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Wednesday 23 September 2020
Peripheral Arterial Disease (PAD) is a very common condition affecting millions of people worldwide. It is estimated that there are currently more than 500,000 Australians aged 40 years and older with PAD.
In Australian primary care settings, up to 10% of patients have a diagnosis of PAD. As patients age, incidence increases, with 22% of Australians aged >75 years diagnosed.
Despite significant improvements in the treatment of PAD, the overall prevalence in Australian patients remains high. General practitioners (GPs) are ideally positioned to identify and help manage at risk patients.
In PAD three of the arteries most commonly blocked are the iliac artery, the superficial femoral artery, and the infrapopliteal arteries that are below the knee. When the main arteries in the legs become blocked by plaque, smaller arteries, called collateral pathways, take over as the main route to supply blood to the leg muscles. These smaller arteries can supply the muscles with enough blood when a person is at rest, but they can’t do a good enough job when a person is physically active and the leg muscles need more blood and oxygen.
Patients with blocked arteries below the knee may also develop the most severe form of PAD, critical limb ischemia, which can result in non-healing leg ulcers and increased risk of amputation.
Diagnosis
Careful history and clinical examination remain the initial means of diagnosing PAD. Ankle-brachial index (ABI) measurement should be the initial diagnostic tool used in general practice:
For atypical exertional leg pain, post-exercise ABI should be measured. This involves walking on a treadmill for a period of time, usually about 5 minutes, or until limited by leg discomfort. Some patients with normal resting ABI’s will show a significant drop in pressure with exercise.
The role of diagnostic imaging
Duplex ultrasound is non-invasive, is useful to define sites of stenosis or occlusion, and is often the only imaging required to plan endovascular interventions.
Both computed tomography angiography (CTA) and magnetic resonance angiography (MRA) provide good sensitivity and specificity compared to digital subtraction catheter angiography (DSA), although CTA can be more problematic with heavily calcified arteries.
Management of PAD
PAD management goals can be attained through a comprehensive treatment program, which includes lifestyle modifications, exercise and diet, and pharmacotherapy for all PAD patients; and invasive revascularisation for patients with limiting claudication or critical limb ischaemia (CLI). These will be covered in a subsequent update.
Surgical intervention
Patients should be referred to a vascular surgeon when:
The main options include endovascular angioplasty or stenting, or open surgical reconstruction by peripheral bypass or endarterectomy. The choice of procedure will depend on the anatomic location of the stenotic/occlusive disease, its extent, and the patient’s comorbidities.
A recent case:
52 year old female Peripheral Vascular Disease, Diabetes, dislipidaemia, smoker, hypertension Presents with acute gangrene of her first toe. [click through to view image - contains graphic content]
CT angiogram showed superficial femoral occlusion.
This was confirmed on angiogram, the lesion was crossed, treated with atherectomy and drug eluting balloon angioplasty. These treatments are explained below.
click on images to enlarge
Image 1 Pre and post atherectomy
Image 2 Atherectomised plaque removed from the device
Laser cut, self expanding stents have been the workhorse for peripheral vascular intervention for many years and usually have very good short and medium term patency. The Achilles heel has been treatment in mobile segments of artery, like behind the knee, which tend to fracture or occlude the stent, as well as what to do when the stent starts to narrow.
The option to avoid using stents at all
Drug-Coated Balloon (DCB) angioplasty is similar to plain balloon angioplasty procedurally, but there is the addition of an anti-proliferative medication coating the balloon, as well as an excipient to aid in drug transfer, which may help prevent restenosis. Restenosis is the re-narrowing of the vessel at a site that was previously treated. Using a drug-coated balloon has the potential to prohibit cell division, limiting the amount of restenosis, or blockage re-growth after treatment.
Percutaneous debulking or “Atherectomy”
"Ather" refers to an atherosclerotic plaque within an artery; "ectomy" means to cut it out. Atherectomy is often part of an angioplasty procedure, but instead of compressing the plaque into the artery wall, as is done with Balloon Angioplasty, Atherectomy actually cuts away and removes fatty plaque to widen the artery and improve blood flow. It works in a similar way to traditional open endarterectomy. A catheter is inserted into an artery usually in the groin. Inside the artery, the cutting device cuts away at the plaque, widening the artery so blood flow improves.
There are two different devices commonly used to perform Atherectomy:
Directional Atherectomy uses a very small rotating blade to cut out the plaque and remove it safely from the blood vessel.
Rotational Atherectomy uses a diamond-studded, acorn-shaped drill to grind plaque down and is especially useful for calcified plaques.
Use of stents
A stent is a small, expandable, mesh-like tube that supports the artery and helps to keep it open.
Once inserted the stent is expanded, flattening the plaque against the artery wall and holding the artery open with a mesh tube.
The catheter used to deliver the stent is then removed, but the stent stays in the artery permanently to maintain blood flow.
Interwoven stents are made from individual flexible nitinol wires are woven for greater flexibility, kink resistance, and the ability to mimic the natural movement of the anatomy.
This is specifically relevant to the twisting and compression characteristics of the superficial femoral and popliteal arteries.
Interwoven stents exhibit more than 4 times the compression resistance of all other self-expanding nitinol stents, which are laser cut from an inflexible nitinol tube.
In conclusion
Advances in endovascular therapies have broadened the options for treating peripheral arterial disease, and can offer a lower risk alternative to open surgery in many patients with multiple comorbidities.
At Mater, our Vascular surgeons and teams make use of recent cutting edge vascular surgery advancements that aim to address these issues and improve patient outcomes.
Dr Daniel Hagley is a Consultant Vascular Surgeon at Mater Hospital Brisbane, and conducts his private practice from Wickham Terrace, admitting patients to Mater Private Hospital Brisbane.
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