Quantitative assessment of flow in antegrade and retrograde collateral channels serving the brachiocephalic area.

Abstract

An increasing number of review articles and case reports dealing with the demonstration of reversal of arterial flow, secondary to obliterative and occlusive disease, reflect the interest in this field. Particularly, the “vertebral steal” syndrome has been widely popularized and searched for (2, 4, 10, 13, 17). However, existing antegrade collateral pathways, particularly of the intracerebral circulation, have been recently recognized and rival the retrograde collateral systems in their importance in contributing a blood supply to an area deprived of normal circulation (8, 11, 16, 17). Various conditions influencing and determining the development of collateral circulation have been the target of recent investigations (15). Our knowledge of the development of collateral systems and their magnitude will guide our selection of surgical vs. medical treatment modalities (1). Apart from the progressive type of obstructive intra-arterial lesions, the hemodynamic significance of intermittent temporary obstruction of vessels, occasioned by certain positional changes, is recognized (7,10). The thoracic outlet syndromes and hemodynamic changes in the vertebral arteries occasioned by positional change have been investigated by arteriography and pressure studies. Research on cadavers has been attempted to assess the effect of position and traction (3, 5). The flow rate through retrograde and antegrade collateral pathways appears to be subject to constant change. Different collateral pathways serving the same effector organ may carry a varying load and surpass each other in percentage contribution over a period of observation. Extensive studies of this phenomenon have been carried out on patients with occlusion of intracranial vessels. The same phenomenon, however, has been demonstrated by serial arteriograms in the extracranial vessels in patients with vertebral steal syndrome, following surgical severance of the subclavian artery after a Blalock-Taussig or similar bypass procedure. The early symptoms of a substantial vertebral steal syndrome gradually diminish, concomitant with the development of other collateral systems via the internal mammary, thyrocervical trunk, and intercostal vessels, serving as bypass system to the same supply area. The arteriograms, however, allow only an estimate of the hemodynamic significance of this development. Flow studies, both dye dilution technics and radioisotope technics as well as strain gauge plethysmography, have been advocated for the assessment of the effective flow rate via major as well as microscopic collaterals to a given region (6, 8, 12, 14). Although present radioisotope technics are still quite crude, a fairly accurate measurement of the effective flow rate to a given area can be rendered. This examination combines the advantage of reproducibility and multiple re-examinations.