Upper Limb Arterial Anatomy

Upper Limb Arterial Anatomy

• Subclavian arteries originate from the brachiocephalic trunk on the right side and directly from the arch of the aorta on the left.
• There can be considerable normal variation in the origination patterns of these arteries.
• The right subclavian artery's origin can be examined behind the right sternoclavicular joint.
• At this joint the brachiocephalic trunk splits into the right subclavian and common carotid arteries.
• The left subclavian artery's origin from the arch of the aorta is difficult to visualize, but more distal segments are visible.
• The subclavian artery runs to the outer border of the first rib, transitioning into the axillary artery.
• The subclavian vein is positioned in front of the subclavian artery.
• A cervical rib, if present, causes cranial and anterior displacement of the subclavian artery.
• Key branches of the subclavian artery include the vertebral, thyrocervical trunk, internal thoracic (mammary), and costocervical trunk.
• The axillary artery spans from the first rib's lateral border to the outer, inferior edge of the pectoralis major.
• The brachial artery runs along the medial upper arm to the cubital fossa, then into radial and ulnar arteries.
• The division point of the brachial artery into the radial and ulnar arteries can sometimes lie higher in the upper arm.
• The brachial, apart from muscular branches, gives off the profunda brachii artery in the upper arm, passing behind the humerus.
• The superior and inferior ulnar collateral arteries branch off from the lower brachial artery.
• The radial artery descends along the forearm's radial (lateral) side to the wrist.
• At the wrist it goes over the radial styloid process and the carpus' lateral side.
• It passes through the first interosseous space, forming the deep palmar arch's lateral aspect.
• A superficial branch of the radial artery connects with a corresponding branch of the ulnar artery to form the superficial palmar arch.
• The ulnar artery descends along the forearm's anterior ulnar (medial) side to the wrist's medial side.
• At the wrist it passes over the flexor retinaculum before dividing into superficial and deep branches.
• The superficial and deep branches of the ulnar anastomose with the radial artery's branches, forming the superficial and deep palmar arches.
• Below the elbow, the ulnar artery gives off recurrent ulnar arteries and the common interosseous artery.
• The common interosseous forms anterior and posterior divisions along both sides of the interosseous membrane.
• The primary branches of the superficial arch give off the common palmar digital arteries, which then form the proper palmar digital arteries.
• The proper palmar digital arteries are main vessels that supply the fingers.
• A complete connection between superficial and deep palmar arches are present in 80%–90% of individuals.

Examination Protocol and Technique

• A 7–12 MHz transducer is suitable for examining upper limb arteries due to less tissue penetration needed compared to the leg.
• Use a medium-frequency linear array transducer is indicated when imaging vessels closer to the elbow.
• A phased array transducer with a small footprint should be used for the suprasternal notch and for imaging vessels at the base of the neck.
• Put the patient in a supine position with their head turned away from the examined side, arm abducted.
• Flex the elbow and rest the hand's back on a pillow near the patient's head.
• Align for examination of the axilla and medial upper arm.
• As an alternative the arm can be abducted, and supported on a shelf, or held by the patient on part of the ultrasound machine.
• Upper arm arteries are easily found via B-mode scanning with a sonoanatomic knowledge.
• The vessels which make up the palmar arch and fingers can be localized with the aid of color duplex ultrasound.
• Spectral Doppler information should be sampled in longitudinal orientation with a smaller angle of insonation.

Vessels in the Thoracic Outlet

• Position the patient seated or standing to examine proximal vessels.
• This allows the shoulder girdle to relax and fall, increasing access.
• Examine the brachiocephalic, subclavian, and axillary vessels via suprasternal, supraclavicular, and infraclavicular windows.
• Apply copious gel in the suprasternal notch to maintain skin contact.
• The axillary artery is easier to visualize with the arm abducted for an axillary approach.
• An axillary approach may be scanned through an anterior window.
• It's important to examine both arms, even with unilateral symptoms being present.
• Subclavian arteries are located on either side behind the subclavian vein as they cross the first rib.
• For patients with arterial compression, the artery is scanned at various positions looking for narrowing or occlusions.
• The axillary artery is examined below the clavicle and followed distally to the pectoralis muscles via the axilla, then the medial upper arm.
• Track the axillary artery down to the cubital fossa.
• Forearm branch division usually happens below the cubital fossa.
• When the radial or ulnar artery is hard to trace at the elbow, find it at the wrist and follow it back.

Pitfalls!

• Bony structures can obscure a proximal subclavian thrombus.
• When a color gain is set too high, it can obscure a non-occlusive thrombus.
• Vessels will not color-fill is the insonation angle is at 90°.
• Subclavian vessels can be mirrored because of a high impedance mismatch of the pleura-lung interface.

Assessment of Disease

• Lower limb atheroma is more complex to assess than carotids given the potential for collateral supply around stenoses or occlusions.
• Differentiate between haemodynamically and clinically significant disease.
• Individuals could have the same degree of stenosis in their superficial femoral artery.
• An 80% acute diameter reduction will be more symptomatic.
• The same stenosis acquired over time, and with collateral channels may be less disabling.
• Interpret Doppler findings with the context of the complete clinical picture.
• Colour Doppler allows identification of normal and abnormal vessel segments.
• Stenoses may show a colour Doppler 'bruit' due to tissue caused by blood passing through the stenosis.
• Relate any diseased segments found on the ultrasound with bony landmarks visible on angiography.
• Comparing the 2 examinations helps confirm if the lesion's abnormality on arteriogram aligns with the ultrasound location.
• Some patients can show diffuse disease on much of the superficial femoral artery, without localized stenoses.
• Recognize this appearance due to its overall haemodynamic effect can produce pressure reductions, lowering limb perfusion.
• Extensive diffuse disease is not suitable for angioplasty.
• Patients can contain stenoses along the vessel, none being haemodynamically significant.
• Additive effects can lead to reduced perfusion pressure distal to the segment.
• The presence of serial stenoses can affect determining the degree of distal stenosis, if not recognized.
• Significant proximal stenosis or occlusion will lower the perfusion and velocity which make it difficult to quantify stenosis.
• Power Doppler and echo-enhancing agents aid in assessing distal stenosis severity.

Diagnostic Criteria

• The principles of disease assessment for the upper limb remain the same, but the type of disease differs from the lower limb.
• Arm ischemic symptoms can be from compression, embolic occlusion, or vasospasm, and are infrequently from localized atheroma.
• Lower limb diagnostic criteria important to assessment include direct stenosis measurements, PSV ratios, and waveform changes.
• It can be difficult to perform direct measurements of stenosis in the lower limb due to smaller arteries.
• Smaller arteries that are in the thigh's deeper parts, particularly with disease, can be hard to see the lumen in the deeper sections.
• Direct measurements of stenosis may be possible in the lower external iliac, common femoral, profunda femoris, and upper superficial femoral.
• After a plaque distribution assessment in the longitudinal and transverse planes, measurement of diameter reduction can be done.
• Measure length of affected segment when detecting stenosis or occlusion to determine lesion suitability for angioplasty.
• Disease segments, mainly occlusions longer than 10 cm, aren't normally for percutaneous treatment.
• Direct stenosis measurement can be impossible in the lower limb, assess the severity using peak systolic velocity changes by stenosis.
• Normal lower limb artery velocities at rest are approximately 120 cm/s in the iliac segments, 90 cm/s in the superficial femoral segments.
• Normal arterial velocity in the popliteal segment is approximately 70 cm/s.
• Ratio of PSV at the stenosis compared with the velocity in a non-diseased segment 1–2 cm upstream.

Waveform Changes

• A normal waveform in the resting lower limb's main arteries has 3 components.
• This represents pressure changes in the resting lower limb arteries during the cardiac cycle.
• The acceleration of blood flow and onset of systole rises in pressure and a reversed flow occurs when the pressure wave is reflected.
• Distal arterioles constrict and elastic compliance of the main arteries in diastole facilitates forward flow production.
• Exercise modifies the normal waveform by lowering the peripheral resistance.
• A reversed component is lost, diastolic flow throughout the cardiac cycle will be increased.
• Examination of the lower limb arteries is best when the patient has not had exercise of the leg muscles for about 15 min.
• Examination after exercise, or reactive hyperaemia, used to 'stress' the lower limb.
• Stenoses are often insignificant at rest, with low blood flow, but are clearer with the higher blood flow when the muscles open.
• Vessel disease can happen where it is measured, above it, or below it can affect the waveform.
• Discontinuity prevents visualization so waveform changes are an indicator of disease.
• How the waveform shapes and degree of spectral broadening are the two main areas that are altered.
• Spectral broadening is seen throughout the spectrum if a stenosis is close to the point of measurement.
• If the distance increases from the stenosis the spectral broadening appears in the postsystolic deceleration phase.
• Stenosis from flow disturbance might take centimeters to resolve.
• The spectral broadening is lost, the systolic forward flow is regained, and the reverse and third components are less likely to reappear.
• Distal limb ischemia may cause capillary dilatation and raise flow in diastole, which requires proximal vessel examination.
• Distal disease impacts waveform and reduces 3rd component, but also can increases pulsatility and reduce distal flow.
• Superficial femoral artery origins with distal disease are seen most often, but the exact changes vary with the collateral channels capacity.

Assessment of Aortoiliac Disease

• The clinical or waveform findings at the groin may suggest aortoiliac segment disease.
• Up to 90% of cases report performing successful examinations via scanning and proper preparation.
• Power Doppler and echo-enhancing agents can improve visualization and assessment using ultrasound.