Arterial
stenosis or occlusion
Cause
and effect
Arterial stenosis or occlusion is
commonly caused by atherosclerosis, but can occur acutely as a result of
emboli or trauma. Stenosis or occlusion produces symptoms related to the organ
which is supplied by the artery: e.g. lower limb — claudication, rest pain and
gangrene; brain — transient ischaemic attacks and hemiplegia; myocardium —
angina and myocardial infarction; kidney — hypertension or infarction (Fig.
15.1); intestine —abdominal pain and infarction. The
severity of the symptoms is related to the size of the vessel occluded and the
alternative routes (collaterals)1 available (Fig. 15.2).
•
•
is not present on taking the first step (contrast osteoarthrosis, Chapter
26);
•
is relieved by standing still (contrast lumbar intervertebral disc nerve
compression, Chapter 33).
The
distance walked is called the claudication distance. It is a very subjective
distance which varies only slightly from day to day in the same patient. It is
altered by walking up hill or
The
pain of claudication is most commonly felt in the calf, but can affect the thigh
or buttock. Pain in the buttock occurring on exercise (walking) and associated
sexual impotence, which result from arterial ischaemia, are given the eponymous
title ‘Leriche syndrome’. Claudication less commonly occurs in the upper
limb in subclavian, axillary or brachial artery obstruction, the pain being
brought on by such activities as writing or manual labour.
Rest pain is severe pain felt in the foot at rest, made worse by lying
down or elevation of the foot. Characteristically, the pain is worse at night;
it may be somewhat relieved by hanging the foot out of bed or by sleeping in a
chair. Night cramps, which are short, severe muscle cramps of unknown origin,
should not be confused with rest pain.
Ulceration
and gangrene
Ulceration occurs with severe arterial insufficiency and often presents
as a painful, superficial erosion between toes. Alternatively, small, shallow,
indolent nonhealing ulcers may occur on the dorsum of the feet, on the shins and
especially around the malleoli. The blackened mummified skin and
Temperature
Harvey’s
sign
If the two index fingers are placed firmly side by side on a vein and
the finger nearer the heart is moved so as to empty a short length of vein, the
release of the distal finger will allow the speed of venous refilling to be
observed. Increased venous return and varicosities of veins are associated with
arteriovenous fistulas.
Impotence from failure to achieve an erection is often a feature in male
patients with an occlusion in the region of the bifurcation of the aorta and the
internal iliac arteries (Leriche’s syndrome).
Relationship
of clinical findings to the site of disease
By associating the symptoms and signs found in a case of arterial
disease, the site of the major arterial obstruction can be determined (Table 15.1).
Double
blocks
The presence of another (secondary) obstruction can usually be inferred.
For example, a patient with signs of iliac artery obstruction, but with rest
pain and pregangrene of the foot, must have a secondary obstruction as
collateral circulation around an isolated iliac artery obstruction is usually
excellent. The severe symptoms indicate a secondary obstruction, probably in the
femoral or popliteal arteries.
Many patients with symptoms due to arterial disease without stenosis or
occlusion do not need active treatment. This decision can often be made without
submitting the patient to a series of special investigations. Active treatment
includes angioplasty and surgical reconstruction.
General
Patients with arterial disease tend to be elderly and atherosclerosis is
a generalised disease. If surgery is indicated, a full assessment is essential.
Investigations
Investigations relevant to diabetes, abnormalities of lipid metabolism,
anaemia, conditions causing high blood viscosity, e.g. polycythaemia and
thrombocythaemia (in small-vessel disease), include a full blood count
(including erythrocyte sedimentation rate and platelets), plasma fibrinogen,
protein
This is an
isotope technique measuring left ventricular ejection fraction which correlates
well with cardiac function.
Doppler ultrasound blood flow detection (Fig 15.7 and
Fig 15.8)
A
continuous wave ultrasound signal is beamed at an artery and the reflected beam
picked up by a receiver. The change in frequency in the reflected beam compared
with that of the transmitted beam is due to the Doppler shift, resulting from
the reflection of the beam by moving blood cells. The frequency change may be
converted into an audio signal and, in arteries, a pulsatile sound typically
results. Doppler ultrasound equipment can, therefore, be used as a very
sensitive type of stethoscope in conjunction with a sphygmomanometer to assess
the systolic pressure in relatively small vessels. This is often possible even
at sites where the arterial pulse cannot be palpated.
The
ankle:brachial pressure index (ABPI) is the ratio of systolic pressure at the
ankle to that in the arm. Generally, the higher of the recordings of pressure in
the dorsalis pedis and posterior tibial arteries serves as the numerator, with
the higher systolic pressure between the brachials serving as the denominator.
The resting ABPI is normally about 1.0; values below 0.9 indicate some degree of
arterial obstruction. A value of less than 0.3 suggests imminent necrosis. It
must be appreciated, however, that values approaching normality at rest may
still be associated with intermittent claudication. Retesting after exercise is
useful in this context: in normality ABPI will rise while occlusive disease may
result in a depression of ABPI.
A
Doppler ultrasound probe can also be used to assess differences in arterial
blood pressure between segments of a limb, thereby giving an indication of the
site of a stenosis. In the leg, the cuff is commonly placed above the ankle, at
midcalf and midthigh, to provide ‘segmental pressures’. Artifacts are due
especially to calcified arteries, which may be incompressible and lead to a
falsely high limb pressure or ABPI result. This is particularly the case in
diabetics.
Duplex
imaging
second
type of ultrasound, namely Doppler ultrasound, is then used to insonate the
imaged vessels and the Doppler shift obtained is analysed by a dedicated
computer in the duplex scanner. Such shifts can give detailed knowledge of
vessel blood flow turbulence, etc. Some scanners have the added sophistication
of colour coding which allows visualisation of blood flow on the image. The
various colours indicate change in direction and velocity of flow; points of
high flow generally indicate a stenosis. It should be appreciated that modern
duplex scanning is at least as accurate as angiography in certain circumstances.
In terms of cost-effectiveness and safety, duplex scanning is generally to be
preferred to angiography if they are considered to be equally useful in any
given clinical context.
Plethysmography
Oculoplethysmography
Oculoplethysmography
(OPG) uses fluid- or air-filled cups attached to the eye by suction to
investigate carotid artery disease. Once again, the technique has largely been
superseded by duplex scanning.
Treadmill
A
treadmill with a slight incline is a useful diagnostic apparatus in the
assessment of walking distance in claudicants. Patients are known to be very
poor assessors of walking ability in terms of distance; objective measurement
using the treadmill is recommended.
Arteriography
involves the injection of a radio-opaque solution into the arterial tree,
generally by a retrograde percutaneous method usually involving the femoral
(occasionally the brachial or axillary) artery. This retrograde method is
known as the Seldinger technique (Fig 15.11 and Fig
15.12). Direct
arteriography, by puncturing, for example, the carotid artery or aorta, is more
hazardous; it is outdated and no longer in use. Hazards include thrombosis,
arterial dissection, haematoma, neurological dysfunction and anaphylaxis.
Anaphylactic reactions can occur even with a trial injection and informed
consent should always be obtained for this form of imaging.
Digital
subtraction angiography (DSA)
The latter avoids
the need for arterial puncture completely, although rather high volumes of
contrast agent must be injected into a large vein.
Management
of arterial stenosis or occlusion
Explanation
and advice
Patients
are worried by the presence of pain on walking. Once told that walking is not
doing harm, many are content to live within the limitations imposed by their
claudication. Spontaneous improvement occurs in some patients over the first 6
months after an occlusive episode as collateral vessels are developed.
Adjustment of lifestyle
Adjustments
to everyday habits of transport can increase mobility within the claudication
distance, e.g. the use of a bicycle or a car.
Stopping smoking
Particularly
for patients with Buerger’s disease (see later in this chapter). Progression
of the disease and graft failure after surgery are more common in any patient
who continues to smoke.
Taking
regular exercise
To reduce
weight in the obese and, more specifically, in the treatment of hyperlipidaemia.
•
Trental (oxpentifylline) has some effect on whole blood viscosity.
•
Prostacyclin is currently being evaluated and may have a role in the
management of the critically ischaemic limb.
The first
line of treatment is dietary to reduce weight (if necessary) and to reduce fat
intake. Patients who have no primary metabolic disease and who achieve an ideal
weight but remain lipaemic should be considered for drug treatment.
Diabetes
and hypertension
These
should be treated by standard methods. In hypertension, the overzealous
reduction of blood pressure by the use of beta-adrenoceptor blocking drugs can
worsen claudication.
Care of the feet
This
includes avoiding socks with holes and amateur chiropody, which can spark off
gangrene in the toes and heels, particularly in diabetic patients.
Heel raise
Claudication
distance may be increased by raising the heels of shoes by 1 cm. The work of the
calf muscles is reduced thereby.
Rest pain
can be relieved to some extent in some patients by the use of analgesics and
elevation of the head of the bed (Buerger’s position).
Aspirin
In
dispersible form this may be prescribed for its anti-adhesive effect on
platelets. A dose of 150 mg/day is usual.
Sympathectomy
Sympathectomy
is not effective in claudication but occasionally it may relieve ischaemic rest
pain and ulceration. However, it must be recognised that the results of
sympathectomy are very much poorer than those of bypass surgery or percutaneous
transluminal angioplasty. Sympathectomy can only be justified when it is not
technically possible to operate or employ balloon angioplasty. The details of
lumbar sympathectomy (operative and chemical) are given at the end of this
chapter.
Transluminal angioplasty (Fig 15.14 and
Fig 15.15)
Arterial
occlusive disease may be treated by inserting a balloon catheter into an artery
and inflating it within a narrowed area. This may be done
Technique.
A femoral arteriogram is performed and a guidewire inserted through any stenosis
to be treated. The balloon catheter is then inserted over the guidewire. The
balloon is positioned within the stenosis (confirmed by angiography). The
balloon is then inflated for approximately 1 minute and then deflated. This is
repeated before withdrawal of the catheter.
Atherectomy
A variety
of new devices is available to allow the percutaneous removal of atheroma from
within the vessel in the radiology department. These cutting catheters have
several styles and their use in certain circumstances, e.g. eccentric plaque,
may be efficacious.
lntraluminal stents (Fig 15.18 and
Fig 15.19)
In certain
circumstances after balloon dilatation, the vessel fails to stay adequately
dilated and it may then be possible to hold the lumen open using a metal stent.
Such a device may be introduced on a balloon catheter; the balloon itself when
inflated expanding the stent, which acts as a rigid skeleton for the vessel,
keeping it widely patent. The catheter balloon is deflated and the catheter
removed. An alternative type of self-expanding stent is held compressed by a
sheath of plastic in a delivery system. When the stent has been positioned at
the appropriate arterial site the sheath is withdrawn and the stent self-expands
to hold the lumen open. The results of stenting have not been fully assessed but
early results suggest that the technique has considerable promise.
Operations
for arterial stenosis or occlusion
Site
of disease and type of operation
Aortoiliac
occlusion with good calibre vessels below the site of disease responds well to
aortofemoral bypass (Fig. 15.20a). If the disease is limited in extent, an iliac
endarterectomy might be considered, but PTA with or without a stent is probably
a better alternative if technically possible. In the patient who is unable to
withstand major abdominal surgery and who has pronounced ischaemia due to
aortoiliac occlusion, a femoro—femoral or ilio—femoral crossover bypass may
be considered (if only one iliac system is involved with disease) or an axillo—bifemoral
bypass may be done (if both iliac segments are diseased).
Superficial
femoral and profunda femoris artery occlusive disease often produce unilateral
symptoms. For long-distance claudication, conservative treatment is usually
suitable. For more severe disease a supervised exercise programme may be
appropriate. In certain circumstances, when the occlusive appearance on
angiography is favourable and the patient fully understands the risks and
benefits of intervention, angioplasty or bypass may be considered. A
femoropopliteal bypass graft (Fig. 15.20b) is the most usual operation (to
overcome a blocked superficial femoral artery). Long-term graft patency is
related to the inflow and outflow from the graft. It is also related to the
material used for the bypass. The patient’s own saphenous vein gives the best
results when used either as a reversed conduit or in situ after valve
disruption. In some patients a profunda femoris origin stenosis is noted and
this situation can be helped by a small patch angioplasty to relieve the
diseased site.
Occlusive disease
below the popliteal artery used to be
widely regarded as unreconstructable but it is increasingly
recognised that bypass to the tibial vessels, even down to ankle level, can be
met with reasonable success. The most usual and successful conduit is the long
saphenous vein used in the in situ fashion after disrupting the valves
with a valvulotome. If the saphenous vein is not available from either leg, it
may still be realistic to carry out the surgery with a polytetrafluoroethylene (PTFE)
graft; many surgeons construct the lower anastomosis using a small collar of
vein between the PTFE and the recipient artery. This technique (Miller cuff) may
give prolonged patency.
Prosthetic materials
For bypass
of the aortoiliac segment the favoured material is Dacron (Fig.
15.21a).
Prostheses come in two types: woven and knitted. Woven grafts tend to leak less
when first exposed to blood flow during surgery, but newer knitted prostheses
may be sealed with gelatin or collagen by the manufacturer and may leak even
less than their woven counterparts. In the final analysis, there is probably
little to choose between any of the styles of Dacron graft; all achieve
satisfactory results. For bypass in the femoropopliteal region, if autogenous
long saphenous vein (or other veins such as the short saphenous or arm vein) is
not available, PTFE (Fig. 15.21b) or glutaraldehyde-tanned,
Dacron-supported, human umbilical vein (Fig. 15.21c) may be employed. In
general, any vein used requires a diameter of at least 3.5mm. For
profundaplasty, a small piece of vein may be used or, alternatively, PTFE or
Dacron.
Suture
materials for vascular surgery are usually monofilament in nature; polypropylene
has been particularly popular. In the aorta it is
usual
to use 2/0 or 3/0 polypropylene. In the femoral artery at the groin it is usual
to use 4/0 or 5/0 polypropylene. Finer sutures, up to 7/0, may be needed
further down the limb. PTFE may (alternatively) be stitched using a suture of
the same material. PTFE sutures tend to cause less bleeding through stitch holes
in the graft substance.
Operative
details
Aortofemoral
bypass graft. The aorta is approached through a midline or transverse abdominal
incision. The common femoral arteries and their branches are exposed through
vertical groin incisions. The small bowel is retracted to the right and the
posterior peritoneum opened. Retroperitoneal tunnels are made from the aorta to
the groins. Heparin (5000 units) is given intravenously and the vessels are
clamped. A vertical incision is made in the anterior aspect of the aorta to
which an obliquely cut, bifurcated Dacron graft is sutured. The graft limbs are
then fed down to the groins where they are in turn anastomosed to the common
femoral arteries or, if there is evidence of profunda stenosis, to an
arteriotomy running from the common femoral vessel down into the profunda. The
posterior peritoneum is closed carefully over the Dacron to prevent adhesion of
the graft to bowel. The abdomen and groin wounds are closed without drainage.
Femoropopliteal bypass. The popliteal artery above
or below the knee is exposed through a medial incision. The femoral artery is
exposed at groin level. The long saphenous vein may be treated in two different
ways. First, it may be excised, its tributaries tied, reversed and sutured into
the limb as a bypass. Second, it may be left in place (in situ) and the
valves disrupted with a valvulotome, either blindly or using an angioscope. The
graft is then sutured to the femoral artery proximally and to the popliteal
vessel distally. Suction drains are rarely necessary.
Femorodistal
bypass. This surgery is usually carried out using long saphenous vein in
the in situ mode. Great care must be taken at the conclusion of the
procedure to assess the conduit and the lower anastomosis. This may be done
using completion angiography or angioscopy (Fig 15.22 and
Fig 15.23).
Profundaplasty.
The common femoral artery and its branches are exposed through a
vertical incision. After giving intravenous heparin and clamping the vessels, an
incision is made into the common femoral artery and carried down into the
profunda, effectively dividing the stenotic profunda origin. The arteriotomy is
then closed with a vein, Dacron or PTFE patch to widen the narrowed segment.
Other
arterial operations and salvage procedures
Femorofemoral
crossover graft is useful for relieving an iliac artery occlusion when the other
iliac artery is patent with a strong femoral pulse. An 8-mm Dacron or PTFE graft
is tunnelled subcutaneously above the pubis and anastomosed end-to-side to the
common femoral arteries on each side. Blood from the patent iliac system is then
carried through this graft to vascularise the ischaemic limb.
Axillofemoral
graft is useful for salvaging a pregangrenous limb in a poor-risk patient with
bilateral iliac obstruction. A long 8-mm PTFE graft is tunnelled subcutaneously,
from an end-to-side anastomosis with the axillary artery proximally, to reach
the femoral artery of the involved limb in the groin where the distal
anastomosis is made. The axillary artery will carry a sufficient volume of blood
to maintain the circulation in the arm and revascularise the lower limb. The
short-term results are usually good and in these patients with their poor
general condition, the poorer, long-term result is usually less important. An
axillobifemoral bypass carries twice as much bloodflow through its long limb as
does an axillo(uni)femoral bypass; the former has a correspondingly improved
patency rate. Salvage operations should not be performed for intermittent
claudication alone. Gangrene and loss of limb may result if the operation should
fail.
Adjuncts
to direct arterial surgery. Blood-flow estimations (by Doppler
ultrasonography or electromagnetic flowmeter) or on-table arteriography at the
completion of the operation are useful techniques for ensuring that there have
been no errors of surgical technique before the wound is closed.
Results
of operation
The
long-term results of aortoiliac reconstructive surgery are good; they are
usually only marred by progressive disease producing femoropopliteal occlusions
at a later date. Femoropopliteal surgery is less successful. The immediate
postoperative success rate for vein bypass exceeds 90 per cent but many cases
fail in the first 18 months after operation and, at the end of 5 years,
the success rate is usually only between 50 and 60 per cent. The results of
femoropopliteal endarterectomy are less good in both the short and long term.
Dacron or PTFE bypass also gives a poorer result than vein, with 5-year success
rates of less than 50 per cent. The rather poor long-term results of
femoropopliteal surgery emphasise that these operations should only be used for
clear indications.
Carotid
stenosis may cause transient ischaemic attacks (TIAs). These are recurrent and,
by definition, short-lived mini-strokes. Resolution
Carotid
atheroma classically affects the internal carotid artery origin (Fig.
15.24).
The usual procedure is a carotid endarterectomy which involves clamping the
vessels, an arteriotomy in the common carotid artery continued up into the
internal carotid artery through the diseased segment, removal of the occlusive
disease (endarterectomy) and closure of the arteriotomy, often with a patch
(vein, PTFE or Dacron). During clamping, some patients will have inadequate
cerebral blood flow (especially if the contralateral carotid vessels are
compromised). Such a situation may be recognised by recording a low pressure in
the distal internal carotid artery above the level of the clamp. It may be
necessary in such Circumstances to insert a temporary silicone shunt over the
arterial field being worked upon.
Subclavian
artery stenosis may cause claudication and (rarely) frank ischaemia of an arm.
The subclavian lesion may also have an effect by causing artery-to-artery
embolisation. This may lead to loss of digits. The condition may be treated by
endarterectomy or bypass but nowadays percutaneous transluminal balloon
angioplasty is the treatment of choice. It must be noted, however, that some
Subclavian
steal syndrome. If the first part of the subclavian artery is obstructed, the
vertebral artery may provide a collateral circulation into the arm by reversing
its direction of flow. This may cause periods of cerebral ischaemia. The classic
syndrome of syncopal attack and
Enteric
artery occlusive disease. Pain after eating that has no obvious diagnosis in a
patient with known atheromatous disease and weight loss may be due to coterie
artery occlusion. In general, two of the three coterie vessels (coeliac axis,
superior mesenteric artery, inferior mesenteric artery) must be occluded to
produce ‘intestinal claudication’. Great care must be taken to exclude all
other diagnoses before contemplating surgical endarterectomy or bypass.
Renal
artery stenosis may be responsible for hypertension and, eventually, loss of
renal function. In general it is possible to control hypertension using drugs.
When this pathology is associated with loss of renal tissue, however, arterial
intervention is indicated. Both percutaneous transluminal angioplasty and
arterial surgery have their specific place in this disease. A variety of
operations is available ranging from endarterectomy, aortorenal bypass, renal
artery revascularisation using another vessel (such as the splenic artery), to
renal autotransplantation.
Coronary artery disease .See Chapter 48