Subclavian Steal Syndrome

Published on 13/02/2015 by admin

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Last modified 13/02/2015

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CHAPTER 96 Subclavian Steal Syndrome

The aortic arch extends from approximately the level of the upper border of the second sternocostal articulation on the right, runs superiorly, posteriorly, and to the left in front of the trachea, where it then turns posteriorly left of the trachea and finally inferiorly on the left side of the body. The branches that conventionally arise from the arch are the right brachiocephalic artery, the left common carotid artery, and the left subclavian artery (see Chapter 71).

When stenosis or occlusion involves the subclavian artery, the vertebral artery can reverse direction to serve as a collateral pathway to reconstitute the subclavian artery, a phenomenon known as subclavian steal phenomenon, which can lead to brainstem ischemia and neurologic symptoms. This chapter will discuss the clinical manifestations, imaging evaluation, and treatment of subclavian steal.

ETIOLOGY AND PATHOPHYSIOLOGY

Atherosclerosis is the most common cause of subclavian steal syndrome. Although Takayasu arteritis is an infrequent cause of the syndrome, it occurs more commonly in people of Asian descent.2

Subclavian artery stenosis or occlusion proximal to the vertebral artery origin results in the alteration of vertebral artery hemodynamics. The low pressure in the subclavian system eventually results in reversal of flow in the ipsilateral vertebral artery, which serves as a source of collateral flow to the distal subclavian artery.

Vollmar and colleagues3 have described four categories of subclavian steal phenomenon based on the vascular territories that provide and receive flow—vertebrovertebral, carotid-basilar, external carotid-vertebral, and carotid-subclavian. Another classification scheme4 is based on the degree of hemodynamic disturbances of the vertebral artery: stage I (occult steal, decreased blood flow), stage II (partial steal, transient or partial reversal of flow), and stage III (complete steal, permanent reversal of flow).

When the collateral flow directs a large amount of flow into the subclavian artery and away from the brain, neurologic symptoms can occur. Such symptoms have been reported to occur in approximately 36% of patients.5 Often, the circle of Willis can provide enough collateral circulation to the brainstem to avert neurologic symptoms. If the posterior communicating artery is stenotic, occluded, or absent, or if there is concomitant carotid disease, then neurologic symptoms are more likely to occur.

MANIFESTATIONS OF DISEASE

Imaging Techniques and Findings

Ultrasound

Sonography is the initial imaging examination when subclavian steal syndrome is suspected. Ultrasound with pulsed Doppler spectral analysis can demonstrate patency and flow direction in the vertebral artery and can establish the presence of subclavian steal.11,12

Subclavian steal phenomenon is associated with specific vertebral artery waveforms. There are four types of waveforms that indicate the degree of abnormal hemodynamics11:

In occult steal (Branchereau stage I),4 the pulsed wave Doppler spectrum typically demonstrates antegrade vertebral flow with midsystolic deceleration.11,12 The waveform may show a reversed late systolic flow as a response to reactive hyperemia in the upper extremity after arm exercise (see Fig. 96-1B). In partial subclavian steal (stage II), pulsed wave Doppler depicts partial flow reversal. The Doppler waveform in occult and partial subclavian steal has been described as the bunny rabbit sign because of its resemblance to the outline of a rabbit (Fig. 96-1A).11,12