For Referring Physicians
Newsletter

June, 2002

Blocked Leg Arteries Linked To Heart Disease

Physicians have long known the complex nature of peripheral arterial disease (PAD). A recent research study (the PARTNERS study) published in JAMA, September 19, 2001, has shed new light on the underestimated prevalence and the associated morbidity and mortality of the atherosclerotic process. Atherosclerosis is a disease that significantly affects larger numbers of the elderly since life expectancy has been prolonged. Thus, the clinical problem of atherosclerosis has expanded, but at the same time the amount of information available as to its exact cause and prevention has not kept pace with the enlarging scope of the problem.

Atherosclerosis is the most common cause of chronic arterial occlusive disease of the lower extremities and as the PARTNERS study has shown, the diagnosis of PAD may also be a predictor of cardiovascular and cerebrovascular disease. Early diagnosis of PAD can provide a better overall "picture" of the patient's vascular health and may help guide us in the early detection or prevention of limb ischemia, atheroembolism, transient ischemic attacks, stroke, or even heart attacks.

Narrowing or obstruction of blood vessels that occurs as a result of the atherosclerotic process reduces blood flow to the lower limb at rest or during exercise. Significant blockages (those that narrow the vessel lumen by >50%) produce a pressure gradient across the stenosis. A measurable drop in systolic pressure is a good indication of the presence of a proximal arterial stenosis or occlusion. A blockage that does not cause a pressure drop under resting conditions may become significant with increased flow across the stenosis as the result of exercise. The measured changes in blood pressure that occur as a result of an arterial blockage are the basis for physiologic non-invasive arterial testing.

The simplest and often the most reliable method for evaluating lower extremity circulation is the ankle-brachial index (ABI). This test can be performed in the office by primary care providers or at the hospital bedside. The equipment necessary is inexpensive and consists of a blood pressure cuff and Doppler ultrasonic blood flow detector. Blood pressures, using the Doppler, are obtained at the posterior tibial and the dorsalis pedis locations and compared to the highest brachial systolic blood pressure of the two arm readings. The ABI is obtained by dividing the ankle pressure reading by the highest arm pressure. The ABI is only an indicator of whether or not there is a drop in distal systolic pressure that would suggest PAD is present and the amount of blood flow (ischemia) to the feet. It does not, however, localize the areas of blockage within the peripheral arterial system and may be located anywhere from the heart to the ankle. Note: The use of a simple hand-held or other Doppler device that does not produce hard copy, or that does not permit analysis of bi-directional vascular flow, is considered part of the physical examination and is not separately reimbursable.

Usually the ABI correlates well with functional symptoms. In a normal individual, the ABI ranges from .90 to 1.30. Patients with severe vascular occlusive disease who are experiencing ischemic rest pain or ischemic ulcerations will usually have an ABI of <.40.

The absolute ankle pressure may be erroneous (non-detectable) in diabetics who present with calcified, non-compressible arteries. These patients, in whom you might suspect PAD, or if the ankle/pressure index is found to be abnormal (less than .90), it is advisable to obtain a more complete lower extremity arterial evaluation performed in an accredited vascular laboratory. Pulse volume recording, digital plethysmography and pressures, or even color duplex imaging may be necessary to better evaluate this group of patients.

The Lower Extremity arterial Doppler evaluation (LED) combines the use of systolic pressure measurements and flow measurements, Pulse Volume Recording (PVR) at five different segments of both lower extremities. A drop in the systolic pressure and pulse wave between the segments indicates the presence of occlusive disease at that region. This type of testing takes less than 30 minutes to complete and can provide a location of the diseased segment, as well as the ability to quantify the severity of the limb ischemia.

For differentiation of true vascular claudication from pseudo-claudication, a more definitive non-invasive test to perform is a Lower Extremity arterial Doppler evaluation with TreadMill stress testing (LED/TM). The patient describes pain or discomfort in the lower extremity (usually the calf) brought on by walking, which ceases when stopping. Claudication occurs as a result of the build-up of lactic acid in the ischemic muscle. The pain goes away with rest after the lactic acid concentration has cleared from the muscle. The onset is gradual and may go unrecognized for years by patients and physicians who may attribute the symptoms to arthritis, muscular pain, or simply aging. Resting blood flow over a stenotic region may be sufficient to maintain normal distal pressures. When flow is increased over the stenosis as a result of the exercising muscle distal pressure may drop, "unmasking" the presence of disease. This is sometimes evident in patients with isolated short-segment stenosis of the iliac arteries. Patients are walked on the treadmill for up to five minutes at 1.5mph at an incline of 10%. Contraindications to LED/TM include questionable cardiac status, severe pulmonary disease, inability to ambulate, rest pain, and ischemic limb ulceration. The referring physician must order treadmill exercise testing at the time of scheduling. The technologist will not walk the patient with suspected claudication without an order.
Non-invasive physiological studies have been performed for more than 30 years to confirm the presence of clinically suspected peripheral arterial occlusive disease. These studies can reveal the most significant location of arterial disease and can help predict whether the patient will require an inflow procedure or infrainguinal bypass. Once the decision has been made for surgical intervention, a conventional angiogram is performed prior to surgery to "map" the arterial system. This map provides the surgeon with the best target vessel for the bypass procedure.

Recently, duplex ultrasound has been utilized to "map" the lower extremity arterial system. Duplex ultrasound is inexpensive, non-invasive and well tolerated by the patient when compared to the "gold standard" angiogram. It can clearly aid in the decision process as to what type of vascular intervention should be performed. Also, with advancing technology, the distal bypass target vessels can be clearly shown. Due to the complexity of the duplex ultrasound, we strongly believe that this test should be requested by the vascular surgeon once a decision has been made for intervention and not utilized as first-line evaluation for the differentiation of vascular occlusive disease.

The prevalence of PAD is high, especially in patients with diabetes, hypertension, and/or cigarette smoking. By adding a simple non-invasive test (ABI) in the evaluation of these high-risk patients, PAD can easily be found and may be the best predictor of cardiovascular and cerebro- vascular disease. The choice to perform a more complete non-invasive vascular test should be based on the questions to be answered. These studies must be ordered with a clinically appropriate diagnosis code as found in the American Medical Association's listing, ICD-9-CM.

We at Apple Hill Vascular Associates, Ltd are committed to providing the highest quality of vascular services. Please don't hesitate to call us if there is anything we can do to be of further service to you and your patients.

Thank you for your continued support!