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Principles of angioplasty


Angioplasty and stenting are cornerstone techniques in interventional radiology and have widespread non-vascular and vascular applications. The key skills and equipment choices remain largely the same, regardless of the site.

The main indication for angioplasty is the treatment of atherosclerotic plaque. Concentric plaque splits during balloon angioplasty and the intima and media stretch and tear ( Fig. 32.1 ). When there is eccentric plaque, the tears occur at the interface between the plaque and the adjacent normal artery ( Fig. 32.2 ). This often causes deep clefts and rarely results in distal embolization of part or all of the plaque. Balloon dilation stimulates nerve fibres in the adventitia, causing discomfort. Severe pain usually indicates that the vessel is being excessively dilated and at risk of rupture. Luminal gain occurs because progressive dilation irreversibly stretches the adventitia. Over a period of weeks, the damaged intima undergoes a period of ‘remodelling’. This involves neointimal hyperplasia, which restores the smooth intimal surface. In non-vascular systems, the mechanism of plaque disruption triggering remodelling does not apply and balloon dilatation is usually used only to pre-dilate prior to stent placement

Fig. 32.1
Angioplasty of concentric plaque.
(A) Balloon ‘waisting’ in stenosis before plaque rupture. (B) Balloon dilation – the plaque is ruptured but the plaque volume unchanged. (C) Balloon deflation – the luminal area is increased because of stretching of the media/adventitia and intimal clefts.

Fig. 32.2
Angioplasty of eccentric plaques.
(A) Balloon ‘waisting’ in stenosis before plaque rupture. (B) Plaque has ruptured at its thinnest point – eccentric media/adventitia stretching. (C) Post-angioplasty dissection flaps in eccentric lumen. Plaque volume is unchanged.

Fig. 32.3
Burst angioplasty balloons.
(A) ‘Pin-hole’ tear: common and of no significance. (B) ‘Longitudinal’ tear: rare, but seldom a problem. (C) ‘Circumferential’ tear: very rare, but serious, as balloon will impact in sheath when it is withdrawn.

Equipment

This is covered in more detail in the essential equipment section ( Ch. 18 ). Choose the simplest balloon which you think will do the job, this is usually the workhorse over the wire device. To achieve an effective dilatation in the vascular system, use a balloon roughly 1 mm greater in diameter than the reference lumen diameter. Remember not to measure at a point where the lumen is dilated, e.g. beyond a tight arterial stenosis.

Key steps

By the time you are reaching for an angioplasty balloon you will already have established access and assessed the lesion, prior to navigating a passage across it. Remember the purpose of the guidewire now changes from steering to support. It is generally safest to exchange a hydrophilic guidewire for a conventional J-wire before trying to introduce a balloon. If you are performing vascular angioplasty you will normally give heparin before balloon dilatation.

Step 1: Position the balloon

  • Image to delineate the lesion and store an image on the reference monitor, noting any key landmarks. Techniques which allow the live fluoroscopic image to be superimposed on a reference image are particularly useful for positioning.

  • Failing this, inject some contrast and position some long sponge forceps over the midpoint of the lesion, then either apply a metallic marker, e.g. a towel clip on the drape or use a chinagraph pencil to mark the position on the screen. Confirm this is in the correct position with another contrast injection.

  • Remember: Do not move the table after marking the lesion.

  • Advance the balloon until the markers are centred on the target lesion.

  • Fix the balloon and wire in position, paying attention to key landmarks.

Troubleshooting

Balloon will not cross the lesion

This is particularly likely if the balloon has already been inflated. In this case, reach for a fresh balloon and try again. If this fails, pass a low-profile catheter across the lesion and exchange for a stiffer wire and try again. Still no luck – replace the low-profile catheter and place a supportive 0.018-inch wire; a low-profile over the wire balloon will almost always get through. Note that monorail systems are less likely to cross the lesion unless used with a guiding catheter, as the shaft is not supported. You can either pre-dilate or you may have the option of a low-profile balloon of the target size, in which case proceed directly to angioplasty.

Step 2: Inflate the balloon

  • Ask your assistant to slowly inflate the balloon using an inflation device (you are busy with the balloon and wire).

  • Fluoroscope throughout balloon inflation using the lowest-dose fluoroscopy, which allows you to see the balloon clearly.

  • Make sure that the balloon does not migrate forwards or backwards as it inflates; this is particularly likely in short high-grade fibrotic lesions.

  • Look for the waist at the site of the stenosis; the idea is to inflate until the waist disappears.

  • If you are controlling the inflation (your assistant is holding the balloon and wire), regularly check the pressure gauge to ensure that you do not exceed the recommended balloon burst pressures.

Alarm

Do not try this at home. Inflating an angioplasty balloon with saline and air until it bursts makes an impressive bang, and gives an idea of the damage it could cause in a blood vessel.

  • Decide how long to leave the balloon inflated, the duration of inflation varies from operator to operator (depending on their attention span) and between lesions. There is no real science here but you will not go far wrong using the following principles:

    • For a stenosis, inflate for 1 min.

    • For a resistant stenosis, keep topping up the balloon to sustain the inflation pressure until the stenosis yields or you give in and get a cutting balloon.

    • For an occlusion, allow 2–3 min.

    • For a dissection flap, allow 3–5 min at low pressure.

Troubleshooting

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