Treating acute limb ischaemia

Acute limb ischaemia describes a sudden reduction in perfusion of <3 days' duration. The ischaemia is usually due to thrombosis in native arteries or bypass grafts secondary to an underlying stenotic lesion. The severity of ischaemia is categorized using the Rutherford classification ( Table 47.1 ). Patients with rest pain without neuromuscular complications (Rutherford grade IIa) are the optimal candidates for thrombolysis in terms of time available to restore flow and risk–benefit ratio.

Table 47.1

Clinical categories of acute limb ischaemia

Modified from the Consensus Report on Thrombolysis. J Intern Med 1996; 240:343–355.

Category	Description	Capillary return	Muscle paralysis	Sensory loss	Doppler signal
Category	Description	Capillary return	Muscle paralysis	Sensory loss	Arterial	Venous
I Viable	Not immediately threatened	Intact	None	None	+	+
IIa Threatened	Salvageable, if promptly treated	Intact/slow	None	Partial	−	+
IIb Threatened	Salvageable, if immediately treated	Slow/absent	Partial	Partial	−	+
III Irreversible	Amputation regardless of treatment	Absent	Complete	Complete	−	−

The aim of thrombectomy and thrombolysis is to restore perfusion, and reveal the vascular anatomy by breaking down or extracting the blood clot. When the vessel has been cleared, an underlying lesion should be carefully looked for and treated or re-thrombosis is inevitable. The use of thrombolysis and thrombectomy in the management of dialysis access salvage and venous thrombosis (especially axillary vein and massive iliofemoral vein thrombosis) will be discussed elsewhere. The use of thrombolysis and thrombectomy in the specialist management of myocardial infarction and stroke is beyond the scope of this book.

Thrombolysis

This is the use of drugs to break up a blood clot by breaking down the fibrin holding the clot together. Acute thrombosis is particularly likely to clear, thrombolysis is not usually clinically indicated >6 weeks after the thrombotic event. Several agents are licenced for use in thrombolysis and there is no randomized evidence of clinical superiority for any of these. In practice, the majority of thrombolysis is undertaken with tissue-plasminogen activator (rt-PA).

Indications for treatment

Acute or acute-on-chronic critical limb ischaemia due to:

Acute native vessel thrombosis
Bypass graft thrombosis.

Thrombosed popliteal aneurysm:

the aim here is to clear the run-off vessels to allow bypass grafting.

Peri-procedural thrombolysis:

thrombosis may occur during interventional procedures and surgery. Acute thrombus is particularly likely to clear, and thrombolysis may salvage the procedure.

Contraindications

Thrombolysis is not without risk, particularly bleeding and CVA; the risk–benefit ratio is so unfavourable in some patients that thrombolysis is contraindicated.

Absolute contraindications:

Irreversible ischaemia (Rutherford class III)
Major trauma, surgery or cardiopulmonary resuscitation within the past 2 weeks
Stroke within the last 2 months, primary or secondary cerebral tumour. Risk of cerebral haemorrhage. Note: this does not apply to hyperacute cerebrovascular accident (CVA) where the intention is to restore cerebral perfusion
Active bleeding diathesis with the potential for major haemorrhage
Pregnancy.

Relative contraindications:

Age >80 years; these patients have the highest risk of stroke and haemorrhagic complications
The white limb (Rutherford class IIb) where urgent revascularization is required
Graft thrombosis within 4 weeks of surgery. Early graft failure is almost always due to a technical problem with the surgery, e.g. poor-quality vein, graft kinking.
Anticoagulation
Knitted Dacron grafts: these rely on deposition of thrombus to be impermeable; hence they become porous during thrombolysis and marked extravasation may occur.
Vein graft: the vein relies on perfusion for its viability, and after about 3 days, the vein is irreversibly damaged. However, the run-off may be cleared, allowing subsequent re-grafting. Recent thrombolysis with no underlying cause demonstrable. Re-thrombosis is very likely. Thrombolysis with streptokinase within the previous 5 years. This is only relevant if using streptokinase, as antibodies persist for many years and limit the effectiveness of the treatment, while increasing the risk of adverse reaction.
Cardiac emboli: thrombolysis may lead to further embolization.

Consent issues

It is essential to discuss the risks of haemorrhage requiring transfusion or surgery in up to 7% of patients and CVA due to haemorrhage or thrombosis in 1–3%. There is some evidence that the risks are lower in younger patients but this reduction has not been quantified.

Equipment

There are different techniques for performing thrombolysis, and the equipment varies according to the strategy being used:

Ultrasound to guide puncture
Mini access kit
Basic angiography set
Infusion catheters: a 4F straight catheter with sideholes is suitable in most cases
A pump suitable for arterial infusion
Co-axial systems or microcatheters may be helpful
Pulse spray techniques require special catheters and pumps.

Procedure

The key to thrombolysis is to establish the vascular anatomy; before starting, perform magnetic resonance angiography (MRA) or computed tomography angiography (CTA) to demonstrate the extent of the thrombosis, inflow anatomy and, with luck, the run-off vessels. Remember that you may need to obtain delayed images to see the distal circulation.

Tip

Avoid unpleasant surprises by clarifying what bypass grafts are in situ. Look for operation notes and talk to the patient and a senior surgeon.

Approach

As always, the shortest most direct approach is usually the best, as it affords the greatest scope for adjunctive intervention. In some cases, the best approach will involve direct puncture of a bypass graft. Table 47.2 provides suggestions but these are not set in stone and you should consider the pros and cons of each approach in the context of the individual patient. If possible, avoid the brachial approach, as there is a risk of peri-catheter thrombus embolizing to cause CVA.

Table 47.2

Guidelines for best arterial access

Site of occlusion	Optimal arterial access
Iliac artery	Ipsilateral CFA if patent, otherwise contralateral CFA
CFA	Contralateral CFA or exceptionally brachial
SFA, PFA or femoropopliteal graft	Ipsilateral CFA
Femoro-femoral cross-over	Direct graft puncture or inflow CFA
Axillo-femoral graft	Consider surgery

Arterial puncture:

At the risk of stating the obvious, try to make a single arterial puncture. Thrombolysis is sure to lead to bleeding from any extra puncture sites. This is a good time to use ultrasound to ensure safe arterial puncture. Use a mini access kit to keep the size of any unwanted holes to a minimum. Infra-inguinal grafts almost invariably arise from the anterior aspect of the common femoral artery (CFA). Arterial puncture must be sufficiently proximal to allow manipulation of a shaped catheter (Cobra or RDC) to direct a straight guidewire toward the graft origin.

Tip

To catheterize the graft origin, it is often helpful to obtain an angiogram in a steep oblique projection. Use roadmapping or fluoroscopy fade if these options are available.

Direct prosthetic graft puncture:

Ultrasound guidance is still the preferred option. When the graft is palpable, fix it between forefinger and thumb and then perform a single wall puncture in the conventional manner. There is a very distinctive give and fall in resistance as the needle enters the graft lumen. Depending on the direction of catheterization, direct graft puncture will preclude accessing either the origin or the outflow. Retrograde lysis often occurs but sometimes it is necessary to make a second puncture from the other end of the graft – the ‘crossed catheter technique’.

Techniques and regimens

There are several different techniques used for performing thrombolysis, none has been shown to be superior to any of the others. Accelerated regimens may restore flow more rapidly but at the price of increased complication rates.

All the techniques share a common principle; the thrombolytic agent is delivered directly into the thrombus and this requires the delivery catheter to be embedded in the thrombus. This is only possible if a guidewire can be passed through the thrombus. Failing this ‘guidewire traversal test’ indicates that the thrombus is organized and hence is much less likely to clear with thrombolysis.

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