Page 179 - Libro 2

10 — Upper Extremity Arterial Duplex Scanning
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Figure 10-5 Longitudinal color flow image of the brachioce- phalic artery giving rise to the right common carotid artery (CCA) and the right subclavian artery (SCA).
The subclavian artery is followed as it crosses un- der the clavicle and over the first rib. The axillary artery is identified in an anterior approach deep to the pectoralis major and minor muscles. In the ax- illa, it is seen deep to the axillary fat pad. The axil- lary artery becomes the brachial artery after crossing the teres major muscle. There is normally no differ- ence noted in the artery as the subclavian artery be- comes the axillary artery. The brachial artery takes a more superficial course in the medial arm between the biceps muscle anteriorly and the triceps muscles posteriorly. Views of the proximal, mid, and distal brachial, radial, and ulnar arteries are obtained. Any areas of stenosis, occlusion, or aneurysmal enlarge- ment are documented as previously described.
TECHNICAL CONSIDERATIONS
To prevent any missed occlusions or false-negative examinations, many laboratories choose to include physiologic testing as a component of the upper extremity arterial exam. The physiologic testing performed with multilevel pressures or waveforms provide a qualitative assessment of global perfu- sion. The duplex ultrasound evaluation can be conducted using physiologic waveforms as a guide. When significant changes are encountered by these indirect noninvasive tests, the subclavian veloci- ties and waveforms should be recorded with ultra- sound. Chapter 8 describes these physiologic tests in more detail.
PITFALLS
Potential impediments to the examination include the presence of wounds/dressings, intravenous cath- eters, and orthopedic fixation devices. Multiple ap- proaches must be used to maximize visualization around these obstacles.
DIAGNOSIS
The normal upper extremity artery waveform is tri- phasic with a sharp systolic peak followed by a brief period of diastolic flow reversal and then minimal continued forward flow in diastole. This is charac- teristic of a normal high resistance peripheral artery (Fig. 10-6).
The normal peak systolic velocities range from 80 to 120 cm/s in the subclavian arteries and 40 to 60 cm/s in the forearm arteries, with similar velocities in radial and ulnar arteries. Stenosis results in ele- vated peak systolic velocities (jets), poststenotic tur- bulence, and dampened distal waveforms with loss of end-systolic flow reversal (Figs. 10-7 and 10-8). There are no generally accepted velocity criteria to determine the degree of stenosis in upper extremity arteries.5 Although there are no universally accepted criteria for upper extremity arterial stenosis, general guidelines are listed in Table 10-1.
Arterial duplex ultrasound was performed in 57 patients to evaluate 578 arterial segments in 66 upper extremities to determine the clinical utility of velocity criteria to detect a 􏰀50% stenosis. The criteria used for 􏰀50% stenosis was a PSV ratio of greater than 2, relating the narrowed segment to that of the artery immediately proximal to the le- sion. All of the extremities underwent intra-arterial digital subtraction angiography. Duplex ultrasound correctly identified 15 of 19 hemodynamically sig- nificant stenoses giving a sensitivity of 79% and a specificity of 100%.6 In another comparison study of duplex ultrasound and angiography, loss of diastolic flow reversal was the earliest sign of significant ar- terial stenosis in 21 patients with ischemic upper extremities when compared to controls.7 The angle of insonation can be difficult to determine when
Figure 10-6 A normal high resistance upper extremity artery waveform (triphasic). There is a rapid systolic upstroke, an end- systolic reverse flow component with minimal or no flow at the end of diastole.