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Principles of stenting and stent-grafting


Expandable stents are used to manage luminal narrowing in many systems from the aorta to the trachea. As with angioplasty, there is a common skill-set required for deployment, regardless of location but the indications and outcomes are very different so try to avoid a ‘have stent, will travel’ mentality. There is a simple basic concept regarding intent, which transcends most applications.

A procedure may be undertaken with the express intention of deploying a stent, so-called primary stenting , e.g. oesophageal stenting for tumour dysphagia and iliac artery occlusions (often primarily stented to reduce the incidence of distal embolization). Most angiographers will primarily stent ostial lesions of the visceral arteries without trying angioplasty because they really represent aortic disease, which will inevitably have elastic recoil.

A stent may be deployed to salvage an unsuccessful balloon dilatation procedure, e.g. recurrence of a benign stricture of the trachea. This secondary stenting is the commonest indication for using a stent in the vascular system, e.g. failed iliac angioplasty with residual pressure gradient, stenosis or flow-limiting dissection ( Table 33.1 ).

Table 33.1
Indications for arterial stenting
Indication Primary Secondary
Failed angioplasty ✗ ✓
Risk of embolization ✓ ✗
Iliac occlusion ✓ ✗
Ostial renal artery stenosis ✓ ✗
Restenosis ✓ ✗
Carotid artery ✓ ✗

Equipment

This is covered in more detail in the essential equipment section ( Chs 20 and 21 ). Choose the simplest stent which you think will do the job. Use pre-procedure imaging to gauge the size of stent you are likely to use (length and diameter) and make sure that you have a long enough delivery system.

Alarm

There are no prizes for selecting a stent just to find it will only reach part of the way to the target.

Key steps in stenting

Whether primary or secondary stenting you will have imaged the target, achieved access, crossed the lesion and have a sufficiently supportive guidewire in place.

Position the stent

This involves the same elements as positioning a balloon for angioplasty and these are summarized below:

  • Image to delineate and measure the lesion and mark the position either on the patient or on a reference monitor.

  • Remember: Do not move the patient, image intensifier or table after marking the lesion.

Alarm

If something moves, repeat the imaging to confirm position.

  • Advance the stent into position so that the relevant markers are centred across the lesion and image again to confirm correct placement. This is the time to be sure that you know the significance of each marker ( Fig. 33.1 ; See also Figs. 20.2 and 20.4 ).

    Fig. 33.1, Stent positioning and deployment in iliac stenosis.

  • Consider the implications of incorrect positioning, in particular the effects of covering vital vessels! If necessary, protect these with guidewires or balloons.

Troubleshooting

Stent will not cross the lesion

This is most likely to occur in long high lesions, particularly if the stent is following a tortuous path. In arteries calcified occlusions are particularly problematic. There are several possible solutions:

  • Make sure you have a stiff enough wire: this is usually the time to use an Amplatz wire or something of equivalent strength. When performing aortic stent-grafting use a Lunderquist or equivalent.

  • Pre-dilate the lesion: Angioplasty with a 3–4-mm balloon is usually sufficient for arterial stents but scale things up for the oesophagus.

  • Pass a sheath across the lesion: Sometimes the profile of the sheath and dilator is more favourable than the tip of the sheath catheter. The stent is subsequently introduced through the sheath and the sheath pulled back.

  • Try a different stent: This is most likely to help if you can exchange for a stent that has better trackability and pushability. A low-profile self-expanding stent is more likely to cross the lesion than a balloon-mounted stent.

  • If all of the above fail, consider a rendezvous procedure: Remember that if the guidewire is fixed in two places, you can apply considerable force, so proceed with great care.

The stent comes off the balloon

This is commoner with operator stents hand-crimped onto the balloon and is pretty rare now we have manufacturer-crimped stents. It often occurs incrementally and the situation can sometimes be salvaged if recognized early. When things do go wrong, try to keep the situation in perspective. Remember not to cause more harm than necessary. It is often best to summon a more senior colleague or obtain surgical help.

  • The stent moves proximal or distal to the balloon markers prior to deployment ( Fig. 33.2 ): Do not attempt deployment if either end of the stent has moved outside the balloon markers. If there has been significant stent movement, asymmetrical balloon inflation will push the stent off the balloon.

    Fig. 33.2, (A) High-grade calcified EIA stenosis prior to femoropopliteal grafting. (B) During deployment, the balloon has ‘been pushed out’ of the stent (arrows); note the stent has not moved and remains perfectly placed in relation to the origin of the IIA (arrowheads). In this case, the balloon was deflated and repositioned to deploy the remainder of the stent. (C) Completion.

  • If the whole stent remains on the balloon: Stay calm and slowly inflate the balloon with contrast, the ends of the balloon normally open first, leaving the stent in the middle in its compressed state. On fluoroscopy, this should resemble the shape of a dog bone. If this works it will usually help the stent to grip the balloon, allowing it to be positioned and deployed. If balloon expansion is asymmetric, stop and take stock.

  • The stent begins to migrate off the balloon: Things are taking a turn for the worse, deflate the balloon and gently try to recapture the stent. This is safest and most likely to succeed if the stent is held in the stenosis with the balloon being advanced into it. If you are in a vessel like the renal artery, take great care if you are pulling the balloon back as the stent is likely to be dislodged and come completely off the balloon catheter. As always, remember to keep the wire in position!

  • If repositioning is successful, slowly inflate the balloon. Deploy the stent as normal if it remains in position.

  • In you are not succeeding and the stent is partly covering the lesion, then it is probably best to deploy it where it is. If this is unsafe or impossible, then try to move the stent to a safe site for deployment, such as the iliac artery.

If the stent has come off the balloon and is missing in action

  • First, find the stent! Fortunately, it is usually on the catheter shaft or has stuck in the groin sheath. Some stents are poorly opaque and it may be necessary to take spot radiographs to locate them.

  • If the stent is on the catheter: pull the balloon back and if necessary slightly inflate it to withdraw the stent into the sheath, then remove the sheath and catheter and insert a new sheath (use one that you have prepared earlier). Consider a different type of stent but if you need to proceed with the same one make sure you crimp it on this time. If it is in the sheath, the same applies.

  • If the stent has come completely off the balloon catheter: with luck, it will still be on the wire. This is much harder! Pass a 4Fr straight catheter through the stent and exchange for a 0.018-inch wire. Try to capture the stent with a small-profile angioplasty balloon. Alternatively, pass a GooseNeck snare alongside the guidewire and snare the stent by lassoing the wire.

Deploying the stent

  • Take your time and use continuous fluoroscopy while deploying the stent and constantly maintain the position as you deploy.

  • Use an empty 20-mL syringe to completely deflate the balloon.

  • Screen during withdrawal of the delivery system to ensure that the stent is not dislodged.

  • Use angioplasty to ‘tailor’ the stent to the vessel wall. All stents, including self-expanding stents, need a balloon for complete deployment.

Troubleshooting

The stent starts to move off the target

If the stent is only partly open and not yet opposing the wall, it can sometimes be repositioned by gentle traction or pushing. Once the stent has engaged, there is usually little that can be done. You can try gentle traction but self-expanding stents tend just to deploy as you do this. If the lesion is only partly covered, you can deploy a second stent to treat the remainder of the lesion.

Completion imaging

This is the same as following angioplasty, check the treatment site and the run-off.

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