Cardiac Catheterization in Congenital Heart Disease: Pediatric and Adult - Part 7 ppt

CHAPTER 22 Intravascular stentsageneral information 559 Encore™ indeflator device The Encore™ device (Medi-Tech, Boston Scientific, Natick, MA) has a clear polycarbonate syringe barrel encased in a covering that holds an analog manometer. The manome- ter is attached to the syringe lumen and has a maximum pressure of 26 atms. The syringe has a capacity of 20 ml. The ratchet mechanism on the syringe plunger is engaged all of the time unless deliberately released by compressing a squeeze/release button on the side of the barrel. B. Braun™ angioplasty inflation device The B. Braun™ angioplasty inflation device (B. Braun Medical Inc., Bethlehem, PA) has a 25 ml clear polycar- bonate syringe barrel with an analog pressure gauge, which reaches and holds 30 atms pressure. The syringe has a rapid action “winged” locking mechanism, which locks very quickly, adjusts very accurately and holds at high pressures. Merit Medical™ inflation devices Merit Medical (Merit Medical Systems, Salt Lake City, UT) has four different inflation devices, all with a clear 20 ml polycarbonate barrel. The syringe has a squeeze “bar” on a “T” handle to release the ratchet mechanism. The difference in the four inflation devices is in the type of manometer gauge. All of the gauges are electronic, but are available in analog or digital and in local or remote configurations and with, or without, built in timers. Bard Max 30™ inflation device The Max 30™ (C.R. Bard, Inc., Covington, GA) has a “T” shaped handle over the polycarbonate barrel of a 20 ml capacity syringe. A lever which moves from side to side across the “T” locks or releases the ratchet mechanism of the syringe. The Max 30™ inflation devices can deliver 30 atmospheres of pressure. The only additional criterion for the use of any of these inflation devices is that the operator must be very familiar with the operation of the specific device that is being used. Technique for the implant of intravascular stents The technique for the delivery and implant of the J & J™, Palmaz™ stents (Johnson & Johnson, Warren, NJ) has been developed and modified extensively during the fifteen years of the clinical use of these stents in congenital and pediatric cardiac patients. Unfortunately, the stent and balloon technology for this “non-approved” use has not kept pace adequately with the complex congenital lesions for which stent therapy now is routinely utilized. Relative to the developments in stents and stent tech- niques for coronary arteries, the stents and delivery equipment for congenital lesions are a decade behind in development and in their introduction for clinical use in the United States. There have been some improvements in the stents which are approved for use in adult periph- eral vascular disease and which have filtered down to the pediatric/congenital population. At the same time, the changes/improvements in the delivery/implant tech- niques for congenital heart patients were developed pre- dominately in pediatric/congenital catheterization labor- atories during the decade and a half of the use of stents in these patients. All “self-mounted” or “hand-mounted” stents are cur- rently delivered through or with the use of a long sheath advanced to and past the lesion where the stent is to be implanted. To date, there are no satisfactory ways of hand-mounting stents and securing them tightly enough on the balloons to allow confident and safe delivery of a stent without the use of a long sheath. Even if secured to the balloon, without the use of a long sheath, the stiff, sharp exposed ends of a rigid stent that is hand-mounted on a balloon, easily extend off the balloon, catch on in- travascular structures, and are displaced off the balloon during its passage through the vascular channels to the lesion. If the stent catches on structures as the stent/ balloon is being advanced, the stent is displaced prox- imally on the balloon catheter. This prevents delivery to the lesion and creates a problem in getting the stent out of the vessel and body, but usually does not result in an errant, free-floating stent. If the stent catches on structures during the withdrawal of the balloon/stent/catheter, the stent is displaced onto the wire distal to the balloon. Without sophisticated and difficult retrieval techniques, this results in a stent potentially free floating in the circula- tion! At present, a long-sheath technique is recommended and is always used for the delivery of hand-mounted stents. The equipment and techniques for the delivery of all of the available large diameter, hand-mounted stents to the proximal pulmonary arteries, to the central systemic veins, and to the large systemic arteries are almost ident- ical, although the delivery to the pulmonary arteries is usually more complex and difficult. The similarities in the equipment, and the general techniques for the delivery and implant used for all of the stents currently available for the larger vessels are described in this chapter. The delivery and implant of the rigid Palmaz™ P _ _ 8 and P _ _ 10 stents are the most difficult and dangerous. Familiarity with the techniques for delivering those stents should make the delivery of most other stents relatively straightforward. The availability of pre-mounted large CHAPTER 22 Intravascular stentsageneral information 560 stents on appropriate sized balloons may change these techniques dramatically within the next few years. The peculiarities and particular difficulties with the delivery of stents to specific locations in specific vessels are discussed in Chapters 23, 24 and 25, which cover the use of intravascular stents in pulmonary arteries, systemic veins and systemic arteries, respectively. Peculiarities in the general delivery of the newer, more recently available stents are discussed at the end of this section on technique. General technique for stent delivery Most intravascular stent implants in congenital heart patients can be performed with well controlled, deep sedation and liberal local anesthesia. However, since the procedures can be very long, which becomes uncomfort- able for the patient, general anesthesia often is used elect- ively. General anesthesia becomes essential when the implant of a stent or even part of the procedure is per- formed from the neck, when it is known that the proced- ure definitely will be of a very long duration, or when the patient needs endotracheal intubation for some other reason. General anesthesia has the advantage of another physician besides the catheterizing physician monitoring the patient and having some responsibility for the patient’s degree of sedation and the control of the patient’s airway. With the use of either sedation alone, or when general anesthesia is used, the patient requires a secure intra- venous line for the administration of supplemental seda- tion and other medications during the procedure. Often, just before the actual expansion of the stent for implant and even though the patient appears sound asleep, the patient is given a supplemental dose of sedation/anesthesia in order to ensure that the patient remains absolutely still at the moment of implant. All patients undergoing stent implant have an indwelling arterial line in place during the entire proced- ure. This line allows instantaneous and continuous moni- toring of systemic blood pressure and the obtaining of necessary blood gases throughout the procedure. It al- ways is better to anticipate and, in turn, to prevent prob- lems with the patient than to try to compensate for a catastrophe once it has occurred. A subtle change in the continuously displayed intravascular blood pressure which is on a monitor provides an early indicator of impending trouble, while the periodically displayed pres- sure from a “cycling” arm blood pressure cuff recorder may well appear long after the adverse event begins. Every patient undergoing a stent implant has an indwelling bladder catheter (Foley™) placed at the begin- ning of the procedure. No amount of sedation or analgesia compensates for the discomfort of an over-distended uri- nary bladder during a long procedureaparticularly if it is unexpectedly long! In a patient undergoing stent implant in the pulmonary arteries or systemic venous systems, one extra venous catheter is introduced into the venous system in addition to the venous line(s) which will be necessary for the delivery of the stent(s), in order to have an extra catheter in the venous system in addition to the number of catheters through which stents will be delivered. Thus, in a patient in whom two stents are to be implanted simultaneously, three venous catheters are introduced. A separate line is used for each individual stent delivery, while the additional venous line is used to perform precise selective angiograms pre, during, and immediately after the expansion of and implant of the stent. The additional, angiographic catheter is positioned in the same vessel, close in proximity and proximally in the flow of blood to the stenosis/stent implant area. Some operators advocate performing the “placement” angiograms during the stent implant through the long delivery sheath after the sheath has been withdrawn off the stent/balloon combination and back into the more proximal vessel. This technique is of no use during the positioning of the stent/balloon combination before it is completely out of the delivery sheath (and no longer retrievable). Often the details of the anatomy from angiograms with injections through the sheath are not suitable. The shaft of the balloon catheter fills and com- promises most of the lumen of the sheath and the pressure of the injection through the side port of the sheath is limited by the loose “seal” of the back-bleed valve of the sheath over the shaft of the catheter. As a consequence, a sufficient amount of contrast cannot be delivered rapidly enough with a high enough pressure to visualize the stenosis–stent relationships accurately. In addition, in order to perform the angiogram through the sheath during the stent implant, the sheath must be withdrawn completely off the balloon and not just off the stent. Once the sheath is completely off the balloon/stent, further readjustment of the stent/balloon position is more difficult. In addition, this places the distal tip of the sheath very proximal to both the stent and the area of stenosis in the vessel. As the contrast is injected relatively slowly through the sheath and into the more proximal vessel, the contrast is diluted by adjacent, rapidly flowing blood, pre- venting an adequate visualization of the area of interest. Also when the sheath tip is far proximal to the area of stenosis, the tip is often proximal to a bifurcation or a large branching vessel, in which case, the majority of the small quantity of slowly injected contrast is diverted into the branch vessel and away from the stenotic area. Poor angiographic imaging is more “the rule” than the excep- tion with the “through-the-sheath” technique and, as a consequence, this technique is not recommended. Inad- equate angiograms compromise the precise positioning of the balloon/stent. CHAPTER 22 Intravascular stentsageneral information 561 The implant of stents into smaller, more peripheral veins is the one exception where through-the-sheath angiograms can be useful. In this circumstance the vessel is small, the sheath is “upstream” in the flow of blood, the blood (and contrast) flow is slow and the injection is into a very confined channel that is being stented. Occasionally, however, when the implant of a venous stent is “retro- grade” in the vein (e.g. a stent delivered into a femoral vein from the jugular approach) the end of the sheath is “downstream” in the flow from the lesion, with the result that the contrast injected through the sheath flows away from the lesion/stent and is of no value. The area(s) to be stented is(are) identified and quantit- ated both hemodynamically from the pressure measure- ments and angiographically with selective angiograms into the precise vessel/area to be stented. The techniques for accurate, quantitative measurement are described in detail in Chapter 11 and definitely should be adhered to for the implant of intravascular stents. After identifying and measuring the stenosed area(s) of the involved vessel(s) very accurately, an end-hole catheter is advanced from the access site, across and well beyond the area of obstruction. It is extremely important that the vessel that is entered distal to the obstruction is of a large diameter and is the longest distal branch or tributary beyond the stenosis. This vessel must be long enough to allow the very distal placement of the tip of the supporting guide wire and of a large enough diameter to accommodate the distal end of the fully inflated balloon which will be used to deliver and implant the stent. When the balloon and stent are centered on the stenotic lesion during the stent expansion, the distal end of the implanting balloon will always extend well beyond the lesion and into the distal vessel. Considerable extra time is often required to enter this largest, distal vessel. The extra time spent in locating and achieving a good position in this largest vessel with the end-hole catheter is essential. Once the catheter has been manipulated far into the largest distal vessel, it is replaced with a Super Stiff™ exchange length guide wire. If a long “floppy-tipped” Super Stiff™ wire is used, the vessel must be very long (and large enough in diameter) to accommodate the entire curled up (“balled-up”) long floppy portion of the wire. It is imperative that the entire, long floppy tip, along with the transition zone of the wire and a significant portion of the extra stiff portion of the wire all extend a significant dis- tance beyond the lesion. The balloon and stent are sup- ported only by the very stiff portion of the wire and by a wire that is in a very secure distal position without the capability of any to-and-fro movement. The precise wire position contributes significantly to the ultimate success and safety of the procedure. All the extra time required in positioning the wire securely and very distally adds to the likely success of the procedure, while any compromised location of the wire is inviting a catastrophe. Over-dilation and tearing of a smaller branch vessel that is just distal to the stenosis, is one of the greatest haz- ards during the implant of intravascular stents. It usually is a consequence of the wire and tip of the balloon being malpositioned prior to the stent implant. When the bal- loon tip is positioned and fixed in, and then inflated in, an erroneous and unusually small vessel that is just distal to the lesion, either it will rupture the vessel or the balloon will be “milked” back out of the vessel during the inflation and, in turn, the stent will be displaced proximally. When there is a question about the size and configura- tion of the particular anatomy in the area of the stenosis and, in particular, a question about the adequacy of the vessel distal to the stenosis, the anatomy is defined pre- cisely with a low-pressure, “sizing” balloon. This is not a pre-dilation of the area but rather, a “zero-pressure” inflation with a very low-pressure sizing balloon in the area to determine the contour of the entire area! The most satisfactory balloon for this sizing is the NuMED™ low- pressure “angioplasty” (“sizing”) balloon (NuMED Inc., Hopkinton, NY), although any angioplasty type balloon can be used for the sizing if it is inflated only at very low pressure. The sizing balloon is advanced over the pre- positioned stiff guide wire and positioned exactly in the area of stenosis where the balloon/stent is to be inflated. The sizing balloon is inflated at a very low (zero!) pressure. The balloon at this “zero” inflation pressure fills, and con- forms to, the exact anatomy of the stenosis and vessel(s) both proximal and distal to the lesion without dilating the area at all. This technique is useful particularly to deter- mine if there is sufficient diameter distal to the stenosis to accommodate the distal tip of the balloon during inflation of the balloon for the stent implant. If the vessel distally is too small, the zero pressure “sizing” balloon either does not inflate in the area or it gently “milks” back out of the vessel. The only disadvantage of this particular low-pressure sizing balloon is that it requires a 9-French introductory sheath, but at least this size will usually be required for the delivery of the stent. As long as the stenosis is more than 3 to 4 mm in dia- meter, pre-dilation of stenotic lesions before implanting a stent is not performed. Only very tight stenoses, which are too tight to allow a large, long delivery sheath for the delivery of the stent to pass through the lesion, are pre- dilated routinely. When pre-dilation is performed, the stenosis is pre-dilated only enough to allow the particular delivery sheath to pass through the stenotic area. When the vessel adjacent to the stenosis (either proximal or dis- tal to the obstruction) is significantly larger than the pro- posed initial delivery balloon for the stent, pre-dilation unequivocally should not be performed. A “successful” pre-dilation of a stenotic area temporarily will dilate the area acutely, but it also temporarily makes the area of the stenosis very compliant and even “patulous”. When a CHAPTER 22 Intravascular stentsageneral information 562 stent is implanted in this patulous or “softened” area, the stent does not fix securely to the now elastic walls, even when it is fully expanded and is in the proper position. As a consequence, the stent/balloon can be displaced very easily either during the balloon inflation or, even more likely, during the attempted removal of the balloon from within the lumen of the stent after the implant. Any move- ment of the stent immediately after implant usually results in migration of the stent to a non-stenosed area of the vessel or, even worse, results in a stent “free floating” in a vessel/chamber. The main argument in favor of pre-dilation of a lesion in which a stent is going to be implanted, is to ensure that the balloon/stent combination can open the lesion sufficiently during the implant/expansion of the stent to allow removal of the balloon from the stent after implant. The inability to dilate the lesion during the implant of the balloon/stent combination can leave not only the original vessel stenosis, but also a stent with the same stenosis in it. The presence of the stent on the balloon does not add any additional dilating force or dilating capability in addition to that of the balloon alone. The expanded intravascular stent only maintains the degree of dilation that is achieved acutely by the particular balloon. When a significant re- sidual stenosis persists in the stent/vessel after a stent is implanted with a usual “standard-pressure” balloon, the original implanting balloon is replaced with a high- pressure balloon and the dilation of the stent/vessel re- peated. Very few (no!) residual stenoses do not respond to a balloon dilation when a non-compliant, high-pressure balloon is used for the reinflation and the balloon is inflated to 20 to 25 atmospheres within a stent! This is true particularly when the attempt at re-dilation is six, or more, months after the original stent implant. Pre-dilation of the area and the diameter of the pre- dilation constitute a judgment decision during each stent implant procedure. The decision is individualized in the catheterization laboratory as the anatomy is visualized and sized. When pre-dilation of the vessel is performed before a stent implant, there is one major “rule” for the pre-dilation. The pre-dilation of any stenotic lesion which precedes the implant of an intravascular stent should be only to a dia- meter that will accommodate the delivery sheath and which is significantly smaller in diameter (at least 3 mm smaller in diameter) than the diameter of the adjacent vessel or to the diameter to which the stent is to be expanded at its initial implant. In order to ensure fixation of the stent into some residual, more rigid tissues in the vessel wall, pre-dilation with a minimal diameter balloon ensures that the balloon that is used for the delivery of the stent can be larger and can expand the stent to a diameter which is definitely larger than the pre-dilated (“softened”) stenotic area. The pre-dilation is performed over the same Super- Stiff™ wire over which the long sheath/dilator eventually will be delivered. Once the wire is securely in place, a stand- ard pressure dilation balloon is advanced over the wire to the obstruction. The pre-dilation balloon used is only 2– 3 mm larger in diameter than the diameter of the stenosis in the vessel and is at least 3 mm smaller than the adjacent ves- sel, which should be the anticipated implant diameter of the stent. The pre-dilation documents at least some “give” to the stenosis in the vessel as well as opening the vessel to accommodate the large sheath for the stent delivery. After a pre-dilation is performed, the Super Stiff™ wire is main- tained in its secure distal location, while the separate balloon used for the pre-dilation is withdrawn, leaving the wire in place across, and well beyond, the stenosis. If a very tight area of stenosis cannot be pre-dilated at all with a standard-pressure balloon, a high-pressure balloon which is similar in size to the standard-pressure balloon is used over the same wire in a repeat attempt to pre-dilate the stenosis to the minimal diameter that will accommodate the delivery sheath. Pre-dilation with the high-pressure, but smaller, balloon ensures that if the standard, lower- pressure balloon for the delivery of the stent does not fully expand the area of stenosis, the area of stenosis will be expanded to at least the diameter of the high-pressure, pre-dilation balloon. This newly permitted increase in the diameter provides sufficient evidence to be certain that the implanting balloon can be removed from a partially expanded (but secured) stent without displacing the stent. Long indwelling sheath stent delivery technique A long sheath/dilator set which will accommodate the particular balloon/stent combination is advanced over the pre-positioned Super Stiff™ wire and past the area of stenosis which usually has not been pre-dilated. The tip of the sheath is positioned at least several centimeters distal to the area of obstruction in the vessel. The delivery of the sheath to the lesion and securing the sheath in posi- tion without creating kinks in the sheath, particularly to branch pulmonary artery lesions, often is the most difficult and challenging part of the entire procedure for the implant of an intravascular stent. Once the sheath and dilator are in position with the tip of the sheath well beyond the lesion, the Super Stiff™ wire in the distal ves- sel and the long sheath are fixed in place while the dilator is slowly and carefully withdrawn over the wire and out of the sheath. The sheath is allowed to bleed back from the side port on the back-bleed valve until it is clear of all air and possible clotsa remembering that the large, long sheaths hold 10–15 ml of fluid (or air and/or clot!). Once cleared by “passive drainage”, the sheath is flushed thor- oughly by hand and then is attached to a continuous slow flush to prevent the development of clots in the large potential dead space within the sheath and around the wire. After any pre-dilation is accomplished and as soon CHAPTER 22 Intravascular stentsageneral information 563 as the delivery sheath is in position, if not administered earlier, the patient is administered systemic heparin in a dose of 100 mg/kilogram of body weight. If a long sheath with an attached back-bleed valve/ flush port or a separate back-bleed valve/flush port that which will accommodate the delivery catheter and fit on the long sheath is not available in the particular catheterization laboratory, the massive bleeding which would occur from the open sheath can be prevented with a “make-shift” solution. The bleeding through a non- valved sheath with a wire within it is stopped effectively (and temporarily) with a “rubber-shod” Kelly™ clamp placed across the sheath (containing the wire) just outside of the body where the sheath exits the skin. This prevents the massive blood loss around the wire and through the sheath after the dilator is removed from the sheath. Of equal importance, it prevents air from being sucked into the sheath during a deep inspiratory effort by the patient. The clamp on the sheath does not allow any acute or continuous flush of the sheath, and the clamp indents the sheath, but only in an area outside of the body where the clamp is applied. This indentation in the sheath does not interfere with the passage through that segment of the sheath that is outside of the body and can be straightened manually, nor with the eventual delivery of the stent. Of most importance, the “external” indentation does not involve any areas that are in tight curves or bends in the sheath in the course of the sheath to the target site. When a separate, detachable back-bleed valve, which is not built onto the sheath, is used for a stent delivery on a large sheath with no built-in back-bleed valve, the balloon alone is passed through the detached, separate back-bleed valve and is slid back onto the shaft of the balloon dilation catheter before the stent is mounted on the balloon. In this way the stent mounted on the balloon does not have to be forced through the smaller diameter lumen of the remov- able, back-bleed valve. After the stent has been mounted on the balloon, the stent/balloon unit is introduced com- pletely into the non-valved sheath, the pre-mounted back- bleed valve is advanced forward on the shaft of the catheter onto the proximal hub of the sheath, and attached to the hub. The clamp on the sheath is released, the sheath is allowed to bleed back thoroughly through the side port of the attached back-bleed valve, and then the side port is attached to the flush system. The exact stent and balloon that are used depend upon the current, desired and eventual adult size of the vessel and the location of the lesion in the vessel. For all vessels, a stent always is used which eventually can be dilated to the eventual adult diameter of the particular area of the vessel. The length of the stent depends upon the length of the actual lesion, the expected shrinkage in the length of the stent with full expansion, the curvature of the vessel, and the distances within the vessel before any branching or bifurcations. The exact anatomy is defined angiograph- ically or, when there is any question, by inflating the “sizing” angioplasty balloon in the precise area at a very low pressure. In choosing the appropriate stent for a particular lesion, the operator must always consider the amount of shrink- age in the length of the stents with each increase in dia- meter of the stents. This is particularly important with the J & J™ Palmaz™ (Cordis Corp., Miami Lakes, FL) and Genesis XD™ stents (Johnson & Johnson–Cordis Corp., Miami Lakes, FL), which shrink as much as 50% when inflated to their largest diameters. Shrinkage in length to some degree must be considered with almost all stents. When a stent is to be expanded to 15 mm or larger in dia- meter, in order to account for the shrinkage, the stent used often must be longer in its collapsed state than the length of the vessel where it is to be implanted. This shrinkage in length makes it extremely important that the balloon and stent are positioned precisely over the exact lesion at the beginning of, and maintained in that position throughout, the expansion of the stent during its implant. With a stent properly and precisely placed on the delivery balloon, the shrinkage usually, but not necessarily, is symmetrical from both ends of the stent. As a consequence, most bal- loon/stent inflations should be slow and observed very carefully so that any asymmetric expansion or movement in the position of the stent relative to the anatomy can be adjusted before the stent is fully expanded and fixed securely in an abnormal position. The expected shrinkage of a stent occasionally is used to the operator’s advantage, utilizing the further decrease in length with further expansion of a stent to move the ends of the stent away from crossing or branching vessels. The use of a BIB™ bal- loon (NuMED Inc., Hopkinton, NY) is helpful in order to allow some purposeful adjustment for an asymmetrical inflation or shrinkage after the stent has been expanded to only half of its final diameter. The balloon is chosen specifically for the stent that is being used and the diameters adjacent to the area of implant while the exact stent is chosen for the particular anatomy of the lesion as well as the diameters of the immediately adjacent vessels. To prepare the balloon for the stent, the balloon lumen is attached to the inflation device and the balloon is inflated partially, but not to a high pressure. The balloon is cleared of air by repeated partial inflations/deflations while holding the balloon in a vertical position with the tip of the balloon facing down. Once the balloon is cleared of air, the balloon is deflated slowly while simultaneously refolding the balloon manu- ally around the shaft of the catheter. Once the balloon is refolded as smoothly as possible, the balloon is main- tained on “negative pressure” by withdrawing the plunger of the inflation device and locking it in the fully withdrawn position. The appearance of a continual CHAPTER 22 Intravascular stentsageneral information 564 stream of tiny bubbles after applying negative pressure to the balloon with an inflation device indicates a leak in the balloon or the inflation system. The source of any leak is identified and eliminated before proceeding, even if it requires replacing the balloon or the inflation device. There are some special preparations for the BIB™ bal- loons. Each BIB™ balloon catheter has three lumens: one lumen (with a blue hub) to the inner balloon, one lumen (with a white hub) to the outer balloon, and a central catheter lumen of the catheter itself (with a green hub). In the original BIB™ balloons, where the central lumen passed through the area of the balloons and before it passed out through the tip of the catheter, the tubing of the central lumen was very narrow and thin walled. This nar- row tubing allowed the collapsed balloons to compress to a diameter only slightly larger than the diameter of the catheter shaft, but did not provide much longitudinal sup- port in that area when there was no wire in this lumen. To compensate for this during the preparation of the bal- loons, each balloon catheter comes with a blunt, solid metal, 0.035″ stylus. This metal stylus is inserted into the distal end of the catheter lumen during balloon prepara- tion and while the stent is being crimped on the balloon. The stylus passes through the area of the balloon(s) and back into the shaft of the catheter well proximal to the bal- loons and, in this position, keeps that area of the catheter and the balloons very straight and elongated. For preparation of BIB™ balloons, both balloon lumens are connected to manometered inflation devices. The inner balloon is inflated and cleared of air and then the outer balloon is inflated and cleared separately. Once the balloons have been prepared, cleared of all air and rewrapped around the catheter, the balloon lumens are opened to neutral pressure and the stylus is removed. The stent is passed over the refolded balloons, the stylus is reinserted, and both balloons are again placed on negative pressure. Since the stent over the balloons covers the radio-opaque “markers” on the catheter within the bal- loons, the BIB balloons with the stent mounted are viewed under fluoroscopy in order to align the stent precisely and evenly within the marks within the balloons. The stent then is compressed (crimped) over the balloons by hand exactly as with any other stent–balloon combination. The stylus remains in the catheter during the “crimping” and until just before introduction over the delivery wire. Any balloons that have a Silicon™ or other “slippery” coating also require “pre-preparation” before a stent is mounted on them. The balloon is inflated until it is tense and then the “slippery” coating is rubbed off the balloon surface very vigorously with a dampened, 4 × 4 gauze sponge. Once it is “rubbed clean” the balloon is manually rewrapped over the catheter as it is deflated. When the balloon has been cleared of air, the balloon is placed on negative pressure and simultaneously is rotated and “refolded” onto the shaft of the catheter in order to col- lapse the balloon maximally onto the catheter shaft. Some slight “irregularities” on the surface of refolded balloons actually are desirable when using balloons for the deliv- ery of stents. The irregular surface of the balloon helps to keep the stent, which is hand-crimped on the balloon, from sliding on the balloon during its passage through the sheath. Before the stent is advanced over any balloon for mounting on the balloon, the stent and surface of the balloon are both coated with undiluted contrast solution. As the contrast dries, it becomes very sticky and serves as a “glue” that will help to hold the stent on the balloon. To prepare the stent for mounting on the delivery bal- loon, the entire length of the stent is dilated sufficiently to allow the stent to pass easily over the balloon, and one end of the stent is flared even wider by inserting the tip of a large dilator (the dilator from the delivery sheath) into one end of, and advancing it through the length of, the stent. As the dilator is withdrawn from the end of the stent, the dilator is angled slightly and rotated around within the proximal tip of the stent, which, in turn, “flares” or makes a “funnel-like” opening in one end of the stent. When much larger delivery balloons are used, the entire stent is dilated even further before introducing the stent by gently advancing an even larger dilator into, and through, the stent. The dilation and flaring of the stent facilitate advancing the stent over the balloon and help to prevent the ends of the stent from catching on the folds of the bal- loon. With the Palmaz™ J & J™ stents, this is essential to prevent the puncture of the balloon by a sharp tip at the end of the stent. With negative pressure applied to the balloon lumen, the tip of the balloon catheter is introduced carefully into the flared end of the stent and while the stent is allowed to rotate slowly and very slightly (less than 360 ° ) to corres- pond to the direction of the folds of the balloon, the bal- loon is advanced very gently into the stent. The catheter and balloon always should slide freely into the stent. The introduction of the stent over the balloon is performed very gently and slowly to prevent a sharp tip at the end of a stent from digging into, and puncturing, the balloon during the mounting process. Particular care is necessary with the J & J™ Palmaz™ stents (Johnson & Johnson, Warren, NJ) which all have multiple sharp tips at each end. If the stent catches on the balloon at all, the stent is with- drawn, the balloon is re-formed or the stent dilated/flared further. The stent is advanced over the balloon until it is positioned over the exact center of the length of the balloon. The stent is centered lengthwise as precisely as possible by aligning the ends of the stent with, or equally between, the metal markers on the shaft of the catheter beneath the bal- loon material. When there is any question about the exact positioning of the stent on the balloon, the stent/balloon should be visualized under fluoroscopy. CHAPTER 22 Intravascular stentsageneral information 565 Once the stent is centered exactly on the balloon, the metal stylet of the BIB™ balloons is introduced into the distal end of the catheter lumen of the balloon catheter and pushed far enough into the distal end of the catheter lumen of the balloon catheter to be entirely proximal to the balloon. This stylet within the lumen supports the lumen of the catheter during the subsequent forceful com- pression of the stent over the balloon. Strong negative pressure is maintained on the balloon lumen while the connecting tubing and the inflator are inspected carefully for any balloon leaks. A new puncture or leak is indicated by a continual stream of small bubbles flowing into the tubing or the inflator as the negative pressure is applied. Once assured that there are no leaks, the stent is com- pressed (crimped) uniformly on the balloon by manual finger compression. There are no “crimping tools” avail- able that are applicable universally for the large variety of stents, balloon sizes, and balloon types or for the different diameters of the catheter shafts of the different large balloon dilation catheters used for the large variety of congenital lesions. As a consequence, the crimping of all non-pre-mounted stents is performed by hand. Several more drops of contrast are placed on the surface of the stent before the manual crimping on the balloon is started. Starting with light finger pressure, finger pressure is gradually increased while moving the fingers over the entire length and around the circumference of the stent. The circumference of the stent is squeezed onto the bal- loon as the stent/balloon is rolled between the fingers. Once the stent is relatively smooth and secure on the bal- loon, then the fingers are squeezed as tightly as possible and repeatedly over the entire surface of the stent/balloon as the combination is rotated between the fingers. The process is repeated using the tips of the fingernails to compress the individual longitudinal struts forcefully between the circumferential “bands” of the stent. This fingernail compression creates a slightly irregular surface on the mounted stent, which, in turn, helps to secure the stent on the balloon, but does not affect the eventual stent expansion or strength. The short length of plastic tubing which is present over the balloon in its sterile package is occasionally used as a “smoothing” tool over the stent once it is mounted on the balloon. When the stent has been compressed over the bal- loon, the plastic tube is advanced over the combination of the balloon/stent. The tube over the stent/balloon is compressed manually between the fingers as tightly as possible while the tube, stent, and balloon are rotated between the fingers. However, this step usually is not nec- essary and does not crimp the stent as tightly as direct finger compression on the stent. Once the stent is compressed securely on the balloon, several more drops of undiluted contrast solution or albu- min solution are spread on the surface of the balloon–stent combination. The additional contrast is allowed to dry briefly on the surface of the balloon–stent. This serves as additional “glue” to help retain the stent on the balloon and keep it from “sliding” on the balloon during delivery through the sheath. The contrast “glue” works most effect- ively if it is allowed to dry for 15–20 minutes. Stent delivery over a wire and through a pre-positioned sheath The delivery of the stent/balloon combination to the lesion, over a pre-positioned stiff wire and through a pre- positioned long sheath, is the original and established technique for the delivery of stents to the various congeni- tal lesions. This technique is the most tested and reliable technique available for the delivery of the current stents. With the sheath and wire fixed in their position beyond the area of obstruction, the balloon catheter with the mounted stent is introduced over the proximal end of the wire and advanced to the valve of the sheath. The intro- duction of the balloon with the mounted stent into and through the valved sheath depends on the length and type of stent. The J & J™ Palmaz™ stents, which are longer than 3 cm, can be pushed directly through the back-bleed valve by gripping the most proximal end of the stent very tightly with the tips of the fingers. As the proximal tip of the stent is squeezed tightly and continuously in order to maintain the stent in its exact position on the balloon, the entire length of the stent is advanced through the valve of the sheath, and the combination stent/balloon is advanced into, and all of the way through, the attached back-bleed valve chamber and into the sheath. There is a small “flare” at the proximal end of the sheath within the distal end of the back-bleed valve housing (chamber) where the back-bleed apparatus is attached to the sheath (Figure 22.7). This flare of the sheath creates a flange or “ridge” within the back-bleed valve chamber between the distal end of the valve housing and the proximal end of the sheath within the valve “chamber”. This ridge is not visible from outside of the back-bleed housing, but can catch the distal end of the stent and block the passage of the mounted stent from passing into the lumen of the sheath from the back-bleed valve chamber. Longer stents can be held securely at the proximal end of the stent with the tips of the fingers and supported on the balloon as the stent is advanced all of the way through the “valve” and past this ridge. The shorter P 108, 188, and 204 stents are too short to maintain a grip with the fingers on the proximal end of the stent as it is advanced all of the way through the back- bleed valve and past the flange. When introducing the shorter stents is attempted by just holding the stent with the fingers, the stent is easily displaced proximally off of the balloon as the proximal end of the stent passes CHAPTER 22 Intravascular stentsageneral information 566 through the valve beyond the grasp of the fingers. This is overcome by using the short “metal introducing tube” supplied by J & J™ (Johnson & Johnson, Warren, NJ), or a short, cut-off length of sheath as an introducing sleeve (see Figure 22.1). The short length of “introducer” sheath should be the same diameter as the delivery sheath, made from a fairly stiff sheath material and approximately five centimeters long. The proximal, cut, end of the short seg- ment of sheath can be dilated with a forceps to flare the end slightly. The balloon with the mounted stent is intro- duced very carefully into the flared end of this sleeve until the stent is completely within the sleeve. The sleeve along with the contained balloon/stent are all held together and are passed through the back-bleed valve and into the long sheath until the sleeve seats on the flange between the valve apparatus and the proximal end of the sheath (see Figure 22.1). The balloon, stent, and catheter are advanced out of the sleeve and into the shaft of the long sheath. The sleeve is withdrawn out of the valve and back to the hub on the shaft of the balloon catheter. The introduction of the stent/balloon through the short sleeve can be used for the P 308 stents, and may make their introduction through the valve more secure. The short sleeve should definitely be used with all of the open-cell stents (ev3, Plymouth, MN). The pattern and the “looseness” of the cells of the open- cell stents cause them to catch on the back-bleed valve itself and cause the cells to pull apart if they are pushed directly through a back-bleed valve. When a long sheath with a separate and non-attached back- bleed valve/flush port is the only long sheath available, the balloon and the balloon catheter are passed through the removable back-bleed valve/flush port separately before the stent is mounted as described previously. The balloon with the mounted stent is introduced into the open end of the stent and the back-bleed valve, which is on the more proximal shaft of the catheter, is pushed forward on the shaft of the catheter and attached to the large sheath with a continuous flush delivered to the pre-mounted back- bleed valve. The remainder of the stent delivery then becomes identical to the delivery through a long sheath with a built-in attached back-bleed valve. Once the proximal end of the stent/balloon combination has been introduced and advanced several centimeters beyond the valve and hub of the sheath, the balloon is inflated very gently (~1 atmosphere) with the inflator and the inflator is locked to maintain this pressure in the bal- loon. This minimal pressure to the balloon expands the exposed shoulders of the balloon, which extend beyond each end of the stent, very slightly, without expanding the stent at all. This is particularly useful when the balloon is the same length or slightly longer than the stent. The slightly expanded balloon and the “exposed” shoulders of the balloon help to keep the stent from sliding proximally on the balloon as it is advanced through the sheath. Unless the balloon is inflated too vigorously, this still allows the balloon to pass easily through the sheath. If the bal- loon/stent does not move easily within the straight area of the sheath, the balloon has been inflated with too much pressure, and some of the pressure on the inflator should be released. This slight inflation of the ends of the balloon is important, particularly where there is a very tortuous course of the delivery sheath through tight bends in the vascular system. While frequently observing the balloon/stent combina- tion within the sheath as well as the position of the tip of the wire and sheath and the course of the wire and sheath on fluoroscopy, the balloon catheter with the mounted stent is advanced over the wire within the sheath to the involved narrowing in the vessel. As long as the wire and sheath are maintained securely in place, advancing the balloon and stent is usually accomplished quite easily. It is important to repeatedly observe the entire course of the sheath as well as the tip of the sheath and wire while the catheter and the balloon/stent are being advanced within the sheath. Occasionally, the “circumference” of a long curve in the course of the sheath/wire as it passes through the heart is widened as the balloon, stent, and catheter are pushed against the outer circumference of any curve in the sheath while it is passing through a dilated chamber or vessel within the heart. As the balloon, stent, and catheter push on and increase the curvature of the sheath, the dis- tance along the wire from the skin entry site to the lesion lengthens. If the increasing circumference of this curve in the sheath/wire and, in turn, the actual length of the dis- tance to the lesion are not noticed and not compensated for by advancing the sheath and wire along with the catheter at Figure 22.7 Flange (or flare) on proximal end of sheath within the back- bleed valve chamber. CHAPTER 22 Intravascular stentsageneral information 567 the skin, the tip of the sheath and the wire will be with- drawn out of their secure positions distal to the lesion. As soon as this “widening of the circumference” of the curve begins to occur, instead of the sheath and wire remaining firmly fixed outside of the body, the sheath and wire outside of the body are advanced along with the bal- loon/stent/catheter just enough to compensate for the increased length being caused by the large curvature within the heart. Once the stent and balloon have been advanced through the sheath to the area of the lesion, the stent (on the balloon) is centered exactly at the area of maximal narrowing. The slight pressure in the balloon lumen is released and the balloon deflated completely before the sheath is withdrawn off the stent/balloon. With the stent/balloon still within the sheath and with the guide wire still buried far out into the lung parenchyma, the wire, catheter, and balloon/stent are fixed in this location while the sheath alone is carefully withdrawn off the balloon/stent/catheter/wire combination. This uncovers the stent on the balloon over the wire centered in the proper location in the area of narrowing. After withdrawing the sheath, it is important to repeat a selective angiogram through the separate venous catheter either within, or just proximal to, the lesion in order to verify the exact positioning of the stent in the stenosis. Because of the stiffness of the wire, the catheter and the sheath, often there is distortion of the vessel and a change in the curvature and position of the wire/balloon/stent combination relative to the stenosis or to relatively fixed landmarks in the thorax after the sheath has been with- drawn. This can displace the stent/balloon away from the exact central area of stenosis compared to the location before the wire was introduced. The repeat selective angiocardiogram identifies any changes in relative posi- tions and allows the stent/balloon to be readjusted into the precise area of narrowing. Repositioning of the stent/balloon/catheter in the area is similar to the reposi- tioning of a balloon/catheter for angioplasty. The stent, balloon, and catheter are advanced over the fixed wire to advance the stent further into the lesion, but in order to withdraw the stent/balloon/catheter, the wire alone is pushed forward forcefully. As the wire advances, it pushes the stent/balloon/catheter backwards while, at the same time, keeping the wire forced forward into the distal loca- tion in a very secure position. During the passage of the balloon/stent/catheter through the sheath, occasionally the stent slips on the bal- loon and is displaced proximally on the balloon. If this displacement is less than 1–2 mm and the stent is still completely over the balloon, it usually is of little or no con- sequence. However, the balloon and stent positions should be inspected very carefully while the balloon and stent are still within the sheath and before the sheath is withdrawn. If the stent is displaced more proximally on the balloon, the stent still may be in its proper position within the lesion, but the distal end of the balloon, off of which the stent is displaced, will be positioned further into the distal vessel and away from the narrowing. A distal positioning of the balloon usually results in the balloon/stent combination milking backwards before the stent even begins to expand during the initial balloon inflation. This results in the stent’s being displaced and implanted in an improper location. If the “extra distal balloon” extends into a small distal vessel and the distally displaced balloon does not milk back out of the vessel, the expansion of the balloon can result in rupture of the small vessel. If the stent is displaced more than 1–2 mm on the balloon, and certainly if the stent extends completely off the balloon at all while the stent and balloon are still within the sheath, the implant procedure is abandoned temporarily and the sheath is not withdrawn off the balloon/stent combination. With the balloon/stent still within the sheath and with the stent now positioned over only the proximal end of the balloon, the balloon again is inflated very slightly. This inflates only the distal end of the balloon and creates a larger “shoulder” of balloon distal to the stent. The entire catheter/balloon/stent is withdrawn through the sheath, over the wire, and out of the body. The larger “shoulder” of the balloon, which is now completely distal to the displaced stent, helps to keep the stent from sliding distally off the balloon as the combi- nation is withdrawn through, and out of, the sheath. Even with the “distal shoulder” on the balloon the stent often catches at the valve of the sheath and is retained in the valve chamber of the sheath after the balloon has been withdrawn. Usually, the very end of the stent is visible just within the valve and still over the wire. When the end of the stent is visible just within the valve, a tip of the vis- ible end of the stent is grasped with a small forceps and pulled out through the valve. If the stent cannot be retrieved from within the sheath/valve, the entire sheath must be withdrawn over the wire. Once the sheath is completely out of the body and off the wire, the stent is pushed forward, through and out of the distal end of the sheath with a dilator or balloon catheter. Once the stent is retrieved from the withdrawn sheath, the dilator is replaced in the sheath and the sheath/dilator is re-advanced over the wire into the vessel and to the lesion. If the sheath is damaged at all, a new sheath/dilator set is used. Unless it was damaged in the removal process, the retrieved stent is re-mounted on the same or a new bal- loon. When re-mounted, the stent is positioned 1–2 mm forward (distally) of the center of the balloon. This leaves the stent mounted slightly more distally on the balloon with more “shoulder” exposed “behind” and more prox- imal to the stent toward the shaft of the catheter. The CHAPTER 22 Intravascular stentsageneral information 568 balloon catheter with the re-mounted stent is reintro- duced over the wire, into and through the back-bleed valve of the sheath, and advanced several centimeters into the sheath. The balloon is again inflated minimally (with approximately one atmosphere of pressure). The “for- ward” positioning of the stent on the balloon allows more of the proximal “shoulder” of the balloon to expand slightly behind the stent, which, in turn, helps to prevent the stent from sliding backward as the balloon/stent is advanced through the sheath. Once the balloon/stent has been advanced to the proper position as verified fluoroscopic- ally, the balloon again is deflated before the sheath is withdrawn off the balloon/stent. Very rarely, as the sheath is being withdrawn off of the stent/balloon, the stent again slides backward (prox- imally) on the balloon along with the sheath or, inadvert- ently, the stent/balloon is exposed with the stent already displaced proximally on the balloon. In this circumstance, after the sheath is completely off the stent but still partially over the proximal balloon, the sheath is gently read- vanced over the balloon. Usually, the edge of the distal end of the sheath catches on the proximal end of the stent and does not allow the stent to be withdrawn back into the sheath. By continuing to advance the sheath forward very gently, the stent can be pushed forward, and often can be positioned back onto the proper location on the balloon! This maneuver must be performed very gently and care- fully with no excessive force. If the stent does not move forward easily, it suggests that the sharp distal ends of the stent struts are caught on the balloon. Any excessive force applied to the sheath can push one of the sharp tips of the end of the stent into the wall of the balloon and puncture the balloon. This is a particular problem with the J & J™ Palmaz™ stents with the very sharp tips at both ends. Fortunately, even the Palmaz™ stents and all of the other stents can usually be re-advanced over the balloon quite safely by using this maneuver with the tip of the sheath. The sheath is withdrawn off the proximal end of the balloon but no further. The sheath positioned in close proximity to the balloon helps to support the shaft of the balloon catheter during the implant. Once the stent is in the exact, proper position in the stenosis and its correct position on the balloon has been verified, the balloon is inflated slowly to its maximum advertised pressure and hopefully to the maximum diameter of the balloon. During the inflation the stent is observed continuously and recorded on biplane angiography or biplane stored fluoroscopy. The inflation of the balloon expands the stent into the stenosed area of the vessel to the diameter of the implanting balloon. If there is even the suggestion of stent displacement during the initial slow inflation, the in- flation is stopped and the stent/balloon repositioned correctly within the stenosis using manipulations of the catheter, wire or sheath. Once the stent is expanded fully or the balloon has reached its maximum pressure, the balloon is deflated rapidly. Often, there is some waist or incomplete expansion of the stent with the first inflation of the balloon; however, with accurate prior sizing and posi- tioning, the stent will be centered on the lesion and fixed securely in the vessel. The deflated balloon is repositioned over the wire very slightly forward or backward and the inflation is repeated several times to achieve maximal expansion of the entire length of the stent with the particu- lar balloon. After implanting the stent securely in the area of stenosis and while the balloon is still within the stent, the stent position and fixation are confirmed with a repeat angiogram through the adjacent catheter. With the balloon still positioned within the stent, the balloon is reinflated at a low pressure. Then, simultaneously, as the balloon is being deflated slowly and with the balloon still within the stent, the long delivery sheath is re-advanced gently and gradually over the balloon and into the stent as the balloon deflates within the stent 10 . The inflated bal- loon within the stent centers the proximal shaft of the bal- loon catheter and the advancing edges of the tip of the sheath within the lumen of the stent. This “centering” keeps the edge of the distal end of the sheath from catching on the proximal end of the stent as the sheath is reintroduced into and through the stent. Often, as the sheath tip is pushed against the balloon and as the balloon is deflating, the balloon and the following tip of the sheath slide for- ward together and through the stent before the balloon deflates completely. This still accomplishes the goal of the sheath advancing completely through the stent without catching on, or dislodging, the stent. Once the sheath is in or completely through the stent, the balloon is deflated completely by applying negative pressure to the balloon lumen. When the balloon has been deflated completely, the negative pressure is released from the inflating syringe. The balloon is withdrawn over the wire and into the sheath with the balloon lumen on “neu- tral” pressure while the balloon catheter is rotated very slightly in the direction of the balloon folds (determined earlier while preparing the balloon), and it is withdrawn into the sheath. The release of the strong negative pressure “softens” the folds or “wings” on the deflated balloon. When the sheath can be repositioned and maintained in its position through the stent, the sheath allows the balloon to be withdrawn through the stent while the stent walls are “protected” completely by the sheath from any rough folds or “wings” on the deflated balloon as the balloon is withdrawn. With the long sheath through the stent, a catheter or a new, larger or different balloon can easily be advanced reliably and safely through, or into, the newly implanted stent without danger of dislodging the stent. This balloon-assisted procedure for re-entering the stent is extremely valuable in even the most straightforward [...]... balloon large enough to expand and fix the stent in the caudal inferior vena cava is advanced over the wire and into the loose, partially expanded stent The balloon is expanded at a very low pressure and just enough to fill and “trap” the partially expanded stent This usually results in the ends of the balloon expanding slightly larger than the stent and, in turn, “covering” or extending over the ends of the... cut and polished stents are no longer produced for any use The only current alternative for the “Ing” open-ring stent is to “handcut” the stents, which would leave the edges rough and not coated and, in turn, create some added unknowns for a clinical trial Hand cutting in order to individually produce the “open-ring” stents also increases the difficulty and consistency of preparing each stent, and certainly... for the advancing sheath as the true long dilator The biggest disadvantage to this technique, however, is that the “special tips” for the balloon catheters must be “hand-made” and “hand-mounted”, which requires some talent and considerable additional time on the part of the operator during each case “Sheath-within-a-sheath” technique for the delivery of stentsccombined front-loading and pre-positioned... “available” and “custom” sizes, and its availability with an expandable “covering”, the C-P™ stent has had some unique investigational and compassionate use applications throughout the world, including even in the US The most innovative of these uses is the “re-building” or “creation” of “internal venous tunnels” with very large, long and covered C-P™ stents for the “completion of the Fontan” in the catheterization. .. technique for stent delivery is a combination of the standard pre-positioned long sheath delivery and a front-loading delivery technique It is used in very extenuating circumstances where a large stent must be delivered through an extremely dilated heart or a very tortuous course within the heart, and particularly to lesions in the pulmonary arteries The “sheath-within-asheath” technique usually is not... balloon should always be positioned in and in ated within the original stent in order to “protect” the original stent and prevent its compression by an expanding balloon in an adjacent vessel Most stents which are compressed only partially and remain in place, can be treated by re-expansion with a balloon and the implant of an additional stent within the original stent The most significant potential late... requires at least two pairs of “knowledgeable” hands! It is impossible for a single catheterizing physician to advance the sheath while at the same time keeping the catheter and sheath fixed together as one unit and maintaining the wire securely in place The hands of the additional and knowledgeable operator or assistant maintain the wire in position and the sheath and catheter fixed together while the primary... other in place, each separate stent should be appropriate for the size of the separate branch vessel in which it is implanted and be capable of fixing securely into the walls of that vessel on its own Occasionally, one of the stents in a bifurcating or crossing situation can be implanted without in ating and expanding the second balloon and stent simultaneously However, access to the branching vessel, in. .. stents shrink in length as they expand and to allow for subsequent growth of the vessel in length P _ _ 8 stents shrink ~50% in length with expansion to their largest diameters The newer ITI™ stents (ev3, Plymouth, MN) shrink minimally in length when expanded sequentially and do not require as much overlap to allow for the initial shrinkage or for shrinkage later with further dilation When tandem stents... a partially in ated stent is fixed in the vessel and the vessel and stent are still stenotic, the initial implanting balloon is replaced with a high-pressure balloon to further expand the stent and vessel together Occasionally the sheath cannot be re-advanced into the stent even over the actively “deflating” balloon, and on withdrawal of the balloon through the stent, the balloon catches on, and begins . some talent and con- siderable additional time on the part of the operator dur- ing each case. “Sheath-within-a-sheath” technique for the delivery of stentsccombined front-loading and pre-positioned. without in ating and expanding the second balloon and stent simultaneously. However, access to the branching vessel, in which the stent is not being implanted (expanded) initially and simultan- eously,. the pediatric /congenital population. At the same time, the changes/improvements in the delivery/implant tech- niques for congenital heart patients were developed pre- dominately in pediatric/ congenital