Stenting : Τεχνική

Θεματική ενότητα: Stenting

Μ. Ματσάγκας, MD, PhD, FEBVSΣάββατο 1 Φεβρουαρίου

2014

Impact of Stents

Vascular stents have made it possible to reline a diseased artery

Stents have had a major impact on the development of endovascular surgery that is manifested in four ways

Impact of Stents

1. The complications of balloon angioplasty, such as dissection and residual stenosis, may be immediately treated

2. Lesions that otherwise would have required open surgery, such as occlusions or long lesions or recurrent stenoses, may be treated with endovascular surgery

3. The overall spectrum of arterial lesions that can be approached with endovascular techniques has broadened dramatically

4. Combining stents with graft material to create covered stents has permitted the endovascular treatment of more advanced disease

Impact of Stents

Each stent application has its own cost and complication risks

the sheath must usually be upsized

a foreign body is implanted

the procedure time is often extended somewhat

stents have their own unique complications

Impact of Stents

The cost of a single stent substantially increases the cost of an endovascular intervention

The placing of stents may be motivated by the wish to extend the short- or long-term success of

balloon angioplasty to avoid surgery to avoid repeat balloon angioplasty

But should be considered in each case !!

Impact of Stents

Future applications of stents may

include further miniaturization

the ability to release antithrombotic agents

emit irradiation

prevent intimal hyperplasia through bioengineering design changes

Type of Stents

Stents are either balloon-expandable or self-expanding

The Wallstent is a special flexible self-expanding, wire mesh tube

Type of Stents

The balloon-expandable stent design

This is a straight, metal, rigid, and balloon-expandable cylinder

The stent is premounted onto a standard angioplasty balloon

It is deployed when the balloon is inflated

Type of Stents


The rigid balloon-expandable stent has excellent hoop strength

but can be crimped by external forces

Type of Stents


Perform best when placed in locations that have no mobilityPerform best when they are relatively short in length since they are rigidShorten slightly as they expand in diameter

Most renal artery stents are between 1 and 2 cm, and most iliac stents are 3 to 4 cm

These are the places where balloon-expandable stents are most useful

Type of Stents

The self-expanding stent design

More commonly constructed of Nitinol, a nickel-titanium alloy

Have thermal memory and a high degree of contourability

Are packaged on their own delivery catheters

Are deployed by retracting the covering sheath

Type of Stents


Maintain continual outward radial force after deployment

Are not as susceptible to damage from external forces since they are more flexible

Have much less hoop strength

Type of Stents


are intentionally oversized at the time of deployment in the artery, usually by 2 to 3 mm

cover more distance

are more difficult to place with great accuracy

Type of Stents

Balloon-expandable

Self-expanding

Wallstent

Type of Stents

Type of Stents

Self-expanding and balloon-expandable stents tend to play complementary roles

Deciding which type of stent to use may be somewhat subjective from one practice to another

Endovascular specialists must become facile with the use of each of these two general stent types

In addition, there are numerous stents, both balloon- and self-expanding, that are available

Indications for Stents

Primary stent placement the operator knows ahead of time that a

stent will be placed

Selective stent placement the selective approach where the operator

must decide during the procedure


The concept of primary stent placement presupposes that the patient is better off with a stent, regardless of the results of treatment of the lesion with balloon angioplasty alone

Appears to work best for some lesions that were treated with balloon angioplasty alone in the past with marginal to mediocre results, including recurrent lesions, occlusions, orifice lesions, and others renal artery origin lesions carotid bifurcation aortoiliac occlusive disease


The idea behind primary stent placement is that the short- and/or long-term results are generally improved with stent placement to the point where it justifies the up-front increase in risk and cost

Taken to its fullest extent, however, every lesion in every patient would receive a stent, and this would be expensive and unnecessary

Indications for Stents Reasonable long-term results with balloon

angioplasty for many aortoiliac, infrainguinal, nonorifice renal lesions, and some upper extremity lesions

The concept of selective stenting. Balloon angioplasty is performed. The results are assessed. If the results are not acceptable, stent placement is performed residual stenosis persistent pressure gradient significant dissection


The temptation with stents is to continue to lay them in place until the entire arterial tree appears to be perfect

The “stack of stents” phenomenon should be avoided

Which Lesions Should Be Stented?

Although each specialist must decide

what the appropriate level of stent

placement aggressiveness is, there are

specific situations where stents are

useful, or even obligatory


Post-angioplasty dissection

Stent placement should be considered for any significant dissection after angioplasty, even if there is no gradient

Stents should be placed for any false channel or for any intimal flap that impede flow, increase in size during the procedure, or extend into a previously uninvolved segment of artery


Residual stenosis after angioplasty

The concept of preventing recurrence by eliminating residual stenosis makes empiric sense

A 30% postangioplasty stenosis is used as a general threshold for continued intervention


Pressure gradient

A pressure gradient (>10mm Hg systolic) after angioplasty usually indicates a residual stenosis or dissection that requires treatment

The threshold for treatment is somewhat arbitrary


Recurrent stenosis after angioplasty

Treating recurrence with stent

placement after previous angioplasty is

an empiric approach with reasonable

results


Occlusion

Balloon angioplasty alone for occlusions has only fair results and these may be improved with stent placement

Stent placement may make the procedure safer by stabilizing residual thrombus that could embolize from the lesion site, especially if covered stents were used

Stent placement in the treatment of iliac and superficial femoral artery occlusions is widely accepted


Embolizing lesion

Stent placement at the site of an embolizing lesion is thought to trap the embologenic plaque and prevent further embolization during intervention.

The use of covered stents could be considered in such cases

Placement Techniques

Balloon-Expandable Stents

Placement Techniques: Balloon-Expandable Stents

The selection of the diameter is an important decision in the placement of balloon-expandable stents

The stent size is selected based on the anticipated diameter of the reconstructed artery

If the selected stent is too small in diameter, it may not adhere to the vessel wall after deployment and could migrate

If the stent is too large, it will overstretch the artery and may cause rupture


If selective stent placement is performed, the inflated balloon profile from the initial angioplasty may be used to size the artery

When primary stent placement is performed, sometimes it is necessary to dilate the lesion with the balloon alone to size the lesion and to create enough space for the stent delivery catheter to be placed across the lesion


Balloon-expandable stents can be dilated a few millimeters larger than the intended specifications

But as the diameter increases, the length decreases

The shortest stent that covers the lesion (usually 1–4 cm) is placed

Longer balloon-expandable stents are available (up to almost 8 cm) but there are disadvantages to the rigidity of these stents over longer distances. They do not conform to any tortuosity or any change in vessel diameter along the length of the stent.


Most premounted ballon-expandable stents can be placed using a 6-Fr sheath

Larger vessel stents, such as that used for large iliacs up to 12mm are placed through larger sheaths


The general approach to balloon-expandable stent placement has been to pass the appropriate sheath and dilator combination through the lesion and proceed to stent placement

If the lesion has a residual lumen of less than the diameter of the sheath (for a 6 Fr sheath it is approximately 2.0mm and for a 7 Fr sheath it is about 2.3 mm), the lesion should be predilated or the sheath and dilator will dotter the lesion

The sheath must be of adequate length to pass from the skin entry site to near the lesion


The sheath is withdrawn, exposing the balloon and stent

Before deployment, it is important to make sure that the stent is still in the correct place on the balloon and that it is well positioned to cover the lesion

The balloon is then inflated to expand the stent

The stent should be slightly overdilated to embed its metal struts into the plaque


If there is a sense that the stent is loose in the lesion, either because it is under-dilated or because it migrated during deployment to an area that is slightly less narrow

Advance the tip of the sheath up to the expanded end of the stent and catch the edge of the stent and support it so that it cannot move

Re-advanced the balloon and over-dilate it


Many times after placement of a balloon-expandable stent, the balloon wings will stick a bit, perhaps getting caught under the tines of the stent

If this is the case, first try a more than a gentle pull

Do a super-aspiration, implosion level negative pressure on the balloon. Support the stent by advancing the sheath as described

Try rotating and/or advancing the balloon catheter before withdrawing it

Sometimes, re-inflating the balloon will loosen the balloon material


Precise stent deployment is challenging

The stent may be difficult to visualize in larger individuals, especially if it is in a location with a lot of ventilatory motion, such as the visceral and renal arteries

Bony landmarks may be useful, especially the vertebral bodies

If there are no suitable landmarks, use an external marker (adherent, radiopaque measuring tape). Be cautioned that external markers are susceptible to parallax error if the field of view is modified. They are also in error if there is any change in angle of view, or any significant ventilatory motion

Road mapping may also be used, but the roadmap image degrades with time and motion


Guidewire control must be maintained across the stent until the reconstruction is complete

If additional stents are required, the dilator is placed back through the sheath and advanced into the appropriate position

If numerous overlapping stents are required, the distal stent is placed first and built proximally to create a “telescope” effect

A balloon-expandable stent does not taper well but can be dilated to a slightly larger size on one end if necessary to match vessel size and taper (newer balloon-expandable stents that are constructed of lighter metal)


A completion arteriogram is performed by placing the tip of the sheath at the distal end of the stent and injecting contrast so that it refluxes through the area of stent placement

Another option is to place a 5-Fr straight catheter through the sheath, over the guidewire, and position the tip of the catheter at the location proximal to the stent

Placement Techniques

Self-Expanding Stents

Placement Techniques: Self-Expanding Stents

Self-expanding stents must be oversized by 1 to 3mm so that they exert continuous outward radial force at the site of deployment

These stents cannot be dilated beyond their maximum list diameter (if in doubt, go a little bigger)

The prepackaged stent delivery catheter is placed through a 6-9 Fr sheath, as recommended by the manufacturer

Self-expanding stents are manufactured in multiple lengths, from 20 to 120mm and beyond

They are generally simple to place, and they adapt to tortuosity, calcification, and ectopic atherosclerosis


The Wallstent is a closed cell structure having a relatively smooth outer surface without any “v” shaped stent joints extruding beyond the profile of the open or partially open stent

It’s length changes significantly at deployment depending upon the final resting diameter

The constrained length of the Wallstent (in the package) is longer than the deployed length (partially constrained by the artery), which in turn is longer than the stent would be if it were to be completely expanded (unconstrained)

The Wallstent in practice is never completely expanded, since it is oversized for the artery into which it is placed


The self-expanding stent delivery catheter is advanced over the guidewire without the need of a larger sheath

The stent is marked by radiopaque markers on its proximal and distal ends, which are observed using fluoroscopy

To deploy the stent, use the release mechanism, which removes the covering membrane so the proximal end of the stent begins to expand

Fluoroscopy is used because it is easy to move the stent with minimal force

A road map can be used to assist in placement


After stent deployment, the delivery catheter is removed and balloon angioplasty is performed of the length and ends of the stent, especially in sections where there is residual crimping of the stent by the lesion

It is sometimes difficult to assess whether the stent is fully expanded

The guidewire is maintained across the stented segment until after satisfactory completion studies are performed

Completion arteriography is performed in the same manner as with balloon-expanded stents

Placement Techniques: Self-Expanding Stents Are more likely to be used for lesions in conduit arteries

(e.g., iliac artery, superficial femoral artery) that may be longer and that have some degree of tortuosity (e.g., carotid artery, iliac artery)

Have the disadvantage that only the leading end of the stent, usually the end toward the tip of the catheter, can be placed with a high degree of accuracy

Somewhere in the course of deployment, but before that there is full engagement of the stent with the artery wall, the stent can be moved and position can be readjusted

Most self-expanding Nitinol stents can deploy about 15% to 20% of their length or 1 cm and still be possible to withdraw the whole stent to readjust position


The open cell stents contour well and they are able to go from a very small diameter to a large diameter over a very short longitudinal distance

This property is needed for the management of tortuous or tapered arteries

But it also creates rough edges where stent joints are under stress and protrude into the lumen

Built-up energy in the stent delivery catheter, when released, tends to make the stent pop forward a bit (toward the tip end) during deployment

What to consider when selecting a stent What are the length and diameter requirements

of the diseased segment?

What is the location of the lesion and what type of lesion is it?

Are there delivery restrictions posed by diseased access arteries, sheath size, vessel tortuosity, working room, or distance to the lesion?

Can the number of required stents be minimized?

Are the preferable stents in your inventory?

Which Stent for Which Lesion?

In general, orifice lesions and those that are heavily calcified are best treated with balloon-expandable stents

Lesions located in flexible, tortuous, and those with significant taper arteries, or that are more than several centimeters in length are usually treated with self-expanding stents


Short focal lesions may be treated with balloon-expandable stents

Placement is precise and the single stent is less expensive

Self-expanding stents are well suited to longer lesions (longer than 2–3 cm)

Placement of a single longer self-expanding stent is usually simpler, faster, and less expensive than placing multiple balloon-expandable stents


Precise, “kissing”, and side-to-side placement is possible with self-expanding stents but difficult

Self-expanding stents don’t have as much hoop strength, which is desirable for the aortic bifurcation and other orifice lesions

Distal iliac artery lesions that are close to the groin should be treated with self-expanding stents


Self-expanding stents are better for stenting in flexible arteries, such as the superficial femoral, popliteal, and distal subclavian arteries

Lesions in an aortic branch orifice, such as the proximal innominate, common carotid, subclavian, visceral, or renal arteries, are best treated with balloon-expandable stents. The combination of placement accuracy and hoop strength is better in this setting

How Do You Select the Best Stent for the Job?

There is substantial overlap in the capabilities of the various stents

Most specialists develop a short list of one or two favorites in each stent category, balloon-expandable and self-expanding

Plan ahead well enough so that specific items are anticipated and ordered

The distance to the lesion is an important variable

Having too many options is a good problem to have !!

Tricks of the Trade

Tapering a stent

Moving a self-expanding stent

Crossing a stent

Going naked: placement of a balloon-expandable stent without a sheath

Tapering a stent

The various self-expanding stents tend to taper naturally with diminishing distal arterial diameter

The Wallstent may be tapered by slightly overdilating the proximal end. The Wallstent shortens with expansion

The shorter, more rigid balloon-expandable stents can also be tapered, but to a lesser degree (1–2mm maximum). One end of the stent is selectively dilated using only the shoulder of the balloon

Tapering a stent

Moving a self-expanding stent Self-expanding stents can be withdrawn or pulled

back but not advanced forward after partial deployment

The entire deployment catheter apparatus must be withdrawn in a retracted position to move the stent

Moving the stent can be helpful in achieving very precise placement of its proximal end

It is not possible to move a stent after it has been fully deployed

Moving a self-expanding stent

Crossing a stent

Once a stent has been deployed, the guidewire position across the stent is not relinquished until the procedure is completed

If the guidewire position is lost, it is best to cross the stent using a J-tip guidewire. It is less likely to pass through the struts of the stent

The J-tip guidewire should be able to twirl and bob freely within the lumen of the stent

Crossing a stent

After the guidewire is across the stent, intraluminal position can be checked using a 5-Fr straight angiographic catheter passed over the guidewire. Any resistance as the catheter passes through the stent indicates a false passage


Placement of balloon-expandable stents was designed to be performed with a sheath

Sometimes, however, placement of the sheath into the desired location across the lesion is difficult, dangerous, or both, especially with highly tortuous approach arteries or when the sizable sheath hangs up on the lesion itself


One option is to use a short-access sheath. Advance the balloon and premounted stent over the guidewire and through the lesion without a sheath to protect them

If treating a critical stenosis, predilate the lesion so that the stent will pass through without being dislodged from the balloon

Stenting : Τεχνική

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