Arterial system

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Chapter 9 Arterial system

Methods of imaging the arterial system

1. Catheter angiography
2. Ultrasound (US)
3. Computed tomography (CT)
4. Magnetic resonance imaging (MRI)

Further reading

Collins R., Cranny G., Burch J., et al. A systematic review of duplex ultrasound, magnetic resonance angiography and computed tomography angiography for the diagnosis and assessment of symptomatic, lower limb peripheral arterial disease. Health Technol. Assess.. 2007;11(20):iii-iv. xi–xiii, 1–184

Kaufman J.A., Lee M.J., editors. Vascular and Interventional Radiology: The Requisites. Philadelphia: Elsevier-Mosby, 2004.

Introduction to Catheter Techniques

The basic technique of arterial catheterization is also applicable to veins.

Patient preparation

1. The patient will need admission to hospital. Careful preparation before the procedure and observation after are required. With the introduction of smaller diameter catheters, day case admission may be appropriate for routine peripheral angiography and some angioplasty cases.
2. If the patient is on anticoagulant treatment, blood clotting should be within an acceptable therapeutic ‘window’.
3. The radiologist or a suitably trained person should see the patient preferably several days prior to the procedure in order to:

a explain the procedure
b obtain informed consent
c assess the patient, with special reference to renal function, blood pressure and peripheral pulses as a baseline for post-arteriographic problems.

Puncture sites

1. Femoral artery – most frequently used
2. Brachial artery – a high approach is preferable
3. Axillary artery
4. Radial artery.

Equipment for the Seldinger technique

Needles

The technique of catheter insertion via double-wall needle puncture and guidewire is known as the Seldinger technique. The original Seldinger needle consisted of three parts:

1. An outer thin-walled blunt cannula
2. An inner needle
3. A stilette.

Many radiologists now prefer to use modified needles:

1. Double-wall puncture with a two-piece needle consisting of a bevelled central stilette and an outer tube
2. Single-wall puncture with a simple sharp needle (without a stilette) with a bore just wide enough to accommodate the guidewire.

Guidewires

Basic guidewires consist of two central cores of straight wire around which is a tightly wound coiled wire spring (Fig. 9.1). The ends are sealed with solder. One of the central core wires is secured at both ends – a safety feature in case of fracturing. The other is anchored in solder at one end, but terminates 5 cm from the other end, leaving a soft flexible tip. Some guidewires have a movable central core so the tip can be flexible or stiff. Others have a J-shaped tip which is useful for negotiating vessels with irregular walls. The size of the J-curve is denoted by its radius in mm. Guidewires are polyethylene coated but may be coated with a thin film of Teflon to reduce friction. Teflon, however, also increases the thrombogenicity, which can be countered by using heparin-bonded Teflon. The most common sizes are 0.035 and 0.038 inch diameter. A more recent development is hydrophilic guidewires. These frequently have a metal mandrel as their core. They are very slippery with excellent torque and are useful in negotiating narrow tortuous vessels. They require constant lubrication with saline.

image

Figure 9.1 Guidewire construction. (a) Fixed core, straight. (b) Movable core, straight. (c) Fixed core, J-curve.

Catheters

Most catheters are manufactured commercially, complete with end hole, side holes, preformed curves and Luer lock connection. They are made of polyurethane or polyethylene. Details of the specific catheter types are given with the appropriate technique.

Some straight catheters may be shaped by immersion in hot sterile water until they become malleable, forming the desired shape and then fixing the shape by cooling in cold sterile water. For the average adult a 100-cm catheter with a 145-cm guidewire is suitable for reaching the aortic branches from a femoral puncture.

The introduction of a catheter over a guidewire is facilitated by dilation of the track with a dilator (short length of graded diameter tubing). If the patient has a large amount of subcutaneous fat in the puncture area, catheter control will be better if it is manipulated through an introducer sheath. This is also indicated where it is anticipated that frequent catheter exchanges may be required.

Taps and connectors

These should have a large internal diameter that will not increase resistance to flow. Luer locks stop the tap detaching during high-pressure injections.

FEMORAL ARTERY PUNCTURE

This is the most frequently used puncture site providing access to the left ventricle, aorta and its branches and has the lowest complication rate of the peripheral sites.

Relative contraindications

1. Blood dyscrasias
2. Femoral artery aneurysm or pseudoaneurysm
3. Local soft-tissue infection
4. Severe hypertension
5. Ehlers–Danlos syndrome (due to the vessel wall being easily torn).

Technique (Fig. 9.2)

1. The patient lies supine on the X-ray table. Both femoral arteries are palpated and if pulsations are of similar strength the side opposite the symptomatic leg may be chosen. This leaves the symptomatic side untouched and free from groin puncture complications if future vascular surgery is undertaken. If all else is equal, then the right side is technically easier (for right-handed operators).
2. The appropriate catheter and guidewire are selected and their compatibility checked by passing the guidewire through the catheter and needle.
3. The location and point of puncture of the femoral artery must be considered. The external iliac artery arches anteriorly and laterally as it passes under the inguinal ligament and continues as the femoral artery. Attempts to puncture the artery cephalad to the ligament may result in a puncture deep in the pelvis at a point where haemostasis is difficult to secure by manual compression and where peri-catheter and post-procedure bleeding may be obscured by preferential passage of blood into the retroperitoneum. Brief preliminary fluoroscopy of the groin can identify the centre of the femoral head with the intention of puncturing the artery at this point. This increases the likelihood of hitting the common femoral artery and facilitates haemostasis post-procedure by allowing the artery to be compressed against bone. The inguinal skin fold does not reliably correlate with the position of the inguinal ligament. The entire common femoral artery lies above the skin fold in more than 75% of western European subjects.1 Direct US guidance is increasingly routinely used for vascular puncture.
4. Using aseptic technique, local anaesthetic is infiltrated either side of the artery down to the periosteum. A 3–5-mm stab incision is made over the artery to reduce binding of soft tissues on the catheter. In thin patients the artery may be very superficial and the skin may need to be pinched-up or deflected laterally, to avoid cutting the artery.
5. The artery is immobilized by placing the index and middle fingers of the left hand on either side of the artery, and the needle is held in the right hand. The needle is advanced through the soft tissues until transmitted pulsations are felt. Both walls of the artery are punctured through-and-through (single-wall puncture increases the risk of intimal dissection). The stilette is removed, and the needle hub is depressed so that it runs more parallel to the skin and is then withdrawn until pulsatile blood flow indicates a satisfactory puncture. Poor flow may be due to:

a the end of the needle lying in or against the vessel wall or within plaque
b aorto-iliac stenosis giving low femoral artery pressure
c hypotension – due to vasovagal reaction during the puncture
d femoral vein puncture.

6. When good flow is obtained the guidewire is introduced through the needle and advanced gently along the artery using intermittent fluoroscopy to avoid engaging the vessel wall. When the wire is in the descending thoracic aorta the needle is withdrawn over the guidewire, keeping firm pressure on the puncture site to reduce bleeding. The free portion of guidewire is then wiped clean with a wet sponge and the catheter threaded over it. For 5-F or greater diameter catheters, particularly those which are curved, a dilator is recommended matched to catheter size. The catheter is advanced up the descending aorta, under fluoroscopic control, and when in a satisfactory position the guidewire is withdrawn.
7. Catheter patency can be maintained by continuous flushing from a pressurized bag of heparinized saline (2500 units in 500 ml of 0.9% saline) attached through a three-way tap, or by intermittent manual flushing throughout the procedure. Flushing should be done rapidly otherwise the more distal catheter holes will remain unflushed.
8. At the end of the procedure the catheter is withdrawn and manual compression of the puncture site should be maintained for 5–10 min.
image

Figure 9.2 Seldinger technique. (a) Both walls of vessel punctured. (b) Stilette removed. Needle withdrawn so that bevel is within the lumen of the vessel and blood flows from the hub. (c) Guidewire inserted through needle. (d) Needle withdrawn, leaving guidewire in situ. (e) Catheter threaded over wire. (f) Guidewire withdrawn.

Aftercare

1. Bed rest – typically for 4 h, but longer at the discretion of the operator. Larger catheters, antiplatelet therapy and anticoagulation require longer observation
2. Careful observation of the puncture site for hemorrhage
3. Pulse and blood pressure observation, e.g. half-hourly for 4 h and then 4-hourly for the remainder of 24 h, if the larger catheter systems are used.

Reference

1 Lechner G., Jantsch H., Waneck R., et al. The relationship between the common femoral artery, the inguinal crease, and the inguinal ligament: a guide to accurate angiographic puncture. Cardiovasc. Intervent. Radiol.. 1988;11:165-169.

High Brachial Artery Puncture

Indications

As for femoral artery puncture, but as this approach is associated with a higher incidence of complications, it should only be used if femoral artery puncture is not possible.

Contraindications

1. Atherosclerosis of the axillary or subclavian arteries
2. Subclavian artery aneurysm.

Technique

1. The patient lies on the X-ray table with his arm in supination. The peripheral pulses are palpated and the brachial artery localized approximately 10 cm above the elbow.
2. A small incision is made in the skin, 1–2 cm distal to the selected point of arterial puncture.
3. A single-wall puncture needle is used, with an acute angle of entry into the artery.
4. A straight, soft-tipped guidewire is introduced when good pulsatile flow is obtained.
5. A 5-F pigtail catheter is introduced over the guidewire and its pigtail formed in the aorta.
6. At the end of the procedure the catheter tip is straightened using the guidewire and then removed. This reduces the risk of intimal damage and flap formation during withdrawal of the catheter.

AXILLARY ARTERY PUNCTURE

Indications

As for femoral artery puncture, but this approach is associated with a higher incidence of complications than femoral or high brachial artery puncture and should only be used if these techniques are not possible.

Contraindications

1. Atherosclerosis of the axillary or subclavian arteries
2. Subclavian artery aneurysm.

Technique

1. The patient lies supine on the X-ray table with his arm fully abducted. The puncture point is just distal to the axillary fold. It is infiltrated with local anaesthetic.
2. A small incision is made in the skin 1–2 cm distal to the point of the arterial puncture.
3. The needle is directed more horizontally than the femoral approach and along the line of the humerus.
4. Following satisfactory puncture the remainder of the technique is as for femoral artery catheterization.

GENERAL COMPLICATIONS OF CATHETER TECHNIQUES

Due to the anaesthetic

See Chapter 18.

Due to the contrast medium

See Chapter 2.

Due to the technique

Diagnostic angiography is an invasive procedure and complications are expected. The majority of these are minor, e.g. groin haematoma. Recommended upper limits for complication rates have been produced by the Society of Cardiovascular and Interventional Radiology (SCVIR):1 these rates are included in the following discussion.

Local

The most frequent complications occur at the puncture site. Complication rate is lowest with a femoral puncture site:

1. Haemorrhage/haematoma – the commonest complication. Small haematomas occur in up to 20% of examinations and large haematomas in up to 4%. The SCVIR threshold for haematomas requiring transfusion, surgery or delayed discharge after diagnostic angiography is 0.5%. Haematoma formation is greater with larger catheters, more frequent catheter exchanges and heparin, antiplatelet or thrombolytic agents. Haematoma formation is also greater when the femoral artery is punctured high because of inadequate compression of the artery following catheter removal.
2. Arterial thrombus may be due to:

a stripping of thrombus from the catheter wall as it is withdrawn
b trauma to the vessel wall.
Factors implicated in increased thrombus formation are:
a large catheters
b excessive time in the artery
c many catheter changes
d inexperience of the radiologist
e polyurethane catheters, because of their rough surface.
The incidence is decreased by the use of:
a heparin-bonded catheters
b heparin-bonded guidewires
c flushing with heparinized saline.

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