch vessel from aorta is great.

Figure 2-19, How to use a cobra catheter. 1, The catheter is advanced to a position proximal to the branch over the guidewire, then pulled down (arrow) . 2, The catheter tip engages the orifice of the branch. Contrast is injected gently to confirm location. 3, Soft-tipped selective guidewire has been advanced into branch. The guidewire is held firmly and the catheter advanced (arrow) . 4, Catheter in selected position.

Figure 2-20, How to use a Simmons catheter. 1, The catheter is positioned above the branch vessel with at least 1 cm of floppy straight guidewire beyond the catheter tip. 2, The catheter is gently pulled down (arrow) until the guidewire and tip engage the orifice of the branch. 3, Continued gentle traction results in deeper placement of catheter tip. To deselect the branch, push the catheter back into the aorta (reverse steps 1-3). To straighten the Simmons, apply continued traction after step 3.

Small-diameter catheters that are specially designed to fit coaxially within the lumen of a standard angiographic catheter are termed microcatheters ( Fig. 2-21 ). These soft, flexible catheters are 2- to 3-French in diameter, with 0.010- to 0.027-inch inner lumens. They are designed to reach beyond standard catheters into small or tortuous vessels. The ability to reliably select these vessels without creating spasm, dissection, or thrombosis has allowed certain subspecialties (e.g., neurointerventional radiology) to flourish. To use a microcatheter, a standard angiographic catheter that accepts a 0.038- or 0.035-inch guidewire is placed securely in a proximal position in the blood vessel. The microcatheter is then advanced in conjunction with a specially designed 0.010- to 0.018-inch selective guidewire through the standard catheter lumen. Once a super-selective position has been achieved with the microcatheter, a variety of procedures can be performed such as embolization, sampling, or low-volume angiography. The resistance to flow in the small lumen prevents the use of most microcatheters for routine angiography. High-flow microcatheters can accept up to 3 mL/sec of contrast at a lower PSI than standard catheters. Contrast and flush solutions are most easily injected through these catheters with 3-mL or smaller high-pressure Luer-lock syringes.

Figure 2-21, Use of a microcatheter. A, Typical microcatheter that tapers from 3-French proximally to 2.3-French at the tip. Note the radiopaque marker at the tip. B, Extremely tortuous splenic artery in a patient with hypersplenism. C, Microcatheter has been advanced over a 0.016-inch guidewire into the distal splenic artery through a 6.5-French Simmons-1 catheter.

Large guiding catheters may be used for positioning and stabilizing standard catheters and devices. These nontapered catheters have extra large lumens and a preformed simple shape that accepts standard sized catheters and devices ( Fig. 2-22 ). Guiding catheters with tips can be reshaped within the patient using controls at the back end of the catheter. There are many circumstances in which standard catheters are difficult to position selectively, such as in the case of a renal artery that arises from a tortuous or aneurysmal abdominal aorta. In this situation, a larger outer catheter that can guide the standard catheter toward the renal artery and prevent it from floundering around is very helpful. Guiding catheters are usually shorter than standard angiographic catheters, and frequently have a radiopaque band at the tip.

Figure 2-22, Two examples of nontapered large-diameter guide catheters, which can accommodate standard 5-French catheters. French size of guide catheters refers to the outer diameter.

Be aware that guiding catheter size in French refers to the outer, not the inner diameter. The inner diameter is often described in hundredths of an inch, which must be converted to French to determine whether a standard catheter will fit (1 French = 0.012 in = 0.333 mm).

Sheaths

Most vascular interventions and many diagnostic procedures are performed through vascular access sheaths. These devices are plastic tubes of varying thickness and construction that are open at one end and capped with a hemostatic valve at the other ( Fig. 2-23 ). The open end is not tapered, although the edges are carefully beveled to create a smooth transition to the tapered dilator that is used to introduce the sheath over a guidewire. The valve end usually has a short, flexible, and clear side arm that can be connected to a constant flush (to prevent thrombus from forming in the sheath) or an arterial pressure monitor. The valve may be a split membrane or rotating hub. The purpose of the sheath is to simplify multiple catheter exchanges through a single puncture site. When not using a sheath, it is unwise to downsize catheters during a procedure owing to the risk of bleeding around the smaller diameter catheter. Perhaps more important, devices that are irregular in contour or even nontapered can be introduced through a sheath without damaging the device or traumatizing the access vessel. Long sheaths can be used to straighten a tortuous access artery or negotiate a tortuous aorta. By convention, sheaths are described by the maximum size (in French) of the device that will fit through the sheath. Because the walls of the sheath have some thickness, the actual hole in the blood vessel is 1.5- to 2-French larger than the sheath “size.” Sheaths are available in a variety of lengths, depending on the requirements of the procedure.

Figure 2-23, Typical hemostatic sheath. French size of sheaths refers to the inner diameter.

A useful sheath variant is the peel-away sheath ( Fig. 2-24 ). Used frequently when inserting venous access devices, this sheath is removed by splitting lengthwise into two halves. Two wings or tabs at the hub are pulled apart to split the sheath. Some peel-away sheaths have hemostatic valves, although these are usually not as robust or efficient (particularly for air) as the valves in conventional sheaths. The sheath is introduced in standard fashion over a guidewire with a tapered plastic dilator. Once in position, the dilator is removed. The only way to achieve hemostasis with a nonvalved sheath is to block the open end with a finger or to clamp the sheath. After inserting the device or catheter through the sheath, the plastic wings are pulled in opposite directions parallel to the skin. This “breaks” the sheath into two long strips of plastic and allows complete disengagement from the catheter without having to slide it off the back end.

Figure 2-24, Peel-away sheath. To peel the sheath away, wings are pulled in opposite directions at 90 degrees from the catheter shaft.

Stopcocks/Flow Switches

Controlling flow in and out of catheters once they are in the body is a priority. Stopcocks are plastic devices that allow one or more syringes to be connected to a catheter, and by turning a handle or sliding a switch, allow or block flow ( Fig. 2-25 ). Rotating hub adaptors have one or more potential entry points for a guidewire or catheter. Hemostasis is achieved by tightening the hub by rotating it clockwise. Metal stopcocks are needed when handling oil-based contrast agents because many plastics become brittle and disintegrate when exposed to the oil.

Figure 2-25, Examples of flow-control devices. 1, One-way stopcock in open position. 2, Two-way stopcock (often called three-way ) turned off to all lumens. 3, Flow-switch. 4, Metal stopcock. 5, Rotating hub hemostatic valve (Tuohy-Borst adapter) with side arm for flushing.

Contrast Agents

Safe and well-tolerated contrast agents are as important to angiography as the Seldinger technique. The ideal contrast agent has excellent radiopacity, mixes well with blood, is easy to use, and does not harm the patient. Iodinated contrast agents (based on benzene rings with three bound iodine atoms, termed triiodinated ) are, as of yet, closest to ideal.

There are two major classes of triiodinated contrast agents: ionic and non-ionic ( Table 2-3 ). Ionic contrast agents are bound to a radiolucent cation, usually sodium and meglumine (N-methylglucamine), but also sometimes magnesium and calcium. This results in a highly soluble, low-viscosity, but high osmolar (two particles per iodinated ring) contrast agent. High osmolality relative to a patient’s blood is believed to be a major contributing factor to adverse reactions to contrast agents. Non-ionic contrast agents have no electrical charge, so cations are not necessary. This reduces the osmolality of the contrast agent (one particle per iodinated ring), which improves the safety profile, but increases viscosity. The two major classes of contrast agents are further subdivided as either monomeric (one triiodinated benzene ring) or dimeric (two linked triiodinated benzene rings).

Table 2-3
Contrast Agents
Class of Contrast Agent Contrast Agent Commercial Name Iodine (Atoms Per Molecule) Approximate Osmolality (300 mg I/mL Concentration)
Ionic monomer Diatrizoate
Iothalamate
Hypaque
Renografin
Conray
3 1500-1700
Non-ionic monomer Iopamidol
Iohexol
Ioversol
Ioxilan
Iopromide
Isovue
Omnipaque
Optiray
Oxilan
Optivist
3 600-700
Ionic dimer Ioxaglate Hexabrix 6 560
Non-ionic dimer Iodixanol Visipaque 6 300

mOsm/kg water.

Adverse reactions to iodinated contrast agents are relatively common, but the majority are minor, such as nausea ( Table 2-4 ). Most minor complications are linked to the osmolality of the contrast, so that the overall incidence is lower with non-ionic contrast agents. Adverse reactions may be immediate (within seconds to minutes of injection) or delayed (hours to days).

Table 2-4
Contrast Reactions
Reaction Ionic Contrast Non-Ionic Contrast
Nausea 4.6% 1%
Vomiting 1.8% 0.4%
Itching 3.0% 0.5%
Urticaria 3.2% 0.5%
Sneezing 1.7% 0.2%
Dyspnea 0.2% 0.04%
Hypotension 0.1% 0.01%
Sialadenitis <0.1% <0.1%
Delayed rash 2%-3% 2%-3%
Death 1:40,000 1:170,000

The two major adverse reactions to iodinated contrast agents are anaphylaxis and renal failure. True anaphylaxis occurs shortly after contrast injection and is distinguished from a vasovagal response by tachycardia and respiratory distress ( Table 2-5 ). The incidence of life-threatening anaphylaxis due to iodinated contrast is approximately 1 per 40,000 to 170,000, with the higher rate associated with ionic contrast. Mild reactions such as urticaria and nasal stuffiness occur more commonly (especially with ionic contrast). Contrast reactions must be treated promptly and aggressively; the most common cause of death is airway obstruction ( Boxes 2-1 to 2-3 ). The patient with a history of prior contrast allergy should receive steroid prophylaxis beginning at least 12 hours before the procedure (unless a true emergency exists) ( Box 2-4 ). Patients label many symptoms experienced during prior contrast injections as an “allergy,” such as nausea, vagal nerve–mediated bradycardia and hypotension, or ischemic cardiac events. Whenever the precise nature of the “allergic” reaction cannot be determined from the history, steroid prophylaxis is prudent. Non-ionic contrast should be used throughout the procedure in any patient with a history of contrast allergy.

Table 2-5
Anaphylaxis vs. Vasovagal Reaction
Feature Anaphylaxis Vasovagal
Blood pressure Low Low
Pulse Fast Slow
Breathing Labored, wheezes Normal
Skin Flushed, urticaria Cool, clammy

Box 2-1
Treatment of Vasovagal Reactions

  • Lay down patient

  • Elevate legs

  • Intravenous fluid bolus (300-500 mL normal saline)

  • Atropine 1 mg intravenous push (doses less than 0.5 mg may worsen bradycardia)

Box 2-2
Treatment of Mild Contrast Reactions

  • Assess airway, administer 100% oxygen

  • Secure intravenous access

  • Obtain vital signs

  • Benadryl 50 mg intravenously

  • Hydrocortisone 100-250 mg intravenously

  • Observe patient for 4 hours

  • For mild bronchospasm:

    • Albuterol 0.5 mL (2.5 mg) or metaproterenol 0.3 mL (15 mg) in 2.5 mL normal saline, inhalation nebulizer

    • OR

    • Epinephrine (1:1000) 0.3 mL subcutaneously or intramuscularly, repeated every 20 minutes as necessary

Box 2-3
Treatment of Severe Anaphylaxis

  • Call a “Code”

  • Secure an airway (cricothyroidotomy if necessary) and administer 100% oxygen

  • Secure intravenous access

  • Epinephrine (1:10,000) 1 mL intravenously or via endotracheal tube

  • Initiate pressor support

  • Methylprednisolone 125 mg or hydrocortisone 500 mg intravenously

  • Aggressive fluid resuscitation with normal saline or lactated Ringer’s solution

  • Admit patient to intensive care unit

Box 2-4
Suggested Preparation of Patient with Contrast Allergy

  • Prednisone 50 mg (oral) 13, 7, and 1 hour prior to the procedure (three doses) OR hydrocortisone 200 mg intravenously 2-3 hours prior to the procedure

  • Diphenhydramine (Benadryl) 50 mg (oral) 1 hour prior to procedure or intravenously upon arrival in angiography suite

  • H 2 -blocker intravenously upon arrival in angiography suite

  • Alternative oral steroid regimen: prednisone 50 mg at 12 and 2 hours before the procedure

  • Pediatric dosing: prednisone 0.5 mg/kg/dose, maximum 50 mg; Benadryl 1.25 mg/kg, maximum 50 mg

Renal failure following administration of iodinated contrast agents is more common in patients with diabetes, preexisting renal insufficiency (stage 2-5 renal failure), and multiple myeloma ( Box 2-5 ; Table 2-6 ). The exact mechanism is not known, so that several different protective measures are in common use ( Table 2-7 ). The classic presentation is an increase in creatinine 24-48 hours following exposure to contrast, peaking at 72-96 hours. Patients are usually oliguric but may become anuric. Management is usually expectant, because renal function should return to baseline in 7-14 days. However, in patients with severe preexisting renal insufficiency and diabetes, the risk of permanent dialysis after angiography may be as high as 15% despite the use of low-osmolar contrast agents and other protective measures.

Box 2-5
Risk Factors for Contrast-Induced Acute Renal Failure

  • Underlying renal insufficiency

  • Diabetes mellitus

  • Dehydration

  • Nephrotoxic medications

  • Age >60 years

  • Longstanding hypertension

  • Cardiovascular disease

  • Multiple myeloma

  • Hyperuricemia

  • High-osmolar contrast

  • Large volume of contrast in short period of time

  • Recent exposure to large contrast load

Table 2-6
Stages of Renal Failure
Stage Glomerular Filtration Rate (mL/min/1.73 m 2 )
1 >90 (normal GFR; can be present with abnormal kidneys)
2 60-89
3 30-59
4 15-29
5 <15
GFR, Glomerular filtration rate.

Table 2-7
Preventive Measures for Contrast-Induced Acute Renal Failure
Agent Protocol
Hydration 1 mL/kg/hr 0.9% saline for 12 hours prior to procedure; 1 mL/kg/hr 0.9% saline for 12 hours postprocedure
Sodium bicarbonate 154 mmol/L at 3 mL/kg/hr prior to the procedure; 1 mL/kg/hr for 6 hours after the procedure
N-Acetylcysteine 1200 mg orally every 12 hours beginning 24 hours before the procedure, including one dose on morning of the angiogram, and one dose the night after the procedure. Total of 4 doses.

Patients taking Metformin, an oral hypoglycemic agent, should be instructed to wait 48 hours after the procedure before resuming this medication. Metformin does not increase the risk of acute contrast-induced renal failure, but patients can develop fatal lactic acidosis from the drug if renal failure does occur.

Contrast is administered during angiographic procedures by hand or mechanical injection ( Table 2-8 ). Injection by hand is useful during the initial stages of the procedure, or for low-volume and low-pressure angiograms of small vessels or through precariously situated catheters. The use of mechanical injectors is necessary for optimal contrast delivery, particularly when large volumes or high flow rates are required. In addition, there is less radiation exposure to the physician when a mechanical injector is used. Catheters are rated for both flow rates and maximum injection pressure. This information is provided on the catheter packaging. Exceeding these limits may result in bursting the catheter (usually at the hub), or premature termination of the injection by the power injector software. Careful technique is necessary when connecting a catheter to a power injector to avoid air bubbles, contamination of the catheter, or disconnection during injection ( Box 2-6 ).

Table 2-8
Weight-Based Contrast Injection Rates
Data from Heran MK, Marshalleck F, Temple M, et al. Joint quality improvement guidelines for pediatric arterial access and arteriography: from the Societies of Interventional Radiology and Pediatric Radiology. J Vasc Interv Radiol 2010;21:32-43.
Artery Patient Weight
10-20 kg 20-50 kg >50 kg
Aorta 5-10 for 8-15 10-20 for 20-40 20-25 for 25-50
Celiac 2-3 for 10-20 3-5 for 15-30 5-8 for 30-60
Splenic 2-3 for 10-15 3-5 for 15-20 5-8 for 20-50
Hepatic 2-3 for 5-10 3-5 for 10-15 5-8 for 15-25
Superior mesenteric artery 2-3 for 10-15 3-5 for 15-30 5-8 for 30-50
Inferior mesenteric artery # 1-3 for 6-9 2-3 for 10-15
Renal 2-4 for 3-5 3-5 for 6-9 5-8 for 10-15
Subclavian 2-3 for 4-6 3-4 for 6-15 5-8 for 15-25
Common carotid 2-3 for 3-5 4-6 for 5-10 6-8 for 10-15
Internal carotid 1-2 for 3-5 2-4 for 5-8 4-5 for 6-10
External carotid # # 2-3 for 6-9
Vertebral # 2-5 for 4-6 4-7 for 6-9
#= hand injection.
For weights less than 10 kg, use hand injections.

= X-Y mL/sec for a total volume of A-B mL, for entire table.

Box 2-6
Connecting Catheter to Power Injector

  • Use sterile, clear, high-pressure Luer-lock tubing between injector and catheter

  • If injecting through a stopcock, be sure that it tolerates high pressures

  • Turn injector tubing hub counterclockwise several rotations prior to hook-up (so that potential rotational energy is not built up in tubing during attachment to catheter)

  • Allow backbleeding from catheter and advance contrast slowly through tubing during connection (“wet hook-up”)

  • Make sure that connection is tight

    If the patient or injector is moved suddenly, the catheter can be pulled out of position.

  • Withdraw contrast in tubing until blood is seen to exclude air bubbles

  • Advance contrast slowly to clear blood from catheter

  • Check catheter tip with fluoroscopy to ensure that it has remained in position after hook-up

Alternative Contrast Agents

The low but real incidence of adverse reactions to iodinated contrast agents has led to the use of alternative contrast agents in selected circumstances, particularly in patients with past histories of true anaphylactic reactions to iodinated contrast, or precarious renal function. Two alternative contrast agents have been described for patients who cannot tolerate iodinated contrast agents: carbon dioxide (CO 2 ) gas and gadolinium chelates.

Carbon Dioxide Gas

There is extensive experience with CO 2 gas as an angiographic contrast agent. There is no nephrotoxicity, and allergy does not exist. The gas functions as a negative contrast agent by briefly displacing the blood volume in the lumen of the vessel, resulting in decreased attenuation of the x-ray beam ( Box 2-7 ). Dedicated CO 2 digital subtraction techniques are standard on most modern angiographic equipment ( Fig. 2-26 ). The buoyant nature of CO 2 results in preferential filling of anterior structures. The CO 2 gas is highly soluble and excreted from the lungs.

Box 2-7
Advantages of CO 2 Gas as an Angiographic Contrast Agent

  • Readily available

  • No allergic reactions

  • No renal toxicity

  • Low viscosity

  • Highly soluble

  • No maximum total dose

  • Low cost

Figure 2-26, CO 2 portal venogram. A, Unsubtracted image from wedged hepatic venogram shows CO 2 filling portal vein (curved arrow) . Density of the CO 2 is the same as gas in the bowel (straight arrow). B, Digital subtraction of the same frame. Visualization of the portal venous system is excellent.

Mechanical injectors for CO 2 are not available in the United States. All injections must therefore be performed by hand ( Box 2-8 ). Because of the invisible nature of gases, scrupulous handling of CO 2 is necessary to prevent contamination by less soluble room air. An additional key technical aspect of CO 2 angiography is to avoid explosive delivery of gas by purging the catheter with a small volume of gas before the angiogram; otherwise tremendous pressure is generated as the gas is compressed behind the column of fluid in the catheter.

Box 2-8
Simple Technique for Hand Injection CO 2 Angiography

  • 60-mL Luer lock syringe containing 10 mL of flush solution, equipped with stopcock

  • Purge all air from syringe, so that only fluid remains

  • Attach to purged CO 2 source

  • Allow 30-40 mL of uncompressed CO 2 gas to enter syringe; use stopcock to control flow

  • Turn stopcock to “closed” position; disconnect from CO 2 source (closed stopcock remains on the syringe)

  • Keep tip of syringe pointed down

  • Attach to catheter while applying gentle positive pressure and opening stopcock, ensuring “wet” connection

  • Purge blood from catheter with small amount of CO 2 gas

  • Close stopcock

  • Compress gas with syringe plunger

  • Initiate digital subtraction angiography using CO 2 acquisition program

  • Open stopcock and vigorously inject compressed CO 2

The extremely low viscosity of CO 2 is advantageous for wedged hepatic vein portography, and demonstration of subtle bleeding. CO 2 can be used for abdominal aortography, selective visceral injections, lower extremity runoffs, as well as most venous studies. For abdomen studies it is helpful to administer intravenous glucagon (1 mg intravenously) to decrease bowel peristalsis. CO 2 is contraindicated for angiography of the thoracic aorta, cerebral arteries, or upper extremity arteries owing to potential neurologic complications. Rarely, CO 2 gas can cause a “vapor lock” in a vessel, which obstructs blood flow and induces distal ischemia. An excessive volume of gas in the heart can obstruct the pulmonary outflow tract, with severe cardiovascular consequences.

Gadolinium Chelates

Gadolinium chelates were developed as intravenous contrast for magnetic resonance imaging. Gadolinium (Gd) has a k-edge of 50 keV, slightly higher than iodine (33 keV). This permits visualization of gadolinium with current digital subtraction angiographic equipment adjusted for a higher KVP ( Fig. 2-27 ). The overall safety profile of these contrast agents is superior to that of iodinated contrast in normal individuals, and there is no cross-reactivity in patients with anaphylaxis to iodinated contrast. However, patients with stage 3 or higher renal insufficiency are at risk for development of nephrogenic systemic fibrosis (NSF) after injection of gadolinium agents. NSF is a debilitating, potentially fatal illness that appears to be associated with gadolinium contrast preparations that contain higher quantities of unchelated Gd (e.g., gadodiamide). Until the relationship of gadolinium to NSF is clearly understood, these contrast agents are generally only indicated in patients with normal renal function and true anaphylaxis to iodinated contrast when CO 2 is contraindicated.

Figure 2-27, Gadolinium digital subtraction angiogram. A, Unsubtracted image from aortic injection in a patient with infrarenal aortic occlusion shows weak vascular opacification. B, Digital subtraction of the same frame. There is excellent opacification of the visceral vessels.

Although the approved doses of most gadolinium-based agents are 0.1-0.3 mL/kg, volumes of 40-60 mL have been used for many years. Gadolinium-based contrast agents have been used in every vascular application, including carotid and coronary angiography. Gadolinium-based contrast agents are liquids, so special injection techniques or equipment is not required. Digital subtraction angiography (DSA) is necessary, in that the low gadolinium concentration in the available formulations results in relatively weak opacification of deep arteries.

Intraprocedural Care

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