© 2007 WebMD, Inc. All rights reserved.                                                               ACS Surgery: Princip...
© 2007 WebMD, Inc. All rights reserved.                                                             ACS Surgery: Principle...
© 2007 WebMD, Inc. All rights reserved.                                                              ACS Surgery: Principl...
© 2007 WebMD, Inc. All rights reserved.                                                               ACS Surgery: Princip...
© 2007 WebMD, Inc. All rights reserved.                                                            ACS Surgery: Principles...
© 2007 WebMD, Inc. All rights reserved.                                                              ACS Surgery: Principl...
© 2007 WebMD, Inc. All rights reserved.                                                                ACS Surgery: Princi...
© 2007 WebMD, Inc. All rights reserved.                                                              ACS Surgery: Principl...
© 2007 WebMD, Inc. All rights reserved.                                                                                 AC...
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Acs0608 Fundamentals Of Endovascular Surgery


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Acs0608 Fundamentals Of Endovascular Surgery

  1. 1. © 2007 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 8 Fundamentals of Endovascular Surgery — 1 8 FUNDAMENTALS OF ENDOVASCULAR SURGERY Jon Matsumura, M.D., F.A.C.S., and Joseph Vijungco, M.D. Endovascular techniques are now an important part of vascular Certain principles apply to both methods.The needle is advanced surgery. Ongoing technological advances have made it possible to at an angle of 45° to 60°. When it is within the subcutaneous tis- treat the majority of vascular diseases by minimally invasive sue, it should proceed in a straight line: the needle tip is sharp, and means. To perform these new therapeutic techniques, it is neces- side-to-side movement may cause inadvertent laceration of a neu- sary to possess certain basic endovascular skills. In this chapter, we rovascular structure. When a needle must be repositioned, it describe some of the fundamental techniques that a skilled vascu- should be withdrawn into the subcutaneous tissue superficial to lar interventionalist must master. the intended target and redirected along another course. If the needle becomes dulled as a result of contact with bone or other hard surfaces, it should be discarded and a new one used. Choice of Vascular Access Site The double-wall entry method involves a through-and-through The initial step in endovascular surgery is selection of the vascu- puncture of both the anterior wall and the posterior wall of the lar access site. Several choices are available.The ideal access vessel vessel. A multipart needle with an inner trochar may be helpful. is large, close to the treatment site, free of disease, and only mini- After the needle is advanced through both walls of the artery, the mally tortuous. Such a vessel is least likely to be associated with inner trocar is removed.The needle is then slowly withdrawn until complications.1 For most endovascular interventions, the femoral arterial pulsation is noted. The needle is stabilized, and a guide artery is the preferred choice, though the axillary, brachial, subcla- wire is advanced through it into the artery. Once the guide wire is vian, common carotid, and iliac arteries may also be used. in place, the needle is removed. Occasionally, the aorta is accessed via direct puncture, laparotomy, In the single-wall entry method, the needle is slowly moved or thoracotomy. toward the anterior wall of the vessel.The arterial pulsation can be Before puncture, the vessel undergoes evaluation, including pal- felt through the shaft of the needle. Gentle pressure is applied, and pation to assess the strength of the pulse in comparison with the the needle is advanced through the anterior wall only. It may be opposite side. A weak pulse suggests disease at or proximal to the helpful to think of the arterial pulse wave as pushing the anterior area, and the vessel should therefore be used with caution. Pre- arterial wall onto the needle.The appearance of pulsatile flow con- operative assessment may include noninvasive imaging (e.g., duplex firms entry into the arterial lumen. The needle may be rotated or ultrasonography, computed tomography, or magnetic resonance deflected slightly to optimize pulsatile back-bleeding. A guide wire angiography) to visualize significant lesions. Finally, with any endo- is then passed into the needle, and the needle is removed. vascular procedure, it is helpful to assess and document the peri- Pulsations should be transmitted through the needle shaft in an pheral pulses and the ankle-brachial index (ABI) beforehand to anterior-to-posterior manner. If the needle is either medial or later- provide reference points for possible subsequent complications. al to the artery, the pulsations may deflect the needle from side to side.2 Once the needle is in the vessel, the flow pattern should be observed. A forceful but irregular spraying flow may indicate arte- Puncture of Artery rial stenosis in the vicinity of the needle. A barely pulsatile flow may signal occlusive disease, a subintimal location of the needle, or a GENERAL TECHNICAL PRINCIPLES venous puncture.2 If the guide wire cannot be passed with minimal Once the skin site has been prepared and draped, 1% lidocaine resistance after access is obtained, the needle tip may be against the is infiltrated into the skin and the perivascular tissue. Besides pro- wall or against plaque, or (if the needle tip has already entered the viding anesthesia to the area, lidocaine helps prevent vasospasm.2 wall) a dissection may have been started. Often, the situation can The pain and discomfort from intradermal injection of lidocaine be remedied by making a small change in the needle’s insertion is caused by the low pH of commercially available preparations angle or by withdrawing the needle slightly. and can be reduced by adding sodium bicarbonate (1 ml of a 1 FEMORAL ARTERY PUNCTURE mEq/ml NaHCO3 solution in 10 ml of 1% lidocaine).3 A small nick should be made in the skin about 1 to 2 cm beyond the As noted, the common femoral artery (CFA) is the vessel most intended site of arterial entry, and the subcutaneous tissue should commonly used for arterial access. It is generally quite well suited to be gently dissected with a clamp; this measure allows smoother this purpose, being readily accessible, fairly large, and easily com- entry of the needle, the guide wire, the sheath, and the catheter. pressible. CFA puncture facilitates study and treatment of a number Access needles are available in different sizes, of which the two of key structures, including the lower-extremity arteries, the abdom- most common are the 18-gauge thin-walled needle, which accepts inal aorta and its branches, the thoracic aorta, the brachiocephalic a 0.035-in. guide wire, and the 21-gauge needle, which accepts an vessels, the coronary arteries, and the left ventricle. In addition, it is 0.018-in. guide wire. The latter is used for micropuncture tech- associated with a lower complication rate than puncture of other niques and is favored for brachial approaches. Longer needles are arteries.1 The CFA should, however, be avoided when the patient is used for translumbar puncture. known to have severe iliofemoral occlusive disease, a local infection, There are two main methods of cannulating the artery with the a femoral artery aneurysm, or marked tortuosity of the iliac arteries needle [see Figure 1]: double-wall entry and single-wall entry. that would preclude catheter placement or manipulation.
  2. 2. © 2007 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 8 Fundamentals of Endovascular Surgery — 2 The CFA runs lateral to the common femoral vein (CFV) and anatomic relations of the arteries in this area vary little with body beneath the inguinal ligament. It may be localized by palpation just habitus, gender, or age. A 1999 anatomic study showed that the proximal to its bifurcation into the superficial femoral artery (SFA) CFA bifurcates into the SFA and the PF approximately 2 cm and the profunda femoris (PF).The inguinal ligament, which runs below the femoral head.5 Occasionally, calcifications in the arter- from the anterior superior iliac spine to the pubic tubercle, is a con- ies may serve as landmarks for locating the CFA. venient landmark for localization of the CFA, but these bony land- Another localization approach involves palpation of anatomic marks provide only a rough approximation of the location of the landmarks; this approach may be especially useful when the artery inguinal ligament.The CFA typically lies about two fingerbreadths is pulseless.6 With a finger placed immediately lateral to the pubic lateral to the pubic tubercle along the line of the inguinal ligament. tubercle and inferior to the inguinal ligament, palpation is carried The artery should be punctured over the middle of the medial out to locate the point allowing the greatest degree of posterior third of the femoral head in the posterior-anterior projection [see depression. Anatomically, this point of maximal depression lies Figure 2]. The window available for safe CFA puncture is small— between the iliopsoas muscle laterally and the pectineus muscle only 3 to 5 cm. medially. The CFV lies in the floor of this depression, and the There are several methods that can be used to localize the CFA CFA lies 1.5 cm lateral to the depression.6 in patients with difficult anatomy (e.g., those who have previous- Ultrasonography has also proved useful for finding the CFA. ly undergone groin surgery, those who are obese, and those who The projection of choice with real-time ultrasonography is the have a pulseless artery).The bony landmarks are even less reliable transverse plane.The nonpalpable CFA is identified lateral to the guides to the location of the inguinal ligament in these patients. compressible CFV. Occasionally, the artery can be identified on According to a 1993 anatomic study, in the majority of cases, the the basis of sonographic shadowing from calcified atheromatous position of the inguinal ligament is about 1 to 2 cm below where plaques.7 A second ultrasonographic technique involves the use of palpation would suggest it to be, and the average position of the a so-called smart needle, which has an ultrasound probe at its tip. ligament is approximately 1.5 cm superior to the midfemoral The needle emits a signal as it approaches the artery, thereby giv- head.4 ing notice of proximity to the vessel. Fluoroscopy may help localize the CFA over the medial third Another method of localizing and puncturing a pulseless CFA of the femoral head. The chances of hitting the artery are maxi- involves performing a contralateral femoral artery puncture, obtain- mized by aiming for the middle (craniocaudal) portion of the ing a diagnostic angiogram, and roadmapping. A similar method medial third of the femoral head.To minimize parallax errors, the that is useful in patients who may be moving or who cannot receive femoral head should be centered in the image intensifier. The additional contrast material is to pass a guide wire over the aortic a b Figure 1 Shown are the two methods of entry into an artery: (a) through-and-through puncture of both walls and (b) puncture of the anterior wall only.
  3. 3. © 2007 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 8 Fundamentals of Endovascular Surgery — 3 bifurcation and then antegrade through the iliac artery into the tar- get femoral artery.8 Under fluoroscopy, the guide wire becomes a visible target for introduction of the needle into the CFA. Troubleshooting a The CFA is typically described as lateral to the CFV; however, one study showed that attempts to puncture the CFA frequently result in puncture of the CFV, signaled by the appearance of dark, nonpulsatile venous blood. If this occurs, one should note the position of the original puncture, move the needle 1 to 1.5 cm lat- erally, and reinsert the needle. At times, especially in emergency procedures, arterial blood may be dark and may resemble venous blood. If it is unclear whether the blood is coming from an artery or a vein, a small amount of a contrast agent should be gently injected into the needle by hand; the source of the blood should then be easily identifiable.When contrast is injected in the femoral sheath outside the artery, the resulting tubular “filling defect” can be used to identify the femoral artery. If the puncture is done too high (in the external iliac artery), the inguinal ligament and the deeper location of the external iliac artery may make adequate compression of the vessel impossible. Many closure systems will not work in the external iliac artery. High puncture is associated with retroperitoneal bleeding, which b should be suspected in any patient with an unexplained drop in the hematocrit, hypotension, or flank pain.To minimize this prob- lem, the artery should be entered caudal to the inguinal ligament at a site where it can be compressed against the femoral head.9 If the puncture is done too low (in the SFA or the PF), there is a greater incidence of hematoma, pseudoaneurysm, arterio- venous fistula, and catheter-related thrombosis.4,10 The reason for this increased incidence may be that it is harder to com- press the SFA and the PF adequately than it is to compress the CFA, which lies over bone for most of its length. The CFA is larger in diameter than either the SFA or the PF and thus is better suited for the passage of large catheters and sheaths. Experience is critical for achieving easy and complication-free femoral artery access. Although standard learning points are help- Figure 2 Puncture of common femoral artery. (a) The needle ful in the accumulation of this experience, veteran interventional- enters the CFA. (b) The guide wire is passed through the needle. ists typically develop their own individual procedural algorithms, based on what is most familiar to and works best for them. Routine use of femoral arteriography and ultrasonography can tion of the brachial artery is entered just above the antecubital shorten the learning period by visually demonstrating the nuances fossa. Because this vessel is very mobile, it may be advisable to fix of the anatomy in tandem with the tactile learning. Thoughtful it between the surgeon’s middle and index fingers before puncture. study of failed or complicated access cases, including observing the vascular anatomy when surgical repair becomes necessary, can Troubleshooting also help develop experience more rapidly. In such cases, explo- The brachial artery is typically smaller than the CFA and more ration often reveals altered femoral anatomy, side-wall punctures, prone to thrombosis. Accordingly, the needles, guide wires, low and high punctures, and posterior wall dissection. For even catheters, and sheaths used for brachial artery puncture must be the most masterful interventionalist, femoral puncture complica- smaller as well. Occasionally, the median nerve or the radial nerve tions are an ever-present risk, despite his or her best efforts. may be damaged by the puncture. Any distal neurologic symp- toms (e.g., median nerve distribution paresthesias or pain or weak- BRACHIAL ARTERY PUNCTURE ness of the opponens muscle) that arise are evaluated on an urgent The brachial artery is typically the second choice for arterial basis; on occasion, emergency exploration proves necessary. access after the femoral artery. This vessel is located in the lower Frequently, there is no palpable hematoma, and the symptoms are third of the upper arm, anteromedial to the humerus.The median attributable to a very small hematoma adjacent to the nerve. Not nerve lies just medial to the brachial artery at this level, and the uncommonly, the brachial artery goes into spasm after puncture. radial nerve lies posterior to the artery. Even though the brachial Intra-arterial injection of papaverine, tolazoline, or nitroglycerin artery is best palpated in the lower middle third of the arm, some may reduce the risk of spasm. clinicians prefer to puncture it in the high brachial position because complications may be less frequent with this approach. AXILLARY ARTERY PUNCTURE The patient’s arm is extended and supinated.The upper portion The axillary artery is divided into three parts on the basis of its of the brachial artery is entered several fingerbreadths distal to the relation to the overlying pectoralis minor.The third portion of the axillary crease, over the proximal humeral shaft. The middle por- artery lies lateral to the pectoralis minor, and its most distal por-
  4. 4. © 2007 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 8 Fundamentals of Endovascular Surgery — 4 tion extends beyond the pectoralis major, at which location it is very superficial.2 The axillary artery is typically used for vascular access when neither the femoral nor the brachial artery is avail- able. The use of this approach may be restricted in patients who have subclavian artery occlusive disease or aneurysmal disease. A physical examination should be performed before the procedure to look for a blood pressure differential between the two arms, as well as to auscultate for the presence of a supraclavicular bruit. A blood pressure differential greater than 20 mm Hg suggests the presence of hemodynamically significant arterial stenosis in the arm with the lower pressure. Axillary artery puncture is useful in patients with a steeply downward-coursing (caudal) mesenteric or renal artery, patients with infrarenal aortic or bilateral iliac occlusion, and patients with a history of embolization from infrarenal aortic catheterization.3 However, access at this site poses an added risk, in that the artery is located near the brachial plexus, which may be damaged by direct trauma or compression from a hematoma. In addition, access via the axillary artery is relatively uncomfortable for both patient and physician. Generally, for access to the descending tho- racic aorta, the abdominal aorta, and the lower-extremity vessels, the left axillary artery may be preferred, whereas for access to the ascending aorta and the coronary vessels, the right axillary artery may be preferred. The arm can be placed in either of two positions: (1) abducted 90° or (2) maximally abducted with the patient’s hand placed under the head.The second position stretches the artery and fixes it in place.The artery is palpated along the lateral axillary fold over the proximal humerus at the neck so that the underlying bone pro- vides support during compression.11 The vessel is then entered over the proximal humeral shaft just distal to the axillary fold. Like the brachial artery, the axillary artery is relatively mobile. It may be compressed along its length between the index and middle fin- Figure 3 Translumbar puncture of aorta. The vessel is gers to fix it in place for subsequent puncture. approached at the level of T12. Troubleshooting Thrombosis and pseudoaneurysm formation are more com- will be felt, followed by release of tension and a very slight give or mon with the axillary artery approach.3 In addition, the median “pop” when the needle enters the aorta. Only the proximal wall and ulnar nerves run along with the axillary and proximal brachial should be punctured. The needle is then advanced about 3 to 5 arteries in a fascial sheath, so that a small hematoma can cause mm to the middle of the lumen [see Figure 3]. nerve compression. If a sensory or motor deficit develops, surgical A lower translumbar approach may be used to access an aor- decompression may be required. Cerebral embolization occurs in tic aneurysm sac after endovascular repair. The puncture site is as many as 4% of cases of axillary artery puncture.3 located via fluoroscopy of radiopaque markers on the device already in place. With the patient in the prone position, the TRANSLUMBAR PUNCTURE needle is introduced 8 to 10 cm lateral to the spinous process Translumbar puncture of the aorta is indicated when femoral, of L2 and directed anterior to the lumbar spine. Often, careful axillary, and brachial methods are all relatively unsuitable. It is review of the CT images suggests a specific target and tract. As frequently used in patients who have abdominal aneurysms after with an upper translumbar puncture, a “pop” can be felt when endovascular repair. the needle enters the aneurysm sac; alternatively, the needle An upper translumbar approach is indicated if visualization of can be visualized entering a calcified wall. the visceral and renal arteries is required.The patient is placed in a prone position.The 12th thoracic vertebra is located either by pal- Troubleshooting pating the 12th rib or, more accurately, by means of fluoroscopy. The high translumbar technique is limited by its inability to The skin is entered 1 to 2 cm below the level of the 12th rib and 8 deliver the contrast material at the bifurcation of the aorta or to to 10 cm to the left, lateral to the posterior spinous process of the perform selective catheterization of vessels. Too high a puncture 12th vertebra. The needle is aimed ventrally and cephalad toward (e.g., at T11) can lead to inadvertent puncture of the lung and the level of the middle to lower portion of the body of T12 until cause a hemothorax or a pneumothorax. If the needle moves with the needle strikes the vertebra. Care must be taken to keep the nee- the respiratory diaphragmatic movements of the patient, it may be dle below the diaphragm so that it does not hit the lung and the in the thoracic cavity. If the initial needle stick is too medial, only pleura. Particular care must also be taken to avoid the renal arter- the lateral wall of the aorta is reached. If the needle stick is too lat- ies inferiorly. After striking T12, the needle is withdrawn several eral, the needle passes between the vertebral body and the aorta. centimeters and aimed laterally and ventrally until the pulsations of If the needle is advanced at too shallow an angle, it may enter the the aorta are felt. When the needle hits the aorta, slight resistance spinal canal.2 If resistance is felt when the guide wire is placed, the
  5. 5. © 2007 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 8 Fundamentals of Endovascular Surgery — 5 wire may have entered the renal, celiac, or superior mesenteric whenever any other devices are manipulated. As a general rule, the artery. Small retroperitoneal hematomas develop in most patients guide wire is not removed until the very end of the procedure. who undergo translumbar puncture, but the incidence of major After removal, guide wires are rinsed and loosely coiled for stor- complications is only 3%. age (in case they are needed later). TROUBLESHOOTING Placement of Guide Wires The guide wire should never be forcefully introduced into the Once vascular access has been obtained through arterial vessel. If significant resistance is encountered, the end of the nee- puncture, it is maintained through placement of a guide wire. dle may be against the vessel wall or partially within the wall. In Most guide wires consist of a soft tip and a stiffer main body. this situation, the needle should be repositioned slightly and The flexibility of the soft tip allows the surgeon to manipulate another attempt made to pass the wire. Occasionally, the guide the guide wire past stenoses while minimizing the risk of per- wire may pass easily for several centimeters before encountering foration or dissection. For best results, the guide wire must be resistance to further advancement. Such resistance may be sec- suitable for the intended procedure in terms of (1) tip config- ondary to stenosis or tortuosity of the vessel. Placement of a dif- uration, (2) diameter, and (3) length. Sometimes, multiple wires ferent wire with a different tip configuration or insertion of a guide are used at different stages of the procedure. catheter may be necessary to advance the wire further. Guide wires come in several different tip configurations, includ- Wiping the guide wire with heparinized saline minimizes throm- ing straight, angled, and J-shaped. Straight-tipped wires are used bus formation on the wire. If thrombus is allowed to build up, fric- in vessels that are relatively straight and free of disease. J-tipped tion will increase during catheter exchange, making the exchange guide wires are sometimes preferred for atherosclerotic vessels more difficult. Some hydrophilic-coated guide wires require con- because the shape of the tip reduces the likelihood that the wire stant wetting to maintain their characteristics. Other guide wire will pass subintimally and cause unintentional dissection. Many coatings swell after prolonged wetting and thus may inhibit cathe- specialty wires are available for specific uses (e.g., crossing chron- ter exchanges. Hydrophilic wires should not be used for initial ic total occlusions). cannulation through the access needle, because they may be Guide wires also come in a variety of diameters, typically rang- sheared off by the needle tip when withdrawn. Damaged or kinked ing from 0.014 to 0.052 in. The diameters most commonly used guide wires should be exchanged for new undamaged wires when for endovascular procedures are 0.035 and 0.014 in. Larger guide this can be done safely. wires are typically stiffer, which makes it easier to deliver sheaths and catheters over them. Smaller wires are typically used for Placement of Sheaths endovascular work involving the carotid, renal, or infragenicular vessels. In choosing the diameter of the wire, the interventionalist Once guide wire access is achieved, a sheath or guide is typical- must keep in mind the gauge of the needle that was used to access ly placed over the guide wire to maintain a stable pathway for the vessel.The guide wire should fit the needle yet be large enough catheter exchange or for placement of a device. Before the sheath to allow delivery of interventional devices. is placed, dilators are first passed over the guide wire to create a The length of the guide wire is an important concern because smooth tract through the soft tissue into the vessel. Whereas choosing an appropriate length facilitates exchange of catheters or sheaths are measured according to their inner circumference (1 interventional devices without loss of access across a remote mm circumference = 1 French), guides are measured according to their outer circumference; thus, a 6 French guide fits inside a 6 lesion. A general rule for determining optimal guide wire length is French sheath. Dilators are also measured according to their outer as follows12: circumference.Therefore, when a 5 French sheath is to be placed Optimal guide wire length = Length from outer edge of in scarred fibrous tissue, a 6 French dilator must be placed to cre- sheath or insertion site to lesion + length of longest ate a similarly sized tract. Most commonly, a dilator and a sheath catheter or interventional device + at least 10 cm of the same size are pinned and placed together. Most introducer sheaths have hemostatic valves and side ports. In an average adult, the wire used for selective angiography is typ- Guide catheters can be effectively converted to sheaths by adding ically about 145 to 180 cm long. Longer wires (260 to 300 cm) a Touhy-Borst valve apparatus.These valves seal around a smaller are used for exchanging long over-the-wire vascular devices. catheter and reduce back-bleeding. The side port can be used for Occasionally, a 450 cm long wire is needed for combined brachial- continuous infusion of heparinized saline to reduce the risk of femoral access. thrombus formation. The sheath can also be used to straighten Once arterial access is obtained, several safety measures should tortuous arteries (e.g., the iliac arteries). For example, when a be undertaken.The needle should have its bevel facing upward to guide wire has been passed through the iliac artery and into the optimize conditions for wire advancement; a downward-facing abdominal aorta, the sheath can be advanced over the wire into bevel may cause the sharp edge of the needle to damage or even the abdominal aorta. Passage of a sheath through the tortuous sever the wire. The floppy end of the wire should be used for ini- iliac vessel facilitates subsequent passage of catheters and devices. tial introduction into the needle and the vessel; the stiff end may Once properly placed, sheaths should be secured in position damage the vessel if used for initial entry. Caution should be exer- (i.e., pinned or sutured) so that they are not inadvertently cised in introducing the guide wire if there is unexpected poor advanced without the introducer or accidentally withdrawn. flow from the needle. After entry into the lumen, the guide wire is advanced about 15 to 20 cm.The needle is then removed, and a catheter or an intro- Insertion of Catheters ducer sheath is placed over the wire. Further advancement of the There are many differentiating characteristics by which various wire is done under fluoroscopic guidance. Once placed, the guide types of catheters can be distinguished from one other, including wire should be carefully monitored and kept in place (pinned) size, shape, stiffness, coating, radiopacity, and side-hole configura-
  6. 6. © 2007 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 8 Fundamentals of Endovascular Surgery — 6 misidentification of bone landmarks) and (2) failing to recognize when the appropriate vessel has been entered (particularly in pa- tients with anomalous vessels or postoperative changes).13 These errors can be prevented by first performing roadmapping with nonselective catheterization and angiography; often, repeated roadmapping in multiple projections is required. Another poten- tial problem is accidental loss of guide wire access, which may be more common with inexperienced operators who are not pinning the guide wire in place while a catheter is being pulled out. There are many advanced techniques for handling catheters and guide wires, but these are outside the scope of this discussion. Use of Balloon Catheters The purpose of a balloon catheter is to exert a radial force on the luminal surface of a blood vessel to dilate a stenotic lesion. As the balloon inflates, the media and adventitia of the artery stretch, causing a longitudinal fracture of the plaque. Minor arterial dis- section is expected with this technique. Thus, the compression of Figure 4 Catheters come with various tip configurations. the plaque is not the principal means of increasing the cross-sec- Shown are straight, pigtail, angled, and double-angled tips tional area of the vessel. (left to right). Several features are considered in selecting a balloon catheter for a specific intervention, including balloon diameter and length, catheter size and length, trackability, balloon type (e.g., compliant, tion. As a rule, catheters are sized according to their outer diame- noncompliant, cutting, or trilobed), and catheter profile [see Figure ter (French) and their length (cm). Numerous tip shapes are avail- 5]. Typically, balloons range from 1.5 to 40 mm in diameter and able [see Figure 4] (e.g., straight, cobra, headhunter, angled, shep- from 1.5 to 10 cm in length.The vessel should be slightly overdis- herd’s hook, reverse curve, pigtail, and racquet).The initial catheter tended when the balloon is inflated. Thus, measuring the diame- shape is selected on the basis of the specific requirements of the ter of the normal vessel distal to the lesion will help determine an procedure and the individual patient anatomy. Generally, within appropriate balloon diameter. If the operator is unsure of the the abdominal aorta, the angle of the primary curve of the catheter proper balloon diameter, it is best to choose a smaller-diameter tip should be similar to that of the vessel takeoff. In some cases, balloon and then move to a larger balloon if necessary.The short- multiple catheters may be needed, used either in sequence or coax- est balloon length that spans the entire lesion with a slight exten- ially to perform superselective catheterizations. A variety of com- plex catheter shapes may be used to select vessels that have steep sion into the normal artery should be chosen, so that the shoulder angles of origin.The use of coatings (e.g., hydrophilic surfaces and of the balloon dilates as little as possible of the normal portion of Teflon) can facilitate advancement of the catheter in tortuous ves- the vessel. If the balloon is too short and is not centered, it may be sels. Specialty catheters may come with radiopaque tips or with squeezed away from the stenosis during inflation (the so-called multiple radiopaque markers placed at 1 cm intervals for reference watermelon seed effect). Balloon catheters typically range from 70 during vessel sizing. Multi–side-hole catheters have a spiraling set to 150 cm in length. The shortest catheter length that reaches the of holes that allow more even distribution of a large volume of con- lesion from the access site is preferred because a shorter catheter trast or other infusate; they are typically used to opacify large ves- is easier to manipulate. The diameter (or profile) of the catheter sels with high flows. Generally, opacification of smaller vessels depends on the type and size of the balloon and typically ranges requires a smaller dose of contrast material administered at a slow- from 3 to 14 French. Sometimes, a smaller-profile balloon may be er rate; for this purpose, an end-hole catheter suffices. used if a smaller-diameter guide wire provides enough support for Before contrast is injected, the catheter should be aspirated to treatment of the lesion. If the balloon catheter is smaller than the remove any air bubbles and to verify intraluminal location by sheath, contrast injection is possible when the balloon is in posi- means of free-flowing back-bleeding. A small test injection is use- tion; this allows the balloon’s position to be fine-tuned immediate- ful for checking the catheter’s position. Depending on the clinical ly before inflation. circumstances, the patient may undergo anticoagulation to reduce The balloon catheter is advanced over the guide wire through the risk of thrombus formation on the outside of the catheter. the sheath to the lesion, and the balloon is centered over the lesion. Periodically, the catheter may be flushed with heparinized saline to The balloon is inflated with a dilute contrast solution so that its prevent thrombus formation within it. When a stiffer catheter is expansion can be monitored fluoroscopically. Guidelines for infla- advanced forward, it is usually advanced over a guide wire; how- tion and deflation techniques vary with respect to speed and dura- ever, a softer catheter can be used in the same way as a guide wire. tion of inflation, number of dilatations, and balloon pressure. Some complex curved catheters may have to be removed over a Typically, the balloon is inflated to a pressure that results in a wire to reduce the risk that the catheter will scrape the vessel wall. smooth parallel profile of the balloon walls, held for 20 to 60 sec- onds, and then deflated. In most clinical circumstances, the infla- TROUBLESHOOTING tion pressure should not exceed rated burst pressures. After dilata- There are several areas in the handling of catheters where atten- tion, the balloon catheter is removed, with the guide wire left in place tion to detail and good technique can help optimize results. Two across the lesion (in case stenting proves necessary). Completion common errors of selective catheterization are (1) looking for a angiography is performed for evaluation of the results, including specific artery in the wrong location (e.g., as a consequence of assessment of distal vascular beds.
  7. 7. © 2007 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 8 Fundamentals of Endovascular Surgery — 7 Shoulder Balloon Length Balloon Diameter Profile Shaft Diameter Radiopaque Markers Balloon Inflation Port Working Length Guide Wire Port Figure 5 Shown is a balloon angioplasty catheter. Dilatation may be considered successful if (1) flow-limiting dis- Stenting can often remedy these situations by providing physical section is absent, (2) residual luminal diameter stenosis is less than support to keep the vessel open. Many physicians now regard pri- 30%, and (3) the systolic pressure gradient is less than 5 to 10 mm mary stenting (i.e., routine use of stents) as a preferred approach Hg.Vasodilators can unmask a significant gradient. for many vascular lesions. TROUBLESHOOTING CHOICE OF STENT TYPE Complications associated with the use of balloon catheters Stents are divided into two categories: balloon-expandable include thrombosis, vessel rupture, embolization, and dissection. stents and self-expanding stents. They may also be described as The incidence of these complications is influenced by patient being covered (with a graft material), coated (with a therapeutic selection and by the nature of the lesion being treated. For exam- compound), absorbable, or radioactive. Stent types differ with ple, complications may be more likely with treatment of stenoses respect to hoop strength (for resisting arterial recoil), cell size, cell adjacent to aneurysms, long segments of occlusion, tandem structure, shape (e.g., tapered or nontapered), radiopacity, longi- lesions, lesions near major branches, and calcified eccentric tudinal flexibility (for crossing tortuous vessels), radial elasticity plaques. Even though some degree of dissection is expected after (for resisting repeated external compression), and profile. Stents balloon angioplasty, larger flow-limiting dissections may call for come in many different lengths and expanded diameters on a wide further management.This problem can often be solved by placing variety of deployment catheters. a stent over the dissection. Most patients feel discomfort and mild pain during balloon Balloon-Expandable Stents inflation. If a patient experiences severe pain that persists after Balloon-expandable stents come either premounted on balloon deflation of the balloon, the possibility of vessel rupture must be catheters or unmounted; unmounted stents must be manually considered. If the vessel ruptures, the balloon may be reinflated crimped onto a balloon to be delivered.With unmounted stents, a over the injury to tamponade it. Prolonged balloon inflation often smaller inventory can be maintained, and a wider range of stent- closes the leak, but at the risk of causing thrombosis. If the vessel balloon combinations is available. Premounted stents, however, continues to leak, a covered stent may be placed over the injury, tend to be more solidly mounted and less likely to be lost during or open vascular repair may be necessary. delivery. Once the stent is at the desired lesion, the balloon is If inflation of the balloon fails to dilate the vessel completely, it inflated and the stent expanded. may be helpful to use a larger-diameter balloon or a higher infla- The main advantage balloon-expandable stents have over self- tion pressure. Higher inflation pressures may be cautiously expanding stents is that they have greater hoop strength, which attempted, but the vessel may simply recoil after dilatation.14 A means that they can better resist the recoil of the vessel after full stent is often useful in this scenario. expansion of the stent. In addition, many interventionalists feel If the balloon crosses the lesions only partially, it should not be that balloon-expandable stents can be more precisely placed than inflated.The position of the guide wire should be checked: the wire self-expanding stents and thus are preferable when accuracy is of may be in a subintimal location. If the stenosis is very tight, the high clinical importance. However, older balloon-expandable lesion may be predilated with a smaller-profile balloon catheter. stents are less flexible than current models, and navigating such older devices in a tortuous vessel can be difficult. Placement of Vascular Stents Self-Expanding Stents Intravascular stents are commonly used in endovascular Self-expanding stents are placed within a delivery catheter and surgery, particularly after failed percutaneous transluminal angio- rely on a self-expansion mechanism for full deployment. A com- plasty. Placement of an iliac artery stent is indicated when there is mon deployment mechanism involves the use of an outer jacket significant residual stenosis, flow-limiting dissection, or a persis- and a plunger: the jacket is withdrawn while the stent is held in tent pressure gradient. Although angioplasty is often successful, it position by the plunger, and the stent then expands to its prede- may fail when there is elastic recoil of the arterial wall or when the termined diameter. Commonly, a balloon is employed to ensure lesion is resistant to dilatation because of heavy calcification. that the stent is fully expanded and impacted into the plaque.
  8. 8. © 2007 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 8 Fundamentals of Endovascular Surgery — 8 a b c d e Figure 6 Deployment of a balloon-expandable stent. (a) The guide wire is passed across the lesion. (b) The sheath-dilator combination is passed over the guide wire across the lesion. (c) The dilator is removed, and the bal- loon-expandable stent is advanced. (d) The sheath is retracted and the balloon inflated. (e) The balloon is deflated and withdrawn, leaving the stent fully deployed. An advantage self-expanding stents have over balloon-expand- to be delivered without precrossing the lesion with a guide or able stents is that they offer a greater degree of longitudinal flexibil- sheath. Multiple stents are sometimes required to complete the ity and thus are more easily tracked into position. Self-expanding procedure. stents come in lengths of up to 20 cm, which means that fewer TROUBLESHOOTING overlap zones and fewer stents are required in the treatment of long lesions. In addition, they may be delivered by catheters with small- It is often helpful to place the leading end of a self-expanding er profiles, which may reduce arterial-access complications. Self- stent slightly beyond the lesion, then draw it back. This measure expanding stents may also be placed in regions of the body where removes loaded tension from the system; it also allows the stent to they are subject to crushing forces (e.g., the carotid artery) because be pulled back slightly after the initiation of deployment, at which they are capable of recovering from the deformation and maintain- point various forces sometimes cause the stent to move forward. ing the arterial lumen.15 As noted, however, self-expanding stents However, the partially deployed struts of the stent can injure the have less hoop strength than the balloon-expandable stents. vessel wall if moved too much or advanced forward. It is also important to keep in mind the potential for foreshortening of the Covered Stents stent during deployment. Failure to cover the entire lesion with the Stents may be covered with polyester, polytetrafluoroethyl- stent results in residual disease after the procedure, which can ene, or other materials. Currently, covered stents are being used cause subsequent thrombosis and necessitate the placement of an more frequently for treating occlusive lesions, but they are more additional stent.To prevent restenosis, multiple stents should gen- commonly employed for treating aneurysms, arterial rupture, erally be placed so as to overlap one another, but doing so may and arteriovenous fistulas.15,16 increase the risk of fatigue fractures. Clearly, the nuances of stent deployment vary according to the system being used; frequent use GENERAL TECHNICAL PRINCIPLES of a particular system will enhance the interventionalist’s familiar- Conceptually, stent placement is very similar to balloon angio- ity with the behavior of the device and improve the subsequent plasty [see Figure 6]. Preoperatively, the patient is often given an clinical results. antiplatelet agent, which may be continued for 4 weeks or longer postoperatively to reduce the risk of thrombosis. In general, the diameter of the fully deployed stent should slightly exceed that of Postprocedural Management of Arterial Access Site the vessel, though many interventionalists do not fully dilate stents After any endovascular procedure, the arterial access site must in the aorta and the carotid bifurcation.11 If occlusion makes the be addressed. Manual compression is still the most common exact diameter of the artery difficult to measure, the vessel’s con- method of hemostasis and is effective in most instances.The artery tralateral counterpart can be used as a guide.16 The stent should often must be compressed for longer than 20 minutes to prevent also be slightly longer than the lesion to ensure that the entire bleeding complications. If the patient is receiving anticoagulant lesion is covered. In this way, good wall apposition can be achieved therapy, it may be necessary to wait until the coagulation parame- and stent migration prevented. ters have normalized before pulling out the sheath. This can be The classic approach is to advance a guide (or a long sheath) done when the patient is out of the OR or the interventional suite across the stenosis over the previously placed guide wire; the vas- and in the recovery room or when the patient has been moved cular stent is then passed through the guide and positioned at the onto the hospital floor. After hemostasis has been achieved at the lesion, the guide is withdrawn, and the stent is deployed. With access site, the patient should refrain from walking for about 6 newer stent delivery systems, the leading tip often allows the stent hours, after which period the puncture site generally is sufficient-
  9. 9. © 2007 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 8 Fundamentals of Endovascular Surgery — 9 ly stable. After therapeutic procedures involving relatively large are placed simultaneously. Remove the dilator. devices, use of an arterial closure device may be advantageous. 12. Administer anticoagulation as indicated. Several such closure devices are now commercially available. 13. Manipulate the guide wire to the appropriate position past These devices are improving in quality and are certain to be used the lesion (in cases of nonselective catheterization). more frequently in the future. 14. Pass the catheter over the guide wire and through the sheath. Manipulate the catheter to select the branches for guide wire cannulation. Summary: Basic Steps in Endovascular Procedures 15. Perform angiography through the catheter or the sheath to 1. Before operation, assess the patient with respect to renal clarify the anatomy. function, allergies, active infections, anticoagulant manage- 16. Remove the catheter while pinning the guide wire. ment, and skin condition (in cases of planned access). 17. Pass the balloon catheter over the guide wire. Advance the Consider prescribing antiplatelet agents. balloon across and center it over the lesion. If indicated, 2. Monitor and sedate the patient as necessary. primary stenting may be performed. 3. Prepare and drape the selected arterial access site or sites. 18. Inflate the balloon. 4. Infiltrate a local anesthetic at the selected site. 19. Deflate the balloon. 20. Remove the balloon catheter while pinning the guide wire. 5. Use a scalpel to nick the skin at the planned needle entry 21. Perform angiography. site, a few centimeters distal to the intended arterial punc- 22. If necessary, pass the vascular stent over the guide wire and ture site. advance it across the lesion. 6. Cannulate the artery with the entry needle. 23. Deploy the stent. 7. Pass the guide wire into the needle for at least 20 to 25 cm. 24. Perform completion angiography. Use fluoroscopy to follow the guide wire as indicated. 25. If the angiogram is satisfactory, remove the guide wire, the 8. Remove the needle while pinning the guide wire in place. catheter, and the sheath. 9. Apply manual compression during exchanges to prevent 26. Apply manual compression to the access site, or use a closure hematoma formation around the artery. device. 10. Use dilators to create an appropriate tract while pinning the guide wire. Dr. Matsumura has received grants, research support, or consulting fees from 11. Pass a sheath over the pinned guide wire. Often, with small Abbott Laboratories; C. R. Bard, Inc.; Cook Biotech Inc.; Cordis Corp.; ev3 sheaths and minimal scarring, the dilator and the sheath Inc.; W L. Gore and Associates; and Medtronic, Inc. . References 1. Tortorici M: Fundamentals of Angiography. CV that uses palpation of anatomic landmarks. J Vasc 12. Moore WS, Ahn SS: Endovascular Surgery, 3rd ed. Mosby Co, St Louis, 1982 Intervent Radiol 4:415, 1993 WB Saunders Co, Philadelphia, 2001 2. Johnsrude I, Jackson D, Dunnick N: A Practical 7. Jaques PF, Mauro MA, Keefe B: US guidance for 13. Neiman HL, Yao JST: Angiography of Vascular Approach to Angiography, 2nd ed. Little, Brown & vascular access: technical note. J Vasc Intervent Disease. Churchill Livingstone, New York, 1985 Co, Boston, 1987 Radiol 3:427, 1992 14. Hood DB, Hodgson KJ: Percutaneous transluminal 3. Valji K:Vascular and Interventional Radiology.WB 8. Khangure MS, Chow KC, Christensen MA: angioplasty and stenting for iliac artery occlusive Saunders Co, Philadelphia, 1999 Accurate and safe puncture of a pulseless femoral disease. Surg Clin North Am 79:575, 1999 4. Rupp SB, Vogelzang RL, Nemcek AA, et al: artery. Radiology 144:927, 1982 15. Nicholson T: Stents: an overview. Hosp Med Relationship of the inguinal ligament to pelvic 60:571, 1999 9. Spijkerboer AM, Scholten FG, Mali WPTM, et al: radiographic landmarks: anatomic correlation and Antegrade puncture of the femoral artery: mor- 16. Henry M, Clonaris C, Amor M, et al: Which stent its role in femoral arteriography. J Vasc Intervent Radiol 4:409, 1993 phologic study. Radiology 176:57, 1990 for which lesion in peripheral interventions? Texas 10. Grier D, Hartnell G: Percutaneous femoral artery Heart Inst J 27:119, 2000 5. Baum PA, Matsumoto AH, Teitelbaum GP, et al: Anatomic relationship between the common puncture: practice and anatomy. Br J Radiol femoral artery and vein: CT evaluation and clinical 63:602, 1990 significance. Cardiovasc Radiol 173:775, 1999 11. Kandarpa K, Aruny JE: Handbook of Interven- Acknowledgment 6. Millward SF, Burbride BE, Luna G: Puncturing tional Radiologic Procedures. Lippincott Williams the pulseless femoral artery: a simple technique & Wilkins, Philadelphia, 2002 Figures 1 through 6 Alice Y. Chen.