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Carotid duplex scan
The scan provides gray scale images of the cervical portions of the common, the internal and the external carotid arteries. Color flow images localize areas of abnormal flow and Doppler velocity waveform recordings provide quantitative measurements to determine the severity of stenosis. The combination of the images and the velocity data are used to arrive at a final impression. The proximal portion of each vertebral artery is assessed, looking for abnormalities including reversed flow caused by subclavian steal.
The Laboratory has adopted standardized categories of stenosis, used for reporting severity of carotid disease. These are normal, 1-19%, 20-59%, 60-79%, 80-99% and occlusion.
Indications: The typical indications include stroke, TIA, amaurosis fugax, asymptomatic carotid bruit and known carotid stenosis (being checked for progression.) In most asymptomatic patients with known disease tests do not need to be performed more often that once a year. Medicare and some other programs often do not pay for screening tests (i.e., tests done to look for significant disease before a major operation). Other non-accepted indications include the initial work-up for dizziness or syncope.
Considerations when ordering test: The initial examination should be ordered as a bilateral test, because side to side comparisons provide important information. Unilateral tests should only be ordered for special indications such as follow-up after carotid endarterectomy or reassessment of a stenosis contralateral to a known internal carotid occlusion.
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Peripheral arterial tests:
Ankle pressures with Doppler velocity waveforms-
Pressure determination in the extremity provides an objective measurement of the severity of occlusive arterial disease. (Only the systolic pressure is obtained with the method.) The overall effects of occlusive disease in the leg down to the ankle level is reflected by the ankle-arm index, AAI (sometimes called ABI, ankle brachial index). This number is the ratio of the pressure in the ankle vessel with the higher pressure to the higher brachial systolic pressure. A normal resting pressure is 1.0 or higher. The Doppler velocity waveform recording serves to identify artifacts produced in pressure measurements by pathological stiffening of the arteries.
Segmental pressures with Doppler velocity waveforms-
Measurements at multiple levels help to determine the level(s) of significant occlusive disease. Segmental pressures are measured at high thigh, above knee, below knee and ankle levels. Waveforms are recorded at the common femoral, popliteal and the tibial branches at the ankle.
Indications: The test is used to document the severity and location of arterial occlusive disease in the leg. The test is typically ordered for patients with intermittent claudication, rest pain or chronic ulcers with arterial etiology. . Medicare and some other programs often do not pay for test done to confirm findings on physical examination of decreased or missing extremity pulses.
Considerations when ordering test- The standard evaluation includes a bilateral study to permit side-to side comparisons. The first time the test is ordered it is helpful to have segmental assessments to help to define level of occlusive disease. Limited (ankle pressures and waveforms) often suffice for follow-up studies.
Treadmill stress test-
Moderate stenoses may not limit flow at rest and only have a hemodynamic effect with the increased flow occurring with exercise. In this situation the regular ankle pressures and ratios may be entirely normal. In such patients occlusive disease may be identified as the etiology by measuring the pressures immediately after standardized low-level exercise. Ankle and arm pressures are measured at rest. The patient then walks on a treadmill at 2 mph at a 10% grade for five minutes. Pressures are measured repeatedly after completion of exercise.
With normal arterial circulation, this level of exercise does not result in any significant drop in leg pressure. With flow limiting lesions there is compensatory vasodilation such that the ankle pressure drops. The severity of the pressure drop and the duration correlate with the severity of arterial insufficiency.
Indications: This test is normally limited to the detection of significant arterial disease in patients with typical symptoms but a normal resting study. The laboratory will not carry out a stress test on any patient with an AAI below 0.90.
Considerations when ordering test: Even though the test requires only a low level of exercise, it is contraindicated in any patient with active angina or in the presence of congestive heart failure. Uncontrolled hypertension is a relative contraindication. By ordering the test, we assume that you have evaluated these contraindication and consider your patient to be appropriate for the test. The personnel will always query the patient about current symptoms and if any concerns arise, they will contact you before proceeding with this test.
Digital arterial photoplethysmography-
The method uses a photoelectric cell to detect light reflected from the capillary circulation in the subcutaneous tissue. A pulsatile waveform is generated and changes from normal are used to determine alterations from normal perfusion. The routine test records waveforms from the distal phalanx of each digit bilaterally.
Indications: In our laboratory the test is used most commonly to assess the presence of small vessel disease in the hand or foot. Some patients with diabetes may have forefoot ischemia in spite of palpable ankle pulses. The test may also help in the documentation of distal disease in-patients with vasculitis or atheroembolism.
Arterial duplex scan:
The scanner is used to obtain gray scale images of the native vessels or bypass graft as well as recording velocity tracings to provide hemodynamic information. Extremity arteries are usually easy to study. In many cases it is possible to study the abdominal aorta, the iliacs and the visceral vessels. The scan can be used to diagnose not only occlusive disease but also aneurysms, pseudoaneurysms (most commonly seen in the femoral artery following invasive arterial studies) and arteriovenous communications.
Indications: The physiologic tests listed above are the first tier of diagnosis for lower extremity arterial occlusive disease. The duplex scan should be reserved for obtaining detailed information to make a therapeutic decision about interventional therapy. Other indications include definition of aneurysm size, diagnosis of visceral artery occlusive disease and the postoperative evaluation of bypass grafts in the leg.
Considerations when ordering: In the initial workup of the patient it is not necessary to add a duplex scan to the segmental pressure and waveform test. In general, a duplex scan should only be ordered by the physician who is planning upcoming intervention or by the physician who is carrying out post-intervention evaluation.
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Peripheral venous tests:
Venous duplex scan-
The veins of the abdomen and the extremities can be scanned in much the same as is done for the arteries. The most common application for the examination is to determine the presence of deep vein thrombosis in the extremity. In order to perform a careful search, the deep veins are examined every 1-2 cm and gentle pressure is applied with the scan head to demonstrate that the walls of the vein can be easily collapsed. When thrombus is present there is little if any compressibility. The flow patterns are also assessed with Doppler recording. The presence or absence of venous valve insufficiency is assessed with compression maneuvers of the extremity.
Indications: The most common indication in our lab is to check for the presence of deep vein thrombosis. Another indication is the documentation of venous valvular reflux in-patients with unexplained (specially unilateral) leg swelling. Duplex scanning is not indicated in the routine evaluation of primary varicose veins.
Considerations when ordering: The scan is often ordered for the diagnosis of DVT, in many patients because of the finding of leg swelling. Physicians often order unilateral scans in patients with unilateral symptoms. When the patient has multiple clinical risk factors for thrombosis, it is best to order a bilateral examination to reduce the chance of missing silent contralateral pathology. A scan is sometimes ordered "to rule out pulmonary embolus." It is important to understand that the test cannot exclude this diagnosis. If the scan shows thrombus in the extremity, one has a source for potential embolization. A negative study does not exclude a pulmonary embolus and the work-up must not conclude with the scan.
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