15 Assessment of Upper Extremity Arterial Occlusive Disease
The unique structure and function of the upper extremity create challenges for the diagnosis of vascular abnormalities. Unlike the lower extremity, where atherosclerosis or thrombi are almost always the cause of symptomatic disease, upper extremity vascular problems can be more complex. Mechanical compression occurring in the troublesome thoracic outlet region, vasospasm in digital arteries, trauma-related thrombi in the hand and wrist, and embolic thrombi from the heart or from proximal arm aneurysms all must be considered when troubleshooting in the upper extremity. Hand arterial anatomy is confusing and variable and therefore requires a high level of technical expertise. Specialized probes that are capable of resolving small vessels, and displaying flow within them, are required for optimal studies. Finally, physicians and sonographers are generally out of their comfort zone when working in the arm, because arterial disease occurs less commonly in the upper extremity than in the lower extremity. Only about 5% of arterial cases involve the upper extremities.1
The first steps in solving the diagnostic puzzle of hand and arm problems are to take a careful history and closely examine the fingers, hand, and arm. Both arms should be examined side by side, with attention to the following findings: Are any fingers discolored? Is there a temperature difference from one hand or finger compared with another? Are there ulcers on fingertips? Is there pain, and if so, how long has it been present? Did the pain or discomfort come on suddenly or slowly? Is the pain constant or transient? What makes the pain or discomfort better or worse? Does exposure to cold or stressful situations bring on or intensify symptoms?
Observations and historical information affect the types of tests that should be done to pinpoint the problem. Common basic noninvasive tools to investigate upper extremity arterial problems include the following:
One or all of these tools may be needed to diagnose a given problem. For instance, if fingers are cool and discolored with exposure to cold but fine otherwise, the examination will focus on the question of whether this is a vasospastic disorder (for example, Raynaud’s disease) versus a situation in which digital thrombus is present, or a combination of the two. Extensive diagnostic work will have to be done, with close attention to each finger (usually with PPG) and then some kind of cold challenge to provoke symptoms. If cold does not seem to be a factor, the cold challenge may be omitted. If the problem is positional, a baseline PPG study should be done, followed by monitoring of flow in as many different arm positions as possible. Finally, if Doppler and PPG information suggest obstruction, duplex imaging should be done to identify the cause.
Once the examiner has in mind the nature of the problem, a plan of action can be formulated for that individual. This plan may change as new information becomes available during the examination. For example, a patient with no positional symptoms turns out to have thrombus in a distal radial artery. Extra attention should then be given to the subclavian and axillary arteries, using duplex ultrasound to check for an embolic source, such as an aneurysm or atherosclerosis. It would also be wise to have the patient go through different arm positions, with the PPG cuffs attached, to check for thoracic outlet impingement.
For almost every situation where arterial disease is suspected in the upper extremity, the standard noninvasive starting point is the pulse volume recording (PVR) of arm waveforms, combined with segmental pressure measurements (Figure 15-1). Continuous-wave Doppler signal assessment of the subclavian, axillary, brachial, radial, and ulnar arteries (Figure 15-2) is complementary to the segmental pressures and PVR information. If the fingers are symptomatic, PPGs (see Figure 15-1, B) of all digits should be obtained as well. With this simple group of tests, one can answer the basic clinical question: Is hemodynamically significant arterial obstruction present in a major arm artery?
FIGURE 15-1 Normal pressures and waveforms. A, Upper arm and forearm (segmental) blood pressure is shown in the boxes on the illustration. The pulse volume recording (PVR) waveforms show a very short “time to peak” (from end diastole to peak systole), and a prominent dicrotic notch is present in the descending portion of the waveform. B, Normal digital photoplethysmographic (PPG) waveform shows the same features as the pneumatic, volume-based waveforms seen in part A. Note the dicrotic notch (D).
FIGURE 15-2 Normal continuous-wave Doppler waveforms have a high-impedance, triphasic shape characteristic of extremity arteries (with the limb at rest). Note that time to peak is very short, the systolic peak is narrow, and flow is absent in late diastole.
The PVR and Doppler examinations are conducted as follows. Blood pressure cuffs are placed about the midportion of the arm and the forearm, and PVR waveforms are taken at both levels. Then, the systolic blood pressure is measured at both levels, using the audible Doppler signal as an indication of systolic pressure. The measured blood pressures should be similar side to side, as well as from one level to the other (see Figure 15-1, A). A side-to-side blood pressure difference of more than 20 mm Hg or between levels, accompanied by an abnormal PVR (Figure 15-3), may indicate a hemodynamically significant lesion on the side/level with the lower pressure. This finding requires additional testing to determine the cause, usually with direct ultrasound imaging of the vessel(s) in question, as described later in this chapter.
FIGURE 15-3 Subclavian occlusive disease. The right arm shows normal pressures and pulse volume recording (PVR) waveforms. On the left, the pressure measurements are more than 20 mm Hg lower than on the right, and the PVR waveforms are damped (slowed time to peak, broad waveform, absent dicrotic notch).
If pressures and waveforms are normal, one can assume there is no hemodynamically significant obstruction in the arteries of the upper extremity. This observation may be an appropriate stopping point, especially if the referring physician only needs to rule out major, limb-threatening disease. It must be understood, however, that normal results of these indirect tests cannot rule out nonobstructive plaque or thrombus, aneurysm, transient mechanical compression of vessels, vasospasm, or other pathologies (such as arteritis). If any of these problems are suspected, additional testing may be required.
When a patient presents with an upper extremity circulatory problem, such as a cold, painful, or numb extremity that varies with limb positioning, a potential cause that should be identified or eliminated from the differential diagnosis early on is mechanical vascular compression at the thoracic outlet. As shown in Figure 15-4, the thoracic outlet is bounded by the clavicle, the first rib, and the scalene muscles. The thoracic outlet syndrome is a common problem, caused by impingement of the subclavian vessels and/or the brachial plexus as they leave the chest. Restriction at the thoracic outlet causes the vessels to be partially or completely compressed when the arm is in certain positions. The repeated vascular irritation over time may injure the artery or vein, leading to intimal damage or thrombus formation. Arterial emboli from thrombus formed in this area may travel distally to other parts of the upper extremity. Therefore, whenever emboli are found, one should consider that they might have originated in the subclavian or axillary arteries.
FIGURE 15-4 Thoracic outlet anatomy. The subclavian artery, brachial plexus, and subclavian vein pass through a narrow opening framed by the anterior and posterior scalene muscles, the clavicle, and the first rib. a, artery; v, vein.
Most patients with uncomplicated thoracic outlet syndrome (without thrombus, plaque, or aneurysm) have no arm complaints unless the arm is in a certain position. The discomfort the patient experiences is likely, at least originally, to result from nerve compression, rather than transient loss of blood flow from arterial impingement. The patient describes pain or numbness and loss of sensation when the upper extremity is in a predictable and reproducible position, such as occurs with hair brushing or driving a car (with the hands in a constant position on the steering wheel). The symptoms go away soon after the arm is repositioned.
If the examiner is presented with symptoms suggesting thoracic outlet problems, the upper extremity examination should begin routinely with resting PVRs and segmental pressures, as described previously, but this assessment should be supplemented with a check for the thoracic outlet syndrome, using the following technique. The examiner has the patient sit very straight and, using continuous-wave Doppler to monitor radial or ulnar artery flow, guides the patient through maneuvers that begin with the arm abducted and externally rotated. The blood pressure cuffs are left on the arms to monitor the pulse volume waveforms during the position changes, providing the examiner with two independent indicators of the quality of blood flow in the arm as the patient moves through the provocative position changes. This can be a clumsy operation for one examiner, so two examiners should be present during this procedure, if possible. One of the examiners is positioned behind the patient and maintains gentle pressure on the patient’s back with the left hand, to keep the back straight, while holding the Doppler probe used to monitor the radial or ulnar artery in the right hand. The other examiner operates the PVR device and monitors the PVR waveforms during the arm position changes. (Note: A PPG sensor attached to a finger may be used instead of continuous-wave Doppler, if desired.)
Once a good-quality Doppler signal is acquired at the radial or ulnar artery and the PVR device is adequately registering PVR waveforms, the examiner holding the Doppler probe guides the patient through the arm maneuvers. We usually start with the arm maximally abducted and externally rotated, with the shoulders pulled back as far as possible. The arm is then directed through every conceivable position, while the operators watch the PVR waveform tracing for diminished amplitude or total flattening of the waveform, accompanied by dampening or total loss of the Doppler signal. If a position is identified where such changes occur (Figure 15-5), with recovery of the signals when the arm is moved out of the position, the test is positive and indicates thoracic outlet impingement. This arm position should be repeated, however, and the findings should be the same every time the arm is moved into the obstructing position. Care should be taken to make sure the examiner did not simply move the Doppler probe off the monitored artery during positioning, as this can be a potential source of false-positive results. If the Doppler signal disappears, yet the PVR continues to be robust, recheck the Doppler probe orientation and repeat the maneuver.
FIGURE 15-5 Thoracic outlet impingement. The Doppler signal at the radial artery goes flat (small arrow), as the arm is positioned such that the subclavian artery is compressed. The signal resumes (large arrow) when the arm is repositioned.
A positive result, as described previously, suggests the presence of the thoracic outlet syndrome, but many patients without symptoms may test positive when an arm is in an extreme position, such as that used for this test. This fact contributes to the controversy surrounding the use of this test alone in making the diagnosis of thoracic outlet syndrome. The diagnosis is much more solid, however, if subclavian artery stenosis is visualized with duplex imaging with the arm in the position that causes abnormal Doppler and PVR findings, or if an aneurysm is demonstrated with duplex ultrasound. The latter finding proves the occurrence of significant and repeated arterial impingement.
If Doppler signals and PVR waveforms do not diminish with various arm positions, these positions should be repeated with the head in a neutral position, with the head turned to the left, with the head to the right, with the head tilted up, and finally, with the chin on the chest. Only after every conceivable position has been tested can the examination be terminated. If all of these maneuvers fail to identify a position where flow is diminished, the test is determined to be negative for thoracic outlet impingement. This does not necessarily mean that the condition does not exist in the given patient, only that this test has been unable to identify it.
After flow in the arms has been checked, attention is next turned to the digits. If there are any problems such as cold, discolored, or painful fingers, arterial flow in the digits should be checked. This is commonly done with PPG sensors that are applied to the pads of the fingers. Double-stick tape is usually used to secure the PPG probe to the fingers. A normal digital PPG waveform has a rapid upstroke, a downstroke that bows toward the baseline, a dicrotic notch, and normal amplitude (see Figure 15-1, B). A person with normal digital arteries may have small, abnormal-looking waveforms if the extremity is cold, so care must be taken to ensure that the examination room is sufficiently warm. If there is any question of the PPG waveforms’ being adversely affected by cold temperature, have the patient warm the hands with a warming blanket before testing. If good-quality, normal waveforms are present in all of the digits, the examination is complete. If the waveforms are blunted, rounded, or absent, additional testing is required.