Peripheral Arterial Disease: Underdiagnosed and Undertreated
Peripheral Arterial Disease (PAD) is responsible for
significant morbidity and mortality in the United States and around the world.
It is estimated that approximately 8 to 12 million Americans are affected by
PAD; this is nearly as great as the roughly 13 million Americans with coronary
artery disease (CAD). Yet, only about
25% of these people have been diagnosed with the disease and roughly just 4%
are treated interventionally. The prevalence of PAD increases with age such
that nearly one in five Americans over the age of 70 have PAD. Furthermore, the
prevalence of the disease is on the increase, undoubtedly a result of multiple
factors but certainly, at least in part, a consequence of increasing obesity
and diabetes as well as poor diet and sedentary lifestyle. While most physicians are familiar with the
typical symptoms of leg claudication (leg cramping when walking), many do not appreciate the increased
mortality associated with PAD. A diagnosis of PAD carries with it five times
the relative risk of heart attack and stroke. Some studies suggest that as many
as 75% of patients with PAD harbor some degree of CAD. The 5 year mortality of
patients with PAD is 30% compared to just 10% in a matched population without
PAD, a mortality rate that exceeds that of breast cancer. As one might expect,
the cause of mortality in 75% of the cases is cardiovascular (predominantly heart attacks). Consequently, the
importance of making the diagnosis of PAD relates not only to reducing the
morbidity associated with the disease but also to minimize the associated
cardiovascular mortality.
Making a diagnosis of PAD is a relatively simple matter and
begins with screening the population at risk. Apart from age, the most
important risk factors are diabetes and cigarette smoking. These each confer an
increased relative risk of 3 to 4 times. Other risk factors include
hyperlipidmia, hypertension and hyperhomocysteinemia. The most common symptom
elicited in the history is leg claudication manifested by muscle cramping in
the calves, thighs or buttocks (depending upon the level of blockage) brought
on by walking and relieved by rest. Erectile dysfunction may be present in men.
Other confounding disorders such as spinal stenosis and osteoarthritis are
commonly also present at rest and affected by body position and therefore
usually can be differentiated. Keep in mind that the majority of people (about
two thirds to three quarters) with PAD will be asymptomatic or have atypical
symptoms but still need to be diagnosed because of their increased
cardiovascular mortality and need for appropriate medical therapy and testing. The
most common finding on physical exam is diminished pulses. Palpating for pulses
in the femoral, popliteal and pedal regions may help to locate the culprit
obstruction. At this point, confirming the diagnosis is as simple as obtaining
an ankle-brachial-index (ABI). This is done by taking the blood pressure in
both arms and using the higher of the two as the denominator of the ratio.
Then, using a simple Doppler probe, the systolic pressure obtained over the
dorsalis pedis artery on the top and the posterior tibial artery just behind
the medial maleolus on each foot provides the respective indices. An index of
less than 0.97 is abnormal. Keep in mind that with calcified arteries as may be
commonly found in diabetics or dialysis patients, the ABI may be falsely
elevated and an index greater than 1.3 to 1.4 is suggestive of this phenomenon
but, nonetheless, is associated with increased cardiovascular morbidity and
mortality. Symptomatic patients with PAD may then undergo additional testing
such as segmental pressures and volume pulse recording, exercise ABI, duplex
scanning, CT or MR angiography, or invasive angiography if revascularization is
contemplated. Myocardial perfusion
stress testing or carotid imaging may also be appropriate in some of these
patients.
Therapy for all patients diagnosed with PAD, regardless of
symptom status, consists of risk factor modification including antiplatelet and
statin therapy if indicated as well as a supervised exercise program for
claudicants. Patients should be made to walk 30 to 60 minutes per session,
stopping as needed for claudication symptoms, at least three times per week.
The objective is to improve functional capacity and minimize progression of
disease. If after 3 months of therapy the individual continues to suffer from
“lifestyle-limiting” claudication, referral for angiography and possible
revascularization may be considered.
The most severe form of PAD is known as critical limb
ischemia (CLI). These patients, who make up about 2% of people with PAD, have
such severe arterial insufficiency to the lower extremity that limb
preservation becomes an immediate goal. There are usually obstructions on
multiple levels (inflow, outflow and runoff vessels) which almost always
involve the tibial (runoff) vessels. Clinically, CLI may manifest as rest pain
of the forefoot (usually at night when the patient is supine and gravity is no
longer helping), foot ulcers or gangrene.
Diabetics are at greatest risk and one in four will face CLI sometime
during their lifetime. CLI accounts for
more than 150,000 amputations per year in the U.S. The risk of limb amputation
for a diabetic is 7 – 40 times that of a nondiabetic and 70% of limb
amputations performed in this country are performed on diabetics. 25% of
patients with CLI will require limb amputation within one year of
diagnosis. Less than half of all
patients requiring an amputation ever achieve full mobility and many end up in
nursing homes costing in excess of $100,000 per year. 30 – 50% of diabetic amputees
will face contralateral CLI and undergo a second leg amputation within 3 – 5
years. The mortality of CLI patients is
very high at 25% in the first year, 31.6% at 2 years and more than 60% after 3
years. Clearly, this is a very high risk group that deserves special, and
prompt, attention.
The statistics do not need to be this dismal, however. With
prompt diagnosis and therapy studies show that up to an 80% limb salvage rate may
be achieved. Lower limb amputations are preceded by foot ulcers in 85% of
diabetic patients and approximately 15% of the more than 15 million diabetics
in this country will develop a foot ulcer in their lifetime. An evaluation for
PAD at this stage can still result in a positive outcome. Unfortunately, due to
lack of physician awareness and education, this is too often not accomplished.
A recent study of 417 CLI patients treated between 1999 and 2001 showed that
67% were treated with a primary amputation without any consideration for
revascularization. Only 35% had an ABI
and 16% angiography; we can and must do better than this. We have the tools to
improve upon this outcome and there has been great success in many institutions
around the country who have dedicated themselves to treating these patients. At the Flint Hills Heart, Vascular and Vein Clinic we are making a significant positive impact on the outcome of CLI patients. We recently
initiated the first Amputation Prevention Clinic in the region and, along with our state-of-the-art Wound Clinic (with hyperbaric oxygen chamber), we are salvaging limbs in patients who might otherwise require amputation. Early diagnosis, however, remains the cornerstone of success and it is
the primary care physician who is usually the first to see the patient. Prompt
recognition and referral is critical.
Upon referral to the endovascular specialist and after
appropriate studies, revascularization should be performed without delay.
Except in cases of “wet gangrene,” this should be done prior to wound
debridement. An endovascular approach is usually preferred to surgery as these
patients are usually high surgical risk, often do not have suitable venous
conduit and an endovascular procedure is easily repeatable, if needed. Straight
line, pulsatile flow must be restored to the wound site on the foot. It takes
roughly three times more blood flow to heal a wound than what is normally
required and this cannot be achieved with a partial (above knee)
revascularization only; the appropriate tibial vessel(s) must be opened for
ultimate success. There have been significant improvements in endovascular
technologies which allow us often to revascularize patients with severe PAD who
were, until recently, thought to be without a revascularization option. The
development of devices to help traverse long total occlusions and advanced
techniques, such as pedal access, have improved the success of an endovascular
approach. Furthermore, the revascularized vessels only have to stay open long
enough for the wound to heal, usually about 6 to 9 months. About 20% of
patients will need a second interventional procedure to achieve complete wound
healing. In advanced cases where amputation is required such as with gangrene,
angiography with an eye toward endovascular revascularization should still be
performed as this may lessen the extent or level of amputation. Transforming a
below-knee-amputation (BKA) into a simpler transmetatarsal amputation (TMA)
will pay dividends in terms of improved patient function, quality of life and
survival. I have seen what should have been a TMA turn into a BKA or a BKA into
an above-knee amputation (AKA) due to lack of arterial imaging prior to the
surgery.
Peripheral arterial disease
affects millions of people in this country and its prevalence continues to
increase. It is associated with significant morbidity and mortality as well as
economic impact. Improved physician and patient education along with the
development of specialized centers of care with the multidisciplinary expertise
to treat these patients, improvements in quality of life, limb salvage and
decreased mortality can be achieved. Economic benefit in the form of reduced
health care dollars spent and reduction in lost wages should also be realized.
